2015-06-23 Paolo Carlini <paolo.carlini@oracle.com>

[official-gcc.git] / gcc / ada / gnat_ugn.texi

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@settitle GNAT User's Guide for Native Platforms
@defindex ge
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@dircategory GNU Ada Tools 
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* gnat_ugn: (gnat_ugn.info). gnat_ugn
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@quotation
GNAT User's Guide for Native Platforms , May 12, 2015

AdaCore

Copyright @copyright{} 2008-2015, Free Software Foundation
@end quotation

@end copying

@titlepage
@title GNAT User's Guide for Native Platforms
@insertcopying
@end titlepage
@contents

@c %** start of user preamble

@c %** end of user preamble

@ifnottex
@node Top
@top GNAT User's Guide for Native Platforms
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@c %**start of body
@anchor{gnat_ugn doc}@anchor{0}
@emph{GNAT, The GNU Ada Development Environment}


@include gcc-common.texi
GCC version @value{version-GCC}@*
AdaCore

Permission is granted to copy, distribute and/or modify this document
under the terms of the GNU Free Documentation License, Version 1.3 or
any later version published by the Free Software Foundation; with no
Invariant Sections, with the Front-Cover Texts being
"GNAT User's Guide for Native Platforms",
and with no Back-Cover Texts.  A copy of the license is
included in the section entitled @ref{1,,GNU Free Documentation License}.

@menu
* About This Guide:: 
* Getting Started with GNAT:: 
* The GNAT Compilation Model:: 
* Building Executable Programs with GNAT:: 
* GNAT Project Manager:: 
* Tools Supporting Project Files:: 
* GNAT Utility Programs:: 
* GNAT and Program Execution:: 
* Platform-Specific Information:: 
* Example of Binder Output File:: 
* Elaboration Order Handling in GNAT:: 
* Inline Assembler:: 
* GNU Free Documentation License:: 
* Index:: 

@detailmenu
 --- The Detailed Node Listing ---

About This Guide

* What This Guide Contains:: 
* What You Should Know before Reading This Guide:: 
* Related Information:: 
* A Note to Readers of Previous Versions of the Manual:: 
* Conventions:: 

Getting Started with GNAT

* Running GNAT:: 
* Running a Simple Ada Program:: 
* Running a Program with Multiple Units:: 
* Using the gnatmake Utility:: 

The GNAT Compilation Model

* Source Representation:: 
* Foreign Language Representation:: 
* File Naming Topics and Utilities:: 
* Configuration Pragmas:: 
* Generating Object Files:: 
* Source Dependencies:: 
* The Ada Library Information Files:: 
* Binding an Ada Program:: 
* GNAT and Libraries:: 
* Conditional Compilation:: 
* Mixed Language Programming:: 
* GNAT and Other Compilation Models:: 
* Using GNAT Files with External Tools:: 

Foreign Language Representation

* Latin-1:: 
* Other 8-Bit Codes:: 
* Wide_Character Encodings:: 
* Wide_Wide_Character Encodings:: 

File Naming Topics and Utilities

* File Naming Rules:: 
* Using Other File Names:: 
* Alternative File Naming Schemes:: 
* Handling Arbitrary File Naming Conventions with gnatname:: 
* File Name Krunching with gnatkr:: 
* Renaming Files with gnatchop:: 

Handling Arbitrary File Naming Conventions with gnatname

* Arbitrary File Naming Conventions:: 
* Running gnatname:: 
* Switches for gnatname:: 
* Examples of gnatname Usage:: 

File Name Krunching with gnatkr

* About gnatkr:: 
* Using gnatkr:: 
* Krunching Method:: 
* Examples of gnatkr Usage:: 

Renaming Files with gnatchop

* Handling Files with Multiple Units:: 
* Operating gnatchop in Compilation Mode:: 
* Command Line for gnatchop:: 
* Switches for gnatchop:: 
* Examples of gnatchop Usage:: 

Configuration Pragmas

* Handling of Configuration Pragmas:: 
* The Configuration Pragmas Files:: 

GNAT and Libraries

* Introduction to Libraries in GNAT:: 
* General Ada Libraries:: 
* Stand-alone Ada Libraries:: 
* Rebuilding the GNAT Run-Time Library:: 

General Ada Libraries

* Building a library:: 
* Installing a library:: 
* Using a library:: 

Stand-alone Ada Libraries

* Introduction to Stand-alone Libraries:: 
* Building a Stand-alone Library:: 
* Creating a Stand-alone Library to be used in a non-Ada context:: 
* Restrictions in Stand-alone Libraries:: 

Conditional Compilation

* Modeling Conditional Compilation in Ada:: 
* Preprocessing with gnatprep:: 
* Integrated Preprocessing:: 

Modeling Conditional Compilation in Ada

* Use of Boolean Constants:: 
* Debugging - A Special Case:: 
* Conditionalizing Declarations:: 
* Use of Alternative Implementations:: 
* Preprocessing:: 

Preprocessing with gnatprep

* Preprocessing Symbols:: 
* Using gnatprep:: 
* Switches for gnatprep:: 
* Form of Definitions File:: 
* Form of Input Text for gnatprep:: 

Mixed Language Programming

* Interfacing to C:: 
* Calling Conventions:: 
* Building Mixed Ada and C++ Programs:: 
* Generating Ada Bindings for C and C++ headers:: 

Building Mixed Ada and C++ Programs

* Interfacing to C++:: 
* Linking a Mixed C++ & Ada Program:: 
* A Simple Example:: 
* Interfacing with C++ constructors:: 
* Interfacing with C++ at the Class Level:: 

Generating Ada Bindings for C and C++ headers

* Running the binding generator:: 
* Generating bindings for C++ headers:: 
* Switches:: 

GNAT and Other Compilation Models

* Comparison between GNAT and C/C++ Compilation Models:: 
* Comparison between GNAT and Conventional Ada Library Models:: 

Using GNAT Files with External Tools

* Using Other Utility Programs with GNAT:: 
* The External Symbol Naming Scheme of GNAT:: 

Building Executable Programs with GNAT

* Building with gnatmake:: 
* Compiling with gcc:: 
* Compiler Switches:: 
* Binding with gnatbind:: 
* Linking with gnatlink:: 
* Using the GNU make Utility:: 

Building with gnatmake

* Running gnatmake:: 
* Switches for gnatmake:: 
* Mode Switches for gnatmake:: 
* Notes on the Command Line:: 
* How gnatmake Works:: 
* Examples of gnatmake Usage:: 

Compiling with gcc

* Compiling Programs:: 
* Search Paths and the Run-Time Library (RTL): Search Paths and the Run-Time Library RTL. 
* Order of Compilation Issues:: 
* Examples:: 

Compiler Switches

* Alphabetical List of All Switches:: 
* Output and Error Message Control:: 
* Warning Message Control:: 
* Debugging and Assertion Control:: 
* Validity Checking:: 
* Style Checking:: 
* Run-Time Checks:: 
* Using gcc for Syntax Checking:: 
* Using gcc for Semantic Checking:: 
* Compiling Different Versions of Ada:: 
* Character Set Control:: 
* File Naming Control:: 
* Subprogram Inlining Control:: 
* Auxiliary Output Control:: 
* Debugging Control:: 
* Exception Handling Control:: 
* Units to Sources Mapping Files:: 
* Code Generation Control:: 

Binding with gnatbind

* Running gnatbind:: 
* Switches for gnatbind:: 
* Command-Line Access:: 
* Search Paths for gnatbind:: 
* Examples of gnatbind Usage:: 

Switches for gnatbind

* Consistency-Checking Modes:: 
* Binder Error Message Control:: 
* Elaboration Control:: 
* Output Control:: 
* Dynamic Allocation Control:: 
* Binding with Non-Ada Main Programs:: 
* Binding Programs with No Main Subprogram:: 

Linking with gnatlink

* Running gnatlink:: 
* Switches for gnatlink:: 

Using the GNU make Utility

* Using gnatmake in a Makefile:: 
* Automatically Creating a List of Directories:: 
* Generating the Command Line Switches:: 
* Overcoming Command Line Length Limits:: 

GNAT Project Manager

* Introduction:: 
* Building With Projects:: 
* Organizing Projects into Subsystems:: 
* Scenarios in Projects:: 
* Library Projects:: 
* Project Extension:: 
* Aggregate Projects:: 
* Aggregate Library Projects:: 
* Project File Reference:: 

Building With Projects

* Source Files and Directories:: 
* Duplicate Sources in Projects:: 
* Object and Exec Directory:: 
* Main Subprograms:: 
* Tools Options in Project Files:: 
* Compiling with Project Files:: 
* Executable File Names:: 
* Avoid Duplication With Variables:: 
* Naming Schemes:: 
* Installation:: 
* Distributed support:: 

Organizing Projects into Subsystems

* Project Dependencies:: 
* Cyclic Project Dependencies:: 
* Sharing Between Projects:: 
* Global Attributes:: 

Library Projects

* Building Libraries:: 
* Using Library Projects:: 
* Stand-alone Library Projects:: 
* Installing a library with project files:: 

Project Extension

* Project Hierarchy Extension:: 

Aggregate Projects

* Building all main programs from a single project tree:: 
* Building a set of projects with a single command:: 
* Define a build environment:: 
* Performance improvements in builder:: 
* Syntax of aggregate projects:: 
* package Builder in aggregate projects:: 

Aggregate Library Projects

* Building aggregate library projects:: 
* Syntax of aggregate library projects:: 

Project File Reference

* Project Declaration:: 
* Qualified Projects:: 
* Declarations:: 
* Packages:: 
* Expressions:: 
* External Values:: 
* Typed String Declaration:: 
* Variables:: 
* Case Constructions:: 
* Attributes:: 

Attributes

* Project Level Attributes:: 
* Package Binder Attributes:: 
* Package Builder Attributes:: 
* Package Clean Attributes:: 
* Package Compiler Attributes:: 
* Package Cross_Reference Attributes:: 
* Package Finder Attributes:: 
* Package gnatls Attributes:: 
* Package IDE Attributes:: 
* Package Install Attributes:: 
* Package Linker Attributes:: 
* Package Naming Attributes:: 
* Package Remote Attributes:: 
* Package Stack Attributes:: 
* Package Synchronize Attributes:: 

Tools Supporting Project Files

* gnatmake and Project Files:: 
* The GNAT Driver and Project Files:: 

gnatmake and Project Files

* Switches Related to Project Files:: 
* Switches and Project Files:: 
* Specifying Configuration Pragmas:: 
* Project Files and Main Subprograms:: 
* Library Project Files:: 

GNAT Utility Programs

* The File Cleanup Utility gnatclean:: 
* The GNAT Library Browser gnatls:: 
* The Cross-Referencing Tools gnatxref and gnatfind:: 
* The Ada to HTML Converter gnathtml:: 

The File Cleanup Utility gnatclean

* Running gnatclean:: 
* Switches for gnatclean:: 

The GNAT Library Browser gnatls

* Running gnatls:: 
* Switches for gnatls:: 
* Example of gnatls Usage:: 

The Cross-Referencing Tools gnatxref and gnatfind

* gnatxref Switches:: 
* gnatfind Switches:: 
* Project Files for gnatxref and gnatfind:: 
* Regular Expressions in gnatfind and gnatxref:: 
* Examples of gnatxref Usage:: 
* Examples of gnatfind Usage:: 

Examples of gnatxref Usage

* General Usage:: 
* Using gnatxref with vi:: 

The Ada to HTML Converter gnathtml

* Invoking gnathtml:: 
* Installing gnathtml:: 

GNAT and Program Execution

* Running and Debugging Ada Programs:: 
* Code Coverage and Profiling:: 
* Improving Performance:: 
* Overflow Check Handling in GNAT:: 
* Performing Dimensionality Analysis in GNAT:: 
* Stack Related Facilities:: 
* Memory Management Issues:: 

Running and Debugging Ada Programs

* The GNAT Debugger GDB:: 
* Running GDB:: 
* Introduction to GDB Commands:: 
* Using Ada Expressions:: 
* Calling User-Defined Subprograms:: 
* Using the next Command in a Function:: 
* Stopping When Ada Exceptions Are Raised:: 
* Ada Tasks:: 
* Debugging Generic Units:: 
* Remote Debugging with gdbserver:: 
* GNAT Abnormal Termination or Failure to Terminate:: 
* Naming Conventions for GNAT Source Files:: 
* Getting Internal Debugging Information:: 
* Stack Traceback:: 

Stack Traceback

* Non-Symbolic Traceback:: 
* Symbolic Traceback:: 

Code Coverage and Profiling

* Code Coverage of Ada Programs with gcov:: 
* Profiling an Ada Program with gprof:: 

Code Coverage of Ada Programs with gcov

* Quick startup guide:: 
* GNAT specifics:: 

Profiling an Ada Program with gprof

* Compilation for profiling:: 
* Program execution:: 
* Running gprof:: 
* Interpretation of profiling results:: 

Improving Performance

* Performance Considerations:: 
* Text_IO Suggestions:: 
* Reducing Size of Executables with Unused Subprogram/Data Elimination:: 

Performance Considerations

* Controlling Run-Time Checks:: 
* Use of Restrictions:: 
* Optimization Levels:: 
* Debugging Optimized Code:: 
* Inlining of Subprograms:: 
* Floating_Point_Operations:: 
* Vectorization of loops:: 
* Other Optimization Switches:: 
* Optimization and Strict Aliasing:: 
* Aliased Variables and Optimization:: 
* Atomic Variables and Optimization:: 
* Passive Task Optimization:: 

Reducing Size of Executables with Unused Subprogram/Data Elimination

* About unused subprogram/data elimination:: 
* Compilation options:: 
* Example of unused subprogram/data elimination:: 

Overflow Check Handling in GNAT

* Background:: 
* Overflow Checking Modes in GNAT:: 
* Specifying the Desired Mode:: 
* Default Settings:: 
* Implementation Notes:: 

Stack Related Facilities

* Stack Overflow Checking:: 
* Static Stack Usage Analysis:: 
* Dynamic Stack Usage Analysis:: 

Memory Management Issues

* Some Useful Memory Pools:: 
* The GNAT Debug Pool Facility:: 

Platform-Specific Information

* Run-Time Libraries:: 
* Specifying a Run-Time Library:: 
* Microsoft Windows Topics:: 
* Mac OS Topics:: 

Run-Time Libraries

* Summary of Run-Time Configurations:: 

Specifying a Run-Time Library

* Choosing the Scheduling Policy:: 
* Solaris-Specific Considerations:: 
* Solaris Threads Issues:: 
* AIX-Specific Considerations:: 

Microsoft Windows Topics

* Using GNAT on Windows:: 
* Using a network installation of GNAT:: 
* CONSOLE and WINDOWS subsystems:: 
* Temporary Files:: 
* Mixed-Language Programming on Windows:: 

Mixed-Language Programming on Windows

* Windows Calling Conventions:: 
* Introduction to Dynamic Link Libraries (DLLs): Introduction to Dynamic Link Libraries DLLs. 
* Using DLLs with GNAT:: 
* Building DLLs with GNAT Project files:: 
* Building DLLs with GNAT:: 
* Building DLLs with gnatdll:: 
* Ada DLLs and Finalization:: 
* Creating a Spec for Ada DLLs:: 
* GNAT and Windows Resources:: 
* Debugging a DLL:: 
* Setting Stack Size from gnatlink:: 
* Setting Heap Size from gnatlink:: 

Windows Calling Conventions

* C Calling Convention:: 
* Stdcall Calling Convention:: 
* Win32 Calling Convention:: 
* DLL Calling Convention:: 

Using DLLs with GNAT

* Creating an Ada Spec for the DLL Services:: 
* Creating an Import Library:: 

Building DLLs with gnatdll

* Limitations When Using Ada DLLs from Ada:: 
* Exporting Ada Entities:: 
* Ada DLLs and Elaboration:: 

Creating a Spec for Ada DLLs

* Creating the Definition File:: 
* Using gnatdll:: 

GNAT and Windows Resources

* Building Resources:: 
* Compiling Resources:: 
* Using Resources:: 

Debugging a DLL

* Program and DLL Both Built with GCC/GNAT:: 
* Program Built with Foreign Tools and DLL Built with GCC/GNAT:: 

Mac OS Topics

* Codesigning the Debugger:: 

Elaboration Order Handling in GNAT

* Elaboration Code:: 
* Checking the Elaboration Order:: 
* Controlling the Elaboration Order:: 
* Controlling Elaboration in GNAT - Internal Calls:: 
* Controlling Elaboration in GNAT - External Calls:: 
* Default Behavior in GNAT - Ensuring Safety:: 
* Treatment of Pragma Elaborate:: 
* Elaboration Issues for Library Tasks:: 
* Mixing Elaboration Models:: 
* What to Do If the Default Elaboration Behavior Fails:: 
* Elaboration for Indirect Calls:: 
* Summary of Procedures for Elaboration Control:: 
* Other Elaboration Order Considerations:: 
* Determining the Chosen Elaboration Order:: 

Inline Assembler

* Basic Assembler Syntax:: 
* A Simple Example of Inline Assembler:: 
* Output Variables in Inline Assembler:: 
* Input Variables in Inline Assembler:: 
* Inlining Inline Assembler Code:: 
* Other Asm Functionality:: 

Other Asm Functionality

* The Clobber Parameter:: 
* The Volatile Parameter:: 

@end detailmenu
@end menu

@node About This Guide,Getting Started with GNAT,Top,Top
@anchor{gnat_ugn/about_this_guide about-this-guide}@anchor{2}@anchor{gnat_ugn/about_this_guide doc}@anchor{3}@anchor{gnat_ugn/about_this_guide gnat-user-s-guide-for-native-platforms}@anchor{4}@anchor{gnat_ugn/about_this_guide id1}@anchor{5}
@chapter About This Guide



This guide describes the use of GNAT,
a compiler and software development
toolset for the full Ada programming language.
It documents the features of the compiler and tools, and explains
how to use them to build Ada applications.

GNAT implements Ada 95, Ada 2005 and Ada 2012, and it may also be
invoked in Ada 83 compatibility mode.
By default, GNAT assumes Ada 2012, but you can override with a
compiler switch (@ref{6,,Compiling Different Versions of Ada})
to explicitly specify the language version.
Throughout this manual, references to 'Ada' without a year suffix
apply to all Ada 95/2005/2012 versions of the language.

@menu
* What This Guide Contains:: 
* What You Should Know before Reading This Guide:: 
* Related Information:: 
* A Note to Readers of Previous Versions of the Manual:: 
* Conventions:: 

@end menu

@node What This Guide Contains,What You Should Know before Reading This Guide,,About This Guide
@anchor{gnat_ugn/about_this_guide what-this-guide-contains}@anchor{7}
@section What This Guide Contains


This guide contains the following chapters:


@itemize *

@item 
@ref{8,,Getting Started with GNAT} describes how to get started compiling
and running Ada programs with the GNAT Ada programming environment.

@item 
@ref{9,,The GNAT Compilation Model} describes the compilation model used
by GNAT.

@item 
@ref{a,,Building Executable Programs with GNAT} describes how to use the
main GNAT tools to build executable programs, and it also gives examples of
using the GNU make utility with GNAT.

@item 
@ref{b,,GNAT Project Manager} describes how to use project files
to organize large projects.

@item 
@ref{c,,Tools Supporting Project Files} described how to use the project
facility in conjunction with various GNAT tools.

@item 
@ref{d,,GNAT Utility Programs} explains the various utility programs that
are included in the GNAT environment

@item 
@ref{e,,GNAT and Program Execution} covers a number of topics related to
running, debugging, and tuning the performace of programs developed
with GNAT
@end itemize

Appendices cover several additional topics:


@itemize *

@item 
@ref{f,,Platform-Specific Information} describes the different run-time
library implementations and also presents information on how to use
GNAT on several specific platforms

@item 
@ref{10,,Example of Binder Output File} shows the source code for the binder
output file for a sample program.

@item 
@ref{11,,Elaboration Order Handling in GNAT} describes how GNAT helps
you deal with elaboration order issues.

@item 
@ref{12,,Inline Assembler} shows how to use the inline assembly facility
in an Ada program.
@end itemize

@node What You Should Know before Reading This Guide,Related Information,What This Guide Contains,About This Guide
@anchor{gnat_ugn/about_this_guide what-you-should-know-before-reading-this-guide}@anchor{13}
@section What You Should Know before Reading This Guide


@geindex Ada 95 Language Reference Manual

@geindex Ada 2005 Language Reference Manual

This guide assumes a basic familiarity with the Ada 95 language, as
described in the International Standard ANSI/ISO/IEC-8652:1995, January
1995.
It does not require knowledge of the features introduced by Ada 2005
or Ada 2012.
Reference manuals for Ada 95, Ada 2005, and Ada 2012 are included in
the GNAT documentation package.

@node Related Information,A Note to Readers of Previous Versions of the Manual,What You Should Know before Reading This Guide,About This Guide
@anchor{gnat_ugn/about_this_guide related-information}@anchor{14}
@section Related Information


For further information about Ada and related tools, please refer to the
following documents:


@itemize *

@item 
@cite{Ada 95 Reference Manual}, @cite{Ada 2005 Reference Manual}, and
@cite{Ada 2012 Reference Manual}, which contain reference
material for the several revisions of the Ada language standard.

@item 
@cite{GNAT Reference_Manual}, which contains all reference material for the GNAT
implementation of Ada.

@item 
@cite{Using the GNAT Programming Studio}, which describes the GPS
Integrated Development Environment.

@item 
@cite{GNAT Programming Studio Tutorial}, which introduces the
main GPS features through examples.

@item 
@cite{Debugging with GDB},
for all details on the use of the GNU source-level debugger.

@item 
@cite{GNU Emacs Manual},
for full information on the extensible editor and programming
environment Emacs.
@end itemize

@node A Note to Readers of Previous Versions of the Manual,Conventions,Related Information,About This Guide
@anchor{gnat_ugn/about_this_guide a-note-to-readers-of-previous-versions-of-the-manual}@anchor{15}
@section A Note to Readers of Previous Versions of the Manual


In early 2015 the GNAT manuals were transitioned to the
reStructuredText (rst) / Sphinx documentation generator technology.
During that process the @cite{GNAT User's Guide} was reorganized
so that related topics would be described together in the same chapter
or appendix.  Here's a summary of the major changes realized in
the new document structure.


@itemize *

@item 
@ref{9,,The GNAT Compilation Model} has been extended so that it now covers
the following material:


@itemize -

@item 
The @cite{gnatname}, @cite{gnatkr}, and @cite{gnatchop} tools

@item 
@ref{16,,Configuration Pragmas}

@item 
@ref{17,,GNAT and Libraries}

@item 
@ref{18,,Conditional Compilation} including @ref{19,,Preprocessing with gnatprep}
and @ref{1a,,Integrated Preprocessing}

@item 
@ref{1b,,Generating Ada Bindings for C and C++ headers}

@item 
@ref{1c,,Using GNAT Files with External Tools}
@end itemize

@item 
@ref{a,,Building Executable Programs with GNAT} is a new chapter consolidating
the following content:


@itemize -

@item 
@ref{1d,,Building with gnatmake}

@item 
@ref{1e,,Compiling with gcc}

@item 
@ref{1f,,Binding with gnatbind}

@item 
@ref{20,,Linking with gnatlink}

@item 
@ref{21,,Using the GNU make Utility}
@end itemize

@item 
@ref{d,,GNAT Utility Programs} is a new chapter consolidating the information about several
GNAT tools:



@itemize -

@item 
@ref{22,,The File Cleanup Utility gnatclean}

@item 
@ref{23,,The GNAT Library Browser gnatls}

@item 
@ref{24,,The Cross-Referencing Tools gnatxref and gnatfind}

@item 
@ref{25,,The Ada to HTML Converter gnathtml}
@end itemize

@item 
@ref{e,,GNAT and Program Execution} is a new chapter consolidating the following:


@itemize -

@item 
@ref{26,,Running and Debugging Ada Programs}

@item 
@ref{27,,Code Coverage and Profiling}

@item 
@ref{28,,Improving Performance}

@item 
@ref{29,,Overflow Check Handling in GNAT}

@item 
@ref{2a,,Performing Dimensionality Analysis in GNAT}

@item 
@ref{2b,,Stack Related Facilities}

@item 
@ref{2c,,Memory Management Issues}
@end itemize

@item 
@ref{f,,Platform-Specific Information} is a new appendix consolidating the following:


@itemize -

@item 
@ref{2d,,Run-Time Libraries}

@item 
@ref{2e,,Microsoft Windows Topics}

@item 
@ref{2f,,Mac OS Topics}
@end itemize

@item 
The @cite{Compatibility and Porting Guide} appendix has been moved to the
@cite{GNAT Reference Manual}. It now includes a section
@cite{Writing Portable Fixed-Point Declarations} which was previously
a separate chapter in the @cite{GNAT User's Guide}.
@end itemize

@node Conventions,,A Note to Readers of Previous Versions of the Manual,About This Guide
@anchor{gnat_ugn/about_this_guide conventions}@anchor{30}
@section Conventions


@geindex Conventions
@geindex typographical

@geindex Typographical conventions

Following are examples of the typographical and graphic conventions used
in this guide:


@itemize *

@item 
@cite{Functions}, @cite{utility program names}, @cite{standard names},
and @cite{classes}.

@item 
@cite{Option flags}

@item 
@code{File names}

@item 
@cite{Variables}

@item 
@emph{Emphasis}

@item 
[optional information or parameters]

@item 
Examples are described by text

@example
and then shown this way.
@end example

@item 
Commands that are entered by the user are shown as preceded by a prompt string
comprising the @code{$} character followed by a space.

@item 
Full file names are shown with the '/' character
as the directory separator; e.g., @code{parent-dir/subdir/myfile.adb}.
If you are using GNAT on a Windows platform, please note that
the '\' character should be used instead.
@end itemize

@node Getting Started with GNAT,The GNAT Compilation Model,About This Guide,Top
@anchor{gnat_ugn/getting_started_with_gnat getting-started-with-gnat}@anchor{8}@anchor{gnat_ugn/getting_started_with_gnat doc}@anchor{31}@anchor{gnat_ugn/getting_started_with_gnat id1}@anchor{32}
@chapter Getting Started with GNAT


This chapter describes how to use GNAT's command line interface to build
executable Ada programs.
On most platforms a visually oriented Integrated Development Environment
is also available, the GNAT Programming Studio (GPS).
GPS offers a graphical "look and feel", support for development in
other programming languages, comprehensive browsing features, and
many other capabilities.
For information on GPS please refer to
@cite{Using the GNAT Programming Studio}.

@menu
* Running GNAT:: 
* Running a Simple Ada Program:: 
* Running a Program with Multiple Units:: 
* Using the gnatmake Utility:: 

@end menu

@node Running GNAT,Running a Simple Ada Program,,Getting Started with GNAT
@anchor{gnat_ugn/getting_started_with_gnat running-gnat}@anchor{33}@anchor{gnat_ugn/getting_started_with_gnat id2}@anchor{34}
@section Running GNAT


Three steps are needed to create an executable file from an Ada source
file:


@itemize *

@item 
The source file(s) must be compiled.

@item 
The file(s) must be bound using the GNAT binder.

@item 
All appropriate object files must be linked to produce an executable.
@end itemize

All three steps are most commonly handled by using the @emph{gnatmake}
utility program that, given the name of the main program, automatically
performs the necessary compilation, binding and linking steps.

@node Running a Simple Ada Program,Running a Program with Multiple Units,Running GNAT,Getting Started with GNAT
@anchor{gnat_ugn/getting_started_with_gnat running-a-simple-ada-program}@anchor{35}@anchor{gnat_ugn/getting_started_with_gnat id3}@anchor{36}
@section Running a Simple Ada Program


Any text editor may be used to prepare an Ada program.
(If Emacs is used, the optional Ada mode may be helpful in laying out the
program.)
The program text is a normal text file. We will assume in our initial
example that you have used your editor to prepare the following
standard format text file:

@example
with Ada.Text_IO; use Ada.Text_IO;
procedure Hello is
begin
   Put_Line ("Hello WORLD!");
end Hello;
@end example

This file should be named @code{hello.adb}.
With the normal default file naming conventions, GNAT requires
that each file
contain a single compilation unit whose file name is the
unit name,
with periods replaced by hyphens; the
extension is @code{ads} for a
spec and @code{adb} for a body.
You can override this default file naming convention by use of the
special pragma @cite{Source_File_Name} (for further information please
see @ref{37,,Using Other File Names}).
Alternatively, if you want to rename your files according to this default
convention, which is probably more convenient if you will be using GNAT
for all your compilations, then the @cite{gnatchop} utility
can be used to generate correctly-named source files
(see @ref{38,,Renaming Files with gnatchop}).

You can compile the program using the following command (@cite{$} is used
as the command prompt in the examples in this document):

@example
$ gcc -c hello.adb
@end example

@emph{gcc} is the command used to run the compiler. This compiler is
capable of compiling programs in several languages, including Ada and
C. It assumes that you have given it an Ada program if the file extension is
either @code{.ads} or @code{.adb}, and it will then call
the GNAT compiler to compile the specified file.

The @code{-c} switch is required. It tells @emph{gcc} to only do a
compilation. (For C programs, @emph{gcc} can also do linking, but this
capability is not used directly for Ada programs, so the @code{-c}
switch must always be present.)

This compile command generates a file
@code{hello.o}, which is the object
file corresponding to your Ada program. It also generates
an 'Ada Library Information' file @code{hello.ali},
which contains additional information used to check
that an Ada program is consistent.
To build an executable file,
use @cite{gnatbind} to bind the program
and @emph{gnatlink} to link it. The
argument to both @cite{gnatbind} and @emph{gnatlink} is the name of the
@code{ALI} file, but the default extension of @code{.ali} can
be omitted. This means that in the most common case, the argument
is simply the name of the main program:

@example
$ gnatbind hello
$ gnatlink hello
@end example

A simpler method of carrying out these steps is to use @emph{gnatmake},
a master program that invokes all the required
compilation, binding and linking tools in the correct order. In particular,
@emph{gnatmake} automatically recompiles any sources that have been
modified since they were last compiled, or sources that depend
on such modified sources, so that 'version skew' is avoided.

@geindex Version skew (avoided by *gnatmake*)

@example
$ gnatmake hello.adb
@end example

The result is an executable program called @code{hello}, which can be
run by entering:

@example
$ hello
@end example

assuming that the current directory is on the search path
for executable programs.

and, if all has gone well, you will see:

@example
Hello WORLD!
@end example

appear in response to this command.

@node Running a Program with Multiple Units,Using the gnatmake Utility,Running a Simple Ada Program,Getting Started with GNAT
@anchor{gnat_ugn/getting_started_with_gnat id4}@anchor{39}@anchor{gnat_ugn/getting_started_with_gnat running-a-program-with-multiple-units}@anchor{3a}
@section Running a Program with Multiple Units


Consider a slightly more complicated example that has three files: a
main program, and the spec and body of a package:

@example
package Greetings is
   procedure Hello;
   procedure Goodbye;
end Greetings;

with Ada.Text_IO; use Ada.Text_IO;
package body Greetings is
   procedure Hello is
   begin
      Put_Line ("Hello WORLD!");
   end Hello;

   procedure Goodbye is
   begin
      Put_Line ("Goodbye WORLD!");
   end Goodbye;
end Greetings;

with Greetings;
procedure Gmain is
begin
   Greetings.Hello;
   Greetings.Goodbye;
end Gmain;
@end example

Following the one-unit-per-file rule, place this program in the
following three separate files:


@table @asis

@item @emph{greetings.ads}

spec of package @cite{Greetings}

@item @emph{greetings.adb}

body of package @cite{Greetings}

@item @emph{gmain.adb}

body of main program
@end table

To build an executable version of
this program, we could use four separate steps to compile, bind, and link
the program, as follows:

@example
$ gcc -c gmain.adb
$ gcc -c greetings.adb
$ gnatbind gmain
$ gnatlink gmain
@end example

Note that there is no required order of compilation when using GNAT.
In particular it is perfectly fine to compile the main program first.
Also, it is not necessary to compile package specs in the case where
there is an accompanying body; you only need to compile the body. If you want
to submit these files to the compiler for semantic checking and not code
generation, then use the @code{-gnatc} switch:

@example
$ gcc -c greetings.ads -gnatc
@end example

Although the compilation can be done in separate steps as in the
above example, in practice it is almost always more convenient
to use the @emph{gnatmake} tool. All you need to know in this case
is the name of the main program's source file. The effect of the above four
commands can be achieved with a single one:

@example
$ gnatmake gmain.adb
@end example

In the next section we discuss the advantages of using @emph{gnatmake} in
more detail.

@node Using the gnatmake Utility,,Running a Program with Multiple Units,Getting Started with GNAT
@anchor{gnat_ugn/getting_started_with_gnat using-the-gnatmake-utility}@anchor{3b}@anchor{gnat_ugn/getting_started_with_gnat id5}@anchor{3c}
@section Using the @emph{gnatmake} Utility


If you work on a program by compiling single components at a time using
@emph{gcc}, you typically keep track of the units you modify. In order to
build a consistent system, you compile not only these units, but also any
units that depend on the units you have modified.
For example, in the preceding case,
if you edit @code{gmain.adb}, you only need to recompile that file. But if
you edit @code{greetings.ads}, you must recompile both
@code{greetings.adb} and @code{gmain.adb}, because both files contain
units that depend on @code{greetings.ads}.

@emph{gnatbind} will warn you if you forget one of these compilation
steps, so that it is impossible to generate an inconsistent program as a
result of forgetting to do a compilation. Nevertheless it is tedious and
error-prone to keep track of dependencies among units.
One approach to handle the dependency-bookkeeping is to use a
makefile. However, makefiles present maintenance problems of their own:
if the dependencies change as you change the program, you must make
sure that the makefile is kept up-to-date manually, which is also an
error-prone process.

The @emph{gnatmake} utility takes care of these details automatically.
Invoke it using either one of the following forms:

@example
$ gnatmake gmain.adb
$ gnatmake gmain
@end example

The argument is the name of the file containing the main program;
you may omit the extension. @emph{gnatmake}
examines the environment, automatically recompiles any files that need
recompiling, and binds and links the resulting set of object files,
generating the executable file, @code{gmain}.
In a large program, it
can be extremely helpful to use @emph{gnatmake}, because working out by hand
what needs to be recompiled can be difficult.

Note that @emph{gnatmake} takes into account all the Ada rules that
establish dependencies among units. These include dependencies that result
from inlining subprogram bodies, and from
generic instantiation. Unlike some other
Ada make tools, @emph{gnatmake} does not rely on the dependencies that were
found by the compiler on a previous compilation, which may possibly
be wrong when sources change. @emph{gnatmake} determines the exact set of
dependencies from scratch each time it is run.

@c -- Example: A |withing| unit has a |with| clause, it |withs| a |withed| unit

@node The GNAT Compilation Model,Building Executable Programs with GNAT,Getting Started with GNAT,Top
@anchor{gnat_ugn/the_gnat_compilation_model doc}@anchor{3d}@anchor{gnat_ugn/the_gnat_compilation_model the-gnat-compilation-model}@anchor{9}@anchor{gnat_ugn/the_gnat_compilation_model id1}@anchor{3e}
@chapter The GNAT Compilation Model


@geindex GNAT compilation model

@geindex Compilation model

This chapter describes the compilation model used by GNAT. Although
similar to that used by other languages such as C and C++, this model
is substantially different from the traditional Ada compilation models,
which are based on a centralized program library. The chapter covers
the following material:


@itemize *

@item 
Topics related to source file makeup and naming


@itemize *

@item 
@ref{3f,,Source Representation}

@item 
@ref{40,,Foreign Language Representation}

@item 
@ref{41,,File Naming Topics and Utilities}
@end itemize

@item 
@ref{16,,Configuration Pragmas}

@item 
@ref{42,,Generating Object Files}

@item 
@ref{43,,Source Dependencies}

@item 
@ref{44,,The Ada Library Information Files}

@item 
@ref{45,,Binding an Ada Program}

@item 
@ref{17,,GNAT and Libraries}

@item 
@ref{18,,Conditional Compilation}

@item 
@ref{46,,Mixed Language Programming}

@item 
@ref{47,,GNAT and Other Compilation Models}

@item 
@ref{1c,,Using GNAT Files with External Tools}
@end itemize

@menu
* Source Representation:: 
* Foreign Language Representation:: 
* File Naming Topics and Utilities:: 
* Configuration Pragmas:: 
* Generating Object Files:: 
* Source Dependencies:: 
* The Ada Library Information Files:: 
* Binding an Ada Program:: 
* GNAT and Libraries:: 
* Conditional Compilation:: 
* Mixed Language Programming:: 
* GNAT and Other Compilation Models:: 
* Using GNAT Files with External Tools:: 

@end menu

@node Source Representation,Foreign Language Representation,,The GNAT Compilation Model
@anchor{gnat_ugn/the_gnat_compilation_model source-representation}@anchor{3f}@anchor{gnat_ugn/the_gnat_compilation_model id2}@anchor{48}
@section Source Representation


@geindex Latin-1

@geindex VT
@geindex HT
@geindex CR
@geindex LF
@geindex FF

Ada source programs are represented in standard text files, using
Latin-1 coding. Latin-1 is an 8-bit code that includes the familiar
7-bit ASCII set, plus additional characters used for
representing foreign languages (see @ref{40,,Foreign Language Representation}
for support of non-USA character sets). The format effector characters
are represented using their standard ASCII encodings, as follows:

@quotation


@multitable {xxxxxxxxxxxxx} {xxxxxxxxxxxxxxxxxxxxxxxxx} {xxxxxxxxxxx} 
@item

Character

@tab

Effect

@tab

Code

@item

@code{VT}

@tab

Vertical tab

@tab

@cite{16#0B#}

@item

@code{HT}

@tab

Horizontal tab

@tab

@cite{16#09#}

@item

@code{CR}

@tab

Carriage return

@tab

@cite{16#0D#}

@item

@code{LF}

@tab

Line feed

@tab

@cite{16#0A#}

@item

@code{FF}

@tab

Form feed

@tab

@cite{16#0C#}

@end multitable

@end quotation

Source files are in standard text file format. In addition, GNAT will
recognize a wide variety of stream formats, in which the end of
physical lines is marked by any of the following sequences:
@cite{LF}, @cite{CR}, @cite{CR-LF}, or @cite{LF-CR}. This is useful
in accommodating files that are imported from other operating systems.

@geindex End of source file; Source file@comma{} end

@geindex SUB (control character)

The end of a source file is normally represented by the physical end of
file. However, the control character @cite{16#1A#} (@code{SUB}) is also
recognized as signalling the end of the source file. Again, this is
provided for compatibility with other operating systems where this
code is used to represent the end of file.

@geindex spec (definition)
@geindex compilation (definition)

Each file contains a single Ada compilation unit, including any pragmas
associated with the unit. For example, this means you must place a
package declaration (a package @cite{spec}) and the corresponding body in
separate files. An Ada @cite{compilation} (which is a sequence of
compilation units) is represented using a sequence of files. Similarly,
you will place each subunit or child unit in a separate file.

@node Foreign Language Representation,File Naming Topics and Utilities,Source Representation,The GNAT Compilation Model
@anchor{gnat_ugn/the_gnat_compilation_model foreign-language-representation}@anchor{40}@anchor{gnat_ugn/the_gnat_compilation_model id3}@anchor{49}
@section Foreign Language Representation


GNAT supports the standard character sets defined in Ada as well as
several other non-standard character sets for use in localized versions
of the compiler (@ref{4a,,Character Set Control}).

@menu
* Latin-1:: 
* Other 8-Bit Codes:: 
* Wide_Character Encodings:: 
* Wide_Wide_Character Encodings:: 

@end menu

@node Latin-1,Other 8-Bit Codes,,Foreign Language Representation
@anchor{gnat_ugn/the_gnat_compilation_model id4}@anchor{4b}@anchor{gnat_ugn/the_gnat_compilation_model latin-1}@anchor{4c}
@subsection Latin-1


@geindex Latin-1

The basic character set is Latin-1. This character set is defined by ISO
standard 8859, part 1. The lower half (character codes @cite{16#00#}
... @cite{16#7F#)} is identical to standard ASCII coding, but the upper
half is used to represent additional characters. These include extended letters
used by European languages, such as French accents, the vowels with umlauts
used in German, and the extra letter A-ring used in Swedish.

@geindex Ada.Characters.Latin_1

For a complete list of Latin-1 codes and their encodings, see the source
file of library unit @cite{Ada.Characters.Latin_1} in file
@code{a-chlat1.ads}.
You may use any of these extended characters freely in character or
string literals. In addition, the extended characters that represent
letters can be used in identifiers.

@node Other 8-Bit Codes,Wide_Character Encodings,Latin-1,Foreign Language Representation
@anchor{gnat_ugn/the_gnat_compilation_model other-8-bit-codes}@anchor{4d}@anchor{gnat_ugn/the_gnat_compilation_model id5}@anchor{4e}
@subsection Other 8-Bit Codes


GNAT also supports several other 8-bit coding schemes:

@geindex Latin-2

@geindex ISO 8859-2


@table @asis

@item @emph{ISO 8859-2 (Latin-2)}

Latin-2 letters allowed in identifiers, with uppercase and lowercase
equivalence.
@end table

@geindex Latin-3

@geindex ISO 8859-3


@table @asis

@item @emph{ISO 8859-3 (Latin-3)}

Latin-3 letters allowed in identifiers, with uppercase and lowercase
equivalence.
@end table

@geindex Latin-4

@geindex ISO 8859-4


@table @asis

@item @emph{ISO 8859-4 (Latin-4)}

Latin-4 letters allowed in identifiers, with uppercase and lowercase
equivalence.
@end table

@geindex ISO 8859-5

@geindex Cyrillic


@table @asis

@item @emph{ISO 8859-5 (Cyrillic)}

ISO 8859-5 letters (Cyrillic) allowed in identifiers, with uppercase and
lowercase equivalence.
@end table

@geindex ISO 8859-15

@geindex Latin-9


@table @asis

@item @emph{ISO 8859-15 (Latin-9)}

ISO 8859-15 (Latin-9) letters allowed in identifiers, with uppercase and
lowercase equivalence
@end table

@geindex code page 437 (IBM PC)


@table @asis

@item @emph{IBM PC (code page 437)}

This code page is the normal default for PCs in the U.S. It corresponds
to the original IBM PC character set. This set has some, but not all, of
the extended Latin-1 letters, but these letters do not have the same
encoding as Latin-1. In this mode, these letters are allowed in
identifiers with uppercase and lowercase equivalence.
@end table

@geindex code page 850 (IBM PC)


@table @asis

@item @emph{IBM PC (code page 850)}

This code page is a modification of 437 extended to include all the
Latin-1 letters, but still not with the usual Latin-1 encoding. In this
mode, all these letters are allowed in identifiers with uppercase and
lowercase equivalence.

@item @emph{Full Upper 8-bit}

Any character in the range 80-FF allowed in identifiers, and all are
considered distinct. In other words, there are no uppercase and lowercase
equivalences in this range. This is useful in conjunction with
certain encoding schemes used for some foreign character sets (e.g.,
the typical method of representing Chinese characters on the PC).

@item @emph{No Upper-Half}

No upper-half characters in the range 80-FF are allowed in identifiers.
This gives Ada 83 compatibility for identifier names.
@end table

For precise data on the encodings permitted, and the uppercase and lowercase
equivalences that are recognized, see the file @code{csets.adb} in
the GNAT compiler sources. You will need to obtain a full source release
of GNAT to obtain this file.

@node Wide_Character Encodings,Wide_Wide_Character Encodings,Other 8-Bit Codes,Foreign Language Representation
@anchor{gnat_ugn/the_gnat_compilation_model id6}@anchor{4f}@anchor{gnat_ugn/the_gnat_compilation_model wide-character-encodings}@anchor{50}
@subsection Wide_Character Encodings


GNAT allows wide character codes to appear in character and string
literals, and also optionally in identifiers, by means of the following
possible encoding schemes:


@table @asis

@item @emph{Hex Coding}

In this encoding, a wide character is represented by the following five
character sequence:

@example
ESC a b c d
@end example

where @cite{a}, @cite{b}, @cite{c}, @cite{d} are the four hexadecimal
characters (using uppercase letters) of the wide character code. For
example, ESC A345 is used to represent the wide character with code
@cite{16#A345#}.
This scheme is compatible with use of the full Wide_Character set.

@item @emph{Upper-Half Coding}

@geindex Upper-Half Coding

The wide character with encoding @cite{16#abcd#} where the upper bit is on
(in other words, 'a' is in the range 8-F) is represented as two bytes,
@cite{16#ab#} and @cite{16#cd#}. The second byte cannot be a format control
character, but is not required to be in the upper half. This method can
be also used for shift-JIS or EUC, where the internal coding matches the
external coding.

@item @emph{Shift JIS Coding}

@geindex Shift JIS Coding

A wide character is represented by a two-character sequence,
@cite{16#ab#} and
@cite{16#cd#}, with the restrictions described for upper-half encoding as
described above. The internal character code is the corresponding JIS
character according to the standard algorithm for Shift-JIS
conversion. Only characters defined in the JIS code set table can be
used with this encoding method.

@item @emph{EUC Coding}

@geindex EUC Coding

A wide character is represented by a two-character sequence
@cite{16#ab#} and
@cite{16#cd#}, with both characters being in the upper half. The internal
character code is the corresponding JIS character according to the EUC
encoding algorithm. Only characters defined in the JIS code set table
can be used with this encoding method.

@item @emph{UTF-8 Coding}

A wide character is represented using
UCS Transformation Format 8 (UTF-8) as defined in Annex R of ISO
10646-1/Am.2. Depending on the character value, the representation
is a one, two, or three byte sequence:

@example
16#0000#-16#007f#: 2#0`xxxxxxx`#
16#0080#-16#07ff#: 2#110`xxxxx`# 2#10`xxxxxx`#
16#0800#-16#ffff#: 2#1110`xxxx`# 2#10`xxxxxx`# 2#10`xxxxxx`#
@end example

where the @cite{xxx} bits correspond to the left-padded bits of the
16-bit character value. Note that all lower half ASCII characters
are represented as ASCII bytes and all upper half characters and
other wide characters are represented as sequences of upper-half
(The full UTF-8 scheme allows for encoding 31-bit characters as
6-byte sequences, and in the following section on wide wide
characters, the use of these sequences is documented).

@item @emph{Brackets Coding}

In this encoding, a wide character is represented by the following eight
character sequence:

@example
[ " a b c d " ]
@end example

where @cite{a}, @cite{b}, @cite{c}, @cite{d} are the four hexadecimal
characters (using uppercase letters) of the wide character code. For
example, ['A345'] is used to represent the wide character with code
@cite{16#A345#}. It is also possible (though not required) to use the
Brackets coding for upper half characters. For example, the code
@cite{16#A3#} can be represented as @cite{['A3']}.

This scheme is compatible with use of the full Wide_Character set,
and is also the method used for wide character encoding in some standard
ACATS (Ada Conformity Assessment Test Suite) test suite distributions.
@end table

@cartouche
@quotation Note 
Some of these coding schemes do not permit the full use of the
Ada character set. For example, neither Shift JIS nor EUC allow the
use of the upper half of the Latin-1 set.
@end quotation
@end cartouche

@node Wide_Wide_Character Encodings,,Wide_Character Encodings,Foreign Language Representation
@anchor{gnat_ugn/the_gnat_compilation_model id7}@anchor{51}@anchor{gnat_ugn/the_gnat_compilation_model wide-wide-character-encodings}@anchor{52}
@subsection Wide_Wide_Character Encodings


GNAT allows wide wide character codes to appear in character and string
literals, and also optionally in identifiers, by means of the following
possible encoding schemes:


@table @asis

@item @emph{UTF-8 Coding}

A wide character is represented using
UCS Transformation Format 8 (UTF-8) as defined in Annex R of ISO
10646-1/Am.2. Depending on the character value, the representation
of character codes with values greater than 16#FFFF# is a
is a four, five, or six byte sequence:

@example
16#01_0000#-16#10_FFFF#:     11110xxx 10xxxxxx 10xxxxxx
                             10xxxxxx
16#0020_0000#-16#03FF_FFFF#: 111110xx 10xxxxxx 10xxxxxx
                             10xxxxxx 10xxxxxx
16#0400_0000#-16#7FFF_FFFF#: 1111110x 10xxxxxx 10xxxxxx
                             10xxxxxx 10xxxxxx 10xxxxxx
@end example

where the @cite{xxx} bits correspond to the left-padded bits of the
32-bit character value.

@item @emph{Brackets Coding}

In this encoding, a wide wide character is represented by the following ten or
twelve byte character sequence:

@example
[ " a b c d e f " ]
[ " a b c d e f g h " ]
@end example

where @cite{a-h} are the six or eight hexadecimal
characters (using uppercase letters) of the wide wide character code. For
example, ["1F4567"] is used to represent the wide wide character with code
@cite{16#001F_4567#}.

This scheme is compatible with use of the full Wide_Wide_Character set,
and is also the method used for wide wide character encoding in some standard
ACATS (Ada Conformity Assessment Test Suite) test suite distributions.
@end table

@node File Naming Topics and Utilities,Configuration Pragmas,Foreign Language Representation,The GNAT Compilation Model
@anchor{gnat_ugn/the_gnat_compilation_model id8}@anchor{53}@anchor{gnat_ugn/the_gnat_compilation_model file-naming-topics-and-utilities}@anchor{41}
@section File Naming Topics and Utilities


GNAT has a default file naming scheme and also provides the user with
a high degree of control over how the names and extensions of the
source files correspond to the Ada compilation units that they contain.

@menu
* File Naming Rules:: 
* Using Other File Names:: 
* Alternative File Naming Schemes:: 
* Handling Arbitrary File Naming Conventions with gnatname:: 
* File Name Krunching with gnatkr:: 
* Renaming Files with gnatchop:: 

@end menu

@node File Naming Rules,Using Other File Names,,File Naming Topics and Utilities
@anchor{gnat_ugn/the_gnat_compilation_model file-naming-rules}@anchor{54}@anchor{gnat_ugn/the_gnat_compilation_model id9}@anchor{55}
@subsection File Naming Rules


The default file name is determined by the name of the unit that the
file contains. The name is formed by taking the full expanded name of
the unit and replacing the separating dots with hyphens and using
lowercase for all letters.

An exception arises if the file name generated by the above rules starts
with one of the characters
@cite{a}, @cite{g}, @cite{i}, or @cite{s}, and the second character is a
minus. In this case, the character tilde is used in place
of the minus. The reason for this special rule is to avoid clashes with
the standard names for child units of the packages System, Ada,
Interfaces, and GNAT, which use the prefixes
@cite{s-}, @cite{a-}, @cite{i-}, and @cite{g-},
respectively.

The file extension is @code{.ads} for a spec and
@code{.adb} for a body. The following table shows some
examples of these rules.

@quotation


@multitable {xxxxxxxxxxxxxxxxxxxxxxxxxxxxxx} {xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx} 
@item

Source File

@tab

Ada Compilation Unit

@item

@code{main.ads}

@tab

Main (spec)

@item

@code{main.adb}

@tab

Main (body)

@item

@code{arith_functions.ads}

@tab

Arith_Functions (package spec)

@item

@code{arith_functions.adb}

@tab

Arith_Functions (package body)

@item

@code{func-spec.ads}

@tab

Func.Spec (child package spec)

@item

@code{func-spec.adb}

@tab

Func.Spec (child package body)

@item

@code{main-sub.adb}

@tab

Sub (subunit of Main)

@item

@code{a~bad.adb}

@tab

A.Bad (child package body)

@end multitable

@end quotation

Following these rules can result in excessively long
file names if corresponding
unit names are long (for example, if child units or subunits are
heavily nested). An option is available to shorten such long file names
(called file name 'krunching'). This may be particularly useful when
programs being developed with GNAT are to be used on operating systems
with limited file name lengths. @ref{56,,Using gnatkr}.

Of course, no file shortening algorithm can guarantee uniqueness over
all possible unit names; if file name krunching is used, it is your
responsibility to ensure no name clashes occur. Alternatively you
can specify the exact file names that you want used, as described
in the next section. Finally, if your Ada programs are migrating from a
compiler with a different naming convention, you can use the gnatchop
utility to produce source files that follow the GNAT naming conventions.
(For details see @ref{38,,Renaming Files with gnatchop}.)

Note: in the case of Windows or Mac OS operating systems, case is not
significant. So for example on @cite{Windows} if the canonical name is
@cite{main-sub.adb}, you can use the file name @code{Main-Sub.adb} instead.
However, case is significant for other operating systems, so for example,
if you want to use other than canonically cased file names on a Unix system,
you need to follow the procedures described in the next section.

@node Using Other File Names,Alternative File Naming Schemes,File Naming Rules,File Naming Topics and Utilities
@anchor{gnat_ugn/the_gnat_compilation_model id10}@anchor{57}@anchor{gnat_ugn/the_gnat_compilation_model using-other-file-names}@anchor{37}
@subsection Using Other File Names


@geindex File names

In the previous section, we have described the default rules used by
GNAT to determine the file name in which a given unit resides. It is
often convenient to follow these default rules, and if you follow them,
the compiler knows without being explicitly told where to find all
the files it needs.

@geindex Source_File_Name pragma

However, in some cases, particularly when a program is imported from
another Ada compiler environment, it may be more convenient for the
programmer to specify which file names contain which units. GNAT allows
arbitrary file names to be used by means of the Source_File_Name pragma.
The form of this pragma is as shown in the following examples:

@example
pragma Source_File_Name (My_Utilities.Stacks,
  Spec_File_Name => "myutilst_a.ada");
pragma Source_File_name (My_Utilities.Stacks,
  Body_File_Name => "myutilst.ada");
@end example

As shown in this example, the first argument for the pragma is the unit
name (in this example a child unit). The second argument has the form
of a named association. The identifier
indicates whether the file name is for a spec or a body;
the file name itself is given by a string literal.

The source file name pragma is a configuration pragma, which means that
normally it will be placed in the @code{gnat.adc}
file used to hold configuration
pragmas that apply to a complete compilation environment.
For more details on how the @code{gnat.adc} file is created and used
see @ref{58,,Handling of Configuration Pragmas}.

@geindex gnat.adc

GNAT allows completely arbitrary file names to be specified using the
source file name pragma. However, if the file name specified has an
extension other than @code{.ads} or @code{.adb} it is necessary to use
a special syntax when compiling the file. The name in this case must be
preceded by the special sequence @emph{-x} followed by a space and the name
of the language, here @cite{ada}, as in:

@example
$ gcc -c -x ada peculiar_file_name.sim
@end example

@cite{gnatmake} handles non-standard file names in the usual manner (the
non-standard file name for the main program is simply used as the
argument to gnatmake). Note that if the extension is also non-standard,
then it must be included in the @cite{gnatmake} command, it may not
be omitted.

@node Alternative File Naming Schemes,Handling Arbitrary File Naming Conventions with gnatname,Using Other File Names,File Naming Topics and Utilities
@anchor{gnat_ugn/the_gnat_compilation_model id11}@anchor{59}@anchor{gnat_ugn/the_gnat_compilation_model alternative-file-naming-schemes}@anchor{5a}
@subsection Alternative File Naming Schemes


@geindex File naming schemes
@geindex alternative

@geindex File names

The previous section described the use of the @cite{Source_File_Name}
pragma to allow arbitrary names to be assigned to individual source files.
However, this approach requires one pragma for each file, and especially in
large systems can result in very long @code{gnat.adc} files, and also create
a maintenance problem.

@geindex Source_File_Name pragma

GNAT also provides a facility for specifying systematic file naming schemes
other than the standard default naming scheme previously described. An
alternative scheme for naming is specified by the use of
@cite{Source_File_Name} pragmas having the following format:

@example
pragma Source_File_Name (
   Spec_File_Name  => FILE_NAME_PATTERN
 [ , Casing          => CASING_SPEC]
 [ , Dot_Replacement => STRING_LITERAL ] );

pragma Source_File_Name (
   Body_File_Name  => FILE_NAME_PATTERN
 [ , Casing          => CASING_SPEC ]
 [ , Dot_Replacement => STRING_LITERAL ] ) ;

pragma Source_File_Name (
   Subunit_File_Name  => FILE_NAME_PATTERN
 [ , Casing          => CASING_SPEC ]
 [ , Dot_Replacement => STRING_LITERAL ] ) ;

FILE_NAME_PATTERN ::= STRING_LITERAL
CASING_SPEC ::= Lowercase | Uppercase | Mixedcase
@end example

The @cite{FILE_NAME_PATTERN} string shows how the file name is constructed.
It contains a single asterisk character, and the unit name is substituted
systematically for this asterisk. The optional parameter
@cite{Casing} indicates
whether the unit name is to be all upper-case letters, all lower-case letters,
or mixed-case. If no
@cite{Casing} parameter is used, then the default is all
lower-case.

The optional @cite{Dot_Replacement} string is used to replace any periods
that occur in subunit or child unit names. If no @cite{Dot_Replacement}
argument is used then separating dots appear unchanged in the resulting
file name.
Although the above syntax indicates that the
@cite{Casing} argument must appear
before the @cite{Dot_Replacement} argument, but it
is also permissible to write these arguments in the opposite order.

As indicated, it is possible to specify different naming schemes for
bodies, specs, and subunits. Quite often the rule for subunits is the
same as the rule for bodies, in which case, there is no need to give
a separate @cite{Subunit_File_Name} rule, and in this case the
@cite{Body_File_name} rule is used for subunits as well.

The separate rule for subunits can also be used to implement the rather
unusual case of a compilation environment (e.g., a single directory) which
contains a subunit and a child unit with the same unit name. Although
both units cannot appear in the same partition, the Ada Reference Manual
allows (but does not require) the possibility of the two units coexisting
in the same environment.

The file name translation works in the following steps:


@itemize *

@item 
If there is a specific @cite{Source_File_Name} pragma for the given unit,
then this is always used, and any general pattern rules are ignored.

@item 
If there is a pattern type @cite{Source_File_Name} pragma that applies to
the unit, then the resulting file name will be used if the file exists. If
more than one pattern matches, the latest one will be tried first, and the
first attempt resulting in a reference to a file that exists will be used.

@item 
If no pattern type @cite{Source_File_Name} pragma that applies to the unit
for which the corresponding file exists, then the standard GNAT default
naming rules are used.
@end itemize

As an example of the use of this mechanism, consider a commonly used scheme
in which file names are all lower case, with separating periods copied
unchanged to the resulting file name, and specs end with @code{.1.ada}, and
bodies end with @code{.2.ada}. GNAT will follow this scheme if the following
two pragmas appear:

@example
pragma Source_File_Name
  (Spec_File_Name => ".1.ada");
pragma Source_File_Name
  (Body_File_Name => ".2.ada");
@end example

The default GNAT scheme is actually implemented by providing the following
default pragmas internally:

@example
pragma Source_File_Name
  (Spec_File_Name => ".ads", Dot_Replacement => "-");
pragma Source_File_Name
  (Body_File_Name => ".adb", Dot_Replacement => "-");
@end example

Our final example implements a scheme typically used with one of the
Ada 83 compilers, where the separator character for subunits was '__'
(two underscores), specs were identified by adding @code{_.ADA}, bodies
by adding @code{.ADA}, and subunits by
adding @code{.SEP}. All file names were
upper case. Child units were not present of course since this was an
Ada 83 compiler, but it seems reasonable to extend this scheme to use
the same double underscore separator for child units.

@example
pragma Source_File_Name
  (Spec_File_Name => "_.ADA",
   Dot_Replacement => "__",
   Casing = Uppercase);
pragma Source_File_Name
  (Body_File_Name => ".ADA",
   Dot_Replacement => "__",
   Casing = Uppercase);
pragma Source_File_Name
  (Subunit_File_Name => ".SEP",
   Dot_Replacement => "__",
   Casing = Uppercase);
@end example

@geindex gnatname

@node Handling Arbitrary File Naming Conventions with gnatname,File Name Krunching with gnatkr,Alternative File Naming Schemes,File Naming Topics and Utilities
@anchor{gnat_ugn/the_gnat_compilation_model handling-arbitrary-file-naming-conventions-with-gnatname}@anchor{5b}@anchor{gnat_ugn/the_gnat_compilation_model id12}@anchor{5c}
@subsection Handling Arbitrary File Naming Conventions with @cite{gnatname}


@geindex File Naming Conventions

@menu
* Arbitrary File Naming Conventions:: 
* Running gnatname:: 
* Switches for gnatname:: 
* Examples of gnatname Usage:: 

@end menu

@node Arbitrary File Naming Conventions,Running gnatname,,Handling Arbitrary File Naming Conventions with gnatname
@anchor{gnat_ugn/the_gnat_compilation_model arbitrary-file-naming-conventions}@anchor{5d}@anchor{gnat_ugn/the_gnat_compilation_model id13}@anchor{5e}
@subsubsection Arbitrary File Naming Conventions


The GNAT compiler must be able to know the source file name of a compilation
unit.  When using the standard GNAT default file naming conventions
(@cite{.ads} for specs, @cite{.adb} for bodies), the GNAT compiler
does not need additional information.

When the source file names do not follow the standard GNAT default file naming
conventions, the GNAT compiler must be given additional information through
a configuration pragmas file (@ref{16,,Configuration Pragmas})
or a project file.
When the non-standard file naming conventions are well-defined,
a small number of pragmas @cite{Source_File_Name} specifying a naming pattern
(@ref{5a,,Alternative File Naming Schemes}) may be sufficient. However,
if the file naming conventions are irregular or arbitrary, a number
of pragma @cite{Source_File_Name} for individual compilation units
must be defined.
To help maintain the correspondence between compilation unit names and
source file names within the compiler,
GNAT provides a tool @cite{gnatname} to generate the required pragmas for a
set of files.

@node Running gnatname,Switches for gnatname,Arbitrary File Naming Conventions,Handling Arbitrary File Naming Conventions with gnatname
@anchor{gnat_ugn/the_gnat_compilation_model running-gnatname}@anchor{5f}@anchor{gnat_ugn/the_gnat_compilation_model id14}@anchor{60}
@subsubsection Running @cite{gnatname}


The usual form of the @cite{gnatname} command is:

@example
$ gnatname [`switches`] `naming_pattern` [`naming_patterns`]
    [--and [`switches`] `naming_pattern` [`naming_patterns`]]
@end example

All of the arguments are optional. If invoked without any argument,
@cite{gnatname} will display its usage.

When used with at least one naming pattern, @cite{gnatname} will attempt to
find all the compilation units in files that follow at least one of the
naming patterns. To find these compilation units,
@cite{gnatname} will use the GNAT compiler in syntax-check-only mode on all
regular files.

One or several Naming Patterns may be given as arguments to @cite{gnatname}.
Each Naming Pattern is enclosed between double quotes (or single
quotes on Windows).
A Naming Pattern is a regular expression similar to the wildcard patterns
used in file names by the Unix shells or the DOS prompt.

@cite{gnatname} may be called with several sections of directories/patterns.
Sections are separated by switch @cite{--and}. In each section, there must be
at least one pattern. If no directory is specified in a section, the current
directory (or the project directory is @cite{-P} is used) is implied.
The options other that the directory switches and the patterns apply globally
even if they are in different sections.

Examples of Naming Patterns are:

@example
"*.[12].ada"
"*.ad[sb]*"
"body_*"    "spec_*"
@end example

For a more complete description of the syntax of Naming Patterns,
see the second kind of regular expressions described in @code{g-regexp.ads}
(the 'Glob' regular expressions).

When invoked with no switch @cite{-P}, @cite{gnatname} will create a
configuration pragmas file @code{gnat.adc} in the current working directory,
with pragmas @cite{Source_File_Name} for each file that contains a valid Ada
unit.

@node Switches for gnatname,Examples of gnatname Usage,Running gnatname,Handling Arbitrary File Naming Conventions with gnatname
@anchor{gnat_ugn/the_gnat_compilation_model id15}@anchor{61}@anchor{gnat_ugn/the_gnat_compilation_model switches-for-gnatname}@anchor{62}
@subsubsection Switches for @cite{gnatname}


Switches for @cite{gnatname} must precede any specified Naming Pattern.

You may specify any of the following switches to @cite{gnatname}:

@geindex --version (gnatname)


@table @asis

@item @code{--version}

Display Copyright and version, then exit disregarding all other options.
@end table

@geindex --help (gnatname)


@table @asis

@item @code{--help}

If @emph{--version} was not used, display usage, then exit disregarding
all other options.

@item @code{--subdirs=@emph{dir}}

Real object, library or exec directories are subdirectories <dir> of the
specified ones.

@item @code{--no-backup}

Do not create a backup copy of an existing project file.

@item @code{--and}

Start another section of directories/patterns.
@end table

@geindex -c (gnatname)


@table @asis

@item @code{-c@emph{filename}}

Create a configuration pragmas file @code{filename} (instead of the default
@code{gnat.adc}).
There may be zero, one or more space between @emph{-c} and
@code{filename}.
@code{filename} may include directory information. @code{filename} must be
writable. There may be only one switch @emph{-c}.
When a switch @emph{-c} is
specified, no switch @emph{-P} may be specified (see below).
@end table

@geindex -d (gnatname)


@table @asis

@item @code{-d@emph{dir}}

Look for source files in directory @code{dir}. There may be zero, one or more
spaces between @emph{-d} and @code{dir}.
@code{dir} may end with @cite{/**}, that is it may be of the form
@cite{root_dir/**}. In this case, the directory @cite{root_dir} and all of its
subdirectories, recursively, have to be searched for sources.
When a switch @emph{-d}
is specified, the current working directory will not be searched for source
files, unless it is explicitly specified with a @emph{-d}
or @emph{-D} switch.
Several switches @emph{-d} may be specified.
If @code{dir} is a relative path, it is relative to the directory of
the configuration pragmas file specified with switch
@emph{-c},
or to the directory of the project file specified with switch
@emph{-P} or,
if neither switch @emph{-c}
nor switch @emph{-P} are specified, it is relative to the
current working directory. The directory
specified with switch @emph{-d} must exist and be readable.
@end table

@geindex -D (gnatname)


@table @asis

@item @code{-D@emph{filename}}

Look for source files in all directories listed in text file @code{filename}.
There may be zero, one or more spaces between @emph{-D}
and @code{filename}.
@code{filename} must be an existing, readable text file.
Each nonempty line in @code{filename} must be a directory.
Specifying switch @emph{-D} is equivalent to specifying as many
switches @emph{-d} as there are nonempty lines in
@code{file}.

@item @code{-eL}

Follow symbolic links when processing project files.

@geindex -f (gnatname)

@item @code{-f@emph{pattern}}

Foreign patterns. Using this switch, it is possible to add sources of languages
other than Ada to the list of sources of a project file.
It is only useful if a -P switch is used.
For example,

@example
gnatname -Pprj -f"*.c" "*.ada"
@end example

will look for Ada units in all files with the @code{.ada} extension,
and will add to the list of file for project @code{prj.gpr} the C files
with extension @code{.c}.

@geindex -h (gnatname)

@item @code{-h}

Output usage (help) information. The output is written to @code{stdout}.

@geindex -P (gnatname)

@item @code{-P@emph{proj}}

Create or update project file @code{proj}. There may be zero, one or more space
between @emph{-P} and @code{proj}. @code{proj} may include directory
information. @code{proj} must be writable.
There may be only one switch @emph{-P}.
When a switch @emph{-P} is specified,
no switch @emph{-c} may be specified.
On all platforms, except on VMS, when @cite{gnatname} is invoked for an
existing project file <proj>.gpr, a backup copy of the project file is created
in the project directory with file name <proj>.gpr.saved_x. 'x' is the first
non negative number that makes this backup copy a new file.

@geindex -v (gnatname)

@item @code{-v}

Verbose mode. Output detailed explanation of behavior to @code{stdout}.
This includes name of the file written, the name of the directories to search
and, for each file in those directories whose name matches at least one of
the Naming Patterns, an indication of whether the file contains a unit,
and if so the name of the unit.
@end table

@geindex -v -v (gnatname)


@table @asis

@item @code{-v -v}

Very Verbose mode. In addition to the output produced in verbose mode,
for each file in the searched directories whose name matches none of
the Naming Patterns, an indication is given that there is no match.

@geindex -x (gnatname)

@item @code{-x@emph{pattern}}

Excluded patterns. Using this switch, it is possible to exclude some files
that would match the name patterns. For example,

@example
gnatname -x "*_nt.ada" "*.ada"
@end example

will look for Ada units in all files with the @code{.ada} extension,
except those whose names end with @code{_nt.ada}.
@end table

@node Examples of gnatname Usage,,Switches for gnatname,Handling Arbitrary File Naming Conventions with gnatname
@anchor{gnat_ugn/the_gnat_compilation_model examples-of-gnatname-usage}@anchor{63}@anchor{gnat_ugn/the_gnat_compilation_model id16}@anchor{64}
@subsubsection Examples of @cite{gnatname} Usage


@example
$ gnatname -c /home/me/names.adc -d sources "[a-z]*.ada*"
@end example

In this example, the directory @code{/home/me} must already exist
and be writable. In addition, the directory
@code{/home/me/sources} (specified by
@emph{-d sources}) must exist and be readable.

Note the optional spaces after @emph{-c} and @emph{-d}.

@example
$ gnatname -P/home/me/proj -x "*_nt_body.ada"
-dsources -dsources/plus -Dcommon_dirs.txt "body_*" "spec_*"
@end example

Note that several switches @emph{-d} may be used,
even in conjunction with one or several switches
@emph{-D}. Several Naming Patterns and one excluded pattern
are used in this example.

@node File Name Krunching with gnatkr,Renaming Files with gnatchop,Handling Arbitrary File Naming Conventions with gnatname,File Naming Topics and Utilities
@anchor{gnat_ugn/the_gnat_compilation_model file-name-krunching-with-gnatkr}@anchor{65}@anchor{gnat_ugn/the_gnat_compilation_model id17}@anchor{66}
@subsection File Name Krunching with @cite{gnatkr}


@geindex gnatkr

This chapter discusses the method used by the compiler to shorten
the default file names chosen for Ada units so that they do not
exceed the maximum length permitted. It also describes the
@cite{gnatkr} utility that can be used to determine the result of
applying this shortening.

@menu
* About gnatkr:: 
* Using gnatkr:: 
* Krunching Method:: 
* Examples of gnatkr Usage:: 

@end menu

@node About gnatkr,Using gnatkr,,File Name Krunching with gnatkr
@anchor{gnat_ugn/the_gnat_compilation_model id18}@anchor{67}@anchor{gnat_ugn/the_gnat_compilation_model about-gnatkr}@anchor{68}
@subsubsection About @cite{gnatkr}


The default file naming rule in GNAT
is that the file name must be derived from
the unit name. The exact default rule is as follows:


@itemize *

@item 
Take the unit name and replace all dots by hyphens.

@item 
If such a replacement occurs in the
second character position of a name, and the first character is
@code{a}, @code{g}, @code{s}, or @code{i},
then replace the dot by the character
@code{~} (tilde)
instead of a minus.

The reason for this exception is to avoid clashes
with the standard names for children of System, Ada, Interfaces,
and GNAT, which use the prefixes
@code{s-}, @code{a-}, @code{i-}, and @code{g-},
respectively.
@end itemize

The @code{-gnatk@emph{nn}}
switch of the compiler activates a 'krunching'
circuit that limits file names to nn characters (where nn is a decimal
integer).

The @cite{gnatkr} utility can be used to determine the krunched name for
a given file, when krunched to a specified maximum length.

@node Using gnatkr,Krunching Method,About gnatkr,File Name Krunching with gnatkr
@anchor{gnat_ugn/the_gnat_compilation_model id19}@anchor{69}@anchor{gnat_ugn/the_gnat_compilation_model using-gnatkr}@anchor{56}
@subsubsection Using @cite{gnatkr}


The @cite{gnatkr} command has the form:

@example
$ gnatkr `name` [`length`]
@end example

@cite{name} is the uncrunched file name, derived from the name of the unit
in the standard manner described in the previous section (i.e., in particular
all dots are replaced by hyphens). The file name may or may not have an
extension (defined as a suffix of the form period followed by arbitrary
characters other than period). If an extension is present then it will
be preserved in the output. For example, when krunching @code{hellofile.ads}
to eight characters, the result will be hellofil.ads.

Note: for compatibility with previous versions of @cite{gnatkr} dots may
appear in the name instead of hyphens, but the last dot will always be
taken as the start of an extension. So if @cite{gnatkr} is given an argument
such as @code{Hello.World.adb} it will be treated exactly as if the first
period had been a hyphen, and for example krunching to eight characters
gives the result @code{hellworl.adb}.

Note that the result is always all lower case.
Characters of the other case are folded as required.

@cite{length} represents the length of the krunched name. The default
when no argument is given is 8 characters. A length of zero stands for
unlimited, in other words do not chop except for system files where the
implied crunching length is always eight characters.

The output is the krunched name. The output has an extension only if the
original argument was a file name with an extension.

@node Krunching Method,Examples of gnatkr Usage,Using gnatkr,File Name Krunching with gnatkr
@anchor{gnat_ugn/the_gnat_compilation_model id20}@anchor{6a}@anchor{gnat_ugn/the_gnat_compilation_model krunching-method}@anchor{6b}
@subsubsection Krunching Method


The initial file name is determined by the name of the unit that the file
contains. The name is formed by taking the full expanded name of the
unit and replacing the separating dots with hyphens and
using lowercase
for all letters, except that a hyphen in the second character position is
replaced by a tilde if the first character is
@code{a}, @code{i}, @code{g}, or @code{s}.
The extension is @cite{.ads} for a
spec and @cite{.adb} for a body.
Krunching does not affect the extension, but the file name is shortened to
the specified length by following these rules:


@itemize *

@item 
The name is divided into segments separated by hyphens, tildes or
underscores and all hyphens, tildes, and underscores are
eliminated. If this leaves the name short enough, we are done.

@item 
If the name is too long, the longest segment is located (left-most
if there are two of equal length), and shortened by dropping
its last character. This is repeated until the name is short enough.

As an example, consider the krunching of @code{our-strings-wide_fixed.adb}
to fit the name into 8 characters as required by some operating systems:

@example
our-strings-wide_fixed 22
our strings wide fixed 19
our string  wide fixed 18
our strin   wide fixed 17
our stri    wide fixed 16
our stri    wide fixe  15
our str     wide fixe  14
our str     wid  fixe  13
our str     wid  fix   12
ou  str     wid  fix   11
ou  st      wid  fix   10
ou  st      wi   fix   9
ou  st      wi   fi    8
Final file name: oustwifi.adb
@end example

@item 
The file names for all predefined units are always krunched to eight
characters. The krunching of these predefined units uses the following
special prefix replacements:


@multitable {xxxxxxxxxxxxxxxxxxxxxxx} {xxxxxxxxxxxxxxxx} 
@item

Prefix

@tab

Replacement

@item

@code{ada-}

@tab

@code{a-}

@item

@code{gnat-}

@tab

@code{g-}

@item

@code{interfac es-}

@tab

@code{i-}

@item

@code{system-}

@tab

@code{s-}

@end multitable


These system files have a hyphen in the second character position. That
is why normal user files replace such a character with a
tilde, to avoid confusion with system file names.

As an example of this special rule, consider
@code{ada-strings-wide_fixed.adb}, which gets krunched as follows:

@example
ada-strings-wide_fixed 22
a-  strings wide fixed 18
a-  string  wide fixed 17
a-  strin   wide fixed 16
a-  stri    wide fixed 15
a-  stri    wide fixe  14
a-  str     wide fixe  13
a-  str     wid  fixe  12
a-  str     wid  fix   11
a-  st      wid  fix   10
a-  st      wi   fix   9
a-  st      wi   fi    8
Final file name: a-stwifi.adb
@end example
@end itemize

Of course no file shortening algorithm can guarantee uniqueness over all
possible unit names, and if file name krunching is used then it is your
responsibility to ensure that no name clashes occur. The utility
program @cite{gnatkr} is supplied for conveniently determining the
krunched name of a file.

@node Examples of gnatkr Usage,,Krunching Method,File Name Krunching with gnatkr
@anchor{gnat_ugn/the_gnat_compilation_model id21}@anchor{6c}@anchor{gnat_ugn/the_gnat_compilation_model examples-of-gnatkr-usage}@anchor{6d}
@subsubsection Examples of @cite{gnatkr} Usage


@example
$ gnatkr very_long_unit_name.ads      --> velounna.ads
$ gnatkr grandparent-parent-child.ads --> grparchi.ads
$ gnatkr Grandparent.Parent.Child.ads --> grparchi.ads
$ gnatkr grandparent-parent-child     --> grparchi
$ gnatkr very_long_unit_name.ads/count=6 --> vlunna.ads
$ gnatkr very_long_unit_name.ads/count=0 --> very_long_unit_name.ads
@end example

@node Renaming Files with gnatchop,,File Name Krunching with gnatkr,File Naming Topics and Utilities
@anchor{gnat_ugn/the_gnat_compilation_model id22}@anchor{6e}@anchor{gnat_ugn/the_gnat_compilation_model renaming-files-with-gnatchop}@anchor{38}
@subsection Renaming Files with @cite{gnatchop}


@geindex gnatchop

This chapter discusses how to handle files with multiple units by using
the @cite{gnatchop} utility. This utility is also useful in renaming
files to meet the standard GNAT default file naming conventions.

@menu
* Handling Files with Multiple Units:: 
* Operating gnatchop in Compilation Mode:: 
* Command Line for gnatchop:: 
* Switches for gnatchop:: 
* Examples of gnatchop Usage:: 

@end menu

@node Handling Files with Multiple Units,Operating gnatchop in Compilation Mode,,Renaming Files with gnatchop
@anchor{gnat_ugn/the_gnat_compilation_model id23}@anchor{6f}@anchor{gnat_ugn/the_gnat_compilation_model handling-files-with-multiple-units}@anchor{70}
@subsubsection Handling Files with Multiple Units


The basic compilation model of GNAT requires that a file submitted to the
compiler have only one unit and there be a strict correspondence
between the file name and the unit name.

The @cite{gnatchop} utility allows both of these rules to be relaxed,
allowing GNAT to process files which contain multiple compilation units
and files with arbitrary file names. @cite{gnatchop}
reads the specified file and generates one or more output files,
containing one unit per file. The unit and the file name correspond,
as required by GNAT.

If you want to permanently restructure a set of 'foreign' files so that
they match the GNAT rules, and do the remaining development using the
GNAT structure, you can simply use @emph{gnatchop} once, generate the
new set of files and work with them from that point on.

Alternatively, if you want to keep your files in the 'foreign' format,
perhaps to maintain compatibility with some other Ada compilation
system, you can set up a procedure where you use @emph{gnatchop} each
time you compile, regarding the source files that it writes as temporary
files that you throw away.

Note that if your file containing multiple units starts with a byte order
mark (BOM) specifying UTF-8 encoding, then the files generated by gnatchop
will each start with a copy of this BOM, meaning that they can be compiled
automatically in UTF-8 mode without needing to specify an explicit encoding.

@node Operating gnatchop in Compilation Mode,Command Line for gnatchop,Handling Files with Multiple Units,Renaming Files with gnatchop
@anchor{gnat_ugn/the_gnat_compilation_model operating-gnatchop-in-compilation-mode}@anchor{71}@anchor{gnat_ugn/the_gnat_compilation_model id24}@anchor{72}
@subsubsection Operating gnatchop in Compilation Mode


The basic function of @cite{gnatchop} is to take a file with multiple units
and split it into separate files. The boundary between files is reasonably
clear, except for the issue of comments and pragmas. In default mode, the
rule is that any pragmas between units belong to the previous unit, except
that configuration pragmas always belong to the following unit. Any comments
belong to the following unit. These rules
almost always result in the right choice of
the split point without needing to mark it explicitly and most users will
find this default to be what they want. In this default mode it is incorrect to
submit a file containing only configuration pragmas, or one that ends in
configuration pragmas, to @cite{gnatchop}.

However, using a special option to activate 'compilation mode',
@cite{gnatchop}
can perform another function, which is to provide exactly the semantics
required by the RM for handling of configuration pragmas in a compilation.
In the absence of configuration pragmas (at the main file level), this
option has no effect, but it causes such configuration pragmas to be handled
in a quite different manner.

First, in compilation mode, if @cite{gnatchop} is given a file that consists of
only configuration pragmas, then this file is appended to the
@code{gnat.adc} file in the current directory. This behavior provides
the required behavior described in the RM for the actions to be taken
on submitting such a file to the compiler, namely that these pragmas
should apply to all subsequent compilations in the same compilation
environment. Using GNAT, the current directory, possibly containing a
@code{gnat.adc} file is the representation
of a compilation environment. For more information on the
@code{gnat.adc} file, see @ref{58,,Handling of Configuration Pragmas}.

Second, in compilation mode, if @cite{gnatchop}
is given a file that starts with
configuration pragmas, and contains one or more units, then these
configuration pragmas are prepended to each of the chopped files. This
behavior provides the required behavior described in the RM for the
actions to be taken on compiling such a file, namely that the pragmas
apply to all units in the compilation, but not to subsequently compiled
units.

Finally, if configuration pragmas appear between units, they are appended
to the previous unit. This results in the previous unit being illegal,
since the compiler does not accept configuration pragmas that follow
a unit. This provides the required RM behavior that forbids configuration
pragmas other than those preceding the first compilation unit of a
compilation.

For most purposes, @cite{gnatchop} will be used in default mode. The
compilation mode described above is used only if you need exactly
accurate behavior with respect to compilations, and you have files
that contain multiple units and configuration pragmas. In this
circumstance the use of @cite{gnatchop} with the compilation mode
switch provides the required behavior, and is for example the mode
in which GNAT processes the ACVC tests.

@node Command Line for gnatchop,Switches for gnatchop,Operating gnatchop in Compilation Mode,Renaming Files with gnatchop
@anchor{gnat_ugn/the_gnat_compilation_model id25}@anchor{73}@anchor{gnat_ugn/the_gnat_compilation_model command-line-for-gnatchop}@anchor{74}
@subsubsection Command Line for @cite{gnatchop}


The @cite{gnatchop} command has the form:

@example
$ gnatchop switches file_name [file_name ...]
      [directory]
@end example

The only required argument is the file name of the file to be chopped.
There are no restrictions on the form of this file name. The file itself
contains one or more Ada units, in normal GNAT format, concatenated
together. As shown, more than one file may be presented to be chopped.

When run in default mode, @cite{gnatchop} generates one output file in
the current directory for each unit in each of the files.

@cite{directory}, if specified, gives the name of the directory to which
the output files will be written. If it is not specified, all files are
written to the current directory.

For example, given a
file called @code{hellofiles} containing

@example
procedure Hello;

with Ada.Text_IO; use Ada.Text_IO;
procedure Hello is
begin
   Put_Line ("Hello");
end Hello;
@end example

the command

@example
$ gnatchop hellofiles
@end example

generates two files in the current directory, one called
@code{hello.ads} containing the single line that is the procedure spec,
and the other called @code{hello.adb} containing the remaining text. The
original file is not affected. The generated files can be compiled in
the normal manner.

When gnatchop is invoked on a file that is empty or that contains only empty
lines and/or comments, gnatchop will not fail, but will not produce any
new sources.

For example, given a
file called @code{toto.txt} containing

@example
--  Just a comment
@end example

the command

@example
$ gnatchop toto.txt
@end example

will not produce any new file and will result in the following warnings:

@example
toto.txt:1:01: warning: empty file, contains no compilation units
no compilation units found
no source files written
@end example

@node Switches for gnatchop,Examples of gnatchop Usage,Command Line for gnatchop,Renaming Files with gnatchop
@anchor{gnat_ugn/the_gnat_compilation_model switches-for-gnatchop}@anchor{75}@anchor{gnat_ugn/the_gnat_compilation_model id26}@anchor{76}
@subsubsection Switches for @cite{gnatchop}


@emph{gnatchop} recognizes the following switches:

@geindex --version (gnatchop)


@table @asis

@item @code{--version}

Display Copyright and version, then exit disregarding all other options.
@end table

@geindex --help (gnatchop)


@table @asis

@item @code{--help}

If @emph{--version} was not used, display usage, then exit disregarding
all other options.
@end table

@geindex -c (gnatchop)


@table @asis

@item @code{-c}

Causes @cite{gnatchop} to operate in compilation mode, in which
configuration pragmas are handled according to strict RM rules. See
previous section for a full description of this mode.

@item @code{-gnat@emph{xxx}}

This passes the given @emph{-gnat`xxx*` switch to `gnat` which is
used to parse the given file. Not all `xxx` options make sense,
but for example, the use of *-gnati2} allows @cite{gnatchop} to
process a source file that uses Latin-2 coding for identifiers.

@item @code{-h}

Causes @cite{gnatchop} to generate a brief help summary to the standard
output file showing usage information.
@end table

@geindex -k (gnatchop)


@table @asis

@item @code{-k@emph{mm}}

Limit generated file names to the specified number @cite{mm}
of characters.
This is useful if the
resulting set of files is required to be interoperable with systems
which limit the length of file names.
No space is allowed between the @emph{-k} and the numeric value. The numeric
value may be omitted in which case a default of @emph{-k8},
suitable for use
with DOS-like file systems, is used. If no @emph{-k} switch
is present then
there is no limit on the length of file names.
@end table

@geindex -p (gnatchop)


@table @asis

@item @code{-p}

Causes the file modification time stamp of the input file to be
preserved and used for the time stamp of the output file(s). This may be
useful for preserving coherency of time stamps in an environment where
@cite{gnatchop} is used as part of a standard build process.
@end table

@geindex -q (gnatchop)


@table @asis

@item @code{-q}

Causes output of informational messages indicating the set of generated
files to be suppressed. Warnings and error messages are unaffected.
@end table

@geindex -r (gnatchop)

@geindex Source_Reference pragmas


@table @asis

@item @code{-r}

Generate @cite{Source_Reference} pragmas. Use this switch if the output
files are regarded as temporary and development is to be done in terms
of the original unchopped file. This switch causes
@cite{Source_Reference} pragmas to be inserted into each of the
generated files to refers back to the original file name and line number.
The result is that all error messages refer back to the original
unchopped file.
In addition, the debugging information placed into the object file (when
the @emph{-g} switch of @emph{gcc} or @emph{gnatmake} is
specified)
also refers back to this original file so that tools like profilers and
debuggers will give information in terms of the original unchopped file.

If the original file to be chopped itself contains
a @cite{Source_Reference}
pragma referencing a third file, then gnatchop respects
this pragma, and the generated @cite{Source_Reference} pragmas
in the chopped file refer to the original file, with appropriate
line numbers. This is particularly useful when @cite{gnatchop}
is used in conjunction with @cite{gnatprep} to compile files that
contain preprocessing statements and multiple units.
@end table

@geindex -v (gnatchop)


@table @asis

@item @code{-v}

Causes @cite{gnatchop} to operate in verbose mode. The version
number and copyright notice are output, as well as exact copies of
the gnat1 commands spawned to obtain the chop control information.
@end table

@geindex -w (gnatchop)


@table @asis

@item @code{-w}

Overwrite existing file names. Normally @cite{gnatchop} regards it as a
fatal error if there is already a file with the same name as a
file it would otherwise output, in other words if the files to be
chopped contain duplicated units. This switch bypasses this
check, and causes all but the last instance of such duplicated
units to be skipped.
@end table

@geindex --GCC= (gnatchop)


@table @asis

@item @code{--GCC=@emph{xxxx}}

Specify the path of the GNAT parser to be used. When this switch is used,
no attempt is made to add the prefix to the GNAT parser executable.
@end table

@node Examples of gnatchop Usage,,Switches for gnatchop,Renaming Files with gnatchop
@anchor{gnat_ugn/the_gnat_compilation_model id27}@anchor{77}@anchor{gnat_ugn/the_gnat_compilation_model examples-of-gnatchop-usage}@anchor{78}
@subsubsection Examples of @cite{gnatchop} Usage


@example
$ gnatchop -w hello_s.ada prerelease/files
@end example

Chops the source file @code{hello_s.ada}. The output files will be
placed in the directory @code{prerelease/files},
overwriting any
files with matching names in that directory (no files in the current
directory are modified).

@example
$ gnatchop archive
@end example

Chops the source file @code{archive}
into the current directory. One
useful application of @cite{gnatchop} is in sending sets of sources
around, for example in email messages. The required sources are simply
concatenated (for example, using a Unix @cite{cat}
command), and then
@emph{gnatchop} is used at the other end to reconstitute the original
file names.

@example
$ gnatchop file1 file2 file3 direc
@end example

Chops all units in files @code{file1}, @code{file2}, @code{file3}, placing
the resulting files in the directory @code{direc}. Note that if any units
occur more than once anywhere within this set of files, an error message
is generated, and no files are written. To override this check, use the
@emph{-w} switch,
in which case the last occurrence in the last file will
be the one that is output, and earlier duplicate occurrences for a given
unit will be skipped.

@node Configuration Pragmas,Generating Object Files,File Naming Topics and Utilities,The GNAT Compilation Model
@anchor{gnat_ugn/the_gnat_compilation_model id28}@anchor{79}@anchor{gnat_ugn/the_gnat_compilation_model configuration-pragmas}@anchor{16}
@section Configuration Pragmas


@geindex Configuration pragmas

@geindex Pragmas
@geindex configuration

Configuration pragmas include those pragmas described as
such in the Ada Reference Manual, as well as
implementation-dependent pragmas that are configuration pragmas.
See the @cite{Implementation_Defined_Pragmas} chapter in the
@cite{GNAT_Reference_Manual} for details on these
additional GNAT-specific configuration pragmas.
Most notably, the pragma @cite{Source_File_Name}, which allows
specifying non-default names for source files, is a configuration
pragma. The following is a complete list of configuration pragmas
recognized by GNAT:

@example
Ada_83
Ada_95
Ada_05
Ada_2005
Ada_12
Ada_2012
Allow_Integer_Address
Annotate
Assertion_Policy
Assume_No_Invalid_Values
C_Pass_By_Copy
Check_Name
Check_Policy
Compile_Time_Error
Compile_Time_Warning
Compiler_Unit
Component_Alignment
Convention_Identifier
Debug_Policy
Detect_Blocking
Default_Storage_Pool
Discard_Names
Elaboration_Checks
Eliminate
Extend_System
Extensions_Allowed
External_Name_Casing
Fast_Math
Favor_Top_Level
Float_Representation
Implicit_Packing
Initialize_Scalars
Interrupt_State
License
Locking_Policy
Long_Float
No_Run_Time
No_Strict_Aliasing
Normalize_Scalars
Optimize_Alignment
Persistent_BSS
Polling
Priority_Specific_Dispatching
Profile
Profile_Warnings
Propagate_Exceptions
Queuing_Policy
Ravenscar
Restricted_Run_Time
Restrictions
Restrictions_Warnings
Reviewable
Short_Circuit_And_Or
Source_File_Name
Source_File_Name_Project
SPARK_Mode
Style_Checks
Suppress
Suppress_Exception_Locations
Task_Dispatching_Policy
Universal_Data
Unsuppress
Use_VADS_Size
Validity_Checks
Warnings
Wide_Character_Encoding
@end example

@menu
* Handling of Configuration Pragmas:: 
* The Configuration Pragmas Files:: 

@end menu

@node Handling of Configuration Pragmas,The Configuration Pragmas Files,,Configuration Pragmas
@anchor{gnat_ugn/the_gnat_compilation_model id29}@anchor{7a}@anchor{gnat_ugn/the_gnat_compilation_model handling-of-configuration-pragmas}@anchor{58}
@subsection Handling of Configuration Pragmas


Configuration pragmas may either appear at the start of a compilation
unit, or they can appear in a configuration pragma file to apply to
all compilations performed in a given compilation environment.

GNAT also provides the @cite{gnatchop} utility to provide an automatic
way to handle configuration pragmas following the semantics for
compilations (that is, files with multiple units), described in the RM.
See @ref{71,,Operating gnatchop in Compilation Mode} for details.
However, for most purposes, it will be more convenient to edit the
@code{gnat.adc} file that contains configuration pragmas directly,
as described in the following section.

In the case of @cite{Restrictions} pragmas appearing as configuration
pragmas in individual compilation units, the exact handling depends on
the type of restriction.

Restrictions that require partition-wide consistency (like
@cite{No_Tasking}) are
recognized wherever they appear
and can be freely inherited, e.g. from a @emph{with}ed unit to the @emph{with}ing
unit. This makes sense since the binder will in any case insist on seeing
consistent use, so any unit not conforming to any restrictions that are
anywhere in the partition will be rejected, and you might as well find
that out at compile time rather than at bind time.

For restrictions that do not require partition-wide consistency, e.g.
SPARK or No_Implementation_Attributes, in general the restriction applies
only to the unit in which the pragma appears, and not to any other units.

The exception is No_Elaboration_Code which always applies to the entire
object file from a compilation, i.e. to the body, spec, and all subunits.
This restriction can be specified in a configuration pragma file, or it
can be on the body and/or the spec (in eithe case it applies to all the
relevant units). It can appear on a subunit only if it has previously
appeared in the body of spec.

@node The Configuration Pragmas Files,,Handling of Configuration Pragmas,Configuration Pragmas
@anchor{gnat_ugn/the_gnat_compilation_model the-configuration-pragmas-files}@anchor{7b}@anchor{gnat_ugn/the_gnat_compilation_model id30}@anchor{7c}
@subsection The Configuration Pragmas Files


@geindex gnat.adc

In GNAT a compilation environment is defined by the current
directory at the time that a compile command is given. This current
directory is searched for a file whose name is @code{gnat.adc}. If
this file is present, it is expected to contain one or more
configuration pragmas that will be applied to the current compilation.
However, if the switch @emph{-gnatA} is used, @code{gnat.adc} is not
considered. When taken into account, @code{gnat.adc} is added to the
dependencies, so that if @code{gnat.adc} is modified later, an invocation of
@emph{gnatmake} will recompile the source.

Configuration pragmas may be entered into the @code{gnat.adc} file
either by running @cite{gnatchop} on a source file that consists only of
configuration pragmas, or more conveniently by direct editing of the
@code{gnat.adc} file, which is a standard format source file.

Besides @code{gnat.adc}, additional files containing configuration
pragmas may be applied to the current compilation using the switch
@code{-gnatec=@emph{path}} where @cite{path} must designate an existing file that
contains only configuration pragmas. These configuration pragmas are
in addition to those found in @code{gnat.adc} (provided @code{gnat.adc}
is present and switch @emph{-gnatA} is not used).

It is allowable to specify several switches @emph{-gnatec=}, all of which
will be taken into account.

Files containing configuration pragmas specified with switches
@emph{-gnatec=} are added to the dependencies, unless they are
temporary files. A file is considered temporary if its name ends in
@code{.tmp} or @code{.TMP}. Certain tools follow this naming
convention because they pass information to @emph{gcc} via
temporary files that are immediately deleted; it doesn't make sense to
depend on a file that no longer exists. Such tools include
@emph{gprbuild}, @emph{gnatmake}, and @emph{gnatcheck}.

If you are using project file, a separate mechanism is provided using
project attributes, see @ref{7d,,Specifying Configuration Pragmas} for more
details.

@node Generating Object Files,Source Dependencies,Configuration Pragmas,The GNAT Compilation Model
@anchor{gnat_ugn/the_gnat_compilation_model generating-object-files}@anchor{42}@anchor{gnat_ugn/the_gnat_compilation_model id31}@anchor{7e}
@section Generating Object Files


An Ada program consists of a set of source files, and the first step in
compiling the program is to generate the corresponding object files.
These are generated by compiling a subset of these source files.
The files you need to compile are the following:


@itemize *

@item 
If a package spec has no body, compile the package spec to produce the
object file for the package.

@item 
If a package has both a spec and a body, compile the body to produce the
object file for the package. The source file for the package spec need
not be compiled in this case because there is only one object file, which
contains the code for both the spec and body of the package.

@item 
For a subprogram, compile the subprogram body to produce the object file
for the subprogram. The spec, if one is present, is as usual in a
separate file, and need not be compiled.
@end itemize

@geindex Subunits


@itemize *

@item 
In the case of subunits, only compile the parent unit. A single object
file is generated for the entire subunit tree, which includes all the
subunits.

@item 
Compile child units independently of their parent units
(though, of course, the spec of all the ancestor unit must be present in order
to compile a child unit).

@geindex Generics

@item 
Compile generic units in the same manner as any other units. The object
files in this case are small dummy files that contain at most the
flag used for elaboration checking. This is because GNAT always handles generic
instantiation by means of macro expansion. However, it is still necessary to
compile generic units, for dependency checking and elaboration purposes.
@end itemize

The preceding rules describe the set of files that must be compiled to
generate the object files for a program. Each object file has the same
name as the corresponding source file, except that the extension is
@code{.o} as usual.

You may wish to compile other files for the purpose of checking their
syntactic and semantic correctness. For example, in the case where a
package has a separate spec and body, you would not normally compile the
spec. However, it is convenient in practice to compile the spec to make
sure it is error-free before compiling clients of this spec, because such
compilations will fail if there is an error in the spec.

GNAT provides an option for compiling such files purely for the
purposes of checking correctness; such compilations are not required as
part of the process of building a program. To compile a file in this
checking mode, use the @emph{-gnatc} switch.

@node Source Dependencies,The Ada Library Information Files,Generating Object Files,The GNAT Compilation Model
@anchor{gnat_ugn/the_gnat_compilation_model id32}@anchor{7f}@anchor{gnat_ugn/the_gnat_compilation_model source-dependencies}@anchor{43}
@section Source Dependencies


A given object file clearly depends on the source file which is compiled
to produce it. Here we are using "depends" in the sense of a typical
@cite{make} utility; in other words, an object file depends on a source
file if changes to the source file require the object file to be
recompiled.
In addition to this basic dependency, a given object may depend on
additional source files as follows:


@itemize *

@item 
If a file being compiled @emph{with}s a unit @cite{X}, the object file
depends on the file containing the spec of unit @cite{X}. This includes
files that are @emph{with}ed implicitly either because they are parents
of @emph{with}ed child units or they are run-time units required by the
language constructs used in a particular unit.

@item 
If a file being compiled instantiates a library level generic unit, the
object file depends on both the spec and body files for this generic
unit.

@item 
If a file being compiled instantiates a generic unit defined within a
package, the object file depends on the body file for the package as
well as the spec file.
@end itemize

@geindex Inline

@geindex -gnatn switch


@itemize *

@item 
If a file being compiled contains a call to a subprogram for which
pragma @cite{Inline} applies and inlining is activated with the
@emph{-gnatn} switch, the object file depends on the file containing the
body of this subprogram as well as on the file containing the spec. Note
that for inlining to actually occur as a result of the use of this switch,
it is necessary to compile in optimizing mode.

@geindex -gnatN switch

The use of @emph{-gnatN} activates  inlining optimization
that is performed by the front end of the compiler. This inlining does
not require that the code generation be optimized. Like @emph{-gnatn},
the use of this switch generates additional dependencies.

When using a gcc-based back end (in practice this means using any version
of GNAT other than for the JVM, .NET or GNAAMP platforms), then the use of
@emph{-gnatN} is deprecated, and the use of @emph{-gnatn} is preferred.
Historically front end inlining was more extensive than the gcc back end
inlining, but that is no longer the case.

@item 
If an object file @code{O} depends on the proper body of a subunit through
inlining or instantiation, it depends on the parent unit of the subunit.
This means that any modification of the parent unit or one of its subunits
affects the compilation of @code{O}.

@item 
The object file for a parent unit depends on all its subunit body files.

@item 
The previous two rules meant that for purposes of computing dependencies and
recompilation, a body and all its subunits are treated as an indivisible whole.

These rules are applied transitively: if unit @cite{A} @emph{with}s
unit @cite{B}, whose elaboration calls an inlined procedure in package
@cite{C}, the object file for unit @cite{A} will depend on the body of
@cite{C}, in file @code{c.adb}.

The set of dependent files described by these rules includes all the
files on which the unit is semantically dependent, as dictated by the
Ada language standard. However, it is a superset of what the
standard describes, because it includes generic, inline, and subunit
dependencies.

An object file must be recreated by recompiling the corresponding source
file if any of the source files on which it depends are modified. For
example, if the @cite{make} utility is used to control compilation,
the rule for an Ada object file must mention all the source files on
which the object file depends, according to the above definition.
The determination of the necessary
recompilations is done automatically when one uses @emph{gnatmake}.
@end itemize

@node The Ada Library Information Files,Binding an Ada Program,Source Dependencies,The GNAT Compilation Model
@anchor{gnat_ugn/the_gnat_compilation_model id33}@anchor{80}@anchor{gnat_ugn/the_gnat_compilation_model the-ada-library-information-files}@anchor{44}
@section The Ada Library Information Files


@geindex Ada Library Information files

@geindex ALI files

Each compilation actually generates two output files. The first of these
is the normal object file that has a @code{.o} extension. The second is a
text file containing full dependency information. It has the same
name as the source file, but an @code{.ali} extension.
This file is known as the Ada Library Information (@code{ALI}) file.
The following information is contained in the @code{ALI} file.


@itemize *

@item 
Version information (indicates which version of GNAT was used to compile
the unit(s) in question)

@item 
Main program information (including priority and time slice settings,
as well as the wide character encoding used during compilation).

@item 
List of arguments used in the @emph{gcc} command for the compilation

@item 
Attributes of the unit, including configuration pragmas used, an indication
of whether the compilation was successful, exception model used etc.

@item 
A list of relevant restrictions applying to the unit (used for consistency)
checking.

@item 
Categorization information (e.g., use of pragma @cite{Pure}).

@item 
Information on all @emph{with}ed units, including presence of
Elaborate` or @cite{Elaborate_All} pragmas.

@item 
Information from any @cite{Linker_Options} pragmas used in the unit

@item 
Information on the use of @cite{Body_Version} or @cite{Version}
attributes in the unit.

@item 
Dependency information. This is a list of files, together with
time stamp and checksum information. These are files on which
the unit depends in the sense that recompilation is required
if any of these units are modified.

@item 
Cross-reference data. Contains information on all entities referenced
in the unit. Used by tools like @cite{gnatxref} and @cite{gnatfind} to
provide cross-reference information.
@end itemize

For a full detailed description of the format of the @code{ALI} file,
see the source of the body of unit @cite{Lib.Writ}, contained in file
@code{lib-writ.adb} in the GNAT compiler sources.

@node Binding an Ada Program,GNAT and Libraries,The Ada Library Information Files,The GNAT Compilation Model
@anchor{gnat_ugn/the_gnat_compilation_model id34}@anchor{81}@anchor{gnat_ugn/the_gnat_compilation_model binding-an-ada-program}@anchor{45}
@section Binding an Ada Program


When using languages such as C and C++, once the source files have been
compiled the only remaining step in building an executable program
is linking the object modules together. This means that it is possible to
link an inconsistent version of a program, in which two units have
included different versions of the same header.

The rules of Ada do not permit such an inconsistent program to be built.
For example, if two clients have different versions of the same package,
it is illegal to build a program containing these two clients.
These rules are enforced by the GNAT binder, which also determines an
elaboration order consistent with the Ada rules.

The GNAT binder is run after all the object files for a program have
been created. It is given the name of the main program unit, and from
this it determines the set of units required by the program, by reading the
corresponding ALI files. It generates error messages if the program is
inconsistent or if no valid order of elaboration exists.

If no errors are detected, the binder produces a main program, in Ada by
default, that contains calls to the elaboration procedures of those
compilation unit that require them, followed by
a call to the main program. This Ada program is compiled to generate the
object file for the main program. The name of
the Ada file is @code{b~xxx}.adb` (with the corresponding spec
@code{b~xxx}.ads`) where @cite{xxx} is the name of the
main program unit.

Finally, the linker is used to build the resulting executable program,
using the object from the main program from the bind step as well as the
object files for the Ada units of the program.

@node GNAT and Libraries,Conditional Compilation,Binding an Ada Program,The GNAT Compilation Model
@anchor{gnat_ugn/the_gnat_compilation_model gnat-and-libraries}@anchor{17}@anchor{gnat_ugn/the_gnat_compilation_model id35}@anchor{82}
@section GNAT and Libraries


@geindex Library building and using

This chapter describes how to build and use libraries with GNAT, and also shows
how to recompile the GNAT run-time library. You should be familiar with the
Project Manager facility (@ref{b,,GNAT Project Manager}) before reading this
chapter.

@menu
* Introduction to Libraries in GNAT:: 
* General Ada Libraries:: 
* Stand-alone Ada Libraries:: 
* Rebuilding the GNAT Run-Time Library:: 

@end menu

@node Introduction to Libraries in GNAT,General Ada Libraries,,GNAT and Libraries
@anchor{gnat_ugn/the_gnat_compilation_model introduction-to-libraries-in-gnat}@anchor{83}@anchor{gnat_ugn/the_gnat_compilation_model id36}@anchor{84}
@subsection Introduction to Libraries in GNAT


A library is, conceptually, a collection of objects which does not have its
own main thread of execution, but rather provides certain services to the
applications that use it. A library can be either statically linked with the
application, in which case its code is directly included in the application,
or, on platforms that support it, be dynamically linked, in which case
its code is shared by all applications making use of this library.

GNAT supports both types of libraries.
In the static case, the compiled code can be provided in different ways. The
simplest approach is to provide directly the set of objects resulting from
compilation of the library source files. Alternatively, you can group the
objects into an archive using whatever commands are provided by the operating
system. For the latter case, the objects are grouped into a shared library.

In the GNAT environment, a library has three types of components:


@itemize *

@item 
Source files,

@item 
@code{ALI} files (see @ref{44,,The Ada Library Information Files}), and

@item 
Object files, an archive or a shared library.
@end itemize

A GNAT library may expose all its source files, which is useful for
documentation purposes. Alternatively, it may expose only the units needed by
an external user to make use of the library. That is to say, the specs
reflecting the library services along with all the units needed to compile
those specs, which can include generic bodies or any body implementing an
inlined routine. In the case of @emph{stand-alone libraries} those exposed
units are called @emph{interface units} (@ref{85,,Stand-alone Ada Libraries}).

All compilation units comprising an application, including those in a library,
need to be elaborated in an order partially defined by Ada's semantics. GNAT
computes the elaboration order from the @code{ALI} files and this is why they
constitute a mandatory part of GNAT libraries.
@emph{Stand-alone libraries} are the exception to this rule because a specific
library elaboration routine is produced independently of the application(s)
using the library.

@node General Ada Libraries,Stand-alone Ada Libraries,Introduction to Libraries in GNAT,GNAT and Libraries
@anchor{gnat_ugn/the_gnat_compilation_model general-ada-libraries}@anchor{86}@anchor{gnat_ugn/the_gnat_compilation_model id37}@anchor{87}
@subsection General Ada Libraries


@menu
* Building a library:: 
* Installing a library:: 
* Using a library:: 

@end menu

@node Building a library,Installing a library,,General Ada Libraries
@anchor{gnat_ugn/the_gnat_compilation_model building-a-library}@anchor{88}@anchor{gnat_ugn/the_gnat_compilation_model id38}@anchor{89}
@subsubsection Building a library


The easiest way to build a library is to use the Project Manager,
which supports a special type of project called a @emph{Library Project}
(see @ref{8a,,Library Projects}).

A project is considered a library project, when two project-level attributes
are defined in it: @cite{Library_Name} and @cite{Library_Dir}. In order to
control different aspects of library configuration, additional optional
project-level attributes can be specified:


@itemize *

@item 

@table @asis

@item @emph{Library_Kind}

This attribute controls whether the library is to be static or dynamic
@end table

@item 

@table @asis

@item @emph{Library_Version}

This attribute specifies the library version; this value is used
during dynamic linking of shared libraries to determine if the currently
installed versions of the binaries are compatible.
@end table

@item 
@emph{Library_Options}

@item 

@table @asis

@item @emph{Library_GCC}

These attributes specify additional low-level options to be used during
library generation, and redefine the actual application used to generate
library.
@end table
@end itemize

The GNAT Project Manager takes full care of the library maintenance task,
including recompilation of the source files for which objects do not exist
or are not up to date, assembly of the library archive, and installation of
the library (i.e., copying associated source, object and @code{ALI} files
to the specified location).

Here is a simple library project file:

@example
project My_Lib is
  for Source_Dirs use ("src1", "src2");
  for Object_Dir use "obj";
  for Library_Name use "mylib";
  for Library_Dir use "lib";
  for Library_Kind use "dynamic";
end My_lib;
@end example

and the compilation command to build and install the library:

@example
$ gnatmake -Pmy_lib
@end example

It is not entirely trivial to perform manually all the steps required to
produce a library. We recommend that you use the GNAT Project Manager
for this task. In special cases where this is not desired, the necessary
steps are discussed below.

There are various possibilities for compiling the units that make up the
library: for example with a Makefile (@ref{21,,Using the GNU make Utility}) or
with a conventional script. For simple libraries, it is also possible to create
a dummy main program which depends upon all the packages that comprise the
interface of the library. This dummy main program can then be given to
@emph{gnatmake}, which will ensure that all necessary objects are built.

After this task is accomplished, you should follow the standard procedure
of the underlying operating system to produce the static or shared library.

Here is an example of such a dummy program:

@example
with My_Lib.Service1;
with My_Lib.Service2;
with My_Lib.Service3;
procedure My_Lib_Dummy is
begin
   null;
end;
@end example

Here are the generic commands that will build an archive or a shared library.

@example
# compiling the library
$ gnatmake -c my_lib_dummy.adb

# we don't need the dummy object itself
$ rm my_lib_dummy.o my_lib_dummy.ali

# create an archive with the remaining objects
$ ar rc libmy_lib.a *.o
# some systems may require "ranlib" to be run as well

# or create a shared library
$ gcc -shared -o libmy_lib.so *.o
# some systems may require the code to have been compiled with -fPIC

# remove the object files that are now in the library
$ rm *.o

# Make the ALI files read-only so that gnatmake will not try to
# regenerate the objects that are in the library
$ chmod -w *.ali
@end example

Please note that the library must have a name of the form @code{lib@emph{xxx}.a}
or @code{lib@emph{xxx}.so} (or @code{lib@emph{xxx}.dll} on Windows) in order to
be accessed by the directive @code{-l@emph{xxx}} at link time.

@node Installing a library,Using a library,Building a library,General Ada Libraries
@anchor{gnat_ugn/the_gnat_compilation_model installing-a-library}@anchor{8b}@anchor{gnat_ugn/the_gnat_compilation_model id39}@anchor{8c}
@subsubsection Installing a library


@geindex ADA_PROJECT_PATH

@geindex GPR_PROJECT_PATH

If you use project files, library installation is part of the library build
process (@ref{8d,,Installing a library with project files}).

When project files are not an option, it is also possible, but not recommended,
to install the library so that the sources needed to use the library are on the
Ada source path and the ALI files & libraries be on the Ada Object path (see
@ref{8e,,Search Paths and the Run-Time Library (RTL)}. Alternatively, the system
administrator can place general-purpose libraries in the default compiler
paths, by specifying the libraries' location in the configuration files
@code{ada_source_path} and @code{ada_object_path}. These configuration files
must be located in the GNAT installation tree at the same place as the gcc spec
file. The location of the gcc spec file can be determined as follows:

@example
$ gcc -v
@end example

The configuration files mentioned above have a simple format: each line
must contain one unique directory name.
Those names are added to the corresponding path
in their order of appearance in the file. The names can be either absolute
or relative; in the latter case, they are relative to where theses files
are located.

The files @code{ada_source_path} and @code{ada_object_path} might not be
present in a
GNAT installation, in which case, GNAT will look for its run-time library in
the directories @code{adainclude} (for the sources) and @code{adalib} (for the
objects and @code{ALI} files). When the files exist, the compiler does not
look in @code{adainclude} and @code{adalib}, and thus the
@code{ada_source_path} file
must contain the location for the GNAT run-time sources (which can simply
be @code{adainclude}). In the same way, the @code{ada_object_path} file must
contain the location for the GNAT run-time objects (which can simply
be @code{adalib}).

You can also specify a new default path to the run-time library at compilation
time with the switch @emph{--RTS=rts-path}. You can thus choose / change
the run-time library you want your program to be compiled with. This switch is
recognized by @emph{gcc}, @emph{gnatmake}, @emph{gnatbind},
@emph{gnatls}, @emph{gnatfind} and @emph{gnatxref}.

It is possible to install a library before or after the standard GNAT
library, by reordering the lines in the configuration files. In general, a
library must be installed before the GNAT library if it redefines
any part of it.

@node Using a library,,Installing a library,General Ada Libraries
@anchor{gnat_ugn/the_gnat_compilation_model using-a-library}@anchor{8f}@anchor{gnat_ugn/the_gnat_compilation_model id40}@anchor{90}
@subsubsection Using a library


Once again, the project facility greatly simplifies the use of
libraries. In this context, using a library is just a matter of adding a
@emph{with} clause in the user project. For instance, to make use of the
library @cite{My_Lib} shown in examples in earlier sections, you can
write:

@example
with "my_lib";
project My_Proj is
  ...
end My_Proj;
@end example

Even if you have a third-party, non-Ada library, you can still use GNAT's
Project Manager facility to provide a wrapper for it. For example, the
following project, when @emph{with}ed by your main project, will link with the
third-party library @code{liba.a}:

@example
project Liba is
   for Externally_Built use "true";
   for Source_Files use ();
   for Library_Dir use "lib";
   for Library_Name use "a";
   for Library_Kind use "static";
end Liba;
@end example

This is an alternative to the use of @cite{pragma Linker_Options}. It is
especially interesting in the context of systems with several interdependent
static libraries where finding a proper linker order is not easy and best be
left to the tools having visibility over project dependence information.

In order to use an Ada library manually, you need to make sure that this
library is on both your source and object path
(see @ref{8e,,Search Paths and the Run-Time Library (RTL)}
and @ref{91,,Search Paths for gnatbind}). Furthermore, when the objects are grouped
in an archive or a shared library, you need to specify the desired
library at link time.

For example, you can use the library @code{mylib} installed in
@code{/dir/my_lib_src} and @code{/dir/my_lib_obj} with the following commands:

@example
$ gnatmake -aI/dir/my_lib_src -aO/dir/my_lib_obj my_appl \\
  -largs -lmy_lib
@end example

This can be expressed more simply:

@example
$ gnatmake my_appl
@end example

when the following conditions are met:


@itemize *

@item 
@code{/dir/my_lib_src} has been added by the user to the environment
variable 
@geindex ADA_INCLUDE_PATH
@geindex environment variable; ADA_INCLUDE_PATH
@code{ADA_INCLUDE_PATH}, or by the administrator to the file
@code{ada_source_path}

@item 
@code{/dir/my_lib_obj} has been added by the user to the environment
variable 
@geindex ADA_OBJECTS_PATH
@geindex environment variable; ADA_OBJECTS_PATH
@code{ADA_OBJECTS_PATH}, or by the administrator to the file
@code{ada_object_path}

@item 
a pragma @cite{Linker_Options} has been added to one of the sources.
For example:

@example
pragma Linker_Options ("-lmy_lib");
@end example
@end itemize

Note that you may also load a library dynamically at
run time given its filename, as illustrated in the GNAT @code{plugins} example
in the directory @code{share/examples/gnat/plugins} within the GNAT
install area.

@node Stand-alone Ada Libraries,Rebuilding the GNAT Run-Time Library,General Ada Libraries,GNAT and Libraries
@anchor{gnat_ugn/the_gnat_compilation_model stand-alone-ada-libraries}@anchor{85}@anchor{gnat_ugn/the_gnat_compilation_model id41}@anchor{92}
@subsection Stand-alone Ada Libraries


@geindex Stand-alone libraries

@menu
* Introduction to Stand-alone Libraries:: 
* Building a Stand-alone Library:: 
* Creating a Stand-alone Library to be used in a non-Ada context:: 
* Restrictions in Stand-alone Libraries:: 

@end menu

@node Introduction to Stand-alone Libraries,Building a Stand-alone Library,,Stand-alone Ada Libraries
@anchor{gnat_ugn/the_gnat_compilation_model introduction-to-stand-alone-libraries}@anchor{93}@anchor{gnat_ugn/the_gnat_compilation_model id42}@anchor{94}
@subsubsection Introduction to Stand-alone Libraries


A Stand-alone Library (abbreviated 'SAL') is a library that contains the
necessary code to
elaborate the Ada units that are included in the library. In contrast with
an ordinary library, which consists of all sources, objects and @code{ALI}
files of the
library, a SAL may specify a restricted subset of compilation units
to serve as a library interface. In this case, the fully
self-sufficient set of files will normally consist of an objects
archive, the sources of interface units' specs, and the @code{ALI}
files of interface units.
If an interface spec contains a generic unit or an inlined subprogram,
the body's
source must also be provided; if the units that must be provided in the source
form depend on other units, the source and @code{ALI} files of those must
also be provided.

The main purpose of a SAL is to minimize the recompilation overhead of client
applications when a new version of the library is installed. Specifically,
if the interface sources have not changed, client applications do not need to
be recompiled. If, furthermore, a SAL is provided in the shared form and its
version, controlled by @cite{Library_Version} attribute, is not changed,
then the clients do not need to be relinked.

SALs also allow the library providers to minimize the amount of library source
text exposed to the clients.  Such 'information hiding' might be useful or
necessary for various reasons.

Stand-alone libraries are also well suited to be used in an executable whose
main routine is not written in Ada.

@node Building a Stand-alone Library,Creating a Stand-alone Library to be used in a non-Ada context,Introduction to Stand-alone Libraries,Stand-alone Ada Libraries
@anchor{gnat_ugn/the_gnat_compilation_model id43}@anchor{95}@anchor{gnat_ugn/the_gnat_compilation_model building-a-stand-alone-library}@anchor{96}
@subsubsection Building a Stand-alone Library


GNAT's Project facility provides a simple way of building and installing
stand-alone libraries; see @ref{97,,Stand-alone Library Projects}.
To be a Stand-alone Library Project, in addition to the two attributes
that make a project a Library Project (@cite{Library_Name} and
@cite{Library_Dir}; see @ref{8a,,Library Projects}), the attribute
@cite{Library_Interface} must be defined.  For example:

@example
for Library_Dir use "lib_dir";
for Library_Name use "dummy";
for Library_Interface use ("int1", "int1.child");
@end example

Attribute @cite{Library_Interface} has a non-empty string list value,
each string in the list designating a unit contained in an immediate source
of the project file.

When a Stand-alone Library is built, first the binder is invoked to build
a package whose name depends on the library name
(@code{b~dummy.ads/b} in the example above).
This binder-generated package includes initialization and
finalization procedures whose
names depend on the library name (@cite{dummyinit} and @cite{dummyfinal}
in the example
above). The object corresponding to this package is included in the library.

You must ensure timely (e.g., prior to any use of interfaces in the SAL)
calling of these procedures if a static SAL is built, or if a shared SAL
is built
with the project-level attribute @cite{Library_Auto_Init} set to
@cite{"false"}.

For a Stand-Alone Library, only the @code{ALI} files of the Interface Units
(those that are listed in attribute @cite{Library_Interface}) are copied to
the Library Directory. As a consequence, only the Interface Units may be
imported from Ada units outside of the library. If other units are imported,
the binding phase will fail.

It is also possible to build an encapsulated library where not only
the code to elaborate and finalize the library is embedded but also
ensuring that the library is linked only against static
libraries. So an encapsulated library only depends on system
libraries, all other code, including the GNAT runtime, is embedded. To
build an encapsulated library the attribute
@cite{Library_Standalone} must be set to @cite{encapsulated}:

@example
for Library_Dir use "lib_dir";
for Library_Name use "dummy";
for Library_Kind use "dynamic";
for Library_Interface use ("int1", "int1.child");
for Library_Standalone use "encapsulated";
@end example

The default value for this attribute is @cite{standard} in which case
a stand-alone library is built.

The attribute @cite{Library_Src_Dir} may be specified for a
Stand-Alone Library. @cite{Library_Src_Dir} is a simple attribute that has a
single string value. Its value must be the path (absolute or relative to the
project directory) of an existing directory. This directory cannot be the
object directory or one of the source directories, but it can be the same as
the library directory. The sources of the Interface
Units of the library that are needed by an Ada client of the library will be
copied to the designated directory, called the Interface Copy directory.
These sources include the specs of the Interface Units, but they may also
include bodies and subunits, when pragmas @cite{Inline} or @cite{Inline_Always}
are used, or when there is a generic unit in the spec. Before the sources
are copied to the Interface Copy directory, an attempt is made to delete all
files in the Interface Copy directory.

Building stand-alone libraries by hand is somewhat tedious, but for those
occasions when it is necessary here are the steps that you need to perform:


@itemize *

@item 
Compile all library sources.

@item 
Invoke the binder with the switch @emph{-n} (No Ada main program),
with all the @code{ALI} files of the interfaces, and
with the switch @emph{-L} to give specific names to the @cite{init}
and @cite{final} procedures.  For example:

@example
$ gnatbind -n int1.ali int2.ali -Lsal1
@end example

@item 
Compile the binder generated file:

@example
$ gcc -c b~int2.adb
@end example

@item 
Link the dynamic library with all the necessary object files,
indicating to the linker the names of the @cite{init} (and possibly
@cite{final}) procedures for automatic initialization (and finalization).
The built library should be placed in a directory different from
the object directory.

@item 
Copy the @cite{ALI} files of the interface to the library directory,
add in this copy an indication that it is an interface to a SAL
(i.e., add a word @emph{SL} on the line in the @code{ALI} file that starts
with letter 'P') and make the modified copy of the @code{ALI} file
read-only.
@end itemize

Using SALs is not different from using other libraries
(see @ref{8f,,Using a library}).

@node Creating a Stand-alone Library to be used in a non-Ada context,Restrictions in Stand-alone Libraries,Building a Stand-alone Library,Stand-alone Ada Libraries
@anchor{gnat_ugn/the_gnat_compilation_model creating-a-stand-alone-library-to-be-used-in-a-non-ada-context}@anchor{98}@anchor{gnat_ugn/the_gnat_compilation_model id44}@anchor{99}
@subsubsection Creating a Stand-alone Library to be used in a non-Ada context


It is easy to adapt the SAL build procedure discussed above for use of a SAL in
a non-Ada context.

The only extra step required is to ensure that library interface subprograms
are compatible with the main program, by means of @cite{pragma Export}
or @cite{pragma Convention}.

Here is an example of simple library interface for use with C main program:

@example
package My_Package is

   procedure Do_Something;
   pragma Export (C, Do_Something, "do_something");

   procedure Do_Something_Else;
   pragma Export (C, Do_Something_Else, "do_something_else");

end My_Package;
@end example

On the foreign language side, you must provide a 'foreign' view of the
library interface; remember that it should contain elaboration routines in
addition to interface subprograms.

The example below shows the content of @cite{mylib_interface.h} (note
that there is no rule for the naming of this file, any name can be used)

@example
/* the library elaboration procedure */
extern void mylibinit (void);

/* the library finalization procedure */
extern void mylibfinal (void);

/* the interface exported by the library */
extern void do_something (void);
extern void do_something_else (void);
@end example

Libraries built as explained above can be used from any program, provided
that the elaboration procedures (named @cite{mylibinit} in the previous
example) are called before the library services are used. Any number of
libraries can be used simultaneously, as long as the elaboration
procedure of each library is called.

Below is an example of a C program that uses the @cite{mylib} library.

@example
#include "mylib_interface.h"

int
main (void)
@{
   /* First, elaborate the library before using it */
   mylibinit ();

   /* Main program, using the library exported entities */
   do_something ();
   do_something_else ();

   /* Library finalization at the end of the program */
   mylibfinal ();
   return 0;
@}
@end example

Note that invoking any library finalization procedure generated by
@cite{gnatbind} shuts down the Ada run-time environment.
Consequently, the
finalization of all Ada libraries must be performed at the end of the program.
No call to these libraries or to the Ada run-time library should be made
after the finalization phase.

Note also that special care must be taken with multi-tasks
applications. The initialization and finalization routines are not
protected against concurrent access. If such requirement is needed it
must be ensured at the application level using a specific operating
system services like a mutex or a critical-section.

@node Restrictions in Stand-alone Libraries,,Creating a Stand-alone Library to be used in a non-Ada context,Stand-alone Ada Libraries
@anchor{gnat_ugn/the_gnat_compilation_model id45}@anchor{9a}@anchor{gnat_ugn/the_gnat_compilation_model restrictions-in-stand-alone-libraries}@anchor{9b}
@subsubsection Restrictions in Stand-alone Libraries


The pragmas listed below should be used with caution inside libraries,
as they can create incompatibilities with other Ada libraries:


@itemize *

@item 
pragma @cite{Locking_Policy}

@item 
pragma @cite{Partition_Elaboration_Policy}

@item 
pragma @cite{Queuing_Policy}

@item 
pragma @cite{Task_Dispatching_Policy}

@item 
pragma @cite{Unreserve_All_Interrupts}
@end itemize

When using a library that contains such pragmas, the user must make sure
that all libraries use the same pragmas with the same values. Otherwise,
@cite{Program_Error} will
be raised during the elaboration of the conflicting
libraries. The usage of these pragmas and its consequences for the user
should therefore be well documented.

Similarly, the traceback in the exception occurrence mechanism should be
enabled or disabled in a consistent manner across all libraries.
Otherwise, Program_Error will be raised during the elaboration of the
conflicting libraries.

If the @cite{Version} or @cite{Body_Version}
attributes are used inside a library, then you need to
perform a @cite{gnatbind} step that specifies all @code{ALI} files in all
libraries, so that version identifiers can be properly computed.
In practice these attributes are rarely used, so this is unlikely
to be a consideration.

@node Rebuilding the GNAT Run-Time Library,,Stand-alone Ada Libraries,GNAT and Libraries
@anchor{gnat_ugn/the_gnat_compilation_model id46}@anchor{9c}@anchor{gnat_ugn/the_gnat_compilation_model rebuilding-the-gnat-run-time-library}@anchor{9d}
@subsection Rebuilding the GNAT Run-Time Library


@geindex GNAT Run-Time Library
@geindex rebuilding

@geindex Building the GNAT Run-Time Library

@geindex Rebuilding the GNAT Run-Time Library

@geindex Run-Time Library
@geindex rebuilding

It may be useful to recompile the GNAT library in various contexts, the
most important one being the use of partition-wide configuration pragmas
such as @cite{Normalize_Scalars}. A special Makefile called
@cite{Makefile.adalib} is provided to that effect and can be found in
the directory containing the GNAT library. The location of this
directory depends on the way the GNAT environment has been installed and can
be determined by means of the command:

@example
$ gnatls -v
@end example

The last entry in the object search path usually contains the
gnat library. This Makefile contains its own documentation and in
particular the set of instructions needed to rebuild a new library and
to use it.

@geindex Conditional compilation

@node Conditional Compilation,Mixed Language Programming,GNAT and Libraries,The GNAT Compilation Model
@anchor{gnat_ugn/the_gnat_compilation_model id47}@anchor{9e}@anchor{gnat_ugn/the_gnat_compilation_model conditional-compilation}@anchor{18}
@section Conditional Compilation


This section presents some guidelines for modeling conditional compilation in Ada and describes the
gnatprep preprocessor utility.

@geindex Conditional compilation

@menu
* Modeling Conditional Compilation in Ada:: 
* Preprocessing with gnatprep:: 
* Integrated Preprocessing:: 

@end menu

@node Modeling Conditional Compilation in Ada,Preprocessing with gnatprep,,Conditional Compilation
@anchor{gnat_ugn/the_gnat_compilation_model modeling-conditional-compilation-in-ada}@anchor{9f}@anchor{gnat_ugn/the_gnat_compilation_model id48}@anchor{a0}
@subsection Modeling Conditional Compilation in Ada


It is often necessary to arrange for a single source program
to serve multiple purposes, where it is compiled in different
ways to achieve these different goals. Some examples of the
need for this feature are


@itemize *

@item 
Adapting a program to a different hardware environment

@item 
Adapting a program to a different target architecture

@item 
Turning debugging features on and off

@item 
Arranging for a program to compile with different compilers
@end itemize

In C, or C++, the typical approach would be to use the preprocessor
that is defined as part of the language. The Ada language does not
contain such a feature. This is not an oversight, but rather a very
deliberate design decision, based on the experience that overuse of
the preprocessing features in C and C++ can result in programs that
are extremely difficult to maintain. For example, if we have ten
switches that can be on or off, this means that there are a thousand
separate programs, any one of which might not even be syntactically
correct, and even if syntactically correct, the resulting program
might not work correctly. Testing all combinations can quickly become
impossible.

Nevertheless, the need to tailor programs certainly exists, and in
this section we will discuss how this can
be achieved using Ada in general, and GNAT in particular.

@menu
* Use of Boolean Constants:: 
* Debugging - A Special Case:: 
* Conditionalizing Declarations:: 
* Use of Alternative Implementations:: 
* Preprocessing:: 

@end menu

@node Use of Boolean Constants,Debugging - A Special Case,,Modeling Conditional Compilation in Ada
@anchor{gnat_ugn/the_gnat_compilation_model id49}@anchor{a1}@anchor{gnat_ugn/the_gnat_compilation_model use-of-boolean-constants}@anchor{a2}
@subsubsection Use of Boolean Constants


In the case where the difference is simply which code
sequence is executed, the cleanest solution is to use Boolean
constants to control which code is executed.

@example
FP_Initialize_Required : constant Boolean := True;
...
if FP_Initialize_Required then
...
end if;
@end example

Not only will the code inside the @cite{if} statement not be executed if
the constant Boolean is @cite{False}, but it will also be completely
deleted from the program.
However, the code is only deleted after the @cite{if} statement
has been checked for syntactic and semantic correctness.
(In contrast, with preprocessors the code is deleted before the
compiler ever gets to see it, so it is not checked until the switch
is turned on.)

@geindex Preprocessors (contrasted with conditional compilation)

Typically the Boolean constants will be in a separate package,
something like:

@example
package Config is
   FP_Initialize_Required : constant Boolean := True;
   Reset_Available        : constant Boolean := False;
   ...
end Config;
@end example

The @cite{Config} package exists in multiple forms for the various targets,
with an appropriate script selecting the version of @cite{Config} needed.
Then any other unit requiring conditional compilation can do a @emph{with}
of @cite{Config} to make the constants visible.

@node Debugging - A Special Case,Conditionalizing Declarations,Use of Boolean Constants,Modeling Conditional Compilation in Ada
@anchor{gnat_ugn/the_gnat_compilation_model debugging-a-special-case}@anchor{a3}@anchor{gnat_ugn/the_gnat_compilation_model id50}@anchor{a4}
@subsubsection Debugging - A Special Case


A common use of conditional code is to execute statements (for example
dynamic checks, or output of intermediate results) under control of a
debug switch, so that the debugging behavior can be turned on and off.
This can be done using a Boolean constant to control whether the code
is active:

@example
if Debugging then
   Put_Line ("got to the first stage!");
end if;
@end example

or

@example
if Debugging and then Temperature > 999.0 then
   raise Temperature_Crazy;
end if;
@end example

@geindex pragma Assert

Since this is a common case, there are special features to deal with
this in a convenient manner. For the case of tests, Ada 2005 has added
a pragma @cite{Assert} that can be used for such tests. This pragma is modeled
on the @cite{Assert} pragma that has always been available in GNAT, so this
feature may be used with GNAT even if you are not using Ada 2005 features.
The use of pragma @cite{Assert} is described in the
@cite{GNAT_Reference_Manual}, but as an
example, the last test could be written:

@example
pragma Assert (Temperature <= 999.0, "Temperature Crazy");
@end example

or simply

@example
pragma Assert (Temperature <= 999.0);
@end example

In both cases, if assertions are active and the temperature is excessive,
the exception @cite{Assert_Failure} will be raised, with the given string in
the first case or a string indicating the location of the pragma in the second
case used as the exception message.

@geindex pragma Assertion_Policy

You can turn assertions on and off by using the @cite{Assertion_Policy}
pragma.

@geindex -gnata switch

This is an Ada 2005 pragma which is implemented in all modes by
GNAT. Alternatively, you can use the @emph{-gnata} switch
to enable assertions from the command line, which applies to
all versions of Ada.

@geindex pragma Debug

For the example above with the @cite{Put_Line}, the GNAT-specific pragma
@cite{Debug} can be used:

@example
pragma Debug (Put_Line ("got to the first stage!"));
@end example

If debug pragmas are enabled, the argument, which must be of the form of
a procedure call, is executed (in this case, @cite{Put_Line} will be called).
Only one call can be present, but of course a special debugging procedure
containing any code you like can be included in the program and then
called in a pragma @cite{Debug} argument as needed.

One advantage of pragma @cite{Debug} over the @cite{if Debugging then}
construct is that pragma @cite{Debug} can appear in declarative contexts,
such as at the very beginning of a procedure, before local declarations have
been elaborated.

@geindex pragma Debug_Policy

Debug pragmas are enabled using either the @emph{-gnata} switch that also
controls assertions, or with a separate Debug_Policy pragma.

The latter pragma is new in the Ada 2005 versions of GNAT (but it can be used
in Ada 95 and Ada 83 programs as well), and is analogous to
pragma @cite{Assertion_Policy} to control assertions.

@cite{Assertion_Policy} and @cite{Debug_Policy} are configuration pragmas,
and thus they can appear in @code{gnat.adc} if you are not using a
project file, or in the file designated to contain configuration pragmas
in a project file.
They then apply to all subsequent compilations. In practice the use of
the @emph{-gnata} switch is often the most convenient method of controlling
the status of these pragmas.

Note that a pragma is not a statement, so in contexts where a statement
sequence is required, you can't just write a pragma on its own. You have
to add a @cite{null} statement.

@example
if ... then
   ... -- some statements
else
   pragma Assert (Num_Cases < 10);
   null;
end if;
@end example

@node Conditionalizing Declarations,Use of Alternative Implementations,Debugging - A Special Case,Modeling Conditional Compilation in Ada
@anchor{gnat_ugn/the_gnat_compilation_model conditionalizing-declarations}@anchor{a5}@anchor{gnat_ugn/the_gnat_compilation_model id51}@anchor{a6}
@subsubsection Conditionalizing Declarations


In some cases it may be necessary to conditionalize declarations to meet
different requirements. For example we might want a bit string whose length
is set to meet some hardware message requirement.

This may be possible using declare blocks controlled
by conditional constants:

@example
if Small_Machine then
   declare
      X : Bit_String (1 .. 10);
   begin
      ...
   end;
else
   declare
      X : Large_Bit_String (1 .. 1000);
   begin
      ...
   end;
end if;
@end example

Note that in this approach, both declarations are analyzed by the
compiler so this can only be used where both declarations are legal,
even though one of them will not be used.

Another approach is to define integer constants, e.g., @cite{Bits_Per_Word},
or Boolean constants, e.g., @cite{Little_Endian}, and then write declarations
that are parameterized by these constants. For example

@example
for Rec use
  Field1 at 0 range Boolean'Pos (Little_Endian) * 10 .. Bits_Per_Word;
end record;
@end example

If @cite{Bits_Per_Word} is set to 32, this generates either

@example
for Rec use
  Field1 at 0 range 0 .. 32;
end record;
@end example

for the big endian case, or

@example
for Rec use record
    Field1 at 0 range 10 .. 32;
end record;
@end example

for the little endian case. Since a powerful subset of Ada expression
notation is usable for creating static constants, clever use of this
feature can often solve quite difficult problems in conditionalizing
compilation (note incidentally that in Ada 95, the little endian
constant was introduced as @cite{System.Default_Bit_Order}, so you do not
need to define this one yourself).

@node Use of Alternative Implementations,Preprocessing,Conditionalizing Declarations,Modeling Conditional Compilation in Ada
@anchor{gnat_ugn/the_gnat_compilation_model use-of-alternative-implementations}@anchor{a7}@anchor{gnat_ugn/the_gnat_compilation_model id52}@anchor{a8}
@subsubsection Use of Alternative Implementations


In some cases, none of the approaches described above are adequate. This
can occur for example if the set of declarations required is radically
different for two different configurations.

In this situation, the official Ada way of dealing with conditionalizing
such code is to write separate units for the different cases. As long as
this does not result in excessive duplication of code, this can be done
without creating maintenance problems. The approach is to share common
code as far as possible, and then isolate the code and declarations
that are different. Subunits are often a convenient method for breaking
out a piece of a unit that is to be conditionalized, with separate files
for different versions of the subunit for different targets, where the
build script selects the right one to give to the compiler.

@geindex Subunits (and conditional compilation)

As an example, consider a situation where a new feature in Ada 2005
allows something to be done in a really nice way. But your code must be able
to compile with an Ada 95 compiler. Conceptually you want to say:

@example
if Ada_2005 then
   ... neat Ada 2005 code
else
   ... not quite as neat Ada 95 code
end if;
@end example

where @cite{Ada_2005} is a Boolean constant.

But this won't work when @cite{Ada_2005} is set to @cite{False},
since the @cite{then} clause will be illegal for an Ada 95 compiler.
(Recall that although such unreachable code would eventually be deleted
by the compiler, it still needs to be legal.  If it uses features
introduced in Ada 2005, it will be illegal in Ada 95.)

So instead we write

@example
procedure Insert is separate;
@end example

Then we have two files for the subunit @cite{Insert}, with the two sets of
code.
If the package containing this is called @cite{File_Queries}, then we might
have two files


@itemize *

@item 
@code{file_queries-insert-2005.adb}

@item 
@code{file_queries-insert-95.adb}
@end itemize

and the build script renames the appropriate file to @code{file_queries-insert.adb} and then carries out the compilation.

This can also be done with project files' naming schemes. For example:

@example
for body ("File_Queries.Insert") use "file_queries-insert-2005.ada";
@end example

Note also that with project files it is desirable to use a different extension
than @code{ads} / @code{adb} for alternative versions. Otherwise a naming
conflict may arise through another commonly used feature: to declare as part
of the project a set of directories containing all the sources obeying the
default naming scheme.

The use of alternative units is certainly feasible in all situations,
and for example the Ada part of the GNAT run-time is conditionalized
based on the target architecture using this approach. As a specific example,
consider the implementation of the AST feature in VMS. There is one
spec: @code{s-asthan.ads} which is the same for all architectures, and three
bodies:


@itemize *

@item 

@table @asis

@item @code{s-asthan.adb}

used for all non-VMS operating systems
@end table

@item 

@table @asis

@item @code{s-asthan-vms-alpha.adb}

used for VMS on the Alpha
@end table

@item 

@table @asis

@item @code{s-asthan-vms-ia64.adb}

used for VMS on the ia64
@end table
@end itemize

The dummy version @code{s-asthan.adb} simply raises exceptions noting that
this operating system feature is not available, and the two remaining
versions interface with the corresponding versions of VMS to provide
VMS-compatible AST handling. The GNAT build script knows the architecture
and operating system, and automatically selects the right version,
renaming it if necessary to @code{s-asthan.adb} before the run-time build.

Another style for arranging alternative implementations is through Ada's
access-to-subprogram facility.
In case some functionality is to be conditionally included,
you can declare an access-to-procedure variable @cite{Ref} that is initialized
to designate a 'do nothing' procedure, and then invoke @cite{Ref.all}
when appropriate.
In some library package, set @cite{Ref} to @cite{Proc'Access} for some
procedure @cite{Proc} that performs the relevant processing.
The initialization only occurs if the library package is included in the
program.
The same idea can also be implemented using tagged types and dispatching
calls.

@node Preprocessing,,Use of Alternative Implementations,Modeling Conditional Compilation in Ada
@anchor{gnat_ugn/the_gnat_compilation_model preprocessing}@anchor{a9}@anchor{gnat_ugn/the_gnat_compilation_model id53}@anchor{aa}
@subsubsection Preprocessing


@geindex Preprocessing

Although it is quite possible to conditionalize code without the use of
C-style preprocessing, as described earlier in this section, it is
nevertheless convenient in some cases to use the C approach. Moreover,
older Ada compilers have often provided some preprocessing capability,
so legacy code may depend on this approach, even though it is not
standard.

To accommodate such use, GNAT provides a preprocessor (modeled to a large
extent on the various preprocessors that have been used
with legacy code on other compilers, to enable easier transition).

@geindex gnatprep

The preprocessor may be used in two separate modes. It can be used quite
separately from the compiler, to generate a separate output source file
that is then fed to the compiler as a separate step. This is the
@cite{gnatprep} utility, whose use is fully described in
@ref{19,,Preprocessing with gnatprep}.

The preprocessing language allows such constructs as

@example
#if DEBUG or else (PRIORITY > 4) then
   bunch of declarations
#else
   completely different bunch of declarations
#end if;
@end example

The values of the symbols @cite{DEBUG} and @cite{PRIORITY} can be
defined either on the command line or in a separate file.

The other way of running the preprocessor is even closer to the C style and
often more convenient. In this approach the preprocessing is integrated into
the compilation process. The compiler is fed the preprocessor input which
includes @cite{#if} lines etc, and then the compiler carries out the
preprocessing internally and processes the resulting output.
For more details on this approach, see @ref{1a,,Integrated Preprocessing}.

@node Preprocessing with gnatprep,Integrated Preprocessing,Modeling Conditional Compilation in Ada,Conditional Compilation
@anchor{gnat_ugn/the_gnat_compilation_model id54}@anchor{ab}@anchor{gnat_ugn/the_gnat_compilation_model preprocessing-with-gnatprep}@anchor{19}
@subsection Preprocessing with @cite{gnatprep}


@geindex gnatprep

@geindex Preprocessing (gnatprep)

This section discusses how to use GNAT's @cite{gnatprep} utility for simple
preprocessing.
Although designed for use with GNAT, @cite{gnatprep} does not depend on any
special GNAT features.
For further discussion of conditional compilation in general, see
@ref{18,,Conditional Compilation}.

@menu
* Preprocessing Symbols:: 
* Using gnatprep:: 
* Switches for gnatprep:: 
* Form of Definitions File:: 
* Form of Input Text for gnatprep:: 

@end menu

@node Preprocessing Symbols,Using gnatprep,,Preprocessing with gnatprep
@anchor{gnat_ugn/the_gnat_compilation_model id55}@anchor{ac}@anchor{gnat_ugn/the_gnat_compilation_model preprocessing-symbols}@anchor{ad}
@subsubsection Preprocessing Symbols


Preprocessing symbols are defined in definition files and referred to in
sources to be preprocessed. A Preprocessing symbol is an identifier, following
normal Ada (case-insensitive) rules for its syntax, with the restriction that
all characters need to be in the ASCII set (no accented letters).

@node Using gnatprep,Switches for gnatprep,Preprocessing Symbols,Preprocessing with gnatprep
@anchor{gnat_ugn/the_gnat_compilation_model using-gnatprep}@anchor{ae}@anchor{gnat_ugn/the_gnat_compilation_model id56}@anchor{af}
@subsubsection Using @cite{gnatprep}


To call @cite{gnatprep} use:

@example
$ gnatprep [`switches`] `infile` `outfile` [`deffile`]
@end example

where


@itemize *

@item 

@table @asis

@item @emph{switches}

is an optional sequence of switches as described in the next section.
@end table

@item 

@table @asis

@item @emph{infile}

is the full name of the input file, which is an Ada source
file containing preprocessor directives.
@end table

@item 

@table @asis

@item @emph{outfile}

is the full name of the output file, which is an Ada source
in standard Ada form. When used with GNAT, this file name will
normally have an ads or adb suffix.
@end table

@item 

@table @asis

@item @emph{deffile}

is the full name of a text file containing definitions of
preprocessing symbols to be referenced by the preprocessor. This argument is
optional, and can be replaced by the use of the @emph{-D} switch.
@end table
@end itemize

@node Switches for gnatprep,Form of Definitions File,Using gnatprep,Preprocessing with gnatprep
@anchor{gnat_ugn/the_gnat_compilation_model switches-for-gnatprep}@anchor{b0}@anchor{gnat_ugn/the_gnat_compilation_model id57}@anchor{b1}
@subsubsection Switches for @cite{gnatprep}


@geindex -b (gnatprep)


@table @asis

@item @code{-b}

Causes both preprocessor lines and the lines deleted by
preprocessing to be replaced by blank lines in the output source file,
preserving line numbers in the output file.
@end table

@geindex -c (gnatprep)


@table @asis

@item @code{-c}

Causes both preprocessor lines and the lines deleted
by preprocessing to be retained in the output source as comments marked
with the special string @cite{"--! "}. This option will result in line numbers
being preserved in the output file.
@end table

@geindex -C (gnatprep)


@table @asis

@item @code{-C}

Causes comments to be scanned. Normally comments are ignored by gnatprep.
If this option is specified, then comments are scanned and any $symbol
substitutions performed as in program text. This is particularly useful
when structured comments are used (e.g., when writing programs in the
SPARK dialect of Ada). Note that this switch is not available when
doing integrated preprocessing (it would be useless in this context
since comments are ignored by the compiler in any case).
@end table

@geindex -D (gnatprep)


@table @asis

@item @code{-D@emph{symbol}=@emph{value}}

Defines a new preprocessing symbol, associated with value. If no value is given
on the command line, then symbol is considered to be @cite{True}. This switch
can be used in place of a definition file.
@end table

@geindex -r (gnatprep)


@table @asis

@item @code{-r}

Causes a @cite{Source_Reference} pragma to be generated that
references the original input file, so that error messages will use
the file name of this original file. The use of this switch implies
that preprocessor lines are not to be removed from the file, so its
use will force @emph{-b} mode if @emph{-c}
has not been specified explicitly.

Note that if the file to be preprocessed contains multiple units, then
it will be necessary to @cite{gnatchop} the output file from
@cite{gnatprep}. If a @cite{Source_Reference} pragma is present
in the preprocessed file, it will be respected by
@cite{gnatchop -r}
so that the final chopped files will correctly refer to the original
input source file for @cite{gnatprep}.
@end table

@geindex -s (gnatprep)


@table @asis

@item @code{-s}

Causes a sorted list of symbol names and values to be
listed on the standard output file.
@end table

@geindex -u (gnatprep)


@table @asis

@item @code{-u}

Causes undefined symbols to be treated as having the value FALSE in the context
of a preprocessor test. In the absence of this option, an undefined symbol in
a @cite{#if} or @cite{#elsif} test will be treated as an error.
@end table

Note: if neither @emph{-b} nor @emph{-c} is present,
then preprocessor lines and
deleted lines are completely removed from the output, unless -r is
specified, in which case -b is assumed.

@node Form of Definitions File,Form of Input Text for gnatprep,Switches for gnatprep,Preprocessing with gnatprep
@anchor{gnat_ugn/the_gnat_compilation_model form-of-definitions-file}@anchor{b2}@anchor{gnat_ugn/the_gnat_compilation_model id58}@anchor{b3}
@subsubsection Form of Definitions File


The definitions file contains lines of the form:

@example
symbol := value
@end example

where @cite{symbol} is a preprocessing symbol, and @cite{value} is one of the following:


@itemize *

@item 
Empty, corresponding to a null substitution,

@item 
A string literal using normal Ada syntax, or

@item 
Any sequence of characters from the set @{letters, digits, period, underline@}.
@end itemize

Comment lines may also appear in the definitions file, starting with
the usual @code{--},
and comments may be added to the definitions lines.

@node Form of Input Text for gnatprep,,Form of Definitions File,Preprocessing with gnatprep
@anchor{gnat_ugn/the_gnat_compilation_model id59}@anchor{b4}@anchor{gnat_ugn/the_gnat_compilation_model form-of-input-text-for-gnatprep}@anchor{b5}
@subsubsection Form of Input Text for @cite{gnatprep}


The input text may contain preprocessor conditional inclusion lines,
as well as general symbol substitution sequences.

The preprocessor conditional inclusion commands have the form:

@example
#if <expression> [then]
   lines
#elsif <expression> [then]
   lines
#elsif <expression> [then]
   lines
...
#else
   lines
#end if;
@end example

In this example, <expression> is defined by the following grammar:

@example
<expression> ::=  <symbol>
<expression> ::=  <symbol> = "<value>"
<expression> ::=  <symbol> = <symbol>
<expression> ::=  <symbol> = <integer>
<expression> ::=  <symbol> > <integer>
<expression> ::=  <symbol> >= <integer>
<expression> ::=  <symbol> < <integer>
<expression> ::=  <symbol> <= <integer>
<expression> ::=  <symbol> 'Defined
<expression> ::=  not <expression>
<expression> ::=  <expression> and <expression>
<expression> ::=  <expression> or <expression>
<expression> ::=  <expression> and then <expression>
<expression> ::=  <expression> or else <expression>
<expression> ::=  ( <expression> )
@end example

Note the following restriction: it is not allowed to have "and" or "or"
following "not" in the same expression without parentheses. For example, this
is not allowed:

@example
not X or Y
@end example

This can be expressed instead as one of the following forms:

@example
(not X) or Y
not (X or Y)
@end example

For the first test (<expression> ::= <symbol>) the symbol must have
either the value true or false, that is to say the right-hand of the
symbol definition must be one of the (case-insensitive) literals
@cite{True} or @cite{False}. If the value is true, then the
corresponding lines are included, and if the value is false, they are
excluded.

When comparing a symbol to an integer, the integer is any non negative
literal integer as defined in the Ada Reference Manual, such as 3, 16#FF# or
2#11#. The symbol value must also be a non negative integer. Integer values
in the range 0 .. 2**31-1 are supported.

The test (<expression> ::= <symbol>'Defined) is true only if
the symbol has been defined in the definition file or by a @emph{-D}
switch on the command line. Otherwise, the test is false.

The equality tests are case insensitive, as are all the preprocessor lines.

If the symbol referenced is not defined in the symbol definitions file,
then the effect depends on whether or not switch @emph{-u}
is specified. If so, then the symbol is treated as if it had the value
false and the test fails. If this switch is not specified, then
it is an error to reference an undefined symbol. It is also an error to
reference a symbol that is defined with a value other than @cite{True}
or @cite{False}.

The use of the @cite{not} operator inverts the sense of this logical test.
The @cite{not} operator cannot be combined with the @cite{or} or @cite{and}
operators, without parentheses. For example, "if not X or Y then" is not
allowed, but "if (not X) or Y then" and "if not (X or Y) then" are.

The @cite{then} keyword is optional as shown

The @cite{#} must be the first non-blank character on a line, but
otherwise the format is free form. Spaces or tabs may appear between
the @cite{#} and the keyword. The keywords and the symbols are case
insensitive as in normal Ada code. Comments may be used on a
preprocessor line, but other than that, no other tokens may appear on a
preprocessor line. Any number of @cite{elsif} clauses can be present,
including none at all. The @cite{else} is optional, as in Ada.

The @cite{#} marking the start of a preprocessor line must be the first
non-blank character on the line, i.e., it must be preceded only by
spaces or horizontal tabs.

Symbol substitution outside of preprocessor lines is obtained by using
the sequence:

@example
$symbol
@end example

anywhere within a source line, except in a comment or within a
string literal. The identifier
following the @cite{$} must match one of the symbols defined in the symbol
definition file, and the result is to substitute the value of the
symbol in place of @cite{$symbol} in the output file.

Note that although the substitution of strings within a string literal
is not possible, it is possible to have a symbol whose defined value is
a string literal. So instead of setting XYZ to @cite{hello} and writing:

@example
Header : String := "$XYZ";
@end example

you should set XYZ to @cite{"hello"} and write:

@example
Header : String := $XYZ;
@end example

and then the substitution will occur as desired.

@node Integrated Preprocessing,,Preprocessing with gnatprep,Conditional Compilation
@anchor{gnat_ugn/the_gnat_compilation_model id60}@anchor{b6}@anchor{gnat_ugn/the_gnat_compilation_model integrated-preprocessing}@anchor{1a}
@subsection Integrated Preprocessing


GNAT sources may be preprocessed immediately before compilation.
In this case, the actual
text of the source is not the text of the source file, but is derived from it
through a process called preprocessing. Integrated preprocessing is specified
through switches @emph{-gnatep} and/or @emph{-gnateD}. @emph{-gnatep}
indicates, through a text file, the preprocessing data to be used.
@code{-gnateD} specifies or modifies the values of preprocessing symbol.
Note that integrated preprocessing applies only to Ada source files, it is
not available for configuration pragma files.

Note that when integrated preprocessing is used, the output from the
preprocessor is not written to any external file. Instead it is passed
internally to the compiler. If you need to preserve the result of
preprocessing in a file, then you should use @emph{gnatprep}
to perform the desired preprocessing in stand-alone mode.

It is recommended that @emph{gnatmake} switch -s should be
used when Integrated Preprocessing is used. The reason is that preprocessing
with another Preprocessing Data file without changing the sources will
not trigger recompilation without this switch.

Note that @emph{gnatmake} switch -m will almost
always trigger recompilation for sources that are preprocessed,
because @emph{gnatmake} cannot compute the checksum of the source after
preprocessing.

The actual preprocessing function is described in detail in section
@ref{19,,Preprocessing with gnatprep}. This section only describes how integrated
preprocessing is triggered and parameterized.

@geindex -gnatep (gcc)


@table @asis

@item @code{-gnatep=@emph{file}}

This switch indicates to the compiler the file name (without directory
information) of the preprocessor data file to use. The preprocessor data file
should be found in the source directories. Note that when the compiler is
called by a builder such as (@emph{gnatmake} with a project
file, if the object directory is not also a source directory, the builder needs
to be called with @emph{-x}.

A preprocessing data file is a text file with significant lines indicating
how should be preprocessed either a specific source or all sources not
mentioned in other lines. A significant line is a nonempty, non-comment line.
Comments are similar to Ada comments.

Each significant line starts with either a literal string or the character '*'.
A literal string is the file name (without directory information) of the source
to preprocess. A character '*' indicates the preprocessing for all the sources
that are not specified explicitly on other lines (order of the lines is not
significant). It is an error to have two lines with the same file name or two
lines starting with the character '*'.

After the file name or the character '*', another optional literal string
indicating the file name of the definition file to be used for preprocessing
(@ref{b2,,Form of Definitions File}). The definition files are found by the
compiler in one of the source directories. In some cases, when compiling
a source in a directory other than the current directory, if the definition
file is in the current directory, it may be necessary to add the current
directory as a source directory through switch -I., otherwise
the compiler would not find the definition file.

Then, optionally, switches similar to those of @cite{gnatprep} may
be found. Those switches are:


@table @asis

@item @code{-b}

Causes both preprocessor lines and the lines deleted by
preprocessing to be replaced by blank lines, preserving the line number.
This switch is always implied; however, if specified after @emph{-c}
it cancels the effect of @emph{-c}.

@item @code{-c}

Causes both preprocessor lines and the lines deleted
by preprocessing to be retained as comments marked
with the special string '@cite{--!}'.

@item @code{-Dsymbol=@emph{value}}

Define or redefine a symbol, associated with value. A symbol is an Ada
identifier, or an Ada reserved word, with the exception of @cite{if},
@cite{else}, @cite{elsif}, @cite{end}, @cite{and}, @cite{or} and @cite{then}.
@cite{value} is either a literal string, an Ada identifier or any Ada reserved
word. A symbol declared with this switch replaces a symbol with the
same name defined in a definition file.

@item @code{-s}

Causes a sorted list of symbol names and values to be
listed on the standard output file.

@item @code{-u}

Causes undefined symbols to be treated as having the value @cite{FALSE}
in the context
of a preprocessor test. In the absence of this option, an undefined symbol in
a @cite{#if} or @cite{#elsif} test will be treated as an error.
@end table

Examples of valid lines in a preprocessor data file:

@example
"toto.adb"  "prep.def" -u
--  preprocess "toto.adb", using definition file "prep.def",
--  undefined symbol are False.

* -c -DVERSION=V101
--  preprocess all other sources without a definition file;
--  suppressed lined are commented; symbol VERSION has the value V101.

"titi.adb" "prep2.def" -s
--  preprocess "titi.adb", using definition file "prep2.def";
--  list all symbols with their values.
@end example
@end table

@geindex -gnateD (gcc)


@table @asis

@item @code{-gnateDsymbol[=value]}

Define or redefine a preprocessing symbol, associated with value. If no value
is given on the command line, then the value of the symbol is @cite{True}.
A symbol is an identifier, following normal Ada (case-insensitive)
rules for its syntax, and value is either an arbitrary string between double
quotes or any sequence (including an empty sequence) of characters from the
set (letters, digits, period, underline).
Ada reserved words may be used as symbols, with the exceptions of @cite{if},
@cite{else}, @cite{elsif}, @cite{end}, @cite{and}, @cite{or} and @cite{then}.

Examples:

@example
-gnateDToto=Titi
-gnateDFoo
-gnateDFoo=\"Foo-Bar\"
@end example

A symbol declared with this switch on the command line replaces a
symbol with the same name either in a definition file or specified with a
switch -D in the preprocessor data file.

This switch is similar to switch @emph{-D} of @cite{gnatprep}.

@item @code{-gnateG}

When integrated preprocessing is performed and the preprocessor modifies
the source text, write the result of this preprocessing into a file
<source>.prep.
@end table

@node Mixed Language Programming,GNAT and Other Compilation Models,Conditional Compilation,The GNAT Compilation Model
@anchor{gnat_ugn/the_gnat_compilation_model mixed-language-programming}@anchor{46}@anchor{gnat_ugn/the_gnat_compilation_model id61}@anchor{b7}
@section Mixed Language Programming


@geindex Mixed Language Programming

This section describes how to develop a mixed-language program,
with a focus on combining Ada with C or C++.

@menu
* Interfacing to C:: 
* Calling Conventions:: 
* Building Mixed Ada and C++ Programs:: 
* Generating Ada Bindings for C and C++ headers:: 

@end menu

@node Interfacing to C,Calling Conventions,,Mixed Language Programming
@anchor{gnat_ugn/the_gnat_compilation_model interfacing-to-c}@anchor{b8}@anchor{gnat_ugn/the_gnat_compilation_model id62}@anchor{b9}
@subsection Interfacing to C


Interfacing Ada with a foreign language such as C involves using
compiler directives to import and/or export entity definitions in each
language -- using @cite{extern} statements in C, for instance, and the
@cite{Import}, @cite{Export}, and @cite{Convention} pragmas in Ada.
A full treatment of these topics is provided in Appendix B, section 1
of the Ada Reference Manual.

There are two ways to build a program using GNAT that contains some Ada
sources and some foreign language sources, depending on whether or not
the main subprogram is written in Ada.  Here is a source example with
the main subprogram in Ada:

@example
/* file1.c */
#include <stdio.h>

void print_num (int num)
@{
  printf ("num is %d.\\n", num);
  return;
@}
@end example

@example
/* file2.c */

/* num_from_Ada is declared in my_main.adb */
extern int num_from_Ada;

int get_num (void)
@{
  return num_from_Ada;
@}
@end example

@example
--  my_main.adb
procedure My_Main is

   --  Declare then export an Integer entity called num_from_Ada
   My_Num : Integer := 10;
   pragma Export (C, My_Num, "num_from_Ada");

   --  Declare an Ada function spec for Get_Num, then use
   --  C function get_num for the implementation.
   function Get_Num return Integer;
   pragma Import (C, Get_Num, "get_num");

   --  Declare an Ada procedure spec for Print_Num, then use
   --  C function print_num for the implementation.
   procedure Print_Num (Num : Integer);
   pragma Import (C, Print_Num, "print_num";

begin
   Print_Num (Get_Num);
end My_Main;
@end example

To build this example:


@itemize *

@item 
First compile the foreign language files to
generate object files:

@example
$ gcc -c file1.c
$ gcc -c file2.c
@end example

@item 
Then, compile the Ada units to produce a set of object files and ALI
files:

@example
$ gnatmake -c my_main.adb
@end example

@item 
Run the Ada binder on the Ada main program:

@example
$ gnatbind my_main.ali
@end example

@item 
Link the Ada main program, the Ada objects and the other language
objects:

@example
$ gnatlink my_main.ali file1.o file2.o
@end example
@end itemize

The last three steps can be grouped in a single command:

@example
$ gnatmake my_main.adb -largs file1.o file2.o
@end example

@geindex Binder output file

If the main program is in a language other than Ada, then you may have
more than one entry point into the Ada subsystem. You must use a special
binder option to generate callable routines that initialize and
finalize the Ada units (@ref{ba,,Binding with Non-Ada Main Programs}).
Calls to the initialization and finalization routines must be inserted
in the main program, or some other appropriate point in the code. The
call to initialize the Ada units must occur before the first Ada
subprogram is called, and the call to finalize the Ada units must occur
after the last Ada subprogram returns. The binder will place the
initialization and finalization subprograms into the
@code{b~xxx.adb} file where they can be accessed by your C
sources.  To illustrate, we have the following example:

@example
/* main.c */
extern void adainit (void);
extern void adafinal (void);
extern int add (int, int);
extern int sub (int, int);

int main (int argc, char *argv[])
@{
   int a = 21, b = 7;

   adainit();

   /* Should print "21 + 7 = 28" */
   printf ("%d + %d = %d\\n", a, b, add (a, b));

   /* Should print "21 - 7 = 14" */
   printf ("%d - %d = %d\\n", a, b, sub (a, b));

   adafinal();
@}
@end example

@example
--  unit1.ads
package Unit1 is
   function Add (A, B : Integer) return Integer;
   pragma Export (C, Add, "add");
end Unit1;
@end example

@example
--  unit1.adb
package body Unit1 is
   function Add (A, B : Integer) return Integer is
   begin
      return A + B;
   end Add;
end Unit1;
@end example

@example
--  unit2.ads
package Unit2 is
   function Sub (A, B : Integer) return Integer;
   pragma Export (C, Sub, "sub");
end Unit2;
@end example

@example
--  unit2.adb
package body Unit2 is
   function Sub (A, B : Integer) return Integer is
   begin
      return A - B;
   end Sub;
end Unit2;
@end example

The build procedure for this application is similar to the last
example's:


@itemize *

@item 
First, compile the foreign language files to generate object files:

@example
$ gcc -c main.c
@end example

@item 
Next, compile the Ada units to produce a set of object files and ALI
files:

@example
$ gnatmake -c unit1.adb
$ gnatmake -c unit2.adb
@end example

@item 
Run the Ada binder on every generated ALI file.  Make sure to use the
@code{-n} option to specify a foreign main program:

@example
$ gnatbind -n unit1.ali unit2.ali
@end example

@item 
Link the Ada main program, the Ada objects and the foreign language
objects. You need only list the last ALI file here:

@example
$ gnatlink unit2.ali main.o -o exec_file
@end example

This procedure yields a binary executable called @code{exec_file}.
@end itemize

Depending on the circumstances (for example when your non-Ada main object
does not provide symbol @cite{main}), you may also need to instruct the
GNAT linker not to include the standard startup objects by passing the
@code{-nostartfiles} switch to @cite{gnatlink}.

@node Calling Conventions,Building Mixed Ada and C++ Programs,Interfacing to C,Mixed Language Programming
@anchor{gnat_ugn/the_gnat_compilation_model calling-conventions}@anchor{bb}@anchor{gnat_ugn/the_gnat_compilation_model id63}@anchor{bc}
@subsection Calling Conventions


@geindex Foreign Languages

@geindex Calling Conventions

GNAT follows standard calling sequence conventions and will thus interface
to any other language that also follows these conventions. The following
Convention identifiers are recognized by GNAT:

@geindex Interfacing to Ada

@geindex Other Ada compilers

@geindex Convention Ada


@table @asis

@item @emph{Ada}

This indicates that the standard Ada calling sequence will be
used and all Ada data items may be passed without any limitations in the
case where GNAT is used to generate both the caller and callee. It is also
possible to mix GNAT generated code and code generated by another Ada
compiler. In this case, the data types should be restricted to simple
cases, including primitive types. Whether complex data types can be passed
depends on the situation. Probably it is safe to pass simple arrays, such
as arrays of integers or floats. Records may or may not work, depending
on whether both compilers lay them out identically. Complex structures
involving variant records, access parameters, tasks, or protected types,
are unlikely to be able to be passed.

Note that in the case of GNAT running
on a platform that supports HP Ada 83, a higher degree of compatibility
can be guaranteed, and in particular records are laid out in an identical
manner in the two compilers. Note also that if output from two different
compilers is mixed, the program is responsible for dealing with elaboration
issues. Probably the safest approach is to write the main program in the
version of Ada other than GNAT, so that it takes care of its own elaboration
requirements, and then call the GNAT-generated adainit procedure to ensure
elaboration of the GNAT components. Consult the documentation of the other
Ada compiler for further details on elaboration.

However, it is not possible to mix the tasking run time of GNAT and
HP Ada 83, All the tasking operations must either be entirely within
GNAT compiled sections of the program, or entirely within HP Ada 83
compiled sections of the program.
@end table

@geindex Interfacing to Assembly

@geindex Convention Assembler


@table @asis

@item @emph{Assembler}

Specifies assembler as the convention. In practice this has the
same effect as convention Ada (but is not equivalent in the sense of being
considered the same convention).
@end table

@geindex Convention Asm

@geindex Asm


@table @asis

@item @emph{Asm}

Equivalent to Assembler.

@geindex Interfacing to COBOL

@geindex Convention COBOL
@end table

@geindex COBOL


@table @asis

@item @emph{COBOL}

Data will be passed according to the conventions described
in section B.4 of the Ada Reference Manual.
@end table

@geindex C

@geindex Interfacing to C

@geindex Convention C


@table @asis

@item @emph{C}

Data will be passed according to the conventions described
in section B.3 of the Ada Reference Manual.

A note on interfacing to a C 'varargs' function:

@quotation

@geindex C varargs function

@geindex Interfacing to C varargs function

@geindex varargs function interfaces

In C, @cite{varargs} allows a function to take a variable number of
arguments. There is no direct equivalent in this to Ada. One
approach that can be used is to create a C wrapper for each
different profile and then interface to this C wrapper. For
example, to print an @cite{int} value using @cite{printf},
create a C function @cite{printfi} that takes two arguments, a
pointer to a string and an int, and calls @cite{printf}.
Then in the Ada program, use pragma @cite{Import} to
interface to @cite{printfi}.

It may work on some platforms to directly interface to
a @cite{varargs} function by providing a specific Ada profile
for a particular call. However, this does not work on
all platforms, since there is no guarantee that the
calling sequence for a two argument normal C function
is the same as for calling a @cite{varargs} C function with
the same two arguments.
@end quotation
@end table

@geindex Convention Default

@geindex Default


@table @asis

@item @emph{Default}

Equivalent to C.
@end table

@geindex Convention External

@geindex External


@table @asis

@item @emph{External}

Equivalent to C.
@end table

@geindex C++

@geindex Interfacing to C++

@geindex Convention C++


@table @asis

@item @emph{C_Plus_Plus (or CPP)}

This stands for C++. For most purposes this is identical to C.
See the separate description of the specialized GNAT pragmas relating to
C++ interfacing for further details.
@end table

@geindex Fortran

@geindex Interfacing to Fortran

@geindex Convention Fortran


@table @asis

@item @emph{Fortran}

Data will be passed according to the conventions described
in section B.5 of the Ada Reference Manual.

@item @emph{Intrinsic}

This applies to an intrinsic operation, as defined in the Ada
Reference Manual. If a pragma Import (Intrinsic) applies to a subprogram,
this means that the body of the subprogram is provided by the compiler itself,
usually by means of an efficient code sequence, and that the user does not
supply an explicit body for it. In an application program, the pragma may
be applied to the following sets of names:


@itemize *

@item 
Rotate_Left, Rotate_Right, Shift_Left, Shift_Right, Shift_Right_Arithmetic.
The corresponding subprogram declaration must have
two formal parameters. The
first one must be a signed integer type or a modular type with a binary
modulus, and the second parameter must be of type Natural.
The return type must be the same as the type of the first argument. The size
of this type can only be 8, 16, 32, or 64.

@item 
Binary arithmetic operators: '+', '-', '*', '/'.
The corresponding operator declaration must have parameters and result type
that have the same root numeric type (for example, all three are long_float
types). This simplifies the definition of operations that use type checking
to perform dimensional checks:
@end itemize

@c code-block: ada
@c 
@c   type Distance is new Long_Float;
@c   type Time     is new Long_Float;
@c   type Velocity is new Long_Float;
@c   function "/" (D : Distance; T : Time)
@c     return Velocity;
@c   pragma Import (Intrinsic, "/");
@c 
@c This common idiom is often programmed with a generic definition and an
@c explicit body. The pragma makes it simpler to introduce such declarations.
@c It incurs no overhead in compilation time or code size, because it is
@c implemented as a single machine instruction.


@itemize *

@item 
General subprogram entities. This is used  to bind an Ada subprogram
declaration to
a compiler builtin by name with back-ends where such interfaces are
available. A typical example is the set of @cite{__builtin} functions
exposed by the GCC back-end, as in the following example:

@example
function builtin_sqrt (F : Float) return Float;
pragma Import (Intrinsic, builtin_sqrt, "__builtin_sqrtf");
@end example

Most of the GCC builtins are accessible this way, and as for other
import conventions (e.g. C), it is the user's responsibility to ensure
that the Ada subprogram profile matches the underlying builtin
expectations.
@end itemize
@end table

@geindex Stdcall

@geindex Convention Stdcall


@table @asis

@item @emph{Stdcall}

This is relevant only to Windows XP/2000/NT implementations of GNAT,
and specifies that the @cite{Stdcall} calling sequence will be used,
as defined by the NT API. Nevertheless, to ease building
cross-platform bindings this convention will be handled as a @cite{C} calling
convention on non-Windows platforms.
@end table

@geindex DLL

@geindex Convention DLL


@table @asis

@item @emph{DLL}

This is equivalent to @cite{Stdcall}.
@end table

@geindex Win32

@geindex Convention Win32


@table @asis

@item @emph{Win32}

This is equivalent to @cite{Stdcall}.
@end table

@geindex Stubbed

@geindex Convention Stubbed


@table @asis

@item @emph{Stubbed}

This is a special convention that indicates that the compiler
should provide a stub body that raises @cite{Program_Error}.
@end table

GNAT additionally provides a useful pragma @cite{Convention_Identifier}
that can be used to parameterize conventions and allow additional synonyms
to be specified. For example if you have legacy code in which the convention
identifier Fortran77 was used for Fortran, you can use the configuration
pragma:

@example
pragma Convention_Identifier (Fortran77, Fortran);
@end example

And from now on the identifier Fortran77 may be used as a convention
identifier (for example in an @cite{Import} pragma) with the same
meaning as Fortran.

@node Building Mixed Ada and C++ Programs,Generating Ada Bindings for C and C++ headers,Calling Conventions,Mixed Language Programming
@anchor{gnat_ugn/the_gnat_compilation_model id64}@anchor{bd}@anchor{gnat_ugn/the_gnat_compilation_model building-mixed-ada-and-c-programs}@anchor{be}
@subsection Building Mixed Ada and C++ Programs


A programmer inexperienced with mixed-language development may find that
building an application containing both Ada and C++ code can be a
challenge.  This section gives a few hints that should make this task easier.

@menu
* Interfacing to C++:: 
* Linking a Mixed C++ & Ada Program:: 
* A Simple Example:: 
* Interfacing with C++ constructors:: 
* Interfacing with C++ at the Class Level:: 

@end menu

@node Interfacing to C++,Linking a Mixed C++ & Ada Program,,Building Mixed Ada and C++ Programs
@anchor{gnat_ugn/the_gnat_compilation_model id65}@anchor{bf}@anchor{gnat_ugn/the_gnat_compilation_model id66}@anchor{c0}
@subsubsection Interfacing to C++


GNAT supports interfacing with the G++ compiler (or any C++ compiler
generating code that is compatible with the G++ Application Binary
Interface ---see @indicateurl{http://www.codesourcery.com/archives/cxx-abi}).

Interfacing can be done at 3 levels: simple data, subprograms, and
classes. In the first two cases, GNAT offers a specific @cite{Convention C_Plus_Plus}
(or @cite{CPP}) that behaves exactly like @cite{Convention C}.
Usually, C++ mangles the names of subprograms. To generate proper mangled
names automatically, see @ref{1b,,Generating Ada Bindings for C and C++ headers}).
This problem can also be addressed manually in two ways:


@itemize *

@item 
by modifying the C++ code in order to force a C convention using
the @cite{extern "C"} syntax.

@item 
by figuring out the mangled name (using e.g. @emph{nm}) and using it as the
Link_Name argument of the pragma import.
@end itemize

Interfacing at the class level can be achieved by using the GNAT specific
pragmas such as @cite{CPP_Constructor}.  See the @cite{GNAT_Reference_Manual} for additional information.

@node Linking a Mixed C++ & Ada Program,A Simple Example,Interfacing to C++,Building Mixed Ada and C++ Programs
@anchor{gnat_ugn/the_gnat_compilation_model linking-a-mixed-c-ada-program}@anchor{c1}@anchor{gnat_ugn/the_gnat_compilation_model linking-a-mixed-c-and-ada-program}@anchor{c2}
@subsubsection Linking a Mixed C++ & Ada Program


Usually the linker of the C++ development system must be used to link
mixed applications because most C++ systems will resolve elaboration
issues (such as calling constructors on global class instances)
transparently during the link phase. GNAT has been adapted to ease the
use of a foreign linker for the last phase. Three cases can be
considered:


@itemize *

@item 
Using GNAT and G++ (GNU C++ compiler) from the same GCC installation:
The C++ linker can simply be called by using the C++ specific driver
called @cite{g++}.

Note that if the C++ code uses inline functions, you will need to
compile your C++ code with the @cite{-fkeep-inline-functions} switch in
order to provide an existing function implementation that the Ada code can
link with.

@example
$ g++ -c -fkeep-inline-functions file1.C
$ g++ -c -fkeep-inline-functions file2.C
$ gnatmake ada_unit -largs file1.o file2.o --LINK=g++
@end example

@item 
Using GNAT and G++ from two different GCC installations: If both
compilers are on the :envvar`PATH`, the previous method may be used. It is
important to note that environment variables such as
@geindex C_INCLUDE_PATH
@geindex environment variable; C_INCLUDE_PATH
@code{C_INCLUDE_PATH}, 
@geindex GCC_EXEC_PREFIX
@geindex environment variable; GCC_EXEC_PREFIX
@code{GCC_EXEC_PREFIX},
@geindex BINUTILS_ROOT
@geindex environment variable; BINUTILS_ROOT
@code{BINUTILS_ROOT}, and
@geindex GCC_ROOT
@geindex environment variable; GCC_ROOT
@code{GCC_ROOT} will affect both compilers
at the same time and may make one of the two compilers operate
improperly if set during invocation of the wrong compiler.  It is also
very important that the linker uses the proper @code{libgcc.a} GCC
library -- that is, the one from the C++ compiler installation. The
implicit link command as suggested in the @cite{gnatmake} command
from the former example can be replaced by an explicit link command with
the full-verbosity option in order to verify which library is used:

@example
$ gnatbind ada_unit
$ gnatlink -v -v ada_unit file1.o file2.o --LINK=c++
@end example

If there is a problem due to interfering environment variables, it can
be worked around by using an intermediate script. The following example
shows the proper script to use when GNAT has not been installed at its
default location and g++ has been installed at its default location:

@example
$ cat ./my_script
#!/bin/sh
unset BINUTILS_ROOT
unset GCC_ROOT
c++ $*
$ gnatlink -v -v ada_unit file1.o file2.o --LINK=./my_script
@end example

@item 
Using a non-GNU C++ compiler: The commands previously described can be
used to insure that the C++ linker is used. Nonetheless, you need to add
a few more parameters to the link command line, depending on the exception
mechanism used.

If the @cite{setjmp/longjmp} exception mechanism is used, only the paths
to the libgcc libraries are required:

@example
$ cat ./my_script
#!/bin/sh
CC $* `gcc -print-file-name=libgcc.a` `gcc -print-file-name=libgcc_eh.a`
$ gnatlink ada_unit file1.o file2.o --LINK=./my_script
@end example

where CC is the name of the non-GNU C++ compiler.

If the @cite{zero cost} exception mechanism is used, and the platform
supports automatic registration of exception tables (e.g., Solaris),
paths to more objects are required:

@example
$ cat ./my_script
#!/bin/sh
CC `gcc -print-file-name=crtbegin.o` $* \\
`gcc -print-file-name=libgcc.a` `gcc -print-file-name=libgcc_eh.a` \\
`gcc -print-file-name=crtend.o`
$ gnatlink ada_unit file1.o file2.o --LINK=./my_script
@end example

If the "zero cost exception" mechanism is used, and the platform
doesn't support automatic registration of exception tables (e.g., HP-UX
or AIX), the simple approach described above will not work and
a pre-linking phase using GNAT will be necessary.
@end itemize

Another alternative is to use the @code{gprbuild} multi-language builder
which has a large knowledge base and knows how to link Ada and C++ code
together automatically in most cases.

@node A Simple Example,Interfacing with C++ constructors,Linking a Mixed C++ & Ada Program,Building Mixed Ada and C++ Programs
@anchor{gnat_ugn/the_gnat_compilation_model id67}@anchor{c3}@anchor{gnat_ugn/the_gnat_compilation_model a-simple-example}@anchor{c4}
@subsubsection A Simple Example


The following example, provided as part of the GNAT examples, shows how
to achieve procedural interfacing between Ada and C++ in both
directions. The C++ class A has two methods. The first method is exported
to Ada by the means of an extern C wrapper function. The second method
calls an Ada subprogram. On the Ada side, The C++ calls are modelled by
a limited record with a layout comparable to the C++ class. The Ada
subprogram, in turn, calls the C++ method. So, starting from the C++
main program, the process passes back and forth between the two
languages.

Here are the compilation commands:

@example
$ gnatmake -c simple_cpp_interface
$ g++ -c cpp_main.C
$ g++ -c ex7.C
$ gnatbind -n simple_cpp_interface
$ gnatlink simple_cpp_interface -o cpp_main --LINK=g++ -lstdc++ ex7.o cpp_main.o
@end example

Here are the corresponding sources:

@example
//cpp_main.C

#include "ex7.h"

extern "C" @{
  void adainit (void);
  void adafinal (void);
  void method1 (A *t);
@}

void method1 (A *t)
@{
  t->method1 ();
@}

int main ()
@{
  A obj;
  adainit ();
  obj.method2 (3030);
  adafinal ();
@}
@end example

@example
//ex7.h

class Origin @{
 public:
  int o_value;
@};
class A : public Origin @{
 public:
  void method1 (void);
  void method2 (int v);
  A();
  int   a_value;
@};
@end example

@example
//ex7.C

#include "ex7.h"
#include <stdio.h>

extern "C" @{ void ada_method2 (A *t, int v);@}

void A::method1 (void)
@{
  a_value = 2020;
  printf ("in A::method1, a_value = %d \\n",a_value);
@}

void A::method2 (int v)
@{
   ada_method2 (this, v);
   printf ("in A::method2, a_value = %d \\n",a_value);
@}

A::A(void)
@{
   a_value = 1010;
  printf ("in A::A, a_value = %d \\n",a_value);
@}
@end example

@example
-- simple_cpp_interface.ads
with System;
package Simple_Cpp_Interface is
   type A is limited
      record
         Vptr    : System.Address;
         O_Value : Integer;
         A_Value : Integer;
      end record;
   pragma Convention (C, A);

   procedure Method1 (This : in out A);
   pragma Import (C, Method1);

   procedure Ada_Method2 (This : in out A; V : Integer);
   pragma Export (C, Ada_Method2);

end Simple_Cpp_Interface;
@end example

@example
-- simple_cpp_interface.adb
package body Simple_Cpp_Interface is

   procedure Ada_Method2 (This : in out A; V : Integer) is
   begin
      Method1 (This);
      This.A_Value := V;
   end Ada_Method2;

end Simple_Cpp_Interface;
@end example

@node Interfacing with C++ constructors,Interfacing with C++ at the Class Level,A Simple Example,Building Mixed Ada and C++ Programs
@anchor{gnat_ugn/the_gnat_compilation_model id68}@anchor{c5}@anchor{gnat_ugn/the_gnat_compilation_model interfacing-with-c-constructors}@anchor{c6}
@subsubsection Interfacing with C++ constructors


In order to interface with C++ constructors GNAT provides the
@cite{pragma CPP_Constructor} (see the @cite{GNAT_Reference_Manual}
for additional information).
In this section we present some common uses of C++ constructors
in mixed-languages programs in GNAT.

Let us assume that we need to interface with the following
C++ class:

@example
class Root @{
public:
  int  a_value;
  int  b_value;
  virtual int Get_Value ();
  Root();              // Default constructor
  Root(int v);         // 1st non-default constructor
  Root(int v, int w);  // 2nd non-default constructor
@};
@end example

For this purpose we can write the following package spec (further
information on how to build this spec is available in
@ref{c7,,Interfacing with C++ at the Class Level} and
@ref{1b,,Generating Ada Bindings for C and C++ headers}).

@example
with Interfaces.C; use Interfaces.C;
package Pkg_Root is
  type Root is tagged limited record
     A_Value : int;
     B_Value : int;
  end record;
  pragma Import (CPP, Root);

  function Get_Value (Obj : Root) return int;
  pragma Import (CPP, Get_Value);

  function Constructor return Root;
  pragma Cpp_Constructor (Constructor, "_ZN4RootC1Ev");

  function Constructor (v : Integer) return Root;
  pragma Cpp_Constructor (Constructor, "_ZN4RootC1Ei");

  function Constructor (v, w : Integer) return Root;
  pragma Cpp_Constructor (Constructor, "_ZN4RootC1Eii");
end Pkg_Root;
@end example

On the Ada side the constructor is represented by a function (whose
name is arbitrary) that returns the classwide type corresponding to
the imported C++ class. Although the constructor is described as a
function, it is typically a procedure with an extra implicit argument
(the object being initialized) at the implementation level. GNAT
issues the appropriate call, whatever it is, to get the object
properly initialized.

Constructors can only appear in the following contexts:


@itemize *

@item 
On the right side of an initialization of an object of type @cite{T}.

@item 
On the right side of an initialization of a record component of type @cite{T}.

@item 
In an Ada 2005 limited aggregate.

@item 
In an Ada 2005 nested limited aggregate.

@item 
In an Ada 2005 limited aggregate that initializes an object built in
place by an extended return statement.
@end itemize

In a declaration of an object whose type is a class imported from C++,
either the default C++ constructor is implicitly called by GNAT, or
else the required C++ constructor must be explicitly called in the
expression that initializes the object. For example:

@example
Obj1 : Root;
Obj2 : Root := Constructor;
Obj3 : Root := Constructor (v => 10);
Obj4 : Root := Constructor (30, 40);
@end example

The first two declarations are equivalent: in both cases the default C++
constructor is invoked (in the former case the call to the constructor is
implicit, and in the latter case the call is explicit in the object
declaration). @cite{Obj3} is initialized by the C++ non-default constructor
that takes an integer argument, and @cite{Obj4} is initialized by the
non-default C++ constructor that takes two integers.

Let us derive the imported C++ class in the Ada side. For example:

@example
type DT is new Root with record
   C_Value : Natural := 2009;
end record;
@end example

In this case the components DT inherited from the C++ side must be
initialized by a C++ constructor, and the additional Ada components
of type DT are initialized by GNAT. The initialization of such an
object is done either by default, or by means of a function returning
an aggregate of type DT, or by means of an extension aggregate.

@example
Obj5 : DT;
Obj6 : DT := Function_Returning_DT (50);
Obj7 : DT := (Constructor (30,40) with C_Value => 50);
@end example

The declaration of @cite{Obj5} invokes the default constructors: the
C++ default constructor of the parent type takes care of the initialization
of the components inherited from Root, and GNAT takes care of the default
initialization of the additional Ada components of type DT (that is,
@cite{C_Value} is initialized to value 2009). The order of invocation of
the constructors is consistent with the order of elaboration required by
Ada and C++. That is, the constructor of the parent type is always called
before the constructor of the derived type.

Let us now consider a record that has components whose type is imported
from C++. For example:

@example
type Rec1 is limited record
   Data1 : Root := Constructor (10);
   Value : Natural := 1000;
end record;

type Rec2 (D : Integer := 20) is limited record
   Rec   : Rec1;
   Data2 : Root := Constructor (D, 30);
end record;
@end example

The initialization of an object of type @cite{Rec2} will call the
non-default C++ constructors specified for the imported components.
For example:

@example
Obj8 : Rec2 (40);
@end example

Using Ada 2005 we can use limited aggregates to initialize an object
invoking C++ constructors that differ from those specified in the type
declarations. For example:

@example
Obj9 : Rec2 := (Rec => (Data1 => Constructor (15, 16),
                        others => <>),
                others => <>);
@end example

The above declaration uses an Ada 2005 limited aggregate to
initialize @cite{Obj9}, and the C++ constructor that has two integer
arguments is invoked to initialize the @cite{Data1} component instead
of the constructor specified in the declaration of type @cite{Rec1}. In
Ada 2005 the box in the aggregate indicates that unspecified components
are initialized using the expression (if any) available in the component
declaration. That is, in this case discriminant @cite{D} is initialized
to value @cite{20}, @cite{Value} is initialized to value 1000, and the
non-default C++ constructor that handles two integers takes care of
initializing component @cite{Data2} with values @cite{20@comma{}30}.

In Ada 2005 we can use the extended return statement to build the Ada
equivalent to C++ non-default constructors. For example:

@example
function Constructor (V : Integer) return Rec2 is
begin
   return Obj : Rec2 := (Rec => (Data1  => Constructor (V, 20),
                                 others => <>),
                         others => <>) do
      --  Further actions required for construction of
      --  objects of type Rec2
      ...
   end record;
end Constructor;
@end example

In this example the extended return statement construct is used to
build in place the returned object whose components are initialized
by means of a limited aggregate. Any further action associated with
the constructor can be placed inside the construct.

@node Interfacing with C++ at the Class Level,,Interfacing with C++ constructors,Building Mixed Ada and C++ Programs
@anchor{gnat_ugn/the_gnat_compilation_model interfacing-with-c-at-the-class-level}@anchor{c7}@anchor{gnat_ugn/the_gnat_compilation_model id69}@anchor{c8}
@subsubsection Interfacing with C++ at the Class Level


In this section we demonstrate the GNAT features for interfacing with
C++ by means of an example making use of Ada 2005 abstract interface
types. This example consists of a classification of animals; classes
have been used to model our main classification of animals, and
interfaces provide support for the management of secondary
classifications. We first demonstrate a case in which the types and
constructors are defined on the C++ side and imported from the Ada
side, and latter the reverse case.

The root of our derivation will be the @cite{Animal} class, with a
single private attribute (the @cite{Age} of the animal), a constructor,
and two public primitives to set and get the value of this attribute.

@example
class Animal @{
 public:
   virtual void Set_Age (int New_Age);
   virtual int Age ();
   Animal() @{Age_Count = 0;@};
 private:
   int Age_Count;
@};
@end example

Abstract interface types are defined in C++ by means of classes with pure
virtual functions and no data members. In our example we will use two
interfaces that provide support for the common management of @cite{Carnivore}
and @cite{Domestic} animals:

@example
class Carnivore @{
public:
   virtual int Number_Of_Teeth () = 0;
@};

class Domestic @{
public:
   virtual void Set_Owner (char* Name) = 0;
@};
@end example

Using these declarations, we can now say that a @cite{Dog} is an animal that is
both Carnivore and Domestic, that is:

@example
class Dog : Animal, Carnivore, Domestic @{
 public:
   virtual int  Number_Of_Teeth ();
   virtual void Set_Owner (char* Name);

   Dog(); // Constructor
 private:
   int  Tooth_Count;
   char *Owner;
@};
@end example

In the following examples we will assume that the previous declarations are
located in a file named @cite{animals.h}. The following package demonstrates
how to import these C++ declarations from the Ada side:

@example
with Interfaces.C.Strings; use Interfaces.C.Strings;
package Animals is
  type Carnivore is limited interface;
  pragma Convention (C_Plus_Plus, Carnivore);
  function Number_Of_Teeth (X : Carnivore)
     return Natural is abstract;

  type Domestic is limited interface;
  pragma Convention (C_Plus_Plus, Domestic);
  procedure Set_Owner
    (X    : in out Domestic;
     Name : Chars_Ptr) is abstract;

  type Animal is tagged limited record
    Age : Natural;
  end record;
  pragma Import (C_Plus_Plus, Animal);

  procedure Set_Age (X : in out Animal; Age : Integer);
  pragma Import (C_Plus_Plus, Set_Age);

  function Age (X : Animal) return Integer;
  pragma Import (C_Plus_Plus, Age);

  function New_Animal return Animal;
  pragma CPP_Constructor (New_Animal);
  pragma Import (CPP, New_Animal, "_ZN6AnimalC1Ev");

  type Dog is new Animal and Carnivore and Domestic with record
    Tooth_Count : Natural;
    Owner       : String (1 .. 30);
  end record;
  pragma Import (C_Plus_Plus, Dog);

  function Number_Of_Teeth (A : Dog) return Natural;
  pragma Import (C_Plus_Plus, Number_Of_Teeth);

  procedure Set_Owner (A : in out Dog; Name : Chars_Ptr);
  pragma Import (C_Plus_Plus, Set_Owner);

  function New_Dog return Dog;
  pragma CPP_Constructor (New_Dog);
  pragma Import (CPP, New_Dog, "_ZN3DogC2Ev");
end Animals;
@end example

Thanks to the compatibility between GNAT run-time structures and the C++ ABI,
interfacing with these C++ classes is easy. The only requirement is that all
the primitives and components must be declared exactly in the same order in
the two languages.

Regarding the abstract interfaces, we must indicate to the GNAT compiler by
means of a @cite{pragma Convention (C_Plus_Plus)}, the convention used to pass
the arguments to the called primitives will be the same as for C++. For the
imported classes we use @cite{pragma Import} with convention @cite{C_Plus_Plus}
to indicate that they have been defined on the C++ side; this is required
because the dispatch table associated with these tagged types will be built
in the C++ side and therefore will not contain the predefined Ada primitives
which Ada would otherwise expect.

As the reader can see there is no need to indicate the C++ mangled names
associated with each subprogram because it is assumed that all the calls to
these primitives will be dispatching calls. The only exception is the
constructor, which must be registered with the compiler by means of
@cite{pragma CPP_Constructor} and needs to provide its associated C++
mangled name because the Ada compiler generates direct calls to it.

With the above packages we can now declare objects of type Dog on the Ada side
and dispatch calls to the corresponding subprograms on the C++ side. We can
also extend the tagged type Dog with further fields and primitives, and
override some of its C++ primitives on the Ada side. For example, here we have
a type derivation defined on the Ada side that inherits all the dispatching
primitives of the ancestor from the C++ side.

@example
with Animals; use Animals;
package Vaccinated_Animals is
  type Vaccinated_Dog is new Dog with null record;
  function Vaccination_Expired (A : Vaccinated_Dog) return Boolean;
end Vaccinated_Animals;
@end example

It is important to note that, because of the ABI compatibility, the programmer
does not need to add any further information to indicate either the object
layout or the dispatch table entry associated with each dispatching operation.

Now let us define all the types and constructors on the Ada side and export
them to C++, using the same hierarchy of our previous example:

@example
with Interfaces.C.Strings;
use Interfaces.C.Strings;
package Animals is
  type Carnivore is limited interface;
  pragma Convention (C_Plus_Plus, Carnivore);
  function Number_Of_Teeth (X : Carnivore)
     return Natural is abstract;

  type Domestic is limited interface;
  pragma Convention (C_Plus_Plus, Domestic);
  procedure Set_Owner
    (X    : in out Domestic;
     Name : Chars_Ptr) is abstract;

  type Animal is tagged record
    Age : Natural;
  end record;
  pragma Convention (C_Plus_Plus, Animal);

  procedure Set_Age (X : in out Animal; Age : Integer);
  pragma Export (C_Plus_Plus, Set_Age);

  function Age (X : Animal) return Integer;
  pragma Export (C_Plus_Plus, Age);

  function New_Animal return Animal'Class;
  pragma Export (C_Plus_Plus, New_Animal);

  type Dog is new Animal and Carnivore and Domestic with record
    Tooth_Count : Natural;
    Owner       : String (1 .. 30);
  end record;
  pragma Convention (C_Plus_Plus, Dog);

  function Number_Of_Teeth (A : Dog) return Natural;
  pragma Export (C_Plus_Plus, Number_Of_Teeth);

  procedure Set_Owner (A : in out Dog; Name : Chars_Ptr);
  pragma Export (C_Plus_Plus, Set_Owner);

  function New_Dog return Dog'Class;
  pragma Export (C_Plus_Plus, New_Dog);
end Animals;
@end example

Compared with our previous example the only differences are the use of
@cite{pragma Convention} (instead of @cite{pragma Import}), and the use of
@cite{pragma Export} to indicate to the GNAT compiler that the primitives will
be available to C++. Thanks to the ABI compatibility, on the C++ side there is
nothing else to be done; as explained above, the only requirement is that all
the primitives and components are declared in exactly the same order.

For completeness, let us see a brief C++ main program that uses the
declarations available in @cite{animals.h} (presented in our first example) to
import and use the declarations from the Ada side, properly initializing and
finalizing the Ada run-time system along the way:

@example
#include "animals.h"
#include <iostream>
using namespace std;

void Check_Carnivore (Carnivore *obj) @{...@}
void Check_Domestic (Domestic *obj)   @{...@}
void Check_Animal (Animal *obj)       @{...@}
void Check_Dog (Dog *obj)             @{...@}

extern "C" @{
  void adainit (void);
  void adafinal (void);
  Dog* new_dog ();
@}

void test ()
@{
  Dog *obj = new_dog();  // Ada constructor
  Check_Carnivore (obj); // Check secondary DT
  Check_Domestic (obj);  // Check secondary DT
  Check_Animal (obj);    // Check primary DT
  Check_Dog (obj);       // Check primary DT
@}

int main ()
@{
  adainit ();  test();  adafinal ();
  return 0;
@}
@end example

@node Generating Ada Bindings for C and C++ headers,,Building Mixed Ada and C++ Programs,Mixed Language Programming
@anchor{gnat_ugn/the_gnat_compilation_model id70}@anchor{c9}@anchor{gnat_ugn/the_gnat_compilation_model generating-ada-bindings-for-c-and-c-headers}@anchor{1b}
@subsection Generating Ada Bindings for C and C++ headers


@geindex Binding generation (for C and C++ headers)

@geindex C headers (binding generation)

@geindex C++ headers (binding generation)

GNAT includes a binding generator for C and C++ headers which is
intended to do 95% of the tedious work of generating Ada specs from C
or C++ header files.

Note that this capability is not intended to generate 100% correct Ada specs,
and will is some cases require manual adjustments, although it can often
be used out of the box in practice.

Some of the known limitations include:


@itemize *

@item 
only very simple character constant macros are translated into Ada
constants. Function macros (macros with arguments) are partially translated
as comments, to be completed manually if needed.

@item 
some extensions (e.g. vector types) are not supported

@item 
pointers to pointers or complex structures are mapped to System.Address

@item 
identifiers with identical name (except casing) will generate compilation
errors (e.g. @cite{shm_get} vs @cite{SHM_GET}).
@end itemize

The code generated is using the Ada 2005 syntax, which makes it
easier to interface with other languages than previous versions of Ada.

@menu
* Running the binding generator:: 
* Generating bindings for C++ headers:: 
* Switches:: 

@end menu

@node Running the binding generator,Generating bindings for C++ headers,,Generating Ada Bindings for C and C++ headers
@anchor{gnat_ugn/the_gnat_compilation_model id71}@anchor{ca}@anchor{gnat_ugn/the_gnat_compilation_model running-the-binding-generator}@anchor{cb}
@subsubsection Running the binding generator


The binding generator is part of the @emph{gcc} compiler and can be
invoked via the @emph{-fdump-ada-spec} switch, which will generate Ada
spec files for the header files specified on the command line, and all
header files needed by these files transitively. For example:

@example
$ g++ -c -fdump-ada-spec -C /usr/include/time.h
$ gcc -c -gnat05 *.ads
@end example

will generate, under GNU/Linux, the following files: @code{time_h.ads},
@code{bits_time_h.ads}, @code{stddef_h.ads}, @code{bits_types_h.ads} which
correspond to the files @code{/usr/include/time.h},
@code{/usr/include/bits/time.h}, etc..., and will then compile in Ada 2005
mode these Ada specs.

The @cite{-C} switch tells @emph{gcc} to extract comments from headers,
and will attempt to generate corresponding Ada comments.

If you want to generate a single Ada file and not the transitive closure, you
can use instead the @emph{-fdump-ada-spec-slim} switch.

You can optionally specify a parent unit, of which all generated units will
be children, using @cite{-fada-spec-parent=`@w{`}unit}.

Note that we recommend when possible to use the @emph{g++} driver to
generate bindings, even for most C headers, since this will in general
generate better Ada specs. For generating bindings for C++ headers, it is
mandatory to use the @emph{g++} command, or @emph{gcc -x c++} which
is equivalent in this case. If @emph{g++} cannot work on your C headers
because of incompatibilities between C and C++, then you can fallback to
@emph{gcc} instead.

For an example of better bindings generated from the C++ front-end,
the name of the parameters (when available) are actually ignored by the C
front-end. Consider the following C header:

@example
extern void foo (int variable);
@end example

with the C front-end, @cite{variable} is ignored, and the above is handled as:

@example
extern void foo (int);
@end example

generating a generic:

@example
procedure foo (param1 : int);
@end example

with the C++ front-end, the name is available, and we generate:

@example
procedure foo (variable : int);
@end example

In some cases, the generated bindings will be more complete or more meaningful
when defining some macros, which you can do via the @emph{-D} switch. This
is for example the case with @code{Xlib.h} under GNU/Linux:

@example
$ g++ -c -fdump-ada-spec -DXLIB_ILLEGAL_ACCESS -C /usr/include/X11/Xlib.h
@end example

The above will generate more complete bindings than a straight call without
the @emph{-DXLIB_ILLEGAL_ACCESS} switch.

In other cases, it is not possible to parse a header file in a stand-alone
manner, because other include files need to be included first. In this
case, the solution is to create a small header file including the needed
@cite{#include} and possible @cite{#define} directives. For example, to
generate Ada bindings for @code{readline/readline.h}, you need to first
include @code{stdio.h}, so you can create a file with the following two
lines in e.g. @code{readline1.h}:

@example
#include <stdio.h>
#include <readline/readline.h>
@end example

and then generate Ada bindings from this file:

@example
$ g++ -c -fdump-ada-spec readline1.h
@end example

@node Generating bindings for C++ headers,Switches,Running the binding generator,Generating Ada Bindings for C and C++ headers
@anchor{gnat_ugn/the_gnat_compilation_model id72}@anchor{cc}@anchor{gnat_ugn/the_gnat_compilation_model generating-bindings-for-c-headers}@anchor{cd}
@subsubsection Generating bindings for C++ headers


Generating bindings for C++ headers is done using the same options, always
with the @emph{g++} compiler. Note that generating Ada spec from C++ headers is a
much more complex job and support for C++ headers is much more limited that
support for C headers. As a result, you will need to modify the resulting
bindings by hand more extensively when using C++ headers.

In this mode, C++ classes will be mapped to Ada tagged types, constructors
will be mapped using the @cite{CPP_Constructor} pragma, and when possible,
multiple inheritance of abstract classes will be mapped to Ada interfaces
(see the @emph{Interfacing to C++} section in the @cite{GNAT Reference Manual}
for additional information on interfacing to C++).

For example, given the following C++ header file:

@example
class Carnivore @{
public:
   virtual int Number_Of_Teeth () = 0;
@};

class Domestic @{
public:
   virtual void Set_Owner (char* Name) = 0;
@};

class Animal @{
public:
  int Age_Count;
  virtual void Set_Age (int New_Age);
@};

class Dog : Animal, Carnivore, Domestic @{
 public:
  int  Tooth_Count;
  char *Owner;

  virtual int  Number_Of_Teeth ();
  virtual void Set_Owner (char* Name);

  Dog();
@};
@end example

The corresponding Ada code is generated:

@example
package Class_Carnivore is
  type Carnivore is limited interface;
  pragma Import (CPP, Carnivore);

  function Number_Of_Teeth (this : access Carnivore) return int is abstract;
end;
use Class_Carnivore;

package Class_Domestic is
  type Domestic is limited interface;
  pragma Import (CPP, Domestic);

  procedure Set_Owner
    (this : access Domestic;
     Name : Interfaces.C.Strings.chars_ptr) is abstract;
end;
use Class_Domestic;

package Class_Animal is
  type Animal is tagged limited record
    Age_Count : aliased int;
  end record;
  pragma Import (CPP, Animal);

  procedure Set_Age (this : access Animal; New_Age : int);
  pragma Import (CPP, Set_Age, "_ZN6Animal7Set_AgeEi");
end;
use Class_Animal;

package Class_Dog is
  type Dog is new Animal and Carnivore and Domestic with record
    Tooth_Count : aliased int;
    Owner : Interfaces.C.Strings.chars_ptr;
  end record;
  pragma Import (CPP, Dog);

  function Number_Of_Teeth (this : access Dog) return int;
  pragma Import (CPP, Number_Of_Teeth, "_ZN3Dog15Number_Of_TeethEv");

  procedure Set_Owner
    (this : access Dog; Name : Interfaces.C.Strings.chars_ptr);
  pragma Import (CPP, Set_Owner, "_ZN3Dog9Set_OwnerEPc");

  function New_Dog return Dog;
  pragma CPP_Constructor (New_Dog);
  pragma Import (CPP, New_Dog, "_ZN3DogC1Ev");
end;
use Class_Dog;
@end example

@node Switches,,Generating bindings for C++ headers,Generating Ada Bindings for C and C++ headers
@anchor{gnat_ugn/the_gnat_compilation_model switches}@anchor{ce}@anchor{gnat_ugn/the_gnat_compilation_model switches-for-ada-binding-generation}@anchor{cf}
@subsubsection Switches


@geindex -fdump-ada-spec (gcc)


@table @asis

@item @code{-fdump-ada-spec}

Generate Ada spec files for the given header files transitively (including
all header files that these headers depend upon).
@end table

@geindex -fdump-ada-spec-slim (gcc)


@table @asis

@item @code{-fdump-ada-spec-slim}

Generate Ada spec files for the header files specified on the command line
only.
@end table

@geindex -fada-spec-parent (gcc)


@table @asis

@item @code{-fada-spec-parent=@emph{unit}}

Specifies that all files generated by @emph{-fdump-ada-spec*} are
to be child units of the specified parent unit.
@end table

@geindex -C (gcc)


@table @asis

@item @code{-C}

Extract comments from headers and generate Ada comments in the Ada spec files.
@end table

@node GNAT and Other Compilation Models,Using GNAT Files with External Tools,Mixed Language Programming,The GNAT Compilation Model
@anchor{gnat_ugn/the_gnat_compilation_model id73}@anchor{d0}@anchor{gnat_ugn/the_gnat_compilation_model gnat-and-other-compilation-models}@anchor{47}
@section GNAT and Other Compilation Models


This section compares the GNAT model with the approaches taken in
other environents, first the C/C++ model and then the mechanism that
has been used in other Ada systems, in particular those traditionally
used for Ada 83.

@menu
* Comparison between GNAT and C/C++ Compilation Models:: 
* Comparison between GNAT and Conventional Ada Library Models:: 

@end menu

@node Comparison between GNAT and C/C++ Compilation Models,Comparison between GNAT and Conventional Ada Library Models,,GNAT and Other Compilation Models
@anchor{gnat_ugn/the_gnat_compilation_model comparison-between-gnat-and-c-c-compilation-models}@anchor{d1}@anchor{gnat_ugn/the_gnat_compilation_model id74}@anchor{d2}
@subsection Comparison between GNAT and C/C++ Compilation Models


The GNAT model of compilation is close to the C and C++ models. You can
think of Ada specs as corresponding to header files in C. As in C, you
don't need to compile specs; they are compiled when they are used. The
Ada @emph{with} is similar in effect to the @cite{#include} of a C
header.

One notable difference is that, in Ada, you may compile specs separately
to check them for semantic and syntactic accuracy. This is not always
possible with C headers because they are fragments of programs that have
less specific syntactic or semantic rules.

The other major difference is the requirement for running the binder,
which performs two important functions. First, it checks for
consistency. In C or C++, the only defense against assembling
inconsistent programs lies outside the compiler, in a makefile, for
example. The binder satisfies the Ada requirement that it be impossible
to construct an inconsistent program when the compiler is used in normal
mode.

@geindex Elaboration order control

The other important function of the binder is to deal with elaboration
issues. There are also elaboration issues in C++ that are handled
automatically. This automatic handling has the advantage of being
simpler to use, but the C++ programmer has no control over elaboration.
Where @cite{gnatbind} might complain there was no valid order of
elaboration, a C++ compiler would simply construct a program that
malfunctioned at run time.

@node Comparison between GNAT and Conventional Ada Library Models,,Comparison between GNAT and C/C++ Compilation Models,GNAT and Other Compilation Models
@anchor{gnat_ugn/the_gnat_compilation_model comparison-between-gnat-and-conventional-ada-library-models}@anchor{d3}@anchor{gnat_ugn/the_gnat_compilation_model id75}@anchor{d4}
@subsection Comparison between GNAT and Conventional Ada Library Models


This section is intended for Ada programmers who have
used an Ada compiler implementing the traditional Ada library
model, as described in the Ada Reference Manual.

@geindex GNAT library

In GNAT, there is no 'library' in the normal sense. Instead, the set of
source files themselves acts as the library. Compiling Ada programs does
not generate any centralized information, but rather an object file and
a ALI file, which are of interest only to the binder and linker.
In a traditional system, the compiler reads information not only from
the source file being compiled, but also from the centralized library.
This means that the effect of a compilation depends on what has been
previously compiled. In particular:


@itemize *

@item 
When a unit is @emph{with}ed, the unit seen by the compiler corresponds
to the version of the unit most recently compiled into the library.

@item 
Inlining is effective only if the necessary body has already been
compiled into the library.

@item 
Compiling a unit may obsolete other units in the library.
@end itemize

In GNAT, compiling one unit never affects the compilation of any other
units because the compiler reads only source files. Only changes to source
files can affect the results of a compilation. In particular:


@itemize *

@item 
When a unit is @emph{with}ed, the unit seen by the compiler corresponds
to the source version of the unit that is currently accessible to the
compiler.

@geindex Inlining

@item 
Inlining requires the appropriate source files for the package or
subprogram bodies to be available to the compiler. Inlining is always
effective, independent of the order in which units are compiled.

@item 
Compiling a unit never affects any other compilations. The editing of
sources may cause previous compilations to be out of date if they
depended on the source file being modified.
@end itemize

The most important result of these differences is that order of compilation
is never significant in GNAT. There is no situation in which one is
required to do one compilation before another. What shows up as order of
compilation requirements in the traditional Ada library becomes, in
GNAT, simple source dependencies; in other words, there is only a set
of rules saying what source files must be present when a file is
compiled.

@node Using GNAT Files with External Tools,,GNAT and Other Compilation Models,The GNAT Compilation Model
@anchor{gnat_ugn/the_gnat_compilation_model using-gnat-files-with-external-tools}@anchor{1c}@anchor{gnat_ugn/the_gnat_compilation_model id76}@anchor{d5}
@section Using GNAT Files with External Tools


This section explains how files that are produced by GNAT may be
used with tools designed for other languages.

@menu
* Using Other Utility Programs with GNAT:: 
* The External Symbol Naming Scheme of GNAT:: 

@end menu

@node Using Other Utility Programs with GNAT,The External Symbol Naming Scheme of GNAT,,Using GNAT Files with External Tools
@anchor{gnat_ugn/the_gnat_compilation_model using-other-utility-programs-with-gnat}@anchor{d6}@anchor{gnat_ugn/the_gnat_compilation_model id77}@anchor{d7}
@subsection Using Other Utility Programs with GNAT


The object files generated by GNAT are in standard system format and in
particular the debugging information uses this format. This means
programs generated by GNAT can be used with existing utilities that
depend on these formats.

In general, any utility program that works with C will also often work with
Ada programs generated by GNAT. This includes software utilities such as
gprof (a profiling program), gdb (the FSF debugger), and utilities such
as Purify.

@node The External Symbol Naming Scheme of GNAT,,Using Other Utility Programs with GNAT,Using GNAT Files with External Tools
@anchor{gnat_ugn/the_gnat_compilation_model the-external-symbol-naming-scheme-of-gnat}@anchor{d8}@anchor{gnat_ugn/the_gnat_compilation_model id78}@anchor{d9}
@subsection The External Symbol Naming Scheme of GNAT


In order to interpret the output from GNAT, when using tools that are
originally intended for use with other languages, it is useful to
understand the conventions used to generate link names from the Ada
entity names.

All link names are in all lowercase letters. With the exception of library
procedure names, the mechanism used is simply to use the full expanded
Ada name with dots replaced by double underscores. For example, suppose
we have the following package spec:

@example
package QRS is
   MN : Integer;
end QRS;
@end example

@geindex pragma Export

The variable @cite{MN} has a full expanded Ada name of @cite{QRS.MN}, so
the corresponding link name is @cite{qrs__mn}.
Of course if a @cite{pragma Export} is used this may be overridden:

@example
package Exports is
   Var1 : Integer;
   pragma Export (Var1, C, External_Name => "var1_name");
   Var2 : Integer;
   pragma Export (Var2, C, Link_Name => "var2_link_name");
end Exports;
@end example

In this case, the link name for @cite{Var1} is whatever link name the
C compiler would assign for the C function @cite{var1_name}. This typically
would be either @cite{var1_name} or @cite{_var1_name}, depending on operating
system conventions, but other possibilities exist. The link name for
@cite{Var2} is @cite{var2_link_name}, and this is not operating system
dependent.

One exception occurs for library level procedures. A potential ambiguity
arises between the required name @cite{_main} for the C main program,
and the name we would otherwise assign to an Ada library level procedure
called @cite{Main} (which might well not be the main program).

To avoid this ambiguity, we attach the prefix @cite{_ada_} to such
names. So if we have a library level procedure such as:

@example
procedure Hello (S : String);
@end example

the external name of this procedure will be @cite{_ada_hello}.

@c -- Example: A |withing| unit has a |with| clause, it |withs| a |withed| unit

@node Building Executable Programs with GNAT,GNAT Project Manager,The GNAT Compilation Model,Top
@anchor{gnat_ugn/building_executable_programs_with_gnat building-executable-programs-with-gnat}@anchor{a}@anchor{gnat_ugn/building_executable_programs_with_gnat doc}@anchor{da}@anchor{gnat_ugn/building_executable_programs_with_gnat id1}@anchor{db}
@chapter Building Executable Programs with GNAT


This chapter describes first the gnatmake tool
(@ref{1d,,Building with gnatmake}),
which automatically determines the set of sources
needed by an Ada compilation unit and executes the necessary
(re)compilations, binding and linking.
It also explains how to use each tool individually: the
compiler (gcc, see @ref{1e,,Compiling with gcc}),
binder (gnatbind, see @ref{1f,,Binding with gnatbind}),
and linker (gnatlink, see @ref{20,,Linking with gnatlink})
to build executable programs.
Finally, this chapter provides examples of
how to make use of the general GNU make mechanism
in a GNAT context (see @ref{21,,Using the GNU make Utility}).

@menu
* Building with gnatmake:: 
* Compiling with gcc:: 
* Compiler Switches:: 
* Binding with gnatbind:: 
* Linking with gnatlink:: 
* Using the GNU make Utility:: 

@end menu

@node Building with gnatmake,Compiling with gcc,,Building Executable Programs with GNAT
@anchor{gnat_ugn/building_executable_programs_with_gnat the-gnat-make-program-gnatmake}@anchor{1d}@anchor{gnat_ugn/building_executable_programs_with_gnat building-with-gnatmake}@anchor{dc}
@section Building with @emph{gnatmake}


@geindex gnatmake

A typical development cycle when working on an Ada program consists of
the following steps:


@enumerate 

@item 
Edit some sources to fix bugs;

@item 
Add enhancements;

@item 
Compile all sources affected;

@item 
Rebind and relink; and

@item 
Test.
@end enumerate

@geindex Dependency rules (compilation)

The third step in particular can be tricky, because not only do the modified
files have to be compiled, but any files depending on these files must also be
recompiled. The dependency rules in Ada can be quite complex, especially
in the presence of overloading, @cite{use} clauses, generics and inlined
subprograms.

@emph{gnatmake} automatically takes care of the third and fourth steps
of this process. It determines which sources need to be compiled,
compiles them, and binds and links the resulting object files.

Unlike some other Ada make programs, the dependencies are always
accurately recomputed from the new sources. The source based approach of
the GNAT compilation model makes this possible. This means that if
changes to the source program cause corresponding changes in
dependencies, they will always be tracked exactly correctly by
@emph{gnatmake}.

Note that for advanced description of project structure, we recommend creating
a project file as explained in @ref{b,,GNAT Project Manager} and use the
@emph{gprbuild} tool which supports building with project files and works similarly
to @emph{gnatmake}.

@menu
* Running gnatmake:: 
* Switches for gnatmake:: 
* Mode Switches for gnatmake:: 
* Notes on the Command Line:: 
* How gnatmake Works:: 
* Examples of gnatmake Usage:: 

@end menu

@node Running gnatmake,Switches for gnatmake,,Building with gnatmake
@anchor{gnat_ugn/building_executable_programs_with_gnat running-gnatmake}@anchor{dd}@anchor{gnat_ugn/building_executable_programs_with_gnat id2}@anchor{de}
@subsection Running @emph{gnatmake}


The usual form of the @emph{gnatmake} command is

@example
$ gnatmake [<switches>] <file_name> [<file_names>] [<mode_switches>]
@end example

The only required argument is one @cite{file_name}, which specifies
a compilation unit that is a main program. Several @cite{file_names} can be
specified: this will result in several executables being built.
If @cite{switches} are present, they can be placed before the first
@cite{file_name}, between @cite{file_names} or after the last @cite{file_name}.
If @cite{mode_switches} are present, they must always be placed after
the last @cite{file_name} and all @cite{switches}.

If you are using standard file extensions (@code{.adb} and
@code{.ads}), then the
extension may be omitted from the @cite{file_name} arguments. However, if
you are using non-standard extensions, then it is required that the
extension be given. A relative or absolute directory path can be
specified in a @cite{file_name}, in which case, the input source file will
be searched for in the specified directory only. Otherwise, the input
source file will first be searched in the directory where
@emph{gnatmake} was invoked and if it is not found, it will be search on
the source path of the compiler as described in
@ref{8e,,Search Paths and the Run-Time Library (RTL)}.

All @emph{gnatmake} output (except when you specify @emph{-M}) is sent to
@code{stderr}. The output produced by the
@emph{-M} switch is sent to @code{stdout}.

@node Switches for gnatmake,Mode Switches for gnatmake,Running gnatmake,Building with gnatmake
@anchor{gnat_ugn/building_executable_programs_with_gnat switches-for-gnatmake}@anchor{df}@anchor{gnat_ugn/building_executable_programs_with_gnat id3}@anchor{e0}
@subsection Switches for @emph{gnatmake}


You may specify any of the following switches to @emph{gnatmake}:

@geindex --version (gnatmake)


@table @asis

@item @code{--version}

Display Copyright and version, then exit disregarding all other options.
@end table

@geindex --help (gnatmake)


@table @asis

@item @code{--help}

If @code{--version} was not used, display usage, then exit disregarding
all other options.
@end table

@geindex --GCC=compiler_name (gnatmake)


@table @asis

@item @code{--GCC=@emph{compiler_name}}

Program used for compiling. The default is @code{gcc}. You need to use
quotes around @cite{compiler_name} if @cite{compiler_name} contains
spaces or other separator characters.
As an example @code{--GCC="foo -x  -y"}
will instruct @emph{gnatmake} to use @code{foo -x -y} as your
compiler. A limitation of this syntax is that the name and path name of
the executable itself must not include any embedded spaces. Note that
switch @code{-c} is always inserted after your command name. Thus in the
above example the compiler command that will be used by @emph{gnatmake}
will be @code{foo -c -x -y}. If several @code{--GCC=compiler_name} are
used, only the last @cite{compiler_name} is taken into account. However,
all the additional switches are also taken into account. Thus,
@code{--GCC="foo -x -y" --GCC="bar -z -t"} is equivalent to
@code{--GCC="bar -x -y -z -t"}.
@end table

@geindex --GNATBIND=binder_name (gnatmake)


@table @asis

@item @code{--GNATBIND=@emph{binder_name}}

Program used for binding. The default is @code{gnatbind}. You need to
use quotes around @cite{binder_name} if @cite{binder_name} contains spaces
or other separator characters.
As an example @code{--GNATBIND="bar -x  -y"}
will instruct @emph{gnatmake} to use @cite{bar -x -y} as your
binder. Binder switches that are normally appended by @emph{gnatmake}
to @code{gnatbind} are now appended to the end of @cite{bar -x -y}.
A limitation of this syntax is that the name and path name of the executable
itself must not include any embedded spaces.
@end table

@geindex --GNATLINK=linker_name (gnatmake)


@table @asis

@item @code{--GNATLINK=@emph{linker_name}}

Program used for linking. The default is @code{gnatlink}. You need to
use quotes around @cite{linker_name} if @cite{linker_name} contains spaces
or other separator characters.
As an example @code{--GNATLINK="lan -x  -y"}
will instruct @emph{gnatmake} to use @code{lan -x -y} as your
linker. Linker switches that are normally appended by @code{gnatmake} to
@code{gnatlink} are now appended to the end of @code{lan -x -y}.
A limitation of this syntax is that the name and path name of the executable
itself must not include any embedded spaces.

@item @code{--create-map-file}

When linking an executable, create a map file. The name of the map file
has the same name as the executable with extension ".map".

@item @code{--create-map-file=@emph{mapfile}}

When linking an executable, create a map file with the specified name.
@end table

@geindex --create-missing-dirs (gnatmake)


@table @asis

@item @code{--create-missing-dirs}

When using project files (@code{-P@emph{project}}), automatically create
missing object directories, library directories and exec
directories.

@item @code{--single-compile-per-obj-dir}

Disallow simultaneous compilations in the same object directory when
project files are used.

@item @code{--subdirs=@emph{subdir}}

Actual object directory of each project file is the subdirectory subdir of the
object directory specified or defaulted in the project file.

@item @code{--unchecked-shared-lib-imports}

By default, shared library projects are not allowed to import static library
projects. When this switch is used on the command line, this restriction is
relaxed.

@item @code{--source-info=@emph{source info file}}

Specify a source info file. This switch is active only when project files
are used. If the source info file is specified as a relative path, then it is
relative to the object directory of the main project. If the source info file
does not exist, then after the Project Manager has successfully parsed and
processed the project files and found the sources, it creates the source info
file. If the source info file already exists and can be read successfully,
then the Project Manager will get all the needed information about the sources
from the source info file and will not look for them. This reduces the time
to process the project files, especially when looking for sources that take a
long time. If the source info file exists but cannot be parsed successfully,
the Project Manager will attempt to recreate it. If the Project Manager fails
to create the source info file, a message is issued, but gnatmake does not
fail. @emph{gnatmake} "trusts" the source info file. This means that
if the source files have changed (addition, deletion, moving to a different
source directory), then the source info file need to be deleted and recreated.
@end table

@geindex -a (gnatmake)


@table @asis

@item @code{-a}

Consider all files in the make process, even the GNAT internal system
files (for example, the predefined Ada library files), as well as any
locked files. Locked files are files whose ALI file is write-protected.
By default,
@emph{gnatmake} does not check these files,
because the assumption is that the GNAT internal files are properly up
to date, and also that any write protected ALI files have been properly
installed. Note that if there is an installation problem, such that one
of these files is not up to date, it will be properly caught by the
binder.
You may have to specify this switch if you are working on GNAT
itself. The switch @code{-a} is also useful
in conjunction with @code{-f}
if you need to recompile an entire application,
including run-time files, using special configuration pragmas,
such as a @cite{Normalize_Scalars} pragma.

By default
@code{gnatmake -a} compiles all GNAT
internal files with
@code{gcc -c -gnatpg} rather than @code{gcc -c}.
@end table

@geindex -b (gnatmake)


@table @asis

@item @code{-b}

Bind only. Can be combined with @emph{-c} to do
compilation and binding, but no link.
Can be combined with @emph{-l}
to do binding and linking. When not combined with
@emph{-c}
all the units in the closure of the main program must have been previously
compiled and must be up to date. The root unit specified by @cite{file_name}
may be given without extension, with the source extension or, if no GNAT
Project File is specified, with the ALI file extension.
@end table

@geindex -c (gnatmake)


@table @asis

@item @code{-c}

Compile only. Do not perform binding, except when @emph{-b}
is also specified. Do not perform linking, except if both
@emph{-b} and
@emph{-l} are also specified.
If the root unit specified by @cite{file_name} is not a main unit, this is the
default. Otherwise @emph{gnatmake} will attempt binding and linking
unless all objects are up to date and the executable is more recent than
the objects.
@end table

@geindex -C (gnatmake)


@table @asis

@item @code{-C}

Use a temporary mapping file. A mapping file is a way to communicate
to the compiler two mappings: from unit names to file names (without
any directory information) and from file names to path names (with
full directory information). A mapping file can make the compiler's
file searches faster, especially if there are many source directories,
or the sources are read over a slow network connection. If
@emph{-P} is used, a mapping file is always used, so
@emph{-C} is unnecessary; in this case the mapping file
is initially populated based on the project file. If
@emph{-C} is used without
@emph{-P},
the mapping file is initially empty. Each invocation of the compiler
will add any newly accessed sources to the mapping file.
@end table

@geindex -C= (gnatmake)


@table @asis

@item @code{-C=@emph{file}}

Use a specific mapping file. The file, specified as a path name (absolute or
relative) by this switch, should already exist, otherwise the switch is
ineffective. The specified mapping file will be communicated to the compiler.
This switch is not compatible with a project file
(-P`file`) or with multiple compiling processes
(-jnnn, when nnn is greater than 1).
@end table

@geindex -d (gnatmake)


@table @asis

@item @code{-d}

Display progress for each source, up to date or not, as a single line:

@example
completed x out of y (zz%)
@end example

If the file needs to be compiled this is displayed after the invocation of
the compiler. These lines are displayed even in quiet output mode.
@end table

@geindex -D (gnatmake)


@table @asis

@item @code{-D @emph{dir}}

Put all object files and ALI file in directory @cite{dir}.
If the @emph{-D} switch is not used, all object files
and ALI files go in the current working directory.

This switch cannot be used when using a project file.
@end table

@geindex -eI (gnatmake)


@table @asis

@item @code{-eI@emph{nnn}}

Indicates that the main source is a multi-unit source and the rank of the unit
in the source file is nnn. nnn needs to be a positive number and a valid
index in the source. This switch cannot be used when @emph{gnatmake} is
invoked for several mains.
@end table

@geindex -eL (gnatmake)

@geindex symbolic links


@table @asis

@item @code{-eL}

Follow all symbolic links when processing project files.
This should be used if your project uses symbolic links for files or
directories, but is not needed in other cases.

@geindex naming scheme

This also assumes that no directory matches the naming scheme for files (for
instance that you do not have a directory called "sources.ads" when using the
default GNAT naming scheme).

When you do not have to use this switch (i.e., by default), gnatmake is able to
save a lot of system calls (several per source file and object file), which
can result in a significant speed up to load and manipulate a project file,
especially when using source files from a remote system.
@end table

@geindex -eS (gnatmake)


@table @asis

@item @code{-eS}

Output the commands for the compiler, the binder and the linker
on standard output,
instead of standard error.
@end table

@geindex -f (gnatmake)


@table @asis

@item @code{-f}

Force recompilations. Recompile all sources, even though some object
files may be up to date, but don't recompile predefined or GNAT internal
files or locked files (files with a write-protected ALI file),
unless the @emph{-a} switch is also specified.
@end table

@geindex -F (gnatmake)


@table @asis

@item @code{-F}

When using project files, if some errors or warnings are detected during
parsing and verbose mode is not in effect (no use of switch
-v), then error lines start with the full path name of the project
file, rather than its simple file name.
@end table

@geindex -g (gnatmake)


@table @asis

@item @code{-g}

Enable debugging. This switch is simply passed to the compiler and to the
linker.
@end table

@geindex -i (gnatmake)


@table @asis

@item @code{-i}

In normal mode, @emph{gnatmake} compiles all object files and ALI files
into the current directory. If the @emph{-i} switch is used,
then instead object files and ALI files that already exist are overwritten
in place. This means that once a large project is organized into separate
directories in the desired manner, then @emph{gnatmake} will automatically
maintain and update this organization. If no ALI files are found on the
Ada object path (see @ref{8e,,Search Paths and the Run-Time Library (RTL)}),
the new object and ALI files are created in the
directory containing the source being compiled. If another organization
is desired, where objects and sources are kept in different directories,
a useful technique is to create dummy ALI files in the desired directories.
When detecting such a dummy file, @emph{gnatmake} will be forced to
recompile the corresponding source file, and it will be put the resulting
object and ALI files in the directory where it found the dummy file.
@end table

@geindex -j (gnatmake)

@geindex Parallel make


@table @asis

@item @code{-j@emph{n}}

Use @cite{n} processes to carry out the (re)compilations. On a multiprocessor
machine compilations will occur in parallel. If @cite{n} is 0, then the
maximum number of parallel compilations is the number of core processors
on the platform. In the event of compilation errors, messages from various
compilations might get interspersed (but @emph{gnatmake} will give you the
full ordered list of failing compiles at the end). If this is problematic,
rerun the make process with n set to 1 to get a clean list of messages.
@end table

@geindex -k (gnatmake)


@table @asis

@item @code{-k}

Keep going. Continue as much as possible after a compilation error. To
ease the programmer's task in case of compilation errors, the list of
sources for which the compile fails is given when @emph{gnatmake}
terminates.

If @emph{gnatmake} is invoked with several @code{file_names} and with this
switch, if there are compilation errors when building an executable,
@emph{gnatmake} will not attempt to build the following executables.
@end table

@geindex -l (gnatmake)


@table @asis

@item @code{-l}

Link only. Can be combined with @emph{-b} to binding
and linking. Linking will not be performed if combined with
@emph{-c}
but not with @emph{-b}.
When not combined with @emph{-b}
all the units in the closure of the main program must have been previously
compiled and must be up to date, and the main program needs to have been bound.
The root unit specified by @cite{file_name}
may be given without extension, with the source extension or, if no GNAT
Project File is specified, with the ALI file extension.
@end table

@geindex -m (gnatmake)


@table @asis

@item @code{-m}

Specify that the minimum necessary amount of recompilations
be performed. In this mode @emph{gnatmake} ignores time
stamp differences when the only
modifications to a source file consist in adding/removing comments,
empty lines, spaces or tabs. This means that if you have changed the
comments in a source file or have simply reformatted it, using this
switch will tell @emph{gnatmake} not to recompile files that depend on it
(provided other sources on which these files depend have undergone no
semantic modifications). Note that the debugging information may be
out of date with respect to the sources if the @emph{-m} switch causes
a compilation to be switched, so the use of this switch represents a
trade-off between compilation time and accurate debugging information.
@end table

@geindex Dependencies
@geindex producing list

@geindex -M (gnatmake)


@table @asis

@item @code{-M}

Check if all objects are up to date. If they are, output the object
dependences to @code{stdout} in a form that can be directly exploited in
a @code{Makefile}. By default, each source file is prefixed with its
(relative or absolute) directory name. This name is whatever you
specified in the various @emph{-aI}
and @emph{-I} switches. If you use
@cite{gnatmake -M}  @emph{-q}
(see below), only the source file names,
without relative paths, are output. If you just specify the  @emph{-M}
switch, dependencies of the GNAT internal system files are omitted. This
is typically what you want. If you also specify
the @emph{-a} switch,
dependencies of the GNAT internal files are also listed. Note that
dependencies of the objects in external Ada libraries (see
switch  @code{-aL@emph{dir}} in the following list)
are never reported.
@end table

@geindex -n (gnatmake)


@table @asis

@item @code{-n}

Don't compile, bind, or link. Checks if all objects are up to date.
If they are not, the full name of the first file that needs to be
recompiled is printed.
Repeated use of this option, followed by compiling the indicated source
file, will eventually result in recompiling all required units.
@end table

@geindex -o (gnatmake)


@table @asis

@item @code{-o @emph{exec_name}}

Output executable name. The name of the final executable program will be
@cite{exec_name}. If the @emph{-o} switch is omitted the default
name for the executable will be the name of the input file in appropriate form
for an executable file on the host system.

This switch cannot be used when invoking @emph{gnatmake} with several
@code{file_names}.
@end table

@geindex -p (gnatmake)


@table @asis

@item @code{-p}

Same as @code{--create-missing-dirs}
@end table

@geindex -P (gnatmake)


@table @asis

@item @code{-P@emph{project}}

Use project file @cite{project}. Only one such switch can be used.
@ref{e1,,gnatmake and Project Files}.
@end table

@geindex -q (gnatmake)


@table @asis

@item @code{-q}

Quiet. When this flag is not set, the commands carried out by
@emph{gnatmake} are displayed.
@end table

@geindex -s (gnatmake)


@table @asis

@item @code{-s}

Recompile if compiler switches have changed since last compilation.
All compiler switches but -I and -o are taken into account in the
following way:
orders between different 'first letter' switches are ignored, but
orders between same switches are taken into account. For example,
@emph{-O -O2} is different than @emph{-O2 -O}, but @emph{-g -O}
is equivalent to @emph{-O -g}.

This switch is recommended when Integrated Preprocessing is used.
@end table

@geindex -u (gnatmake)


@table @asis

@item @code{-u}

Unique. Recompile at most the main files. It implies -c. Combined with
-f, it is equivalent to calling the compiler directly. Note that using
-u with a project file and no main has a special meaning
(@ref{e2,,Project Files and Main Subprograms}).
@end table

@geindex -U (gnatmake)


@table @asis

@item @code{-U}

When used without a project file or with one or several mains on the command
line, is equivalent to -u. When used with a project file and no main
on the command line, all sources of all project files are checked and compiled
if not up to date, and libraries are rebuilt, if necessary.
@end table

@geindex -v (gnatmake)


@table @asis

@item @code{-v}

Verbose. Display the reason for all recompilations @emph{gnatmake}
decides are necessary, with the highest verbosity level.
@end table

@geindex -vl (gnatmake)


@table @asis

@item @code{-vl}

Verbosity level Low. Display fewer lines than in verbosity Medium.
@end table

@geindex -vm (gnatmake)


@table @asis

@item @code{-vm}

Verbosity level Medium. Potentially display fewer lines than in verbosity High.
@end table

@geindex -vm (gnatmake)


@table @asis

@item @code{-vh}

Verbosity level High. Equivalent to -v.

@item @code{-vP@emph{x}}

Indicate the verbosity of the parsing of GNAT project files.
See @ref{e3,,Switches Related to Project Files}.
@end table

@geindex -x (gnatmake)


@table @asis

@item @code{-x}

Indicate that sources that are not part of any Project File may be compiled.
Normally, when using Project Files, only sources that are part of a Project
File may be compile. When this switch is used, a source outside of all Project
Files may be compiled. The ALI file and the object file will be put in the
object directory of the main Project. The compilation switches used will only
be those specified on the command line. Even when
@emph{-x} is used, mains specified on the
command line need to be sources of a project file.

@item @code{-X@emph{name}=@emph{value}}

Indicate that external variable @cite{name} has the value @cite{value}.
The Project Manager will use this value for occurrences of
@cite{external(name)} when parsing the project file.
@ref{e3,,Switches Related to Project Files}.
@end table

@geindex -z (gnatmake)


@table @asis

@item @code{-z}

No main subprogram. Bind and link the program even if the unit name
given on the command line is a package name. The resulting executable
will execute the elaboration routines of the package and its closure,
then the finalization routines.
@end table

@subsubheading GCC switches


Any uppercase or multi-character switch that is not a @emph{gnatmake} switch
is passed to @emph{gcc} (e.g., @emph{-O}, @emph{-gnato,} etc.)

@subsubheading Source and library search path switches


@geindex -aI (gnatmake)


@table @asis

@item @code{-aI@emph{dir}}

When looking for source files also look in directory @cite{dir}.
The order in which source files search is undertaken is
described in @ref{8e,,Search Paths and the Run-Time Library (RTL)}.
@end table

@geindex -aL (gnatmake)


@table @asis

@item @code{-aL@emph{dir}}

Consider @cite{dir} as being an externally provided Ada library.
Instructs @emph{gnatmake} to skip compilation units whose @code{.ALI}
files have been located in directory @cite{dir}. This allows you to have
missing bodies for the units in @cite{dir} and to ignore out of date bodies
for the same units. You still need to specify
the location of the specs for these units by using the switches
@code{-aI@emph{dir}}  or @code{-I@emph{dir}}.
Note: this switch is provided for compatibility with previous versions
of @emph{gnatmake}. The easier method of causing standard libraries
to be excluded from consideration is to write-protect the corresponding
ALI files.
@end table

@geindex -aO (gnatmake)


@table @asis

@item @code{-aO@emph{dir}}

When searching for library and object files, look in directory
@cite{dir}. The order in which library files are searched is described in
@ref{91,,Search Paths for gnatbind}.
@end table

@geindex Search paths
@geindex for gnatmake

@geindex -A (gnatmake)


@table @asis

@item @code{-A@emph{dir}}

Equivalent to @code{-aL@emph{dir}} @code{-aI@emph{dir}}.

@geindex -I (gnatmake)

@item @code{-I@emph{dir}}

Equivalent to @code{-aO@emph{dir} -aI@emph{dir}}.
@end table

@geindex -I- (gnatmake)

@geindex Source files
@geindex suppressing search


@table @asis

@item @code{-I-}

Do not look for source files in the directory containing the source
file named in the command line.
Do not look for ALI or object files in the directory
where @emph{gnatmake} was invoked.
@end table

@geindex -L (gnatmake)

@geindex Linker libraries


@table @asis

@item @code{-L@emph{dir}}

Add directory @cite{dir} to the list of directories in which the linker
will search for libraries. This is equivalent to
@code{-largs} @code{-L@emph{dir}}.
Furthermore, under Windows, the sources pointed to by the libraries path
set in the registry are not searched for.
@end table

@geindex -nostdinc (gnatmake)


@table @asis

@item @code{-nostdinc}

Do not look for source files in the system default directory.
@end table

@geindex -nostdlib (gnatmake)


@table @asis

@item @code{-nostdlib}

Do not look for library files in the system default directory.
@end table

@geindex --RTS (gnatmake)


@table @asis

@item @code{--RTS=@emph{rts-path}}

Specifies the default location of the runtime library. GNAT looks for the
runtime
in the following directories, and stops as soon as a valid runtime is found
(@code{adainclude} or @code{ada_source_path}, and @code{adalib} or
@code{ada_object_path} present):


@itemize *

@item 
@emph{<current directory>/$rts_path}

@item 
@emph{<default-search-dir>/$rts_path}

@item 
@emph{<default-search-dir>/rts-$rts_path}

@item 
The selected path is handled like a normal RTS path.
@end itemize
@end table

@node Mode Switches for gnatmake,Notes on the Command Line,Switches for gnatmake,Building with gnatmake
@anchor{gnat_ugn/building_executable_programs_with_gnat id4}@anchor{e4}@anchor{gnat_ugn/building_executable_programs_with_gnat mode-switches-for-gnatmake}@anchor{e5}
@subsection Mode Switches for @emph{gnatmake}


The mode switches (referred to as @cite{mode_switches}) allow the
inclusion of switches that are to be passed to the compiler itself, the
binder or the linker. The effect of a mode switch is to cause all
subsequent switches up to the end of the switch list, or up to the next
mode switch, to be interpreted as switches to be passed on to the
designated component of GNAT.

@geindex -cargs (gnatmake)


@table @asis

@item @code{-cargs @emph{switches}}

Compiler switches. Here @cite{switches} is a list of switches
that are valid switches for @emph{gcc}. They will be passed on to
all compile steps performed by @emph{gnatmake}.
@end table

@geindex -bargs (gnatmake)


@table @asis

@item @code{-bargs @emph{switches}}

Binder switches. Here @cite{switches} is a list of switches
that are valid switches for @cite{gnatbind}. They will be passed on to
all bind steps performed by @emph{gnatmake}.
@end table

@geindex -largs (gnatmake)


@table @asis

@item @code{-largs @emph{switches}}

Linker switches. Here @cite{switches} is a list of switches
that are valid switches for @emph{gnatlink}. They will be passed on to
all link steps performed by @emph{gnatmake}.
@end table

@geindex -margs (gnatmake)


@table @asis

@item @code{-margs @emph{switches}}

Make switches. The switches are directly interpreted by @emph{gnatmake},
regardless of any previous occurrence of @emph{-cargs}, @emph{-bargs}
or @emph{-largs}.
@end table

@node Notes on the Command Line,How gnatmake Works,Mode Switches for gnatmake,Building with gnatmake
@anchor{gnat_ugn/building_executable_programs_with_gnat id5}@anchor{e6}@anchor{gnat_ugn/building_executable_programs_with_gnat notes-on-the-command-line}@anchor{e7}
@subsection Notes on the Command Line


This section contains some additional useful notes on the operation
of the @emph{gnatmake} command.

@geindex Recompilation (by gnatmake)


@itemize *

@item 
If @emph{gnatmake} finds no ALI files, it recompiles the main program
and all other units required by the main program.
This means that @emph{gnatmake}
can be used for the initial compile, as well as during subsequent steps of
the development cycle.

@item 
If you enter @code{gnatmake foo.adb}, where @code{foo}
is a subunit or body of a generic unit, @emph{gnatmake} recompiles
@code{foo.adb} (because it finds no ALI) and stops, issuing a
warning.

@item 
In @emph{gnatmake} the switch @emph{-I}
is used to specify both source and
library file paths. Use @emph{-aI}
instead if you just want to specify
source paths only and @emph{-aO}
if you want to specify library paths
only.

@item 
@emph{gnatmake} will ignore any files whose ALI file is write-protected.
This may conveniently be used to exclude standard libraries from
consideration and in particular it means that the use of the
@emph{-f} switch will not recompile these files
unless @emph{-a} is also specified.

@item 
@emph{gnatmake} has been designed to make the use of Ada libraries
particularly convenient. Assume you have an Ada library organized
as follows: @emph{obj-dir} contains the objects and ALI files for
of your Ada compilation units,
whereas @emph{include-dir} contains the
specs of these units, but no bodies. Then to compile a unit
stored in @cite{main.adb}, which uses this Ada library you would just type:

@example
$ gnatmake -aI`include-dir`  -aL`obj-dir`  main
@end example

@item 
Using @emph{gnatmake} along with the @emph{-m (minimal recompilation)}
switch provides a mechanism for avoiding unnecessary recompilations. Using
this switch,
you can update the comments/format of your
source files without having to recompile everything. Note, however, that
adding or deleting lines in a source files may render its debugging
info obsolete. If the file in question is a spec, the impact is rather
limited, as that debugging info will only be useful during the
elaboration phase of your program. For bodies the impact can be more
significant. In all events, your debugger will warn you if a source file
is more recent than the corresponding object, and alert you to the fact
that the debugging information may be out of date.
@end itemize

@node How gnatmake Works,Examples of gnatmake Usage,Notes on the Command Line,Building with gnatmake
@anchor{gnat_ugn/building_executable_programs_with_gnat id6}@anchor{e8}@anchor{gnat_ugn/building_executable_programs_with_gnat how-gnatmake-works}@anchor{e9}
@subsection How @emph{gnatmake} Works


Generally @emph{gnatmake} automatically performs all necessary
recompilations and you don't need to worry about how it works. However,
it may be useful to have some basic understanding of the @emph{gnatmake}
approach and in particular to understand how it uses the results of
previous compilations without incorrectly depending on them.

First a definition: an object file is considered @emph{up to date} if the
corresponding ALI file exists and if all the source files listed in the
dependency section of this ALI file have time stamps matching those in
the ALI file. This means that neither the source file itself nor any
files that it depends on have been modified, and hence there is no need
to recompile this file.

@emph{gnatmake} works by first checking if the specified main unit is up
to date. If so, no compilations are required for the main unit. If not,
@emph{gnatmake} compiles the main program to build a new ALI file that
reflects the latest sources. Then the ALI file of the main unit is
examined to find all the source files on which the main program depends,
and @emph{gnatmake} recursively applies the above procedure on all these
files.

This process ensures that @emph{gnatmake} only trusts the dependencies
in an existing ALI file if they are known to be correct. Otherwise it
always recompiles to determine a new, guaranteed accurate set of
dependencies. As a result the program is compiled 'upside down' from what may
be more familiar as the required order of compilation in some other Ada
systems. In particular, clients are compiled before the units on which
they depend. The ability of GNAT to compile in any order is critical in
allowing an order of compilation to be chosen that guarantees that
@emph{gnatmake} will recompute a correct set of new dependencies if
necessary.

When invoking @emph{gnatmake} with several @cite{file_names}, if a unit is
imported by several of the executables, it will be recompiled at most once.

Note: when using non-standard naming conventions
(@ref{37,,Using Other File Names}), changing through a configuration pragmas
file the version of a source and invoking @emph{gnatmake} to recompile may
have no effect, if the previous version of the source is still accessible
by @emph{gnatmake}. It may be necessary to use the switch
-f.

@node Examples of gnatmake Usage,,How gnatmake Works,Building with gnatmake
@anchor{gnat_ugn/building_executable_programs_with_gnat examples-of-gnatmake-usage}@anchor{ea}@anchor{gnat_ugn/building_executable_programs_with_gnat id7}@anchor{eb}
@subsection Examples of @emph{gnatmake} Usage



@table @asis

@item @emph{gnatmake hello.adb}

Compile all files necessary to bind and link the main program
@code{hello.adb} (containing unit @cite{Hello}) and bind and link the
resulting object files to generate an executable file @code{hello}.

@item @emph{gnatmake main1 main2 main3}

Compile all files necessary to bind and link the main programs
@code{main1.adb} (containing unit @cite{Main1}), @code{main2.adb}
(containing unit @cite{Main2}) and @code{main3.adb}
(containing unit @cite{Main3}) and bind and link the resulting object files
to generate three executable files @code{main1},
@code{main2}  and @code{main3}.

@item @emph{gnatmake -q Main_Unit -cargs -O2 -bargs -l}

Compile all files necessary to bind and link the main program unit
@cite{Main_Unit} (from file @code{main_unit.adb}). All compilations will
be done with optimization level 2 and the order of elaboration will be
listed by the binder. @emph{gnatmake} will operate in quiet mode, not
displaying commands it is executing.
@end table

@node Compiling with gcc,Compiler Switches,Building with gnatmake,Building Executable Programs with GNAT
@anchor{gnat_ugn/building_executable_programs_with_gnat compiling-with-gcc}@anchor{1e}@anchor{gnat_ugn/building_executable_programs_with_gnat id8}@anchor{ec}
@section Compiling with @emph{gcc}


This section discusses how to compile Ada programs using the @emph{gcc}
command. It also describes the set of switches
that can be used to control the behavior of the compiler.

@menu
* Compiling Programs:: 
* Search Paths and the Run-Time Library (RTL): Search Paths and the Run-Time Library RTL. 
* Order of Compilation Issues:: 
* Examples:: 

@end menu

@node Compiling Programs,Search Paths and the Run-Time Library RTL,,Compiling with gcc
@anchor{gnat_ugn/building_executable_programs_with_gnat compiling-programs}@anchor{ed}@anchor{gnat_ugn/building_executable_programs_with_gnat id9}@anchor{ee}
@subsection Compiling Programs


The first step in creating an executable program is to compile the units
of the program using the @emph{gcc} command. You must compile the
following files:


@itemize *

@item 
the body file (@code{.adb}) for a library level subprogram or generic
subprogram

@item 
the spec file (@code{.ads}) for a library level package or generic
package that has no body

@item 
the body file (@code{.adb}) for a library level package
or generic package that has a body
@end itemize

You need @emph{not} compile the following files


@itemize *

@item 
the spec of a library unit which has a body

@item 
subunits
@end itemize

because they are compiled as part of compiling related units. GNAT
package specs
when the corresponding body is compiled, and subunits when the parent is
compiled.

@geindex cannot generate code

If you attempt to compile any of these files, you will get one of the
following error messages (where @cite{fff} is the name of the file you
compiled):

@quotation

@example
cannot generate code for file `fff` (package spec)
to check package spec, use -gnatc

cannot generate code for file `fff` (missing subunits)
to check parent unit, use -gnatc

cannot generate code for file `fff` (subprogram spec)
to check subprogram spec, use -gnatc

cannot generate code for file `fff` (subunit)
to check subunit, use -gnatc
@end example
@end quotation

As indicated by the above error messages, if you want to submit
one of these files to the compiler to check for correct semantics
without generating code, then use the @emph{-gnatc} switch.

The basic command for compiling a file containing an Ada unit is:

@example
$ gcc -c [switches] <file name>
@end example

where @cite{file name} is the name of the Ada file (usually
having an extension @code{.ads} for a spec or @code{.adb} for a body).
You specify the
@code{-c} switch to tell @emph{gcc} to compile, but not link, the file.
The result of a successful compilation is an object file, which has the
same name as the source file but an extension of @code{.o} and an Ada
Library Information (ALI) file, which also has the same name as the
source file, but with @code{.ali} as the extension. GNAT creates these
two output files in the current directory, but you may specify a source
file in any directory using an absolute or relative path specification
containing the directory information.

@geindex gnat1

@emph{gcc} is actually a driver program that looks at the extensions of
the file arguments and loads the appropriate compiler. For example, the
GNU C compiler is @code{cc1}, and the Ada compiler is @code{gnat1}.
These programs are in directories known to the driver program (in some
configurations via environment variables you set), but need not be in
your path. The @emph{gcc} driver also calls the assembler and any other
utilities needed to complete the generation of the required object
files.

It is possible to supply several file names on the same @emph{gcc}
command. This causes @emph{gcc} to call the appropriate compiler for
each file. For example, the following command lists two separate
files to be compiled:

@example
$ gcc -c x.adb y.adb
@end example

calls @cite{gnat1} (the Ada compiler) twice to compile @code{x.adb} and
@code{y.adb}.
The compiler generates two object files @code{x.o} and @code{y.o}
and the two ALI files @code{x.ali} and @code{y.ali}.

Any switches apply to all the files listed, see @ref{ef,,Compiler Switches} for a
list of available @emph{gcc} switches.

@node Search Paths and the Run-Time Library RTL,Order of Compilation Issues,Compiling Programs,Compiling with gcc
@anchor{gnat_ugn/building_executable_programs_with_gnat id10}@anchor{f0}@anchor{gnat_ugn/building_executable_programs_with_gnat search-paths-and-the-run-time-library-rtl}@anchor{8e}
@subsection Search Paths and the Run-Time Library (RTL)


With the GNAT source-based library system, the compiler must be able to
find source files for units that are needed by the unit being compiled.
Search paths are used to guide this process.

The compiler compiles one source file whose name must be given
explicitly on the command line. In other words, no searching is done
for this file. To find all other source files that are needed (the most
common being the specs of units), the compiler examines the following
directories, in the following order:


@itemize *

@item 
The directory containing the source file of the main unit being compiled
(the file name on the command line).

@item 
Each directory named by an @emph{-I} switch given on the @emph{gcc}
command line, in the order given.

@geindex ADA_PRJ_INCLUDE_FILE

@item 
Each of the directories listed in the text file whose name is given
by the 
@geindex ADA_PRJ_INCLUDE_FILE
@geindex environment variable; ADA_PRJ_INCLUDE_FILE
@code{ADA_PRJ_INCLUDE_FILE} environment variable.
@geindex ADA_PRJ_INCLUDE_FILE
@geindex environment variable; ADA_PRJ_INCLUDE_FILE
@code{ADA_PRJ_INCLUDE_FILE} is normally set by gnatmake or by the gnat
driver when project files are used. It should not normally be set
by other means.

@geindex ADA_INCLUDE_PATH

@item 
Each of the directories listed in the value of the
@geindex ADA_INCLUDE_PATH
@geindex environment variable; ADA_INCLUDE_PATH
@code{ADA_INCLUDE_PATH} environment variable.
Construct this value
exactly as the 
@geindex PATH
@geindex environment variable; PATH
@code{PATH} environment variable: a list of directory
names separated by colons (semicolons when working with the NT version).

@item 
The content of the @code{ada_source_path} file which is part of the GNAT
installation tree and is used to store standard libraries such as the
GNAT Run Time Library (RTL) source files.
@ref{8b,,Installing a library}
@end itemize

Specifying the switch @emph{-I-}
inhibits the use of the directory
containing the source file named in the command line. You can still
have this directory on your search path, but in this case it must be
explicitly requested with a @emph{-I} switch.

Specifying the switch @emph{-nostdinc}
inhibits the search of the default location for the GNAT Run Time
Library (RTL) source files.

The compiler outputs its object files and ALI files in the current
working directory.
Caution: The object file can be redirected with the @emph{-o} switch;
however, @emph{gcc} and @cite{gnat1} have not been coordinated on this
so the @code{ALI} file will not go to the right place. Therefore, you should
avoid using the @emph{-o} switch.

@geindex System.IO

The packages @cite{Ada}, @cite{System}, and @cite{Interfaces} and their
children make up the GNAT RTL, together with the simple @cite{System.IO}
package used in the @cite{"Hello World"} example. The sources for these units
are needed by the compiler and are kept together in one directory. Not
all of the bodies are needed, but all of the sources are kept together
anyway. In a normal installation, you need not specify these directory
names when compiling or binding. Either the environment variables or
the built-in defaults cause these files to be found.

In addition to the language-defined hierarchies (@cite{System}, @cite{Ada} and
@cite{Interfaces}), the GNAT distribution provides a fourth hierarchy,
consisting of child units of @cite{GNAT}. This is a collection of generally
useful types, subprograms, etc. See the @cite{GNAT_Reference_Manual}
for further details.

Besides simplifying access to the RTL, a major use of search paths is
in compiling sources from multiple directories. This can make
development environments much more flexible.

@node Order of Compilation Issues,Examples,Search Paths and the Run-Time Library RTL,Compiling with gcc
@anchor{gnat_ugn/building_executable_programs_with_gnat id11}@anchor{f1}@anchor{gnat_ugn/building_executable_programs_with_gnat order-of-compilation-issues}@anchor{f2}
@subsection Order of Compilation Issues


If, in our earlier example, there was a spec for the @cite{hello}
procedure, it would be contained in the file @code{hello.ads}; yet this
file would not have to be explicitly compiled. This is the result of the
model we chose to implement library management. Some of the consequences
of this model are as follows:


@itemize *

@item 
There is no point in compiling specs (except for package
specs with no bodies) because these are compiled as needed by clients. If
you attempt a useless compilation, you will receive an error message.
It is also useless to compile subunits because they are compiled as needed
by the parent.

@item 
There are no order of compilation requirements: performing a
compilation never obsoletes anything. The only way you can obsolete
something and require recompilations is to modify one of the
source files on which it depends.

@item 
There is no library as such, apart from the ALI files
(@ref{44,,The Ada Library Information Files}, for information on the format
of these files). For now we find it convenient to create separate ALI files,
but eventually the information therein may be incorporated into the object
file directly.

@item 
When you compile a unit, the source files for the specs of all units
that it @emph{with}s, all its subunits, and the bodies of any generics it
instantiates must be available (reachable by the search-paths mechanism
described above), or you will receive a fatal error message.
@end itemize

@node Examples,,Order of Compilation Issues,Compiling with gcc
@anchor{gnat_ugn/building_executable_programs_with_gnat id12}@anchor{f3}@anchor{gnat_ugn/building_executable_programs_with_gnat examples}@anchor{f4}
@subsection Examples


The following are some typical Ada compilation command line examples:

@example
$ gcc -c xyz.adb
@end example

Compile body in file @code{xyz.adb} with all default options.

@example
$ gcc -c -O2 -gnata xyz-def.adb
@end example

Compile the child unit package in file @code{xyz-def.adb} with extensive
optimizations, and pragma @cite{Assert}/@cite{Debug} statements
enabled.

@example
$ gcc -c -gnatc abc-def.adb
@end example

Compile the subunit in file @code{abc-def.adb} in semantic-checking-only
mode.

@node Compiler Switches,Binding with gnatbind,Compiling with gcc,Building Executable Programs with GNAT
@anchor{gnat_ugn/building_executable_programs_with_gnat compiler-switches}@anchor{f5}@anchor{gnat_ugn/building_executable_programs_with_gnat switches-for-gcc}@anchor{ef}
@section Compiler Switches


The @emph{gcc} command accepts switches that control the
compilation process. These switches are fully described in this section:
first an alphabetical listing of all switches with a brief description,
and then functionally grouped sets of switches with more detailed
information.

More switches exist for GCC than those documented here, especially
for specific targets. However, their use is not recommended as
they may change code generation in ways that are incompatible with
the Ada run-time library, or can cause inconsistencies between
compilation units.

@menu
* Alphabetical List of All Switches:: 
* Output and Error Message Control:: 
* Warning Message Control:: 
* Debugging and Assertion Control:: 
* Validity Checking:: 
* Style Checking:: 
* Run-Time Checks:: 
* Using gcc for Syntax Checking:: 
* Using gcc for Semantic Checking:: 
* Compiling Different Versions of Ada:: 
* Character Set Control:: 
* File Naming Control:: 
* Subprogram Inlining Control:: 
* Auxiliary Output Control:: 
* Debugging Control:: 
* Exception Handling Control:: 
* Units to Sources Mapping Files:: 
* Code Generation Control:: 

@end menu

@node Alphabetical List of All Switches,Output and Error Message Control,,Compiler Switches
@anchor{gnat_ugn/building_executable_programs_with_gnat id13}@anchor{f6}@anchor{gnat_ugn/building_executable_programs_with_gnat alphabetical-list-of-all-switches}@anchor{f7}
@subsection Alphabetical List of All Switches


@geindex -b (gcc)


@table @asis

@item @code{-b @emph{target}}

Compile your program to run on @cite{target}, which is the name of a
system configuration. You must have a GNAT cross-compiler built if
@cite{target} is not the same as your host system.
@end table

@geindex -B (gcc)


@table @asis

@item @code{-B@emph{dir}}

Load compiler executables (for example, @cite{gnat1}, the Ada compiler)
from @cite{dir} instead of the default location. Only use this switch
when multiple versions of the GNAT compiler are available.
See the "Options for Directory Search" section in the
@cite{Using the GNU Compiler Collection (GCC)} manual for further details.
You would normally use the @emph{-b} or @emph{-V} switch instead.
@end table

@geindex -c (gcc)


@table @asis

@item @code{-c}

Compile. Always use this switch when compiling Ada programs.

Note: for some other languages when using @emph{gcc}, notably in
the case of C and C++, it is possible to use
use @emph{gcc} without a @emph{-c} switch to
compile and link in one step. In the case of GNAT, you
cannot use this approach, because the binder must be run
and @emph{gcc} cannot be used to run the GNAT binder.
@end table

@geindex -fcallgraph-info (gcc)


@table @asis

@item @code{-fcallgraph-info[=su,da]}

Makes the compiler output callgraph information for the program, on a
per-file basis. The information is generated in the VCG format.  It can
be decorated with additional, per-node and/or per-edge information, if a
list of comma-separated markers is additionally specified. When the
@cite{su} marker is specified, the callgraph is decorated with stack usage
information; it is equivalent to @emph{-fstack-usage}. When the @cite{da}
marker is specified, the callgraph is decorated with information about
dynamically allocated objects.
@end table

@geindex -fdump-scos (gcc)


@table @asis

@item @code{-fdump-scos}

Generates SCO (Source Coverage Obligation) information in the ALI file.
This information is used by advanced coverage tools. See unit @code{SCOs}
in the compiler sources for details in files @code{scos.ads} and
@code{scos.adb}.
@end table

@geindex -fdump-xref (gcc)


@table @asis

@item @code{-fdump-xref}

Generates cross reference information in GLI files for C and C++ sources.
The GLI files have the same syntax as the ALI files for Ada, and can be used
for source navigation in IDEs and on the command line using e.g. gnatxref
and the @emph{--ext=gli} switch.
@end table

@geindex -flto (gcc)


@table @asis

@item @code{-flto[=@emph{n}]}

Enables Link Time Optimization. This switch must be used in conjunction
with the traditional @emph{-Ox} switches and instructs the compiler to
defer most optimizations until the link stage. The advantage of this
approach is that the compiler can do a whole-program analysis and choose
the best interprocedural optimization strategy based on a complete view
of the program, instead of a fragmentary view with the usual approach.
This can also speed up the compilation of big programs and reduce the
size of the executable, compared with a traditional per-unit compilation
with inlining across modules enabled by the @emph{-gnatn} switch.
The drawback of this approach is that it may require more memory and that
the debugging information generated by -g with it might be hardly usable.
The switch, as well as the accompanying @emph{-Ox} switches, must be
specified both for the compilation and the link phases.
If the @cite{n} parameter is specified, the optimization and final code
generation at link time are executed using @cite{n} parallel jobs by
means of an installed @emph{make} program.
@end table

@geindex -fno-inline (gcc)


@table @asis

@item @code{-fno-inline}

Suppresses all inlining, unless requested with pragma @cite{Inline_Always}. The
effect is enforced regardless of other optimization or inlining switches.
Note that inlining can also be suppressed on a finer-grained basis with
pragma @cite{No_Inline}.
@end table

@geindex -fno-inline-functions (gcc)


@table @asis

@item @code{-fno-inline-functions}

Suppresses automatic inlining of subprograms, which is enabled
if @emph{-O3} is used.
@end table

@geindex -fno-inline-small-functions (gcc)


@table @asis

@item @code{-fno-inline-small-functions}

Suppresses automatic inlining of small subprograms, which is enabled
if @emph{-O2} is used.
@end table

@geindex -fno-inline-functions-called-once (gcc)


@table @asis

@item @code{-fno-inline-functions-called-once}

Suppresses inlining of subprograms local to the unit and called once
from within it, which is enabled if @emph{-O1} is used.
@end table

@geindex -fno-ivopts (gcc)


@table @asis

@item @code{-fno-ivopts}

Suppresses high-level loop induction variable optimizations, which are
enabled if @emph{-O1} is used. These optimizations are generally
profitable but, for some specific cases of loops with numerous uses
of the iteration variable that follow a common pattern, they may end
up destroying the regularity that could be exploited at a lower level
and thus producing inferior code.
@end table

@geindex -fno-strict-aliasing (gcc)


@table @asis

@item @code{-fno-strict-aliasing}

Causes the compiler to avoid assumptions regarding non-aliasing
of objects of different types. See
@ref{f8,,Optimization and Strict Aliasing} for details.
@end table

@geindex -fstack-check (gcc)


@table @asis

@item @code{-fstack-check}

Activates stack checking.
See @ref{f9,,Stack Overflow Checking} for details.
@end table

@geindex -fstack-usage (gcc)


@table @asis

@item @code{-fstack-usage}

Makes the compiler output stack usage information for the program, on a
per-subprogram basis. See @ref{fa,,Static Stack Usage Analysis} for details.
@end table

@geindex -g (gcc)


@table @asis

@item @code{-g}

Generate debugging information. This information is stored in the object
file and copied from there to the final executable file by the linker,
where it can be read by the debugger. You must use the
@emph{-g} switch if you plan on using the debugger.
@end table

@geindex -gnat05 (gcc)


@table @asis

@item @code{-gnat05}

Allow full Ada 2005 features.
@end table

@geindex -gnat12 (gcc)


@table @asis

@item @code{-gnat12}

Allow full Ada 2012 features.
@end table

@geindex -gnat83 (gcc)

@geindex -gnat2005 (gcc)


@table @asis

@item @code{-gnat2005}

Allow full Ada 2005 features (same as @emph{-gnat05})
@end table

@geindex -gnat2012 (gcc)


@table @asis

@item @code{-gnat2012}

Allow full Ada 2012 features (same as @emph{-gnat12})

@item @code{-gnat83}

Enforce Ada 83 restrictions.
@end table

@geindex -gnat95 (gcc)


@table @asis

@item @code{-gnat95}

Enforce Ada 95 restrictions.

Note: for compatibility with some Ada 95 compilers which support only
the @cite{overriding} keyword of Ada 2005, the @emph{-gnatd.D} switch can
be used along with @emph{-gnat95} to achieve a similar effect with GNAT.

@emph{-gnatd.D} instructs GNAT to consider @cite{overriding} as a keyword
and handle its associated semantic checks, even in Ada 95 mode.
@end table

@geindex -gnata (gcc)


@table @asis

@item @code{-gnata}

Assertions enabled. @cite{Pragma Assert} and @cite{pragma Debug} to be
activated. Note that these pragmas can also be controlled using the
configuration pragmas @cite{Assertion_Policy} and @cite{Debug_Policy}.
It also activates pragmas @cite{Check}, @cite{Precondition}, and
@cite{Postcondition}. Note that these pragmas can also be controlled
using the configuration pragma @cite{Check_Policy}. In Ada 2012, it
also activates all assertions defined in the RM as aspects: preconditions,
postconditions, type invariants and (sub)type predicates. In all Ada modes,
corresponding pragmas for type invariants and (sub)type predicates are
also activated. The default is that all these assertions are disabled,
and have no effect, other than being checked for syntactic validity, and
in the case of subtype predicates, constructions such as membership tests
still test predicates even if assertions are turned off.
@end table

@geindex -gnatA (gcc)


@table @asis

@item @code{-gnatA}

Avoid processing @code{gnat.adc}. If a @code{gnat.adc} file is present,
it will be ignored.
@end table

@geindex -gnatb (gcc)


@table @asis

@item @code{-gnatb}

Generate brief messages to @code{stderr} even if verbose mode set.
@end table

@geindex -gnatB (gcc)


@table @asis

@item @code{-gnatB}

Assume no invalid (bad) values except for 'Valid attribute use
(@ref{fb,,Validity Checking}).
@end table

@geindex -gnatc (gcc)


@table @asis

@item @code{-gnatc}

Check syntax and semantics only (no code generation attempted). When the
compiler is invoked by @emph{gnatmake}, if the switch @emph{-gnatc} is
only given to the compiler (after @emph{-cargs} or in package Compiler of
the project file, @emph{gnatmake} will fail because it will not find the
object file after compilation. If @emph{gnatmake} is called with
@emph{-gnatc} as a builder switch (before @emph{-cargs} or in package
Builder of the project file) then @emph{gnatmake} will not fail because
it will not look for the object files after compilation, and it will not try
to build and link. This switch may not be given if a previous @cite{-gnatR}
switch has been given, since @cite{-gnatR} requires that the code generator
be called to complete determination of representation information.
@end table

@geindex -gnatC (gcc)


@table @asis

@item @code{-gnatC}

Generate CodePeer intermediate format (no code generation attempted).
This switch will generate an intermediate representation suitable for
use by CodePeer (@code{.scil} files). This switch is not compatible with
code generation (it will, among other things, disable some switches such
as -gnatn, and enable others such as -gnata).
@end table

@geindex -gnatd (gcc)


@table @asis

@item @code{-gnatd}

Specify debug options for the compiler. The string of characters after
the @emph{-gnatd} specify the specific debug options. The possible
characters are 0-9, a-z, A-Z, optionally preceded by a dot. See
compiler source file @code{debug.adb} for details of the implemented
debug options. Certain debug options are relevant to applications
programmers, and these are documented at appropriate points in this
users guide.
@end table

@geindex -gnatD[nn] (gcc)


@table @asis

@item @code{-gnatD}

Create expanded source files for source level debugging. This switch
also suppress generation of cross-reference information
(see @emph{-gnatx}). Note that this switch is not allowed if a previous
-gnatR switch has been given, since these two switches are not compatible.
@end table

@geindex -gnateA (gcc)


@table @asis

@item @code{-gnateA}

Check that the actual parameters of a subprogram call are not aliases of one
another. To qualify as aliasing, the actuals must denote objects of a composite
type, their memory locations must be identical or overlapping, and at least one
of the corresponding formal parameters must be of mode OUT or IN OUT.

@example
type Rec_Typ is record
   Data : Integer := 0;
end record;

function Self (Val : Rec_Typ) return Rec_Typ is
begin
   return Val;
end Self;

procedure Detect_Aliasing (Val_1 : in out Rec_Typ; Val_2 : Rec_Typ) is
begin
   null;
end Detect_Aliasing;

Obj : Rec_Typ;

Detect_Aliasing (Obj, Obj);
Detect_Aliasing (Obj, Self (Obj));
@end example

In the example above, the first call to @cite{Detect_Aliasing} fails with a
@cite{Program_Error} at runtime because the actuals for @cite{Val_1} and
@cite{Val_2} denote the same object. The second call executes without raising
an exception because @cite{Self(Obj)} produces an anonymous object which does
not share the memory location of @cite{Obj}.
@end table

@geindex -gnatec (gcc)


@table @asis

@item @code{-gnatec=@emph{path}}

Specify a configuration pragma file
(the equal sign is optional)
(@ref{7b,,The Configuration Pragmas Files}).
@end table

@geindex -gnateC (gcc)


@table @asis

@item @code{-gnateC}

Generate CodePeer messages in a compiler-like format. This switch is only
effective if @emph{-gnatcC} is also specified and requires an installation
of CodePeer.
@end table

@geindex -gnated (gcc)


@table @asis

@item @code{-gnated}

Disable atomic synchronization
@end table

@geindex -gnateD (gcc)


@table @asis

@item @code{-gnateDsymbol[=@emph{value}]}

Defines a symbol, associated with @cite{value}, for preprocessing.
(@ref{1a,,Integrated Preprocessing}).
@end table

@geindex -gnateE (gcc)


@table @asis

@item @code{-gnateE}

Generate extra information in exception messages. In particular, display
extra column information and the value and range associated with index and
range check failures, and extra column information for access checks.
In cases where the compiler is able to determine at compile time that
a check will fail, it gives a warning, and the extra information is not
produced at run time.
@end table

@geindex -gnatef (gcc)


@table @asis

@item @code{-gnatef}

Display full source path name in brief error messages.
@end table

@geindex -gnateF (gcc)


@table @asis

@item @code{-gnateF}

Check for overflow on all floating-point operations, including those
for unconstrained predefined types. See description of pragma
@cite{Check_Float_Overflow} in GNAT RM.
@end table

@geindex -gnateG (gcc)


@table @asis

@item @code{-gnateG}

Save result of preprocessing in a text file.
@end table

@geindex -gnatei (gcc)


@table @asis

@item @code{-gnatei@emph{nnn}}

Set maximum number of instantiations during compilation of a single unit to
@cite{nnn}. This may be useful in increasing the default maximum of 8000 for
the rare case when a single unit legitimately exceeds this limit.
@end table

@geindex -gnateI (gcc)


@table @asis

@item @code{-gnateI@emph{nnn}}

Indicates that the source is a multi-unit source and that the index of the
unit to compile is @cite{nnn}. @cite{nnn} needs to be a positive number and need
to be a valid index in the multi-unit source.
@end table

@geindex -gnatel (gcc)


@table @asis

@item @code{-gnatel}

This switch can be used with the static elaboration model to issue info
messages showing
where implicit @cite{pragma Elaborate} and @cite{pragma Elaborate_All}
are generated. This is useful in diagnosing elaboration circularities
caused by these implicit pragmas when using the static elaboration
model. See See the section in this guide on elaboration checking for
further details. These messages are not generated by default, and are
intended only for temporary use when debugging circularity problems.
@end table

@geindex -gnatel (gcc)


@table @asis

@item @code{-gnateL}

This switch turns off the info messages about implicit elaboration pragmas.
@end table

@geindex -gnatem (gcc)


@table @asis

@item @code{-gnatem=@emph{path}}

Specify a mapping file
(the equal sign is optional)
(@ref{fc,,Units to Sources Mapping Files}).
@end table

@geindex -gnatep (gcc)


@table @asis

@item @code{-gnatep=@emph{file}}

Specify a preprocessing data file
(the equal sign is optional)
(@ref{1a,,Integrated Preprocessing}).
@end table

@geindex -gnateP (gcc)


@table @asis

@item @code{-gnateP}

Turn categorization dependency errors into warnings.
Ada requires that units that WITH one another have compatible categories, for
example a Pure unit cannot WITH a Preelaborate unit. If this switch is used,
these errors become warnings (which can be ignored, or suppressed in the usual
manner). This can be useful in some specialized circumstances such as the
temporary use of special test software.
@end table

@geindex -gnateS (gcc)


@table @asis

@item @code{-gnateS}

Synonym of @emph{-fdump-scos}, kept for backwards compatibility.
@end table

@geindex -gnatet=file (gcc)


@table @asis

@item @code{-gnatet=@emph{path}}

Generate target dependent information. The format of the output file is
described in the section about switch @emph{-gnateT}.
@end table

@geindex -gnateT (gcc)


@table @asis

@item @code{-gnateT=@emph{path}}

Read target dependent information, such as endianness or sizes and alignments
of base type. If this switch is passed, the default target dependent
information of the compiler is replaced by the one read from the input file.
This is used by tools other than the compiler, e.g. to do
semantic analysis of programs that will run on some other target than
the machine on which the tool is run.

The following target dependent values should be defined,
where @cite{Nat} denotes a natural integer value, @cite{Pos} denotes a
positive integer value, and fields marked with a question mark are
boolean fields, where a value of 0 is False, and a value of 1 is True:

@example
Bits_BE                    : Nat; -- Bits stored big-endian?
Bits_Per_Unit              : Pos; -- Bits in a storage unit
Bits_Per_Word              : Pos; -- Bits in a word
Bytes_BE                   : Nat; -- Bytes stored big-endian?
Char_Size                  : Pos; -- Standard.Character'Size
Double_Float_Alignment     : Nat; -- Alignment of double float
Double_Scalar_Alignment    : Nat; -- Alignment of double length scalar
Double_Size                : Pos; -- Standard.Long_Float'Size
Float_Size                 : Pos; -- Standard.Float'Size
Float_Words_BE             : Nat; -- Float words stored big-endian?
Int_Size                   : Pos; -- Standard.Integer'Size
Long_Double_Size           : Pos; -- Standard.Long_Long_Float'Size
Long_Long_Size             : Pos; -- Standard.Long_Long_Integer'Size
Long_Size                  : Pos; -- Standard.Long_Integer'Size
Maximum_Alignment          : Pos; -- Maximum permitted alignment
Max_Unaligned_Field        : Pos; -- Maximum size for unaligned bit field
Pointer_Size               : Pos; -- System.Address'Size
Short_Enums                : Nat; -- Short foreign convention enums?
Short_Size                 : Pos; -- Standard.Short_Integer'Size
Strict_Alignment           : Nat; -- Strict alignment?
System_Allocator_Alignment : Nat; -- Alignment for malloc calls
Wchar_T_Size               : Pos; -- Interfaces.C.wchar_t'Size
Words_BE                   : Nat; -- Words stored big-endian?
@end example

The format of the input file is as follows. First come the values of
the variables defined above, with one line per value:

@example
name  value
@end example

where @cite{name} is the name of the parameter, spelled out in full,
and cased as in the above list, and @cite{value} is an unsigned decimal
integer. Two or more blanks separates the name from the value.

All the variables must be present, in alphabetical order (i.e. the
same order as the list above).

Then there is a blank line to separate the two parts of the file. Then
come the lines showing the floating-point types to be registered, with
one line per registered mode:

@example
name  digs float_rep size alignment
@end example

where @cite{name} is the string name of the type (which can have
single spaces embedded in the name (e.g. long double), @cite{digs} is
the number of digits for the floating-point type, @cite{float_rep} is
the float representation (I/V/A for IEEE-754-Binary, Vax_Native,
AAMP), @cite{size} is the size in bits, @cite{alignment} is the
alignment in bits. The name is followed by at least two blanks, fields
are separated by at least one blank, and a LF character immediately
follows the alignment field.

Here is an example of a target parameterization file:

@example
Bits_BE                       0
Bits_Per_Unit                 8
Bits_Per_Word                64
Bytes_BE                      0
Char_Size                     8
Double_Float_Alignment        0
Double_Scalar_Alignment       0
Double_Size                  64
Float_Size                   32
Float_Words_BE                0
Int_Size                     64
Long_Double_Size            128
Long_Long_Size               64
Long_Size                    64
Maximum_Alignment            16
Max_Unaligned_Field          64
Pointer_Size                 64
Short_Size                   16
Strict_Alignment              0
System_Allocator_Alignment   16
Wchar_T_Size                 32
Words_BE                      0

float         15  I  64  64
double        15  I  64  64
long double   18  I  80 128
TF            33  I 128 128
@end example
@end table

@geindex -gnateu (gcc)


@table @asis

@item @code{-gnateu}

Ignore unrecognized validity, warning, and style switches that
appear after this switch is given. This may be useful when
compiling sources developed on a later version of the compiler
with an earlier version. Of course the earlier version must
support this switch.
@end table

@geindex -gnateV (gcc)


@table @asis

@item @code{-gnateV}

Check that all actual parameters of a subprogram call are valid according to
the rules of validity checking (@ref{fb,,Validity Checking}).
@end table

@geindex -gnateY (gcc)


@table @asis

@item @code{-gnateY}

Ignore all STYLE_CHECKS pragmas. Full legality checks
are still carried out, but the pragmas have no effect
on what style checks are active. This allows all style
checking options to be controlled from the command line.
@end table

@geindex -gnatE (gcc)


@table @asis

@item @code{-gnatE}

Full dynamic elaboration checks.
@end table

@geindex -gnatf (gcc)


@table @asis

@item @code{-gnatf}

Full errors. Multiple errors per line, all undefined references, do not
attempt to suppress cascaded errors.
@end table

@geindex -gnatF (gcc)


@table @asis

@item @code{-gnatF}

Externals names are folded to all uppercase.
@end table

@geindex -gnatg (gcc)


@table @asis

@item @code{-gnatg}

Internal GNAT implementation mode. This should not be used for
applications programs, it is intended only for use by the compiler
and its run-time library. For documentation, see the GNAT sources.
Note that @emph{-gnatg} implies
@emph{-gnatw.ge} and
@emph{-gnatyg}
so that all standard warnings and all standard style options are turned on.
All warnings and style messages are treated as errors.
@end table

@geindex -gnatG[nn] (gcc)


@table @asis

@item @code{-gnatG=nn}

List generated expanded code in source form.
@end table

@geindex -gnath (gcc)


@table @asis

@item @code{-gnath}

Output usage information. The output is written to @code{stdout}.
@end table

@geindex -gnati (gcc)


@table @asis

@item @code{-gnati@emph{c}}

Identifier character set (@cite{c} = 1/2/3/4/8/9/p/f/n/w).
For details of the possible selections for @cite{c},
see @ref{4a,,Character Set Control}.
@end table

@geindex -gnatI (gcc)


@table @asis

@item @code{-gnatI}

Ignore representation clauses. When this switch is used,
representation clauses are treated as comments. This is useful
when initially porting code where you want to ignore rep clause
problems, and also for compiling foreign code (particularly
for use with ASIS). The representation clauses that are ignored
are: enumeration_representation_clause, record_representation_clause,
and attribute_definition_clause for the following attributes:
Address, Alignment, Bit_Order, Component_Size, Machine_Radix,
Object_Size, Size, Small, Stream_Size, and Value_Size.
Note that this option should be used only for compiling -- the
code is likely to malfunction at run time.

Note that when @cite{-gnatct} is used to generate trees for input
into @cite{ASIS} tools, these representation clauses are removed
from the tree and ignored. This means that the tool will not see them.
@end table

@geindex -gnatjnn (gcc)


@table @asis

@item @code{-gnatj@emph{nn}}

Reformat error messages to fit on @cite{nn} character lines
@end table

@geindex -gnatk (gcc)


@table @asis

@item @code{-gnatk=@emph{n}}

Limit file names to @cite{n} (1-999) characters (@cite{k} = krunch).
@end table

@geindex -gnatl (gcc)


@table @asis

@item @code{-gnatl}

Output full source listing with embedded error messages.
@end table

@geindex -gnatL (gcc)


@table @asis

@item @code{-gnatL}

Used in conjunction with -gnatG or -gnatD to intersperse original
source lines (as comment lines with line numbers) in the expanded
source output.
@end table

@geindex -gnatm (gcc)


@table @asis

@item @code{-gnatm=@emph{n}}

Limit number of detected error or warning messages to @cite{n}
where @cite{n} is in the range 1..999999. The default setting if
no switch is given is 9999. If the number of warnings reaches this
limit, then a message is output and further warnings are suppressed,
but the compilation is continued. If the number of error messages
reaches this limit, then a message is output and the compilation
is abandoned. The equal sign here is optional. A value of zero
means that no limit applies.
@end table

@geindex -gnatn (gcc)


@table @asis

@item @code{-gnatn[12]}

Activate inlining for subprograms for which pragma @cite{Inline} is
specified. This inlining is performed by the GCC back-end. An optional
digit sets the inlining level: 1 for moderate inlining across modules
or 2 for full inlining across modules. If no inlining level is specified,
the compiler will pick it based on the optimization level.
@end table

@geindex -gnatN (gcc)


@table @asis

@item @code{-gnatN}

Activate front end inlining for subprograms for which
pragma @cite{Inline} is specified. This inlining is performed
by the front end and will be visible in the
@emph{-gnatG} output.

When using a gcc-based back end (in practice this means using any version
of GNAT other than the JGNAT, .NET or GNAAMP versions), then the use of
@emph{-gnatN} is deprecated, and the use of @emph{-gnatn} is preferred.
Historically front end inlining was more extensive than the gcc back end
inlining, but that is no longer the case.
@end table

@geindex -gnato0 (gcc)


@table @asis

@item @code{-gnato0}

Suppresses overflow checking. This causes the behavior of the compiler to
match the default for older versions where overflow checking was suppressed
by default. This is equivalent to having
@cite{pragma Suppress (Overflow_Mode)} in a configuration pragma file.
@end table

@geindex -gnato?? (gcc)


@table @asis

@item @code{-gnato??}

Set default mode for handling generation of code to avoid intermediate
arithmetic overflow. Here @cite{??} is two digits, a
single digit, or nothing. Each digit is one of the digits @cite{1}
through @cite{3}:


@multitable {xxxxxxx} {xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx} 
@item

Digit

@tab

Interpretation

@item

@emph{1}

@tab

All intermediate overflows checked against base type (@cite{STRICT})

@item

@emph{2}

@tab

Minimize intermediate overflows (@cite{MINIMIZED})

@item

@emph{3}

@tab

Eliminate intermediate overflows (@cite{ELIMINATED})

@end multitable


If only one digit appears then it applies to all
cases; if two digits are given, then the first applies outside
assertions, and the second within assertions.

If no digits follow the @emph{-gnato}, then it is equivalent to
@emph{-gnato11},
causing all intermediate overflows to be handled in strict mode.

This switch also causes arithmetic overflow checking to be performed
(as though @cite{pragma Unsuppress (Overflow_Mode)} had been specified.

The default if no option @emph{-gnato} is given is that overflow handling
is in @cite{STRICT} mode (computations done using the base type), and that
overflow checking is enabled.

Note that division by zero is a separate check that is not
controlled by this switch (division by zero checking is on by default).

See also @ref{fd,,Specifying the Desired Mode}.
@end table

@geindex -gnatp (gcc)


@table @asis

@item @code{-gnatp}

Suppress all checks. See @ref{fe,,Run-Time Checks} for details. This switch
has no effect if cancelled by a subsequent @emph{-gnat-p} switch.
@end table

@geindex -gnat-p (gcc)


@table @asis

@item @code{-gnat-p}

Cancel effect of previous @emph{-gnatp} switch.
@end table

@geindex -gnatP (gcc)


@table @asis

@item @code{-gnatP}

Enable polling. This is required on some systems (notably Windows NT) to
obtain asynchronous abort and asynchronous transfer of control capability.
See @cite{Pragma_Polling} in the @cite{GNAT_Reference_Manual} for full
details.
@end table

@geindex -gnatq (gcc)


@table @asis

@item @code{-gnatq}

Don't quit. Try semantics, even if parse errors.
@end table

@geindex -gnatQ (gcc)


@table @asis

@item @code{-gnatQ}

Don't quit. Generate @code{ALI} and tree files even if illegalities.
Note that code generation is still suppressed in the presence of any
errors, so even with @emph{-gnatQ} no object file is generated.
@end table

@geindex -gnatr (gcc)


@table @asis

@item @code{-gnatr}

Treat pragma Restrictions as Restriction_Warnings.
@end table

@geindex -gnatR (gcc)


@table @asis

@item @code{-gnatR[0/1/2/3[s]]}

Output representation information for declared types and objects.
Note that this switch is not allowed if a previous @cite{-gnatD} switch has
been given, since these two switches are not compatible.

@item @code{-gnatRm[s]}

Output convention and parameter passing mechanisms for all subprograms.
@end table

@geindex -gnats (gcc)


@table @asis

@item @code{-gnats}

Syntax check only.
@end table

@geindex -gnatS (gcc)


@table @asis

@item @code{-gnatS}

Print package Standard.
@end table

@geindex -gnatt (gcc)


@table @asis

@item @code{-gnatt}

Generate tree output file.
@end table

@geindex -gnatT (gcc)


@table @asis

@item @code{-gnatT@emph{nnn}}

All compiler tables start at @cite{nnn} times usual starting size.
@end table

@geindex -gnatu (gcc)


@table @asis

@item @code{-gnatu}

List units for this compilation.
@end table

@geindex -gnatU (gcc)


@table @asis

@item @code{-gnatU}

Tag all error messages with the unique string 'error:'
@end table

@geindex -gnatv (gcc)


@table @asis

@item @code{-gnatv}

Verbose mode. Full error output with source lines to @code{stdout}.
@end table

@geindex -gnatV (gcc)


@table @asis

@item @code{-gnatV}

Control level of validity checking (@ref{fb,,Validity Checking}).
@end table

@geindex -gnatw (gcc)


@table @asis

@item @code{-gnatw@emph{xxx}}

Warning mode where
@cite{xxx} is a string of option letters that denotes
the exact warnings that
are enabled or disabled (@ref{ff,,Warning Message Control}).
@end table

@geindex -gnatW (gcc)


@table @asis

@item @code{-gnatW@emph{e}}

Wide character encoding method
(@cite{e}=n/h/u/s/e/8).
@end table

@geindex -gnatx (gcc)


@table @asis

@item @code{-gnatx}

Suppress generation of cross-reference information.
@end table

@geindex -gnatX (gcc)


@table @asis

@item @code{-gnatX}

Enable GNAT implementation extensions and latest Ada version.
@end table

@geindex -gnaty (gcc)


@table @asis

@item @code{-gnaty}

Enable built-in style checks (@ref{100,,Style Checking}).
@end table

@geindex -gnatz (gcc)


@table @asis

@item @code{-gnatz@emph{m}}

Distribution stub generation and compilation
(@cite{m}=r/c for receiver/caller stubs).
@end table

@geindex -I (gcc)


@table @asis

@item @code{-I@emph{dir}}

@geindex RTL

Direct GNAT to search the @cite{dir} directory for source files needed by
the current compilation
(see @ref{8e,,Search Paths and the Run-Time Library (RTL)}).
@end table

@geindex -I- (gcc)


@table @asis

@item @code{-I-}

@geindex RTL

Except for the source file named in the command line, do not look for source
files in the directory containing the source file named in the command line
(see @ref{8e,,Search Paths and the Run-Time Library (RTL)}).
@end table

@geindex -o (gcc)


@table @asis

@item @code{-o @emph{file}}

This switch is used in @emph{gcc} to redirect the generated object file
and its associated ALI file. Beware of this switch with GNAT, because it may
cause the object file and ALI file to have different names which in turn
may confuse the binder and the linker.
@end table

@geindex -nostdinc (gcc)


@table @asis

@item @code{-nostdinc}

Inhibit the search of the default location for the GNAT Run Time
Library (RTL) source files.
@end table

@geindex -nostdlib (gcc)


@table @asis

@item @code{-nostdlib}

Inhibit the search of the default location for the GNAT Run Time
Library (RTL) ALI files.
@end table

@geindex -O (gcc)


@table @asis

@item @code{-O[@emph{n}]}

@cite{n} controls the optimization level:


@multitable {xxxxxxxxx} {xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx} 
@item

@emph{n}

@tab

Effect

@item

@emph{0}

@tab

No optimization, the default setting if no @emph{-O} appears

@item

@emph{1}

@tab

Normal optimization, the default if you specify @emph{-O} without an
operand. A good compromise between code quality and compilation
time.

@item

@emph{2}

@tab

Extensive optimization, may improve execution time, possibly at
the cost of substantially increased compilation time.

@item

@emph{3}

@tab

Same as @emph{-O2}, and also includes inline expansion for small
subprograms in the same unit.

@item

@emph{s}

@tab

Optimize space usage

@end multitable


See also @ref{101,,Optimization Levels}.
@end table

@geindex -pass-exit-codes (gcc)


@table @asis

@item @code{-pass-exit-codes}

Catch exit codes from the compiler and use the most meaningful as
exit status.
@end table

@geindex --RTS (gcc)


@table @asis

@item @code{--RTS=@emph{rts-path}}

Specifies the default location of the runtime library. Same meaning as the
equivalent @emph{gnatmake} flag (@ref{df,,Switches for gnatmake}).
@end table

@geindex -S (gcc)


@table @asis

@item @code{-S}

Used in place of @emph{-c} to
cause the assembler source file to be
generated, using @code{.s} as the extension,
instead of the object file.
This may be useful if you need to examine the generated assembly code.
@end table

@geindex -fverbose-asm (gcc)


@table @asis

@item @code{-fverbose-asm}

Used in conjunction with @emph{-S}
to cause the generated assembly code file to be annotated with variable
names, making it significantly easier to follow.
@end table

@geindex -v (gcc)


@table @asis

@item @code{-v}

Show commands generated by the @emph{gcc} driver. Normally used only for
debugging purposes or if you need to be sure what version of the
compiler you are executing.
@end table

@geindex -V (gcc)


@table @asis

@item @code{-V @emph{ver}}

Execute @cite{ver} version of the compiler. This is the @emph{gcc}
version, not the GNAT version.
@end table

@geindex -w (gcc)


@table @asis

@item @code{-w}

Turn off warnings generated by the back end of the compiler. Use of
this switch also causes the default for front end warnings to be set
to suppress (as though @emph{-gnatws} had appeared at the start of
the options).
@end table

@geindex Combining GNAT switches

You may combine a sequence of GNAT switches into a single switch. For
example, the combined switch

@quotation

@example
-gnatofi3
@end example
@end quotation

is equivalent to specifying the following sequence of switches:

@quotation

@example
-gnato -gnatf -gnati3
@end example
@end quotation

The following restrictions apply to the combination of switches
in this manner:


@itemize *

@item 
The switch @emph{-gnatc} if combined with other switches must come
first in the string.

@item 
The switch @emph{-gnats} if combined with other switches must come
first in the string.

@item 
The switches
@emph{-gnatzc} and @emph{-gnatzr} may not be combined with any other
switches, and only one of them may appear in the command line.

@item 
The switch @emph{-gnat-p} may not be combined with any other switch.

@item 
Once a 'y' appears in the string (that is a use of the @emph{-gnaty}
switch), then all further characters in the switch are interpreted
as style modifiers (see description of @emph{-gnaty}).

@item 
Once a 'd' appears in the string (that is a use of the @emph{-gnatd}
switch), then all further characters in the switch are interpreted
as debug flags (see description of @emph{-gnatd}).

@item 
Once a 'w' appears in the string (that is a use of the @emph{-gnatw}
switch), then all further characters in the switch are interpreted
as warning mode modifiers (see description of @emph{-gnatw}).

@item 
Once a 'V' appears in the string (that is a use of the @emph{-gnatV}
switch), then all further characters in the switch are interpreted
as validity checking options (@ref{fb,,Validity Checking}).

@item 
Option 'em', 'ec', 'ep', 'l=' and 'R' must be the last options in
a combined list of options.
@end itemize

@node Output and Error Message Control,Warning Message Control,Alphabetical List of All Switches,Compiler Switches
@anchor{gnat_ugn/building_executable_programs_with_gnat id14}@anchor{102}@anchor{gnat_ugn/building_executable_programs_with_gnat output-and-error-message-control}@anchor{103}
@subsection Output and Error Message Control


@geindex stderr

The standard default format for error messages is called 'brief format'.
Brief format messages are written to @code{stderr} (the standard error
file) and have the following form:

@example
e.adb:3:04: Incorrect spelling of keyword "function"
e.adb:4:20: ";" should be "is"
@end example

The first integer after the file name is the line number in the file,
and the second integer is the column number within the line.
@cite{GPS} can parse the error messages
and point to the referenced character.
The following switches provide control over the error message
format:

@geindex -gnatv (gcc)


@table @asis

@item @code{-gnatv}

The @cite{v} stands for verbose.
The effect of this setting is to write long-format error
messages to @code{stdout} (the standard output file.
The same program compiled with the
@emph{-gnatv} switch would generate:

@example
3. funcion X (Q : Integer)
   |
>>> Incorrect spelling of keyword "function"
4. return Integer;
                 |
>>> ";" should be "is"
@end example

The vertical bar indicates the location of the error, and the @code{>>>}
prefix can be used to search for error messages. When this switch is
used the only source lines output are those with errors.
@end table

@geindex -gnatl (gcc)


@table @asis

@item @code{-gnatl}

The @cite{l} stands for list.
This switch causes a full listing of
the file to be generated. In the case where a body is
compiled, the corresponding spec is also listed, along
with any subunits. Typical output from compiling a package
body @code{p.adb} might look like:

@example
Compiling: p.adb

     1. package body p is
     2.    procedure a;
     3.    procedure a is separate;
     4. begin
     5.    null
               |
        >>> missing ";"

     6. end;

Compiling: p.ads

     1. package p is
     2.    pragma Elaborate_Body
                                |
        >>> missing ";"

     3. end p;

Compiling: p-a.adb

     1. separate p
                |
        >>> missing "("

     2. procedure a is
     3. begin
     4.    null
               |
        >>> missing ";"

     5. end;
@end example

When you specify the @emph{-gnatv} or @emph{-gnatl} switches and
standard output is redirected, a brief summary is written to
@code{stderr} (standard error) giving the number of error messages and
warning messages generated.
@end table

@geindex -gnatl=fname (gcc)


@table @asis

@item @code{-gnatl=@emph{fname}}

This has the same effect as @emph{-gnatl} except that the output is
written to a file instead of to standard output. If the given name
@code{fname} does not start with a period, then it is the full name
of the file to be written. If @code{fname} is an extension, it is
appended to the name of the file being compiled. For example, if
file @code{xyz.adb} is compiled with @emph{-gnatl=.lst},
then the output is written to file xyz.adb.lst.
@end table

@geindex -gnatU (gcc)


@table @asis

@item @code{-gnatU}

This switch forces all error messages to be preceded by the unique
string 'error:'. This means that error messages take a few more
characters in space, but allows easy searching for and identification
of error messages.
@end table

@geindex -gnatb (gcc)


@table @asis

@item @code{-gnatb}

The @cite{b} stands for brief.
This switch causes GNAT to generate the
brief format error messages to @code{stderr} (the standard error
file) as well as the verbose
format message or full listing (which as usual is written to
@code{stdout} (the standard output file).
@end table

@geindex -gnatm (gcc)


@table @asis

@item @code{-gnatm=@emph{n}}

The @cite{m} stands for maximum.
@cite{n} is a decimal integer in the
range of 1 to 999999 and limits the number of error or warning
messages to be generated. For example, using
@emph{-gnatm2} might yield

@example
e.adb:3:04: Incorrect spelling of keyword "function"
e.adb:5:35: missing ".."
fatal error: maximum number of errors detected
compilation abandoned
@end example

The default setting if
no switch is given is 9999. If the number of warnings reaches this
limit, then a message is output and further warnings are suppressed,
but the compilation is continued. If the number of error messages
reaches this limit, then a message is output and the compilation
is abandoned. A value of zero means that no limit applies.

Note that the equal sign is optional, so the switches
@emph{-gnatm2} and @emph{-gnatm=2} are equivalent.
@end table

@geindex -gnatf (gcc)


@table @asis

@item @code{-gnatf}

@geindex Error messages
@geindex suppressing

The @cite{f} stands for full.
Normally, the compiler suppresses error messages that are likely to be
redundant. This switch causes all error
messages to be generated. In particular, in the case of
references to undefined variables. If a given variable is referenced
several times, the normal format of messages is

@example
e.adb:7:07: "V" is undefined (more references follow)
@end example

where the parenthetical comment warns that there are additional
references to the variable @cite{V}. Compiling the same program with the
@emph{-gnatf} switch yields

@example
e.adb:7:07: "V" is undefined
e.adb:8:07: "V" is undefined
e.adb:8:12: "V" is undefined
e.adb:8:16: "V" is undefined
e.adb:9:07: "V" is undefined
e.adb:9:12: "V" is undefined
@end example

The @emph{-gnatf} switch also generates additional information for
some error messages.  Some examples are:


@itemize *

@item 
Details on possibly non-portable unchecked conversion

@item 
List possible interpretations for ambiguous calls

@item 
Additional details on incorrect parameters
@end itemize
@end table

@geindex -gnatjnn (gcc)


@table @asis

@item @code{-gnatjnn}

In normal operation mode (or if @emph{-gnatj0} is used), then error messages
with continuation lines are treated as though the continuation lines were
separate messages (and so a warning with two continuation lines counts as
three warnings, and is listed as three separate messages).

If the @emph{-gnatjnn} switch is used with a positive value for nn, then
messages are output in a different manner. A message and all its continuation
lines are treated as a unit, and count as only one warning or message in the
statistics totals. Furthermore, the message is reformatted so that no line
is longer than nn characters.
@end table

@geindex -gnatq (gcc)


@table @asis

@item @code{-gnatq}

The @cite{q} stands for quit (really 'don't quit').
In normal operation mode, the compiler first parses the program and
determines if there are any syntax errors. If there are, appropriate
error messages are generated and compilation is immediately terminated.
This switch tells
GNAT to continue with semantic analysis even if syntax errors have been
found. This may enable the detection of more errors in a single run. On
the other hand, the semantic analyzer is more likely to encounter some
internal fatal error when given a syntactically invalid tree.
@end table

@geindex -gnatQ (gcc)


@table @asis

@item @code{-gnatQ}

In normal operation mode, the @code{ALI} file is not generated if any
illegalities are detected in the program. The use of @emph{-gnatQ} forces
generation of the @code{ALI} file. This file is marked as being in
error, so it cannot be used for binding purposes, but it does contain
reasonably complete cross-reference information, and thus may be useful
for use by tools (e.g., semantic browsing tools or integrated development
environments) that are driven from the @code{ALI} file. This switch
implies @emph{-gnatq}, since the semantic phase must be run to get a
meaningful ALI file.

In addition, if @emph{-gnatt} is also specified, then the tree file is
generated even if there are illegalities. It may be useful in this case
to also specify @emph{-gnatq} to ensure that full semantic processing
occurs. The resulting tree file can be processed by ASIS, for the purpose
of providing partial information about illegal units, but if the error
causes the tree to be badly malformed, then ASIS may crash during the
analysis.

When @emph{-gnatQ} is used and the generated @code{ALI} file is marked as
being in error, @emph{gnatmake} will attempt to recompile the source when it
finds such an @code{ALI} file, including with switch @emph{-gnatc}.

Note that @emph{-gnatQ} has no effect if @emph{-gnats} is specified,
since ALI files are never generated if @emph{-gnats} is set.
@end table

@node Warning Message Control,Debugging and Assertion Control,Output and Error Message Control,Compiler Switches
@anchor{gnat_ugn/building_executable_programs_with_gnat warning-message-control}@anchor{ff}@anchor{gnat_ugn/building_executable_programs_with_gnat id15}@anchor{104}
@subsection Warning Message Control


@geindex Warning messages

In addition to error messages, which correspond to illegalities as defined
in the Ada Reference Manual, the compiler detects two kinds of warning
situations.

First, the compiler considers some constructs suspicious and generates a
warning message to alert you to a possible error. Second, if the
compiler detects a situation that is sure to raise an exception at
run time, it generates a warning message. The following shows an example
of warning messages:

@example
e.adb:4:24: warning: creation of object may raise Storage_Error
e.adb:10:17: warning: static value out of range
e.adb:10:17: warning: "Constraint_Error" will be raised at run time
@end example

GNAT considers a large number of situations as appropriate
for the generation of warning messages. As always, warnings are not
definite indications of errors. For example, if you do an out-of-range
assignment with the deliberate intention of raising a
@cite{Constraint_Error} exception, then the warning that may be
issued does not indicate an error. Some of the situations for which GNAT
issues warnings (at least some of the time) are given in the following
list. This list is not complete, and new warnings are often added to
subsequent versions of GNAT. The list is intended to give a general idea
of the kinds of warnings that are generated.


@itemize *

@item 
Possible infinitely recursive calls

@item 
Out-of-range values being assigned

@item 
Possible order of elaboration problems

@item 
Size not a multiple of alignment for a record type

@item 
Assertions (pragma Assert) that are sure to fail

@item 
Unreachable code

@item 
Address clauses with possibly unaligned values, or where an attempt is
made to overlay a smaller variable with a larger one.

@item 
Fixed-point type declarations with a null range

@item 
Direct_IO or Sequential_IO instantiated with a type that has access values

@item 
Variables that are never assigned a value

@item 
Variables that are referenced before being initialized

@item 
Task entries with no corresponding @cite{accept} statement

@item 
Duplicate accepts for the same task entry in a @cite{select}

@item 
Objects that take too much storage

@item 
Unchecked conversion between types of differing sizes

@item 
Missing @cite{return} statement along some execution path in a function

@item 
Incorrect (unrecognized) pragmas

@item 
Incorrect external names

@item 
Allocation from empty storage pool

@item 
Potentially blocking operation in protected type

@item 
Suspicious parenthesization of expressions

@item 
Mismatching bounds in an aggregate

@item 
Attempt to return local value by reference

@item 
Premature instantiation of a generic body

@item 
Attempt to pack aliased components

@item 
Out of bounds array subscripts

@item 
Wrong length on string assignment

@item 
Violations of style rules if style checking is enabled

@item 
Unused @emph{with} clauses

@item 
@cite{Bit_Order} usage that does not have any effect

@item 
@cite{Standard.Duration} used to resolve universal fixed expression

@item 
Dereference of possibly null value

@item 
Declaration that is likely to cause storage error

@item 
Internal GNAT unit @emph{with}ed by application unit

@item 
Values known to be out of range at compile time

@item 
Unreferenced or unmodified variables. Note that a special
exemption applies to variables which contain any of the substrings
@cite{DISCARD@comma{} DUMMY@comma{} IGNORE@comma{} JUNK@comma{} UNUSED}, in any casing. Such variables
are considered likely to be intentionally used in a situation where
otherwise a warning would be given, so warnings of this kind are
always suppressed for such variables.

@item 
Address overlays that could clobber memory

@item 
Unexpected initialization when address clause present

@item 
Bad alignment for address clause

@item 
Useless type conversions

@item 
Redundant assignment statements and other redundant constructs

@item 
Useless exception handlers

@item 
Accidental hiding of name by child unit

@item 
Access before elaboration detected at compile time

@item 
A range in a @cite{for} loop that is known to be null or might be null
@end itemize

The following section lists compiler switches that are available
to control the handling of warning messages. It is also possible
to exercise much finer control over what warnings are issued and
suppressed using the GNAT pragma Warnings (see the description
of the pragma in the @cite{GNAT_Reference_manual}).

@geindex -gnatwa (gcc)


@table @asis

@item @code{-gnatwa}

@emph{Activate most optional warnings.}

This switch activates most optional warning messages.  See the remaining list
in this section for details on optional warning messages that can be
individually controlled.  The warnings that are not turned on by this
switch are:


@itemize *

@item 
@code{-gnatwd} (implicit dereferencing)

@item 
@code{-gnatw.d} (tag warnings with -gnatw switch)

@item 
@code{-gnatwh} (hiding)

@item 
@code{-gnatw.h} (holes in record layouts)

@item 
@code{-gnatw.k} (redefinition of names in standard)

@item 
@code{-gnatwl} (elaboration warnings)

@item 
@code{-gnatw.l} (inherited aspects)

@item 
@code{-gnatw.n} (atomic synchronization)

@item 
@code{-gnatwo} (address clause overlay)

@item 
@code{-gnatw.o} (values set by out parameters ignored)

@item 
@code{-gnatw.s} (overridden size clause)

@item 
@code{-gnatwt} (tracking of deleted conditional code)

@item 
@code{-gnatw.u} (unordered enumeration)

@item 
@code{-gnatw.w} (use of Warnings Off)

@item 
@code{-gnatw.y} (reasons for package needing body)
@end itemize

All other optional warnings are turned on.
@end table

@geindex -gnatwA (gcc)


@table @asis

@item @code{-gnatwA}

@emph{Suppress all optional errors.}

This switch suppresses all optional warning messages, see remaining list
in this section for details on optional warning messages that can be
individually controlled. Note that unlike switch @emph{-gnatws}, the
use of switch @emph{-gnatwA} does not suppress warnings that are
normally given unconditionally and cannot be individually controlled
(for example, the warning about a missing exit path in a function).
Also, again unlike switch @emph{-gnatws}, warnings suppressed by
the use of switch @emph{-gnatwA} can be individually turned back
on. For example the use of switch @emph{-gnatwA} followed by
switch @emph{-gnatwd} will suppress all optional warnings except
the warnings for implicit dereferencing.
@end table

@geindex -gnatw.a (gcc)


@table @asis

@item @code{-gnatw.a}

@emph{Activate warnings on failing assertions.}

@geindex Assert failures

This switch activates warnings for assertions where the compiler can tell at
compile time that the assertion will fail. Note that this warning is given
even if assertions are disabled. The default is that such warnings are
generated.
@end table

@geindex -gnatw.A (gcc)


@table @asis

@item @code{-gnatw.A}

@emph{Suppress warnings on failing assertions.}

@geindex Assert failures

This switch suppresses warnings for assertions where the compiler can tell at
compile time that the assertion will fail.
@end table

@geindex -gnatwb (gcc)


@table @asis

@item @code{-gnatwb}

@emph{Activate warnings on bad fixed values.}

@geindex Bad fixed values

@geindex Fixed-point Small value

@geindex Small value

This switch activates warnings for static fixed-point expressions whose
value is not an exact multiple of Small. Such values are implementation
dependent, since an implementation is free to choose either of the multiples
that surround the value. GNAT always chooses the closer one, but this is not
required behavior, and it is better to specify a value that is an exact
multiple, ensuring predictable execution. The default is that such warnings
are not generated.
@end table

@geindex -gnatwB (gcc)


@table @asis

@item @code{-gnatwB}

@emph{Suppress warnings on bad fixed values.}

This switch suppresses warnings for static fixed-point expressions whose
value is not an exact multiple of Small.
@end table

@geindex -gnatw.b (gcc)


@table @asis

@item @code{-gnatw.b}

@emph{Activate warnings on biased representation.}

@geindex Biased representation

This switch activates warnings when a size clause, value size clause, component
clause, or component size clause forces the use of biased representation for an
integer type (e.g. representing a range of 10..11 in a single bit by using 0/1
to represent 10/11). The default is that such warnings are generated.
@end table

@geindex -gnatwB (gcc)


@table @asis

@item @code{-gnatw.B}

@emph{Suppress warnings on biased representation.}

This switch suppresses warnings for representation clauses that force the use
of biased representation.
@end table

@geindex -gnatwc (gcc)


@table @asis

@item @code{-gnatwc}

@emph{Activate warnings on conditionals.}

@geindex Conditionals
@geindex constant

This switch activates warnings for conditional expressions used in
tests that are known to be True or False at compile time. The default
is that such warnings are not generated.
Note that this warning does
not get issued for the use of boolean variables or constants whose
values are known at compile time, since this is a standard technique
for conditional compilation in Ada, and this would generate too many
false positive warnings.

This warning option also activates a special test for comparisons using
the operators '>=' and' <='.
If the compiler can tell that only the equality condition is possible,
then it will warn that the '>' or '<' part of the test
is useless and that the operator could be replaced by '='.
An example would be comparing a @cite{Natural} variable <= 0.

This warning option also generates warnings if
one or both tests is optimized away in a membership test for integer
values if the result can be determined at compile time. Range tests on
enumeration types are not included, since it is common for such tests
to include an end point.

This warning can also be turned on using @emph{-gnatwa}.
@end table

@geindex -gnatwC (gcc)


@table @asis

@item @code{-gnatwC}

@emph{Suppress warnings on conditionals.}

This switch suppresses warnings for conditional expressions used in
tests that are known to be True or False at compile time.
@end table

@geindex -gnatw.c (gcc)


@table @asis

@item @code{-gnatw.c}

@emph{Activate warnings on missing component clauses.}

@geindex Component clause
@geindex missing

This switch activates warnings for record components where a record
representation clause is present and has component clauses for the
majority, but not all, of the components. A warning is given for each
component for which no component clause is present.
@end table

@geindex -gnatwC (gcc)


@table @asis

@item @code{-gnatw.C}

@emph{Suppress warnings on missing component clauses.}

This switch suppresses warnings for record components that are
missing a component clause in the situation described above.
@end table

@geindex -gnatwd (gcc)


@table @asis

@item @code{-gnatwd}

@emph{Activate warnings on implicit dereferencing.}

If this switch is set, then the use of a prefix of an access type
in an indexed component, slice, or selected component without an
explicit @cite{.all} will generate a warning. With this warning
enabled, access checks occur only at points where an explicit
@cite{.all} appears in the source code (assuming no warnings are
generated as a result of this switch). The default is that such
warnings are not generated.
@end table

@geindex -gnatwD (gcc)


@table @asis

@item @code{-gnatwD}

@emph{Suppress warnings on implicit dereferencing.}

@geindex Implicit dereferencing

@geindex Dereferencing
@geindex implicit

This switch suppresses warnings for implicit dereferences in
indexed components, slices, and selected components.
@end table

@geindex -gnatw.d (gcc)


@table @asis

@item @code{-gnatw.d}

@emph{Activate tagging of warning and info messages.}

If this switch is set, then warning messages are tagged, with one of the
following strings:

@quotation


@itemize -

@item 
@emph{[-gnatw?]}
Used to tag warnings controlled by the switch @emph{-gnatwx} where x
is a letter a-z.

@item 
@emph{[-gnatw.?]}
Used to tag warnings controlled by the switch @emph{-gnatw.x} where x
is a letter a-z.

@item 
@emph{[-gnatel]}
Used to tag elaboration information (info) messages generated when the
static model of elaboration is used and the @emph{-gnatel} switch is set.

@item 
@emph{[restriction warning]}
Used to tag warning messages for restriction violations, activated by use
of the pragma @emph{Restriction_Warnings}.

@item 
@emph{[warning-as-error]}
Used to tag warning messages that have been converted to error messages by
use of the pragma Warning_As_Error. Note that such warnings are prefixed by
the string "error: " rather than "warning: ".

@item 
@emph{[enabled by default]}
Used to tag all other warnings that are always given by default, unless
warnings are completely suppressed using pragma @emph{Warnings(Off)} or
the switch @emph{-gnatws}.
@end itemize
@end quotation
@end table

@geindex -gnatw.d (gcc)


@table @asis

@item @code{-gnatw.D}

@emph{Deactivate tagging of warning and info messages messages.}

If this switch is set, then warning messages return to the default
mode in which warnings and info messages are not tagged as described above for
@cite{-gnatw.d}.
@end table

@geindex -gnatwe (gcc)

@geindex Warnings
@geindex treat as error


@table @asis

@item @code{-gnatwe}

@emph{Treat warnings and style checks as errors.}

This switch causes warning messages and style check messages to be
treated as errors.
The warning string still appears, but the warning messages are counted
as errors, and prevent the generation of an object file. Note that this
is the only -gnatw switch that affects the handling of style check messages.
Note also that this switch has no effect on info (information) messages, which
are not treated as errors if this switch is present.
@end table

@geindex -gnatw.e (gcc)


@table @asis

@item @code{-gnatw.e}

@emph{Activate every optional warning}

@geindex Warnings
@geindex activate every optional warning

This switch activates all optional warnings, including those which
are not activated by @cite{-gnatwa}. The use of this switch is not
recommended for normal use. If you turn this switch on, it is almost
certain that you will get large numbers of useless warnings. The
warnings that are excluded from @cite{-gnatwa} are typically highly
specialized warnings that are suitable for use only in code that has
been specifically designed according to specialized coding rules.
@end table

@geindex -gnatwf (gcc)


@table @asis

@item @code{-gnatwf}

@emph{Activate warnings on unreferenced formals.}

@geindex Formals
@geindex unreferenced

This switch causes a warning to be generated if a formal parameter
is not referenced in the body of the subprogram. This warning can
also be turned on using @emph{-gnatwu}. The
default is that these warnings are not generated.
@end table

@geindex -gnatwF (gcc)


@table @asis

@item @code{-gnatwF}

@emph{Suppress warnings on unreferenced formals.}

This switch suppresses warnings for unreferenced formal
parameters. Note that the
combination @emph{-gnatwu} followed by @emph{-gnatwF} has the
effect of warning on unreferenced entities other than subprogram
formals.
@end table

@geindex -gnatwg (gcc)


@table @asis

@item @code{-gnatwg}

@emph{Activate warnings on unrecognized pragmas.}

@geindex Pragmas
@geindex unrecognized

This switch causes a warning to be generated if an unrecognized
pragma is encountered. Apart from issuing this warning, the
pragma is ignored and has no effect. The default
is that such warnings are issued (satisfying the Ada Reference
Manual requirement that such warnings appear).
@end table

@geindex -gnatwG (gcc)


@table @asis

@item @code{-gnatwG}

@emph{Suppress warnings on unrecognized pragmas.}

This switch suppresses warnings for unrecognized pragmas.
@end table

@geindex -gnatw.g (gcc)


@table @asis

@item @code{-gnatw.g}

@emph{Warnings used for GNAT sources}

This switch sets the warning categories that are used by the standard
GNAT style. Currently this is equivalent to
@emph{-gnatwAao.sI.C.V.X}
but more warnings may be added in the future without advanced notice.
@end table

@geindex -gnatwh (gcc)


@table @asis

@item @code{-gnatwh}

@emph{Activate warnings on hiding.}

@geindex Hiding of Declarations

This switch activates warnings on hiding declarations.
A declaration is considered hiding
if it is for a non-overloadable entity, and it declares an entity with the
same name as some other entity that is directly or use-visible. The default
is that such warnings are not generated.
@end table

@geindex -gnatwH (gcc)


@table @asis

@item @code{-gnatwH}

@emph{Suppress warnings on hiding.}

This switch suppresses warnings on hiding declarations.
@end table

@geindex -gnatw.h (gcc)


@table @asis

@item @code{-gnatw.h}

@emph{Activate warnings on holes/gaps in records.}

@geindex Record Representation (gaps)

This switch activates warnings on component clauses in record
representation clauses that leave holes (gaps) in the record layout.
If this warning option is active, then record representation clauses
should specify a contiguous layout, adding unused fill fields if needed.
@end table

@geindex -gnatw.H (gcc)


@table @asis

@item @code{-gnatw.H}

@emph{Suppress warnings on holes/gaps in records.}

This switch suppresses warnings on component clauses in record
representation clauses that leave holes (haps) in the record layout.
@end table

@geindex -gnatwi (gcc)


@table @asis

@item @code{-gnatwi}

@emph{Activate warnings on implementation units.}

This switch activates warnings for a @emph{with} of an internal GNAT
implementation unit, defined as any unit from the @cite{Ada},
@cite{Interfaces}, @cite{GNAT},
or @cite{System}
hierarchies that is not
documented in either the Ada Reference Manual or the GNAT
Programmer's Reference Manual. Such units are intended only
for internal implementation purposes and should not be @emph{with}ed
by user programs. The default is that such warnings are generated
@end table

@geindex -gnatwI (gcc)


@table @asis

@item @code{-gnatwI}

@emph{Disable warnings on implementation units.}

This switch disables warnings for a @emph{with} of an internal GNAT
implementation unit.
@end table

@geindex -gnatw.i (gcc)


@table @asis

@item @code{-gnatw.i}

@emph{Activate warnings on overlapping actuals.}

This switch enables a warning on statically detectable overlapping actuals in
a subprogram call, when one of the actuals is an in-out parameter, and the
types of the actuals are not by-copy types. This warning is off by default.
@end table

@geindex -gnatw.I (gcc)


@table @asis

@item @code{-gnatw.I}

@emph{Disable warnings on overlapping actuals.}

This switch disables warnings on overlapping actuals in a call..
@end table

@geindex -gnatwj (gcc)


@table @asis

@item @code{-gnatwj}

@emph{Activate warnings on obsolescent features (Annex J).}

@geindex Features
@geindex obsolescent

@geindex Obsolescent features

If this warning option is activated, then warnings are generated for
calls to subprograms marked with @cite{pragma Obsolescent} and
for use of features in Annex J of the Ada Reference Manual. In the
case of Annex J, not all features are flagged. In particular use
of the renamed packages (like @cite{Text_IO}) and use of package
@cite{ASCII} are not flagged, since these are very common and
would generate many annoying positive warnings. The default is that
such warnings are not generated.

In addition to the above cases, warnings are also generated for
GNAT features that have been provided in past versions but which
have been superseded (typically by features in the new Ada standard).
For example, @cite{pragma Ravenscar} will be flagged since its
function is replaced by @cite{pragma Profile(Ravenscar)}, and
@cite{pragma Interface_Name} will be flagged since its function
is replaced by @cite{pragma Import}.

Note that this warning option functions differently from the
restriction @cite{No_Obsolescent_Features} in two respects.
First, the restriction applies only to annex J features.
Second, the restriction does flag uses of package @cite{ASCII}.

@item @code{-gnatwJ}

@emph{Suppress warnings on obsolescent features (Annex J).}
.. index:: -gnatwJ  (gcc)

This switch disables warnings on use of obsolescent features.

@item @code{-gnatwk}

@emph{Activate warnings on variables that could be constants.}
.. index:: -gnatwk  (gcc)

This switch activates warnings for variables that are initialized but
never modified, and then could be declared constants. The default is that
such warnings are not given.
@end table

@geindex -gnatwK (gcc)


@table @asis

@item @code{-gnatwK}

@emph{Suppress warnings on variables that could be constants.}

This switch disables warnings on variables that could be declared constants.
@end table

@geindex -gnatw.k (gcc)


@table @asis

@item @code{-gnatw.k}

@emph{Activate warnings on redefinition of names in standard.}

This switch activates warnings for declarations that declare a name that
is defined in package Standard. Such declarations can be confusing,
especially since the names in package Standard continue to be directly
visible, meaning that use visibiliy on such redeclared names does not
work as expected. Names of discriminants and components in records are
not included in this check.
@end table

@geindex -gnatwK (gcc)


@table @asis

@item @code{-gnatw.K}

@emph{Suppress warnings on redefinition of names in standard.}

This switch activates warnings for declarations that declare a name that
is defined in package Standard.
@end table

@geindex -gnatwl (gcc)


@table @asis

@item @code{-gnatwl}

@emph{Activate warnings for elaboration pragmas.}

@geindex Elaboration
@geindex warnings

This switch activates warnings for possible elaboration problems,
including suspicious use
of @cite{Elaborate} pragmas, when using the static elaboration model, and
possible situations that may raise @cite{Program_Error} when using the
dynamic elaboration model.
See the section in this guide on elaboration checking for further details.
The default is that such warnings
are not generated.
@end table

@geindex -gnatwL (gcc)


@table @asis

@item @code{-gnatwL}

@emph{Suppress warnings for elaboration pragmas.}

This switch suppresses warnings for possible elaboration problems.
@end table

@geindex -gnatw.l (gcc)


@table @asis

@item @code{-gnatw.l}

@emph{List inherited aspects.}

This switch causes the compiler to list inherited invariants,
preconditions, and postconditions from Type_Invariant'Class, Invariant'Class,
Pre'Class, and Post'Class aspects. Also list inherited subtype predicates.
@end table

@geindex -gnatw.L (gcc)


@table @asis

@item @code{-gnatw.L}

@emph{Suppress listing of inherited aspects.}

This switch suppresses listing of inherited aspects.
@end table

@geindex -gnatwm (gcc)


@table @asis

@item @code{-gnatwm}

@emph{Activate warnings on modified but unreferenced variables.}

This switch activates warnings for variables that are assigned (using
an initialization value or with one or more assignment statements) but
whose value is never read. The warning is suppressed for volatile
variables and also for variables that are renamings of other variables
or for which an address clause is given.
The default is that these warnings are not given.
@end table

@geindex -gnatwM (gcc)


@table @asis

@item @code{-gnatwM}

@emph{Disable warnings on modified but unreferenced variables.}

This switch disables warnings for variables that are assigned or
initialized, but never read.
@end table

@geindex -gnatw.m (gcc)


@table @asis

@item @code{-gnatw.m}

@emph{Activate warnings on suspicious modulus values.}

This switch activates warnings for modulus values that seem suspicious.
The cases caught are where the size is the same as the modulus (e.g.
a modulus of 7 with a size of 7 bits), and modulus values of 32 or 64
with no size clause. The guess in both cases is that 2**x was intended
rather than x. In addition expressions of the form 2*x for small x
generate a warning (the almost certainly accurate guess being that
2**x was intended). The default is that these warnings are given.
@end table

@geindex -gnatw.M (gcc)


@table @asis

@item @code{-gnatw.M}

@emph{Disable warnings on suspicious modulus values.}

This switch disables warnings for suspicious modulus values.
@end table

@geindex -gnatwn (gcc)


@table @asis

@item @code{-gnatwn}

@emph{Set normal warnings mode.}

This switch sets normal warning mode, in which enabled warnings are
issued and treated as warnings rather than errors. This is the default
mode. the switch @emph{-gnatwn} can be used to cancel the effect of
an explicit @emph{-gnatws} or
@emph{-gnatwe}. It also cancels the effect of the
implicit @emph{-gnatwe} that is activated by the
use of @emph{-gnatg}.
@end table

@geindex -gnatw.n (gcc)

@geindex Atomic Synchronization
@geindex warnings


@table @asis

@item @code{-gnatw.n}

@emph{Activate warnings on atomic synchronization.}

This switch actives warnings when an access to an atomic variable
requires the generation of atomic synchronization code. These
warnings are off by default.
@end table

@geindex -gnatw.N (gcc)


@table @asis

@item @code{-gnatw.N}

@emph{Suppress warnings on atomic synchronization.}

@geindex Atomic Synchronization
@geindex warnings

This switch suppresses warnings when an access to an atomic variable
requires the generation of atomic synchronization code.
@end table

@geindex -gnatwo (gcc)

@geindex Address Clauses
@geindex warnings


@table @asis

@item @code{-gnatwo}

@emph{Activate warnings on address clause overlays.}

This switch activates warnings for possibly unintended initialization
effects of defining address clauses that cause one variable to overlap
another. The default is that such warnings are generated.
@end table

@geindex -gnatwO (gcc)


@table @asis

@item @code{-gnatwO}

@emph{Suppress warnings on address clause overlays.}

This switch suppresses warnings on possibly unintended initialization
effects of defining address clauses that cause one variable to overlap
another.
@end table

@geindex -gnatw.o (gcc)


@table @asis

@item @code{-gnatw.o}

@emph{Activate warnings on modified but unreferenced out parameters.}

This switch activates warnings for variables that are modified by using
them as actuals for a call to a procedure with an out mode formal, where
the resulting assigned value is never read. It is applicable in the case
where there is more than one out mode formal. If there is only one out
mode formal, the warning is issued by default (controlled by -gnatwu).
The warning is suppressed for volatile
variables and also for variables that are renamings of other variables
or for which an address clause is given.
The default is that these warnings are not given.
@end table

@geindex -gnatw.O (gcc)


@table @asis

@item @code{-gnatw.O}

@emph{Disable warnings on modified but unreferenced out parameters.}

This switch suppresses warnings for variables that are modified by using
them as actuals for a call to a procedure with an out mode formal, where
the resulting assigned value is never read.
@end table

@geindex -gnatwp (gcc)

@geindex Inlining
@geindex warnings


@table @asis

@item @code{-gnatwp}

@emph{Activate warnings on ineffective pragma Inlines.}

This switch activates warnings for failure of front end inlining
(activated by @emph{-gnatN}) to inline a particular call. There are
many reasons for not being able to inline a call, including most
commonly that the call is too complex to inline. The default is
that such warnings are not given.
Warnings on ineffective inlining by the gcc back-end can be activated
separately, using the gcc switch -Winline.
@end table

@geindex -gnatwP (gcc)


@table @asis

@item @code{-gnatwP}

@emph{Suppress warnings on ineffective pragma Inlines.}

This switch suppresses warnings on ineffective pragma Inlines. If the
inlining mechanism cannot inline a call, it will simply ignore the
request silently.
@end table

@geindex -gnatw.p (gcc)

@geindex Parameter order
@geindex warnings


@table @asis

@item @code{-gnatw.p}

@emph{Activate warnings on parameter ordering.}

This switch activates warnings for cases of suspicious parameter
ordering when the list of arguments are all simple identifiers that
match the names of the formals, but are in a different order. The
warning is suppressed if any use of named parameter notation is used,
so this is the appropriate way to suppress a false positive (and
serves to emphasize that the "misordering" is deliberate). The
default is that such warnings are not given.
@end table

@geindex -gnatw.P (gcc)


@table @asis

@item @code{-gnatw.P}

@emph{Suppress warnings on parameter ordering.}

This switch suppresses warnings on cases of suspicious parameter
ordering.
@end table

@geindex -gnatwq (gcc)

@geindex Parentheses
@geindex warnings


@table @asis

@item @code{-gnatwq}

@emph{Activate warnings on questionable missing parentheses.}

This switch activates warnings for cases where parentheses are not used and
the result is potential ambiguity from a readers point of view. For example
(not a > b) when a and b are modular means ((not a) > b) and very likely the
programmer intended (not (a > b)). Similarly (-x mod 5) means (-(x mod 5)) and
quite likely ((-x) mod 5) was intended. In such situations it seems best to
follow the rule of always parenthesizing to make the association clear, and
this warning switch warns if such parentheses are not present. The default
is that these warnings are given.
@end table

@geindex -gnatwQ (gcc)


@table @asis

@item @code{-gnatwQ}

@emph{Suppress warnings on questionable missing parentheses.}

This switch suppresses warnings for cases where the association is not
clear and the use of parentheses is preferred.
@end table

@geindex -gnatwr (gcc)


@table @asis

@item @code{-gnatwr}

@emph{Activate warnings on redundant constructs.}

This switch activates warnings for redundant constructs. The following
is the current list of constructs regarded as redundant:


@itemize *

@item 
Assignment of an item to itself.

@item 
Type conversion that converts an expression to its own type.

@item 
Use of the attribute @cite{Base} where @cite{typ'Base} is the same
as @cite{typ}.

@item 
Use of pragma @cite{Pack} when all components are placed by a record
representation clause.

@item 
Exception handler containing only a reraise statement (raise with no
operand) which has no effect.

@item 
Use of the operator abs on an operand that is known at compile time
to be non-negative

@item 
Comparison of boolean expressions to an explicit True value.
@end itemize

The default is that warnings for redundant constructs are not given.
@end table

@geindex -gnatwR (gcc)


@table @asis

@item @code{-gnatwR}

@emph{Suppress warnings on redundant constructs.}

This switch suppresses warnings for redundant constructs.
@end table

@geindex -gnatw.r (gcc)


@table @asis

@item @code{-gnatw.r}

@emph{Activate warnings for object renaming function.}

This switch activates warnings for an object renaming that renames a
function call, which is equivalent to a constant declaration (as
opposed to renaming the function itself).  The default is that these
warnings are given.
@end table

@geindex -gnatwT (gcc)


@table @asis

@item @code{-gnatw.R}

@emph{Suppress warnings for object renaming function.}

This switch suppresses warnings for object renaming function.
@end table

@geindex -gnatws (gcc)


@table @asis

@item @code{-gnatws}

@emph{Suppress all warnings.}

This switch completely suppresses the
output of all warning messages from the GNAT front end, including
both warnings that can be controlled by switches described in this
section, and those that are normally given unconditionally. The
effect of this suppress action can only be cancelled by a subsequent
use of the switch @emph{-gnatwn}.

Note that switch @emph{-gnatws} does not suppress
warnings from the @emph{gcc} back end.
To suppress these back end warnings as well, use the switch @emph{-w}
in addition to @emph{-gnatws}. Also this switch has no effect on the
handling of style check messages.
@end table

@geindex -gnatw.s (gcc)

@geindex Record Representation (component sizes)


@table @asis

@item @code{-gnatw.s}

@emph{Activate warnings on overridden size clauses.}

This switch activates warnings on component clauses in record
representation clauses where the length given overrides that
specified by an explicit size clause for the component type. A
warning is similarly given in the array case if a specified
component size overrides an explicit size clause for the array
component type.
@end table

@geindex -gnatw.S (gcc)


@table @asis

@item @code{-gnatw.S}

@emph{Suppress warnings on overridden size clauses.}

This switch suppresses warnings on component clauses in record
representation clauses that override size clauses, and similar
warnings when an array component size overrides a size clause.
@end table

@geindex -gnatwt (gcc)

@geindex Deactivated code
@geindex warnings

@geindex Deleted code
@geindex warnings


@table @asis

@item @code{-gnatwt}

@emph{Activate warnings for tracking of deleted conditional code.}

This switch activates warnings for tracking of code in conditionals (IF and
CASE statements) that is detected to be dead code which cannot be executed, and
which is removed by the front end. This warning is off by default. This may be
useful for detecting deactivated code in certified applications.
@end table

@geindex -gnatwT (gcc)


@table @asis

@item @code{-gnatwT}

@emph{Suppress warnings for tracking of deleted conditional code.}

This switch suppresses warnings for tracking of deleted conditional code.
@end table

@geindex -gnatw.t (gcc)


@table @asis

@item @code{-gnatw.t}

@emph{Activate warnings on suspicious contracts.}

This switch activates warnings on suspicious contracts. This includes
warnings on suspicious postconditions (whether a pragma @cite{Postcondition} or a
@cite{Post} aspect in Ada 2012) and suspicious contract cases (pragma or aspect
@cite{Contract_Cases}). A function postcondition or contract case is suspicious
when no postcondition or contract case for this function mentions the result
of the function.  A procedure postcondition or contract case is suspicious
when it only refers to the pre-state of the procedure, because in that case
it should rather be expressed as a precondition. This switch also controls
warnings on suspicious cases of expressions typically found in contracts like
quantified expressions and uses of Update attribute. The default is that such
warnings are generated.
@end table

@geindex -gnatw.T (gcc)


@table @asis

@item @code{-gnatw.T}

@emph{Suppress warnings on suspicious contracts.}

This switch suppresses warnings on suspicious contracts.
@end table

@geindex -gnatwu (gcc)


@table @asis

@item @code{-gnatwu}

@emph{Activate warnings on unused entities.}

This switch activates warnings to be generated for entities that
are declared but not referenced, and for units that are @emph{with}ed
and not
referenced. In the case of packages, a warning is also generated if
no entities in the package are referenced. This means that if a with'ed
package is referenced but the only references are in @cite{use}
clauses or @cite{renames}
declarations, a warning is still generated. A warning is also generated
for a generic package that is @emph{with}ed but never instantiated.
In the case where a package or subprogram body is compiled, and there
is a @emph{with} on the corresponding spec
that is only referenced in the body,
a warning is also generated, noting that the
@emph{with} can be moved to the body. The default is that
such warnings are not generated.
This switch also activates warnings on unreferenced formals
(it includes the effect of @emph{-gnatwf}).
@end table

@geindex -gnatwU (gcc)


@table @asis

@item @code{-gnatwU}

@emph{Suppress warnings on unused entities.}

This switch suppresses warnings for unused entities and packages.
It also turns off warnings on unreferenced formals (and thus includes
the effect of @emph{-gnatwF}).
@end table

@geindex -gnatw.u (gcc)


@table @asis

@item @code{-gnatw.u}

@emph{Activate warnings on unordered enumeration types.}

This switch causes enumeration types to be considered as conceptually
unordered, unless an explicit pragma @cite{Ordered} is given for the type.
The effect is to generate warnings in clients that use explicit comparisons
or subranges, since these constructs both treat objects of the type as
ordered. (A @emph{client} is defined as a unit that is other than the unit in
which the type is declared, or its body or subunits.) Please refer to
the description of pragma @cite{Ordered} in the
@cite{GNAT Reference Manual} for further details.
The default is that such warnings are not generated.
@end table

@geindex -gnatw.U (gcc)


@table @asis

@item @code{-gnatw.U}

@emph{Deactivate warnings on unordered enumeration types.}

This switch causes all enumeration types to be considered as ordered, so
that no warnings are given for comparisons or subranges for any type.
@end table

@geindex -gnatwv (gcc)

@geindex Unassigned variable warnings


@table @asis

@item @code{-gnatwv}

@emph{Activate warnings on unassigned variables.}

This switch activates warnings for access to variables which
may not be properly initialized. The default is that
such warnings are generated.
@end table

@geindex -gnatwV (gcc)


@table @asis

@item @code{-gnatwV}

@emph{Suppress warnings on unassigned variables.}

This switch suppresses warnings for access to variables which
may not be properly initialized.
For variables of a composite type, the warning can also be suppressed in
Ada 2005 by using a default initialization with a box. For example, if
Table is an array of records whose components are only partially uninitialized,
then the following code:

@example
Tab : Table := (others => <>);
@end example

will suppress warnings on subsequent statements that access components
of variable Tab.
@end table

@geindex -gnatw.v (gcc)

@geindex bit order warnings


@table @asis

@item @code{-gnatw.v}

@emph{Activate info messages for non-default bit order.}

This switch activates messages (labeled "info", they are not warnings,
just informational messages) about the effects of non-default bit-order
on records to which a component clause is applied. The effect of specifying
non-default bit ordering is a bit subtle (and changed with Ada 2005), so
these messages, which are given by default, are useful in understanding the
exact consequences of using this feature.
@end table

@geindex -gnatw.V (gcc)


@table @asis

@item @code{-gnatw.V}

@emph{Suppress info messages for non-default bit order.}

This switch suppresses information messages for the effects of specifying
non-default bit order on record components with component clauses.
@end table

@geindex -gnatww (gcc)

@geindex String indexing warnings


@table @asis

@item @code{-gnatww}

@emph{Activate warnings on wrong low bound assumption.}

This switch activates warnings for indexing an unconstrained string parameter
with a literal or S'Length. This is a case where the code is assuming that the
low bound is one, which is in general not true (for example when a slice is
passed). The default is that such warnings are generated.
@end table

@geindex -gnatwW (gcc)


@table @asis

@item @code{-gnatwW}

@emph{Suppress warnings on wrong low bound assumption.}

This switch suppresses warnings for indexing an unconstrained string parameter
with a literal or S'Length. Note that this warning can also be suppressed
in a particular case by adding an assertion that the lower bound is 1,
as shown in the following example:

@example
procedure K (S : String) is
   pragma Assert (S'First = 1);
   ...
@end example
@end table

@geindex -gnatw.w (gcc)

@geindex Warnings Off control


@table @asis

@item @code{-gnatw.w}

@emph{Activate warnings on Warnings Off pragmas}

This switch activates warnings for use of @cite{pragma Warnings (Off@comma{} entity)}
where either the pragma is entirely useless (because it suppresses no
warnings), or it could be replaced by @cite{pragma Unreferenced} or
@cite{pragma Unmodified}.
Also activates warnings for the case of
Warnings (Off, String), where either there is no matching
Warnings (On, String), or the Warnings (Off) did not suppress any warning.
The default is that these warnings are not given.
@end table

@geindex -gnatw.W (gcc)


@table @asis

@item @code{-gnatw.W}

@emph{Suppress warnings on unnecessary Warnings Off pragmas}

This switch suppresses warnings for use of @cite{pragma Warnings (Off@comma{} ...)}.
@end table

@geindex -gnatwx (gcc)

@geindex Export/Import pragma warnings


@table @asis

@item @code{-gnatwx}

@emph{Activate warnings on Export/Import pragmas.}

This switch activates warnings on Export/Import pragmas when
the compiler detects a possible conflict between the Ada and
foreign language calling sequences. For example, the use of
default parameters in a convention C procedure is dubious
because the C compiler cannot supply the proper default, so
a warning is issued. The default is that such warnings are
generated.
@end table

@geindex -gnatwX (gcc)


@table @asis

@item @code{-gnatwX}

@emph{Suppress warnings on Export/Import pragmas.}

This switch suppresses warnings on Export/Import pragmas.
The sense of this is that you are telling the compiler that
you know what you are doing in writing the pragma, and it
should not complain at you.
@end table

@geindex -gnatwm (gcc)


@table @asis

@item @code{-gnatw.x}

@emph{Activate warnings for No_Exception_Propagation mode.}

This switch activates warnings for exception usage when pragma Restrictions
(No_Exception_Propagation) is in effect. Warnings are given for implicit or
explicit exception raises which are not covered by a local handler, and for
exception handlers which do not cover a local raise. The default is that these
warnings are not given.

@item @code{-gnatw.X}

@emph{Disable warnings for No_Exception_Propagation mode.}

This switch disables warnings for exception usage when pragma Restrictions
(No_Exception_Propagation) is in effect.
@end table

@geindex -gnatwy (gcc)

@geindex Ada compatibility issues warnings


@table @asis

@item @code{-gnatwy}

@emph{Activate warnings for Ada compatibility issues.}

For the most part, newer versions of Ada are upwards compatible
with older versions. For example, Ada 2005 programs will almost
always work when compiled as Ada 2012.
However there are some exceptions (for example the fact that
@cite{some} is now a reserved word in Ada 2012). This
switch activates several warnings to help in identifying
and correcting such incompatibilities. The default is that
these warnings are generated. Note that at one point Ada 2005
was called Ada 0Y, hence the choice of character.
@end table

@geindex -gnatwY (gcc)

@geindex Ada compatibility issues warnings


@table @asis

@item @code{-gnatwY}

@emph{Disable warnings for Ada compatibility issues.}

This switch suppresses the warnings intended to help in identifying
incompatibilities between Ada language versions.
@end table

@geindex -gnatw.y (gcc)

@geindex Package spec needing body


@table @asis

@item @code{-gnatw.y}

@emph{Activate information messages for why package spec needs body}

There are a number of cases in which a package spec needs a body.
For example, the use of pragma Elaborate_Body, or the declaration
of a procedure specification requiring a completion. This switch
causes information messages to be output showing why a package
specification requires a body. This can be useful in the case of
a large package specification which is unexpectedly requiring a
body. The default is that such information messages are not output.
@end table

@geindex -gnatw.Y (gcc)

@geindex No information messages for why package spec needs body


@table @asis

@item @code{-gnatw.Y}

@emph{Disable information messages for why package spec needs body}

This switch suppresses the output of information messages showing why
a package specification needs a body.
@end table

@geindex -gnatwz (gcc)

@geindex Unchecked_Conversion warnings


@table @asis

@item @code{-gnatwz}

@emph{Activate warnings on unchecked conversions.}

This switch activates warnings for unchecked conversions
where the types are known at compile time to have different
sizes. The default is that such warnings are generated. Warnings are also
generated for subprogram pointers with different conventions.
@end table

@geindex -gnatwZ (gcc)


@table @asis

@item @code{-gnatwZ}

@emph{Suppress warnings on unchecked conversions.}

This switch suppresses warnings for unchecked conversions
where the types are known at compile time to have different
sizes or conventions.
@end table

@geindex -gnatw.z (gcc)

@geindex Size/Alignment warnings


@table @asis

@item @code{-gnatw.z}

@emph{Activate warnings for size not a multiple of alignment.}

This switch activates warnings for cases of record types with
specified @cite{Size} and @cite{Alignment} attributes where the
size is not a multiple of the alignment, resulting in an object
size that is greater than the specified size. The default
is that such warnings are generated.
@end table

@geindex -gnatw.Z (gcc)

@geindex Size/Alignment warnings


@table @asis

@item @code{-gnatw.Z}

@emph{Suppress warnings for size not a multiple of alignment.}

This switch suppresses warnings for cases of record types with
specified @cite{Size} and @cite{Alignment} attributes where the
size is not a multiple of the alignment, resulting in an object
size that is greater than the specified size.
The warning can also be
suppressed by giving an explicit @cite{Object_Size} value.
@end table

@geindex -Wunused (gcc)


@table @asis

@item @code{-Wunused}

The warnings controlled by the @emph{-gnatw} switch are generated by
the front end of the compiler. The @emph{GCC} back end can provide
additional warnings and they are controlled by the @emph{-W} switch.
For example, @emph{-Wunused} activates back end
warnings for entities that are declared but not referenced.
@end table

@geindex -Wuninitialized (gcc)


@table @asis

@item @code{-Wuninitialized}

Similarly, @emph{-Wuninitialized} activates
the back end warning for uninitialized variables. This switch must be
used in conjunction with an optimization level greater than zero.
@end table

@geindex -Wstack-usage (gcc)


@table @asis

@item @code{-Wstack-usage=@emph{len}}

Warn if the stack usage of a subprogram might be larger than @cite{len} bytes.
See @ref{fa,,Static Stack Usage Analysis} for details.
@end table

@geindex -Wall (gcc)


@table @asis

@item @code{-Wall}

This switch enables most warnings from the @emph{GCC} back end.
The code generator detects a number of warning situations that are missed
by the @emph{GNAT} front end, and this switch can be used to activate them.
The use of this switch also sets the default front end warning mode to
@emph{-gnatwa}, that is, most front end warnings activated as well.
@end table

@geindex -w (gcc)


@table @asis

@item @code{-w}

Conversely, this switch suppresses warnings from the @emph{GCC} back end.
The use of this switch also sets the default front end warning mode to
@emph{-gnatws}, that is, front end warnings suppressed as well.
@end table

@geindex -Werror (gcc)


@table @asis

@item @code{-Werror}

This switch causes warnings from the @emph{GCC} back end to be treated as
errors.  The warning string still appears, but the warning messages are
counted as errors, and prevent the generation of an object file.
@end table

A string of warning parameters can be used in the same parameter. For example:

@example
-gnatwaGe
@end example

will turn on all optional warnings except for unrecognized pragma warnings,
and also specify that warnings should be treated as errors.

When no switch @emph{-gnatw} is used, this is equivalent to:

@quotation


@itemize *

@item 
@code{-gnatw.a}

@item 
@code{-gnatwB}

@item 
@code{-gnatw.b}

@item 
@code{-gnatwC}

@item 
@code{-gnatw.C}

@item 
@code{-gnatwD}

@item 
@code{-gnatwF}

@item 
@code{-gnatwg}

@item 
@code{-gnatwH}

@item 
@code{-gnatwi}

@item 
@code{-gnatw.I}

@item 
@code{-gnatwJ}

@item 
@code{-gnatwK}

@item 
@code{-gnatwL}

@item 
@code{-gnatw.L}

@item 
@code{-gnatwM}

@item 
@code{-gnatw.m}

@item 
@code{-gnatwn}

@item 
@code{-gnatwo}

@item 
@code{-gnatw.O}

@item 
@code{-gnatwP}

@item 
@code{-gnatw.P}

@item 
@code{-gnatwq}

@item 
@code{-gnatwR}

@item 
@code{-gnatw.R}

@item 
@code{-gnatw.S}

@item 
@code{-gnatwT}

@item 
@code{-gnatw.T}

@item 
@code{-gnatwU}

@item 
@code{-gnatwv}

@item 
@code{-gnatww}

@item 
@code{-gnatw.W}

@item 
@code{-gnatwx}

@item 
@code{-gnatw.X}

@item 
@code{-gnatwy}

@item 
@code{-gnatwz}
@end itemize
@end quotation

@node Debugging and Assertion Control,Validity Checking,Warning Message Control,Compiler Switches
@anchor{gnat_ugn/building_executable_programs_with_gnat debugging-and-assertion-control}@anchor{105}@anchor{gnat_ugn/building_executable_programs_with_gnat id16}@anchor{106}
@subsection Debugging and Assertion Control


@geindex -gnata (gcc)


@table @asis

@item @code{-gnata}

@geindex Assert

@geindex Debug

@geindex Assertions

The pragmas @cite{Assert} and @cite{Debug} normally have no effect and
are ignored. This switch, where @code{a} stands for assert, causes
@cite{Assert} and @cite{Debug} pragmas to be activated.

The pragmas have the form:

@example
pragma Assert (<Boolean-expression> [, <static-string-expression>])
pragma Debug (<procedure call>)
@end example

The @cite{Assert} pragma causes @cite{Boolean-expression} to be tested.
If the result is @cite{True}, the pragma has no effect (other than
possible side effects from evaluating the expression). If the result is
@cite{False}, the exception @cite{Assert_Failure} declared in the package
@cite{System.Assertions} is
raised (passing @cite{static-string-expression}, if present, as the
message associated with the exception). If no string expression is
given the default is a string giving the file name and line number
of the pragma.

The @cite{Debug} pragma causes @cite{procedure} to be called. Note that
@cite{pragma Debug} may appear within a declaration sequence, allowing
debugging procedures to be called between declarations.
@end table

@node Validity Checking,Style Checking,Debugging and Assertion Control,Compiler Switches
@anchor{gnat_ugn/building_executable_programs_with_gnat validity-checking}@anchor{fb}@anchor{gnat_ugn/building_executable_programs_with_gnat id17}@anchor{107}
@subsection Validity Checking


@geindex Validity Checking

The Ada Reference Manual defines the concept of invalid values (see
RM 13.9.1). The primary source of invalid values is uninitialized
variables. A scalar variable that is left uninitialized may contain
an invalid value; the concept of invalid does not apply to access or
composite types.

It is an error to read an invalid value, but the RM does not require
run-time checks to detect such errors, except for some minimal
checking to prevent erroneous execution (i.e. unpredictable
behavior). This corresponds to the @emph{-gnatVd} switch below,
which is the default. For example, by default, if the expression of a
case statement is invalid, it will raise Constraint_Error rather than
causing a wild jump, and if an array index on the left-hand side of an
assignment is invalid, it will raise Constraint_Error rather than
overwriting an arbitrary memory location.

The @emph{-gnatVa} may be used to enable additional validity checks,
which are not required by the RM. These checks are often very
expensive (which is why the RM does not require them). These checks
are useful in tracking down uninitialized variables, but they are
not usually recommended for production builds, and in particular
we do not recommend using these extra validity checking options in
combination with optimization, since this can confuse the optimizer.
If performance is a consideration, leading to the need to optimize,
then the validity checking options should not be used.

The other @emph{-gnatV}@code{x} switches below allow finer-grained
control; you can enable whichever validity checks you desire. However,
for most debugging purposes, @emph{-gnatVa} is sufficient, and the
default @emph{-gnatVd} (i.e. standard Ada behavior) is usually
sufficient for non-debugging use.

The @emph{-gnatB} switch tells the compiler to assume that all
values are valid (that is, within their declared subtype range)
except in the context of a use of the Valid attribute. This means
the compiler can generate more efficient code, since the range
of values is better known at compile time. However, an uninitialized
variable can cause wild jumps and memory corruption in this mode.

The @emph{-gnatV}@code{x} switch allows control over the validity
checking mode as described below.
The @code{x} argument is a string of letters that
indicate validity checks that are performed or not performed in addition
to the default checks required by Ada as described above.

@geindex -gnatVa (gcc)


@table @asis

@item @code{-gnatVa}

@emph{All validity checks.}

All validity checks are turned on.
That is, @emph{-gnatVa} is
equivalent to @emph{gnatVcdfimorst}.
@end table

@geindex -gnatVc (gcc)


@table @asis

@item @code{-gnatVc}

@emph{Validity checks for copies.}

The right hand side of assignments, and the initializing values of
object declarations are validity checked.
@end table

@geindex -gnatVd (gcc)


@table @asis

@item @code{-gnatVd}

@emph{Default (RM) validity checks.}

Some validity checks are done by default following normal Ada semantics
(RM 13.9.1 (9-11)).
A check is done in case statements that the expression is within the range
of the subtype. If it is not, Constraint_Error is raised.
For assignments to array components, a check is done that the expression used
as index is within the range. If it is not, Constraint_Error is raised.
Both these validity checks may be turned off using switch @emph{-gnatVD}.
They are turned on by default. If @emph{-gnatVD} is specified, a subsequent
switch @emph{-gnatVd} will leave the checks turned on.
Switch @emph{-gnatVD} should be used only if you are sure that all such
expressions have valid values. If you use this switch and invalid values
are present, then the program is erroneous, and wild jumps or memory
overwriting may occur.
@end table

@geindex -gnatVe (gcc)


@table @asis

@item @code{-gnatVe}

@emph{Validity checks for elementary components.}

In the absence of this switch, assignments to record or array components are
not validity checked, even if validity checks for assignments generally
(@emph{-gnatVc}) are turned on. In Ada, assignment of composite values do not
require valid data, but assignment of individual components does. So for
example, there is a difference between copying the elements of an array with a
slice assignment, compared to assigning element by element in a loop. This
switch allows you to turn off validity checking for components, even when they
are assigned component by component.
@end table

@geindex -gnatVf (gcc)


@table @asis

@item @code{-gnatVf}

@emph{Validity checks for floating-point values.}

In the absence of this switch, validity checking occurs only for discrete
values. If @emph{-gnatVf} is specified, then validity checking also applies
for floating-point values, and NaNs and infinities are considered invalid,
as well as out of range values for constrained types. Note that this means
that standard IEEE infinity mode is not allowed. The exact contexts
in which floating-point values are checked depends on the setting of other
options. For example, @emph{-gnatVif} or @emph{-gnatVfi}
(the order does not matter) specifies that floating-point parameters of mode
@cite{in} should be validity checked.
@end table

@geindex -gnatVi (gcc)


@table @asis

@item @code{-gnatVi}

@emph{Validity checks for `in} mode parameters`

Arguments for parameters of mode @cite{in} are validity checked in function
and procedure calls at the point of call.
@end table

@geindex -gnatVm (gcc)


@table @asis

@item @code{-gnatVm}

@emph{Validity checks for `in out} mode parameters.`

Arguments for parameters of mode @cite{in out} are validity checked in
procedure calls at the point of call. The @cite{'m'} here stands for
modify, since this concerns parameters that can be modified by the call.
Note that there is no specific option to test @cite{out} parameters,
but any reference within the subprogram will be tested in the usual
manner, and if an invalid value is copied back, any reference to it
will be subject to validity checking.
@end table

@geindex -gnatVn (gcc)


@table @asis

@item @code{-gnatVn}

@emph{No validity checks.}

This switch turns off all validity checking, including the default checking
for case statements and left hand side subscripts. Note that the use of
the switch @emph{-gnatp} suppresses all run-time checks, including
validity checks, and thus implies @emph{-gnatVn}. When this switch
is used, it cancels any other @emph{-gnatV} previously issued.

@item @code{-gnatVo}

@emph{Validity checks for operator and attribute operands.}
.. index:: -gnatVo  (gcc)

Arguments for predefined operators and attributes are validity checked.
This includes all operators in package @cite{Standard},
the shift operators defined as intrinsic in package @cite{Interfaces}
and operands for attributes such as @cite{Pos}. Checks are also made
on individual component values for composite comparisons, and on the
expressions in type conversions and qualified expressions. Checks are
also made on explicit ranges using @code{..} (e.g., slices, loops etc).
@end table

@geindex -gnatVp (gcc)


@table @asis

@item @code{-gnatVp}

@emph{Validity checks for parameters.}

This controls the treatment of parameters within a subprogram (as opposed
to @emph{-gnatVi} and @emph{-gnatVm} which control validity testing
of parameters on a call. If either of these call options is used, then
normally an assumption is made within a subprogram that the input arguments
have been validity checking at the point of call, and do not need checking
again within a subprogram). If @emph{-gnatVp} is set, then this assumption
is not made, and parameters are not assumed to be valid, so their validity
will be checked (or rechecked) within the subprogram.
@end table

@geindex -gnatVr (gcc)


@table @asis

@item @code{-gnatVr}

@emph{Validity checks for function returns.}

The expression in @cite{return} statements in functions is validity
checked.
@end table

@geindex -gnatVs (gcc)


@table @asis

@item @code{-gnatVs}

@emph{Validity checks for subscripts.}

All subscripts expressions are checked for validity, whether they appear
on the right side or left side (in default mode only left side subscripts
are validity checked).
@end table

@geindex -gnatVt (gcc)


@table @asis

@item @code{-gnatVt}

@emph{Validity checks for tests.}

Expressions used as conditions in @cite{if}, @cite{while} or @cite{exit}
statements are checked, as well as guard expressions in entry calls.
@end table

The @emph{-gnatV} switch may be followed by a string of letters
to turn on a series of validity checking options.
For example, @code{-gnatVcr}
specifies that in addition to the default validity checking, copies and
function return expressions are to be validity checked.
In order to make it easier to specify the desired combination of effects,
the upper case letters @cite{CDFIMORST} may
be used to turn off the corresponding lower case option.
Thus @code{-gnatVaM} turns on all validity checking options except for
checking of @cite{**in out**} procedure arguments.

The specification of additional validity checking generates extra code (and
in the case of @emph{-gnatVa} the code expansion can be substantial).
However, these additional checks can be very useful in detecting
uninitialized variables, incorrect use of unchecked conversion, and other
errors leading to invalid values. The use of pragma @cite{Initialize_Scalars}
is useful in conjunction with the extra validity checking, since this
ensures that wherever possible uninitialized variables have invalid values.

See also the pragma @cite{Validity_Checks} which allows modification of
the validity checking mode at the program source level, and also allows for
temporary disabling of validity checks.

@node Style Checking,Run-Time Checks,Validity Checking,Compiler Switches
@anchor{gnat_ugn/building_executable_programs_with_gnat id18}@anchor{108}@anchor{gnat_ugn/building_executable_programs_with_gnat style-checking}@anchor{100}
@subsection Style Checking


@geindex Style checking

@geindex -gnaty (gcc)

The @emph{-gnatyx} switch causes the compiler to
enforce specified style rules. A limited set of style rules has been used
in writing the GNAT sources themselves. This switch allows user programs
to activate all or some of these checks. If the source program fails a
specified style check, an appropriate message is given, preceded by
the character sequence '(style)'. This message does not prevent
successful compilation (unless the @emph{-gnatwe} switch is used).

Note that this is by no means intended to be a general facility for
checking arbitrary coding standards. It is simply an embedding of the
style rules we have chosen for the GNAT sources. If you are starting
a project which does not have established style standards, you may
find it useful to adopt the entire set of GNAT coding standards, or
some subset of them.


The string @cite{x} is a sequence of letters or digits
indicating the particular style
checks to be performed. The following checks are defined:

@geindex -gnaty[0-9] (gcc)


@table @asis

@item @code{-gnaty0}

@emph{Specify indentation level.}

If a digit from 1-9 appears
in the string after @emph{-gnaty}
then proper indentation is checked, with the digit indicating the
indentation level required. A value of zero turns off this style check.
The general style of required indentation is as specified by
the examples in the Ada Reference Manual. Full line comments must be
aligned with the @cite{--} starting on a column that is a multiple of
the alignment level, or they may be aligned the same way as the following
non-blank line (this is useful when full line comments appear in the middle
of a statement, or they may be aligned with the source line on the previous
non-blank line.
@end table

@geindex -gnatya (gcc)


@table @asis

@item @code{-gnatya}

@emph{Check attribute casing.}

Attribute names, including the case of keywords such as @cite{digits}
used as attributes names, must be written in mixed case, that is, the
initial letter and any letter following an underscore must be uppercase.
All other letters must be lowercase.
@end table

@geindex -gnatyA (gcc)


@table @asis

@item @code{-gnatyA}

@emph{Use of array index numbers in array attributes.}

When using the array attributes First, Last, Range,
or Length, the index number must be omitted for one-dimensional arrays
and is required for multi-dimensional arrays.
@end table

@geindex -gnatyb (gcc)


@table @asis

@item @code{-gnatyb}

@emph{Blanks not allowed at statement end.}

Trailing blanks are not allowed at the end of statements. The purpose of this
rule, together with h (no horizontal tabs), is to enforce a canonical format
for the use of blanks to separate source tokens.
@end table

@geindex -gnatyB (gcc)


@table @asis

@item @code{-gnatyB}

@emph{Check Boolean operators.}

The use of AND/OR operators is not permitted except in the cases of modular
operands, array operands, and simple stand-alone boolean variables or
boolean constants. In all other cases @cite{and then}/@cite{or else} are
required.
@end table

@geindex -gnatyc (gcc)


@table @asis

@item @code{-gnatyc}

@emph{Check comments, double space.}

Comments must meet the following set of rules:


@itemize *

@item 
The '@cite{--}' that starts the column must either start in column one,
or else at least one blank must precede this sequence.

@item 
Comments that follow other tokens on a line must have at least one blank
following the '@cite{--}' at the start of the comment.

@item 
Full line comments must have at least two blanks following the
'@cite{--}' that starts the comment, with the following exceptions.

@item 
A line consisting only of the '@cite{--}' characters, possibly preceded
by blanks is permitted.

@item 
A comment starting with '@cite{--x}' where @cite{x} is a special character
is permitted.
This allows proper processing of the output generated by specialized tools
including @emph{gnatprep} (where '@cite{--!}' is used) and the SPARK
annotation
language (where '@cite{--#}' is used). For the purposes of this rule, a
special character is defined as being in one of the ASCII ranges
@cite{16#21#...16#2F#} or @cite{16#3A#...16#3F#}.
Note that this usage is not permitted
in GNAT implementation units (i.e., when @emph{-gnatg} is used).

@item 
A line consisting entirely of minus signs, possibly preceded by blanks, is
permitted. This allows the construction of box comments where lines of minus
signs are used to form the top and bottom of the box.

@item 
A comment that starts and ends with '@cite{--}' is permitted as long as at
least one blank follows the initial '@cite{--}'. Together with the preceding
rule, this allows the construction of box comments, as shown in the following
example:

@example
---------------------------
-- This is a box comment --
-- with two text lines.  --
---------------------------
@end example
@end itemize
@end table

@geindex -gnatyC (gcc)


@table @asis

@item @code{-gnatyC}

@emph{Check comments, single space.}

This is identical to @cite{c} except that only one space
is required following the @cite{--} of a comment instead of two.
@end table

@geindex -gnatyd (gcc)


@table @asis

@item @code{-gnatyd}

@emph{Check no DOS line terminators present.}

All lines must be terminated by a single ASCII.LF
character (in particular the DOS line terminator sequence CR/LF is not
allowed).
@end table

@geindex -gnatye (gcc)


@table @asis

@item @code{-gnatye}

@emph{Check end/exit labels.}

Optional labels on @cite{end} statements ending subprograms and on
@cite{exit} statements exiting named loops, are required to be present.
@end table

@geindex -gnatyf (gcc)


@table @asis

@item @code{-gnatyf}

@emph{No form feeds or vertical tabs.}

Neither form feeds nor vertical tab characters are permitted
in the source text.
@end table

@geindex -gnatyg (gcc)


@table @asis

@item @code{-gnatyg}

@emph{GNAT style mode.}

The set of style check switches is set to match that used by the GNAT sources.
This may be useful when developing code that is eventually intended to be
incorporated into GNAT. Currently this is equivalent to @emph{-gnatwydISux})
but additional style switches may be added to this set in the future without
advance notice.
@end table

@geindex -gnatyh (gcc)


@table @asis

@item @code{-gnatyh}

@emph{No horizontal tabs.}

Horizontal tab characters are not permitted in the source text.
Together with the b (no blanks at end of line) check, this
enforces a canonical form for the use of blanks to separate
source tokens.
@end table

@geindex -gnatyi (gcc)


@table @asis

@item @code{-gnatyi}

@emph{Check if-then layout.}

The keyword @cite{then} must appear either on the same
line as corresponding @cite{if}, or on a line on its own, lined
up under the @cite{if}.
@end table

@geindex -gnatyI (gcc)


@table @asis

@item @code{-gnatyI}

@emph{check mode IN keywords.}

Mode @cite{in} (the default mode) is not
allowed to be given explicitly. @cite{in out} is fine,
but not @cite{in} on its own.
@end table

@geindex -gnatyk (gcc)


@table @asis

@item @code{-gnatyk}

@emph{Check keyword casing.}

All keywords must be in lower case (with the exception of keywords
such as @cite{digits} used as attribute names to which this check
does not apply).
@end table

@geindex -gnatyl (gcc)


@table @asis

@item @code{-gnatyl}

@emph{Check layout.}

Layout of statement and declaration constructs must follow the
recommendations in the Ada Reference Manual, as indicated by the
form of the syntax rules. For example an @cite{else} keyword must
be lined up with the corresponding @cite{if} keyword.

There are two respects in which the style rule enforced by this check
option are more liberal than those in the Ada Reference Manual. First
in the case of record declarations, it is permissible to put the
@cite{record} keyword on the same line as the @cite{type} keyword, and
then the @cite{end} in @cite{end record} must line up under @cite{type}.
This is also permitted when the type declaration is split on two lines.
For example, any of the following three layouts is acceptable:

@example
type q is record
   a : integer;
   b : integer;
end record;

type q is
   record
      a : integer;
      b : integer;
   end record;

type q is
   record
      a : integer;
      b : integer;
end record;
@end example

Second, in the case of a block statement, a permitted alternative
is to put the block label on the same line as the @cite{declare} or
@cite{begin} keyword, and then line the @cite{end} keyword up under
the block label. For example both the following are permitted:

@example
Block : declare
   A : Integer := 3;
begin
   Proc (A, A);
end Block;

Block :
   declare
      A : Integer := 3;
   begin
      Proc (A, A);
   end Block;
@end example

The same alternative format is allowed for loops. For example, both of
the following are permitted:

@example
Clear : while J < 10 loop
   A (J) := 0;
end loop Clear;

Clear :
   while J < 10 loop
      A (J) := 0;
   end loop Clear;
@end example
@end table

@geindex -gnatyLnnn (gcc)


@table @asis

@item @code{-gnatyL}

@emph{Set maximum nesting level.}

The maximum level of nesting of constructs (including subprograms, loops,
blocks, packages, and conditionals) may not exceed the given value
@emph{nnn}. A value of zero disconnects this style check.
@end table

@geindex -gnatym (gcc)


@table @asis

@item @code{-gnatym}

@emph{Check maximum line length.}

The length of source lines must not exceed 79 characters, including
any trailing blanks. The value of 79 allows convenient display on an
80 character wide device or window, allowing for possible special
treatment of 80 character lines. Note that this count is of
characters in the source text. This means that a tab character counts
as one character in this count and a wide character sequence counts as
a single character (however many bytes are needed in the encoding).
@end table

@geindex -gnatyMnnn (gcc)


@table @asis

@item @code{-gnatyM}

@emph{Set maximum line length.}

The length of lines must not exceed the
given value @emph{nnn}. The maximum value that can be specified is 32767.
If neither style option for setting the line length is used, then the
default is 255. This also controls the maximum length of lexical elements,
where the only restriction is that they must fit on a single line.
@end table

@geindex -gnatyn (gcc)


@table @asis

@item @code{-gnatyn}

@emph{Check casing of entities in Standard.}

Any identifier from Standard must be cased
to match the presentation in the Ada Reference Manual (for example,
@cite{Integer} and @cite{ASCII.NUL}).
@end table

@geindex -gnatyN (gcc)


@table @asis

@item @code{-gnatyN}

@emph{Turn off all style checks.}

All style check options are turned off.
@end table

@geindex -gnatyo (gcc)


@table @asis

@item @code{-gnatyo}

@emph{Check order of subprogram bodies.}

All subprogram bodies in a given scope
(e.g., a package body) must be in alphabetical order. The ordering
rule uses normal Ada rules for comparing strings, ignoring casing
of letters, except that if there is a trailing numeric suffix, then
the value of this suffix is used in the ordering (e.g., Junk2 comes
before Junk10).
@end table

@geindex -gnatyO (gcc)


@table @asis

@item @code{-gnatyO}

@emph{Check that overriding subprograms are explicitly marked as such.}

This applies to all subprograms of a derived type that override a primitive
operation of the type, for both tagged and untagged types. In particular,
the declaration of a primitive operation of a type extension that overrides
an inherited operation must carry an overriding indicator. Another case is
the declaration of a function that overrides a predefined operator (such
as an equality operator).
@end table

@geindex -gnatyp (gcc)


@table @asis

@item @code{-gnatyp}

@emph{Check pragma casing.}

Pragma names must be written in mixed case, that is, the
initial letter and any letter following an underscore must be uppercase.
All other letters must be lowercase. An exception is that SPARK_Mode is
allowed as an alternative for Spark_Mode.
@end table

@geindex -gnatyr (gcc)


@table @asis

@item @code{-gnatyr}

@emph{Check references.}

All identifier references must be cased in the same way as the
corresponding declaration. No specific casing style is imposed on
identifiers. The only requirement is for consistency of references
with declarations.
@end table

@geindex -gnatys (gcc)


@table @asis

@item @code{-gnatys}

@emph{Check separate specs.}

Separate declarations ('specs') are required for subprograms (a
body is not allowed to serve as its own declaration). The only
exception is that parameterless library level procedures are
not required to have a separate declaration. This exception covers
the most frequent form of main program procedures.
@end table

@geindex -gnatyS (gcc)


@table @asis

@item @code{-gnatyS}

@emph{Check no statements after then/else.}

No statements are allowed
on the same line as a @cite{then} or @cite{else} keyword following the
keyword in an @cite{if} statement. @cite{or else} and @cite{and then} are not
affected, and a special exception allows a pragma to appear after @cite{else}.
@end table

@geindex -gnatyt (gcc)


@table @asis

@item @code{-gnatyt}

@emph{Check token spacing.}

The following token spacing rules are enforced:


@itemize *

@item 
The keywords @cite{abs} and @cite{not} must be followed by a space.

@item 
The token @cite{=>} must be surrounded by spaces.

@item 
The token @cite{<>} must be preceded by a space or a left parenthesis.

@item 
Binary operators other than @cite{**} must be surrounded by spaces.
There is no restriction on the layout of the @cite{**} binary operator.

@item 
Colon must be surrounded by spaces.

@item 
Colon-equal (assignment, initialization) must be surrounded by spaces.

@item 
Comma must be the first non-blank character on the line, or be
immediately preceded by a non-blank character, and must be followed
by a space.

@item 
If the token preceding a left parenthesis ends with a letter or digit, then
a space must separate the two tokens.

@item 
If the token following a right parenthesis starts with a letter or digit, then
a space must separate the two tokens.

@item 
A right parenthesis must either be the first non-blank character on
a line, or it must be preceded by a non-blank character.

@item 
A semicolon must not be preceded by a space, and must not be followed by
a non-blank character.

@item 
A unary plus or minus may not be followed by a space.

@item 
A vertical bar must be surrounded by spaces.
@end itemize

Exactly one blank (and no other white space) must appear between
a @cite{not} token and a following @cite{in} token.
@end table

@geindex -gnatyu (gcc)


@table @asis

@item @code{-gnatyu}

@emph{Check unnecessary blank lines.}

Unnecessary blank lines are not allowed. A blank line is considered
unnecessary if it appears at the end of the file, or if more than
one blank line occurs in sequence.
@end table

@geindex -gnatyx (gcc)


@table @asis

@item @code{-gnatyx}

@emph{Check extra parentheses.}

Unnecessary extra level of parentheses (C-style) are not allowed
around conditions in @cite{if} statements, @cite{while} statements and
@cite{exit} statements.
@end table

@geindex -gnatyy (gcc)


@table @asis

@item @code{-gnatyy}

@emph{Set all standard style check options}

This is equivalent to @cite{gnaty3aAbcefhiklmnprst}, that is all checking
options enabled with the exception of @emph{-gnatyB}, @emph{-gnatyd},
@emph{-gnatyI}, @emph{-gnatyLnnn}, @emph{-gnatyo}, @emph{-gnatyO},
@emph{-gnatyS}, @emph{-gnatyu}, and @emph{-gnatyx}.
@end table

@geindex -gnaty- (gcc)


@table @asis

@item @code{-gnaty-}

@emph{Remove style check options}

This causes any subsequent options in the string to act as canceling the
corresponding style check option. To cancel maximum nesting level control,
use @emph{L} parameter witout any integer value after that, because any
digit following @emph{-} in the parameter string of the @emph{-gnaty}
option will be threated as canceling indentation check. The same is true
for @emph{M} parameter. @emph{y} and @emph{N} parameters are not
allowed after @emph{-}.
@end table

@geindex -gnaty+ (gcc)


@table @asis

@item @code{-gnaty+}

@emph{Enable style check options}

This causes any subsequent options in the string to enable the corresponding
style check option. That is, it cancels the effect of a previous -,
if any.
@end table

@c end of switch description (leave this comment to ease automatic parsing for

@c GPS

In the above rules, appearing in column one is always permitted, that is,
counts as meeting either a requirement for a required preceding space,
or as meeting a requirement for no preceding space.

Appearing at the end of a line is also always permitted, that is, counts
as meeting either a requirement for a following space, or as meeting
a requirement for no following space.

If any of these style rules is violated, a message is generated giving
details on the violation. The initial characters of such messages are
always '@cite{(style)}'. Note that these messages are treated as warning
messages, so they normally do not prevent the generation of an object
file. The @emph{-gnatwe} switch can be used to treat warning messages,
including style messages, as fatal errors.

The switch @code{-gnaty} on its own (that is not
followed by any letters or digits) is equivalent
to the use of @emph{-gnatyy} as described above, that is all
built-in standard style check options are enabled.

The switch @code{-gnatyN} clears any previously set style checks.

@node Run-Time Checks,Using gcc for Syntax Checking,Style Checking,Compiler Switches
@anchor{gnat_ugn/building_executable_programs_with_gnat run-time-checks}@anchor{fe}@anchor{gnat_ugn/building_executable_programs_with_gnat id19}@anchor{109}
@subsection Run-Time Checks


@geindex Division by zero

@geindex Access before elaboration

@geindex Checks
@geindex division by zero

@geindex Checks
@geindex access before elaboration

@geindex Checks
@geindex stack overflow checking

By default, the following checks are suppressed: integer overflow
checks, stack overflow checks, and checks for access before
elaboration on subprogram calls. All other checks, including range
checks and array bounds checks, are turned on by default. The
following @emph{gcc} switches refine this default behavior.

@geindex -gnatp (gcc)


@table @asis

@item @code{-gnatp}

@geindex Suppressing checks

@geindex Checks
@geindex suppressing

This switch causes the unit to be compiled
as though @cite{pragma Suppress (All_checks)}
had been present in the source. Validity checks are also eliminated (in
other words @emph{-gnatp} also implies @emph{-gnatVn}.
Use this switch to improve the performance
of the code at the expense of safety in the presence of invalid data or
program bugs.

Note that when checks are suppressed, the compiler is allowed, but not
required, to omit the checking code. If the run-time cost of the
checking code is zero or near-zero, the compiler will generate it even
if checks are suppressed. In particular, if the compiler can prove
that a certain check will necessarily fail, it will generate code to
do an unconditional 'raise', even if checks are suppressed. The
compiler warns in this case. Another case in which checks may not be
eliminated is when they are embedded in certain run time routines such
as math library routines.

Of course, run-time checks are omitted whenever the compiler can prove
that they will not fail, whether or not checks are suppressed.

Note that if you suppress a check that would have failed, program
execution is erroneous, which means the behavior is totally
unpredictable. The program might crash, or print wrong answers, or
do anything else. It might even do exactly what you wanted it to do
(and then it might start failing mysteriously next week or next
year). The compiler will generate code based on the assumption that
the condition being checked is true, which can result in erroneous
execution if that assumption is wrong.

The checks subject to suppression include all the checks defined by
the Ada standard, the additional implementation defined checks
@cite{Alignment_Check},
@cite{Duplicated_Tag_Check}, @cite{Predicate_Check}, and
@cite{Validity_Check}, as well as any checks introduced using
@cite{pragma Check_Name}. Note that @cite{Atomic_Synchronization}
is not automatically suppressed by use of this option.

If the code depends on certain checks being active, you can use
pragma @cite{Unsuppress} either as a configuration pragma or as
a local pragma to make sure that a specified check is performed
even if @emph{gnatp} is specified.

The @emph{-gnatp} switch has no effect if a subsequent
@emph{-gnat-p} switch appears.
@end table

@geindex -gnat-p (gcc)

@geindex Suppressing checks

@geindex Checks
@geindex suppressing

@geindex Suppress


@table @asis

@item @code{-gnat-p}

This switch cancels the effect of a previous @emph{gnatp} switch.
@end table

@geindex -gnato?? (gcc)

@geindex Overflow checks

@geindex Overflow mode

@geindex Check
@geindex overflow


@table @asis

@item @code{-gnato??}

This switch controls the mode used for computing intermediate
arithmetic integer operations, and also enables overflow checking.
For a full description of overflow mode and checking control, see
the 'Overflow Check Handling in GNAT' appendix in this
User's Guide.

Overflow checks are always enabled by this switch. The argument
controls the mode, using the codes


@table @asis

@item @emph{1 = STRICT}

In STRICT mode, intermediate operations are always done using the
base type, and overflow checking ensures that the result is within
the base type range.

@item @emph{2 = MINIMIZED}

In MINIMIZED mode, overflows in intermediate operations are avoided
where possible by using a larger integer type for the computation
(typically @cite{Long_Long_Integer}). Overflow checking ensures that
the result fits in this larger integer type.

@item @emph{3 = ELIMINATED}

In ELIMINATED mode, overflows in intermediate operations are avoided
by using multi-precision arithmetic. In this case, overflow checking
has no effect on intermediate operations (since overflow is impossible).
@end table

If two digits are present after @emph{-gnato} then the first digit
sets the mode for expressions outside assertions, and the second digit
sets the mode for expressions within assertions. Here assertions is used
in the technical sense (which includes for example precondition and
postcondition expressions).

If one digit is present, the corresponding mode is applicable to both
expressions within and outside assertion expressions.

If no digits are present, the default is to enable overflow checks
and set STRICT mode for both kinds of expressions. This is compatible
with the use of @emph{-gnato} in previous versions of GNAT.

@geindex Machine_Overflows

Note that the @emph{-gnato??} switch does not affect the code generated
for any floating-point operations; it applies only to integer semantics.
For floating-point, GNAT has the @cite{Machine_Overflows}
attribute set to @cite{False} and the normal mode of operation is to
generate IEEE NaN and infinite values on overflow or invalid operations
(such as dividing 0.0 by 0.0).

The reason that we distinguish overflow checking from other kinds of
range constraint checking is that a failure of an overflow check, unlike
for example the failure of a range check, can result in an incorrect
value, but cannot cause random memory destruction (like an out of range
subscript), or a wild jump (from an out of range case value). Overflow
checking is also quite expensive in time and space, since in general it
requires the use of double length arithmetic.

Note again that the default is @emph{-gnato00},
so overflow checking is not performed in default mode. This means that out of
the box, with the default settings, GNAT does not do all the checks
expected from the language description in the Ada Reference Manual.
If you want all constraint checks to be performed, as described in this Manual,
then you must explicitly use the @emph{-gnato??}
switch either on the @emph{gnatmake} or @emph{gcc} command.
@end table

@geindex -gnatE (gcc)

@geindex Elaboration checks

@geindex Check
@geindex elaboration


@table @asis

@item @code{-gnatE}

Enables dynamic checks for access-before-elaboration
on subprogram calls and generic instantiations.
Note that @emph{-gnatE} is not necessary for safety, because in the
default mode, GNAT ensures statically that the checks would not fail.
For full details of the effect and use of this switch,
@ref{1e,,Compiling with gcc}.
@end table

@geindex -fstack-check (gcc)

@geindex Stack Overflow Checking

@geindex Checks
@geindex stack overflow checking


@table @asis

@item @code{-fstack-check}

Activates stack overflow checking. For full details of the effect and use of
this switch see @ref{f9,,Stack Overflow Checking}.
@end table

@geindex Unsuppress

The setting of these switches only controls the default setting of the
checks. You may modify them using either @cite{Suppress} (to remove
checks) or @cite{Unsuppress} (to add back suppressed checks) pragmas in
the program source.

@node Using gcc for Syntax Checking,Using gcc for Semantic Checking,Run-Time Checks,Compiler Switches
@anchor{gnat_ugn/building_executable_programs_with_gnat id20}@anchor{10a}@anchor{gnat_ugn/building_executable_programs_with_gnat using-gcc-for-syntax-checking}@anchor{10b}
@subsection Using @emph{gcc} for Syntax Checking


@geindex -gnats (gcc)


@table @asis

@item @code{-gnats}

The @cite{s} stands for 'syntax'.

Run GNAT in syntax checking only mode. For
example, the command

@example
$ gcc -c -gnats x.adb
@end example

compiles file @code{x.adb} in syntax-check-only mode. You can check a
series of files in a single command
, and can use wild cards to specify such a group of files.
Note that you must specify the @emph{-c} (compile
only) flag in addition to the @emph{-gnats} flag.

You may use other switches in conjunction with @emph{-gnats}. In
particular, @emph{-gnatl} and @emph{-gnatv} are useful to control the
format of any generated error messages.

When the source file is empty or contains only empty lines and/or comments,
the output is a warning:

@example
$ gcc -c -gnats -x ada toto.txt
toto.txt:1:01: warning: empty file, contains no compilation units
$
@end example

Otherwise, the output is simply the error messages, if any. No object file or
ALI file is generated by a syntax-only compilation. Also, no units other
than the one specified are accessed. For example, if a unit @cite{X}
@emph{with}s a unit @cite{Y}, compiling unit @cite{X} in syntax
check only mode does not access the source file containing unit
@cite{Y}.

@geindex Multiple units
@geindex syntax checking

Normally, GNAT allows only a single unit in a source file. However, this
restriction does not apply in syntax-check-only mode, and it is possible
to check a file containing multiple compilation units concatenated
together. This is primarily used by the @cite{gnatchop} utility
(@ref{38,,Renaming Files with gnatchop}).
@end table

@node Using gcc for Semantic Checking,Compiling Different Versions of Ada,Using gcc for Syntax Checking,Compiler Switches
@anchor{gnat_ugn/building_executable_programs_with_gnat id21}@anchor{10c}@anchor{gnat_ugn/building_executable_programs_with_gnat using-gcc-for-semantic-checking}@anchor{10d}
@subsection Using @emph{gcc} for Semantic Checking


@geindex -gnatc (gcc)


@table @asis

@item @code{-gnatc}

The @cite{c} stands for 'check'.
Causes the compiler to operate in semantic check mode,
with full checking for all illegalities specified in the
Ada Reference Manual, but without generation of any object code
(no object file is generated).

Because dependent files must be accessed, you must follow the GNAT
semantic restrictions on file structuring to operate in this mode:


@itemize *

@item 
The needed source files must be accessible
(see @ref{8e,,Search Paths and the Run-Time Library (RTL)}).

@item 
Each file must contain only one compilation unit.

@item 
The file name and unit name must match (@ref{54,,File Naming Rules}).
@end itemize

The output consists of error messages as appropriate. No object file is
generated. An @code{ALI} file is generated for use in the context of
cross-reference tools, but this file is marked as not being suitable
for binding (since no object file is generated).
The checking corresponds exactly to the notion of
legality in the Ada Reference Manual.

Any unit can be compiled in semantics-checking-only mode, including
units that would not normally be compiled (subunits,
and specifications where a separate body is present).
@end table

@node Compiling Different Versions of Ada,Character Set Control,Using gcc for Semantic Checking,Compiler Switches
@anchor{gnat_ugn/building_executable_programs_with_gnat compiling-different-versions-of-ada}@anchor{6}@anchor{gnat_ugn/building_executable_programs_with_gnat id22}@anchor{10e}
@subsection Compiling Different Versions of Ada


The switches described in this section allow you to explicitly specify
the version of the Ada language that your programs are written in.
The default mode is Ada 2012,
but you can also specify Ada 95, Ada 2005 mode, or
indicate Ada 83 compatibility mode.

@geindex Compatibility with Ada 83

@geindex -gnat83 (gcc)

@geindex ACVC
@geindex Ada 83 tests

@geindex Ada 83 mode


@table @asis

@item @code{-gnat83 (Ada 83 Compatibility Mode)}

Although GNAT is primarily an Ada 95 / Ada 2005 compiler, this switch
specifies that the program is to be compiled in Ada 83 mode. With
@emph{-gnat83}, GNAT rejects most post-Ada 83 extensions and applies Ada 83
semantics where this can be done easily.
It is not possible to guarantee this switch does a perfect
job; some subtle tests, such as are
found in earlier ACVC tests (and that have been removed from the ACATS suite
for Ada 95), might not compile correctly.
Nevertheless, this switch may be useful in some circumstances, for example
where, due to contractual reasons, existing code needs to be maintained
using only Ada 83 features.

With few exceptions (most notably the need to use @cite{<>} on
.. index:: Generic formal parameters

unconstrained generic formal parameters, the use of the new Ada 95 / Ada 2005
reserved words, and the use of packages
with optional bodies), it is not necessary to specify the
@emph{-gnat83} switch when compiling Ada 83 programs, because, with rare
exceptions, Ada 95 and Ada 2005 are upwardly compatible with Ada 83. Thus
a correct Ada 83 program is usually also a correct program
in these later versions of the language standard. For further information
please refer to the @cite{Compatibility_and_Porting_Guide} chapter in the
@cite{GNAT Reference Manual}.
@end table

@geindex -gnat95 (gcc)

@geindex Ada 95 mode


@table @asis

@item @code{-gnat95} (Ada 95 mode)

This switch directs the compiler to implement the Ada 95 version of the
language.
Since Ada 95 is almost completely upwards
compatible with Ada 83, Ada 83 programs may generally be compiled using
this switch (see the description of the @emph{-gnat83} switch for further
information about Ada 83 mode).
If an Ada 2005 program is compiled in Ada 95 mode,
uses of the new Ada 2005 features will cause error
messages or warnings.

This switch also can be used to cancel the effect of a previous
@emph{-gnat83}, @emph{-gnat05/2005}, or @emph{-gnat12/2012}
switch earlier in the command line.
@end table

@geindex -gnat05 (gcc)

@geindex -gnat2005 (gcc)

@geindex Ada 2005 mode


@table @asis

@item @code{-gnat05} or @code{-gnat2005} (Ada 2005 mode)

This switch directs the compiler to implement the Ada 2005 version of the
language, as documented in the official Ada standards document.
Since Ada 2005 is almost completely upwards
compatible with Ada 95 (and thus also with Ada 83), Ada 83 and Ada 95 programs
may generally be compiled using this switch (see the description of the
@emph{-gnat83} and @emph{-gnat95} switches for further
information).
@end table

@geindex -gnat12 (gcc)

@geindex -gnat2012 (gcc)

@geindex Ada 2012 mode


@table @asis

@item @code{-gnat12} or @code{-gnat2012} (Ada 2012 mode)

This switch directs the compiler to implement the Ada 2012 version of the
language (also the default).
Since Ada 2012 is almost completely upwards
compatible with Ada 2005 (and thus also with Ada 83, and Ada 95),
Ada 83 and Ada 95 programs
may generally be compiled using this switch (see the description of the
@emph{-gnat83}, @emph{-gnat95}, and @emph{-gnat05/2005} switches
for further information).
@end table

@geindex -gnatX (gcc)

@geindex Ada language extensions

@geindex GNAT extensions


@table @asis

@item @code{-gnatX} (Enable GNAT Extensions)

This switch directs the compiler to implement the latest version of the
language (currently Ada 2012) and also to enable certain GNAT implementation
extensions that are not part of any Ada standard. For a full list of these
extensions, see the GNAT reference manual.
@end table

@node Character Set Control,File Naming Control,Compiling Different Versions of Ada,Compiler Switches
@anchor{gnat_ugn/building_executable_programs_with_gnat id23}@anchor{10f}@anchor{gnat_ugn/building_executable_programs_with_gnat character-set-control}@anchor{4a}
@subsection Character Set Control


@geindex -gnati (gcc)


@table @asis

@item @code{-gnati@emph{c}}

Normally GNAT recognizes the Latin-1 character set in source program
identifiers, as described in the Ada Reference Manual.
This switch causes
GNAT to recognize alternate character sets in identifiers. @cite{c} is a
single character  indicating the character set, as follows:


@multitable {xxxxxxxxxxxx} {xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx} 
@item

@emph{1}

@tab

ISO 8859-1 (Latin-1) identifiers

@item

@emph{2}

@tab

ISO 8859-2 (Latin-2) letters allowed in identifiers

@item

@emph{3}

@tab

ISO 8859-3 (Latin-3) letters allowed in identifiers

@item

@emph{4}

@tab

ISO 8859-4 (Latin-4) letters allowed in identifiers

@item

@emph{5}

@tab

ISO 8859-5 (Cyrillic) letters allowed in identifiers

@item

@emph{9}

@tab

ISO 8859-15 (Latin-9) letters allowed in identifiers

@item

@emph{p}

@tab

IBM PC letters (code page 437) allowed in identifiers

@item

@emph{8}

@tab

IBM PC letters (code page 850) allowed in identifiers

@item

@emph{f}

@tab

Full upper-half codes allowed in identifiers

@item

@emph{n}

@tab

No upper-half codes allowed in identifiers

@item

@emph{w}

@tab

Wide-character codes (that is, codes greater than 255)
allowed in identifiers

@end multitable


See @ref{40,,Foreign Language Representation} for full details on the
implementation of these character sets.
@end table

@geindex -gnatW (gcc)


@table @asis

@item @code{-gnatW@emph{e}}

Specify the method of encoding for wide characters.
@cite{e} is one of the following:


@multitable {xxxxxxxxxxxx} {xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx} 
@item

@emph{h}

@tab

Hex encoding (brackets coding also recognized)

@item

@emph{u}

@tab

Upper half encoding (brackets encoding also recognized)

@item

@emph{s}

@tab

Shift/JIS encoding (brackets encoding also recognized)

@item

@emph{e}

@tab

EUC encoding (brackets encoding also recognized)

@item

@emph{8}

@tab

UTF-8 encoding (brackets encoding also recognized)

@item

@emph{b}

@tab

Brackets encoding only (default value)

@end multitable


For full details on these encoding
methods see @ref{50,,Wide_Character Encodings}.
Note that brackets coding is always accepted, even if one of the other
options is specified, so for example @emph{-gnatW8} specifies that both
brackets and UTF-8 encodings will be recognized. The units that are
with'ed directly or indirectly will be scanned using the specified
representation scheme, and so if one of the non-brackets scheme is
used, it must be used consistently throughout the program. However,
since brackets encoding is always recognized, it may be conveniently
used in standard libraries, allowing these libraries to be used with
any of the available coding schemes.

Note that brackets encoding only applies to program text. Within comments,
brackets are considered to be normal graphic characters, and bracket sequences
are never recognized as wide characters.

If no @emph{-gnatW?} parameter is present, then the default
representation is normally Brackets encoding only. However, if the
first three characters of the file are 16#EF# 16#BB# 16#BF# (the standard
byte order mark or BOM for UTF-8), then these three characters are
skipped and the default representation for the file is set to UTF-8.

Note that the wide character representation that is specified (explicitly
or by default) for the main program also acts as the default encoding used
for Wide_Text_IO files if not specifically overridden by a WCEM form
parameter.
@end table

When no @emph{-gnatW?} is specified, then characters (other than wide
characters represented using brackets notation) are treated as 8-bit
Latin-1 codes. The codes recognized are the Latin-1 graphic characters,
and ASCII format effectors (CR, LF, HT, VT). Other lower half control
characters in the range 16#00#..16#1F# are not accepted in program text
or in comments. Upper half control characters (16#80#..16#9F#) are rejected
in program text, but allowed and ignored in comments. Note in particular
that the Next Line (NEL) character whose encoding is 16#85# is not recognized
as an end of line in this default mode. If your source program contains
instances of the NEL character used as a line terminator,
you must use UTF-8 encoding for the whole
source program. In default mode, all lines must be ended by a standard
end of line sequence (CR, CR/LF, or LF).

Note that the convention of simply accepting all upper half characters in
comments means that programs that use standard ASCII for program text, but
UTF-8 encoding for comments are accepted in default mode, providing that the
comments are ended by an appropriate (CR, or CR/LF, or LF) line terminator.
This is a common mode for many programs with foreign language comments.

@node File Naming Control,Subprogram Inlining Control,Character Set Control,Compiler Switches
@anchor{gnat_ugn/building_executable_programs_with_gnat file-naming-control}@anchor{110}@anchor{gnat_ugn/building_executable_programs_with_gnat id24}@anchor{111}
@subsection File Naming Control


@geindex -gnatk (gcc)


@table @asis

@item @code{-gnatk@emph{n}}

Activates file name 'krunching'. @cite{n}, a decimal integer in the range
1-999, indicates the maximum allowable length of a file name (not
including the @code{.ads} or @code{.adb} extension). The default is not
to enable file name krunching.

For the source file naming rules, @ref{54,,File Naming Rules}.
@end table

@node Subprogram Inlining Control,Auxiliary Output Control,File Naming Control,Compiler Switches
@anchor{gnat_ugn/building_executable_programs_with_gnat subprogram-inlining-control}@anchor{112}@anchor{gnat_ugn/building_executable_programs_with_gnat id25}@anchor{113}
@subsection Subprogram Inlining Control


@geindex -gnatn (gcc)


@table @asis

@item @code{-gnatn[12]}

The @cite{n} here is intended to suggest the first syllable of the
word 'inline'.
GNAT recognizes and processes @cite{Inline} pragmas. However, for the
inlining to actually occur, optimization must be enabled and, in order
to enable inlining of subprograms specified by pragma @cite{Inline},
you must also specify this switch.
In the absence of this switch, GNAT does not attempt
inlining and does not need to access the bodies of
subprograms for which @cite{pragma Inline} is specified if they are not
in the current unit.

You can optionally specify the inlining level: 1 for moderate inlining across
modules, which is a good compromise between compilation times and performances
at run time, or 2 for full inlining across modules, which may bring about
longer compilation times. If no inlining level is specified, the compiler will
pick it based on the optimization level: 1 for @emph{-O1}, @emph{-O2} or
@emph{-Os} and 2 for @emph{-O3}.

If you specify this switch the compiler will access these bodies,
creating an extra source dependency for the resulting object file, and
where possible, the call will be inlined.
For further details on when inlining is possible
see @ref{114,,Inlining of Subprograms}.
@end table

@geindex -gnatN (gcc)


@table @asis

@item @code{-gnatN}

This switch activates front-end inlining which also
generates additional dependencies.

When using a gcc-based back end (in practice this means using any version
of GNAT other than the JGNAT, .NET or GNAAMP versions), then the use of
@emph{-gnatN} is deprecated, and the use of @emph{-gnatn} is preferred.
Historically front end inlining was more extensive than the gcc back end
inlining, but that is no longer the case.
@end table

@node Auxiliary Output Control,Debugging Control,Subprogram Inlining Control,Compiler Switches
@anchor{gnat_ugn/building_executable_programs_with_gnat auxiliary-output-control}@anchor{115}@anchor{gnat_ugn/building_executable_programs_with_gnat id26}@anchor{116}
@subsection Auxiliary Output Control


@geindex -gnatt (gcc)

@geindex Writing internal trees

@geindex Internal trees
@geindex writing to file


@table @asis

@item @code{-gnatt}

Causes GNAT to write the internal tree for a unit to a file (with the
extension @code{.adt}.
This not normally required, but is used by separate analysis tools.
Typically
these tools do the necessary compilations automatically, so you should
not have to specify this switch in normal operation.
Note that the combination of switches @emph{-gnatct}
generates a tree in the form required by ASIS applications.
@end table

@geindex -gnatu (gcc)


@table @asis

@item @code{-gnatu}

Print a list of units required by this compilation on @code{stdout}.
The listing includes all units on which the unit being compiled depends
either directly or indirectly.
@end table

@geindex -pass-exit-codes (gcc)


@table @asis

@item @code{-pass-exit-codes}

If this switch is not used, the exit code returned by @emph{gcc} when
compiling multiple files indicates whether all source files have
been successfully used to generate object files or not.

When @emph{-pass-exit-codes} is used, @emph{gcc} exits with an extended
exit status and allows an integrated development environment to better
react to a compilation failure. Those exit status are:


@multitable {xxxxxxxxxxxx} {xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx} 
@item

@emph{5}

@tab

There was an error in at least one source file.

@item

@emph{3}

@tab

At least one source file did not generate an object file.

@item

@emph{2}

@tab

The compiler died unexpectedly (internal error for example).

@item

@emph{0}

@tab

An object file has been generated for every source file.

@end multitable

@end table

@node Debugging Control,Exception Handling Control,Auxiliary Output Control,Compiler Switches
@anchor{gnat_ugn/building_executable_programs_with_gnat debugging-control}@anchor{117}@anchor{gnat_ugn/building_executable_programs_with_gnat id27}@anchor{118}
@subsection Debugging Control


@quotation

@geindex Debugging options
@end quotation

@geindex -gnatd (gcc)


@table @asis

@item @code{-gnatd@emph{x}}

Activate internal debugging switches. @cite{x} is a letter or digit, or
string of letters or digits, which specifies the type of debugging
outputs desired. Normally these are used only for internal development
or system debugging purposes. You can find full documentation for these
switches in the body of the @cite{Debug} unit in the compiler source
file @code{debug.adb}.
@end table

@geindex -gnatG (gcc)


@table @asis

@item @code{-gnatG[=@emph{nn}]}

This switch causes the compiler to generate auxiliary output containing
a pseudo-source listing of the generated expanded code. Like most Ada
compilers, GNAT works by first transforming the high level Ada code into
lower level constructs. For example, tasking operations are transformed
into calls to the tasking run-time routines. A unique capability of GNAT
is to list this expanded code in a form very close to normal Ada source.
This is very useful in understanding the implications of various Ada
usage on the efficiency of the generated code. There are many cases in
Ada (e.g., the use of controlled types), where simple Ada statements can
generate a lot of run-time code. By using @emph{-gnatG} you can identify
these cases, and consider whether it may be desirable to modify the coding
approach to improve efficiency.

The optional parameter @cite{nn} if present after -gnatG specifies an
alternative maximum line length that overrides the normal default of 72.
This value is in the range 40-999999, values less than 40 being silently
reset to 40. The equal sign is optional.

The format of the output is very similar to standard Ada source, and is
easily understood by an Ada programmer. The following special syntactic
additions correspond to low level features used in the generated code that
do not have any exact analogies in pure Ada source form. The following
is a partial list of these special constructions. See the spec
of package @cite{Sprint} in file @code{sprint.ads} for a full list.

@geindex -gnatL (gcc)

If the switch @emph{-gnatL} is used in conjunction with
@emph{-gnatG}, then the original source lines are interspersed
in the expanded source (as comment lines with the original line number).


@table @asis

@item @code{new @emph{xxx} [storage_pool = @emph{yyy}]}

Shows the storage pool being used for an allocator.

@item @code{at end @emph{procedure-name};}

Shows the finalization (cleanup) procedure for a scope.

@item @code{(if @emph{expr} then @emph{expr} else @emph{expr})}

Conditional expression equivalent to the @cite{x?y:z} construction in C.

@item @code{@emph{target}^(@emph{source})}

A conversion with floating-point truncation instead of rounding.

@item @code{@emph{target}?(@emph{source})}

A conversion that bypasses normal Ada semantic checking. In particular
enumeration types and fixed-point types are treated simply as integers.

@item @code{@emph{target}?^(@emph{source})}

Combines the above two cases.
@end table

@code{@emph{x} #/ @emph{y}}

@code{@emph{x} #mod @emph{y}}

@code{@emph{x} # @emph{y}}


@table @asis

@item @code{@emph{x} #rem @emph{y}}

A division or multiplication of fixed-point values which are treated as
integers without any kind of scaling.

@item @code{free @emph{expr} [storage_pool = @emph{xxx}]}

Shows the storage pool associated with a @cite{free} statement.

@item @code{[subtype or type declaration]}

Used to list an equivalent declaration for an internally generated
type that is referenced elsewhere in the listing.

@item @code{freeze @emph{type-name} [@emph{actions}]}

Shows the point at which @cite{type-name} is frozen, with possible
associated actions to be performed at the freeze point.

@item @code{reference @emph{itype}}

Reference (and hence definition) to internal type @cite{itype}.

@item @code{@emph{function-name}! (@emph{arg}, @emph{arg}, @emph{arg})}

Intrinsic function call.

@item @code{@emph{label-name} : label}

Declaration of label @cite{labelname}.

@item @code{#$ @emph{subprogram-name}}

An implicit call to a run-time support routine
(to meet the requirement of H.3.1(9) in a
convenient manner).

@item @code{@emph{expr} && @emph{expr} && @emph{expr} ... && @emph{expr}}

A multiple concatenation (same effect as @cite{expr} & @cite{expr} &
@cite{expr}, but handled more efficiently).

@item @code{[constraint_error]}

Raise the @cite{Constraint_Error} exception.

@item @code{@emph{expression}'reference}

A pointer to the result of evaluating @{expression@}.

@item @code{@emph{target-type}!(@emph{source-expression})}

An unchecked conversion of @cite{source-expression} to @cite{target-type}.

@item @code{[@emph{numerator}/@emph{denominator}]}

Used to represent internal real literals (that) have no exact
representation in base 2-16 (for example, the result of compile time
evaluation of the expression 1.0/27.0).
@end table
@end table

@geindex -gnatD (gcc)


@table @asis

@item @code{-gnatD[=nn]}

When used in conjunction with @emph{-gnatG}, this switch causes
the expanded source, as described above for
@emph{-gnatG} to be written to files with names
@code{xxx.dg}, where @code{xxx} is the normal file name,
instead of to the standard output file. For
example, if the source file name is @code{hello.adb}, then a file
@code{hello.adb.dg} will be written.  The debugging
information generated by the @emph{gcc} @emph{-g} switch
will refer to the generated @code{xxx.dg} file. This allows
you to do source level debugging using the generated code which is
sometimes useful for complex code, for example to find out exactly
which part of a complex construction raised an exception. This switch
also suppress generation of cross-reference information (see
@emph{-gnatx}) since otherwise the cross-reference information
would refer to the @code{.dg} file, which would cause
confusion since this is not the original source file.

Note that @emph{-gnatD} actually implies @emph{-gnatG}
automatically, so it is not necessary to give both options.
In other words @emph{-gnatD} is equivalent to @emph{-gnatDG}).

@geindex -gnatL (gcc)

If the switch @emph{-gnatL} is used in conjunction with
@emph{-gnatDG}, then the original source lines are interspersed
in the expanded source (as comment lines with the original line number).

The optional parameter @cite{nn} if present after -gnatD specifies an
alternative maximum line length that overrides the normal default of 72.
This value is in the range 40-999999, values less than 40 being silently
reset to 40. The equal sign is optional.
@end table

@geindex -gnatr (gcc)

@geindex pragma Restrictions


@table @asis

@item @code{-gnatr}

This switch causes pragma Restrictions to be treated as Restriction_Warnings
so that violation of restrictions causes warnings rather than illegalities.
This is useful during the development process when new restrictions are added
or investigated. The switch also causes pragma Profile to be treated as
Profile_Warnings, and pragma Restricted_Run_Time and pragma Ravenscar set
restriction warnings rather than restrictions.
@end table

@geindex -gnatR (gcc)


@table @asis

@item @code{-gnatR[0|1|2|3[s]]}

This switch controls output from the compiler of a listing showing
representation information for declared types and objects. For
@emph{-gnatR0}, no information is output (equivalent to omitting
the @emph{-gnatR} switch). For @emph{-gnatR1} (which is the default,
so @emph{-gnatR} with no parameter has the same effect), size and alignment
information is listed for declared array and record types. For
@emph{-gnatR2}, size and alignment information is listed for all
declared types and objects. The @cite{Linker_Section} is also listed for any
entity for which the @cite{Linker_Section} is set explicitly or implicitly (the
latter case occurs for objects of a type for which a @cite{Linker_Section}
is set).

Finally @emph{-gnatR3} includes symbolic
expressions for values that are computed at run time for
variant records. These symbolic expressions have a mostly obvious
format with #n being used to represent the value of the n'th
discriminant. See source files @code{repinfo.ads/adb} in the
@cite{GNAT} sources for full details on the format of @emph{-gnatR3}
output. If the switch is followed by an s (e.g., @emph{-gnatR2s}), then
the output is to a file with the name @code{file.rep} where
file is the name of the corresponding source file.

@item @code{-gnatRm[s]}

This form of the switch controls output of subprogram conventions
and parameter passing mechanisms for all subprograms. A following
@cite{s} means output to a file as described above.

Note that it is possible for record components to have zero size. In
this case, the component clause uses an obvious extension of permitted
Ada syntax, for example @cite{at 0 range 0 .. -1}.

Representation information requires that code be generated (since it is the
code generator that lays out complex data structures). If an attempt is made
to output representation information when no code is generated, for example
when a subunit is compiled on its own, then no information can be generated
and the compiler outputs a message to this effect.
@end table

@geindex -gnatS (gcc)


@table @asis

@item @code{-gnatS}

The use of the switch @emph{-gnatS} for an
Ada compilation will cause the compiler to output a
representation of package Standard in a form very
close to standard Ada. It is not quite possible to
do this entirely in standard Ada (since new
numeric base types cannot be created in standard
Ada), but the output is easily
readable to any Ada programmer, and is useful to
determine the characteristics of target dependent
types in package Standard.
@end table

@geindex -gnatx (gcc)


@table @asis

@item @code{-gnatx}

Normally the compiler generates full cross-referencing information in
the @code{ALI} file. This information is used by a number of tools,
including @cite{gnatfind} and @cite{gnatxref}. The @emph{-gnatx} switch
suppresses this information. This saves some space and may slightly
speed up compilation, but means that these tools cannot be used.
@end table

@node Exception Handling Control,Units to Sources Mapping Files,Debugging Control,Compiler Switches
@anchor{gnat_ugn/building_executable_programs_with_gnat id28}@anchor{119}@anchor{gnat_ugn/building_executable_programs_with_gnat exception-handling-control}@anchor{11a}
@subsection Exception Handling Control


GNAT uses two methods for handling exceptions at run-time. The
@cite{setjmp/longjmp} method saves the context when entering
a frame with an exception handler. Then when an exception is
raised, the context can be restored immediately, without the
need for tracing stack frames. This method provides very fast
exception propagation, but introduces significant overhead for
the use of exception handlers, even if no exception is raised.

The other approach is called 'zero cost' exception handling.
With this method, the compiler builds static tables to describe
the exception ranges. No dynamic code is required when entering
a frame containing an exception handler. When an exception is
raised, the tables are used to control a back trace of the
subprogram invocation stack to locate the required exception
handler. This method has considerably poorer performance for
the propagation of exceptions, but there is no overhead for
exception handlers if no exception is raised. Note that in this
mode and in the context of mixed Ada and C/C++ programming,
to propagate an exception through a C/C++ code, the C/C++ code
must be compiled with the @emph{-funwind-tables} GCC's
option.

The following switches may be used to control which of the
two exception handling methods is used.

@geindex --RTS=sjlj (gnatmake)


@table @asis

@item @code{--RTS=sjlj}

This switch causes the setjmp/longjmp run-time (when available) to be used
for exception handling. If the default
mechanism for the target is zero cost exceptions, then
this switch can be used to modify this default, and must be
used for all units in the partition.
This option is rarely used. One case in which it may be
advantageous is if you have an application where exception
raising is common and the overall performance of the
application is improved by favoring exception propagation.
@end table

@geindex --RTS=zcx (gnatmake)

@geindex Zero Cost Exceptions


@table @asis

@item @code{--RTS=zcx}

This switch causes the zero cost approach to be used
for exception handling. If this is the default mechanism for the
target (see below), then this switch is unneeded. If the default
mechanism for the target is setjmp/longjmp exceptions, then
this switch can be used to modify this default, and must be
used for all units in the partition.
This option can only be used if the zero cost approach
is available for the target in use, otherwise it will generate an error.
@end table

The same option @emph{--RTS} must be used both for @emph{gcc}
and @emph{gnatbind}. Passing this option to @emph{gnatmake}
(@ref{df,,Switches for gnatmake}) will ensure the required consistency
through the compilation and binding steps.

@node Units to Sources Mapping Files,Code Generation Control,Exception Handling Control,Compiler Switches
@anchor{gnat_ugn/building_executable_programs_with_gnat id29}@anchor{11b}@anchor{gnat_ugn/building_executable_programs_with_gnat units-to-sources-mapping-files}@anchor{fc}
@subsection Units to Sources Mapping Files


@geindex -gnatem (gcc)


@table @asis

@item @code{-gnatem=@emph{path}}

A mapping file is a way to communicate to the compiler two mappings:
from unit names to file names (without any directory information) and from
file names to path names (with full directory information). These mappings
are used by the compiler to short-circuit the path search.

The use of mapping files is not required for correct operation of the
compiler, but mapping files can improve efficiency, particularly when
sources are read over a slow network connection. In normal operation,
you need not be concerned with the format or use of mapping files,
and the @emph{-gnatem} switch is not a switch that you would use
explicitly. It is intended primarily for use by automatic tools such as
@emph{gnatmake} running under the project file facility. The
description here of the format of mapping files is provided
for completeness and for possible use by other tools.

A mapping file is a sequence of sets of three lines. In each set, the
first line is the unit name, in lower case, with @cite{%s} appended
for specs and @cite{%b} appended for bodies; the second line is the
file name; and the third line is the path name.

Example:

@example
main%b
main.2.ada
/gnat/project1/sources/main.2.ada
@end example

When the switch @emph{-gnatem} is specified, the compiler will
create in memory the two mappings from the specified file. If there is
any problem (nonexistent file, truncated file or duplicate entries),
no mapping will be created.

Several @emph{-gnatem} switches may be specified; however, only the
last one on the command line will be taken into account.

When using a project file, @emph{gnatmake} creates a temporary
mapping file and communicates it to the compiler using this switch.
@end table

@node Code Generation Control,,Units to Sources Mapping Files,Compiler Switches
@anchor{gnat_ugn/building_executable_programs_with_gnat code-generation-control}@anchor{11c}@anchor{gnat_ugn/building_executable_programs_with_gnat id30}@anchor{11d}
@subsection Code Generation Control


The GCC technology provides a wide range of target dependent
@code{-m} switches for controlling
details of code generation with respect to different versions of
architectures. This includes variations in instruction sets (e.g.,
different members of the power pc family), and different requirements
for optimal arrangement of instructions (e.g., different members of
the x86 family). The list of available @emph{-m} switches may be
found in the GCC documentation.

Use of these @emph{-m} switches may in some cases result in improved
code performance.

The GNAT technology is tested and qualified without any
@code{-m} switches,
so generally the most reliable approach is to avoid the use of these
switches. However, we generally expect most of these switches to work
successfully with GNAT, and many customers have reported successful
use of these options.

Our general advice is to avoid the use of @emph{-m} switches unless
special needs lead to requirements in this area. In particular,
there is no point in using @emph{-m} switches to improve performance
unless you actually see a performance improvement.

@node Binding with gnatbind,Linking with gnatlink,Compiler Switches,Building Executable Programs with GNAT
@anchor{gnat_ugn/building_executable_programs_with_gnat binding-with-gnatbind}@anchor{1f}@anchor{gnat_ugn/building_executable_programs_with_gnat id31}@anchor{11e}
@section Binding with @cite{gnatbind}


@geindex gnatbind

This chapter describes the GNAT binder, @cite{gnatbind}, which is used
to bind compiled GNAT objects.

Note: to invoke @cite{gnatbind} with a project file, use the @cite{gnat}
driver (see @ref{11f,,The GNAT Driver and Project Files}).

The @cite{gnatbind} program performs four separate functions:


@itemize *

@item 
Checks that a program is consistent, in accordance with the rules in
Chapter 10 of the Ada Reference Manual. In particular, error
messages are generated if a program uses inconsistent versions of a
given unit.

@item 
Checks that an acceptable order of elaboration exists for the program
and issues an error message if it cannot find an order of elaboration
that satisfies the rules in Chapter 10 of the Ada Language Manual.

@item 
Generates a main program incorporating the given elaboration order.
This program is a small Ada package (body and spec) that
must be subsequently compiled
using the GNAT compiler. The necessary compilation step is usually
performed automatically by @emph{gnatlink}. The two most important
functions of this program
are to call the elaboration routines of units in an appropriate order
and to call the main program.

@item 
Determines the set of object files required by the given main program.
This information is output in the forms of comments in the generated program,
to be read by the @emph{gnatlink} utility used to link the Ada application.
@end itemize

@menu
* Running gnatbind:: 
* Switches for gnatbind:: 
* Command-Line Access:: 
* Search Paths for gnatbind:: 
* Examples of gnatbind Usage:: 

@end menu

@node Running gnatbind,Switches for gnatbind,,Binding with gnatbind
@anchor{gnat_ugn/building_executable_programs_with_gnat running-gnatbind}@anchor{120}@anchor{gnat_ugn/building_executable_programs_with_gnat id32}@anchor{121}
@subsection Running @cite{gnatbind}


The form of the @cite{gnatbind} command is

@example
$ gnatbind [`switches`] `mainprog`[.ali] [`switches`]
@end example

where @code{mainprog.adb} is the Ada file containing the main program
unit body. @cite{gnatbind} constructs an Ada
package in two files whose names are
@code{b~mainprog.ads}, and @code{b~mainprog.adb}.
For example, if given the
parameter @code{hello.ali}, for a main program contained in file
@code{hello.adb}, the binder output files would be @code{b~hello.ads}
and @code{b~hello.adb}.

When doing consistency checking, the binder takes into consideration
any source files it can locate. For example, if the binder determines
that the given main program requires the package @cite{Pack}, whose
@code{.ALI}
file is @code{pack.ali} and whose corresponding source spec file is
@code{pack.ads}, it attempts to locate the source file @code{pack.ads}
(using the same search path conventions as previously described for the
@emph{gcc} command). If it can locate this source file, it checks that
the time stamps
or source checksums of the source and its references to in @code{ALI} files
match. In other words, any @code{ALI} files that mentions this spec must have
resulted from compiling this version of the source file (or in the case
where the source checksums match, a version close enough that the
difference does not matter).

@geindex Source files
@geindex use by binder

The effect of this consistency checking, which includes source files, is
that the binder ensures that the program is consistent with the latest
version of the source files that can be located at bind time. Editing a
source file without compiling files that depend on the source file cause
error messages to be generated by the binder.

For example, suppose you have a main program @code{hello.adb} and a
package @cite{P}, from file @code{p.ads} and you perform the following
steps:


@itemize *

@item 
Enter @cite{gcc -c hello.adb} to compile the main program.

@item 
Enter @cite{gcc -c p.ads} to compile package @cite{P}.

@item 
Edit file @code{p.ads}.

@item 
Enter @cite{gnatbind hello}.
@end itemize

At this point, the file @code{p.ali} contains an out-of-date time stamp
because the file @code{p.ads} has been edited. The attempt at binding
fails, and the binder generates the following error messages:

@example
error: "hello.adb" must be recompiled ("p.ads" has been modified)
error: "p.ads" has been modified and must be recompiled
@end example

Now both files must be recompiled as indicated, and then the bind can
succeed, generating a main program. You need not normally be concerned
with the contents of this file, but for reference purposes a sample
binder output file is given in @ref{10,,Example of Binder Output File}.

In most normal usage, the default mode of @emph{gnatbind} which is to
generate the main package in Ada, as described in the previous section.
In particular, this means that any Ada programmer can read and understand
the generated main program. It can also be debugged just like any other
Ada code provided the @emph{-g} switch is used for
@emph{gnatbind} and @emph{gnatlink}.

@node Switches for gnatbind,Command-Line Access,Running gnatbind,Binding with gnatbind
@anchor{gnat_ugn/building_executable_programs_with_gnat id33}@anchor{122}@anchor{gnat_ugn/building_executable_programs_with_gnat switches-for-gnatbind}@anchor{123}
@subsection Switches for @emph{gnatbind}


The following switches are available with @cite{gnatbind}; details will
be presented in subsequent sections.

@geindex --version (gnatbind)


@table @asis

@item @code{--version}

Display Copyright and version, then exit disregarding all other options.
@end table

@geindex --help (gnatbind)


@table @asis

@item @code{--help}

If @emph{--version} was not used, display usage, then exit disregarding
all other options.
@end table

@geindex -a (gnatbind)


@table @asis

@item @code{-a}

Indicates that, if supported by the platform, the adainit procedure should
be treated as an initialisation routine by the linker (a constructor). This
is intended to be used by the Project Manager to automatically initialize
shared Stand-Alone Libraries.
@end table

@geindex -aO (gnatbind)


@table @asis

@item @code{-aO}

Specify directory to be searched for ALI files.
@end table

@geindex -aI (gnatbind)


@table @asis

@item @code{-aI}

Specify directory to be searched for source file.
@end table

@geindex -A (gnatbind)


@table @asis

@item @code{-A[=@emph{filename}]}

Output ALI list (to standard output or to the named file).
@end table

@geindex -b (gnatbind)


@table @asis

@item @code{-b}

Generate brief messages to @code{stderr} even if verbose mode set.
@end table

@geindex -c (gnatbind)


@table @asis

@item @code{-c}

Check only, no generation of binder output file.
@end table

@geindex -dnn[k|m] (gnatbind)


@table @asis

@item @code{-d@emph{nn}[k|m]}

This switch can be used to change the default task stack size value
to a specified size @cite{nn}, which is expressed in bytes by default, or
in kilobytes when suffixed with @cite{k} or in megabytes when suffixed
with @cite{m}.
In the absence of a @code{[k|m]} suffix, this switch is equivalent,
in effect, to completing all task specs with

@example
pragma Storage_Size (nn);
@end example

When they do not already have such a pragma.
@end table

@geindex -D (gnatbind)


@table @asis

@item @code{-D@emph{nn}[k|m]}

This switch can be used to change the default secondary stack size value
to a specified size @cite{nn}, which is expressed in bytes by default, or
in kilobytes when suffixed with @cite{k} or in megabytes when suffixed
with @cite{m}.

The secondary stack is used to deal with functions that return a variable
sized result, for example a function returning an unconstrained
String. There are two ways in which this secondary stack is allocated.

For most targets, the secondary stack is growing on demand and is allocated
as a chain of blocks in the heap. The -D option is not very
relevant. It only give some control over the size of the allocated
blocks (whose size is the minimum of the default secondary stack size value,
and the actual size needed for the current allocation request).

For certain targets, notably VxWorks 653,
the secondary stack is allocated by carving off a fixed ratio chunk of the
primary task stack. The -D option is used to define the
size of the environment task's secondary stack.
@end table

@geindex -e (gnatbind)


@table @asis

@item @code{-e}

Output complete list of elaboration-order dependencies.
@end table

@geindex -E (gnatbind)


@table @asis

@item @code{-E}

Store tracebacks in exception occurrences when the target supports it.

See also the packages @cite{GNAT.Traceback} and
@cite{GNAT.Traceback.Symbolic} for more information.
Note that on x86 ports, you must not use @emph{-fomit-frame-pointer}
@emph{gcc} option.
@end table

@geindex -F (gnatbind)


@table @asis

@item @code{-F}

Force the checks of elaboration flags. @emph{gnatbind} does not normally
generate checks of elaboration flags for the main executable, except when
a Stand-Alone Library is used. However, there are cases when this cannot be
detected by gnatbind. An example is importing an interface of a Stand-Alone
Library through a pragma Import and only specifying through a linker switch
this Stand-Alone Library. This switch is used to guarantee that elaboration
flag checks are generated.
@end table

@geindex -h (gnatbind)


@table @asis

@item @code{-h}

Output usage (help) information

@geindex -H32 (gnatbind)

@item @code{-H32}

Use 32-bit allocations for @cite{__gnat_malloc} (and thus for access types).
For further details see @ref{124,,Dynamic Allocation Control}.

@geindex -H64 (gnatbind)

@geindex __gnat_malloc

@item @code{-H64}

Use 64-bit allocations for @cite{__gnat_malloc} (and thus for access types).
For further details see @ref{124,,Dynamic Allocation Control}.

@geindex -I (gnatbind)

@item @code{-I}

Specify directory to be searched for source and ALI files.

@geindex -I- (gnatbind)

@item @code{-I-}

Do not look for sources in the current directory where @cite{gnatbind} was
invoked, and do not look for ALI files in the directory containing the
ALI file named in the @cite{gnatbind} command line.

@geindex -l (gnatbind)

@item @code{-l}

Output chosen elaboration order.

@geindex -L (gnatbind)

@item @code{-L@emph{xxx}}

Bind the units for library building. In this case the adainit and
adafinal procedures (@ref{ba,,Binding with Non-Ada Main Programs})
are renamed to @cite{xxx`init and `xxx`final. Implies -n. (:ref:`GNAT_and_Libraries}, for more details.)

@geindex -M (gnatbind)

@item @code{-M@emph{xyz}}

Rename generated main program from main to xyz. This option is
supported on cross environments only.

@geindex -m (gnatbind)

@item @code{-m@emph{n}}

Limit number of detected errors or warnings to @cite{n}, where @cite{n} is
in the range 1..999999. The default value if no switch is
given is 9999. If the number of warnings reaches this limit, then a
message is output and further warnings are suppressed, the bind
continues in this case. If the number of errors reaches this
limit, then a message is output and the bind is abandoned.
A value of zero means that no limit is enforced. The equal
sign is optional.

@geindex -n (gnatbind)

@item @code{-n}

No main program.

@geindex -nostdinc (gnatbind)

@item @code{-nostdinc}

Do not look for sources in the system default directory.

@geindex -nostdlib (gnatbind)

@item @code{-nostdlib}

Do not look for library files in the system default directory.

@geindex --RTS (gnatbind)

@item @code{--RTS=@emph{rts-path}}

Specifies the default location of the runtime library. Same meaning as the
equivalent @emph{gnatmake} flag (@ref{df,,Switches for gnatmake}).

@geindex -o (gnatbind)

@item @code{-o @emph{file}}

Name the output file @cite{file} (default is @code{b~`xxx}.adb`).
Note that if this option is used, then linking must be done manually,
gnatlink cannot be used.

@geindex -O (gnatbind)

@item @code{-O[=@emph{filename}]}

Output object list (to standard output or to the named file).

@geindex -p (gnatbind)

@item @code{-p}

Pessimistic (worst-case) elaboration order

@geindex -P (gnatbind)

@item @code{-P}

Generate binder file suitable for CodePeer.

@geindex -R (gnatbind)

@item @code{-R}

Output closure source list, which includes all non-run-time units that are
included in the bind.

@geindex -Ra (gnatbind)

@item @code{-Ra}

Like @emph{-R} but the list includes run-time units.

@geindex -s (gnatbind)

@item @code{-s}

Require all source files to be present.

@geindex -S (gnatbind)

@item @code{-S@emph{xxx}}

Specifies the value to be used when detecting uninitialized scalar
objects with pragma Initialize_Scalars.
The @cite{xxx} string specified with the switch is one of:


@itemize *

@item 
@code{in} for an invalid value*.

If zero is invalid for the discrete type in question,
then the scalar value is set to all zero bits.
For signed discrete types, the largest possible negative value of
the underlying scalar is set (i.e. a one bit followed by all zero bits).
For unsigned discrete types, the underlying scalar value is set to all
one bits. For floating-point types, a NaN value is set
(see body of package System.Scalar_Values for exact values).

@item 
@code{lo} for low value.

If zero is invalid for the discrete type in question,
then the scalar value is set to all zero bits.
For signed discrete types, the largest possible negative value of
the underlying scalar is set (i.e. a one bit followed by all zero bits).
For unsigned discrete types, the underlying scalar value is set to all
zero bits. For floating-point, a small value is set
(see body of package System.Scalar_Values for exact values).

@item 
@code{hi} for high value.

If zero is invalid for the discrete type in question,
then the scalar value is set to all one bits.
For signed discrete types, the largest possible positive value of
the underlying scalar is set (i.e. a zero bit followed by all one bits).
For unsigned discrete types, the underlying scalar value is set to all
one bits. For floating-point, a large value is set
(see body of package System.Scalar_Values for exact values).

@item 
@cite{xx} for hex value (two hex digits).

The underlying scalar is set to a value consisting of repeated bytes, whose
value corresponds to the given value. For example if @code{BF} is given,
then a 32-bit scalar value will be set to the bit patterm @code{16#BFBFBFBF#}.
@end itemize

@geindex GNAT_INIT_SCALARS

In addition, you can specify @emph{-Sev} to indicate that the value is
to be set at run time. In this case, the program will look for an environment
variable of the form @code{GNAT_INIT_SCALARS=@emph{yy}}, where @cite{yy} is one
of @emph{in/lo/hi/`xx*` with the same meanings as above.
If no environment variable is found, or if it does not have a valid value,
then the default is *in} (invalid values).
@end table

@geindex -static (gnatbind)


@table @asis

@item @code{-static}

Link against a static GNAT run time.

@geindex -shared (gnatbind)

@item @code{-shared}

Link against a shared GNAT run time when available.

@geindex -t (gnatbind)

@item @code{-t}

Tolerate time stamp and other consistency errors

@geindex -T (gnatbind)

@item @code{-T@emph{n}}

Set the time slice value to @cite{n} milliseconds. If the system supports
the specification of a specific time slice value, then the indicated value
is used. If the system does not support specific time slice values, but
does support some general notion of round-robin scheduling, then any
nonzero value will activate round-robin scheduling.

A value of zero is treated specially. It turns off time
slicing, and in addition, indicates to the tasking run time that the
semantics should match as closely as possible the Annex D
requirements of the Ada RM, and in particular sets the default
scheduling policy to @cite{FIFO_Within_Priorities}.

@geindex -u (gnatbind)

@item @code{-u@emph{n}}

Enable dynamic stack usage, with @cite{n} results stored and displayed
at program termination. A result is generated when a task
terminates. Results that can't be stored are displayed on the fly, at
task termination. This option is currently not supported on Itanium
platforms. (See @ref{125,,Dynamic Stack Usage Analysis} for details.)

@geindex -v (gnatbind)

@item @code{-v}

Verbose mode. Write error messages, header, summary output to
@code{stdout}.

@geindex -w (gnatbind)

@item @code{-w@emph{x}}

Warning mode; @cite{x} = s/e for suppress/treat as error

@geindex -Wx (gnatbind)

@item @code{-Wx@emph{e}}

Override default wide character encoding for standard Text_IO files.

@geindex -x (gnatbind)

@item @code{-x}

Exclude source files (check object consistency only).

@geindex -Xnnn (gnatbind)

@item @code{-X@emph{nnn}}

Set default exit status value, normally 0 for POSIX compliance.

@geindex -y (gnatbind)

@item @code{-y}

Enable leap seconds support in @cite{Ada.Calendar} and its children.

@geindex -z (gnatbind)

@item @code{-z}

No main subprogram.
@end table

You may obtain this listing of switches by running @cite{gnatbind} with
no arguments.

@menu
* Consistency-Checking Modes:: 
* Binder Error Message Control:: 
* Elaboration Control:: 
* Output Control:: 
* Dynamic Allocation Control:: 
* Binding with Non-Ada Main Programs:: 
* Binding Programs with No Main Subprogram:: 

@end menu

@node Consistency-Checking Modes,Binder Error Message Control,,Switches for gnatbind
@anchor{gnat_ugn/building_executable_programs_with_gnat consistency-checking-modes}@anchor{126}@anchor{gnat_ugn/building_executable_programs_with_gnat id34}@anchor{127}
@subsubsection Consistency-Checking Modes


As described earlier, by default @cite{gnatbind} checks
that object files are consistent with one another and are consistent
with any source files it can locate. The following switches control binder
access to sources.

@quotation

@geindex -s (gnatbind)
@end quotation


@table @asis

@item @code{-s}

Require source files to be present. In this mode, the binder must be
able to locate all source files that are referenced, in order to check
their consistency. In normal mode, if a source file cannot be located it
is simply ignored. If you specify this switch, a missing source
file is an error.

@geindex -Wx (gnatbind)

@item @code{-Wx@emph{e}}

Override default wide character encoding for standard Text_IO files.
Normally the default wide character encoding method used for standard
[Wide_[Wide_]]Text_IO files is taken from the encoding specified for
the main source input (see description of switch
@emph{-gnatWx} for the compiler). The
use of this switch for the binder (which has the same set of
possible arguments) overrides this default as specified.

@geindex -x (gnatbind)

@item @code{-x}

Exclude source files. In this mode, the binder only checks that ALI
files are consistent with one another. Source files are not accessed.
The binder runs faster in this mode, and there is still a guarantee that
the resulting program is self-consistent.
If a source file has been edited since it was last compiled, and you
specify this switch, the binder will not detect that the object
file is out of date with respect to the source file. Note that this is the
mode that is automatically used by @emph{gnatmake} because in this
case the checking against sources has already been performed by
@emph{gnatmake} in the course of compilation (i.e., before binding).
@end table

@node Binder Error Message Control,Elaboration Control,Consistency-Checking Modes,Switches for gnatbind
@anchor{gnat_ugn/building_executable_programs_with_gnat id35}@anchor{128}@anchor{gnat_ugn/building_executable_programs_with_gnat binder-error-message-control}@anchor{129}
@subsubsection Binder Error Message Control


The following switches provide control over the generation of error
messages from the binder:

@quotation

@geindex -v (gnatbind)
@end quotation


@table @asis

@item @code{-v}

Verbose mode. In the normal mode, brief error messages are generated to
@code{stderr}. If this switch is present, a header is written
to @code{stdout} and any error messages are directed to @code{stdout}.
All that is written to @code{stderr} is a brief summary message.

@geindex -b (gnatbind)

@item @code{-b}

Generate brief error messages to @code{stderr} even if verbose mode is
specified. This is relevant only when used with the
@emph{-v} switch.

@geindex -m (gnatbind)

@item @code{-m@emph{n}}

Limits the number of error messages to @cite{n}, a decimal integer in the
range 1-999. The binder terminates immediately if this limit is reached.

@geindex -M (gnatbind)

@item @code{-M@emph{xxx}}

Renames the generated main program from @cite{main} to @cite{xxx}.
This is useful in the case of some cross-building environments, where
the actual main program is separate from the one generated
by @cite{gnatbind}.

@geindex -ws (gnatbind)

@geindex Warnings

@item @code{-ws}

Suppress all warning messages.

@geindex -we (gnatbind)

@item @code{-we}

Treat any warning messages as fatal errors.

@geindex -t (gnatbind)

@geindex Time stamp checks
@geindex in binder

@geindex Binder consistency checks

@geindex Consistency checks
@geindex in binder

@item @code{-t}

The binder performs a number of consistency checks including:


@itemize *

@item 
Check that time stamps of a given source unit are consistent

@item 
Check that checksums of a given source unit are consistent

@item 
Check that consistent versions of @cite{GNAT} were used for compilation

@item 
Check consistency of configuration pragmas as required
@end itemize

Normally failure of such checks, in accordance with the consistency
requirements of the Ada Reference Manual, causes error messages to be
generated which abort the binder and prevent the output of a binder
file and subsequent link to obtain an executable.

The @emph{-t} switch converts these error messages
into warnings, so that
binding and linking can continue to completion even in the presence of such
errors. The result may be a failed link (due to missing symbols), or a
non-functional executable which has undefined semantics.

@cartouche
@quotation Note 
This means that @emph{-t} should be used only in unusual situations,
with extreme care.
@end quotation
@end cartouche
@end table

@node Elaboration Control,Output Control,Binder Error Message Control,Switches for gnatbind
@anchor{gnat_ugn/building_executable_programs_with_gnat id36}@anchor{12a}@anchor{gnat_ugn/building_executable_programs_with_gnat elaboration-control}@anchor{12b}
@subsubsection Elaboration Control


The following switches provide additional control over the elaboration
order. For full details see @ref{11,,Elaboration Order Handling in GNAT}.

@quotation

@geindex -p (gnatbind)
@end quotation


@table @asis

@item @code{-p}

Normally the binder attempts to choose an elaboration order that is
likely to minimize the likelihood of an elaboration order error resulting
in raising a @cite{Program_Error} exception. This switch reverses the
action of the binder, and requests that it deliberately choose an order
that is likely to maximize the likelihood of an elaboration error.
This is useful in ensuring portability and avoiding dependence on
accidental fortuitous elaboration ordering.

Normally it only makes sense to use the @emph{-p}
switch if dynamic
elaboration checking is used (@emph{-gnatE} switch used for compilation).
This is because in the default static elaboration mode, all necessary
@cite{Elaborate} and @cite{Elaborate_All} pragmas are implicitly inserted.
These implicit pragmas are still respected by the binder in
@emph{-p} mode, so a
safe elaboration order is assured.

Note that @emph{-p} is not intended for
production use; it is more for debugging/experimental use.
@end table

@node Output Control,Dynamic Allocation Control,Elaboration Control,Switches for gnatbind
@anchor{gnat_ugn/building_executable_programs_with_gnat output-control}@anchor{12c}@anchor{gnat_ugn/building_executable_programs_with_gnat id37}@anchor{12d}
@subsubsection Output Control


The following switches allow additional control over the output
generated by the binder.

@quotation

@geindex -c (gnatbind)
@end quotation


@table @asis

@item @code{-c}

Check only. Do not generate the binder output file. In this mode the
binder performs all error checks but does not generate an output file.

@geindex -e (gnatbind)

@item @code{-e}

Output complete list of elaboration-order dependencies, showing the
reason for each dependency. This output can be rather extensive but may
be useful in diagnosing problems with elaboration order. The output is
written to @code{stdout}.

@geindex -h (gnatbind)

@item @code{-h}

Output usage information. The output is written to @code{stdout}.

@geindex -K (gnatbind)

@item @code{-K}

Output linker options to @code{stdout}. Includes library search paths,
contents of pragmas Ident and Linker_Options, and libraries added
by @cite{gnatbind}.

@geindex -l (gnatbind)

@item @code{-l}

Output chosen elaboration order. The output is written to @code{stdout}.

@geindex -O (gnatbind)

@item @code{-O}

Output full names of all the object files that must be linked to provide
the Ada component of the program. The output is written to @code{stdout}.
This list includes the files explicitly supplied and referenced by the user
as well as implicitly referenced run-time unit files. The latter are
omitted if the corresponding units reside in shared libraries. The
directory names for the run-time units depend on the system configuration.

@geindex -o (gnatbind)

@item @code{-o @emph{file}}

Set name of output file to @cite{file} instead of the normal
@code{b~`mainprog}.adb` default. Note that @cite{file} denote the Ada
binder generated body filename.
Note that if this option is used, then linking must be done manually.
It is not possible to use gnatlink in this case, since it cannot locate
the binder file.

@geindex -r (gnatbind)

@item @code{-r}

Generate list of @cite{pragma Restrictions} that could be applied to
the current unit. This is useful for code audit purposes, and also may
be used to improve code generation in some cases.
@end table

@node Dynamic Allocation Control,Binding with Non-Ada Main Programs,Output Control,Switches for gnatbind
@anchor{gnat_ugn/building_executable_programs_with_gnat dynamic-allocation-control}@anchor{124}@anchor{gnat_ugn/building_executable_programs_with_gnat id38}@anchor{12e}
@subsubsection Dynamic Allocation Control


The heap control switches -- @emph{-H32} and @emph{-H64} --
determine whether dynamic allocation uses 32-bit or 64-bit memory.
They only affect compiler-generated allocations via @cite{__gnat_malloc};
explicit calls to @cite{malloc} and related functions from the C
run-time library are unaffected.


@table @asis

@item @code{-H32}

Allocate memory on 32-bit heap

@item @code{-H64}

Allocate memory on 64-bit heap.  This is the default
unless explicitly overridden by a @cite{'Size} clause on the access type.
@end table

These switches are only effective on VMS platforms.

@node Binding with Non-Ada Main Programs,Binding Programs with No Main Subprogram,Dynamic Allocation Control,Switches for gnatbind
@anchor{gnat_ugn/building_executable_programs_with_gnat binding-with-non-ada-main-programs}@anchor{ba}@anchor{gnat_ugn/building_executable_programs_with_gnat id39}@anchor{12f}
@subsubsection Binding with Non-Ada Main Programs


The description so far has assumed that the main
program is in Ada, and that the task of the binder is to generate a
corresponding function @cite{main} that invokes this Ada main
program. GNAT also supports the building of executable programs where
the main program is not in Ada, but some of the called routines are
written in Ada and compiled using GNAT (@ref{46,,Mixed Language Programming}).
The following switch is used in this situation:

@quotation

@geindex -n (gnatbind)
@end quotation


@table @asis

@item @code{-n}

No main program. The main program is not in Ada.
@end table

In this case, most of the functions of the binder are still required,
but instead of generating a main program, the binder generates a file
containing the following callable routines:

@quotation

@geindex adainit


@table @asis

@item @emph{adainit}

You must call this routine to initialize the Ada part of the program by
calling the necessary elaboration routines. A call to @cite{adainit} is
required before the first call to an Ada subprogram.

Note that it is assumed that the basic execution environment must be setup
to be appropriate for Ada execution at the point where the first Ada
subprogram is called. In particular, if the Ada code will do any
floating-point operations, then the FPU must be setup in an appropriate
manner. For the case of the x86, for example, full precision mode is
required. The procedure GNAT.Float_Control.Reset may be used to ensure
that the FPU is in the right state.
@end table

@geindex adafinal


@table @asis

@item @emph{adafinal}

You must call this routine to perform any library-level finalization
required by the Ada subprograms. A call to @cite{adafinal} is required
after the last call to an Ada subprogram, and before the program
terminates.
@end table
@end quotation

@geindex -n (gnatbind)

@geindex Binder
@geindex multiple input files

If the @emph{-n} switch
is given, more than one ALI file may appear on
the command line for @cite{gnatbind}. The normal @emph{closure}
calculation is performed for each of the specified units. Calculating
the closure means finding out the set of units involved by tracing
@emph{with} references. The reason it is necessary to be able to
specify more than one ALI file is that a given program may invoke two or
more quite separate groups of Ada units.

The binder takes the name of its output file from the last specified ALI
file, unless overridden by the use of the @emph{-o file}.

@geindex -o (gnatbind)

The output is an Ada unit in source form that can be compiled with GNAT.
This compilation occurs automatically as part of the @emph{gnatlink}
processing.

Currently the GNAT run time requires a FPU using 80 bits mode
precision. Under targets where this is not the default it is required to
call GNAT.Float_Control.Reset before using floating point numbers (this
include float computation, float input and output) in the Ada code. A
side effect is that this could be the wrong mode for the foreign code
where floating point computation could be broken after this call.

@node Binding Programs with No Main Subprogram,,Binding with Non-Ada Main Programs,Switches for gnatbind
@anchor{gnat_ugn/building_executable_programs_with_gnat binding-programs-with-no-main-subprogram}@anchor{130}@anchor{gnat_ugn/building_executable_programs_with_gnat id40}@anchor{131}
@subsubsection Binding Programs with No Main Subprogram


It is possible to have an Ada program which does not have a main
subprogram. This program will call the elaboration routines of all the
packages, then the finalization routines.

The following switch is used to bind programs organized in this manner:

@quotation

@geindex -z (gnatbind)
@end quotation


@table @asis

@item @code{-z}

Normally the binder checks that the unit name given on the command line
corresponds to a suitable main subprogram. When this switch is used,
a list of ALI files can be given, and the execution of the program
consists of elaboration of these units in an appropriate order. Note
that the default wide character encoding method for standard Text_IO
files is always set to Brackets if this switch is set (you can use
the binder switch
@emph{-Wx} to override this default).
@end table

@node Command-Line Access,Search Paths for gnatbind,Switches for gnatbind,Binding with gnatbind
@anchor{gnat_ugn/building_executable_programs_with_gnat id41}@anchor{132}@anchor{gnat_ugn/building_executable_programs_with_gnat command-line-access}@anchor{133}
@subsection Command-Line Access


The package @cite{Ada.Command_Line} provides access to the command-line
arguments and program name. In order for this interface to operate
correctly, the two variables

@example
int gnat_argc;
char **gnat_argv;
@end example

@geindex gnat_argv

@geindex gnat_argc

are declared in one of the GNAT library routines. These variables must
be set from the actual @cite{argc} and @cite{argv} values passed to the
main program. With no @emph{n} present, @cite{gnatbind}
generates the C main program to automatically set these variables.
If the @emph{n} switch is used, there is no automatic way to
set these variables. If they are not set, the procedures in
@cite{Ada.Command_Line} will not be available, and any attempt to use
them will raise @cite{Constraint_Error}. If command line access is
required, your main program must set @cite{gnat_argc} and
@cite{gnat_argv} from the @cite{argc} and @cite{argv} values passed to
it.

@node Search Paths for gnatbind,Examples of gnatbind Usage,Command-Line Access,Binding with gnatbind
@anchor{gnat_ugn/building_executable_programs_with_gnat search-paths-for-gnatbind}@anchor{91}@anchor{gnat_ugn/building_executable_programs_with_gnat id42}@anchor{134}
@subsection Search Paths for @cite{gnatbind}


The binder takes the name of an ALI file as its argument and needs to
locate source files as well as other ALI files to verify object consistency.

For source files, it follows exactly the same search rules as @emph{gcc}
(see @ref{8e,,Search Paths and the Run-Time Library (RTL)}). For ALI files the
directories searched are:


@itemize *

@item 
The directory containing the ALI file named in the command line, unless
the switch @emph{-I-} is specified.

@item 
All directories specified by @emph{-I}
switches on the @cite{gnatbind}
command line, in the order given.

@geindex ADA_PRJ_OBJECTS_FILE

@item 
Each of the directories listed in the text file whose name is given
by the 
@geindex ADA_PRJ_OBJECTS_FILE
@geindex environment variable; ADA_PRJ_OBJECTS_FILE
@code{ADA_PRJ_OBJECTS_FILE} environment variable.

@geindex ADA_PRJ_OBJECTS_FILE
@geindex environment variable; ADA_PRJ_OBJECTS_FILE
@code{ADA_PRJ_OBJECTS_FILE} is normally set by gnatmake or by the gnat
driver when project files are used. It should not normally be set
by other means.

@geindex ADA_OBJECTS_PATH

@item 
Each of the directories listed in the value of the
@geindex ADA_OBJECTS_PATH
@geindex environment variable; ADA_OBJECTS_PATH
@code{ADA_OBJECTS_PATH} environment variable.
Construct this value
exactly as the 
@geindex PATH
@geindex environment variable; PATH
@code{PATH} environment variable: a list of directory
names separated by colons (semicolons when working with the NT version
of GNAT).

@item 
The content of the @code{ada_object_path} file which is part of the GNAT
installation tree and is used to store standard libraries such as the
GNAT Run Time Library (RTL) unless the switch @emph{-nostdlib} is
specified. See @ref{8b,,Installing a library}
@end itemize

@geindex -I (gnatbind)

@geindex -aI (gnatbind)

@geindex -aO (gnatbind)

In the binder the switch @emph{-I}
is used to specify both source and
library file paths. Use @emph{-aI}
instead if you want to specify
source paths only, and @emph{-aO}
if you want to specify library paths
only. This means that for the binder
@code{-I@emph{dir}} is equivalent to
@code{-aI@emph{dir}}
@code{-aO`@emph{dir}}.
The binder generates the bind file (a C language source file) in the
current working directory.

@geindex Ada

@geindex System

@geindex Interfaces

@geindex GNAT

The packages @cite{Ada}, @cite{System}, and @cite{Interfaces} and their
children make up the GNAT Run-Time Library, together with the package
GNAT and its children, which contain a set of useful additional
library functions provided by GNAT. The sources for these units are
needed by the compiler and are kept together in one directory. The ALI
files and object files generated by compiling the RTL are needed by the
binder and the linker and are kept together in one directory, typically
different from the directory containing the sources. In a normal
installation, you need not specify these directory names when compiling
or binding. Either the environment variables or the built-in defaults
cause these files to be found.

Besides simplifying access to the RTL, a major use of search paths is
in compiling sources from multiple directories. This can make
development environments much more flexible.

@node Examples of gnatbind Usage,,Search Paths for gnatbind,Binding with gnatbind
@anchor{gnat_ugn/building_executable_programs_with_gnat examples-of-gnatbind-usage}@anchor{135}@anchor{gnat_ugn/building_executable_programs_with_gnat id43}@anchor{136}
@subsection Examples of @cite{gnatbind} Usage


Here are some examples of @cite{gnatbind} invovations:

@quotation

@example
gnatbind hello
@end example

The main program @cite{Hello} (source program in @code{hello.adb}) is
bound using the standard switch settings. The generated main program is
@code{b~hello.adb}. This is the normal, default use of the binder.

@example
gnatbind hello -o mainprog.adb
@end example

The main program @cite{Hello} (source program in @code{hello.adb}) is
bound using the standard switch settings. The generated main program is
@code{mainprog.adb} with the associated spec in
@code{mainprog.ads}. Note that you must specify the body here not the
spec. Note that if this option is used, then linking must be done manually,
since gnatlink will not be able to find the generated file.
@end quotation

@node Linking with gnatlink,Using the GNU make Utility,Binding with gnatbind,Building Executable Programs with GNAT
@anchor{gnat_ugn/building_executable_programs_with_gnat id44}@anchor{137}@anchor{gnat_ugn/building_executable_programs_with_gnat linking-with-gnatlink}@anchor{20}
@section Linking with @emph{gnatlink}


@c index: ! gnatlink

This chapter discusses @emph{gnatlink}, a tool that links
an Ada program and builds an executable file. This utility
invokes the system linker (via the @emph{gcc} command)
with a correct list of object files and library references.
@emph{gnatlink} automatically determines the list of files and
references for the Ada part of a program. It uses the binder file
generated by the @emph{gnatbind} to determine this list.

Note: to invoke @cite{gnatlink} with a project file, use the @cite{gnat}
driver (see @ref{11f,,The GNAT Driver and Project Files}).

@menu
* Running gnatlink:: 
* Switches for gnatlink:: 

@end menu

@node Running gnatlink,Switches for gnatlink,,Linking with gnatlink
@anchor{gnat_ugn/building_executable_programs_with_gnat id45}@anchor{138}@anchor{gnat_ugn/building_executable_programs_with_gnat running-gnatlink}@anchor{139}
@subsection Running @emph{gnatlink}


The form of the @emph{gnatlink} command is

@example
$ gnatlink [`switches`] `mainprog`[.ali]
           [`non-Ada objects`] [`linker options`]
@end example

The arguments of @emph{gnatlink} (switches, main @code{ALI} file,
non-Ada objects
or linker options) may be in any order, provided that no non-Ada object may
be mistaken for a main @code{ALI} file.
Any file name @code{F} without the @code{.ali}
extension will be taken as the main @code{ALI} file if a file exists
whose name is the concatenation of @code{F} and @code{.ali}.

@code{mainprog.ali} references the ALI file of the main program.
The @code{.ali} extension of this file can be omitted. From this
reference, @emph{gnatlink} locates the corresponding binder file
@code{b~mainprog.adb} and, using the information in this file along
with the list of non-Ada objects and linker options, constructs a
linker command file to create the executable.

The arguments other than the @emph{gnatlink} switches and the main
@code{ALI} file are passed to the linker uninterpreted.
They typically include the names of
object files for units written in other languages than Ada and any library
references required to resolve references in any of these foreign language
units, or in @cite{Import} pragmas in any Ada units.

@cite{linker options} is an optional list of linker specific
switches.
The default linker called by gnatlink is @emph{gcc} which in
turn calls the appropriate system linker.

One useful option for the linker is @emph{-s}: it reduces the size of the
executable by removing all symbol table and relocation information from the
executable.

Standard options for the linker such as @emph{-lmy_lib} or
@emph{-Ldir} can be added as is.
For options that are not recognized by
@emph{gcc} as linker options, use the @emph{gcc} switches
@emph{-Xlinker} or @emph{-Wl,}.

Refer to the GCC documentation for
details.

Here is an example showing how to generate a linker map:

@example
$ gnatlink my_prog -Wl,-Map,MAPFILE
@end example

Using @cite{linker options} it is possible to set the program stack and
heap size.
See @ref{13a,,Setting Stack Size from gnatlink} and
@ref{13b,,Setting Heap Size from gnatlink}.

@emph{gnatlink} determines the list of objects required by the Ada
program and prepends them to the list of objects passed to the linker.
@emph{gnatlink} also gathers any arguments set by the use of
@cite{pragma Linker_Options} and adds them to the list of arguments
presented to the linker.

@node Switches for gnatlink,,Running gnatlink,Linking with gnatlink
@anchor{gnat_ugn/building_executable_programs_with_gnat id46}@anchor{13c}@anchor{gnat_ugn/building_executable_programs_with_gnat switches-for-gnatlink}@anchor{13d}
@subsection Switches for @emph{gnatlink}


The following switches are available with the @emph{gnatlink} utility:

@geindex --version (gnatlink)


@table @asis

@item @code{--version}

Display Copyright and version, then exit disregarding all other options.
@end table

@geindex --help (gnatlink)


@table @asis

@item @code{--help}

If @emph{--version} was not used, display usage, then exit disregarding
all other options.
@end table

@geindex Command line length

@geindex -f (gnatlink)


@table @asis

@item @code{-f}

On some targets, the command line length is limited, and @emph{gnatlink}
will generate a separate file for the linker if the list of object files
is too long.
The @emph{-f} switch forces this file
to be generated even if
the limit is not exceeded. This is useful in some cases to deal with
special situations where the command line length is exceeded.
@end table

@geindex Debugging information
@geindex including

@geindex -g (gnatlink)


@table @asis

@item @code{-g}

The option to include debugging information causes the Ada bind file (in
other words, @code{b~mainprog.adb}) to be compiled with @emph{-g}.
In addition, the binder does not delete the @code{b~mainprog.adb},
@code{b~mainprog.o} and @code{b~mainprog.ali} files.
Without @emph{-g}, the binder removes these files by default.
@end table

@geindex -n (gnatlink)


@table @asis

@item @code{-n}

Do not compile the file generated by the binder. This may be used when
a link is rerun with different options, but there is no need to recompile
the binder file.
@end table

@geindex -v (gnatlink)


@table @asis

@item @code{-v}

Verbose mode. Causes additional information to be output, including a full
list of the included object files.
This switch option is most useful when you want
to see what set of object files are being used in the link step.
@end table

@geindex -v -v (gnatlink)


@table @asis

@item @code{-v -v}

Very verbose mode. Requests that the compiler operate in verbose mode when
it compiles the binder file, and that the system linker run in verbose mode.
@end table

@geindex -o (gnatlink)


@table @asis

@item @code{-o @emph{exec-name}}

@cite{exec-name} specifies an alternate name for the generated
executable program. If this switch is omitted, the executable has the same
name as the main unit. For example, @cite{gnatlink try.ali} creates
an executable called @code{try}.
@end table

@geindex -b (gnatlink)


@table @asis

@item @code{-b @emph{target}}

Compile your program to run on @cite{target}, which is the name of a
system configuration. You must have a GNAT cross-compiler built if
@cite{target} is not the same as your host system.
@end table

@geindex -B (gnatlink)


@table @asis

@item @code{-B@emph{dir}}

Load compiler executables (for example, @cite{gnat1}, the Ada compiler)
from @cite{dir} instead of the default location. Only use this switch
when multiple versions of the GNAT compiler are available.
See the @cite{Directory Options} section in @cite{The_GNU_Compiler_Collection}
for further details. You would normally use the @emph{-b} or
@emph{-V} switch instead.
@end table

@geindex -M (gnatlink)


@table @asis

@item @code{-M}

When linking an executable, create a map file. The name of the map file
has the same name as the executable with extension ".map".
@end table

@geindex -M= (gnatlink)


@table @asis

@item @code{-M=@emph{mapfile}}

When linking an executable, create a map file. The name of the map file is
@cite{mapfile}.
@end table

@geindex --GCC=compiler_name (gnatlink)


@table @asis

@item @code{--GCC=@emph{compiler_name}}

Program used for compiling the binder file. The default is
@code{gcc}. You need to use quotes around @cite{compiler_name} if
@cite{compiler_name} contains spaces or other separator characters.
As an example @code{--GCC="foo -x -y"} will instruct @emph{gnatlink} to
use @code{foo -x -y} as your compiler. Note that switch @code{-c} is always
inserted after your command name. Thus in the above example the compiler
command that will be used by @emph{gnatlink} will be @code{foo -c -x -y}.
A limitation of this syntax is that the name and path name of the executable
itself must not include any embedded spaces. If the compiler executable is
different from the default one (gcc or <prefix>-gcc), then the back-end
switches in the ALI file are not used to compile the binder generated source.
For example, this is the case with @code{--GCC="foo -x -y"}. But the back end
switches will be used for @code{--GCC="gcc -gnatv"}. If several
@code{--GCC=compiler_name} are used, only the last @cite{compiler_name}
is taken into account. However, all the additional switches are also taken
into account. Thus,
@code{--GCC="foo -x -y" --GCC="bar -z -t"} is equivalent to
@code{--GCC="bar -x -y -z -t"}.
@end table

@geindex --LINK= (gnatlink)


@table @asis

@item @code{--LINK=@emph{name}}

@cite{name} is the name of the linker to be invoked. This is especially
useful in mixed language programs since languages such as C++ require
their own linker to be used. When this switch is omitted, the default
name for the linker is @emph{gcc}. When this switch is used, the
specified linker is called instead of @emph{gcc} with exactly the same
parameters that would have been passed to @emph{gcc} so if the desired
linker requires different parameters it is necessary to use a wrapper
script that massages the parameters before invoking the real linker. It
may be useful to control the exact invocation by using the verbose
switch.
@end table

@node Using the GNU make Utility,,Linking with gnatlink,Building Executable Programs with GNAT
@anchor{gnat_ugn/building_executable_programs_with_gnat id47}@anchor{13e}@anchor{gnat_ugn/building_executable_programs_with_gnat using-the-gnu-make-utility}@anchor{21}
@section Using the GNU @cite{make} Utility


@geindex make (GNU)
@geindex GNU make

This chapter offers some examples of makefiles that solve specific
problems. It does not explain how to write a makefile, nor does it try to replace the
@emph{gnatmake} utility (@ref{1d,,Building with gnatmake}).

All the examples in this section are specific to the GNU version of
make. Although @emph{make} is a standard utility, and the basic language
is the same, these examples use some advanced features found only in
@cite{GNU make}.

@menu
* Using gnatmake in a Makefile:: 
* Automatically Creating a List of Directories:: 
* Generating the Command Line Switches:: 
* Overcoming Command Line Length Limits:: 

@end menu

@node Using gnatmake in a Makefile,Automatically Creating a List of Directories,,Using the GNU make Utility
@anchor{gnat_ugn/building_executable_programs_with_gnat using-gnatmake-in-a-makefile}@anchor{13f}@anchor{gnat_ugn/building_executable_programs_with_gnat id48}@anchor{140}
@subsection Using gnatmake in a Makefile


@c index makefile (GNU make)

Complex project organizations can be handled in a very powerful way by
using GNU make combined with gnatmake. For instance, here is a Makefile
which allows you to build each subsystem of a big project into a separate
shared library. Such a makefile allows you to significantly reduce the link
time of very big applications while maintaining full coherence at
each step of the build process.

The list of dependencies are handled automatically by
@emph{gnatmake}. The Makefile is simply used to call gnatmake in each of
the appropriate directories.

Note that you should also read the example on how to automatically
create the list of directories
(@ref{141,,Automatically Creating a List of Directories})
which might help you in case your project has a lot of subdirectories.

@example
## This Makefile is intended to be used with the following directory
## configuration:
##  - The sources are split into a series of csc (computer software components)
##    Each of these csc is put in its own directory.
##    Their name are referenced by the directory names.
##    They will be compiled into shared library (although this would also work
##    with static libraries
##  - The main program (and possibly other packages that do not belong to any
##    csc is put in the top level directory (where the Makefile is).
##       toplevel_dir __ first_csc  (sources) __ lib (will contain the library)
##                    \\_ second_csc (sources) __ lib (will contain the library)
##                    \\_ ...
## Although this Makefile is build for shared library, it is easy to modify
## to build partial link objects instead (modify the lines with -shared and
## gnatlink below)
##
## With this makefile, you can change any file in the system or add any new
## file, and everything will be recompiled correctly (only the relevant shared
## objects will be recompiled, and the main program will be re-linked).

# The list of computer software component for your project. This might be
# generated automatically.
CSC_LIST=aa bb cc

# Name of the main program (no extension)
MAIN=main

# If we need to build objects with -fPIC, uncomment the following line
#NEED_FPIC=-fPIC

# The following variable should give the directory containing libgnat.so
# You can get this directory through 'gnatls -v'. This is usually the last
# directory in the Object_Path.
GLIB=...

# The directories for the libraries
# (This macro expands the list of CSC to the list of shared libraries, you
# could simply use the expanded form:
# LIB_DIR=aa/lib/libaa.so bb/lib/libbb.so cc/lib/libcc.so
LIB_DIR=$@{foreach dir,$@{CSC_LIST@},$@{dir@}/lib/lib$@{dir@}.so@}

$@{MAIN@}: objects $@{LIB_DIR@}
    gnatbind $@{MAIN@} $@{CSC_LIST:%=-aO%/lib@} -shared
    gnatlink $@{MAIN@} $@{CSC_LIST:%=-l%@}

objects::
    # recompile the sources
    gnatmake -c -i $@{MAIN@}.adb $@{NEED_FPIC@} $@{CSC_LIST:%=-I%@}

# Note: In a future version of GNAT, the following commands will be simplified
# by a new tool, gnatmlib
$@{LIB_DIR@}:
    mkdir -p $@{dir $@@ @}
    cd $@{dir $@@ @} && gcc -shared -o $@{notdir $@@ @} ../*.o -L$@{GLIB@} -lgnat
    cd $@{dir $@@ @} && cp -f ../*.ali .

# The dependencies for the modules
# Note that we have to force the expansion of *.o, since in some cases
# make won't be able to do it itself.
aa/lib/libaa.so: $@{wildcard aa/*.o@}
bb/lib/libbb.so: $@{wildcard bb/*.o@}
cc/lib/libcc.so: $@{wildcard cc/*.o@}

# Make sure all of the shared libraries are in the path before starting the
# program
run::
    LD_LIBRARY_PATH=`pwd`/aa/lib:`pwd`/bb/lib:`pwd`/cc/lib ./$@{MAIN@}

clean::
    $@{RM@} -rf $@{CSC_LIST:%=%/lib@}
    $@{RM@} $@{CSC_LIST:%=%/*.ali@}
    $@{RM@} $@{CSC_LIST:%=%/*.o@}
    $@{RM@} *.o *.ali $@{MAIN@}
@end example

@node Automatically Creating a List of Directories,Generating the Command Line Switches,Using gnatmake in a Makefile,Using the GNU make Utility
@anchor{gnat_ugn/building_executable_programs_with_gnat automatically-creating-a-list-of-directories}@anchor{141}@anchor{gnat_ugn/building_executable_programs_with_gnat id49}@anchor{142}
@subsection Automatically Creating a List of Directories


In most makefiles, you will have to specify a list of directories, and
store it in a variable. For small projects, it is often easier to
specify each of them by hand, since you then have full control over what
is the proper order for these directories, which ones should be
included.

However, in larger projects, which might involve hundreds of
subdirectories, it might be more convenient to generate this list
automatically.

The example below presents two methods. The first one, although less
general, gives you more control over the list. It involves wildcard
characters, that are automatically expanded by @emph{make}. Its
shortcoming is that you need to explicitly specify some of the
organization of your project, such as for instance the directory tree
depth, whether some directories are found in a separate tree, etc.

The second method is the most general one. It requires an external
program, called @emph{find}, which is standard on all Unix systems. All
the directories found under a given root directory will be added to the
list.

@example
# The examples below are based on the following directory hierarchy:
# All the directories can contain any number of files
# ROOT_DIRECTORY ->  a  ->  aa  ->  aaa
#                       ->  ab
#                       ->  ac
#                ->  b  ->  ba  ->  baa
#                       ->  bb
#                       ->  bc
# This Makefile creates a variable called DIRS, that can be reused any time
# you need this list (see the other examples in this section)

# The root of your project's directory hierarchy
ROOT_DIRECTORY=.

####
# First method: specify explicitly the list of directories
# This allows you to specify any subset of all the directories you need.
####

DIRS := a/aa/ a/ab/ b/ba/

####
# Second method: use wildcards
# Note that the argument(s) to wildcard below should end with a '/'.
# Since wildcards also return file names, we have to filter them out
# to avoid duplicate directory names.
# We thus use make's `dir` and `sort` functions.
# It sets DIRs to the following value (note that the directories aaa and baa
# are not given, unless you change the arguments to wildcard).
# DIRS= ./a/a/ ./b/ ./a/aa/ ./a/ab/ ./a/ac/ ./b/ba/ ./b/bb/ ./b/bc/
####

DIRS := $@{sort $@{dir $@{wildcard $@{ROOT_DIRECTORY@}/*/
                    $@{ROOT_DIRECTORY@}/*/*/@}@}@}

####
# Third method: use an external program
# This command is much faster if run on local disks, avoiding NFS slowdowns.
# This is the most complete command: it sets DIRs to the following value:
# DIRS= ./a ./a/aa ./a/aa/aaa ./a/ab ./a/ac ./b ./b/ba ./b/ba/baa ./b/bb ./b/bc
####

DIRS := $@{shell find $@{ROOT_DIRECTORY@} -type d -print@}
@end example

@node Generating the Command Line Switches,Overcoming Command Line Length Limits,Automatically Creating a List of Directories,Using the GNU make Utility
@anchor{gnat_ugn/building_executable_programs_with_gnat id50}@anchor{143}@anchor{gnat_ugn/building_executable_programs_with_gnat generating-the-command-line-switches}@anchor{144}
@subsection Generating the Command Line Switches


Once you have created the list of directories as explained in the
previous section (@ref{141,,Automatically Creating a List of Directories}),
you can easily generate the command line arguments to pass to gnatmake.

For the sake of completeness, this example assumes that the source path
is not the same as the object path, and that you have two separate lists
of directories.

@example
# see "Automatically creating a list of directories" to create
# these variables
SOURCE_DIRS=
OBJECT_DIRS=

GNATMAKE_SWITCHES := $@{patsubst %,-aI%,$@{SOURCE_DIRS@}@}
GNATMAKE_SWITCHES += $@{patsubst %,-aO%,$@{OBJECT_DIRS@}@}

all:
        gnatmake $@{GNATMAKE_SWITCHES@} main_unit
@end example

@node Overcoming Command Line Length Limits,,Generating the Command Line Switches,Using the GNU make Utility
@anchor{gnat_ugn/building_executable_programs_with_gnat overcoming-command-line-length-limits}@anchor{145}@anchor{gnat_ugn/building_executable_programs_with_gnat id51}@anchor{146}
@subsection Overcoming Command Line Length Limits


One problem that might be encountered on big projects is that many
operating systems limit the length of the command line. It is thus hard to give
gnatmake the list of source and object directories.

This example shows how you can set up environment variables, which will
make @emph{gnatmake} behave exactly as if the directories had been
specified on the command line, but have a much higher length limit (or
even none on most systems).

It assumes that you have created a list of directories in your Makefile,
using one of the methods presented in
@ref{141,,Automatically Creating a List of Directories}.
For the sake of completeness, we assume that the object
path (where the ALI files are found) is different from the sources patch.

Note a small trick in the Makefile below: for efficiency reasons, we
create two temporary variables (SOURCE_LIST and OBJECT_LIST), that are
expanded immediately by @cite{make}. This way we overcome the standard
make behavior which is to expand the variables only when they are
actually used.

On Windows, if you are using the standard Windows command shell, you must
replace colons with semicolons in the assignments to these variables.

@example
# In this example, we create both ADA_INCLUDE_PATH and ADA_OBJECTS_PATH.
# This is the same thing as putting the -I arguments on the command line.
# (the equivalent of using -aI on the command line would be to define
#  only ADA_INCLUDE_PATH, the equivalent of -aO is ADA_OBJECTS_PATH).
# You can of course have different values for these variables.
#
# Note also that we need to keep the previous values of these variables, since
# they might have been set before running 'make' to specify where the GNAT
# library is installed.

# see "Automatically creating a list of directories" to create these
# variables
SOURCE_DIRS=
OBJECT_DIRS=

empty:=
space:=$@{empty@} $@{empty@}
SOURCE_LIST := $@{subst $@{space@},:,$@{SOURCE_DIRS@}@}
OBJECT_LIST := $@{subst $@{space@},:,$@{OBJECT_DIRS@}@}
ADA_INCLUDE_PATH += $@{SOURCE_LIST@}
ADA_OBJECTS_PATH += $@{OBJECT_LIST@}
export ADA_INCLUDE_PATH
export ADA_OBJECTS_PATH

all:
        gnatmake main_unit
@end example

@c -- Example: A |withing| unit has a |with| clause, it |withs| a |withed| unit

@node GNAT Project Manager,Tools Supporting Project Files,Building Executable Programs with GNAT,Top
@anchor{gnat_ugn/gnat_project_manager doc}@anchor{147}@anchor{gnat_ugn/gnat_project_manager gnat-project-manager}@anchor{b}@anchor{gnat_ugn/gnat_project_manager id1}@anchor{148}
@chapter GNAT Project Manager


@menu
* Introduction:: 
* Building With Projects:: 
* Organizing Projects into Subsystems:: 
* Scenarios in Projects:: 
* Library Projects:: 
* Project Extension:: 
* Aggregate Projects:: 
* Aggregate Library Projects:: 
* Project File Reference:: 

@end menu

@node Introduction,Building With Projects,,GNAT Project Manager
@anchor{gnat_ugn/gnat_project_manager introduction}@anchor{149}@anchor{gnat_ugn/gnat_project_manager gnat-project-manager-introduction}@anchor{14a}
@section Introduction


This chapter describes GNAT's @emph{Project Manager}, a facility that allows
you to manage complex builds involving a number of source files, directories,
and options for different system configurations. In particular,
project files allow you to specify:


@itemize *

@item 
The directory or set of directories containing the source files, and/or the
names of the specific source files themselves

@item 
The directory in which the compiler's output
(@code{ALI} files, object files, tree files, etc.) is to be placed

@item 
The directory in which the executable programs are to be placed

@item 
Switch settings for any of the project-enabled tools;
you can apply these settings either globally or to individual compilation units.

@item 
The source files containing the main subprogram(s) to be built

@item 
The source programming language(s)

@item 
Source file naming conventions; you can specify these either globally or for
individual compilation units (see @ref{14b,,Naming Schemes}).

@item 
Change any of the above settings depending on external values, thus enabling
the reuse of the projects in various @strong{scenarios} (see @ref{14c,,Scenarios in Projects}).

@item 
Automatically build libraries as part of the build process
(see @ref{8a,,Library Projects}).
@end itemize

Project files are written in a syntax close to that of Ada, using familiar
notions such as packages, context clauses, declarations, default values,
assignments, and inheritance (see @ref{14d,,Project File Reference}).

Project files can be built hierarchically from other project files, simplifying
complex system integration and project reuse (see @ref{14e,,Organizing Projects into Subsystems}).


@itemize *

@item 
One project can import other projects containing needed source files.
More generally, the Project Manager lets you structure large development
efforts into hierarchical subsystems, where build decisions are delegated
to the subsystem level, and thus different compilation environments
(switch settings) used for different subsystems.

@item 
You can organize GNAT projects in a hierarchy: a child project
can extend a parent project, inheriting the parent's source files and
optionally overriding any of them with alternative versions
(see @ref{14f,,Project Extension}).
@end itemize

Several tools support project files, generally in addition to specifying
the information on the command line itself). They share common switches
to control the loading of the project (in particular
@code{-P@emph{projectfile}} and
@code{-X@emph{vbl}=@emph{value}}).

The Project Manager supports a wide range of development strategies,
for systems of all sizes.  Here are some typical practices that are
easily handled:


@itemize *

@item 
Using a common set of source files and generating object files in different
directories via different switch settings. It can be used for instance, for
generating separate sets of object files for debugging and for production.

@item 
Using a mostly-shared set of source files with different versions of
some units or subunits. It can be used for instance, for grouping and hiding
all OS dependencies in a small number of implementation units.
@end itemize

Project files can be used to achieve some of the effects of a source
versioning system (for example, defining separate projects for
the different sets of sources that comprise different releases) but the
Project Manager is independent of any source configuration management tool
that might be used by the developers.

The various sections below introduce the different concepts related to
projects. Each section starts with examples and use cases, and then goes into
the details of related project file capabilities.

@node Building With Projects,Organizing Projects into Subsystems,Introduction,GNAT Project Manager
@anchor{gnat_ugn/gnat_project_manager building-with-projects}@anchor{150}@anchor{gnat_ugn/gnat_project_manager id2}@anchor{151}
@section Building With Projects


In its simplest form, a unique project is used to build a single executable.
This section concentrates on such a simple setup. Later sections will extend
this basic model to more complex setups.

The following concepts are the foundation of project files, and will be further
detailed later in this documentation. They are summarized here as a reference.


@table @asis

@item @strong{Project file}:

A text file using an Ada-like syntax, generally using the @code{.gpr}
extension. It defines build-related characteristics of an application.
The characteristics include the list of sources, the location of those
sources, the location for the generated object files, the name of
the main program, and the options for the various tools involved in the
build process.

@item @strong{Project attribute}:

A specific project characteristic is defined by an attribute clause. Its
value is a string or a sequence of strings. All settings in a project
are defined through a list of predefined attributes with precise
semantics. See @ref{152,,Attributes}.

@item @strong{Package in a project}:

Global attributes are defined at the top level of a project.
Attributes affecting specific tools are grouped in a
package whose name is related to tool's function. The most common
packages are @cite{Builder}, @cite{Compiler}, @cite{Binder},
and @cite{Linker}. See @ref{153,,Packages}.

@item @strong{Project variables}:

In addition to attributes, a project can use variables to store intermediate
values and avoid duplication in complex expressions. It can be initialized
with a value coming from the environment.
A frequent use of variables is to define scenarios.
See @ref{154,,External Values}, @ref{14c,,Scenarios in Projects}, and @ref{155,,Variables}.

@item @strong{Source files} and @strong{source directories}:

A source file is associated with a language through a naming convention. For
instance, @cite{foo.c} is typically the name of a C source file;
@cite{bar.ads} or @cite{bar.1.ada} are two common naming conventions for a
file containing an Ada spec. A compilation unit is often composed of a main
source file and potentially several auxiliary ones, such as header files in C.
The naming conventions can be user defined @ref{14b,,Naming Schemes}, and will
drive the builder to call the appropriate compiler for the given source file.
Source files are searched for in the source directories associated with the
project through the @strong{Source_Dirs} attribute. By default, all the files (in
these source directories) following the naming conventions associated with the
declared languages are considered to be part of the project. It is also
possible to limit the list of source files using the @strong{Source_Files} or
@strong{Source_List_File} attributes. Note that those last two attributes only
accept basenames with no directory information.

@item @strong{Object files} and @strong{object directory}:

An object file is an intermediate file produced by the compiler from a
compilation unit. It is used by post-compilation tools to produce
final executables or libraries. Object files produced in the context of
a given project are stored in a single directory that can be specified by the
@strong{Object_Dir} attribute. In order to store objects in
two or more object directories, the system must be split into
distinct subsystems with their own project file.
@end table

The following subsections introduce gradually all the attributes of interest
for simple build needs. Here is the simple setup that will be used in the
following examples.

The Ada source files @code{pack.ads}, @code{pack.adb}, and @code{proc.adb} are in
the @code{common/} directory. The file @code{proc.adb} contains an Ada main
subprogram @cite{Proc} that @emph{with}s package @cite{Pack}. We want to compile
these source files with the switch
@emph{-O2}, and put the resulting files in
the directory @code{obj/}.

@example
common/
  pack.ads
  pack.adb
  proc.adb
common/obj/
  proc.ali, proc.o pack.ali, pack.o
@end example

Our project is to be called @emph{Build}. The name of the
file is the name of the project (case-insensitive) with the
@code{.gpr} extension, therefore the project file name is @code{build.gpr}. This
is not mandatory, but a warning is issued when this convention is not followed.

This is a very simple example, and as stated above, a single project
file is enough for it. We will thus create a new file, that for now
should contain the following code:

@example
project Build is
end Build;
@end example

@menu
* Source Files and Directories:: 
* Duplicate Sources in Projects:: 
* Object and Exec Directory:: 
* Main Subprograms:: 
* Tools Options in Project Files:: 
* Compiling with Project Files:: 
* Executable File Names:: 
* Avoid Duplication With Variables:: 
* Naming Schemes:: 
* Installation:: 
* Distributed support:: 

@end menu

@node Source Files and Directories,Duplicate Sources in Projects,,Building With Projects
@anchor{gnat_ugn/gnat_project_manager id3}@anchor{156}@anchor{gnat_ugn/gnat_project_manager source-files-and-directories}@anchor{157}
@subsection Source Files and Directories


When you create a new project, the first thing to describe is how to find the
corresponding source files. These are the only settings that are needed by all
the tools that will use this project (builder, compiler, binder and linker for
the compilation, IDEs to edit the source files,...).

@geindex Source directories (GNAT Project Manager)

The first step is to declare the source directories, which are the directories
to be searched to find source files. In the case of the example,
the @code{common} directory is the only source directory.

@geindex Source_Dirs (GNAT Project Manager)

There are several ways of defining source directories:


@itemize *

@item 
When the attribute @strong{Source_Dirs} is not used, a project contains a
single source directory which is the one where the project file itself
resides. In our example, if @code{build.gpr} is placed in the @code{common}
directory, the project has the needed implicit source directory.

@item 
The attribute @strong{Source_Dirs} can be set to a list of path names, one
for each of the source directories. Such paths can either be absolute
names (for instance @code{"/usr/local/common/"} on UNIX), or relative to the
directory in which the project file resides (for instance "." if
@code{build.gpr} is inside @code{common/}, or "common" if it is one level up).
Each of the source directories must exist and be readable.

@geindex portability of path names (GNAT Project Manager)

The syntax for directories is platform specific. For portability, however,
the project manager will always properly translate UNIX-like path names to
the native format of the specific platform. For instance, when the same
project file is to be used both on Unix and Windows, "/" should be used as
the directory separator rather than "\".

@item 
The attribute @strong{Source_Dirs} can automatically include subdirectories
using a special syntax inspired by some UNIX shells. If any of the paths in
the list ends with "@code{**}", then that path and all its subdirectories
(recursively) are included in the list of source directories. For instance,
@code{**} and @code{./**} represent the complete directory tree rooted at
the directory in which the project file resides.

@geindex Source directories (GNAT Project Manager)

@geindex Excluded_Source_Dirs (GNAT Project Manager)

When using that construct, it can sometimes be convenient to also use the
attribute @strong{Excluded_Source_Dirs}, which is also a list of paths. Each entry
specifies a directory whose immediate content, not including subdirs, is to
be excluded. It is also possible to exclude a complete directory subtree
using the "**" notation.

@geindex Ignore_Source_Sub_Dirs (GNAT Project Manager)

It is often desirable to remove, from the source directories, directory
subtrees rooted at some subdirectories. An example is the subdirectories
created by a Version Control System such as Subversion that creates directory
subtrees rooted at subdirectories ".svn". To do that, attribute
@strong{Ignore_Source_Sub_Dirs} can be used. It specifies the list of simple
file names for the roots of these undesirable directory subtrees.

@c code-block: ada-project
@c 
@c for Source_Dirs use ("./**");
@c for Ignore_Source_Sub_Dirs use (".svn");
@end itemize

When applied to the simple example, and because we generally prefer to have
the project file at the toplevel directory rather than mixed with the sources,
we will create the following file

@c code-block: ada-project
@c 
@c build.gpr
@c project Build is
@c    for Source_Dirs use ("common");  --  <<<<
@c end Build;

Once source directories have been specified, one may need to indicate
source files of interest. By default, all source files present in the source
directories are considered by the project manager. When this is not desired,
it is possible to specify the list of sources to consider explicitly.
In such a case, only source file base names are indicated and not
their absolute or relative path names. The project manager is in charge of
locating the specified source files in the specified source directories.


@itemize *

@item 
By default, the project manager searches for all source files of all
specified languages in all the source directories.

Since the project manager was initially developed for Ada environments, the
default language is usually Ada and the above project file is complete: it
defines without ambiguity the sources composing the project: that is to say,
all the sources in subdirectory "common" for the default language (Ada) using
the default naming convention.

@geindex Languages (GNAT Project Manager)

However, when compiling a multi-language application, or a pure C
application, the project manager must be told which languages are of
interest, which is done by setting the @strong{Languages} attribute to a list of
strings, each of which is the name of a language.

@geindex Naming scheme (GNAT Project Manager)

Even when using only Ada, the default naming might not be suitable. Indeed,
how does the project manager recognizes an "Ada file" from any other
file? Project files can describe the naming scheme used for source files,
and override the default (see @ref{14b,,Naming Schemes}). The default is the
standard GNAT extension (@code{.adb} for bodies and @code{.ads} for
specs), which is what is used in our example, explaining why no naming scheme
is explicitly specified.
See @ref{14b,,Naming Schemes}.

@geindex Source_Files (GNAT Project Manager)

@item 
@cite{Source_Files}.
In some cases, source directories might contain files that should not be
included in a project. One can specify the explicit list of file names to
be considered through the @strong{Source_Files} attribute.
When this attribute is defined, instead of looking at every file in the
source directories, the project manager takes only those names into
consideration  reports  errors if they cannot be found in the source
directories or does not correspond to the naming scheme.

@item 
For various reasons, it is sometimes useful to have a project with no
sources (most of the time because the attributes defined in the project
file will be reused in other projects, as explained in
@ref{14e,,Organizing Projects into Subsystems}. To do this, the attribute
@emph{Source_Files} is set to the empty list, i.e. @cite{()}. Alternatively,
@emph{Source_Dirs} can be set to the empty list, with the same
result.

@geindex Source_List_File (GNAT Project Manager)

@item 
@cite{Source_List_File}.
If there is a great number of files, it might be more convenient to use
the attribute @strong{Source_List_File}, which specifies the full path of a file.
This file must contain a list of source file names (one per line, no
directory information) that are searched as if they had been defined
through @emph{Source_Files}. Such a file can easily be created through
external tools.

A warning is issued if both attributes @cite{Source_Files} and
@cite{Source_List_File} are given explicit values. In this case, the
attribute @cite{Source_Files} prevails.

@geindex Excluded_Source_Files (GNAT Project Manager)

@geindex Locally_Removed_Files (GNAT Project Manager)

@geindex Excluded_Source_List_File (GNAT Project Manager)

@item 
@cite{Excluded_Source_Files}.
Specifying an explicit list of files is not always convenient.It might be
more convenient to use the default search rules with specific exceptions.
This can be done thanks to the attribute @strong{Excluded_Source_Files}
(or its synonym @strong{Locally_Removed_Files}).
Its value is the list of file names that should not be taken into account.
This attribute is often used when extending a project,
see @ref{14f,,Project Extension}. A similar attribute
@strong{Excluded_Source_List_File} plays the same
role but takes the name of file containing file names similarly to
@cite{Source_List_File}.
@end itemize

In most simple cases, such as the above example, the default source file search
behavior provides the expected result, and we do not need to add anything after
setting @cite{Source_Dirs}. The project manager automatically finds
@code{pack.ads}, @code{pack.adb}, and @code{proc.adb} as source files of the
project.

Note that by default a warning is issued when a project has no sources attached
to it and this is not explicitly indicated in the project file.

@node Duplicate Sources in Projects,Object and Exec Directory,Source Files and Directories,Building With Projects
@anchor{gnat_ugn/gnat_project_manager duplicate-sources-in-projects}@anchor{158}@anchor{gnat_ugn/gnat_project_manager id4}@anchor{159}
@subsection Duplicate Sources in Projects


If the order of the source directories is known statically, that is if
@cite{"/**"} is not used in the string list @cite{Source_Dirs}, then there may
be several files with the same name sitting in different directories of the
project. In this case, only the file in the first directory is considered as a
source of the project and the others are hidden. If @cite{"/**"} is used in the
string list @cite{Source_Dirs}, it is an error to have several files with the
same name in the same directory @cite{"/**"} subtree, since there would be an
ambiguity as to which one should be used. However, two files with the same name
may exist in two single directories or directory subtrees. In this case, the
one in the first directory or directory subtree is a source of the project.

If there are two sources in different directories of the same @cite{"/**"}
subtree, one way to resolve the problem is to exclude the directory of the
file that should not be used as a source of the project.

@node Object and Exec Directory,Main Subprograms,Duplicate Sources in Projects,Building With Projects
@anchor{gnat_ugn/gnat_project_manager object-and-exec-directory}@anchor{15a}@anchor{gnat_ugn/gnat_project_manager id5}@anchor{15b}
@subsection Object and Exec Directory


The next step when writing a project is to indicate where the compiler should
put the object files. In fact, the compiler and other tools might create
several different kind of files (for GNAT, there is the object file and the ALI
file for instance). One of the important concepts in projects is that most
tools may consider source directories as read-only and do not attempt to create
new or temporary files there. Instead, all files are created in the object
directory. It is of course not true for project-aware IDEs, whose purpose it is
to create the source files.

@geindex Object_Dir (GNAT Project Manager)

The object directory is specified through the @strong{Object_Dir} attribute.
Its value is the path to the object directory, either absolute or
relative to the directory containing the project file. This
directory must already exist and be readable and writable, although
some tools have a switch to create the directory if needed (See
the switch @cite{-p} for @emph{gprbuild}).

If the attribute @cite{Object_Dir} is not specified, it defaults to
the project directory, that is the directory containing the project file.

For our example, we can specify the object dir in this way:

@c code-block: ada-project
@c 
@c project Build is
@c    for Source_Dirs use ("common");
@c    for Object_Dir use "obj";   --  <<<<
@c end Build;

As mentioned earlier, there is a single object directory per project. As a
result, if you have an existing system where the object files are spread across
several directories, you can either move all of them into the same directory if
you want to build it with a single project file, or study the section on
subsystems (see @ref{14e,,Organizing Projects into Subsystems}) to see how each
separate object directory can be associated with one of the subsystems
constituting the application.

When the @emph{linker} is called, it usually creates an executable. By
default, this executable is placed in the object directory of the project. It
might be convenient to store it in its own directory.

@geindex Exec_Dir (GNAT Project Manager)

This can be done through the @cite{Exec_Dir} attribute, which, like
@emph{Object_Dir} contains a single absolute or relative path and must point to
an existing and writable directory, unless you ask the tool to create it on
your behalf. When not specified, It defaults to the object directory and
therefore to the project file's directory if neither @emph{Object_Dir} nor
@emph{Exec_Dir} was specified.

In the case of the example, let's place the executable in the root
of the hierarchy, ie the same directory as @code{build.gpr}. Hence
the project file is now

@c code-block: ada-project
@c 
@c project Build is
@c    for Source_Dirs use ("common");
@c    for Object_Dir use "obj";
@c    for Exec_Dir use ".";  --   <<<<
@c end Build;

@node Main Subprograms,Tools Options in Project Files,Object and Exec Directory,Building With Projects
@anchor{gnat_ugn/gnat_project_manager id6}@anchor{15c}@anchor{gnat_ugn/gnat_project_manager main-subprograms}@anchor{15d}
@subsection Main Subprograms


In the previous section, executables were mentioned. The project manager needs
to be taught what they are. In a project file, an executable is indicated by
pointing to the source file of a main subprogram. In C this is the file that
contains the @cite{main} function, and in Ada the file that contains the main
unit.

There can be any number of such main files within a given project, and thus
several executables can be built in the context of a single project file. Of
course, one given executable might not (and in fact will not) need all the
source files referenced by the project. As opposed to other build environments
such as @emph{makefile}, one does not need to specify the list of
dependencies of each executable, the project-aware builder knows enough of the
semantics of the languages to build and link only the necessary elements.

@geindex Main (GNAT Project Manager)

The list of main files is specified via the @strong{Main} attribute. It contains
a list of file names (no directories). If a project defines this
attribute, it is not necessary to identify  main files on the
command line when invoking a builder, and editors like
@emph{GPS} will be able to create extra menus to spawn or debug the
corresponding executables.

@c code-block: ada-project
@c 
@c project Build is
@c    for Source_Dirs use ("common");
@c    for Object_Dir use "obj";
@c    for Exec_Dir use ".";
@c    for Main use ("proc.adb");  --   <<<<
@c end Build;

If this attribute is defined in the project, then spawning the builder
with a command such as

@example
gprbuild -Pbuild
@end example

automatically builds all the executables corresponding to the files
listed in the @emph{Main} attribute. It is possible to specify one
or more executables on the command line to build a subset of them.

@node Tools Options in Project Files,Compiling with Project Files,Main Subprograms,Building With Projects
@anchor{gnat_ugn/gnat_project_manager tools-options-in-project-files}@anchor{15e}@anchor{gnat_ugn/gnat_project_manager id7}@anchor{15f}
@subsection Tools Options in Project Files


We now have a project file that fully describes our environment, and can be
used to build the application with a simple @emph{gprbuild} command as seen
in the previous section. In fact, the empty project we showed immediately at
the beginning (with no attribute at all) could already fulfill that need if it
was put in the @code{common} directory.

Of course, we might want more control. This section shows you how to specify
the compilation switches that the various tools involved in the building of the
executable should use.

@geindex command line length (GNAT Project Manager)

Since source names and locations are described in the project file, it is not
necessary to use switches on the command line for this purpose (switches such
as -I for gcc). This removes a major source of command line length overflow.
Clearly, the builders will have to communicate this information one way or
another to the underlying compilers and tools they call but they usually use
response files for this and thus are not subject to command line overflows.

Several tools participate to the creation of an executable: the compiler
produces object files from the source files; the binder (in the Ada case)
creates a "source" file that takes care, among other things, of elaboration
issues and global variable initialization; and the linker gathers everything
into a single executable that users can execute. All these tools are known to
the project manager and will be called with user defined switches from the
project files. However, we need to introduce a new project file concept to
express the switches to be used for any of the tools involved in the build.

@geindex project file packages (GNAT Project Manager)

A project file is subdivided into zero or more @strong{packages}, each of which
contains the attributes specific to one tool (or one set of tools). Project
files use an Ada-like syntax for packages. Package names permitted in project
files are restricted to a predefined set (see @ref{153,,Packages}), and the contents
of packages are limited to a small set of constructs and attributes
(see @ref{152,,Attributes}).

Our example project file can be extended with the following empty packages. At
this stage, they could all be omitted since they are empty, but they show which
packages would be involved in the build process.

@c code-block: ada-project
@c 
@c project Build is
@c    for Source_Dirs use ("common");
@c    for Object_Dir use "obj";
@c    for Exec_Dir use ".";
@c    for Main use ("proc.adb");
@c 
@c    package Builder is  --<<<  for gprbuild
@c    end Builder;
@c 
@c    package Compiler is --<<<  for the compiler
@c    end Compiler;
@c 
@c    package Binder is   --<<<  for the binder
@c    end Binder;
@c 
@c    package Linker is   --<<<  for the linker
@c    end Linker;
@c end Build;

Let's first examine the compiler switches. As stated in the initial description
of the example, we want to compile all files with @emph{-O2}. This is a
compiler switch, although it is usual, on the command line, to pass it to the
builder which then passes it to the compiler. It is recommended to use directly
the right package, which will make the setup easier to understand for other
people.

Several attributes can be used to specify the switches:

@geindex Default_Switches (GNAT Project Manager)

@strong{Default_Switches}:

@quotation

This is the first mention in this manual of an @strong{indexed attribute}. When
this attribute is defined, one must supply an @emph{index} in the form of a
literal string.
In the case of @emph{Default_Switches}, the index is the name of the
language to which the switches apply (since a different compiler will
likely be used for each language, and each compiler has its own set of
switches). The value of the attribute is a list of switches.

In this example, we want to compile all Ada source files with the switch
@emph{-O2}, and the resulting project file is as follows
(only the @cite{Compiler} package is shown):

@c code-block: ada-project
@c 
@c package Compiler is
@c   for Default_Switches ("Ada") use ("-O2");
@c end Compiler;
@end quotation

@geindex Switches (GNAT Project Manager)

@strong{Switches}:

@quotation

In some cases, we might want to use specific switches
for one or more files. For instance, compiling @code{proc.adb} might not be
possible at high level of optimization because of a compiler issue.
In such a case, the @emph{Switches}
attribute (indexed on the file name) can be used and will override the
switches defined by @emph{Default_Switches}. Our project file would
become:

@c code-block: ada-project
@c 
@c 
@c package Compiler is
@c    for Default_Switches ("Ada")
@c        use ("-O2");
@c    for Switches ("proc.adb")
@c        use ("-O0");
@c end Compiler;

@cite{Switches} may take a pattern as an index, such as in:

@c code-block: ada-project
@c 
@c package Compiler is
@c   for Default_Switches ("Ada")
@c       use ("-O2");
@c   for Switches ("pkg*")
@c       use ("-O0");
@c end Compiler;

Sources @code{pkg.adb} and @code{pkg-child.adb} would be compiled with -O0,
not -O2.

@cite{Switches} can also be given a language name as index instead of a file
name in which case it has the same semantics as @emph{Default_Switches}.
However, indexes with wild cards are never valid for language name.
@end quotation

@geindex Local_Configuration_Pragmas (GNAT Project Manager)

@strong{Local_Configuration_Pragmas}:

@quotation

This attribute may specify the path
of a file containing configuration pragmas for use by the Ada compiler,
such as @cite{pragma Restrictions (No_Tasking)}. These pragmas will be
used for all the sources of the project.
@end quotation

The switches for the other tools are defined in a similar manner through the
@strong{Default_Switches} and @strong{Switches} attributes, respectively in the
@emph{Builder} package (for @emph{gprbuild}),
the @emph{Binder} package (binding Ada executables) and the @emph{Linker}
package (for linking executables).

@node Compiling with Project Files,Executable File Names,Tools Options in Project Files,Building With Projects
@anchor{gnat_ugn/gnat_project_manager compiling-with-project-files}@anchor{160}@anchor{gnat_ugn/gnat_project_manager id8}@anchor{161}
@subsection Compiling with Project Files


Now that our project files are written, let's build our executable.
Here is the command we would use from the command line:

@example
gprbuild -Pbuild
@end example

This will automatically build the executables specified through the
@emph{Main} attribute: for each, it will compile or recompile the
sources for which the object file does not exist or is not up-to-date; it
will then run the binder; and finally run the linker to create the
executable itself.

The @emph{gprbuild} builder, can automatically manage C files the
same way: create the file @code{utils.c} in the @code{common} directory,
set the attribute @emph{Languages} to @cite{"(Ada@comma{} C)"}, and re-run

@example
gprbuild -Pbuild
@end example

Gprbuild knows how to recompile the C files and will
recompile them only if one of their dependencies has changed. No direct
indication on how to build the various elements is given in the
project file, which describes the project properties rather than a
set of actions to be executed. Here is the invocation of
@emph{gprbuild} when building a multi-language program:

@example
$ gprbuild -Pbuild
gcc -c proc.adb
gcc -c pack.adb
gcc -c utils.c
gprbind proc
...
gcc proc.o -o proc
@end example

Notice the three steps described earlier:


@itemize *

@item 
The first three gcc commands correspond to the compilation phase.

@item 
The gprbind command corresponds to the post-compilation phase.

@item 
The last gcc command corresponds to the final link.
@end itemize

@geindex -v option (for GPRbuild)

The default output of GPRbuild's execution is kept reasonably simple and easy
to understand. In particular, some of the less frequently used commands are not
shown, and some parameters are abbreviated. So it is not possible to rerun the
effect of the @emph{gprbuild} command by cut-and-pasting its output.
GPRbuild's option @cite{-v} provides a much more verbose output which includes,
among other information, more complete compilation, post-compilation and link
commands.

@node Executable File Names,Avoid Duplication With Variables,Compiling with Project Files,Building With Projects
@anchor{gnat_ugn/gnat_project_manager executable-file-names}@anchor{162}@anchor{gnat_ugn/gnat_project_manager id9}@anchor{163}
@subsection Executable File Names


@geindex Executable (GNAT Project Manager)

By default, the executable name corresponding to a main file is
computed from the main source file name. Through the attribute
@strong{Builder.Executable}, it is possible to change this default.

For instance, instead of building @emph{proc} (or @emph{proc.exe}
on Windows), we could configure our project file to build "proc1"
(resp proc1.exe) with the following addition:

@example
project Build is
   ...  --  same as before
   package Builder is
      for Executable ("proc.adb") use "proc1";
   end Builder
end Build;
@end example

@geindex Executable_Suffix (GNAT Project Manager)

Attribute @strong{Executable_Suffix}, when specified, may change the suffix
of the executable files, when no attribute @cite{Executable} applies:
its value replaces the platform-specific executable suffix.
The default executable suffix is empty on UNIX and ".exe" on Windows.

It is also possible to change the name of the produced executable by using the
command line switch @emph{-o}. When several mains are defined in the project,
it is not possible to use the @emph{-o} switch and the only way to change the
names of the executable is provided by Attributes @cite{Executable} and
@cite{Executable_Suffix}.

@node Avoid Duplication With Variables,Naming Schemes,Executable File Names,Building With Projects
@anchor{gnat_ugn/gnat_project_manager id10}@anchor{164}@anchor{gnat_ugn/gnat_project_manager avoid-duplication-with-variables}@anchor{165}
@subsection Avoid Duplication With Variables


To illustrate some other project capabilities, here is a slightly more complex
project using similar sources and a main program in C:

@example
project C_Main is
   for Languages    use ("Ada", "C");
   for Source_Dirs  use ("common");
   for Object_Dir   use  "obj";
   for Main         use ("main.c");
   package Compiler is
      C_Switches := ("-pedantic");
      for Default_Switches ("C")   use C_Switches;
      for Default_Switches ("Ada") use ("-gnaty");
      for Switches ("main.c") use C_Switches & ("-g");
   end Compiler;
end C_Main;
@end example

This project has many similarities with the previous one.
As expected, its @cite{Main} attribute now refers to a C source.
The attribute @emph{Exec_Dir} is now omitted, thus the resulting
executable will be put in the directory @code{obj}.

The most noticeable difference is the use of a variable in the
@emph{Compiler} package to store settings used in several attributes.
This avoids text duplication, and eases maintenance (a single place to
modify if we want to add new switches for C files). We will revisit
the use of variables in the context of scenarios (see @ref{14c,,Scenarios in Projects}).

In this example, we see how the file @code{main.c} can be compiled with
the switches used for all the other C files, plus @emph{-g}.
In this specific situation the use of a variable could have been
replaced by a reference to the @cite{Default_Switches} attribute:

@example
for Switches ("c_main.c") use Compiler'Default_Switches ("C") & ("-g");
@end example

Note the tick (@emph{'}) used to refer to attributes defined in a package.

Here is the output of the GPRbuild command using this project:

@example
$ gprbuild -Pc_main
gcc -c -pedantic -g main.c
gcc -c -gnaty proc.adb
gcc -c -gnaty pack.adb
gcc -c -pedantic utils.c
gprbind main.bexch
...
gcc main.o -o main
@end example

The default switches for Ada sources,
the default switches for C sources (in the compilation of @code{lib.c}),
and the specific switches for @code{main.c} have all been taken into
account.

@node Naming Schemes,Installation,Avoid Duplication With Variables,Building With Projects
@anchor{gnat_ugn/gnat_project_manager id11}@anchor{166}@anchor{gnat_ugn/gnat_project_manager naming-schemes}@anchor{14b}
@subsection Naming Schemes


Sometimes an Ada software system is ported from one compilation environment to
another (say GNAT), and the file are not named using the default GNAT
conventions. Instead of changing all the file names, which for a variety of
reasons might not be possible, you can define the relevant file naming scheme
in the @strong{Naming} package of your project file.

The naming scheme has two distinct goals for the project manager: it
allows finding of source files when searching in the source
directories, and given a source file name it makes it possible to guess
the associated language, and thus the compiler to use.

Note that the use by the Ada compiler of pragmas Source_File_Name is not
supported when using project files. You must use the features described in this
paragraph. You can however specify other configuration pragmas.

The following attributes can be defined in package @cite{Naming}:

@geindex Casing (GNAT Project Manager)

@strong{Casing}:

@quotation

Its value must be one of @cite{"lowercase"} (the default if
unspecified), @cite{"uppercase"} or @cite{"mixedcase"}. It describes the
casing of file names with regards to the Ada unit name. Given an Ada unit
My_Unit, the file name will respectively be @code{my_unit.adb} (lowercase),
@code{MY_UNIT.ADB} (uppercase) or @code{My_Unit.adb} (mixedcase).
On Windows, file names are case insensitive, so this attribute is
irrelevant.
@end quotation

@geindex Dot_Replacement (GNAT Project Manager)

@strong{Dot_Replacement}:

@quotation

This attribute specifies the string that should replace the "." in unit
names. Its default value is @cite{"-"} so that a unit
@cite{Parent.Child} is expected to be found in the file
@code{parent-child.adb}. The replacement string must satisfy the following
requirements to avoid ambiguities in the naming scheme:


@itemize *

@item 
It must not be empty

@item 
It cannot start or end with an alphanumeric character

@item 
It cannot be a single underscore

@item 
It cannot start with an underscore followed by an alphanumeric

@item 
It cannot contain a dot @cite{'.'} except if the entire string is @cite{"."}
@end itemize
@end quotation

@geindex Spec_Suffix (GNAT Project Manager)

@geindex Specification_Suffix (GNAT Project Manager)

@strong{Spec_Suffix} and @strong{Specification_Suffix}:

@quotation

For Ada, these attributes give the suffix used in file names that contain
specifications. For other languages, they give the extension for files
that contain declaration (header files in C for instance). The attribute
is indexed on the language.
The two attributes are equivalent, but the latter is obsolescent.

If the value of the attribute is the empty string, it indicates to the
Project Manager that the only specifications/header files for the language
are those specified with attributes @cite{Spec} or
@cite{Specification_Exceptions}.

If @cite{Spec_Suffix ("Ada")} is not specified, then the default is
@cite{".ads"}.

A non empty value must satisfy the following requirements:


@itemize *

@item 
It must include at least one dot

@item 
If @cite{Dot_Replacement} is a single dot, then it cannot include
more than one dot.
@end itemize
@end quotation

@geindex Body_Suffix (GNAT Project Manager)

@geindex Implementation_Suffix (GNAT Project Manager)

@strong{Body_Suffix} and @strong{Implementation_Suffix}:

@quotation

These attributes give the extension used for file names that contain
code (bodies in Ada). They are indexed on the language. The second
version is obsolescent and fully replaced by the first attribute.

For each language of a project, one of these two attributes need to be
specified, either in the project itself or in the configuration project file.

If the value of the attribute is the empty string, it indicates to the
Project Manager that the only source files for the language
are those specified with attributes @cite{Body} or
@cite{Implementation_Exceptions}.

These attributes must satisfy the same requirements as @cite{Spec_Suffix}.
In addition, they must be different from any of the values in
@cite{Spec_Suffix}.
If @cite{Body_Suffix ("Ada")} is not specified, then the default is
@cite{".adb"}.

If @cite{Body_Suffix ("Ada")} and @cite{Spec_Suffix ("Ada")} end with the
same string, then a file name that ends with the longest of these two
suffixes will be a body if the longest suffix is @cite{Body_Suffix ("Ada")}
or a spec if the longest suffix is @cite{Spec_Suffix ("Ada")}.

If the suffix does not start with a '.', a file with a name exactly equal to
the suffix will also be part of the project (for instance if you define the
suffix as @cite{Makefile.in}, a file called @code{Makefile.in} will be part
of the project. This capability is usually not interesting when building.
However, it might become useful when a project is also used to
find the list of source files in an editor, like the GNAT Programming System
(GPS).
@end quotation

@geindex Separate_Suffix (GNAT Project Manager)

@strong{Separate_Suffix}:

@quotation

This attribute is specific to Ada. It denotes the suffix used in file names
that contain separate bodies. If it is not specified, then it defaults to
same value as @cite{Body_Suffix ("Ada")}.

The value of this attribute cannot be the empty string.

Otherwise, the same rules apply as for the
@cite{Body_Suffix} attribute. The only accepted index is "Ada".
@end quotation

@strong{Spec} or @strong{Specification}:

@quotation

@geindex Spec (GNAT Project Manager)

@geindex Specification (GNAT Project Manager)

This attribute @cite{Spec} can be used to define the source file name for a
given Ada compilation unit's spec. The index is the literal name of the Ada
unit (case insensitive). The value is the literal base name of the file that
contains this unit's spec (case sensitive or insensitive depending on the
operating system). This attribute allows the definition of exceptions to the
general naming scheme, in case some files do not follow the usual
convention.

When a source file contains several units, the relative position of the unit
can be indicated. The first unit in the file is at position 1

@example
for Spec ("MyPack.MyChild") use "mypack.mychild.spec";
for Spec ("top") use "foo.a" at 1;
for Spec ("foo") use "foo.a" at 2;
@end example
@end quotation

@geindex Body (GNAT Project Manager)

@geindex Implementation (GNAT Project Manager)

@strong{Body} or @strong{Implementation}:

@quotation

These attribute play the same role as @emph{Spec} for Ada bodies.
@end quotation

@geindex Specification_Exceptions (GNAT Project Manager)

@geindex Implementation_Exceptions (GNAT Project Manager)

@strong{Specification_Exceptions} and @strong{Implementation_Exceptions}:

@quotation

These attributes define exceptions to the naming scheme for languages
other than Ada. They are indexed on the language name, and contain
a list of file names respectively for headers and source code.
@end quotation

For example, the following package models the Apex file naming rules:

@example
package Naming is
  for Casing               use "lowercase";
  for Dot_Replacement      use ".";
  for Spec_Suffix ("Ada")  use ".1.ada";
  for Body_Suffix ("Ada")  use ".2.ada";
end Naming;
@end example

@node Installation,Distributed support,Naming Schemes,Building With Projects
@anchor{gnat_ugn/gnat_project_manager id12}@anchor{167}@anchor{gnat_ugn/gnat_project_manager installation}@anchor{168}
@subsection Installation


After building an application or a library it is often required to
install it into the development environment. For instance this step is
required if the library is to be used by another application.
The @emph{gprinstall} tool provides an easy way to install
libraries, executable or object code generated during the build. The
@strong{Install} package can be used to change the default locations.

The following attributes can be defined in package @cite{Install}:

@geindex Active (GNAT Project Manager)


@table @asis

@item @strong{Active}

Whether the project is to be installed, values are @cite{true}
(default) or @cite{false}.
@end table

@geindex Artifacts (GNAT Project Manager)

@strong{Artifacts}

@quotation

An array attribute to declare a set of files not part of the sources
to be installed. The array discriminant is the directory where the
file is to be installed. If a relative directory then Prefix (see
below) is prepended.
@end quotation

@geindex Prefix (GNAT Project Manager)

@strong{Prefix}:

@quotation

Root directory for the installation.
@end quotation

@strong{Exec_Subdir}

@quotation

Subdirectory of @strong{Prefix} where executables are to be
installed. Default is @strong{bin}.
@end quotation

@strong{Lib_Subdir}

@quotation

Subdirectory of @strong{Prefix} where directory with the library or object
files is to be installed. Default is @strong{lib}.
@end quotation

@strong{Sources_Subdir}

@quotation

Subdirectory of @strong{Prefix} where directory with sources is to be
installed. Default is @strong{include}.
@end quotation

@strong{Project_Subdir}

@quotation

Subdirectory of @strong{Prefix} where the generated project file is to be
installed. Default is @strong{share/gpr}.
@end quotation

@strong{Mode}

@quotation

The installation mode, it is either @strong{dev} (default) or @strong{usage}.
See @strong{gprbuild} user's guide for details.
@end quotation

@strong{Install_Name}

@quotation

Specify the name to use for recording the installation. The default is
the project name without the extension.
@end quotation

@node Distributed support,,Installation,Building With Projects
@anchor{gnat_ugn/gnat_project_manager id13}@anchor{169}@anchor{gnat_ugn/gnat_project_manager distributed-support}@anchor{16a}
@subsection Distributed support


For large projects the compilation time can become a limitation in
the development cycle. To cope with that, GPRbuild supports
distributed compilation.

The following attributes can be defined in package @cite{Remote}:

@geindex Root_Dir (GNAT Project Manager)

@strong{Root_Dir}:

@quotation

Root directory of the project's sources. The default value is the
project's directory.
@end quotation

@node Organizing Projects into Subsystems,Scenarios in Projects,Building With Projects,GNAT Project Manager
@anchor{gnat_ugn/gnat_project_manager organizing-projects-into-subsystems}@anchor{14e}@anchor{gnat_ugn/gnat_project_manager id14}@anchor{16b}
@section Organizing Projects into Subsystems


A @strong{subsystem} is a coherent part of the complete system to be built. It is
represented by a set of sources and one single object directory. A system can
be composed of a single subsystem when it is simple as we have seen in the
first section. Complex systems are usually composed of several interdependent
subsystems. A subsystem is dependent on another subsystem if knowledge of the
other one is required to build it, and in particular if visibility on some of
the sources of this other subsystem is required. Each subsystem is usually
represented by its own project file.

In this section, the previous example is being extended. Let's assume some
sources of our @cite{Build} project depend on other sources.
For instance, when building a graphical interface, it is usual to depend upon
a graphical library toolkit such as GtkAda. Furthermore, we also need
sources from a logging module we had previously written.

@menu
* Project Dependencies:: 
* Cyclic Project Dependencies:: 
* Sharing Between Projects:: 
* Global Attributes:: 

@end menu

@node Project Dependencies,Cyclic Project Dependencies,,Organizing Projects into Subsystems
@anchor{gnat_ugn/gnat_project_manager project-dependencies}@anchor{16c}@anchor{gnat_ugn/gnat_project_manager id15}@anchor{16d}
@subsection Project Dependencies


GtkAda comes with its own project file (appropriately called
@code{gtkada.gpr}), and we will assume we have already built a project
called @code{logging.gpr} for the logging module. With the information provided
so far in @code{build.gpr}, building the application would fail with an error
indicating that the gtkada and logging units that are relied upon by the sources
of this project cannot be found.

This is solved by adding the following @strong{with} clauses at the beginning of our
project:

@example
with "gtkada.gpr";
with "a/b/logging.gpr";
project Build is
  ...  --  as before
end Build;
@end example

@geindex Externally_Built (GNAT Project Manager)

When such a project is compiled, @emph{gprbuild} will automatically check
the other projects and recompile their sources when needed. It will also
recompile the sources from @cite{Build} when needed, and finally create the
executable. In some cases, the implementation units needed to recompile a
project are not available, or come from some third party and you do not want to
recompile it yourself. In this case, set the attribute @strong{Externally_Built} to
"true", indicating to the builder that this project can be assumed to be
up-to-date, and should not be considered for recompilation. In Ada, if the
sources of this externally built project were compiled with another version of
the compiler or with incompatible options, the binder will issue an error.

The project's @emph{with} clause has several effects. It provides source
visibility between projects during the compilation process. It also guarantees
that the necessary object files from @cite{Logging} and @cite{GtkAda} are
available when linking @cite{Build}.

As can be seen in this example, the syntax for importing projects is similar
to the syntax for importing compilation units in Ada. However, project files
use literal strings instead of names, and the @emph{with} clause identifies
project files rather than packages.

Each literal string after @emph{with} is the path
(absolute or relative) to a project file. The @cite{.gpr} extension is
optional, although we recommend adding it. If no extension is specified,
and no project file with the @code{.gpr} extension is found, then
the file is searched for exactly as written in the @emph{with} clause,
that is with no extension.

As mentioned above, the path after a @emph{with} has to be a literal
string, and you cannot use concatenation, or lookup the value of external
variables to change the directories from which a project is loaded.
A solution if you need something like this is to use aggregate projects
(see @ref{16e,,Aggregate Projects}).

@geindex project path (GNAT Project Manager)

When a relative path or a base name is used, the
project files are searched relative to each of the directories in the
@strong{project path}. This path includes all the directories found with the
following algorithm, in this order; the first matching file is used:


@itemize *

@item 
First, the file is searched relative to the directory that contains the
current project file.

@geindex GPR_PROJECT_PATH_FILE (GNAT Project Manager)

@geindex GPR_PROJECT_PATH (GNAT Project Manager)

@geindex ADA_PROJECT_PATH (GNAT Project Manager)

@item 
Then it is searched relative to all the directories specified in the
environment variables @strong{GPR_PROJECT_PATH_FILE},
@strong{GPR_PROJECT_PATH} and @strong{ADA_PROJECT_PATH} (in that order) if they exist.
The value of @strong{GPR_PROJECT_PATH_FILE}, when defined, is the path name of
a text file that contains project directory path names, one per line.
@strong{GPR_PROJECT_PATH} and @strong{ADA_PROJECT_PATH}, when defined, contain
project directory path names separated by directory separators.
@strong{ADA_PROJECT_PATH} is used for compatibility, it is recommended to
use @strong{GPR_PROJECT_PATH_FILE} or @strong{GPR_PROJECT_PATH}.

@item 
Finally, it is searched relative to the default project directories.
Such directories depend on the tool used. The locations searched in the
specified order are:


@itemize *

@item 
@code{<prefix>/<target>/lib/gnat} if option @emph{--target} is specified

@item 
@code{<prefix>/<target>/share/gpr} if option @emph{--target} is specified

@item 
@code{<prefix>/share/gpr/}

@item 
@code{<prefix>/lib/gnat/}
@end itemize

In our example, @code{gtkada.gpr} is found in the predefined directory if
it was installed at the same root as GNAT.
@end itemize

Some tools also support extending the project path from the command line,
generally through the @emph{-aP}. You can see the value of the project
path by using the @emph{gnatls -v} command.

Any symbolic link will be fully resolved in the directory of the
importing project file before the imported project file is examined.

Any source file in the imported project can be used by the sources of the
importing project, transitively.
Thus if @cite{A} imports @cite{B}, which imports @cite{C}, the sources of
@cite{A} may depend on the sources of @cite{C}, even if @cite{A} does not
import @cite{C} explicitly. However, this is not recommended, because if
and when @cite{B} ceases to import @cite{C}, some sources in @cite{A} will
no longer compile. @emph{gprbuild} has a switch @emph{--no-indirect-imports}
that will report such indirect dependencies.

@cartouche
@quotation Note 
One very important aspect of a project hierarchy is that
@strong{a given source can only belong to one project} (otherwise the project manager
would not know which settings apply to it and when to recompile it). It means
that different project files do not usually share source directories or
when they do, they need to specify precisely which project owns which sources
using attribute @cite{Source_Files} or equivalent. By contrast, 2 projects
can each own a source with the same base file name as long as they live in
different directories. The latter is not true for Ada Sources because of the
correlation between source files and Ada units.
@end quotation
@end cartouche

@node Cyclic Project Dependencies,Sharing Between Projects,Project Dependencies,Organizing Projects into Subsystems
@anchor{gnat_ugn/gnat_project_manager id16}@anchor{16f}@anchor{gnat_ugn/gnat_project_manager cyclic-project-dependencies}@anchor{170}
@subsection Cyclic Project Dependencies


Cyclic dependencies are mostly forbidden:
if @cite{A} imports @cite{B} (directly or indirectly) then @cite{B}
is not allowed to import @cite{A}. However, there are cases when cyclic
dependencies would be beneficial. For these cases, another form of import
between projects exists: the @strong{limited with}.  A project @cite{A} that
imports a project @cite{B} with a straight @emph{with} may also be imported,
directly or indirectly, by @cite{B} through a @cite{limited with}.

The difference between straight @emph{with} and @cite{limited with} is that
the name of a project imported with a @cite{limited with} cannot be used in the
project importing it. In particular, its packages cannot be renamed and
its variables cannot be referred to.

@example
with "b.gpr";
with "c.gpr";
project A is
    for Exec_Dir use B'Exec_Dir; -- ok
end A;

limited with "a.gpr";   --  Cyclic dependency: A -> B -> A
project B is
   for Exec_Dir use A'Exec_Dir; -- not ok
end B;

with "d.gpr";
project C is
end C;

limited with "a.gpr";  --  Cyclic dependency: A -> C -> D -> A
project D is
   for Exec_Dir use A'Exec_Dir; -- not ok
end D;
@end example

@node Sharing Between Projects,Global Attributes,Cyclic Project Dependencies,Organizing Projects into Subsystems
@anchor{gnat_ugn/gnat_project_manager sharing-between-projects}@anchor{171}@anchor{gnat_ugn/gnat_project_manager id17}@anchor{172}
@subsection Sharing Between Projects


When building an application, it is common to have similar needs in several of
the projects corresponding to the subsystems under construction. For instance,
they will all have the same compilation switches.

As seen before (see @ref{15e,,Tools Options in Project Files}), setting compilation
switches for all sources of a subsystem is simple: it is just a matter of
adding a @cite{Compiler.Default_Switches} attribute to each project files with
the same value. Of course, that means duplication of data, and both places need
to be changed in order to recompile the whole application with different
switches. It can become a real problem if there are many subsystems and thus
many project files to edit.

There are two main approaches to avoiding this duplication:


@itemize *

@item 
Since @code{build.gpr} imports @code{logging.gpr}, we could change it
to reference the attribute in Logging, either through a package renaming,
or by referencing the attribute. The following example shows both cases:

@example
project Logging is
   package Compiler is
      for Switches ("Ada")
          use ("-O2");
   end Compiler;
   package Binder is
      for Switches ("Ada")
          use ("-E");
   end Binder;
end Logging;

with "logging.gpr";
project Build is
   package Compiler renames Logging.Compiler;
   package Binder is
      for Switches ("Ada") use Logging.Binder'Switches ("Ada");
   end Binder;
end Build;
@end example

The solution used for @cite{Compiler} gets the same value for all
attributes of the package, but you cannot modify anything from the
package (adding extra switches or some exceptions). The second
version is more flexible, but more verbose.

If you need to refer to the value of a variable in an imported
project, rather than an attribute, the syntax is similar but uses
a "." rather than an apostrophe. For instance:

@example
with "imported";
project Main is
   Var1 := Imported.Var;
end Main;
@end example

@item 
The second approach is to define the switches in a third project.
That project is set up without any sources (so that, as opposed to
the first example, none of the project plays a special role), and
will only be used to define the attributes. Such a project is
typically called @code{shared.gpr}.

@example
abstract project Shared is
   for Source_Files use ();   --  no sources
   package Compiler is
      for Switches ("Ada")
          use ("-O2");
   end Compiler;
end Shared;

with "shared.gpr";
project Logging is
   package Compiler renames Shared.Compiler;
end Logging;

with "shared.gpr";
project Build is
   package Compiler renames Shared.Compiler;
end Build;
@end example

As for the first example, we could have chosen to set the attributes
one by one rather than to rename a package. The reason we explicitly
indicate that @cite{Shared} has no sources is so that it can be created
in any directory and we are sure it shares no sources with @cite{Build}
or @cite{Logging}, which of course would be invalid.

@geindex project qualifier (GNAT Project Manager)

Note the additional use of the @strong{abstract} qualifier in @code{shared.gpr}.
This qualifier is optional, but helps convey the message that we do not
intend this project to have sources (see @ref{173,,Qualified Projects} for
more qualifiers).
@end itemize

@node Global Attributes,,Sharing Between Projects,Organizing Projects into Subsystems
@anchor{gnat_ugn/gnat_project_manager global-attributes}@anchor{174}@anchor{gnat_ugn/gnat_project_manager id18}@anchor{175}
@subsection Global Attributes


We have already seen many examples of attributes used to specify a special
option of one of the tools involved in the build process. Most of those
attributes are project specific. That it to say, they only affect the invocation
of tools on the sources of the project where they are defined.

There are a few additional attributes that apply to all projects in a
hierarchy as long as they are defined on the "main" project.
The main project is the project explicitly mentioned on the command-line.
The project hierarchy is the "with"-closure of the main project.

Here is a list of commonly used global attributes:

@geindex Global_Configuration_Pragmas (GNAT Project Manager)

@strong{Builder.Global_Configuration_Pragmas}:

@quotation

This attribute points to a file that contains configuration pragmas
to use when building executables. These pragmas apply for all
executables built from this project hierarchy. As we have seen before,
additional pragmas can be specified on a per-project basis by setting the
@cite{Compiler.Local_Configuration_Pragmas} attribute.
@end quotation

@geindex Global_Compilation_Switches (GNAT Project Manager)

@strong{Builder.Global_Compilation_Switches}:

@quotation

This attribute is a list of compiler switches to use when compiling any
source file in the project hierarchy. These switches are used in addition
to the ones defined in the @cite{Compiler} package, which only apply to
the sources of the corresponding project. This attribute is indexed on
the name of the language.
@end quotation

Using such global capabilities is convenient. It can also lead to unexpected
behavior. Especially when several subsystems are shared among different main
projects and the different global attributes are not
compatible. Note that using aggregate projects can be a safer and more powerful
replacement to global attributes.

@node Scenarios in Projects,Library Projects,Organizing Projects into Subsystems,GNAT Project Manager
@anchor{gnat_ugn/gnat_project_manager id19}@anchor{176}@anchor{gnat_ugn/gnat_project_manager scenarios-in-projects}@anchor{14c}
@section Scenarios in Projects


Various aspects of the projects can be modified based on @strong{scenarios}. These
are user-defined modes that change the behavior of a project. Typical
examples are the setup of platform-specific compiler options, or the use of
a debug and a release mode (the former would activate the generation of debug
information, while the second will focus on improving code optimization).

Let's enhance our example to support debug and release modes. The issue is to
let the user choose what kind of system he is building: use @emph{-g} as
compiler switches in debug mode and @emph{-O2} in release mode. We will also
set up the projects so that we do not share the same object directory in both
modes; otherwise switching from one to the other might trigger more
recompilations than needed or mix objects from the two modes.

One naive approach is to create two different project files, say
@code{build_debug.gpr} and @code{build_release.gpr}, that set the appropriate
attributes as explained in previous sections. This solution does not scale
well, because in the presence of multiple projects depending on each other, you
will also have to duplicate the complete hierarchy and adapt the project files
to point to the right copies.

@geindex scenarios (GNAT Project Manager)

Instead, project files support the notion of scenarios controlled
by external values. Such values can come from several sources (in decreasing
order of priority):

@geindex -X (usage with GNAT Project Manager)


@table @asis

@item @strong{Command line}:

When launching @emph{gprbuild}, the user can pass
extra @emph{-X} switches to define the external value. In
our case, the command line might look like

@example
gprbuild -Pbuild.gpr -Xmode=release
@end example

@item @strong{Environment variables}:

When the external value does not come from the command line, it can come from
the value of environment variables of the appropriate name.
In our case, if an environment variable called "mode"
exists, its value will be taken into account.
@end table

@geindex external (GNAT Project Manager)

@strong{External function second parameter}.

We now need to get that value in the project. The general form is to use
the predefined function @strong{external} which returns the current value of
the external. For instance, we could set up the object directory to point to
either @code{obj/debug} or @code{obj/release} by changing our project to

@example
project Build is
    for Object_Dir use "obj/" & external ("mode", "debug");
    ... --  as before
end Build;
@end example

The second parameter to @cite{external} is optional, and is the default
value to use if "mode" is not set from the command line or the environment.

In order to set the switches according to the different scenarios, other
constructs have to be introduced such as typed variables and case constructions.

@geindex typed variable (GNAT Project Manager)

@geindex case construction (GNAT Project Manager)

A @strong{typed variable} is a variable that
can take only a limited number of values, similar to an enumeration in Ada.
Such a variable can then be used in a @strong{case construction} and create conditional
sections in the project. The following example shows how this can be done:

@example
project Build is
   type Mode_Type is ("debug", "release");  --  all possible values
   Mode : Mode_Type := external ("mode", "debug"); -- a typed variable

   package Compiler is
      case Mode is
         when "debug" =>
            for Switches ("Ada")
                use ("-g");
         when "release" =>
            for Switches ("Ada")
                use ("-O2");
      end case;
   end Compiler;
end Build;
@end example

The project has suddenly grown in size, but has become much more flexible.
@cite{Mode_Type} defines the only valid values for the @cite{mode} variable. If
any other value is read from the environment, an error is reported and the
project is considered as invalid.

The @cite{Mode} variable is initialized with an external value
defaulting to @cite{"debug"}. This default could be omitted and that would
force the user to define the value. Finally, we can use a case construction to set the
switches depending on the scenario the user has chosen.

Most aspects of the projects can depend on scenarios. The notable exception
are project dependencies (@emph{with} clauses), which cannot depend on a scenario.

Scenarios work the same way with @strong{project hierarchies}: you can either
duplicate a variable similar to @cite{Mode} in each of the project (as long
as the first argument to @cite{external} is always the same and the type is
the same), or simply set the variable in the @code{shared.gpr} project
(see @ref{171,,Sharing Between Projects}).

@node Library Projects,Project Extension,Scenarios in Projects,GNAT Project Manager
@anchor{gnat_ugn/gnat_project_manager library-projects}@anchor{8a}@anchor{gnat_ugn/gnat_project_manager id20}@anchor{177}
@section Library Projects


So far, we have seen examples of projects that create executables. However,
it is also possible to create libraries instead. A @strong{library} is a specific
type of subsystem where, for convenience, objects are grouped together
using system-specific means such as archives or windows DLLs.

Library projects provide a system- and language-independent way of building
both @strong{static} and @strong{dynamic} libraries. They also support the concept of
@strong{standalone libraries} (SAL) which offer two significant properties: the
elaboration (e.g. initialization) of the library is either automatic or
very simple; a change in the
implementation part of the library implies minimal post-compilation actions on
the complete system and potentially no action at all for the rest of the
system in the case of dynamic SALs.

There is a restriction on shared library projects: by default, they are only
allowed to import other shared library projects. They are not allowed to
import non library projects or static library projects.

The GNAT Project Manager takes complete care of the library build, rebuild and
installation tasks, including recompilation of the source files for which
objects do not exist or are not up to date, assembly of the library archive, and
installation of the library (i.e., copying associated source, object and
@code{ALI} files to the specified location).

@menu
* Building Libraries:: 
* Using Library Projects:: 
* Stand-alone Library Projects:: 
* Installing a library with project files:: 

@end menu

@node Building Libraries,Using Library Projects,,Library Projects
@anchor{gnat_ugn/gnat_project_manager id21}@anchor{178}@anchor{gnat_ugn/gnat_project_manager building-libraries}@anchor{179}
@subsection Building Libraries


Let's enhance our example and transform the @cite{logging} subsystem into a
library.  In order to do so, a few changes need to be made to
@code{logging.gpr}.  Some attributes need to be defined: at least
@cite{Library_Name} and @cite{Library_Dir}; in addition, some other attributes
can be used to specify specific aspects of the library. For readability, it is
also recommended (although not mandatory), to use the qualifier @cite{library}
in front of the @cite{project} keyword.

@geindex Library_Name (GNAT Project Manager)

@strong{Library_Name}:

@quotation

This attribute is the name of the library to be built. There is no
restriction on the name of a library imposed by the project manager, except
for stand-alone libraries whose names must follow the syntax of Ada
identifiers; however, there may be system-specific restrictions on the name.
In general, it is recommended to stick to alphanumeric characters (and
possibly single underscores) to help portability.
@end quotation

@geindex Library_Dir (GNAT Project Manager)

@strong{Library_Dir}:

@quotation

This attribute  is the path (absolute or relative) of the directory where
the library is to be installed. In the process of building a library,
the sources are compiled, the object files end up  in the explicit or
implicit @cite{Object_Dir} directory. When all sources of a library
are compiled, some of the compilation artifacts, including the library itself,
are copied to the library_dir directory. This directory must exist and be
writable. It must also be different from the object directory so that cleanup
activities in the Library_Dir do not affect recompilation needs.
@end quotation

Here is the new version of @code{logging.gpr} that makes it a library:

@example
library project Logging is          --  "library" is optional
   for Library_Name use "logging";  --  will create "liblogging.a" on Unix
   for Object_Dir   use "obj";
   for Library_Dir  use "lib";      --  different from object_dir
end Logging;
@end example

Once the above two attributes are defined, the library project is valid and
is enough for building a library with default characteristics.
Other library-related attributes can be used to change the defaults:

@geindex Library_Kind (GNAT Project Manager)

@strong{Library_Kind}:

@quotation

The value of this attribute must be either @cite{"static"}, @cite{"dynamic"} or
@cite{"relocatable"} (the latter is a synonym for dynamic). It indicates
which kind of library should be built (the default is to build a
static library, that is an archive of object files that can potentially
be linked into a static executable). When the library is set to be dynamic,
a separate image is created that will be loaded independently, usually
at the start of the main program execution. Support for dynamic libraries is
very platform specific, for instance on Windows it takes the form of a DLL
while on GNU/Linux, it is a dynamic elf image whose suffix is usually
@code{.so}. Library project files, on the other hand, can be written in
a platform independent way so that the same project file can be used to build
a library on different operating systems.

If you need to build both a static and a dynamic library, it is recommended
to use two different object directories, since in some cases some extra code
needs to be generated for the latter. For such cases, one can either define
two different project files, or a single one that uses scenarios to indicate
the various kinds of library to be built and their corresponding object_dir.
@end quotation

@geindex Library_ALI_Dir (GNAT Project Manager)

@strong{Library_ALI_Dir}:

@quotation

This attribute may be specified to indicate the directory where the ALI
files of the library are installed. By default, they are copied into the
@cite{Library_Dir} directory, but as for the executables where we have a
separate @cite{Exec_Dir} attribute, you might want to put them in a separate
directory since there can be hundreds of them. The same restrictions as for
the @cite{Library_Dir} attribute apply.
@end quotation

@geindex Library_Version (GNAT Project Manager)

@strong{Library_Version}:

@quotation

This attribute is platform dependent, and has no effect on Windows.
On Unix, it is used only for dynamic libraries as the internal
name of the library (the @cite{"soname"}). If the library file name (built
from the @cite{Library_Name}) is different from the @cite{Library_Version},
then the library file will be a symbolic link to the actual file whose name
will be @cite{Library_Version}. This follows the usual installation schemes
for dynamic libraries on many Unix systems.

@example
project Logging is
   Version := "1";
   for Library_Dir use "lib";
   for Library_Name use "logging";
   for Library_Kind use "dynamic";
   for Library_Version use "liblogging.so." & Version;
end Logging;
@end example

After the compilation, the directory @code{lib} will contain both a
@code{libdummy.so.1} library and a symbolic link to it called
@code{libdummy.so}.
@end quotation

@geindex Library_GCC (GNAT Project Manager)

@strong{Library_GCC}:

@quotation

This attribute is the name of the tool to use instead of "gcc" to link shared
libraries. A common use of this attribute is to define a wrapper script that
accomplishes specific actions before calling gcc (which itself calls the
linker to build the library image).
@end quotation

@geindex Library_Options (GNAT Project Manager)

@strong{Library_Options}:

@quotation

This attribute may be used to specify additional switches (last switches)
when linking a shared library.

It may also be used to add foreign object files to a static library.
Each string in Library_Options is an absolute or relative path of an object
file. When a relative path, it is relative to the object directory.
@end quotation

@geindex Leading_Library_Options (GNAT Project Manager)

@strong{Leading_Library_Options}:

@quotation

This attribute, that is taken into account only by @emph{gprbuild}, may be
used to specified leading options (first switches) when linking a shared
library.
@end quotation

@geindex Linker_Options (GNAT Project Manager)

@strong{Linker.Linker_Options}:

@quotation

This attribute specifies additional switches to be given to the linker when
linking an executable. It is ignored when defined in the main project and
taken into account in all other projects that are imported directly or
indirectly. These switches complement the @cite{Linker.Switches}
defined in the main project. This is useful when a particular subsystem
depends on an external library: adding this dependency as a
@cite{Linker_Options} in the project of the subsystem is more convenient than
adding it to all the @cite{Linker.Switches} of the main projects that depend
upon this subsystem.
@end quotation

@node Using Library Projects,Stand-alone Library Projects,Building Libraries,Library Projects
@anchor{gnat_ugn/gnat_project_manager id22}@anchor{17a}@anchor{gnat_ugn/gnat_project_manager using-library-projects}@anchor{17b}
@subsection Using Library Projects


When the builder detects that a project file is a library project file, it
recompiles all sources of the project that need recompilation and rebuild the
library if any of the sources have been recompiled. It then groups all object
files into a single file, which is a shared or a static library. This library
can later on be linked with multiple executables. Note that the use
of shard libraries reduces the size of the final executable and can also reduce
the memory footprint at execution time when the library is shared among several
executables.

@emph{gprbuild also allows to build **multi-language libraries*} when specifying
sources from multiple languages.

A non-library project can import a library project. When the builder is invoked
on the former, the library of the latter is only rebuilt when absolutely
necessary. For instance, if a unit of the library is not up-to-date but none of
the executables need this unit, then the unit is not recompiled and the library
is not reassembled.  For instance, let's assume in our example that logging has
the following sources: @code{log1.ads}, @code{log1.adb}, @code{log2.ads} and
@code{log2.adb}. If @code{log1.adb} has been modified, then the library
@code{liblogging} will be rebuilt when compiling all the sources of
@cite{Build} only if @code{proc.ads}, @code{pack.ads} or @code{pack.adb}
include a @cite{"with Log1"}.

To ensure that all the sources in the @cite{Logging} library are
up to date, and that all the sources of @cite{Build} are also up to date,
the following two commands need to be used:

@example
gprbuild -Plogging.gpr
gprbuild -Pbuild.gpr
@end example

All @code{ALI} files will also be copied from the object directory to the
library directory. To build executables, @emph{gprbuild} will use the
library rather than the individual object files.

Library projects can also be useful to describe a library that needs to be used
but, for some reason, cannot be rebuilt. For instance, it is the case when some
of the library sources are not available. Such library projects need to use the
@cite{Externally_Built} attribute as in the example below:

@c code-block: ada-project
@c 
@c library project Extern_Lib is
@c    for Languages    use ("Ada", "C");
@c    for Source_Dirs  use ("lib_src");
@c    for Library_Dir  use "lib2";
@c    for Library_Kind use "dynamic";
@c    for Library_Name use "l2";
@c    for Externally_Built use "true";  --  <<<<
@c end Extern_Lib;

In the case of externally built libraries, the @cite{Object_Dir}
attribute does not need to be specified because it will never be
used.

The main effect of using such an externally built library project is mostly to
affect the linker command in order to reference the desired library. It can
also be achieved by using @cite{Linker.Linker_Options} or @cite{Linker.Switches}
in the project corresponding to the subsystem needing this external library.
This latter method is more straightforward in simple cases but when several
subsystems depend upon the same external library, finding the proper place
for the @cite{Linker.Linker_Options} might not be easy and if it is
not placed properly, the final link command is likely to present ordering issues.
In such a situation, it is better to use the externally built library project
so that all other subsystems depending on it can declare this dependency thanks
to a project @emph{with} clause, which in turn will trigger the builder to find
the proper order of libraries in the final link command.

@node Stand-alone Library Projects,Installing a library with project files,Using Library Projects,Library Projects
@anchor{gnat_ugn/gnat_project_manager id23}@anchor{17c}@anchor{gnat_ugn/gnat_project_manager stand-alone-library-projects}@anchor{97}
@subsection Stand-alone Library Projects


@geindex standalone libraries (usage with GNAT Project Manager)

A @strong{stand-alone library} is a library that contains the necessary code to
elaborate the Ada units that are included in the library. A stand-alone
library is a convenient way to add an Ada subsystem to a more global system
whose main is not in Ada since it makes the elaboration of the Ada part mostly
transparent. However, stand-alone libraries are also useful when the main is in
Ada: they provide a means for minimizing relinking & redeployment of complex
systems when localized changes are made.

The name of a stand-alone library, specified with attribute
@cite{Library_Name}, must have the syntax of an Ada identifier.

The most prominent characteristic of a stand-alone library is that it offers a
distinction between interface units and implementation units. Only the former
are visible to units outside the library. A stand-alone library project is thus
characterised by a third attribute, usually @strong{Library_Interface}, in addition
to the two attributes that make a project a Library Project
(@cite{Library_Name} and @cite{Library_Dir}). This third attribute may also be
@strong{Interfaces}. @strong{Library_Interface} only works when the interface is in Ada
and takes a list of units as parameter. @strong{Interfaces} works for any supported
language and takes a list of sources as parameter.

@geindex Library_Interface (GNAT Project Manager)

@strong{Library_Interface}:

@quotation

This attribute defines an explicit subset of the units of the project. Units
from projects importing this library project may only "with" units whose
sources are listed in the @cite{Library_Interface}. Other sources are
considered implementation units.

@example
for Library_Dir use "lib";
for Library_Name use "logging";
for Library_Interface use ("lib1", "lib2");  --  unit names
@end example
@end quotation

@strong{Interfaces}

@quotation

This attribute defines an explicit subset of the source files of a project.
Sources from projects importing this project, can only depend on sources from
this subset. This attribute can be used on non library projects. It can also
be used as a replacement for attribute @cite{Library_Interface}, in which
case, units have to be replaced by source files. For multi-language library
projects, it is the only way to make the project a Stand-Alone Library project
whose interface is not purely Ada.
@end quotation

@geindex Library_Standalone (GNAT Project Manager)

@strong{Library_Standalone}:

@quotation

This attribute defines the kind of standalone library to
build. Values are either @cite{standard} (the default), @cite{no} or
@cite{encapsulated}. When @cite{standard} is used the code to elaborate and
finalize the library is embedded, when @cite{encapsulated} is used the
library can furthermore depend only on static libraries (including
the GNAT runtime). This attribute can be set to @cite{no} to make it clear
that the library should not be standalone in which case the
@cite{Library_Interface} should not defined. Note that this attribute
only applies to shared libraries, so @cite{Library_Kind} must be set
to @cite{dynamic}.

@example
for Library_Dir use "lib";
for Library_Name use "logging";
for Library_Kind use "dynamic";
for Library_Interface use ("lib1", "lib2");  --  unit names
for Library_Standalone use "encapsulated";
@end example
@end quotation

In order to include the elaboration code in the stand-alone library, the binder
is invoked on the closure of the library units creating a package whose name
depends on the library name (b~logging.ads/b in the example).
This binder-generated package includes @strong{initialization} and @strong{finalization}
procedures whose names depend on the library name (@cite{logginginit} and
@cite{loggingfinal} in the example). The object corresponding to this package is
included in the library.

@geindex Library_Auto_Init (GNAT Project Manager)

@strong{Library_Auto_Init}:

@quotation

A dynamic stand-alone Library is automatically initialized
if automatic initialization of Stand-alone Libraries is supported on the
platform and if attribute @strong{Library_Auto_Init} is not specified or
is specified with the value "true". A static Stand-alone Library is never
automatically initialized. Specifying "false" for this attribute
prevents automatic initialization.

When a non-automatically initialized stand-alone library is used in an
executable, its initialization procedure must be called before any service of
the library is used. When the main subprogram is in Ada, it may mean that the
initialization procedure has to be called during elaboration of another
package.
@end quotation

@geindex Library_Dir (GNAT Project Manager)

@strong{Library_Dir}:

@quotation

For a stand-alone library, only the @code{ALI} files of the interface units
(those that are listed in attribute @cite{Library_Interface}) are copied to
the library directory. As a consequence, only the interface units may be
imported from Ada units outside of the library. If other units are imported,
the binding phase will fail.
@end quotation

@strong{Binder.Default_Switches}:

@quotation

When a stand-alone library is bound, the switches that are specified in
the attribute @strong{Binder.Default_Switches ("Ada")} are
used in the call to @emph{gnatbind}.
@end quotation

@geindex Library_Src_Dir (GNAT Project Manager)

@strong{Library_Src_Dir}:

@quotation

This attribute defines the location (absolute or relative to the project
directory) where the sources of the interface units are copied at
installation time.
These sources includes the specs of the interface units along with the
closure of sources necessary to compile them successfully. That may include
bodies and subunits, when pragmas @cite{Inline} are used, or when there are
generic units in specs. This directory cannot point to the object directory
or one of the source directories, but it can point to the library directory,
which is the default value for this attribute.
@end quotation

@geindex Library_Symbol_Policy (GNAT Project Manager)

@strong{Library_Symbol_Policy}:

@quotation

This attribute controls the export of symbols and, on some platforms (like
VMS) that have the notions of major and minor IDs built in the library
files, it controls the setting of these IDs. It is not supported on all
platforms (where it will just have no effect). It may have one of the
following values:


@itemize *

@item 
@cite{"autonomous"} or @cite{"default"}: exported symbols are not controlled

@item 
@cite{"compliant"}: if attribute @strong{Library_Reference_Symbol_File}
is not defined, then it is equivalent to policy "autonomous". If there
are exported symbols in the reference symbol file that are not in the
object files of the interfaces, the major ID of the library is increased.
If there are symbols in the object files of the interfaces that are not
in the reference symbol file, these symbols are put at the end of the list
in the newly created symbol file and the minor ID is increased.

@item 
@cite{"controlled"}: the attribute @strong{Library_Reference_Symbol_File} must be
defined. The library will fail to build if the exported symbols in the
object files of the interfaces do not match exactly the symbol in the
symbol file.

@item 
@cite{"restricted"}: The attribute @strong{Library_Symbol_File} must be defined.
The library will fail to build if there are symbols in the symbol file that
are not in the exported symbols of the object files of the interfaces.
Additional symbols in the object files are not added to the symbol file.

@item 
@cite{"direct"}: The attribute @strong{Library_Symbol_File} must be defined and
must designate an existing file in the object directory. This symbol file
is passed directly to the underlying linker without any symbol processing.
@end itemize
@end quotation

@geindex Library_Reference_Symbol_File (GNAT Project Manager)

@strong{Library_Reference_Symbol_File}

@quotation

This attribute may define the path name of a reference symbol file that is
read when the symbol policy is either "compliant" or "controlled", on
platforms that support symbol control, such as VMS, when building a
stand-alone library. The path may be an absolute path or a path relative
to the project directory.
@end quotation

@geindex Library_Symbol_File (GNAT Project Manager)

@strong{Library_Symbol_File}

@quotation

This attribute may define the name of the symbol file to be created when
building a stand-alone library when the symbol policy is either "compliant",
"controlled" or "restricted", on platforms that support symbol control,
such as VMS. When symbol policy is "direct", then a file with this name
must exist in the object directory.
@end quotation

@node Installing a library with project files,,Stand-alone Library Projects,Library Projects
@anchor{gnat_ugn/gnat_project_manager installing-a-library-with-project-files}@anchor{8d}@anchor{gnat_ugn/gnat_project_manager id24}@anchor{17d}
@subsection Installing a library with project files


When using project files, a usable version of the library is created in the
directory specified by the @cite{Library_Dir} attribute of the library
project file. Thus no further action is needed in order to make use of
the libraries that are built as part of the general application build.

You may want to install a library in a context different from where the library
is built. This situation arises with third party suppliers, who may want
to distribute a library in binary form where the user is not expected to be
able to recompile the library. The simplest option in this case is to provide
a project file slightly different from the one used to build the library, by
using the @cite{externally_built} attribute. See @ref{17b,,Using Library Projects}

Another option is to use @emph{gprinstall} to install the library in a
different context than the build location. @emph{gprinstall} automatically
generates a project to use this library, and also copies the minimum set of
sources needed to use the library to the install location.
@ref{168,,Installation}

@node Project Extension,Aggregate Projects,Library Projects,GNAT Project Manager
@anchor{gnat_ugn/gnat_project_manager id25}@anchor{17e}@anchor{gnat_ugn/gnat_project_manager project-extension}@anchor{14f}
@section Project Extension


During development of a large system, it is sometimes necessary to use
modified versions of some of the source files, without changing the original
sources. This can be achieved through the @strong{project extension} facility.

Suppose for instance that our example @cite{Build} project is built every night
for the whole team, in some shared directory. A developer usually needs to work
on a small part of the system, and might not want to have a copy of all the
sources and all the object files (mostly because that would require too much
disk space, time to recompile everything). He prefers to be able to override
some of the source files in his directory, while taking advantage of all the
object files generated at night.

Another example can be taken from large software systems, where it is common to have
multiple implementations of a common interface; in Ada terms, multiple
versions of a package body for the same spec.  For example, one implementation
might be safe for use in tasking programs, while another might be used only
in sequential applications.  This can be modeled in GNAT using the concept
of @emph{project extension}.  If one project (the 'child') @emph{extends}
another project (the 'parent') then by default all source files of the
parent project are inherited by the child, but the child project can
override any of the parent's source files with new versions, and can also
add new files or remove unnecessary ones.
This facility is the project analog of a type extension in
object-oriented programming.  Project hierarchies are permitted (an extending
project may itself be extended), and a project that
extends a project can also import other projects.

A third example is that of using project extensions to provide different
versions of the same system. For instance, assume that a @cite{Common}
project is used by two development branches. One of the branches has now
been frozen, and no further change can be done to it or to @cite{Common}.
However, the other development branch still needs evolution of @cite{Common}.
Project extensions provide a flexible solution to create a new version
of a subsystem while sharing and reusing as much as possible from the original
one.

A project extension implicitly inherits all the sources and objects from the
project it extends. It is possible to create a new version of some of the
sources in one of the additional source directories of the extending
project. Those new versions hide the original versions. Adding new sources or
removing existing ones is also possible. Here is an example on how to extend
the project @cite{Build} from previous examples:

@example
project Work extends "../bld/build.gpr" is
end Work;
@end example

The project after @strong{extends} is the one being extended. As usual, it can be
specified using an absolute path, or a path relative to any of the directories
in the project path (see @ref{16c,,Project Dependencies}). This project does not
specify source or object directories, so the default values for these
attributes will be used that is to say the current directory (where project
@cite{Work} is placed). We can compile that project with

@example
gprbuild -Pwork
@end example

If no sources have been placed in the current directory, this command
won't do anything, since this project does not change the
sources it inherited from @cite{Build}, therefore all the object files
in @cite{Build} and its dependencies are still valid and are reused
automatically.

Suppose we now want to supply an alternate version of @code{pack.adb} but use
the existing versions of @code{pack.ads} and @code{proc.adb}.  We can create
the new file in Work's current directory (likely by copying the one from the
@cite{Build} project and making changes to it. If new packages are needed at
the same time, we simply create new files in the source directory of the
extending project.

When we recompile, @emph{gprbuild} will now automatically recompile
this file (thus creating @code{pack.o} in the current directory) and
any file that depends on it (thus creating @code{proc.o}). Finally, the
executable is also linked locally.

Note that we could have obtained the desired behavior using project import
rather than project inheritance. A @cite{base} project would contain the
sources for @code{pack.ads} and @code{proc.adb}, and @cite{Work} would
import @cite{base} and add @code{pack.adb}. In this scenario,  @cite{base}
cannot contain the original version of @code{pack.adb} otherwise there would be
2 versions of the same unit in the closure of the project and this is not
allowed. Generally speaking, it is not recommended to put the spec and the
body of a unit in different projects since this affects their autonomy and
reusability.

In a project file that extends another project, it is possible to
indicate that an inherited source is @strong{not part} of the sources of the
extending project. This is necessary sometimes when a package spec has
been overridden and no longer requires a body: in this case, it is
necessary to indicate that the inherited body is not part of the sources
of the project, otherwise there will be a compilation error
when compiling the spec.

@geindex Excluded_Source_Files (GNAT Project Manager)

@geindex Excluded_Source_List_File (GNAT Project Manager)

For that purpose, the attribute @strong{Excluded_Source_Files} is used.
Its value is a list of file names.
It is also possible to use attribute @cite{Excluded_Source_List_File}.
Its value is the path of a text file containing one file name per
line.

@example
project Work extends "../bld/build.gpr" is
   for Source_Files use ("pack.ads");
   --  New spec of Pkg does not need a completion
   for Excluded_Source_Files use ("pack.adb");
end Work;
@end example

All packages that are not declared in the extending project are inherited from
the project being extended, with their attributes, with the exception of
@cite{Linker'Linker_Options} which is never inherited. In particular, an
extending project retains all the switches specified in the project being
extended.

At the project level, if they are not declared in the extending project, some
attributes are inherited from the project being extended. They are:
@cite{Languages}, @cite{Main} (for a root non library project) and
@cite{Library_Name} (for a project extending a library project).

@menu
* Project Hierarchy Extension:: 

@end menu

@node Project Hierarchy Extension,,,Project Extension
@anchor{gnat_ugn/gnat_project_manager project-hierarchy-extension}@anchor{17f}@anchor{gnat_ugn/gnat_project_manager id26}@anchor{180}
@subsection Project Hierarchy Extension


One of the fundamental restrictions in project extension is the following:
@strong{A project is not allowed to import directly or indirectly at the same time an extending project and one of its ancestors}.

For example, consider the following hierarchy of projects.

@example
a.gpr  contains package A1
b.gpr, imports a.gpr and contains B1, which depends on A1
c.gpr, imports b.gpr and contains C1, which depends on B1
@end example

If we want to locally extend the packages @cite{A1} and @cite{C1}, we need to
create several extending projects:

@example
a_ext.gpr which extends a.gpr, and overrides A1
b_ext.gpr which extends b.gpr and imports a_ext.gpr
c_ext.gpr which extends c.gpr, imports b_ext.gpr and overrides C1
@end example

@example
project A_Ext extends "a.gpr" is
   for Source_Files use ("a1.adb", "a1.ads");
end A_Ext;

with "a_ext.gpr";
project B_Ext extends "b.gpr" is
end B_Ext;

with "b_ext.gpr";
project C_Ext extends "c.gpr" is
   for Source_Files use ("c1.adb");
end C_Ext;
@end example

The extension @code{b_ext.gpr} is required, even though we are not overriding
any of the sources of @code{b.gpr} because otherwise @code{c_expr.gpr} would
import @code{b.gpr} which itself knows nothing about @code{a_ext.gpr}.

@geindex extends all (GNAT Project Manager)

When extending a large system spanning multiple projects, it is often
inconvenient to extend every project in the hierarchy that is impacted by a
small change introduced in a low layer. In such cases, it is possible to create
an @strong{implicit extension} of an entire hierarchy using @strong{extends all}
relationship.

When the project is extended using @cite{extends all} inheritance, all projects
that are imported by it, both directly and indirectly, are considered virtually
extended. That is, the project manager creates implicit projects
that extend every project in the hierarchy; all these implicit projects do not
control sources on their own and use the object directory of
the "extending all" project.

It is possible to explicitly extend one or more projects in the hierarchy
in order to modify the sources. These extending projects must be imported by
the "extending all" project, which will replace the corresponding virtual
projects with the explicit ones.

When building such a project hierarchy extension, the project manager will
ensure that both modified sources and sources in implicit extending projects
that depend on them are recompiled.

Thus, in our example we could create the following projects instead:

@example
a_ext.gpr, extends a.gpr and overrides A1
c_ext.gpr, "extends all" c.gpr, imports a_ext.gpr and overrides C1
@end example

@example
project A_Ext extends "a.gpr" is
   for Source_Files use ("a1.adb", "a1.ads");
end A_Ext;

with "a_ext.gpr";
project C_Ext extends all "c.gpr" is
  for Source_Files use ("c1.adb");
end C_Ext;
@end example

When building project @code{c_ext.gpr}, the entire modified project space is
considered for recompilation, including the sources of @code{b.gpr} that are
impacted by the changes in @cite{A1} and @cite{C1}.

@node Aggregate Projects,Aggregate Library Projects,Project Extension,GNAT Project Manager
@anchor{gnat_ugn/gnat_project_manager aggregate-projects}@anchor{16e}@anchor{gnat_ugn/gnat_project_manager id27}@anchor{181}
@section Aggregate Projects


Aggregate projects are an extension of the project paradigm, and are
meant to solve a few specific use cases that cannot be solved directly
using standard projects. This section will go over a few of these use
cases to try to explain what you can use aggregate projects for.

@menu
* Building all main programs from a single project tree:: 
* Building a set of projects with a single command:: 
* Define a build environment:: 
* Performance improvements in builder:: 
* Syntax of aggregate projects:: 
* package Builder in aggregate projects:: 

@end menu

@node Building all main programs from a single project tree,Building a set of projects with a single command,,Aggregate Projects
@anchor{gnat_ugn/gnat_project_manager id28}@anchor{182}@anchor{gnat_ugn/gnat_project_manager building-all-main-programs-from-a-single-project-tree}@anchor{183}
@subsection Building all main programs from a single project tree


Most often, an application is organized into modules and submodules,
which are very conveniently represented as a project tree or graph
(the root project A @emph{with}s the projects for each modules (say B and C),
which in turn @emph{with} projects for submodules.

Very often, modules will build their own executables (for testing
purposes for instance), or libraries (for easier reuse in various
contexts).

However, if you build your project through @emph{gprbuild}, using a syntax similar to

@example
gprbuild -PA.gpr
@end example

this will only rebuild the main programs of project A, not those of the
imported projects B and C. Therefore you have to spawn several
@emph{gprbuild} commands, one per project, to build all executables.
This is a little inconvenient, but more importantly is inefficient
because @emph{gprbuild} needs to do duplicate work to ensure that sources are
up-to-date, and cannot easily compile things in parallel when using
the -j switch.

Also libraries are always rebuilt when building a project.

You could therefore define an aggregate project Agg that groups A, B
and C. Then, when you build with

@example
gprbuild -PAgg.gpr
@end example

this will build all mains from A, B and C.

@example
aggregate project Agg is
   for Project_Files use ("a.gpr", "b.gpr", "c.gpr");
end Agg;
@end example

If B or C do not define any main program (through their Main
attribute), all their sources are built. When you do not group them
in the aggregate project, only those sources that are needed by A
will be built.

If you add a main to a project P not already explicitly referenced in the
aggregate project, you will need to add "p.gpr" in the list of project
files for the aggregate project, or the main will not be built when
building the aggregate project.

@node Building a set of projects with a single command,Define a build environment,Building all main programs from a single project tree,Aggregate Projects
@anchor{gnat_ugn/gnat_project_manager building-a-set-of-projects-with-a-single-command}@anchor{184}@anchor{gnat_ugn/gnat_project_manager id29}@anchor{185}
@subsection Building a set of projects with a single command


One other case is when you have multiple applications and libraries
that are built independently from each other (but can be built in
parallel). For instance, you have a project tree rooted at A, and
another one (which might share some subprojects) rooted at B.

Using only @emph{gprbuild}, you could do

@example
gprbuild -PA.gpr
gprbuild -PB.gpr
@end example

to build both. But again, @emph{gprbuild} has to do some duplicate work for
those files that are shared between the two, and cannot truly build
things in parallel efficiently.

If the two projects are really independent, share no sources other
than through a common subproject, and have no source files with a
common basename, you could create a project C that imports A and
B. But these restrictions are often too strong, and one has to build
them independently. An aggregate project does not have these
limitations and can aggregate two project trees that have common
sources.

This scenario is particularly useful in environments like VxWorks 653
where the applications running in the multiple partitions can be built
in parallel through a single @emph{gprbuild} command. This also works nicely
with Annex E.

@node Define a build environment,Performance improvements in builder,Building a set of projects with a single command,Aggregate Projects
@anchor{gnat_ugn/gnat_project_manager id30}@anchor{186}@anchor{gnat_ugn/gnat_project_manager define-a-build-environment}@anchor{187}
@subsection Define a build environment


The environment variables at the time you launch @emph{gprbuild}
will influence the view these tools have of the project
(PATH to find the compiler, ADA_PROJECT_PATH or GPR_PROJECT_PATH to find the
projects, environment variables that are referenced in project files
through the "external" built-in function, ...). Several command line switches
can be used to override those (-X or -aP), but on some systems and
with some projects, this might make the command line too long, and on
all systems often make it hard to read.

An aggregate project can be used to set the environment for all
projects built through that aggregate. One of the nice aspects is that
you can put the aggregate project under configuration management, and
make sure all your user have a consistent environment when
building. The syntax looks like

@example
aggregate project Agg is
   for Project_Files use ("A.gpr", "B.gpr");
   for Project_Path use ("../dir1", "../dir1/dir2");
   for External ("BUILD") use "PRODUCTION";

   package Builder is
      for Switches ("Ada") use ("-q");
   end Builder;
end Agg;
@end example

One of the often requested features in projects is to be able to
reference external variables in @emph{with} declarations, as in

@example
with external("SETUP") & "path/prj.gpr";   --  ILLEGAL
project MyProject is
   ...
end MyProject;
@end example

For various reasons, this is not allowed. But using aggregate projects provide
an elegant solution. For instance, you could use a project file like:

@example
aggregate project Agg is
    for Project_Path use (external("SETUP") & "path");
    for Project_Files use ("myproject.gpr");
end Agg;

with "prj.gpr";  --  searched on Agg'Project_Path
project MyProject is
   ...
end MyProject;
@end example

@node Performance improvements in builder,Syntax of aggregate projects,Define a build environment,Aggregate Projects
@anchor{gnat_ugn/gnat_project_manager performance-improvements-in-builder}@anchor{188}@anchor{gnat_ugn/gnat_project_manager id31}@anchor{189}
@subsection Performance improvements in builder


The loading of aggregate projects is optimized in @emph{gprbuild},
so that all files are searched for only once on the disk
(thus reducing the number of system calls and contributing to faster
compilation times, especially on systems with sources on remote
servers). As part of the loading, @emph{gprbuild}
computes how and where a source file should be compiled, and even if it is
found several times in the aggregated projects it will be compiled only
once.

Since there is no ambiguity as to which switches should be used, files
can be compiled in parallel (through the usual -j switch) and this can
be done while maximizing the use of CPUs (compared to launching
multiple @emph{gprbuild} commands in parallel).

@node Syntax of aggregate projects,package Builder in aggregate projects,Performance improvements in builder,Aggregate Projects
@anchor{gnat_ugn/gnat_project_manager id32}@anchor{18a}@anchor{gnat_ugn/gnat_project_manager syntax-of-aggregate-projects}@anchor{18b}
@subsection Syntax of aggregate projects


An aggregate project follows the general syntax of project files. The
recommended extension is still @code{.gpr}. However, a special
@cite{aggregate} qualifier must be put before the keyword
@cite{project}.

An aggregate project cannot @emph{with} any other project (standard or
aggregate), except an abstract project which can be used to share attribute
values. Also, aggregate projects cannot be extended or imported though a
@emph{with} clause by any other project. Building other aggregate projects from
an aggregate project is done through the Project_Files attribute (see below).

An aggregate project does not have any source files directly (only
through other standard projects). Therefore a number of the standard
attributes and packages are forbidden in an aggregate project. Here is the
(non exhaustive) list:


@itemize *

@item 
Languages

@item 
Source_Files, Source_List_File and other attributes dealing with
list of sources.

@item 
Source_Dirs, Exec_Dir and Object_Dir

@item 
Library_Dir, Library_Name and other library-related attributes

@item 
Main

@item 
Roots

@item 
Externally_Built

@item 
Inherit_Source_Path

@item 
Excluded_Source_Dirs

@item 
Locally_Removed_Files

@item 
Excluded_Source_Files

@item 
Excluded_Source_List_File

@item 
Interfaces
@end itemize

The only package that is authorized (albeit optional) is
Builder. Other packages (in particular Compiler, Binder and Linker)
are forbidden.

The following three attributes can be used only in an aggregate project:

@geindex Project_Files (GNAT Project Manager)

@strong{Project_Files}:

@quotation

This attribute is compulsory (or else we are not aggregating any project,
and thus not doing anything). It specifies a list of @code{.gpr} files
that are grouped in the aggregate. The list may be empty. The project
files can be either other aggregate projects, or standard projects. When
grouping standard projects, you can have both the root of a project tree
(and you do not need to specify all its imported projects), and any project
within the tree.

Basically, the idea is to specify all those projects that have
main programs you want to build and link, or libraries you want to
build. You can even specify projects that do not use the Main
attribute nor the @cite{Library_*} attributes, and the result will be to
build all their source files (not just the ones needed by other
projects).

The file can include paths (absolute or relative). Paths are relative to
the location of the aggregate project file itself (if you use a base name,
we expect to find the .gpr file in the same directory as the aggregate
project file). The environment variables @cite{ADA_PROJECT_PATH},
@cite{GPR_PROJECT_PATH} and @cite{GPR_PROJECT_PATH_FILE} are not used to find
the project files. The extension @code{.gpr} is mandatory, since this attribute
contains file names, not project names.

Paths can also include the @cite{"*"} and @cite{"**"} globbing patterns. The
latter indicates that any subdirectory (recursively) will be
searched for matching files. The latter (@cite{"**"}) can only occur at the
last position in the directory part (ie @cite{"a/**/*.gpr"} is supported, but
not @cite{"**/a/*.gpr"}). Starting the pattern with @cite{"**"} is equivalent
to starting with @cite{"./**"}.

For now, the pattern @cite{"*"} is only allowed in the filename part, not
in the directory part. This is mostly for efficiency reasons to limit the
number of system calls that are needed.

Here are a few valid examples:

@example
for Project_Files use ("a.gpr", "subdir/b.gpr");
--  two specific projects relative to the directory of agg.gpr

for Project_Files use ("/.gpr");
--  all projects recursively
@end example
@end quotation

@geindex Project_Path (GNAT Project Manager)

@strong{Project_Path}:

@quotation

This attribute can be used to specify a list of directories in
which to look for project files in @emph{with} declarations.

When you specify a project in Project_Files (say @cite{x/y/a.gpr}), and
@cite{a.gpr} imports a project @cite{b.gpr}, only @cite{b.gpr} is searched in
the project path. @cite{a.gpr} must be exactly at
@cite{<dir of the aggregate>/x/y/a.gpr}.

This attribute, however, does not affect the search for the aggregated
project files specified with @cite{Project_Files}.

Each aggregate project has its own @cite{Project_Path} (that is if
@cite{agg1.gpr} includes @cite{agg2.gpr}, they can potentially both have a
different @cite{Project_Path}).

This project path is defined as the concatenation, in that order, of:


@itemize *

@item 
the current directory;

@item 
followed by the command line -aP switches;

@item 
then the directories from the GPR_PROJECT_PATH and ADA_PROJECT_PATH environment
variables;

@item 
then the directories from the Project_Path attribute;

@item 
and finally the predefined directories.
@end itemize

In the example above, agg2.gpr's project path is not influenced by
the attribute agg1'Project_Path, nor is agg1 influenced by
agg2'Project_Path.

This can potentially lead to errors. Consider the following example:

@example
--
--  +---------------+                  +----------------+
--  | Agg1.gpr      |-=--includes--=-->| Agg2.gpr       |
--  |  'project_path|                  |  'project_path |
--  |               |                  |                |
--  +---------------+                  +----------------+
--        :                                   :
--        includes                        includes
--        :                                   :
--        v                                   v
--    +-------+                          +---------+
--    | P.gpr |<---------- withs --------|  Q.gpr  |
--    +-------+---------\                +---------+
--        |             |
--        withs         |
--        |             |
--        v             v
--    +-------+      +---------+
--    | R.gpr |      | R'.gpr  |
--    +-------+      +---------+
@end example

When looking for p.gpr, both aggregates find the same physical file on
the disk. However, it might happen that with their different project
paths, both aggregate projects would in fact find a different r.gpr.
Since we have a common project (p.gpr) "with"ing two different r.gpr,
this will be reported as an error by the builder.

Directories are relative to the location of the aggregate project file.

Example:

@example
for Project_Path use ("/usr/local/gpr", "gpr/");
@end example
@end quotation

@geindex External (GNAT Project Manager)

@strong{External}:

@quotation

This attribute can be used to set the value of environment
variables as retrieved through the @cite{external} function
in projects. It does not affect the environment variables
themselves (so for instance you cannot use it to change the value
of your PATH as seen from the spawned compiler).

This attribute affects the external values as seen in the rest of
the aggregate project, and in the aggregated projects.

The exact value of external a variable comes from one of three
sources (each level overrides the previous levels):


@itemize *

@item 
An External attribute in aggregate project, for instance
@cite{for External ("BUILD_MODE") use "DEBUG"};

@item 
Environment variables.
These override the value given by the attribute, so that
users can override the value set in the (presumably shared
with others team members) aggregate project.

@item 
The -X command line switch to @emph{gprbuild}.
This always takes precedence.
@end itemize

This attribute is only taken into account in the main aggregate
project (i.e. the one specified on the command line to @emph{gprbuild}),
and ignored in other aggregate projects. It is invalid
in standard projects.
The goal is to have a consistent value in all
projects that are built through the aggregate, which would not
be the case in the diamond case: A groups the aggregate
projects B and C, which both (either directly or indirectly)
build the project P. If B and C could set different values for
the environment variables, we would have two different views of
P, which in particular might impact the list of source files in P.
@end quotation

@node package Builder in aggregate projects,,Syntax of aggregate projects,Aggregate Projects
@anchor{gnat_ugn/gnat_project_manager package-builder-in-aggregate-projects}@anchor{18c}@anchor{gnat_ugn/gnat_project_manager id33}@anchor{18d}
@subsection package Builder in aggregate projects


As mentioned above, only the package Builder can be specified in
an aggregate project. In this package, only the following attributes
are valid:

@geindex Switches (GNAT Project Manager)

@strong{Switches}:

@quotation

This attribute gives the list of switches to use for @emph{gprbuild}.
Because no mains can be specified for aggregate projects, the only possible
index for attribute @cite{Switches} is @cite{others}. All other indexes will
be ignored.

Example:

@example
for Switches (others) use ("-v", "-k", "-j8");
@end example

These switches are only read from the main aggregate project (the
one passed on the command line), and ignored in all other aggregate
projects or projects.

It can only contain builder switches, not compiler switches.
@end quotation

@geindex Global_Compilation_Switches (GNAT Project Manager)

@strong{Global_Compilation_Switches}

@quotation

This attribute gives the list of compiler switches for the various
languages. For instance,

@example
for Global_Compilation_Switches ("Ada") use ("O1", "-g");
for Global_Compilation_Switches ("C")   use ("-O2");
@end example

This attribute is only taken into account in the aggregate project
specified on the command line, not in other aggregate projects.

In the projects grouped by that aggregate, the attribute
Builder.Global_Compilation_Switches is also ignored. However, the
attribute Compiler.Default_Switches will be taken into account (but
that of the aggregate have higher priority). The attribute
Compiler.Switches is also taken into account and can be used to
override the switches for a specific file. As a result, it always
has priority.

The rules are meant to avoid ambiguities when compiling. For
instance, aggregate project Agg groups the projects A and B, that
both depend on C. Here is an extra for all of these projects:

@example
aggregate project Agg is
    for Project_Files use ("a.gpr", "b.gpr");
    package Builder is
       for Global_Compilation_Switches ("Ada") use ("-O2");
    end Builder;
end Agg;

with "c.gpr";
project A is
    package Builder is
       for Global_Compilation_Switches ("Ada") use ("-O1");
       --  ignored
    end Builder;

    package Compiler is
       for Default_Switches ("Ada")
           use ("-O1", "-g");
       for Switches ("a_file1.adb")
           use ("-O0");
    end Compiler;
end A;

with "c.gpr";
project B is
    package Compiler is
       for Default_Switches ("Ada") use ("-O0");
    end Compiler;
end B;

project C is
    package Compiler is
       for Default_Switches ("Ada")
           use ("-O3",
                "-gnatn");
       for Switches ("c_file1.adb")
           use ("-O0", "-g");
    end Compiler;
end C;
@end example

then the following switches are used:


@itemize *

@item 
all files from project A except a_file1.adb are compiled
with "-O2 -g", since the aggregate project has priority.

@item 
the file a_file1.adb is compiled with
"-O0", since the Compiler.Switches has priority

@item 
all files from project B are compiled with
"-O2", since the aggregate project has priority

@item 
all files from C are compiled with "-O2 -gnatn", except for
c_file1.adb which is compiled with "-O0 -g"
@end itemize

Even though C is seen through two paths (through A and through
B), the switches used by the compiler are unambiguous.
@end quotation

@geindex Global_Configuration_Pragmas (GNAT Project Manager)

@strong{Global_Configuration_Pragmas}

@quotation

This attribute can be used to specify a file containing
configuration pragmas, to be passed to the Ada compiler.  Since we
ignore the package Builder in other aggregate projects and projects,
only those pragmas defined in the main aggregate project will be
taken into account.

Projects can locally add to those by using the
@cite{Compiler.Local_Configuration_Pragmas} attribute if they need.
@end quotation

@geindex Global_Config_File (GNAT Project Manager)

@strong{Global_Config_File}

@quotation

This attribute, indexed with a language name, can be used to specify a config
when compiling sources of the language. For Ada, these files are configuration
pragmas files.
@end quotation

For projects that are built through the aggregate, the package Builder
is ignored, except for the Executable attribute which specifies the
name of the executables resulting from the link of the main programs, and
for the Executable_Suffix.

@node Aggregate Library Projects,Project File Reference,Aggregate Projects,GNAT Project Manager
@anchor{gnat_ugn/gnat_project_manager id34}@anchor{18e}@anchor{gnat_ugn/gnat_project_manager aggregate-library-projects}@anchor{18f}
@section Aggregate Library Projects


Aggregate library projects make it possible to build a single library
using object files built using other standard or library
projects. This gives the flexibility to describe an application as
having multiple modules (a GUI, database access, ...) using different
project files (so possibly built with different compiler options) and
yet create a single library (static or relocatable) out of the
corresponding object files.

@menu
* Building aggregate library projects:: 
* Syntax of aggregate library projects:: 

@end menu

@node Building aggregate library projects,Syntax of aggregate library projects,,Aggregate Library Projects
@anchor{gnat_ugn/gnat_project_manager building-aggregate-library-projects}@anchor{190}@anchor{gnat_ugn/gnat_project_manager id35}@anchor{191}
@subsection Building aggregate library projects


For example, we can define an aggregate project Agg that groups A, B
and C:

@example
aggregate library project Agg is
   for Project_Files use ("a.gpr", "b.gpr", "c.gpr");
   for Library_Name use ("agg");
   for Library_Dir use ("lagg");
end Agg;
@end example

Then, when you build with:

@example
gprbuild agg.gpr
@end example

This will build all units from projects A, B and C and will create a
static library named @code{libagg.a} in the @code{lagg}
directory. An aggregate library project has the same set of
restriction as a standard library project.

Note that a shared aggregate library project cannot aggregate a
static library project. In platforms where a compiler option is
required to create relocatable object files, a Builder package in the
aggregate library project may be used:

@example
aggregate library project Agg is
   for Project_Files use ("a.gpr", "b.gpr", "c.gpr");
   for Library_Name use ("agg");
   for Library_Dir use ("lagg");
   for Library_Kind use "relocatable";

   package Builder is
      for Global_Compilation_Switches ("Ada") use ("-fPIC");
   end Builder;
end Agg;
@end example

With the above aggregate library Builder package, the @cite{-fPIC}
option will be passed to the compiler when building any source code
from projects @code{a.gpr}, @code{b.gpr} and @code{c.gpr}.

@node Syntax of aggregate library projects,,Building aggregate library projects,Aggregate Library Projects
@anchor{gnat_ugn/gnat_project_manager syntax-of-aggregate-library-projects}@anchor{192}@anchor{gnat_ugn/gnat_project_manager id36}@anchor{193}
@subsection Syntax of aggregate library projects


An aggregate library project follows the general syntax of project
files. The recommended extension is still @code{.gpr}. However, a special
@cite{aggregate library} qualifier must be put before the keyword
@cite{project}.

An aggregate library project cannot @emph{with} any other project
(standard or aggregate), except an abstract project which can be used
to share attribute values.

An aggregate library project does not have any source files directly (only
through other standard projects). Therefore a number of the standard
attributes and packages are forbidden in an aggregate library
project. Here is the (non exhaustive) list:


@itemize *

@item 
Languages

@item 
Source_Files, Source_List_File and other attributes dealing with
list of sources.

@item 
Source_Dirs, Exec_Dir and Object_Dir

@item 
Main

@item 
Roots

@item 
Externally_Built

@item 
Inherit_Source_Path

@item 
Excluded_Source_Dirs

@item 
Locally_Removed_Files

@item 
Excluded_Source_Files

@item 
Excluded_Source_List_File

@item 
Interfaces
@end itemize

The only package that is authorized (albeit optional) is Builder.

The Project_Files attribute (See @ref{16e,,Aggregate Projects}) is used to
described the aggregated projects whose object files have to be
included into the aggregate library. The environment variables
@cite{ADA_PROJECT_PATH}, @cite{GPR_PROJECT_PATH} and
@cite{GPR_PROJECT_PATH_FILE} are not used to find the project files.

@node Project File Reference,,Aggregate Library Projects,GNAT Project Manager
@anchor{gnat_ugn/gnat_project_manager id37}@anchor{194}@anchor{gnat_ugn/gnat_project_manager project-file-reference}@anchor{14d}
@section Project File Reference


This section describes the syntactic structure of project files, the various
constructs that can be used. Finally, it ends with a summary of all available
attributes.

@menu
* Project Declaration:: 
* Qualified Projects:: 
* Declarations:: 
* Packages:: 
* Expressions:: 
* External Values:: 
* Typed String Declaration:: 
* Variables:: 
* Case Constructions:: 
* Attributes:: 

@end menu

@node Project Declaration,Qualified Projects,,Project File Reference
@anchor{gnat_ugn/gnat_project_manager id38}@anchor{195}@anchor{gnat_ugn/gnat_project_manager project-declaration}@anchor{196}
@subsection Project Declaration


Project files have an Ada-like syntax. The minimal project file is:

@example
project Empty is
end Empty;
@end example

The identifier @cite{Empty} is the name of the project.
This project name must be present after the reserved
word @cite{end} at the end of the project file, followed by a semi-colon.

@strong{Identifiers} (i.e., the user-defined names such as project or variable names)
have the same syntax as Ada identifiers: they must start with a letter,
and be followed by zero or more letters, digits or underscore characters;
it is also illegal to have two underscores next to each other. Identifiers
are always case-insensitive ("Name" is the same as "name").

@example
simple_name ::= identifier
name        ::= simple_name @{ . simple_name @}
@end example

@strong{Strings} are used for values of attributes or as indexes for these
attributes. They are in general case sensitive, except when noted
otherwise (in particular, strings representing file names will be case
insensitive on some systems, so that "file.adb" and "File.adb" both
represent the same file).

@strong{Reserved words} are the same as for standard Ada 95, and cannot
be used for identifiers. In particular, the following words are currently
used in project files, but others could be added later on. In bold are the
extra reserved words in project files:
@code{all}, @code{at}, @code{case}, @code{end}, @code{for}, @code{is}, @code{limited},
@code{null}, @code{others}, @code{package}, @code{renames}, @code{type}, @code{use}, @code{when},
@code{with}, @strong{extends}, @strong{external}, @strong{project}.

@strong{Comments} in project files have the same syntax as in Ada, two consecutive
hyphens through the end of the line.

A project may be an @strong{independent project}, entirely defined by a single
project file. Any source file in an independent project depends only
on the predefined library and other source files in the same project.
But a project may also depend on other projects, either by importing them
through @strong{with clauses}, or by @strong{extending} at most one other project. Both
types of dependency can be used in the same project.

A path name denotes a project file. It can be absolute or relative.
An absolute path name includes a sequence of directories, in the syntax of
the host operating system, that identifies uniquely the project file in the
file system. A relative path name identifies the project file, relative
to the directory that contains the current project, or relative to a
directory listed in the environment variables ADA_PROJECT_PATH and
GPR_PROJECT_PATH. Path names are case sensitive if file names in the host
operating system are case sensitive. As a special case, the directory
separator can always be "/" even on Windows systems, so that project files
can be made portable across architectures.
The syntax of the environment variables ADA_PROJECT_PATH and
GPR_PROJECT_PATH is a list of directory names separated by colons on UNIX and
semicolons on Windows.

A given project name can appear only once in a context clause.

It is illegal for a project imported by a context clause to refer, directly
or indirectly, to the project in which this context clause appears (the
dependency graph cannot contain cycles), except when one of the with clauses
in the cycle is a @strong{limited with}.

@example
with "other_project.gpr";
project My_Project extends "extended.gpr" is
end My_Project;
@end example

These dependencies form a @strong{directed graph}, potentially cyclic when using
@strong{limited with}. The subgraph reflecting the @strong{extends} relations is a tree.

A project's @strong{immediate sources} are the source files directly defined by
that project, either implicitly by residing in the project source directories,
or explicitly through any of the source-related attributes.
More generally, a project's @strong{sources} are the immediate sources of the
project together with the immediate sources (unless overridden) of any project
on which it depends directly or indirectly.

A @strong{project hierarchy} can be created, where projects are children of
other projects. The name of such a child project must be @cite{Parent.Child},
where @cite{Parent} is the name of the parent project. In particular, this
makes all @emph{with} clauses of the parent project automatically visible
in the child project.

@example
project        ::= context_clause project_declaration

context_clause ::= @{with_clause@}
with_clause    ::= *with* path_name @{ , path_name @} ;
path_name      ::= string_literal

project_declaration ::= simple_project_declaration | project_extension
simple_project_declaration ::=
  project <project_>name is
    @{declarative_item@}
  end <project_>simple_name;
@end example

@node Qualified Projects,Declarations,Project Declaration,Project File Reference
@anchor{gnat_ugn/gnat_project_manager qualified-projects}@anchor{173}@anchor{gnat_ugn/gnat_project_manager id39}@anchor{197}
@subsection Qualified Projects


Before the reserved @cite{project}, there may be one or two @strong{qualifiers}, that
is identifiers or reserved words, to qualify the project.
The current list of qualifiers is:


@table @asis

@item @strong{abstract}:

Qualifies a project with no sources.
Such a   project must either have no declaration of attributes @cite{Source_Dirs},
@cite{Source_Files}, @cite{Languages} or @cite{Source_List_File}, or one of
@cite{Source_Dirs}, @cite{Source_Files}, or @cite{Languages} must be declared
as empty. If it extends another project, the project it extends must also be a
qualified abstract project.

@item @strong{standard}:

A standard project is a non library project with sources.
This is the default (implicit) qualifier.

@item @strong{aggregate}:

A project whose sources are aggregated from other project files.

@item @strong{aggregate library}:

A library whose sources are aggregated from other project
or library project files.

@item @strong{library}:

A library project must declare both attributes
Library_Name` and @cite{Library_Dir}.

@item @strong{configuration}:

A configuration project cannot be in a project tree.
It describes compilers and other tools to @emph{gprbuild}.
@end table

@node Declarations,Packages,Qualified Projects,Project File Reference
@anchor{gnat_ugn/gnat_project_manager declarations}@anchor{198}@anchor{gnat_ugn/gnat_project_manager id40}@anchor{199}
@subsection Declarations


Declarations introduce new entities that denote types, variables, attributes,
and packages. Some declarations can only appear immediately within a project
declaration. Others can appear within a project or within a package.

@example
declarative_item ::= simple_declarative_item
  | typed_string_declaration
  | package_declaration

simple_declarative_item ::= variable_declaration
  | typed_variable_declaration
  | attribute_declaration
  | case_construction
  | empty_declaration

empty_declaration ::= *null* ;
@end example

An empty declaration is allowed anywhere a declaration is allowed. It has
no effect.

@node Packages,Expressions,Declarations,Project File Reference
@anchor{gnat_ugn/gnat_project_manager packages}@anchor{153}@anchor{gnat_ugn/gnat_project_manager id41}@anchor{19a}
@subsection Packages


A project file may contain @strong{packages}, that group attributes (typically
all the attributes that are used by one of the GNAT tools).

A package with a given name may only appear once in a project file.
The following packages are currently supported in project files
(See @ref{152,,Attributes} for the list of attributes that each can contain).


@table @asis

@item @emph{Binder}

This package specifies characteristics useful when invoking the binder either
directly via the @emph{gnat} driver or when using @emph{gprbuild}.
See @ref{15d,,Main Subprograms}.

@item @emph{Builder}

This package specifies the compilation options used when building an
executable or a library for a project. Most of the options should be
set in one of @cite{Compiler}, @cite{Binder} or @cite{Linker} packages,
but there are some general options that should be defined in this
package. See @ref{15d,,Main Subprograms}, and @ref{162,,Executable File Names} in
particular.
@end table



@table @asis

@item @emph{Clean}

This package specifies the options used when cleaning a project or a project
tree using the tools @emph{gnatclean} or @emph{gprclean}.

@item @emph{Compiler}

This package specifies the compilation options used by the compiler for
each languages. See @ref{15e,,Tools Options in Project Files}.

@item @emph{Cross_Reference}

This package specifies the options used when calling the library tool
@emph{gnatxref} via the @emph{gnat} driver. Its attributes
@strong{Default_Switches} and @strong{Switches} have the same semantics as for the
package @cite{Builder}.
@end table



@table @asis

@item @emph{Finder}

This package specifies the options used when calling the search tool
@emph{gnatfind} via the @emph{gnat} driver. Its attributes
@strong{Default_Switches} and @strong{Switches} have the same semantics as for the
package @cite{Builder}.

@item @emph{Gnatls}

This package specifies the options to use when invoking @emph{gnatls}
via the @emph{gnat} driver.
@end table



@table @asis

@item @emph{IDE}

This package specifies the options used when starting an integrated
development environment, for instance @emph{GPS} or @emph{Gnatbench}.

@item @emph{Install}

This package specifies the options used when installing a project
with @emph{gprinstall}. See @ref{168,,Installation}.

@item @emph{Linker}

This package specifies the options used by the linker.
See @ref{15d,,Main Subprograms}.
@end table



@table @asis

@item @emph{Naming}

@quotation

This package specifies the naming conventions that apply
to the source files in a project. In particular, these conventions are
used to automatically find all source files in the source directories,
or given a file name to find out its language for proper processing.
See @ref{14b,,Naming Schemes}.
@end quotation

@c only: PRO or GPL
@c 
@c *Pretty_Printer*
@c   This package specifies the options used when calling the formatting tool
@c   *gnatpp* via the *gnat* driver. Its attributes
@c   **Default_Switches** and **Switches** have the same semantics as for the
@c   package `Builder`.

@item @emph{Remote}

This package is used by @emph{gprbuild} to describe how distributed
compilation should be done.

@item @emph{Stack}

This package specifies the options used when calling the tool
@emph{gnatstack} via the @emph{gnat} driver. Its attributes
@strong{Default_Switches} and @strong{Switches} have the same semantics as for the
package @cite{Builder}.

@item @emph{Synchronize}

This package specifies the options used when calling the tool
@emph{gnatsync} via the @emph{gnat} driver.
@end table

In its simplest form, a package may be empty:

@example
project Simple is
  package Builder is
  end Builder;
end Simple;
@end example

A package may contain @strong{attribute declarations},
@strong{variable declarations} and @strong{case constructions}, as will be
described below.

When there is ambiguity between a project name and a package name,
the name always designates the project. To avoid possible confusion, it is
always a good idea to avoid naming a project with one of the
names allowed for packages or any name that starts with @cite{gnat}.

A package can also be defined by a @strong{renaming declaration}. The new package
renames a package declared in a different project file, and has the same
attributes as the package it renames. The name of the renamed package
must be the same as the name of the renaming package. The project must
contain a package declaration with this name, and the project
must appear in the context clause of the current project, or be its parent
project. It is not possible to add or override attributes to the renaming
project. If you need to do so, you should use an @strong{extending declaration}
(see below).

Packages that are renamed in other project files often come from project files
that have no sources: they are just used as templates. Any modification in the
template will be reflected automatically in all the project files that rename
a package from the template. This is a very common way to share settings
between projects.

Finally, a package can also be defined by an @strong{extending declaration}. This is
similar to a @strong{renaming declaration}, except that it is possible to add or
override attributes.

@example
package_declaration ::= package_spec | package_renaming | package_extension
package_spec ::=
  package <package_>simple_name is
    @{simple_declarative_item@}
  end package_identifier ;
package_renaming ::==
  package <package_>simple_name renames <project_>simple_name.package_identifier ;
package_extension ::==
  package <package_>simple_name extends <project_>simple_name.package_identifier is
    @{simple_declarative_item@}
  end package_identifier ;
@end example

@node Expressions,External Values,Packages,Project File Reference
@anchor{gnat_ugn/gnat_project_manager expressions}@anchor{19b}@anchor{gnat_ugn/gnat_project_manager id42}@anchor{19c}
@subsection Expressions


An expression is any value that can be assigned to an attribute or a
variable. It is either a literal value, or a construct requiring runtime
computation by the project manager. In a project file, the computed value of
an expression is either a string or a list of strings.

A string value is one of:


@itemize *

@item 
A literal string, for instance @cite{"comm/my_proj.gpr"}

@item 
The name of a variable that evaluates to a string (see @ref{155,,Variables})

@item 
The name of an attribute that evaluates to a string (see @ref{152,,Attributes})

@item 
An external reference (see @ref{154,,External Values})

@item 
A concatenation of the above, as in @cite{"prefix_" & Var}.
@end itemize

A list of strings is one of the following:


@itemize *

@item 
A parenthesized comma-separated list of zero or more string expressions, for
instance @cite{(File_Name@comma{} "gnat.adc"@comma{} File_Name & ".orig")} or @cite{()}.

@item 
The name of a variable that evaluates to a list of strings

@item 
The name of an attribute that evaluates to a list of strings

@item 
A concatenation of a list of strings and a string (as defined above), for
instance @cite{("A"@comma{} "B") & "C"}

@item 
A concatenation of two lists of strings
@end itemize

The following is the grammar for expressions

@example
string_literal ::= "@{string_element@}"  --  Same as Ada
string_expression ::= string_literal
    | *variable_*name
    | external_value
    | attribute_reference
    | ( string_expression @{ & string_expression @} )
string_list  ::= ( string_expression @{ , string_expression @} )
   | *string_variable*_name
   | *string_*attribute_reference
term ::= string_expression | string_list
expression ::= term @{ & term @}     --  Concatenation
@end example

Concatenation involves strings and list of strings. As soon as a list of
strings is involved, the result of the concatenation is a list of strings. The
following Ada declarations show the existing operators:

@example
function "&" (X : String;      Y : String)      return String;
function "&" (X : String_List; Y : String)      return String_List;
function "&" (X : String_List; Y : String_List) return String_List;
@end example

Here are some specific examples:

@example
List := () & File_Name; --  One string in this list
List2 := List & (File_Name & ".orig"); -- Two strings
Big_List := List & Lists2;  --  Three strings
Illegal := "gnat.adc" & List2;  --  Illegal, must start with list
@end example

@node External Values,Typed String Declaration,Expressions,Project File Reference
@anchor{gnat_ugn/gnat_project_manager external-values}@anchor{154}@anchor{gnat_ugn/gnat_project_manager id43}@anchor{19d}
@subsection External Values


An external value is an expression whose value is obtained from the command
that invoked the processing of the current project file (typically a
@emph{gprbuild} command).

There are two kinds of external values, one that returns a single string, and
one that returns a string list.

The syntax of a single string external value is:

@example
external_value ::= *external* ( string_literal [, string_literal] )
@end example

The first string_literal is the string to be used on the command line or
in the environment to specify the external value. The second string_literal,
if present, is the default to use if there is no specification for this
external value either on the command line or in the environment.

Typically, the external value will either exist in the
environment variables
or be specified on the command line through the
@code{-X@emph{vbl}=@emph{value}} switch. If both
are specified, then the command line value is used, so that a user can more
easily override the value.

The function @cite{external} always returns a string. It is an error if the
value was not found in the environment and no default was specified in the
call to @cite{external}.

An external reference may be part of a string expression or of a string
list expression, and can therefore appear in a variable declaration or
an attribute declaration.

Most of the time, this construct is used to initialize typed variables, which
are then used in @strong{case} constructions to control the value assigned to
attributes in various scenarios. Thus such variables are often called
@strong{scenario variables}.

The syntax for a string list external value is:

@example
external_value ::= *external_as_list* ( string_literal , string_literal )
@end example

The first string_literal is the string to be used on the command line or
in the environment to specify the external value. The second string_literal is
the separator between each component of the string list.

If the external value does not exist in the environment or on the command line,
the result is an empty list. This is also the case, if the separator is an
empty string or if the external value is only one separator.

Any separator at the beginning or at the end of the external value is
discarded. Then, if there is no separator in the external value, the result is
a string list with only one string. Otherwise, any string between the beginning
and the first separator, between two consecutive separators and between the
last separator and the end are components of the string list.

@example
*external_as_list* ("SWITCHES", ",")
@end example

If the external value is "-O2,-g",
the result is ("-O2", "-g").

If the external value is ",-O2,-g,",
the result is also ("-O2", "-g").

if the external value is "-gnatv",
the result is ("-gnatv").

If the external value is ",,", the result is ("").

If the external value is ",", the result is (), the empty string list.

@node Typed String Declaration,Variables,External Values,Project File Reference
@anchor{gnat_ugn/gnat_project_manager id44}@anchor{19e}@anchor{gnat_ugn/gnat_project_manager typed-string-declaration}@anchor{19f}
@subsection Typed String Declaration


A @strong{type declaration} introduces a discrete set of string literals.
If a string variable is declared to have this type, its value
is restricted to the given set of literals. These are the only named
types in project files. A string type may only be declared at the project
level, not inside a package.

@example
typed_string_declaration ::=
  *type* *<typed_string_>*_simple_name *is* ( string_literal @{, string_literal@} );
@end example

The string literals in the list are case sensitive and must all be different.
They may include any graphic characters allowed in Ada, including spaces.
Here is an example of a string type declaration:

@example
type OS is ("NT", "nt", "Unix", "GNU/Linux", "other OS");
@end example

Variables of a string type are called @strong{typed variables}; all other
variables are called @strong{untyped variables}. Typed variables are
particularly useful in @cite{case} constructions, to support conditional
attribute declarations. (See @ref{1a0,,Case Constructions}).

A string type may be referenced by its name if it has been declared in the same
project file, or by an expanded name whose prefix is the name of the project
in which it is declared.

@node Variables,Case Constructions,Typed String Declaration,Project File Reference
@anchor{gnat_ugn/gnat_project_manager variables}@anchor{155}@anchor{gnat_ugn/gnat_project_manager id45}@anchor{1a1}
@subsection Variables


@strong{Variables} store values (strings or list of strings) and can appear
as part of an expression. The declaration of a variable creates the
variable and assigns the value of the expression to it. The name of the
variable is available immediately after the assignment symbol, if you
need to reuse its old value to compute the new value. Before the completion
of its first declaration, the value of a variable defaults to the empty
string ("").

A @strong{typed} variable can be used as part of a @strong{case} expression to
compute the value, but it can only be declared once in the project file,
so that all case constructions see the same value for the variable. This
provides more consistency and makes the project easier to understand.
The syntax for its declaration is identical to the Ada syntax for an
object declaration. In effect, a typed variable acts as a constant.

An @strong{untyped} variable can be declared and overridden multiple times
within the same project. It is declared implicitly through an Ada
assignment. The first declaration establishes the kind of the variable
(string or list of strings) and successive declarations must respect
the initial kind. Assignments are executed in the order in which they
appear, so the new value replaces the old one and any subsequent reference
to the variable uses the new value.

A variable may be declared at the project file level, or within a package.

@example
typed_variable_declaration ::=
  *<typed_variable_>*simple_name : *<typed_string_>*name := string_expression;

variable_declaration ::= *<variable_>*simple_name := expression;
@end example

Here are some examples of variable declarations:

@example
This_OS : OS := external ("OS"); --  a typed variable declaration
That_OS := "GNU/Linux";          --  an untyped variable declaration

Name      := "readme.txt";
Save_Name := Name & ".saved";

Empty_List := ();
List_With_One_Element := ("-gnaty");
List_With_Two_Elements := List_With_One_Element & "-gnatg";
Long_List := ("main.ada", "pack1_.ada", "pack1.ada", "pack2_.ada");
@end example

A @strong{variable reference} may take several forms:


@itemize *

@item 
The simple variable name, for a variable in the current package (if any)
or in the current project

@item 
An expanded name, whose prefix is a context name.
@end itemize

A @strong{context} may be one of the following:


@itemize *

@item 
The name of an existing package in the current project

@item 
The name of an imported project of the current project

@item 
The name of an ancestor project (i.e., a project extended by the current
project, either directly or indirectly)

@item 
An expanded name whose prefix is an imported/parent project name, and
whose selector is a package name in that project.
@end itemize

@node Case Constructions,Attributes,Variables,Project File Reference
@anchor{gnat_ugn/gnat_project_manager id46}@anchor{1a2}@anchor{gnat_ugn/gnat_project_manager case-constructions}@anchor{1a0}
@subsection Case Constructions


A @strong{case} construction is used in a project file to effect conditional
behavior. Through this construction, you can set the value of attributes
and variables depending on the value previously assigned to a typed
variable.

All choices in a choice list must be distinct. Unlike Ada, the choice
lists of all alternatives do not need to include all values of the type.
An @cite{others} choice must appear last in the list of alternatives.

The syntax of a @cite{case} construction is based on the Ada case construction
(although the @cite{null} declaration for empty alternatives is optional).

The case expression must be a string variable, either typed or not, whose value
is often given by an external reference (see @ref{154,,External Values}).

Each alternative starts with the reserved word @cite{when}, either a list of
literal strings separated by the @cite{"|"} character or the reserved word
@cite{others}, and the @cite{"=>"} token.
When the case expression is a typed string variable, each literal string must
belong to the string type that is the type of the case variable.
After each @cite{=>}, there are zero or more declarations.  The only
declarations allowed in a case construction are other case constructions,
attribute declarations and variable declarations. String type declarations and
package declarations are not allowed. Variable declarations are restricted to
variables that have already been declared before the case construction.

@example
case_construction ::=
  *case* *<variable_>*name *is* @{case_item@} *end case* ;

case_item ::=
  *when* discrete_choice_list =>
    @{case_declaration
      | attribute_declaration
      | variable_declaration
      | empty_declaration@}

discrete_choice_list ::= string_literal @{| string_literal@} | *others*
@end example

Here is a typical example, with a typed string variable:

@example
project MyProj is
   type OS_Type is ("GNU/Linux", "Unix", "NT", "VMS");
   OS : OS_Type := external ("OS", "GNU/Linux");

   package Compiler is
     case OS is
       when "GNU/Linux" | "Unix" =>
         for Switches ("Ada")
             use ("-gnath");
       when "NT" =>
         for Switches ("Ada")
             use ("-gnatP");
       when others =>
         null;
     end case;
   end Compiler;
end MyProj;
@end example

@node Attributes,,Case Constructions,Project File Reference
@anchor{gnat_ugn/gnat_project_manager id47}@anchor{1a3}@anchor{gnat_ugn/gnat_project_manager attributes}@anchor{152}
@subsection Attributes


A project (and its packages) may have @strong{attributes} that define
the project's properties.  Some attributes have values that are strings;
others have values that are string lists.

@example
attribute_declaration ::=
   simple_attribute_declaration | indexed_attribute_declaration

simple_attribute_declaration ::= *for* attribute_designator *use* expression ;

indexed_attribute_declaration ::=
  *for* *<indexed_attribute_>*simple_name ( string_literal) *use* expression ;

attribute_designator ::=
  *<simple_attribute_>*simple_name
  | *<indexed_attribute_>*simple_name ( string_literal )
@end example

There are two categories of attributes: @strong{simple attributes}
and @strong{indexed attributes}.
Each simple attribute has a default value: the empty string (for string
attributes) and the empty list (for string list attributes).
An attribute declaration defines a new value for an attribute, and overrides
the previous value. The syntax of a simple attribute declaration is similar to
that of an attribute definition clause in Ada.

Some attributes are indexed. These attributes are mappings whose
domain is a set of strings. They are declared one association
at a time, by specifying a point in the domain and the corresponding image
of the attribute.
Like untyped variables and simple attributes, indexed attributes
may be declared several times. Each declaration supplies a new value for the
attribute, and replaces the previous setting.

Here are some examples of attribute declarations:

@example
--  simple attributes
for Object_Dir use "objects";
for Source_Dirs use ("units", "test/drivers");

--  indexed attributes
for Body ("main") use "Main.ada";
for Switches ("main.ada")
    use ("-v", "-gnatv");
for Switches ("main.ada") use Builder'Switches ("main.ada") & "-g";

--  indexed attributes copy (from package Builder in project Default)
--  The package name must always be specified, even if it is the current
--  package.
for Default_Switches use Default.Builder'Default_Switches;
@end example

Attributes references may appear anywhere in expressions, and are used
to retrieve the value previously assigned to the attribute. If an attribute
has not been set in a given package or project, its value defaults to the
empty string or the empty list, with some exceptions.

@example
attribute_reference ::=
  attribute_prefix ' *<simple_attribute>_*simple_name [ (string_literal) ]
attribute_prefix ::= *project*
  | *<project_>*simple_name
  | package_identifier
  | *<project_>*simple_name . package_identifier
@end example

Examples are:

@example
<project>'Object_Dir
Naming'Dot_Replacement
Imported_Project'Source_Dirs
Imported_Project.Naming'Casing
Builder'Default_Switches ("Ada")
@end example

The exceptions to the empty defaults are:


@itemize *

@item 
Object_Dir: default is "."

@item 
Exec_Dir: default is 'Object_Dir, that is the value of attribute
Object_Dir in the same project, declared or defaulted.

@item 
Source_Dirs: default is (".")
@end itemize

The prefix of an attribute may be:


@itemize *

@item 
@cite{project} for an attribute of the current project

@item 
The name of an existing package of the current project

@item 
The name of an imported project

@item 
The name of a parent project that is extended by the current project

@item 
An expanded name whose prefix is imported/parent project name,
and whose selector is a package name
@end itemize

In the following sections, all predefined attributes are succinctly described,
first the project level attributes, that is those attributes that are not in a
package, then the attributes in the different packages.

It is possible for different tools to dynamically create new packages with
attributes, or new attributes in predefined packages. These attributes are
not documented here.

The attributes under Configuration headings are usually found only in
configuration project files.

The characteristics of each attribute are indicated as follows:


@itemize *

@item 
@strong{Type of value}

The value of an attribute may be a single string, indicated by the word
"single", or a string list, indicated by the word "list".

@item 
@strong{Read-only}

When the attribute is read-only, that is when it is not allowed to declare
the attribute, this is indicated by the words "read-only".

@item 
@strong{Optional index}

If it is allowed in the value of the attribute (both single and list) to have
an optional index, this is indicated by the words "optional index".

@item 
@strong{Indexed attribute}

When it is an indexed attribute, this is indicated by the word "indexed".

@item 
@strong{Case-sensitivity of the index}

For an indexed attribute, if the index is case-insensitive, this is indicated
by the words "case-insensitive index".

@item 
@strong{File name index}

For an indexed attribute, when the index is a file name, this is indicated by
the words "file name index". The index may or may not be case-sensitive,
depending on the platform.

@item 
@strong{others allowed in index}

For an indexed attribute, if it is allowed to use @strong{others} as the index,
this is indicated by the words "others allowed".

When @strong{others} is used as the index of an indexed attribute, the value of
the attribute indexed by @strong{others} is used when no other index would apply.
@end itemize

@menu
* Project Level Attributes:: 
* Package Binder Attributes:: 
* Package Builder Attributes:: 
* Package Clean Attributes:: 
* Package Compiler Attributes:: 
* Package Cross_Reference Attributes:: 
* Package Finder Attributes:: 
* Package gnatls Attributes:: 
* Package IDE Attributes:: 
* Package Install Attributes:: 
* Package Linker Attributes:: 
* Package Naming Attributes:: 
* Package Remote Attributes:: 
* Package Stack Attributes:: 
* Package Synchronize Attributes:: 

@end menu

@node Project Level Attributes,Package Binder Attributes,,Attributes
@anchor{gnat_ugn/gnat_project_manager project-level-attributes}@anchor{1a4}@anchor{gnat_ugn/gnat_project_manager id48}@anchor{1a5}
@subsubsection Project Level Attributes



@itemize *

@item 
@strong{General}


@itemize *

@item 
@strong{Name}: single, read-only

The name of the project.

@item 
@strong{Project_Dir}: single, read-only

The path name of the project directory.

@item 
@strong{Main}: list, optional index

The list of main sources for the executables.

@item 
@strong{Languages}: list

The list of languages of the sources of the project.

@item 
@strong{Roots}: list, indexed, file name index

The index is the file name of an executable source. Indicates the list of units
from the main project that need to be bound and linked with their closures
with the executable. The index is either a file name, a language name or "*".
The roots for an executable source are those in @strong{Roots} with an index that
is the executable source file name, if declared. Otherwise, they are those in
@strong{Roots} with an index that is the language name of the executable source,
if present. Otherwise, they are those in @strong{Roots ("*")}, if declared. If none
of these three possibilities are declared, then there are no roots for the
executable source.

@item 
@strong{Externally_Built}: single

Indicates if the project is externally built.
Only case-insensitive values allowed are "true" and "false", the default.
@end itemize

@item 
@strong{Directories}


@itemize *

@item 
@strong{Object_Dir}: single

Indicates the object directory for the project.

@item 
@strong{Exec_Dir}: single

Indicates the exec directory for the project, that is the directory where the
executables are.

@item 
@strong{Source_Dirs}: list

The list of source directories of the project.

@item 
@strong{Inherit_Source_Path}: list, indexed, case-insensitive index

Index is a language name. Value is a list of language names. Indicates that
in the source search path of the index language the source directories of
the languages in the list should be included.

Example:

@example
for Inherit_Source_Path ("C++") use ("C");
@end example

@item 
@strong{Exclude_Source_Dirs}: list

The list of directories that are included in Source_Dirs but are not source
directories of the project.

@item 
@strong{Ignore_Source_Sub_Dirs}: list

Value is a list of simple names for subdirectories that are removed from the
list of source directories, including theur subdirectories.
@end itemize

@item 
@strong{Source Files}


@itemize *

@item 
@strong{Source_Files}: list

Value is a list of source file simple names.

@item 
@strong{Locally_Removed_Files}: list

Obsolescent. Equivalent to Excluded_Source_Files.

@item 
@strong{Excluded_Source_Files}: list

Value is a list of simple file names that are not sources of the project.
Allows to remove sources that are inherited or found in the source directories
and that match the naming scheme.

@item 
@strong{Source_List_File}: single

Value is a text file name that contains a list of source file simple names,
one on each line.

@item 
@strong{Excluded_Source_List_File}: single

Value is a text file name that contains a list of file simple names that
are not sources of the project.

@item 
@strong{Interfaces}: list

Value is a list of file names that constitutes the interfaces of the project.
@end itemize

@item 
@strong{Aggregate Projects}


@itemize *

@item 
@strong{Project_Files}: list

Value is the list of aggregated projects.

@item 
@strong{Project_Path}: list

Value is a list of directories that are added to the project search path when
looking for the aggregated projects.

@item 
@strong{External}: single, indexed

Index is the name of an external reference. Value is the value of the
external reference to be used when parsing the aggregated projects.
@end itemize

@item 
@strong{Libraries}


@itemize *

@item 
@strong{Library_Dir}: single

Value is the name of the library directory. This attribute needs to be
declared for each library project.

@item 
@strong{Library_Name}: single

Value is the name of the library. This attribute needs to be declared or
inherited for each library project.

@item 
@strong{Library_Kind}: single

Specifies the kind of library: static library (archive) or shared library.
Case-insensitive values must be one of "static" for archives (the default) or
"dynamic" or "relocatable" for shared libraries.

@item 
@strong{Library_Version}: single

Value is the name of the library file.

@item 
@strong{Library_Interface}: list

Value is the list of unit names that constitutes the interfaces
of a Stand-Alone Library project.

@item 
@strong{Library_Standalone}: single

Specifies if a Stand-Alone Library (SAL) is encapsulated or not.
Only authorized case-insensitive values are "standard" for non encapsulated
SALs, "encapsulated" for encapsulated SALs or "no" for non SAL library project.

@item 
@strong{Library_Encapsulated_Options}: list

Value is a list of options that need to be used when linking an encapsulated
Stand-Alone Library.

@item 
@strong{Library_Encapsulated_Supported}: single

Indicates if encapsulated Stand-Alone Libraries are supported. Only
authorized case-insensitive values are "true" and "false" (the default).

@item 
@strong{Library_Auto_Init}: single

Indicates if a Stand-Alone Library is auto-initialized. Only authorized
case-insentive values are "true" and "false".

@item 
@strong{Leading_Library_Options}: list

Value is a list of options that are to be used at the beginning of
the command line when linking a shared library.

@item 
@strong{Library_Options}: list

Value is a list of options that are to be used when linking a shared library.

@item 
@strong{Library_Rpath_Options}: list, indexed, case-insensitive index

Index is a language name. Value is a list of options for an invocation of the
compiler of the language. This invocation is done for a shared library project
with sources of the language. The output of the invocation is the path name
of a shared library file. The directory name is to be put in the run path
option switch when linking the shared library for the project.

@item 
@strong{Library_Src_Dir}: single

Value is the name of the directory where copies of the sources of the
interfaces of a Stand-Alone Library are to be copied.

@item 
@strong{Library_ALI_Dir}: single

Value is the name of the directory where the ALI files of the interfaces
of a Stand-Alone Library are to be copied. When this attribute is not declared,
the directory is the library directory.

@item 
@strong{Library_gcc}: single

Obsolescent attribute. Specify the linker driver used to link a shared library.
Use instead attribute Linker'Driver.

@item 
@strong{Library_Symbol_File}: single

Value is the name of the library symbol file.

@item 
@strong{Library_Symbol_Policy}: single

Indicates the symbol policy kind. Only authorized case-insensitive values are
"autonomous", "default", "compliant", "controlled" or "direct".

@item 
@strong{Library_Reference_Symbol_File}: single

Value is the name of the reference symbol file.
@end itemize

@item 
@strong{Configuration - General}


@itemize *

@item 
@strong{Default_Language}: single

Value is the case-insensitive name of the language of a project when attribute
Languages is not specified.

@item 
@strong{Run_Path_Option}: list

Value is the list of switches to be used when specifying the run path option
in an executable.

@item 
@strong{Run_Path_Origin}: single

Value is the the string that may replace the path name of the executable
directory in the run path options.

@item 
@strong{Separate_Run_Path_Options}: single

Indicates if there may be several run path options specified when linking an
executable. Only authorized case-insensitive values are "true" or "false" (the
default).

@item 
@strong{Toolchain_Version}: single, indexed, case-insensitive index

Index is a language name. Specify the version of a toolchain for a language.

@item 
@strong{Toolchain_Description}: single, indexed, case-insensitive index

Obsolescent. No longer used.

@item 
@strong{Object_Generated}: single, indexed, case-insensitive index

Index is a language name. Indicates if invoking the compiler for a language
produces an object file. Only authorized case-insensitive values are "false"
and "true" (the default).

@item 
@strong{Objects_Linked}: single, indexed, case-insensitive index

Index is a language name. Indicates if the object files created by the compiler
for a language need to be linked in the executable. Only authorized
case-insensitive values are "false" and "true" (the default).

@item 
@strong{Target}: single

Value is the name of the target platform. Taken into account only in the main
project.

@item 
@strong{Runtime}: single, indexed, case-insensitive index

Index is a language name. Indicates the runtime directory that is to be used
when using the compiler of the language. Taken into account only in the main
project.
@end itemize

@item 
@strong{Configuration - Libraries}


@itemize *

@item 
@strong{Library_Builder}: single

Value is the path name of the application that is to be used to build
libraries. Usually the path name of "gprlib".

@item 
@strong{Library_Support}: single

Indicates the level of support of libraries. Only authorized case-insensitive
values are "static_only", "full" or "none" (the default).
@end itemize

@item 
@strong{Configuration - Archives}


@itemize *

@item 
@strong{Archive_Builder}: list

Value is the name of the application to be used to create a static library
(archive), followed by the options to be used.

@item 
@strong{Archive_Builder_Append_Option}: list

Value is the list of options to be used when invoking the archive builder
to add project files into an archive.

@item 
@strong{Archive_Indexer}: list

Value is the name of the archive indexer, followed by the required options.

@item 
@strong{Archive_Suffix}: single

Value is the extension of archives. When not declared, the extension is ".a".

@item 
@strong{Library_Partial_Linker}: list

Value is the name of the partial linker executable, followed by the required
options.
@end itemize

@item 
@strong{Configuration - Shared Libraries}


@itemize *

@item 
@strong{Shared_Library_Prefix}: single

Value is the prefix in the name of shared library files. When not declared,
the prefix is "lib".

@item 
@strong{Shared_Library_Suffix}: single

Value is the the extension of the name of shared library files. When not
declared, the extension is ".so".

@item 
@strong{Symbolic_Link_Supported}: single

Indicates if symbolic links are supported on the platform. Only authorized
case-insensitive values are "true" and "false" (the default).

@item 
@strong{Library_Major_Minor_Id_Supported}: single

Indicates if major and minor ids for shared library names are supported on
the platform. Only authorized case-insensitive values are "true" and "false"
(the default).

@item 
@strong{Library_Auto_Init_Supported}: single

Indicates if auto-initialization of Stand-Alone Libraries is supported. Only
authorized case-insensitive values are "true" and "false" (the default).

@item 
@strong{Shared_Library_Minimum_Switches}: list

Value is the list of required switches when linking a shared library.

@item 
@strong{Library_Version_Switches}: list

Value is the list of switches to specify a internal name for a shared library.

@item 
@strong{Library_Install_Name_Option}: single

Value is the name of the option that needs to be used, concatenated with the
path name of the library file, when linking a shared library.

@item 
@strong{Runtime_Library_Dir}: single, indexed, case-insensitive index

Index is a language name. Value is the path name of the directory where the
runtime libraries are located.

@item 
@strong{Runtime_Source_Dir}: single, indexed, case-insensitive index

Index is a language name. Value is the path name of the directory where the
sources of runtime libraries are located.
@end itemize
@end itemize

@node Package Binder Attributes,Package Builder Attributes,Project Level Attributes,Attributes
@anchor{gnat_ugn/gnat_project_manager package-binder-attributes}@anchor{1a6}@anchor{gnat_ugn/gnat_project_manager id49}@anchor{1a7}
@subsubsection Package Binder Attributes



@itemize *

@item 
@strong{General}


@itemize *

@item 
@strong{Default_Switches}: list, indexed, case-insensitive index

Index is a language name. Value is the list of switches to be used when binding
code of the language, if there is no applicable attribute Switches.

@item 
@strong{Switches}: list, optional index, indexed,
case-insensitive index, others allowed

Index is either a language name or a source file name. Value is the list of
switches to be used when binding code. Index is either the source file name
of the executable to be bound or the language name of the code to be bound.
@end itemize

@item 
@strong{Configuration - Binding}


@itemize *

@item 
@strong{Driver}: single, indexed, case-insensitive index

Index is a language name. Value is the name of the application to be used when
binding code of the language.

@item 
@strong{Required_Switches}: list, indexed, case-insensitive index

Index is a language name. Value is the list of the required switches to be
used when binding code of the language.

@item 
@strong{Prefix}: single, indexed, case-insensitive index

Index is a language name. Value is a prefix to be used for the binder exchange
file name for the language. Used to have different binder exchange file names
when binding different languages.

@item 
@strong{Objects_Path}: single,indexed, case-insensitive index

Index is a language name. Value is the name of the environment variable that
contains the path for the object directories.

@item 
@strong{Object_Path_File}: single,indexed, case-insensitive index

Index is a language name. Value is the name of the environment variable. The
value of the environment variable is the path name of a text file that
contains the list of object directories.
@end itemize
@end itemize

@node Package Builder Attributes,Package Clean Attributes,Package Binder Attributes,Attributes
@anchor{gnat_ugn/gnat_project_manager package-builder-attributes}@anchor{1a8}@anchor{gnat_ugn/gnat_project_manager id50}@anchor{1a9}
@subsubsection Package Builder Attributes



@itemize *

@item 
@strong{Default_Switches}: list, indexed, case-insensitive index

Index is a language name. Value is the list of builder switches to be used when
building an executable of the language, if there is no applicable attribute
Switches.

@item 
@strong{Switches}: list, optional index, indexed, case-insensitive index,
others allowed

Index is either a language name or a source file name. Value is the list of
builder switches to be used when building an executable. Index is either the
source file name of the executable to be built or its language name.

@item 
@strong{Global_Compilation_Switches}: list, optional index, indexed,
case-insensitive index

Index is either a language name or a source file name. Value is the list of
compilation switches to be used when building an executable. Index is either
the source file name of the executable to be built or its language name.

@item 
@strong{Executable}: single, indexed, case-insensitive index

Index is an executable source file name. Value is the simple file name of the
executable to be built.

@item 
@strong{Executable_Suffix}: single

Value is the extension of the file names of executable. When not specified,
the extension is the default extension of executables on the platform.

@item 
@strong{Global_Configuration_Pragmas}: single

Value is the file name of a configuration pragmas file that is specified to
the Ada compiler when compiling any Ada source in the project tree.

@item 
@strong{Global_Config_File}: single, indexed, case-insensitive index

Index is a language name. Value is the file name of a configuration file that
is specified to the compiler when compiling any source of the language in the
project tree.
@end itemize


@node Package Clean Attributes,Package Compiler Attributes,Package Builder Attributes,Attributes
@anchor{gnat_ugn/gnat_project_manager package-clean-attributes}@anchor{1aa}@anchor{gnat_ugn/gnat_project_manager id52}@anchor{1ab}
@subsubsection Package Clean Attributes



@itemize *

@item 
@strong{Switches}: list

Value is a list of switches to be used by the cleaning application.

@item 
@strong{Source_Artifact_Extensions}: list, indexed, case-insensitive index

Index is a language names. Value is the list of extensions for file names
derived from object file names that need to be cleaned in the object
directory of the project.

@item 
@strong{Object_Artifact_Extensions}: list, indexed, case-insensitive index

Index is a language names. Value is the list of extensions for file names
derived from source file names that need to be cleaned in the object
directory of the project.

@item 
@strong{Artifacts_In_Object_Dir}: single

Value is a list of file names expressed as regular expressions that are to be
deleted by gprclean in the object directory of the project.

@item 
@strong{Artifacts_In_Exec_Dir}: single

Value is list of file names expressed as regular expressions that are to be
deleted by gprclean in the exec directory of the main project.
@end itemize

@node Package Compiler Attributes,Package Cross_Reference Attributes,Package Clean Attributes,Attributes
@anchor{gnat_ugn/gnat_project_manager id53}@anchor{1ac}@anchor{gnat_ugn/gnat_project_manager package-compiler-attributes}@anchor{1ad}
@subsubsection Package Compiler Attributes



@itemize *

@item 
@strong{General}


@itemize *

@item 
@strong{Default_Switches}: list, indexed, case-insensitive index

Index is a language name. Value is a list of switches to be used when invoking
the compiler for the language for a source of the project, if there is no
applicable attribute Switches.

@item 
@strong{Switches}: list, optional index, indexed, case-insensitive index,
others allowed

Index is a source file name or a language name. Value is the list of switches
to be used when invoking the compiler for the source or for its language.

@item 
@strong{Local_Configuration_Pragmas}: single

Value is the file name of a configuration pragmas file that is specified to
the Ada compiler when compiling any Ada source in the project.

@item 
@strong{Local_Config_File}: single, indexed, case-insensitive index

Index is a language name. Value is the file name of a configuration file that
is specified to the compiler when compiling any source of the language in the
project.
@end itemize

@item 
@strong{Configuration - Compiling}


@itemize *

@item 
@strong{Driver}: single, indexed, case-insensitive index

Index is a language name. Value is the name of the executable for the compiler
of the language.

@item 
@strong{Language_Kind}: single, indexed, case-insensitive index

Index is a language name. Indicates the kind of the language, either file based
or unit based. Only authorized case-insensitive values are "unit_based" and
"file_based" (the default).

@item 
@strong{Dependency_Kind}: single, indexed, case-insensitive index

Index is a language name. Indicates how the dependencies are handled for the
language. Only authorized case-insensitive values are "makefile", "ali_file",
"ali_closure" or "none" (the default).

@item 
@strong{Required_Switches}: list, indexed, case-insensitive index

Equivalent to attribute Leading_Required_Switches.

@item 
@strong{Leading_Required_Switches}: list, indexed, case-insensitive index

Index is a language name. Value is the list of the minimum switches to be used
at the beginning of the command line when invoking the compiler for the
language.

@item 
@strong{Trailing_Required_Switches}: list, indexed, case-insensitive index

Index is a language name. Value is the list of the minimum switches to be used
at the end of the command line when invoking the compiler for the language.

@item 
@strong{PIC_Option}: list, indexed, case-insensitive index

Index is a language name. Value is the list of switches to be used when
compiling a source of the language when the project is a shared library
project.

@item 
@strong{Path_Syntax}: single, indexed, case-insensitive index

Index is a language name. Value is the kind of path syntax to be used when
invoking the compiler for the language. Only authorized case-insensitive
values are "canonical" and "host" (the default).

@item 
@strong{Source_File_Switches}: single, indexed, case-insensitive index

Index is a language name. Value is a list of switches to be used just before
the path name of the source to compile when invoking the compiler for a source
of the language.

@item 
@strong{Object_File_Suffix}: single, indexed, case-insensitive index

Index is a language name. Value is the extension of the object files created
by the compiler of the language. When not specified, the extension is the
default one for the platform.

@item 
@strong{Object_File_Switches}: list, indexed, case-insensitive index

Index is a language name. Value is the list of switches to be used by the
compiler of the language to specify the path name of the object file. When not
specified, the switch used is "-o".

@item 
@strong{Multi_Unit_Switches}: list, indexed, case-insensitive index

Index is a language name. Value is the list of switches to be used to compile
a unit in a multi unit source of the language. The index of the unit in the
source is concatenated with the last switches in the list.

@item 
@strong{Multi_Unit_Object_Separator}: single, indexed, case-insensitive index

Index is a language name. Value is the string to be used in the object file
name before the index of the unit, when compiling a unit in a multi unit source
of the language.
@end itemize

@item 
@strong{Configuration - Mapping Files}


@itemize *

@item 
@strong{Mapping_File_Switches}: list, indexed, case-insensitive index

Index is a language name. Value is the list of switches to be used to specify
a mapping file when invoking the compiler for a source of the language.

@item 
@strong{Mapping_Spec_Suffix}: single, indexed, case-insensitive index

Index is a language name. Value is the suffix to be used in a mapping file
to indicate that the source is a spec.

@item 
@strong{Mapping_Body_Suffix}: single, indexed, case-insensitive index

Index is a language name. Value is the suffix to be used in a mapping file
to indicate that the source is a body.
@end itemize

@item 
@strong{Configuration - Config Files}


@itemize *

@item 
@strong{Config_File_Switches}: list: single, indexed, case-insensitive index

Index is a language name. Value is the list of switches to specify to the
compiler of the language a configuration file.

@item 
@strong{Config_Body_File_Name}: single, indexed, case-insensitive index

Index is a language name. Value is the template to be used to indicate a
configuration specific to a body of the language in a configuration
file.

@item 
@strong{Config_Body_File_Name_Index}: single, indexed, case-insensitive index

Index is a language name. Value is the template to be used to indicate a
configuration specific to the body a unit in a multi unit source of the
language in a configuration file.

@item 
@strong{Config_Body_File_Name_Pattern}: single, indexed,
case-insensitive index

Index is a language name. Value is the template to be used to indicate a
configuration for all bodies of the languages in a configuration file.

@item 
@strong{Config_Spec_File_Name}: single, indexed, case-insensitive index

Index is a language name. Value is the template to be used to indicate a
configuration specific to a spec of the language in a configuration
file.

@item 
@strong{Config_Spec_File_Name_Index}: single, indexed, case-insensitive index

Index is a language name. Value is the template to be used to indicate a
configuration specific to the spec a unit in a multi unit source of the
language in a configuration file.

@item 
@strong{Config_Spec_File_Name_Pattern}: single, indexed,
case-insensitive index

Index is a language name. Value is the template to be used to indicate a
configuration for all specs of the languages in a configuration file.

@item 
@strong{Config_File_Unique}: single, indexed, case-insensitive index

Index is a language name. Indicates if there should be only one configuration
file specified to the compiler of the language. Only authorized
case-insensitive values are "true" and "false" (the default).
@end itemize

@item 
@strong{Configuration - Dependencies}


@itemize *

@item 
@strong{Dependency_Switches}: list, indexed, case-insensitive index

Index is a language name. Value is the list of switches to be used to specify
to the compiler the dependency file when the dependency kind of the language is
file based, and when Dependency_Driver is not specified for the language.

@item 
@strong{Dependency_Driver}: list, indexed, case-insensitive index

Index is a language name. Value is the name of the executable to be used to
create the dependency file for a source of the language, followed by the
required switches.
@end itemize

@item 
@strong{Configuration - Search Paths}


@itemize *

@item 
@strong{Include_Switches}: list, indexed, case-insensitive index

Index is a language name. Value is the list of switches to specify to the
compiler of the language to indicate a directory to look for sources.

@item 
@strong{Include_Path}: single, indexed, case-insensitive index

Index is a language name. Value is the name of an environment variable that
contains the path of all the directories that the compiler of the language
may search for sources.

@item 
@strong{Include_Path_File}: single, indexed, case-insensitive index

Index is a language name. Value is the name of an environment variable the
value of which is the path name of a text file that contains the directories
that the compiler of the language may search for sources.

@item 
@strong{Object_Path_Switches}: list, indexed, case-insensitive index

Index is a language name. Value is the list of switches to specify to the
compiler of the language the name of a text file that contains the list of
object directories. When this attribute is not declared, the text file is
not created.
@end itemize
@end itemize

@node Package Cross_Reference Attributes,Package Finder Attributes,Package Compiler Attributes,Attributes
@anchor{gnat_ugn/gnat_project_manager id54}@anchor{1ae}@anchor{gnat_ugn/gnat_project_manager package-cross-reference-attributes}@anchor{1af}
@subsubsection Package Cross_Reference Attributes



@itemize *

@item 
@strong{Default_Switches}: list, indexed, case-insensitive index

Index is a language name. Value is a list of switches to be used when invoking
@cite{gnatxref} for a source of the language, if there is no applicable
attribute Switches.

@item 
@strong{Switches}: list, optional index, indexed, case-insensitive index,
others allowed

Index is a source file name. Value is the list of switches to be used when
invoking @cite{gnatxref} for the source.
@end itemize


@node Package Finder Attributes,Package gnatls Attributes,Package Cross_Reference Attributes,Attributes
@anchor{gnat_ugn/gnat_project_manager id56}@anchor{1b0}@anchor{gnat_ugn/gnat_project_manager package-finder-attributes}@anchor{1b1}
@subsubsection Package Finder Attributes



@itemize *

@item 
@strong{Default_Switches}: list, indexed, case-insensitive index

Index is a language name. Value is a list of switches to be used when invoking
@cite{gnatfind} for a source of the language, if there is no applicable
attribute Switches.

@item 
@strong{Switches}: list, optional index, indexed, case-insensitive index,
others allowed

Index is a source file name. Value is the list of switches to be used when
invoking @cite{gnatfind} for the source.
@end itemize

@node Package gnatls Attributes,Package IDE Attributes,Package Finder Attributes,Attributes
@anchor{gnat_ugn/gnat_project_manager package-gnatls-attributes}@anchor{1b2}@anchor{gnat_ugn/gnat_project_manager id57}@anchor{1b3}
@subsubsection Package gnatls Attributes



@itemize *

@item 
@strong{Switches}: list

Value is a list of switches to be used when invoking @cite{gnatls}.
@end itemize


@node Package IDE Attributes,Package Install Attributes,Package gnatls Attributes,Attributes
@anchor{gnat_ugn/gnat_project_manager id58}@anchor{1b4}@anchor{gnat_ugn/gnat_project_manager package-ide-attributes}@anchor{1b5}
@subsubsection Package IDE Attributes



@itemize *

@item 
@strong{Default_Switches}: list, indexed

Index is the name of an external tool that the GNAT Programming System (GPS)
is supporting. Value is a list of switches to use when invoking that tool.

@item 
@strong{Remote_Host}: single

Value is a string that designates the remote host in a cross-compilation
environment, to be used for remote compilation and debugging. This attribute
should not be specified when running on the local machine.

@item 
@strong{Program_Host}: single

Value is a string that specifies the name of IP address of the embedded target
in a cross-compilation environment, on which the program should execute.

@item 
@strong{Communication_Protocol}: single

Value is the name of the protocol to use to communicate with the target
in a cross-compilation environment, for example @cite{"wtx"} or
@cite{"vxworks"}.

@item 
@strong{Compiler_Command}: single, indexed, case-insensitive index

Index is a language Name. Value is a string that denotes the command to be
used to invoke the compiler. For historical reasons, the value of
@cite{Compiler_Command ("Ada")} is expected to be a reference to @emph{gnatmake} or
@emph{cross-gnatmake}.

@item 
@strong{Debugger_Command}: single

Value is a string that specifies the name of the debugger to be used, such as
gdb, powerpc-wrs-vxworks-gdb or gdb-4.

@item 
@strong{gnatlist}: single

Value is a string that specifies the name of the @emph{gnatls} utility
to be used to retrieve information about the predefined path; for example,
@cite{"gnatls"}, @cite{"powerpc-wrs-vxworks-gnatls"}.

@item 
@strong{VCS_Kind}: single

Value is a string used to specify the Version Control System (VCS) to be used
for this project, for example "Subversion", "ClearCase". If the
value is set to "Auto", the IDE will try to detect the actual VCS used
on the list of supported ones.

@item 
@strong{VCS_File_Check}: single

Value is a string that specifies the command used by the VCS to check
the validity of a file, either when the user explicitly asks for a check,
or as a sanity check before doing the check-in.

@item 
@strong{VCS_Log_Check}: single

Value is a string that specifies the command used by the VCS to check
the validity of a log file.

@item 
@strong{Documentation_Dir}: single

Value is the directory used to generate the documentation of source code.
@end itemize

@node Package Install Attributes,Package Linker Attributes,Package IDE Attributes,Attributes
@anchor{gnat_ugn/gnat_project_manager package-install-attributes}@anchor{1b6}@anchor{gnat_ugn/gnat_project_manager id59}@anchor{1b7}
@subsubsection Package Install Attributes



@itemize *

@item 
@strong{Artifacts}: list, indexed

An array attribute to declare a set of files not part of the sources
to be installed. The array discriminant is the directory where the
file is to be installed. If a relative directory then Prefix (see
below) is prepended.

@item 
@strong{Prefix}: single

Value is the install destination directory.

@item 
@strong{Sources_Subdir}: single

Value is the sources directory or subdirectory of Prefix.

@item 
@strong{Exec_Subdir}: single

Value is the executables directory or subdirectory of Prefix.

@item 
@strong{Lib_Subdir}: single

Value is library directory or subdirectory of Prefix.

@item 
@strong{Project_Subdir}: single

Value is the project directory or subdirectory of Prefix.

@item 
@strong{Active}: single

Indicates that the project is to be installed or not. Case-insensitive value
"false" means that the project is not to be installed, all other values mean
that the project is to be installed.

@item 
@strong{Mode}: single

Value is the installation mode, it is either @strong{dev} (default) or @strong{usage}.

@item 
@strong{Install_Name}: single

Specify the name to use for recording the installation. The default is
the project name without the extension.
@end itemize

@node Package Linker Attributes,Package Naming Attributes,Package Install Attributes,Attributes
@anchor{gnat_ugn/gnat_project_manager id60}@anchor{1b8}@anchor{gnat_ugn/gnat_project_manager package-linker-attributes}@anchor{1b9}
@subsubsection Package Linker Attributes



@itemize *

@item 
@strong{General}


@itemize *

@item 
@strong{Required_Switches}: list

Value is a list of switches that are required when invoking the linker to link
an executable.

@item 
@strong{Default_Switches}: list, indexed, case-insensitive index

Index is a language name. Value is a list of switches for the linker when
linking an executable for a main source of the language, when there is no
applicable Switches.

@item 
@strong{Leading_Switches}: list, optional index, indexed,
case-insensitive index, others allowed

Index is a source file name or a language name. Value is the list of switches
to be used at the beginning of the command line when invoking the linker to
build an executable for the source or for its language.

@item 
@strong{Switches}: list, optional index, indexed, case-insensitive index,
others allowed

Index is a source file name or a language name. Value is the list of switches
to be used when invoking the linker to build an executable for the source or
for its language.

@item 
@strong{Trailing_Switches}: list, optional index, indexed,
case-insensitive index, others allowed

Index is a source file name or a language name. Value is the list of switches
to be used at the end of the command line when invoking the linker to
build an executable for the source or for its language. These switches may
override the Required_Switches.

@item 
@strong{Linker_Options}: list

Value is a list of switches/options that are to be added when linking an
executable from a project importing the current project directly or indirectly.
Linker_Options are not used when linking an executable from the current
project.

@item 
@strong{Map_File_Option}: single

Value is the switch to specify the map file name that the linker needs to
create.
@end itemize

@item 
@strong{Configuration - Linking}


@itemize *

@item 
@strong{Driver}: single

Value is the name of the linker executable.
@end itemize

@item 
@strong{Configuration - Response Files}


@itemize *

@item 
@strong{Max_Command_Line_Length}: single

Value is the maximum number of character in the command line when invoking
the linker to link an executable.

@item 
@strong{Response_File_Format}: single

Indicates the kind of response file to create when the length of the linking
command line is too large. Only authorized case-insensitive values are "none",
"gnu", "object_list", "gcc_gnu", "gcc_option_list" and "gcc_object_list".

@item 
@strong{Response_File_Switches}: list

Value is the list of switches to specify a response file to the linker.
@end itemize
@end itemize

@c only PRO or GPL
@c 
@c .. _Package_Metrics_Attribute:
@c 
@c Package Metrics Attribute
@c ^^^^^^^^^^^^^^^^^^^^^^^^^
@c 
@c * **Default_Switches**: list, indexed, case-insensitive index
@c 
@c   Index is a language name. Value is a list of switches to be used when invoking
@c   `gnatmetric` for a source of the language, if there is no applicable
@c   attribute Switches.
@c 
@c * **Switches**: list, optional index, indexed, case-insensitive index,
@c   others allowed
@c 
@c   Index is a source file name. Value is the list of switches to be used when
@c   invoking `gnatmetric` for the source.

@node Package Naming Attributes,Package Remote Attributes,Package Linker Attributes,Attributes
@anchor{gnat_ugn/gnat_project_manager package-naming-attributes}@anchor{1ba}@anchor{gnat_ugn/gnat_project_manager id61}@anchor{1bb}
@subsubsection Package Naming Attributes



@itemize *

@item 
@strong{Specification_Suffix}: single, indexed, case-insensitive index

Equivalent to attribute Spec_Suffix.

@item 
@strong{Spec_Suffix}: single, indexed, case-insensitive index

Index is a language name. Value is the extension of file names for specs of
the language.

@item 
@strong{Implementation_Suffix}: single, indexed, case-insensitive index

Equivalent to attribute Body_Suffix.

@item 
@strong{Body_Suffix}: single, indexed, case-insensitive index

Index is a language name. Value is the extension of file names for bodies of
the language.

@item 
@strong{Separate_Suffix}: single

Value is the extension of file names for subunits of Ada.

@item 
@strong{Casing}: single

Indicates the casing of sources of the Ada language. Only authorized
case-insensitive values are "lowercase", "uppercase" and "mixedcase".

@item 
@strong{Dot_Replacement}: single

Value is the string that replace the dot of unit names in the source file names
of the Ada language.

@item 
@strong{Specification}: single, optional index, indexed,
case-insensitive index

Equivalent to attribute Spec.

@item 
@strong{Spec}: single, optional index, indexed, case-insensitive index

Index is a unit name. Value is the file name of the spec of the unit.

@item 
@strong{Implementation}: single, optional index, indexed,
case-insensitive index

Equivalent to attribute Body.

@item 
@strong{Body}: single, optional index, indexed, case-insensitive index

Index is a unit name. Value is the file name of the body of the unit.

@item 
@strong{Specification_Exceptions}: list, indexed, case-insensitive index

Index is a language name. Value is a list of specs for the language that do not
necessarily follow the naming scheme for the language and that may or may not
be found in the source directories of the project.

@item 
@strong{Implementation_Exceptions}: list, indexed, case-insensitive index

Index is a language name. Value is a list of bodies for the language that do not
necessarily follow the naming scheme for the language and that may or may not
be found in the source directories of the project.
@end itemize


@node Package Remote Attributes,Package Stack Attributes,Package Naming Attributes,Attributes
@anchor{gnat_ugn/gnat_project_manager package-remote-attributes}@anchor{1bc}@anchor{gnat_ugn/gnat_project_manager id63}@anchor{1bd}
@subsubsection Package Remote Attributes



@itemize *

@item 
@strong{Included_Patterns}: list

If this attribute is defined it sets the patterns to
synchronized from the master to the slaves. It is exclusive
with Excluded_Patterns, that is it is an error to define
both.

@item 
@strong{Included_Artifact_Patterns}: list

If this attribute is defined it sets the patterns of compilation
artifacts to synchronized from the slaves to the build master.
This attribute replace the default hard-coded patterns.

@item 
@strong{Excluded_Patterns}: list

Set of patterns to ignore when synchronizing sources from the build
master to the slaves. A set of predefined patterns are supported
(e.g. *.o, *.ali, *.exe, etc.), this attributes make it possible to
add some more patterns.

@item 
@strong{Root_Dir}: single

Value is the root directory used by the slave machines.
@end itemize

@node Package Stack Attributes,Package Synchronize Attributes,Package Remote Attributes,Attributes
@anchor{gnat_ugn/gnat_project_manager id64}@anchor{1be}@anchor{gnat_ugn/gnat_project_manager package-stack-attributes}@anchor{1bf}
@subsubsection Package Stack Attributes



@itemize *

@item 
@strong{Switches}: list

Value is the list of switches to be used when invoking @cite{gnatstack}.
@end itemize

@node Package Synchronize Attributes,,Package Stack Attributes,Attributes
@anchor{gnat_ugn/gnat_project_manager package-synchronize-attributes}@anchor{1c0}
@subsubsection Package Synchronize Attributes



@itemize *

@item 
@strong{Default_Switches}: list, indexed, case-insensitive index

Index is a language name. Value is a list of switches to be used when invoking
@cite{gnatsync} for a source of the language, if there is no applicable
attribute Switches.

@item 
@strong{Switches}: list, optional index, indexed, case-insensitive index,
others allowed

Index is a source file name. Value is the list of switches to be used when
invoking @cite{gnatsync} for the source.
@end itemize

@node Tools Supporting Project Files,GNAT Utility Programs,GNAT Project Manager,Top
@anchor{gnat_ugn/tools_supporting_project_files doc}@anchor{1c1}@anchor{gnat_ugn/tools_supporting_project_files tools-supporting-project-files}@anchor{c}@anchor{gnat_ugn/tools_supporting_project_files id1}@anchor{1c2}
@chapter Tools Supporting Project Files


This section describes how project files can be used in conjunction with a number of
GNAT tools.

@menu
* gnatmake and Project Files:: 
* The GNAT Driver and Project Files:: 

@end menu

@node gnatmake and Project Files,The GNAT Driver and Project Files,,Tools Supporting Project Files
@anchor{gnat_ugn/tools_supporting_project_files id2}@anchor{1c3}@anchor{gnat_ugn/tools_supporting_project_files gnatmake-and-project-files}@anchor{e1}
@section gnatmake and Project Files


This section covers several topics related to @emph{gnatmake} and
project files: defining switches for @emph{gnatmake}
and for the tools that it invokes; specifying configuration pragmas;
the use of the @cite{Main} attribute; building and rebuilding library project
files.

@menu
* Switches Related to Project Files:: 
* Switches and Project Files:: 
* Specifying Configuration Pragmas:: 
* Project Files and Main Subprograms:: 
* Library Project Files:: 

@end menu

@node Switches Related to Project Files,Switches and Project Files,,gnatmake and Project Files
@anchor{gnat_ugn/tools_supporting_project_files switches-related-to-project-files}@anchor{e3}@anchor{gnat_ugn/tools_supporting_project_files id3}@anchor{1c4}
@subsection Switches Related to Project Files


The following switches are used by GNAT tools that support project files:

@quotation

@geindex -P (any project-aware tool)
@end quotation


@table @asis

@item @code{-P@emph{project}}

Indicates the name of a project file. This project file will be parsed with
the verbosity indicated by @emph{-vP*x*},
if any, and using the external references indicated
by @emph{-X} switches, if any.
There may zero, one or more spaces between @emph{-P} and @cite{project}.

There must be only one @emph{-P} switch on the command line.

Since the Project Manager parses the project file only after all the switches
on the command line are checked, the order of the switches
@emph{-P},
@emph{-vP*x*}
or @emph{-X} is not significant.

@geindex -X (any project-aware tool)

@item @code{-X@emph{name}=@emph{value}}

Indicates that external variable @cite{name} has the value @cite{value}.
The Project Manager will use this value for occurrences of
@cite{external(name)} when parsing the project file.

If @cite{name} or @cite{value} includes a space, then @cite{name=value} should be
put between quotes.

@example
-XOS=NT
-X"user=John Doe"
@end example

Several @emph{-X} switches can be used simultaneously.
If several @emph{-X} switches specify the same
@cite{name}, only the last one is used.

An external variable specified with a @emph{-X} switch
takes precedence over the value of the same name in the environment.

@geindex -vP (any project-aware tool)

@item @code{-vP@emph{x}}

Indicates the verbosity of the parsing of GNAT project files.

@emph{-vP0} means Default;
@emph{-vP1} means Medium;
@emph{-vP2} means High.

The default is Default: no output for syntactically correct
project files.
If several @emph{-vP*x*} switches are present,
only the last one is used.

@geindex -aP (any project-aware tool)

@item @code{-aP@emph{dir}}

Add directory @cite{dir} at the beginning of the project search path, in order,
after the current working directory.

@geindex -eL (any project-aware tool)

@item @code{-eL}

Follow all symbolic links when processing project files.

@geindex --subdirs= (gnatmake and gnatclean)

@item @code{--subdirs=@emph{subdir}}

This switch is recognized by @emph{gnatmake} and @emph{gnatclean}. It
indicate that the real directories (except the source directories) are the
subdirectories @cite{subdir} of the directories specified in the project files.
This applies in particular to object directories, library directories and
exec directories. If the subdirectories do not exist, they are created
automatically.
@end table

@node Switches and Project Files,Specifying Configuration Pragmas,Switches Related to Project Files,gnatmake and Project Files
@anchor{gnat_ugn/tools_supporting_project_files id4}@anchor{1c5}@anchor{gnat_ugn/tools_supporting_project_files switches-and-project-files}@anchor{1c6}
@subsection Switches and Project Files


For each of the packages @cite{Builder}, @cite{Compiler}, @cite{Binder}, and
@cite{Linker}, you can specify a @cite{Default_Switches}
attribute, a @cite{Switches} attribute, or both;
as their names imply, these switch-related
attributes affect the switches that are used for each of these GNAT
components when
@emph{gnatmake} is invoked.  As will be explained below, these
component-specific switches precede
the switches provided on the @emph{gnatmake} command line.

The @cite{Default_Switches} attribute is an attribute
indexed by language name (case insensitive) whose value is a string list.
For example:

@quotation

@example
package Compiler is
  for Default_Switches ("Ada")
      use ("-gnaty",
           "-v");
end Compiler;
@end example
@end quotation

The @cite{Switches} attribute is indexed on a file name (which may or may
not be case sensitive, depending
on the operating system) whose value is a string list.  For example:

@quotation

@example
package Builder is
   for Switches ("main1.adb")
       use ("-O2");
   for Switches ("main2.adb")
       use ("-g");
end Builder;
@end example
@end quotation

For the @cite{Builder} package, the file names must designate source files
for main subprograms.  For the @cite{Binder} and @cite{Linker} packages, the
file names must designate @code{ALI} or source files for main subprograms.
In each case just the file name without an explicit extension is acceptable.

For each tool used in a program build (@emph{gnatmake}, the compiler, the
binder, and the linker), the corresponding package @@dfn@{contributes@} a set of
switches for each file on which the tool is invoked, based on the
switch-related attributes defined in the package.
In particular, the switches
that each of these packages contributes for a given file @cite{f} comprise:


@itemize *

@item 
the value of attribute @cite{Switches (`f})`,
if it is specified in the package for the given file,

@item 
otherwise, the value of @cite{Default_Switches ("Ada")},
if it is specified in the package.
@end itemize

If neither of these attributes is defined in the package, then the package does
not contribute any switches for the given file.

When @emph{gnatmake} is invoked on a file, the switches comprise
two sets, in the following order: those contributed for the file
by the @cite{Builder} package;
and the switches passed on the command line.

When @emph{gnatmake} invokes a tool (compiler, binder, linker) on a file,
the switches passed to the tool comprise three sets,
in the following order:


@itemize *

@item 
the applicable switches contributed for the file
by the @cite{Builder} package in the project file supplied on the command line;

@item 
those contributed for the file by the package (in the relevant project file --
see below) corresponding to the tool; and

@item 
the applicable switches passed on the command line.
@end itemize

The term @emph{applicable switches} reflects the fact that
@emph{gnatmake} switches may or may not be passed to individual
tools, depending on the individual switch.

@emph{gnatmake} may invoke the compiler on source files from different
projects. The Project Manager will use the appropriate project file to
determine the @cite{Compiler} package for each source file being compiled.
Likewise for the @cite{Binder} and @cite{Linker} packages.

As an example, consider the following package in a project file:

@quotation

@example
project Proj1 is
   package Compiler is
      for Default_Switches ("Ada")
          use ("-g");
      for Switches ("a.adb")
          use ("-O1");
      for Switches ("b.adb")
          use ("-O2",
               "-gnaty");
   end Compiler;
end Proj1;
@end example
@end quotation

If @emph{gnatmake} is invoked with this project file, and it needs to
compile, say, the files @code{a.adb}, @code{b.adb}, and @code{c.adb}, then
@code{a.adb} will be compiled with the switch @emph{-O1},
@code{b.adb} with switches @emph{-O2} and @emph{-gnaty},
and @code{c.adb} with @emph{-g}.

The following example illustrates the ordering of the switches
contributed by different packages:

@quotation

@example
project Proj2 is
   package Builder is
      for Switches ("main.adb")
          use ("-g",
               "-O1",
               "-f");
   end Builder;

   package Compiler is
      for Switches ("main.adb")
          use ("-O2");
   end Compiler;
end Proj2;
@end example
@end quotation

If you issue the command:

@quotation

@example
$ gnatmake -Pproj2 -O0 main
@end example
@end quotation

then the compiler will be invoked on @code{main.adb} with the following
sequence of switches

@quotation

@example
-g -O1 -O2 -O0
@end example
@end quotation

with the last @emph{-O}
switch having precedence over the earlier ones;
several other switches
(such as @emph{-c}) are added implicitly.

The switches @emph{-g}
and @emph{-O1} are contributed by package
@cite{Builder},  @emph{-O2} is contributed
by the package @cite{Compiler}
and @emph{-O0} comes from the command line.

The @emph{-g} switch will also be passed in the invocation of
@emph{Gnatlink.}

A final example illustrates switch contributions from packages in different
project files:

@quotation

@example
project Proj3 is
   for Source_Files use ("pack.ads", "pack.adb");
   package Compiler is
      for Default_Switches ("Ada")
          use ("-gnata");
   end Compiler;
end Proj3;

with "Proj3";
project Proj4 is
   for Source_Files use ("foo_main.adb", "bar_main.adb");
   package Builder is
      for Switches ("foo_main.adb")
          use ("-s",
               "-g");
   end Builder;
end Proj4;
@end example

@example
-- Ada source file:
with Pack;
procedure Foo_Main is
   ...
end Foo_Main;
@end example
@end quotation

If the command is

@quotation

@example
$ gnatmake -PProj4 foo_main.adb -cargs -gnato
@end example
@end quotation

then the switches passed to the compiler for @code{foo_main.adb} are
@emph{-g} (contributed by the package @cite{Proj4.Builder}) and
@emph{-gnato} (passed on the command line).
When the imported package @cite{Pack} is compiled, the switches used
are @emph{-g} from @cite{Proj4.Builder},
@emph{-gnata} (contributed from package @cite{Proj3.Compiler},
and @emph{-gnato} from the command line.

When using @emph{gnatmake} with project files, some switches or
arguments may be expressed as relative paths. As the working directory where
compilation occurs may change, these relative paths are converted to absolute
paths. For the switches found in a project file, the relative paths
are relative to the project file directory, for the switches on the command
line, they are relative to the directory where @emph{gnatmake} is invoked.
The switches for which this occurs are:
-I,
-A,
-L,
-aO,
-aL,
-aI, as well as all arguments that are not switches (arguments to
switch
-o, object files specified in package @cite{Linker} or after
-largs on the command line). The exception to this rule is the switch
--RTS= for which a relative path argument is never converted.

@node Specifying Configuration Pragmas,Project Files and Main Subprograms,Switches and Project Files,gnatmake and Project Files
@anchor{gnat_ugn/tools_supporting_project_files id5}@anchor{1c7}@anchor{gnat_ugn/tools_supporting_project_files specifying-configuration-pragmas}@anchor{7d}
@subsection Specifying Configuration Pragmas


When using @emph{gnatmake} with project files, if there exists a file
@code{gnat.adc} that contains configuration pragmas, this file will be
ignored.

Configuration pragmas can be defined by means of the following attributes in
project files: @cite{Global_Configuration_Pragmas} in package @cite{Builder}
and @cite{Local_Configuration_Pragmas} in package @cite{Compiler}.

Both these attributes are single string attributes. Their values is the path
name of a file containing configuration pragmas. If a path name is relative,
then it is relative to the project directory of the project file where the
attribute is defined.

When compiling a source, the configuration pragmas used are, in order,
those listed in the file designated by attribute
@cite{Global_Configuration_Pragmas} in package @cite{Builder} of the main
project file, if it is specified, and those listed in the file designated by
attribute @cite{Local_Configuration_Pragmas} in package @cite{Compiler} of
the project file of the source, if it exists.

@node Project Files and Main Subprograms,Library Project Files,Specifying Configuration Pragmas,gnatmake and Project Files
@anchor{gnat_ugn/tools_supporting_project_files id6}@anchor{1c8}@anchor{gnat_ugn/tools_supporting_project_files project-files-and-main-subprograms}@anchor{e2}
@subsection Project Files and Main Subprograms


When using a project file, you can invoke @emph{gnatmake}
with one or several main subprograms, by specifying their source files on the
command line.

@quotation

@example
$ gnatmake -Pprj main1.adb main2.adb main3.adb
@end example
@end quotation

Each of these needs to be a source file of the same project, except
when the switch @cite{-u} is used.

When @cite{-u} is not used, all the mains need to be sources of the
same project, one of the project in the tree rooted at the project specified
on the command line. The package @cite{Builder} of this common project, the
"main project" is the one that is considered by @emph{gnatmake}.

When @cite{-u} is used, the specified source files may be in projects
imported directly or indirectly by the project specified on the command line.
Note that if such a source file is not part of the project specified on the
command line, the switches found in package @cite{Builder} of the
project specified on the command line, if any, that are transmitted
to the compiler will still be used, not those found in the project file of
the source file.

When using a project file, you can also invoke @emph{gnatmake} without
explicitly specifying any main, and the effect depends on whether you have
defined the @cite{Main} attribute.  This attribute has a string list value,
where each element in the list is the name of a source file (the file
extension is optional) that contains a unit that can be a main subprogram.

If the @cite{Main} attribute is defined in a project file as a non-empty
string list and the switch @emph{-u} is not used on the command
line, then invoking @emph{gnatmake} with this project file but without any
main on the command line is equivalent to invoking @emph{gnatmake} with all
the file names in the @cite{Main} attribute on the command line.

Example:

@quotation

@example
project Prj is
   for Main use ("main1.adb", "main2.adb", "main3.adb");
end Prj;
@end example
@end quotation

With this project file, @cite{"gnatmake -Pprj"}
is equivalent to
@cite{"gnatmake -Pprj main1.adb main2.adb main3.adb"}.

When the project attribute @cite{Main} is not specified, or is specified
as an empty string list, or when the switch @emph{-u} is used on the command
line, then invoking @emph{gnatmake} with no main on the command line will
result in all immediate sources of the project file being checked, and
potentially recompiled. Depending on the presence of the switch @emph{-u},
sources from other project files on which the immediate sources of the main
project file depend are also checked and potentially recompiled. In other
words, the @emph{-u} switch is applied to all of the immediate sources of the
main project file.

When no main is specified on the command line and attribute @cite{Main} exists
and includes several mains, or when several mains are specified on the
command line, the default switches in package @cite{Builder} will
be used for all mains, even if there are specific switches
specified for one or several mains.

But the switches from package @cite{Binder} or @cite{Linker} will be
the specific switches for each main, if they are specified.

@node Library Project Files,,Project Files and Main Subprograms,gnatmake and Project Files
@anchor{gnat_ugn/tools_supporting_project_files id7}@anchor{1c9}@anchor{gnat_ugn/tools_supporting_project_files library-project-files}@anchor{1ca}
@subsection Library Project Files


When @emph{gnatmake} is invoked with a main project file that is a library
project file, it is not allowed to specify one or more mains on the command
line.

When a library project file is specified, switches @cite{-b} and
@cite{-l} have special meanings.


@itemize *

@item 
@cite{-b} is only allowed for stand-alone libraries. It indicates
to @emph{gnatmake} that @emph{gnatbind} should be invoked for the
library.

@item 
@cite{-l} may be used for all library projects. It indicates
to @emph{gnatmake} that the binder generated file should be compiled
(in the case of a stand-alone library) and that the library should be built.
@end itemize

@node The GNAT Driver and Project Files,,gnatmake and Project Files,Tools Supporting Project Files
@anchor{gnat_ugn/tools_supporting_project_files id8}@anchor{1cb}@anchor{gnat_ugn/tools_supporting_project_files the-gnat-driver-and-project-files}@anchor{11f}
@section The GNAT Driver and Project Files


A number of GNAT tools beyond @emph{gnatmake}
can benefit from project files:



@itemize *

@item 
@emph{gnatbind}

@item 
@emph{gnatclean}

@item 
@emph{gnatfind}

@item 
@emph{gnatlink}

@item 
@emph{gnatls}

@item 
@emph{gnatxref}
@end itemize

However, none of these tools can be invoked
directly with a project file switch (@emph{-P}).
They must be invoked through the @emph{gnat} driver.

The @emph{gnat} driver is a wrapper that accepts a number of commands and
calls the corresponding tool. It was designed initially for VMS platforms (to
convert VMS qualifiers to Unix-style switches), but it is now available on all
GNAT platforms.

On non-VMS platforms, the @emph{gnat} driver accepts the following commands
(case insensitive):



@itemize *

@item 
BIND to invoke @emph{gnatbind}

@item 
CHOP to invoke @emph{gnatchop}

@item 
CLEAN to invoke @emph{gnatclean}

@item 
COMP or COMPILE to invoke the compiler

@item 
FIND to invoke @emph{gnatfind}

@item 
KR or KRUNCH to invoke @emph{gnatkr}

@item 
LINK to invoke @emph{gnatlink}

@item 
LS or LIST to invoke @emph{gnatls}

@item 
MAKE to invoke @emph{gnatmake}

@item 
NAME to invoke @emph{gnatname}

@item 
PREP or PREPROCESS to invoke @emph{gnatprep}

@item 
XREF to invoke @emph{gnatxref}
@end itemize

Note that the command
@emph{gnatmake -c -f -u} is used to invoke the compiler.

On non-VMS platforms, between @emph{gnat} and the command, two
special switches may be used:


@itemize *

@item 
@emph{-v} to display the invocation of the tool.

@item 
@emph{-dn} to prevent the @emph{gnat} driver from removing
the temporary files it has created. These temporary files are
configuration files and temporary file list files.
@end itemize

The command may be followed by switches and arguments for the invoked
tool.

@quotation

@example
$ gnat bind -C main.ali
$ gnat ls -a main
$ gnat chop foo.txt
@end example
@end quotation

Switches may also be put in text files, one switch per line, and the text
files may be specified with their path name preceded by '@@'.

@quotation

@example
$ gnat bind @@args.txt main.ali
@end example
@end quotation

In addition, for the following commands the project file related switches
(@emph{-P}, @emph{-X} and @emph{-vPx}) may be used in addition to
the switches of the invoking tool:



@itemize *

@item 
BIND

@item 
COMP or COMPILE

@item 
FIND

@item 
LS or LIST

@item 
LINK

@item 
XREF
@end itemize


For each of the following commands, there is optionally a corresponding
package in the main project.



@itemize *

@item 
package @cite{Binder} for command BIND (invoking @cite{gnatbind})

@item 
package @cite{Compiler} for command COMP or COMPILE (invoking the compiler)

@item 
package @cite{Cross_Reference} for command XREF (invoking @cite{gnatxref})

@item 
package @cite{Finder} for command FIND (invoking @cite{gnatfind})

@item 
package @cite{Gnatls} for command LS or LIST (invoking @cite{gnatls})

@item 
package @cite{Linker} for command LINK (invoking @cite{gnatlink})
@end itemize

Package @cite{Gnatls} has a unique attribute @cite{Switches},
a simple variable with a string list value. It contains switches
for the invocation of @cite{gnatls}.

@quotation

@example
project Proj1 is
   package gnatls is
      for Switches
          use ("-a",
               "-v");
   end gnatls;
end Proj1;
@end example
@end quotation

All other packages have two attribute @cite{Switches} and
@cite{Default_Switches}.

@cite{Switches} is an indexed attribute, indexed by the
source file name, that has a string list value: the switches to be
used when the tool corresponding to the package is invoked for the specific
source file.

@cite{Default_Switches} is an attribute,
indexed by  the programming language that has a string list value.
@cite{Default_Switches ("Ada")} contains the
switches for the invocation of the tool corresponding
to the package, except if a specific @cite{Switches} attribute
is specified for the source file.

@quotation

@example
project Proj is

   for Source_Dirs use ("");

   package gnatls is
      for Switches use
          ("-a",
           "-v");
   end gnatls;

   package Compiler is
      for Default_Switches ("Ada")
          use ("-gnatv",
               "-gnatwa");
   end Binder;

   package Binder is
      for Default_Switches ("Ada")
          use ("-C",
               "-e");
   end Binder;

   package Linker is
      for Default_Switches ("Ada")
          use ("-C");
      for Switches ("main.adb")
          use ("-C",
               "-v",
               "-v");
   end Linker;

   package Finder is
      for Default_Switches ("Ada")
           use ("-a",
                "-f");
   end Finder;

   package Cross_Reference is
      for Default_Switches ("Ada")
          use ("-a",
               "-f",
               "-d",
               "-u");
   end Cross_Reference;
end Proj;
@end example
@end quotation

With the above project file, commands such as

@quotation

@example
$ gnat comp -Pproj main
$ gnat ls -Pproj main
$ gnat xref -Pproj main
$ gnat bind -Pproj main.ali
$ gnat link -Pproj main.ali
@end example
@end quotation

will set up the environment properly and invoke the tool with the switches
found in the package corresponding to the tool:
@cite{Default_Switches ("Ada")} for all tools,
except @cite{Switches ("main.adb")}
for @cite{gnatlink}.


@node GNAT Utility Programs,GNAT and Program Execution,Tools Supporting Project Files,Top
@anchor{gnat_ugn/gnat_utility_programs doc}@anchor{1cc}@anchor{gnat_ugn/gnat_utility_programs gnat-utility-programs}@anchor{d}@anchor{gnat_ugn/gnat_utility_programs id1}@anchor{1cd}
@chapter GNAT Utility Programs


This chapter describes a number of utility programs:



@itemize *

@item 
@ref{22,,The File Cleanup Utility gnatclean}

@item 
@ref{23,,The GNAT Library Browser gnatls}

@item 
@ref{24,,The Cross-Referencing Tools gnatxref and gnatfind}

@item 
@ref{25,,The Ada to HTML Converter gnathtml}
@end itemize

Other GNAT utilities are described elsewhere in this manual:


@itemize *

@item 
@ref{5b,,Handling Arbitrary File Naming Conventions with gnatname}

@item 
@ref{65,,File Name Krunching with gnatkr}

@item 
@ref{38,,Renaming Files with gnatchop}

@item 
@ref{19,,Preprocessing with gnatprep}
@end itemize

@menu
* The File Cleanup Utility gnatclean:: 
* The GNAT Library Browser gnatls:: 
* The Cross-Referencing Tools gnatxref and gnatfind:: 
* The Ada to HTML Converter gnathtml:: 

@end menu

@node The File Cleanup Utility gnatclean,The GNAT Library Browser gnatls,,GNAT Utility Programs
@anchor{gnat_ugn/gnat_utility_programs id2}@anchor{1ce}@anchor{gnat_ugn/gnat_utility_programs the-file-cleanup-utility-gnatclean}@anchor{22}
@section The File Cleanup Utility @emph{gnatclean}


@geindex File cleanup tool

@geindex gnatclean

@cite{gnatclean} is a tool that allows the deletion of files produced by the
compiler, binder and linker, including ALI files, object files, tree files,
expanded source files, library files, interface copy source files, binder
generated files and executable files.

@menu
* Running gnatclean:: 
* Switches for gnatclean:: 

@end menu

@node Running gnatclean,Switches for gnatclean,,The File Cleanup Utility gnatclean
@anchor{gnat_ugn/gnat_utility_programs running-gnatclean}@anchor{1cf}@anchor{gnat_ugn/gnat_utility_programs id3}@anchor{1d0}
@subsection Running @cite{gnatclean}


The @cite{gnatclean} command has the form:

@quotation

@example
$ gnatclean switches `names`
@end example
@end quotation

where @cite{names} is a list of source file names. Suffixes @code{.ads} and
@code{adb} may be omitted. If a project file is specified using switch
@code{-P}, then @cite{names} may be completely omitted.

In normal mode, @cite{gnatclean} delete the files produced by the compiler and,
if switch @cite{-c} is not specified, by the binder and
the linker. In informative-only mode, specified by switch
@cite{-n}, the list of files that would have been deleted in
normal mode is listed, but no file is actually deleted.

@node Switches for gnatclean,,Running gnatclean,The File Cleanup Utility gnatclean
@anchor{gnat_ugn/gnat_utility_programs id4}@anchor{1d1}@anchor{gnat_ugn/gnat_utility_programs switches-for-gnatclean}@anchor{1d2}
@subsection Switches for @cite{gnatclean}


@cite{gnatclean} recognizes the following switches:

@geindex --version (gnatclean)


@table @asis

@item @code{--version}

Display Copyright and version, then exit disregarding all other options.
@end table

@geindex --help (gnatclean)


@table @asis

@item @code{--help}

If @emph{--version} was not used, display usage, then exit disregarding
all other options.

@item @code{--subdirs=@emph{subdir}}

Actual object directory of each project file is the subdirectory subdir of the
object directory specified or defaulted in the project file.

@item @code{--unchecked-shared-lib-imports}

By default, shared library projects are not allowed to import static library
projects. When this switch is used on the command line, this restriction is
relaxed.
@end table

@geindex -c (gnatclean)


@table @asis

@item @code{-c}

Only attempt to delete the files produced by the compiler, not those produced
by the binder or the linker. The files that are not to be deleted are library
files, interface copy files, binder generated files and executable files.
@end table

@geindex -D (gnatclean)


@table @asis

@item @code{-D @emph{dir}}

Indicate that ALI and object files should normally be found in directory @cite{dir}.
@end table

@geindex -F (gnatclean)


@table @asis

@item @code{-F}

When using project files, if some errors or warnings are detected during
parsing and verbose mode is not in effect (no use of switch
-v), then error lines start with the full path name of the project
file, rather than its simple file name.
@end table

@geindex -h (gnatclean)


@table @asis

@item @code{-h}

Output a message explaining the usage of @cite{gnatclean}.
@end table

@geindex -n (gnatclean)


@table @asis

@item @code{-n}

Informative-only mode. Do not delete any files. Output the list of the files
that would have been deleted if this switch was not specified.
@end table

@geindex -P (gnatclean)


@table @asis

@item @code{-P@emph{project}}

Use project file @cite{project}. Only one such switch can be used.
When cleaning a project file, the files produced by the compilation of the
immediate sources or inherited sources of the project files are to be
deleted. This is not depending on the presence or not of executable names
on the command line.
@end table

@geindex -q (gnatclean)


@table @asis

@item @code{-q}

Quiet output. If there are no errors, do not output anything, except in
verbose mode (switch -v) or in informative-only mode
(switch -n).
@end table

@geindex -r (gnatclean)


@table @asis

@item @code{-r}

When a project file is specified (using switch -P),
clean all imported and extended project files, recursively. If this switch
is not specified, only the files related to the main project file are to be
deleted. This switch has no effect if no project file is specified.
@end table

@geindex -v (gnatclean)


@table @asis

@item @code{-v}

Verbose mode.
@end table

@geindex -vP (gnatclean)


@table @asis

@item @code{-vP@emph{x}}

Indicates the verbosity of the parsing of GNAT project files.
@ref{e3,,Switches Related to Project Files}.
@end table

@geindex -X (gnatclean)


@table @asis

@item @code{-X@emph{name}=@emph{value}}

Indicates that external variable @cite{name} has the value @cite{value}.
The Project Manager will use this value for occurrences of
@cite{external(name)} when parsing the project file.
@ref{e3,,Switches Related to Project Files}.
@end table

@geindex -aO (gnatclean)


@table @asis

@item @code{-aO@emph{dir}}

When searching for ALI and object files, look in directory @cite{dir}.
@end table

@geindex -I (gnatclean)


@table @asis

@item @code{-I@emph{dir}}

Equivalent to @code{-aO@emph{dir}}.
@end table

@geindex -I- (gnatclean)

@geindex Source files
@geindex suppressing search


@table @asis

@item @code{-I-}

Do not look for ALI or object files in the directory
where @cite{gnatclean} was invoked.
@end table

@node The GNAT Library Browser gnatls,The Cross-Referencing Tools gnatxref and gnatfind,The File Cleanup Utility gnatclean,GNAT Utility Programs
@anchor{gnat_ugn/gnat_utility_programs the-gnat-library-browser-gnatls}@anchor{23}@anchor{gnat_ugn/gnat_utility_programs id5}@anchor{1d3}
@section The GNAT Library Browser @cite{gnatls}


@geindex Library browser

@c index: ! gnatls

@cite{gnatls} is a tool that outputs information about compiled
units. It gives the relationship between objects, unit names and source
files. It can also be used to check the source dependencies of a unit
as well as various characteristics.

Note: to invoke @cite{gnatls} with a project file, use the @cite{gnat}
driver (see @ref{11f,,The GNAT Driver and Project Files}).

@menu
* Running gnatls:: 
* Switches for gnatls:: 
* Example of gnatls Usage:: 

@end menu

@node Running gnatls,Switches for gnatls,,The GNAT Library Browser gnatls
@anchor{gnat_ugn/gnat_utility_programs id6}@anchor{1d4}@anchor{gnat_ugn/gnat_utility_programs running-gnatls}@anchor{1d5}
@subsection Running @cite{gnatls}


The @cite{gnatls} command has the form

@quotation

@example
$ gnatls switches `object_or_ali_file`
@end example
@end quotation

The main argument is the list of object or @code{ali} files
(see @ref{44,,The Ada Library Information Files})
for which information is requested.

In normal mode, without additional option, @cite{gnatls} produces a
four-column listing. Each line represents information for a specific
object. The first column gives the full path of the object, the second
column gives the name of the principal unit in this object, the third
column gives the status of the source and the fourth column gives the
full path of the source representing this unit.
Here is a simple example of use:

@quotation

@example
$ gnatls *.o
./demo1.o            demo1            DIF demo1.adb
./demo2.o            demo2             OK demo2.adb
./hello.o            h1                OK hello.adb
./instr-child.o      instr.child      MOK instr-child.adb
./instr.o            instr             OK instr.adb
./tef.o              tef              DIF tef.adb
./text_io_example.o  text_io_example   OK text_io_example.adb
./tgef.o             tgef             DIF tgef.adb
@end example
@end quotation

The first line can be interpreted as follows: the main unit which is
contained in
object file @code{demo1.o} is demo1, whose main source is in
@code{demo1.adb}. Furthermore, the version of the source used for the
compilation of demo1 has been modified (DIF). Each source file has a status
qualifier which can be:


@table @asis

@item @emph{OK (unchanged)}

The version of the source file used for the compilation of the
specified unit corresponds exactly to the actual source file.

@item @emph{MOK (slightly modified)}

The version of the source file used for the compilation of the
specified unit differs from the actual source file but not enough to
require recompilation. If you use gnatmake with the qualifier
@emph{-m (minimal recompilation)}, a file marked
MOK will not be recompiled.

@item @emph{DIF (modified)}

No version of the source found on the path corresponds to the source
used to build this object.

@item @emph{??? (file not found)}

No source file was found for this unit.

@item @emph{HID (hidden,  unchanged version not first on PATH)}

The version of the source that corresponds exactly to the source used
for compilation has been found on the path but it is hidden by another
version of the same source that has been modified.
@end table

@node Switches for gnatls,Example of gnatls Usage,Running gnatls,The GNAT Library Browser gnatls
@anchor{gnat_ugn/gnat_utility_programs id7}@anchor{1d6}@anchor{gnat_ugn/gnat_utility_programs switches-for-gnatls}@anchor{1d7}
@subsection Switches for @cite{gnatls}


@cite{gnatls} recognizes the following switches:

@geindex --version (gnatls)


@table @asis

@item @code{--version}

Display Copyright and version, then exit disregarding all other options.
@end table

@geindex --help (gnatls)


@table @asis

@item @code{*--help}

If @emph{--version} was not used, display usage, then exit disregarding
all other options.
@end table

@geindex -a (gnatls)


@table @asis

@item @code{-a}

Consider all units, including those of the predefined Ada library.
Especially useful with @emph{-d}.
@end table

@geindex -d (gnatls)


@table @asis

@item @code{-d}

List sources from which specified units depend on.
@end table

@geindex -h (gnatls)


@table @asis

@item @code{-h}

Output the list of options.
@end table

@geindex -o (gnatls)


@table @asis

@item @code{-o}

Only output information about object files.
@end table

@geindex -s (gnatls)


@table @asis

@item @code{-s}

Only output information about source files.
@end table

@geindex -u (gnatls)


@table @asis

@item @code{-u}

Only output information about compilation units.
@end table

@geindex -files (gnatls)


@table @asis

@item @code{-files=@emph{file}}

Take as arguments the files listed in text file @cite{file}.
Text file @cite{file} may contain empty lines that are ignored.
Each nonempty line should contain the name of an existing file.
Several such switches may be specified simultaneously.
@end table

@geindex -aO (gnatls)

@geindex -aI (gnatls)

@geindex -I (gnatls)

@geindex -I- (gnatls)


@table @asis

@item @code{-aO@emph{dir}}, @code{-aI@emph{dir}}, @code{-I@emph{dir}}, @code{-I-}, @code{-nostdinc}

Source path manipulation. Same meaning as the equivalent @emph{gnatmake}
flags (@ref{df,,Switches for gnatmake}).
@end table

@geindex -aP (gnatls)


@table @asis

@item @code{-aP@emph{dir}}

Add @cite{dir} at the beginning of the project search dir.
@end table

@geindex --RTS (gnatls)


@table @asis

@item @code{--RTS=@emph{rts-path}`}

Specifies the default location of the runtime library. Same meaning as the
equivalent @emph{gnatmake} flag (@ref{df,,Switches for gnatmake}).
@end table

@geindex -v (gnatls)


@table @asis

@item @code{-v}

Verbose mode. Output the complete source, object and project paths. Do not use
the default column layout but instead use long format giving as much as
information possible on each requested units, including special
characteristics such as:


@itemize *

@item 
@emph{Preelaborable}: The unit is preelaborable in the Ada sense.

@item 
@emph{No_Elab_Code}:  No elaboration code has been produced by the compiler for this unit.

@item 
@emph{Pure}: The unit is pure in the Ada sense.

@item 
@emph{Elaborate_Body}: The unit contains a pragma Elaborate_Body.

@item 
@emph{Remote_Types}: The unit contains a pragma Remote_Types.

@item 
@emph{Shared_Passive}: The unit contains a pragma Shared_Passive.

@item 
@emph{Predefined}: This unit is part of the predefined environment and cannot be modified
by the user.

@item 
@emph{Remote_Call_Interface}: The unit contains a pragma Remote_Call_Interface.
@end itemize
@end table

@node Example of gnatls Usage,,Switches for gnatls,The GNAT Library Browser gnatls
@anchor{gnat_ugn/gnat_utility_programs id8}@anchor{1d8}@anchor{gnat_ugn/gnat_utility_programs example-of-gnatls-usage}@anchor{1d9}
@subsection Example of @cite{gnatls} Usage


Example of using the verbose switch. Note how the source and
object paths are affected by the -I switch.

@quotation

@example
$ gnatls -v -I.. demo1.o

GNATLS 5.03w (20041123-34)
Copyright 1997-2004 Free Software Foundation, Inc.

Source Search Path:
   <Current_Directory>
   ../
   /home/comar/local/adainclude/

Object Search Path:
   <Current_Directory>
   ../
   /home/comar/local/lib/gcc-lib/x86-linux/3.4.3/adalib/

Project Search Path:
   <Current_Directory>
   /home/comar/local/lib/gnat/

./demo1.o
   Unit =>
     Name   => demo1
     Kind   => subprogram body
     Flags  => No_Elab_Code
     Source => demo1.adb    modified
@end example
@end quotation

The following is an example of use of the dependency list.
Note the use of the -s switch
which gives a straight list of source files. This can be useful for
building specialized scripts.

@quotation

@example
$ gnatls -d demo2.o
./demo2.o   demo2        OK demo2.adb
                         OK gen_list.ads
                         OK gen_list.adb
                         OK instr.ads
                         OK instr-child.ads

$ gnatls -d -s -a demo1.o
demo1.adb
/home/comar/local/adainclude/ada.ads
/home/comar/local/adainclude/a-finali.ads
/home/comar/local/adainclude/a-filico.ads
/home/comar/local/adainclude/a-stream.ads
/home/comar/local/adainclude/a-tags.ads
gen_list.ads
gen_list.adb
/home/comar/local/adainclude/gnat.ads
/home/comar/local/adainclude/g-io.ads
instr.ads
/home/comar/local/adainclude/system.ads
/home/comar/local/adainclude/s-exctab.ads
/home/comar/local/adainclude/s-finimp.ads
/home/comar/local/adainclude/s-finroo.ads
/home/comar/local/adainclude/s-secsta.ads
/home/comar/local/adainclude/s-stalib.ads
/home/comar/local/adainclude/s-stoele.ads
/home/comar/local/adainclude/s-stratt.ads
/home/comar/local/adainclude/s-tasoli.ads
/home/comar/local/adainclude/s-unstyp.ads
/home/comar/local/adainclude/unchconv.ads
@end example
@end quotation

@node The Cross-Referencing Tools gnatxref and gnatfind,The Ada to HTML Converter gnathtml,The GNAT Library Browser gnatls,GNAT Utility Programs
@anchor{gnat_ugn/gnat_utility_programs the-cross-referencing-tools-gnatxref-and-gnatfind}@anchor{24}@anchor{gnat_ugn/gnat_utility_programs id9}@anchor{1da}
@section The Cross-Referencing Tools @cite{gnatxref} and @cite{gnatfind}


@geindex gnatxref

@geindex gnatfind

The compiler generates cross-referencing information (unless
you set the @code{-gnatx} switch), which are saved in the @code{.ali} files.
This information indicates where in the source each entity is declared and
referenced. Note that entities in package Standard are not included, but
entities in all other predefined units are included in the output.

Before using any of these two tools, you need to compile successfully your
application, so that GNAT gets a chance to generate the cross-referencing
information.

The two tools @cite{gnatxref} and @cite{gnatfind} take advantage of this
information to provide the user with the capability to easily locate the
declaration and references to an entity. These tools are quite similar,
the difference being that @cite{gnatfind} is intended for locating
definitions and/or references to a specified entity or entities, whereas
@cite{gnatxref} is oriented to generating a full report of all
cross-references.

To use these tools, you must not compile your application using the
@emph{-gnatx} switch on the @emph{gnatmake} command line
(see @ref{1d,,Building with gnatmake}). Otherwise, cross-referencing
information will not be generated.

Note: to invoke @cite{gnatxref} or @cite{gnatfind} with a project file,
use the @cite{gnat} driver (see @ref{11f,,The GNAT Driver and Project Files}).

@menu
* gnatxref Switches:: 
* gnatfind Switches:: 
* Project Files for gnatxref and gnatfind:: 
* Regular Expressions in gnatfind and gnatxref:: 
* Examples of gnatxref Usage:: 
* Examples of gnatfind Usage:: 

@end menu

@node gnatxref Switches,gnatfind Switches,,The Cross-Referencing Tools gnatxref and gnatfind
@anchor{gnat_ugn/gnat_utility_programs id10}@anchor{1db}@anchor{gnat_ugn/gnat_utility_programs gnatxref-switches}@anchor{1dc}
@subsection @cite{gnatxref} Switches


The command invocation for @cite{gnatxref} is:

@quotation

@example
$ gnatxref [`switches`] `sourcefile1` [`sourcefile2` ...]
@end example
@end quotation

where


@table @asis

@item @emph{sourcefile1} [, @emph{sourcefile2} ...]

identify the source files for which a report is to be generated. The
'with'ed units will be processed too. You must provide at least one file.

These file names are considered to be regular expressions, so for instance
specifying @code{source*.adb} is the same as giving every file in the current
directory whose name starts with @code{source} and whose extension is
@code{adb}.

You shouldn't specify any directory name, just base names. @emph{gnatxref}
and @emph{gnatfind} will be able to locate these files by themselves using
the source path. If you specify directories, no result is produced.
@end table

The following switches are available for @emph{gnatxref}:

@geindex --version (gnatxref)


@table @asis

@item @code{-version}

Display Copyright and version, then exit disregarding all other options.
@end table

@geindex --help (gnatxref)


@table @asis

@item @code{-help}

If @emph{--version} was not used, display usage, then exit disregarding
all other options.
@end table

@geindex -a (gnatxref)


@table @asis

@item @code{a}

If this switch is present, @cite{gnatfind} and @cite{gnatxref} will parse
the read-only files found in the library search path. Otherwise, these files
will be ignored. This option can be used to protect Gnat sources or your own
libraries from being parsed, thus making @cite{gnatfind} and @cite{gnatxref}
much faster, and their output much smaller. Read-only here refers to access
or permissions status in the file system for the current user.
@end table

@geindex -aIDIR (gnatxref)


@table @asis

@item @code{aI@emph{DIR}}

When looking for source files also look in directory DIR. The order in which
source file search is undertaken is the same as for @emph{gnatmake}.
@end table

@geindex -aODIR (gnatxref)


@table @asis

@item @code{aO@emph{DIR}}

When searching for library and object files, look in directory
DIR. The order in which library files are searched is the same as for
@emph{gnatmake}.
@end table

@geindex -nostdinc (gnatxref)


@table @asis

@item @code{nostdinc}

Do not look for sources in the system default directory.
@end table

@geindex -nostdlib (gnatxref)


@table @asis

@item @code{nostdlib}

Do not look for library files in the system default directory.
@end table

@geindex --ext (gnatxref)


@table @asis

@item @code{-ext=@emph{extension}}

Specify an alternate ali file extension. The default is @cite{ali} and other
extensions (e.g. @cite{gli} for C/C++ sources when using @emph{-fdump-xref})
may be specified via this switch. Note that if this switch overrides the
default, which means that only the new extension will be considered.
@end table

@geindex --RTS (gnatxref)


@table @asis

@item @code{-RTS=@emph{rts-path}}

Specifies the default location of the runtime library. Same meaning as the
equivalent @emph{gnatmake} flag (@ref{df,,Switches for gnatmake}).
@end table

@geindex -d (gnatxref)


@table @asis

@item @code{d}

If this switch is set @cite{gnatxref} will output the parent type
reference for each matching derived types.
@end table

@geindex -f (gnatxref)


@table @asis

@item @code{f}

If this switch is set, the output file names will be preceded by their
directory (if the file was found in the search path). If this switch is
not set, the directory will not be printed.
@end table

@geindex -g (gnatxref)


@table @asis

@item @code{g}

If this switch is set, information is output only for library-level
entities, ignoring local entities. The use of this switch may accelerate
@cite{gnatfind} and @cite{gnatxref}.
@end table

@geindex -IDIR (gnatxref)


@table @asis

@item @code{I@emph{DIR}}

Equivalent to @code{-aODIR -aIDIR}.
@end table

@geindex -pFILE (gnatxref)


@table @asis

@item @code{p@emph{FILE}}

Specify a project file to use @ref{b,,GNAT Project Manager}.
If you need to use the @code{.gpr}
project files, you should use gnatxref through the GNAT driver
(@emph{gnat xref -Pproject}).

By default, @cite{gnatxref} and @cite{gnatfind} will try to locate a
project file in the current directory.

If a project file is either specified or found by the tools, then the content
of the source directory and object directory lines are added as if they
had been specified respectively by @code{-aI}
and @code{-aO}.

@item @code{u}

Output only unused symbols. This may be really useful if you give your
main compilation unit on the command line, as @cite{gnatxref} will then
display every unused entity and 'with'ed package.

@item @code{v}

Instead of producing the default output, @cite{gnatxref} will generate a
@code{tags} file that can be used by vi. For examples how to use this
feature, see @ref{1dd,,Examples of gnatxref Usage}. The tags file is output
to the standard output, thus you will have to redirect it to a file.
@end table

All these switches may be in any order on the command line, and may even
appear after the file names. They need not be separated by spaces, thus
you can say @code{gnatxref -ag} instead of @code{gnatxref -a -g}.

@node gnatfind Switches,Project Files for gnatxref and gnatfind,gnatxref Switches,The Cross-Referencing Tools gnatxref and gnatfind
@anchor{gnat_ugn/gnat_utility_programs id11}@anchor{1de}@anchor{gnat_ugn/gnat_utility_programs gnatfind-switches}@anchor{1df}
@subsection @cite{gnatfind} Switches


The command invocation for @cite{gnatfind} is:

@quotation

@example
$ gnatfind [`switches`] `pattern`[:`sourcefile`[:`line`[:`column`]]]
      [`file1` `file2` ...]
@end example
@end quotation

with the following iterpretation of the command arguments:


@table @asis

@item @emph{pattern}

An entity will be output only if it matches the regular expression found
in @cite{pattern}, see @ref{1e0,,Regular Expressions in gnatfind and gnatxref}.

Omitting the pattern is equivalent to specifying @code{*}, which
will match any entity. Note that if you do not provide a pattern, you
have to provide both a sourcefile and a line.

Entity names are given in Latin-1, with uppercase/lowercase equivalence
for matching purposes. At the current time there is no support for
8-bit codes other than Latin-1, or for wide characters in identifiers.

@item @emph{sourcefile}

@cite{gnatfind} will look for references, bodies or declarations
of symbols referenced in @code{sourcefile}, at line @cite{line}
and column @cite{column}. See @ref{1e1,,Examples of gnatfind Usage}
for syntax examples.

@item @emph{line}

A decimal integer identifying the line number containing
the reference to the entity (or entities) to be located.

@item @emph{column}

A decimal integer identifying the exact location on the
line of the first character of the identifier for the
entity reference. Columns are numbered from 1.

@item @emph{file1 file2 ...}

The search will be restricted to these source files. If none are given, then
the search will be conducted for every library file in the search path.
These files must appear only after the pattern or sourcefile.

These file names are considered to be regular expressions, so for instance
specifying @code{source*.adb} is the same as giving every file in the current
directory whose name starts with @code{source} and whose extension is
@code{adb}.

The location of the spec of the entity will always be displayed, even if it
isn't in one of @code{file1}, @code{file2}, ... The
occurrences of the entity in the separate units of the ones given on the
command line will also be displayed.

Note that if you specify at least one file in this part, @cite{gnatfind} may
sometimes not be able to find the body of the subprograms.
@end table

At least one of 'sourcefile' or 'pattern' has to be present on
the command line.

The following switches are available:

@geindex --version (gnatfind)


@table @asis

@item @code{--version}

Display Copyright and version, then exit disregarding all other options.
@end table

@geindex --help (gnatfind)


@table @asis

@item @code{-help}

If @emph{--version} was not used, display usage, then exit disregarding
all other options.
@end table

@geindex -a (gnatfind)


@table @asis

@item @code{a}

If this switch is present, @cite{gnatfind} and @cite{gnatxref} will parse
the read-only files found in the library search path. Otherwise, these files
will be ignored. This option can be used to protect Gnat sources or your own
libraries from being parsed, thus making @cite{gnatfind} and @cite{gnatxref}
much faster, and their output much smaller. Read-only here refers to access
or permission status in the file system for the current user.
@end table

@geindex -aIDIR (gnatfind)


@table @asis

@item @code{aI@emph{DIR}}

When looking for source files also look in directory DIR. The order in which
source file search is undertaken is the same as for @emph{gnatmake}.
@end table

@geindex -aODIR (gnatfind)


@table @asis

@item @code{aO@emph{DIR}}

When searching for library and object files, look in directory
DIR. The order in which library files are searched is the same as for
@emph{gnatmake}.
@end table

@geindex -nostdinc (gnatfind)


@table @asis

@item @code{nostdinc}

Do not look for sources in the system default directory.
@end table

@geindex -nostdlib (gnatfind)


@table @asis

@item @code{nostdlib}

Do not look for library files in the system default directory.
@end table

@geindex --ext (gnatfind)


@table @asis

@item @code{-ext=@emph{extension}}

Specify an alternate ali file extension. The default is @cite{ali} and other
extensions (e.g. @cite{gli} for C/C++ sources when using @emph{-fdump-xref})
may be specified via this switch. Note that if this switch overrides the
default, which means that only the new extension will be considered.
@end table

@geindex --RTS (gnatfind)


@table @asis

@item @code{-RTS=@emph{rts-path}}

Specifies the default location of the runtime library. Same meaning as the
equivalent @emph{gnatmake} flag (@ref{df,,Switches for gnatmake}).
@end table

@geindex -d (gnatfind)


@table @asis

@item @code{d}

If this switch is set, then @cite{gnatfind} will output the parent type
reference for each matching derived types.
@end table

@geindex -e (gnatfind)


@table @asis

@item @code{e}

By default, @cite{gnatfind} accept the simple regular expression set for
@cite{pattern}. If this switch is set, then the pattern will be
considered as full Unix-style regular expression.
@end table

@geindex -f (gnatfind)


@table @asis

@item @code{f}

If this switch is set, the output file names will be preceded by their
directory (if the file was found in the search path). If this switch is
not set, the directory will not be printed.
@end table

@geindex -g (gnatfind)


@table @asis

@item @code{g}

If this switch is set, information is output only for library-level
entities, ignoring local entities. The use of this switch may accelerate
@cite{gnatfind} and @cite{gnatxref}.
@end table

@geindex -IDIR (gnatfind)


@table @asis

@item @code{I@emph{DIR}}

Equivalent to @code{-aODIR -aIDIR}.
@end table

@geindex -pFILE (gnatfind)


@table @asis

@item @code{p@emph{FILE}}

Specify a project file (@ref{b,,GNAT Project Manager}) to use.
By default, @cite{gnatxref} and @cite{gnatfind} will try to locate a
project file in the current directory.

If a project file is either specified or found by the tools, then the content
of the source directory and object directory lines are added as if they
had been specified respectively by @code{-aI} and
@code{-aO}.
@end table

@geindex -r (gnatfind)


@table @asis

@item @code{r}

By default, @cite{gnatfind} will output only the information about the
declaration, body or type completion of the entities. If this switch is
set, the @cite{gnatfind} will locate every reference to the entities in
the files specified on the command line (or in every file in the search
path if no file is given on the command line).
@end table

@geindex -s (gnatfind)


@table @asis

@item @code{s}

If this switch is set, then @cite{gnatfind} will output the content
of the Ada source file lines were the entity was found.
@end table

@geindex -t (gnatfind)


@table @asis

@item @code{t}

If this switch is set, then @cite{gnatfind} will output the type hierarchy for
the specified type. It act like -d option but recursively from parent
type to parent type. When this switch is set it is not possible to
specify more than one file.
@end table

All these switches may be in any order on the command line, and may even
appear after the file names. They need not be separated by spaces, thus
you can say @code{gnatxref -ag} instead of
@code{gnatxref -a -g}.

As stated previously, gnatfind will search in every directory in the
search path. You can force it to look only in the current directory if
you specify @cite{*} at the end of the command line.

@node Project Files for gnatxref and gnatfind,Regular Expressions in gnatfind and gnatxref,gnatfind Switches,The Cross-Referencing Tools gnatxref and gnatfind
@anchor{gnat_ugn/gnat_utility_programs project-files-for-gnatxref-and-gnatfind}@anchor{1e2}@anchor{gnat_ugn/gnat_utility_programs id12}@anchor{1e3}
@subsection Project Files for @emph{gnatxref} and @emph{gnatfind}


Project files allow a programmer to specify how to compile its
application, where to find sources, etc.  These files are used
primarily by GPS, but they can also be used
by the two tools @cite{gnatxref} and @cite{gnatfind}.

A project file name must end with @code{.gpr}. If a single one is
present in the current directory, then @cite{gnatxref} and @cite{gnatfind} will
extract the information from it. If multiple project files are found, none of
them is read, and you have to use the @code{-p} switch to specify the one
you want to use.

The following lines can be included, even though most of them have default
values which can be used in most cases.
The lines can be entered in any order in the file.
Except for @code{src_dir} and @code{obj_dir}, you can only have one instance of
each line. If you have multiple instances, only the last one is taken into
account.


@itemize *

@item 

@table @asis

@item @emph{src_dir=DIR}

[default: @cite{"./"}].
Specifies a directory where to look for source files. Multiple @cite{src_dir}
lines can be specified and they will be searched in the order they
are specified.
@end table

@item 

@table @asis

@item @emph{obj_dir=DIR}

[default: @cite{"./"}].
Specifies a directory where to look for object and library files. Multiple
@cite{obj_dir} lines can be specified, and they will be searched in the order
they are specified
@end table

@item 

@table @asis

@item @emph{comp_opt=SWITCHES}

[default: @cite{""}].
Creates a variable which can be referred to subsequently by using
the @cite{$@{comp_opt@}} notation. This is intended to store the default
switches given to @emph{gnatmake} and @emph{gcc}.
@end table

@item 

@table @asis

@item @emph{bind_opt=SWITCHES}

[default: @cite{""}].
Creates a variable which can be referred to subsequently by using
the @code{$@emph{bind_opt}} notation. This is intended to store the default
switches given to @emph{gnatbind}.
@end table

@item 

@table @asis

@item @emph{link_opt=SWITCHES}

[default: @cite{""}].
Creates a variable which can be referred to subsequently by using
the @code{$@emph{link_opt}} notation. This is intended to store the default
switches given to @emph{gnatlink}.
@end table

@item 

@table @asis

@item @emph{main=EXECUTABLE}

[default: @cite{""}].
Specifies the name of the executable for the application. This variable can
be referred to in the following lines by using the @code{@emph{$@{main}} notation.
@end table

@item 

@table @asis

@item @emph{comp_cmd=COMMAND}

[default: @cite{"gcc -c -I$@{src_dir@} -g -gnatq"}].
Specifies the command used to compile a single file in the application.
@end table

@item 

@table @asis

@item @emph{make_cmd=COMMAND}

[default: @cite{"gnatmake $@{main@} -aI$@{src_dir@} -aO$@{obj_dir@} -g -gnatq -cargs $@{comp_opt@} -bargs $@{bind_opt@} -largs $@{link_opt@}"}].
Specifies the command used to recompile the whole application.
@end table

@item 

@table @asis

@item @emph{run_cmd=COMMAND}

[default: @cite{"$@{main@}"}].
Specifies the command used to run the application.
@end table

@item 

@table @asis

@item @emph{debug_cmd=COMMAND}

[default: @cite{"gdb $@{main@}"}].
Specifies the command used to debug the application
@end table
@end itemize

@emph{gnatxref} and @emph{gnatfind} only take into account the
@cite{src_dir} and @cite{obj_dir} lines, and ignore the others.

@node Regular Expressions in gnatfind and gnatxref,Examples of gnatxref Usage,Project Files for gnatxref and gnatfind,The Cross-Referencing Tools gnatxref and gnatfind
@anchor{gnat_ugn/gnat_utility_programs id13}@anchor{1e4}@anchor{gnat_ugn/gnat_utility_programs regular-expressions-in-gnatfind-and-gnatxref}@anchor{1e0}
@subsection Regular Expressions in @cite{gnatfind} and @cite{gnatxref}


As specified in the section about @emph{gnatfind}, the pattern can be a
regular expression. Two kinds of regular expressions
are recognized:


@itemize *

@item 

@table @asis

@item @emph{Globbing pattern}

These are the most common regular expression. They are the same as are
generally used in a Unix shell command line, or in a DOS session.

Here is a more formal grammar:

@example
regexp ::= term
term   ::= elmt            -- matches elmt
term   ::= elmt elmt       -- concatenation (elmt then elmt)
term   ::= *               -- any string of 0 or more characters
term   ::= ?               -- matches any character
term   ::= [char @{char@}]   -- matches any character listed
term   ::= [char - char]   -- matches any character in range
@end example
@end table

@item 

@table @asis

@item @emph{Full regular expression}

The second set of regular expressions is much more powerful. This is the
type of regular expressions recognized by utilities such as @code{grep}.

The following is the form of a regular expression, expressed in same BNF
style as is found in the Ada Reference Manual:

@example
regexp ::= term @{| term@}   -- alternation (term or term ...)

term ::= item @{item@}       -- concatenation (item then item)

item ::= elmt              -- match elmt
item ::= elmt *            -- zero or more elmt's
item ::= elmt +            -- one or more elmt's
item ::= elmt ?            -- matches elmt or nothing

elmt ::= nschar            -- matches given character
elmt ::= [nschar @{nschar@}]   -- matches any character listed
elmt ::= [^ nschar @{nschar@}] -- matches any character not listed
elmt ::= [char - char]     -- matches chars in given range
elmt ::= \\ char            -- matches given character
elmt ::= .                 -- matches any single character
elmt ::= ( regexp )        -- parens used for grouping

char ::= any character, including special characters
nschar ::= any character except ()[].*+?^
@end example

Here are a few examples:

@quotation


@table @asis

@item @code{abcde|fghi}

will match any of the two strings @code{abcde} and @code{fghi},

@item @code{abc*d}

will match any string like @code{abd}, @code{abcd}, @code{abccd},
@code{abcccd}, and so on,

@item @code{[a-z]+}

will match any string which has only lowercase characters in it (and at
least one character.
@end table
@end quotation
@end table
@end itemize

@node Examples of gnatxref Usage,Examples of gnatfind Usage,Regular Expressions in gnatfind and gnatxref,The Cross-Referencing Tools gnatxref and gnatfind
@anchor{gnat_ugn/gnat_utility_programs examples-of-gnatxref-usage}@anchor{1dd}@anchor{gnat_ugn/gnat_utility_programs id14}@anchor{1e5}
@subsection Examples of @cite{gnatxref} Usage


@menu
* General Usage:: 
* Using gnatxref with vi:: 

@end menu

@node General Usage,Using gnatxref with vi,,Examples of gnatxref Usage
@anchor{gnat_ugn/gnat_utility_programs general-usage}@anchor{1e6}
@subsubsection General Usage


For the following examples, we will consider the following units:

@quotation

@example
main.ads:
1: with Bar;
2: package Main is
3:     procedure Foo (B : in Integer);
4:     C : Integer;
5: private
6:     D : Integer;
7: end Main;

main.adb:
1: package body Main is
2:     procedure Foo (B : in Integer) is
3:     begin
4:        C := B;
5:        D := B;
6:        Bar.Print (B);
7:        Bar.Print (C);
8:     end Foo;
9: end Main;

bar.ads:
1: package Bar is
2:     procedure Print (B : Integer);
3: end bar;
@end example
@end quotation

The first thing to do is to recompile your application (for instance, in
that case just by doing a @code{gnatmake main}, so that GNAT generates
the cross-referencing information.
You can then issue any of the following commands:

@quotation


@itemize *

@item 
@code{gnatxref main.adb}
@cite{gnatxref} generates cross-reference information for main.adb
and every unit 'with'ed by main.adb.

The output would be:

@quotation

@example
B                                                      Type: Integer
  Decl: bar.ads           2:22
B                                                      Type: Integer
  Decl: main.ads          3:20
  Body: main.adb          2:20
  Ref:  main.adb          4:13     5:13     6:19
Bar                                                    Type: Unit
  Decl: bar.ads           1:9
  Ref:  main.adb          6:8      7:8
       main.ads           1:6
C                                                      Type: Integer
  Decl: main.ads          4:5
  Modi: main.adb          4:8
  Ref:  main.adb          7:19
D                                                      Type: Integer
  Decl: main.ads          6:5
  Modi: main.adb          5:8
Foo                                                    Type: Unit
  Decl: main.ads          3:15
  Body: main.adb          2:15
Main                                                    Type: Unit
  Decl: main.ads          2:9
  Body: main.adb          1:14
Print                                                   Type: Unit
  Decl: bar.ads           2:15
  Ref:  main.adb          6:12     7:12
@end example
@end quotation

This shows that the entity @cite{Main} is declared in main.ads, line 2, column 9,
its body is in main.adb, line 1, column 14 and is not referenced any where.

The entity @cite{Print} is declared in bar.ads, line 2, column 15 and it
is referenced in main.adb, line 6 column 12 and line 7 column 12.

@item 
@code{gnatxref package1.adb package2.ads}
@cite{gnatxref} will generates cross-reference information for
package1.adb, package2.ads and any other package 'with'ed by any
of these.
@end itemize
@end quotation

@node Using gnatxref with vi,,General Usage,Examples of gnatxref Usage
@anchor{gnat_ugn/gnat_utility_programs using-gnatxref-with-vi}@anchor{1e7}
@subsubsection Using gnatxref with vi


@cite{gnatxref} can generate a tags file output, which can be used
directly from @emph{vi}. Note that the standard version of @emph{vi}
will not work properly with overloaded symbols. Consider using another
free implementation of @emph{vi}, such as @emph{vim}.

@quotation

@example
$ gnatxref -v gnatfind.adb > tags
@end example
@end quotation

The following command will generate the tags file for @cite{gnatfind} itself
(if the sources are in the search path!):

@quotation

@example
$ gnatxref -v gnatfind.adb > tags
@end example
@end quotation

From @emph{vi}, you can then use the command @code{:tag @emph{entity}}
(replacing @cite{entity} by whatever you are looking for), and vi will
display a new file with the corresponding declaration of entity.

@node Examples of gnatfind Usage,,Examples of gnatxref Usage,The Cross-Referencing Tools gnatxref and gnatfind
@anchor{gnat_ugn/gnat_utility_programs id15}@anchor{1e8}@anchor{gnat_ugn/gnat_utility_programs examples-of-gnatfind-usage}@anchor{1e1}
@subsection Examples of @cite{gnatfind} Usage



@itemize *

@item 
@code{gnatfind -f xyz:main.adb}
Find declarations for all entities xyz referenced at least once in
main.adb. The references are search in every library file in the search
path.

The directories will be printed as well (as the @code{-f}
switch is set)

The output will look like:

@quotation

@example
directory/main.ads:106:14: xyz <= declaration
directory/main.adb:24:10: xyz <= body
directory/foo.ads:45:23: xyz <= declaration
@end example
@end quotation

I.e., one of the entities xyz found in main.adb is declared at
line 12 of main.ads (and its body is in main.adb), and another one is
declared at line 45 of foo.ads

@item 
@code{gnatfind -fs xyz:main.adb}
This is the same command as the previous one, but @cite{gnatfind} will
display the content of the Ada source file lines.

The output will look like:

@example
directory/main.ads:106:14: xyz <= declaration
   procedure xyz;
directory/main.adb:24:10: xyz <= body
   procedure xyz is
directory/foo.ads:45:23: xyz <= declaration
   xyz : Integer;
@end example

This can make it easier to find exactly the location your are looking
for.

@item 
@code{gnatfind -r "*x*":main.ads:123 foo.adb}
Find references to all entities containing an x that are
referenced on line 123 of main.ads.
The references will be searched only in main.ads and foo.adb.

@item 
@code{gnatfind main.ads:123}
Find declarations and bodies for all entities that are referenced on
line 123 of main.ads.

This is the same as @code{gnatfind "*":main.adb:123`}

@item 
@code{gnatfind mydir/main.adb:123:45}
Find the declaration for the entity referenced at column 45 in
line 123 of file main.adb in directory mydir. Note that it
is usual to omit the identifier name when the column is given,
since the column position identifies a unique reference.

The column has to be the beginning of the identifier, and should not
point to any character in the middle of the identifier.
@end itemize

@node The Ada to HTML Converter gnathtml,,The Cross-Referencing Tools gnatxref and gnatfind,GNAT Utility Programs
@anchor{gnat_ugn/gnat_utility_programs the-ada-to-html-converter-gnathtml}@anchor{25}@anchor{gnat_ugn/gnat_utility_programs id16}@anchor{1e9}
@section The Ada to HTML Converter @cite{gnathtml}


@geindex gnathtml

@emph{gnathtml} is a Perl script that allows Ada source files to be browsed using
standard Web browsers. For installation information, see @ref{1ea,,Installing gnathtml}.

Ada reserved keywords are highlighted in a bold font and Ada comments in
a blue font. Unless your program was compiled with the gcc @emph{-gnatx}
switch to suppress the generation of cross-referencing information, user
defined variables and types will appear in a different color; you will
be able to click on any identifier and go to its declaration.

@menu
* Invoking gnathtml:: 
* Installing gnathtml:: 

@end menu

@node Invoking gnathtml,Installing gnathtml,,The Ada to HTML Converter gnathtml
@anchor{gnat_ugn/gnat_utility_programs invoking-gnathtml}@anchor{1eb}@anchor{gnat_ugn/gnat_utility_programs id17}@anchor{1ec}
@subsection Invoking @emph{gnathtml}


The command line is as follows:

@quotation

@example
$ perl gnathtml.pl [`switches`] `ada-files`
@end example
@end quotation

You can specify as many Ada files as you want. @cite{gnathtml} will generate
an html file for every ada file, and a global file called @code{index.htm}.
This file is an index of every identifier defined in the files.

The following switches are available:

@geindex -83 (gnathtml)


@table @asis

@item @code{83}

Only the Ada 83 subset of keywords will be highlighted.
@end table

@geindex -cc (gnathtml)


@table @asis

@item @code{cc @emph{color}}

This option allows you to change the color used for comments. The default
value is green. The color argument can be any name accepted by html.
@end table

@geindex -d (gnathtml)


@table @asis

@item @code{d}

If the Ada files depend on some other files (for instance through
@cite{with} clauses, the latter files will also be converted to html.
Only the files in the user project will be converted to html, not the files
in the run-time library itself.
@end table

@geindex -D (gnathtml)


@table @asis

@item @code{D}

This command is the same as @emph{-d} above, but @emph{gnathtml} will
also look for files in the run-time library, and generate html files for them.
@end table

@geindex -ext (gnathtml)


@table @asis

@item @code{ext @emph{extension}}

This option allows you to change the extension of the generated HTML files.
If you do not specify an extension, it will default to @code{htm}.
@end table

@geindex -f (gnathtml)


@table @asis

@item @code{f}

By default, gnathtml will generate html links only for global entities
('with'ed units, global variables and types,...).  If you specify
@emph{-f} on the command line, then links will be generated for local
entities too.
@end table

@geindex -l (gnathtml)


@table @asis

@item @code{l @emph{number}}

If this switch is provided and @cite{number} is not 0, then
@cite{gnathtml} will number the html files every @cite{number} line.
@end table

@geindex -I (gnathtml)


@table @asis

@item @code{I @emph{dir}}

Specify a directory to search for library files (@code{.ALI} files) and
source files. You can provide several -I switches on the command line,
and the directories will be parsed in the order of the command line.
@end table

@geindex -o (gnathtml)


@table @asis

@item @code{o @emph{dir}}

Specify the output directory for html files. By default, gnathtml will
saved the generated html files in a subdirectory named @code{html/}.
@end table

@geindex -p (gnathtml)


@table @asis

@item @code{p @emph{file}}

If you are using Emacs and the most recent Emacs Ada mode, which provides
a full Integrated Development Environment for compiling, checking,
running and debugging applications, you may use @code{.gpr} files
to give the directories where Emacs can find sources and object files.

Using this switch, you can tell gnathtml to use these files.
This allows you to get an html version of your application, even if it
is spread over multiple directories.
@end table

@geindex -sc (gnathtml)


@table @asis

@item @code{sc @emph{color}}

This switch allows you to change the color used for symbol
definitions.
The default value is red. The color argument can be any name accepted by html.
@end table

@geindex -t (gnathtml)


@table @asis

@item @code{t @emph{file}}

This switch provides the name of a file. This file contains a list of
file names to be converted, and the effect is exactly as though they had
appeared explicitly on the command line. This
is the recommended way to work around the command line length limit on some
systems.
@end table

@node Installing gnathtml,,Invoking gnathtml,The Ada to HTML Converter gnathtml
@anchor{gnat_ugn/gnat_utility_programs installing-gnathtml}@anchor{1ea}@anchor{gnat_ugn/gnat_utility_programs id18}@anchor{1ed}
@subsection Installing @cite{gnathtml}


@cite{Perl} needs to be installed on your machine to run this script.
@cite{Perl} is freely available for almost every architecture and
operating system via the Internet.

On Unix systems, you  may want to modify  the  first line of  the script
@cite{gnathtml},  to explicitly  specify  where Perl
is located. The syntax of this line is:

@quotation

@example
#!full_path_name_to_perl
@end example
@end quotation

Alternatively, you may run the script using the following command line:

@quotation

@example
$ perl gnathtml.pl [`switches`] `files`
@end example
@end quotation

@c -- +---------------------------------------------------------------------+

@c -- | The following sections are present only in the PRO and GPL editions |

@c -- +---------------------------------------------------------------------+







@c -- Example: A |withing| unit has a |with| clause, it |withs| a |withed| unit

@node GNAT and Program Execution,Platform-Specific Information,GNAT Utility Programs,Top
@anchor{gnat_ugn/gnat_and_program_execution gnat-and-program-execution}@anchor{e}@anchor{gnat_ugn/gnat_and_program_execution doc}@anchor{1ee}@anchor{gnat_ugn/gnat_and_program_execution id1}@anchor{1ef}
@chapter GNAT and Program Execution


This chapter covers several topics:


@itemize *

@item 
@ref{1f0,,Running and Debugging Ada Programs}

@item 
@ref{1f1,,Code Coverage and Profiling}

@item 
@ref{1f2,,Improving Performance}

@item 
@ref{1f3,,Overflow Check Handling in GNAT}

@item 
@ref{1f4,,Performing Dimensionality Analysis in GNAT}

@item 
@ref{1f5,,Stack Related Facilities}

@item 
@ref{1f6,,Memory Management Issues}
@end itemize

@menu
* Running and Debugging Ada Programs:: 
* Code Coverage and Profiling:: 
* Improving Performance:: 
* Overflow Check Handling in GNAT:: 
* Performing Dimensionality Analysis in GNAT:: 
* Stack Related Facilities:: 
* Memory Management Issues:: 

@end menu

@node Running and Debugging Ada Programs,Code Coverage and Profiling,,GNAT and Program Execution
@anchor{gnat_ugn/gnat_and_program_execution id2}@anchor{1f0}@anchor{gnat_ugn/gnat_and_program_execution running-and-debugging-ada-programs}@anchor{26}
@section Running and Debugging Ada Programs


@geindex Debugging

This section discusses how to debug Ada programs.

An incorrect Ada program may be handled in three ways by the GNAT compiler:


@itemize *

@item 
The illegality may be a violation of the static semantics of Ada. In
that case GNAT diagnoses the constructs in the program that are illegal.
It is then a straightforward matter for the user to modify those parts of
the program.

@item 
The illegality may be a violation of the dynamic semantics of Ada. In
that case the program compiles and executes, but may generate incorrect
results, or may terminate abnormally with some exception.

@item 
When presented with a program that contains convoluted errors, GNAT
itself may terminate abnormally without providing full diagnostics on
the incorrect user program.
@end itemize

@geindex Debugger

@geindex gdb

@menu
* The GNAT Debugger GDB:: 
* Running GDB:: 
* Introduction to GDB Commands:: 
* Using Ada Expressions:: 
* Calling User-Defined Subprograms:: 
* Using the next Command in a Function:: 
* Stopping When Ada Exceptions Are Raised:: 
* Ada Tasks:: 
* Debugging Generic Units:: 
* Remote Debugging with gdbserver:: 
* GNAT Abnormal Termination or Failure to Terminate:: 
* Naming Conventions for GNAT Source Files:: 
* Getting Internal Debugging Information:: 
* Stack Traceback:: 

@end menu

@node The GNAT Debugger GDB,Running GDB,,Running and Debugging Ada Programs
@anchor{gnat_ugn/gnat_and_program_execution the-gnat-debugger-gdb}@anchor{1f7}@anchor{gnat_ugn/gnat_and_program_execution id3}@anchor{1f8}
@subsection The GNAT Debugger GDB


@cite{GDB} is a general purpose, platform-independent debugger that
can be used to debug mixed-language programs compiled with @emph{gcc},
and in particular is capable of debugging Ada programs compiled with
GNAT. The latest versions of @cite{GDB} are Ada-aware and can handle
complex Ada data structures.

See @cite{Debugging with GDB},
for full details on the usage of @cite{GDB}, including a section on
its usage on programs. This manual should be consulted for full
details. The section that follows is a brief introduction to the
philosophy and use of @cite{GDB}.

When GNAT programs are compiled, the compiler optionally writes debugging
information into the generated object file, including information on
line numbers, and on declared types and variables. This information is
separate from the generated code. It makes the object files considerably
larger, but it does not add to the size of the actual executable that
will be loaded into memory, and has no impact on run-time performance. The
generation of debug information is triggered by the use of the
-g switch in the @emph{gcc} or @emph{gnatmake} command
used to carry out the compilations. It is important to emphasize that
the use of these options does not change the generated code.

The debugging information is written in standard system formats that
are used by many tools, including debuggers and profilers. The format
of the information is typically designed to describe C types and
semantics, but GNAT implements a translation scheme which allows full
details about Ada types and variables to be encoded into these
standard C formats. Details of this encoding scheme may be found in
the file exp_dbug.ads in the GNAT source distribution. However, the
details of this encoding are, in general, of no interest to a user,
since @cite{GDB} automatically performs the necessary decoding.

When a program is bound and linked, the debugging information is
collected from the object files, and stored in the executable image of
the program. Again, this process significantly increases the size of
the generated executable file, but it does not increase the size of
the executable program itself. Furthermore, if this program is run in
the normal manner, it runs exactly as if the debug information were
not present, and takes no more actual memory.

However, if the program is run under control of @cite{GDB}, the
debugger is activated.  The image of the program is loaded, at which
point it is ready to run.  If a run command is given, then the program
will run exactly as it would have if @cite{GDB} were not present. This
is a crucial part of the @cite{GDB} design philosophy.  @cite{GDB} is
entirely non-intrusive until a breakpoint is encountered.  If no
breakpoint is ever hit, the program will run exactly as it would if no
debugger were present. When a breakpoint is hit, @cite{GDB} accesses
the debugging information and can respond to user commands to inspect
variables, and more generally to report on the state of execution.

@node Running GDB,Introduction to GDB Commands,The GNAT Debugger GDB,Running and Debugging Ada Programs
@anchor{gnat_ugn/gnat_and_program_execution id4}@anchor{1f9}@anchor{gnat_ugn/gnat_and_program_execution running-gdb}@anchor{1fa}
@subsection Running GDB


This section describes how to initiate the debugger.

The debugger can be launched from a @cite{GPS} menu or
directly from the command line. The description below covers the latter use.
All the commands shown can be used in the @cite{GPS} debug console window,
but there are usually more GUI-based ways to achieve the same effect.

The command to run @cite{GDB} is

@quotation

@example
$ gdb program
@end example
@end quotation

where @cite{program} is the name of the executable file. This
activates the debugger and results in a prompt for debugger commands.
The simplest command is simply @cite{run}, which causes the program to run
exactly as if the debugger were not present. The following section
describes some of the additional commands that can be given to @cite{GDB}.

@node Introduction to GDB Commands,Using Ada Expressions,Running GDB,Running and Debugging Ada Programs
@anchor{gnat_ugn/gnat_and_program_execution introduction-to-gdb-commands}@anchor{1fb}@anchor{gnat_ugn/gnat_and_program_execution id5}@anchor{1fc}
@subsection Introduction to GDB Commands


@cite{GDB} contains a large repertoire of commands.
See @cite{Debugging with GDB} for extensive documentation on the use
of these commands, together with examples of their use. Furthermore,
the command @emph{help} invoked from within GDB activates a simple help
facility which summarizes the available commands and their options.
In this section we summarize a few of the most commonly
used commands to give an idea of what @cite{GDB} is about. You should create
a simple program with debugging information and experiment with the use of
these @cite{GDB} commands on the program as you read through the
following section.


@itemize *

@item 

@table @asis

@item @emph{set args `arguments`}

The @cite{arguments} list above is a list of arguments to be passed to
the program on a subsequent run command, just as though the arguments
had been entered on a normal invocation of the program. The @cite{set args}
command is not needed if the program does not require arguments.
@end table

@item 

@table @asis

@item @emph{run}

The @cite{run} command causes execution of the program to start from
the beginning. If the program is already running, that is to say if
you are currently positioned at a breakpoint, then a prompt will ask
for confirmation that you want to abandon the current execution and
restart.
@end table

@item 

@table @asis

@item @emph{breakpoint `location`}

The breakpoint command sets a breakpoint, that is to say a point at which
execution will halt and @cite{GDB} will await further
commands. @cite{location} is
either a line number within a file, given in the format @cite{file:linenumber},
or it is the name of a subprogram. If you request that a breakpoint be set on
a subprogram that is overloaded, a prompt will ask you to specify on which of
those subprograms you want to breakpoint. You can also
specify that all of them should be breakpointed. If the program is run
and execution encounters the breakpoint, then the program
stops and @cite{GDB} signals that the breakpoint was encountered by
printing the line of code before which the program is halted.
@end table

@item 

@table @asis

@item @emph{catch exception `name`}

This command causes the program execution to stop whenever exception
@cite{name} is raised.  If @cite{name} is omitted, then the execution is
suspended when any exception is raised.
@end table

@item 

@table @asis

@item @emph{print `expression`}

This will print the value of the given expression. Most simple
Ada expression formats are properly handled by @cite{GDB}, so the expression
can contain function calls, variables, operators, and attribute references.
@end table

@item 

@table @asis

@item @emph{continue}

Continues execution following a breakpoint, until the next breakpoint or the
termination of the program.
@end table

@item 

@table @asis

@item @emph{step}

Executes a single line after a breakpoint. If the next statement
is a subprogram call, execution continues into (the first statement of)
the called subprogram.
@end table

@item 

@table @asis

@item @emph{next}

Executes a single line. If this line is a subprogram call, executes and
returns from the call.
@end table

@item 

@table @asis

@item @emph{list}

Lists a few lines around the current source location. In practice, it
is usually more convenient to have a separate edit window open with the
relevant source file displayed. Successive applications of this command
print subsequent lines. The command can be given an argument which is a
line number, in which case it displays a few lines around the specified one.
@end table

@item 

@table @asis

@item @emph{backtrace}

Displays a backtrace of the call chain. This command is typically
used after a breakpoint has occurred, to examine the sequence of calls that
leads to the current breakpoint. The display includes one line for each
activation record (frame) corresponding to an active subprogram.
@end table

@item 

@table @asis

@item @emph{up}

At a breakpoint, @cite{GDB} can display the values of variables local
to the current frame. The command @cite{up} can be used to
examine the contents of other active frames, by moving the focus up
the stack, that is to say from callee to caller, one frame at a time.
@end table

@item 

@table @asis

@item @emph{down}

Moves the focus of @cite{GDB} down from the frame currently being
examined to the frame of its callee (the reverse of the previous command),
@end table

@item 

@table @asis

@item @emph{frame `n`}

Inspect the frame with the given number. The value 0 denotes the frame
of the current breakpoint, that is to say the top of the call stack.
@end table

@item 

@table @asis

@item @emph{kill}

Kills the child process in which the program is running under GDB.
This may be useful for several purposes:


@itemize *

@item 
It allows you to recompile and relink your program, since on many systems
you cannot regenerate an executable file while it is running in a process.

@item 
You can run your program outside the debugger, on systems that do not
permit executing a program outside GDB while breakpoints are set
within GDB.

@item 
It allows you to debug a core dump rather than a running process.
@end itemize
@end table
@end itemize

The above list is a very short introduction to the commands that
@cite{GDB} provides. Important additional capabilities, including conditional
breakpoints, the ability to execute command sequences on a breakpoint,
the ability to debug at the machine instruction level and many other
features are described in detail in @cite{Debugging with GDB}.
Note that most commands can be abbreviated
(for example, c for continue, bt for backtrace).

@node Using Ada Expressions,Calling User-Defined Subprograms,Introduction to GDB Commands,Running and Debugging Ada Programs
@anchor{gnat_ugn/gnat_and_program_execution id6}@anchor{1fd}@anchor{gnat_ugn/gnat_and_program_execution using-ada-expressions}@anchor{1fe}
@subsection Using Ada Expressions


@geindex Ada expressions (in gdb)

@cite{GDB} supports a fairly large subset of Ada expression syntax, with some
extensions. The philosophy behind the design of this subset is

@quotation


@itemize *

@item 
That @cite{GDB} should provide basic literals and access to operations for
arithmetic, dereferencing, field selection, indexing, and subprogram calls,
leaving more sophisticated computations to subprograms written into the
program (which therefore may be called from @cite{GDB}).

@item 
That type safety and strict adherence to Ada language restrictions
are not particularly relevant in a debugging context.

@item 
That brevity is important to the @cite{GDB} user.
@end itemize
@end quotation

Thus, for brevity, the debugger acts as if there were
implicit @cite{with} and @cite{use} clauses in effect for all user-written
packages, thus making it unnecessary to fully qualify most names with
their packages, regardless of context. Where this causes ambiguity,
@cite{GDB} asks the user's intent.

For details on the supported Ada syntax, see @cite{Debugging with GDB}.

@node Calling User-Defined Subprograms,Using the next Command in a Function,Using Ada Expressions,Running and Debugging Ada Programs
@anchor{gnat_ugn/gnat_and_program_execution id7}@anchor{1ff}@anchor{gnat_ugn/gnat_and_program_execution calling-user-defined-subprograms}@anchor{200}
@subsection Calling User-Defined Subprograms


An important capability of @cite{GDB} is the ability to call user-defined
subprograms while debugging. This is achieved simply by entering
a subprogram call statement in the form:

@quotation

@example
call subprogram-name (parameters)
@end example
@end quotation

The keyword @cite{call} can be omitted in the normal case where the
@cite{subprogram-name} does not coincide with any of the predefined
@cite{GDB} commands.

The effect is to invoke the given subprogram, passing it the
list of parameters that is supplied. The parameters can be expressions and
can include variables from the program being debugged. The
subprogram must be defined
at the library level within your program, and @cite{GDB} will call the
subprogram within the environment of your program execution (which
means that the subprogram is free to access or even modify variables
within your program).

The most important use of this facility is in allowing the inclusion of
debugging routines that are tailored to particular data structures
in your program. Such debugging routines can be written to provide a suitably
high-level description of an abstract type, rather than a low-level dump
of its physical layout. After all, the standard
@cite{GDB print} command only knows the physical layout of your
types, not their abstract meaning. Debugging routines can provide information
at the desired semantic level and are thus enormously useful.

For example, when debugging GNAT itself, it is crucial to have access to
the contents of the tree nodes used to represent the program internally.
But tree nodes are represented simply by an integer value (which in turn
is an index into a table of nodes).
Using the @cite{print} command on a tree node would simply print this integer
value, which is not very useful. But the PN routine (defined in file
treepr.adb in the GNAT sources) takes a tree node as input, and displays
a useful high level representation of the tree node, which includes the
syntactic category of the node, its position in the source, the integers
that denote descendant nodes and parent node, as well as varied
semantic information. To study this example in more detail, you might want to
look at the body of the PN procedure in the stated file.

Another useful application of this capability is to deal with situations of
complex data which are not handled suitably by GDB. For example, if you specify
Convention Fortran for a multi-dimensional array, GDB does not know that
the ordering of array elements has been switched and will not properly
address the array elements. In such a case, instead of trying to print the
elements directly from GDB, you can write a callable procedure that prints
the elements in the desired format.

@node Using the next Command in a Function,Stopping When Ada Exceptions Are Raised,Calling User-Defined Subprograms,Running and Debugging Ada Programs
@anchor{gnat_ugn/gnat_and_program_execution using-the-next-command-in-a-function}@anchor{201}@anchor{gnat_ugn/gnat_and_program_execution id8}@anchor{202}
@subsection Using the @emph{next} Command in a Function


When you use the @cite{next} command in a function, the current source
location will advance to the next statement as usual. A special case
arises in the case of a @cite{return} statement.

Part of the code for a return statement is the 'epilogue' of the function.
This is the code that returns to the caller. There is only one copy of
this epilogue code, and it is typically associated with the last return
statement in the function if there is more than one return. In some
implementations, this epilogue is associated with the first statement
of the function.

The result is that if you use the @cite{next} command from a return
statement that is not the last return statement of the function you
may see a strange apparent jump to the last return statement or to
the start of the function. You should simply ignore this odd jump.
The value returned is always that from the first return statement
that was stepped through.

@node Stopping When Ada Exceptions Are Raised,Ada Tasks,Using the next Command in a Function,Running and Debugging Ada Programs
@anchor{gnat_ugn/gnat_and_program_execution stopping-when-ada-exceptions-are-raised}@anchor{203}@anchor{gnat_ugn/gnat_and_program_execution id9}@anchor{204}
@subsection Stopping When Ada Exceptions Are Raised


@geindex Exceptions (in gdb)

You can set catchpoints that stop the program execution when your program
raises selected exceptions.


@itemize *

@item 

@table @asis

@item @emph{catch exception}

Set a catchpoint that stops execution whenever (any task in the) program
raises any exception.
@end table

@item 

@table @asis

@item @emph{catch exception `name`}

Set a catchpoint that stops execution whenever (any task in the) program
raises the exception @cite{name}.
@end table

@item 

@table @asis

@item @emph{catch exception unhandled}

Set a catchpoint that stops executing whenever (any task in the) program
raises an exception for which there is no handler.
@end table

@item 

@table @asis

@item @emph{info exceptions}, @emph{info exceptions `regexp`}

The @cite{info exceptions} command permits the user to examine all defined
exceptions within Ada programs. With a regular expression, @cite{regexp}, as
argument, prints out only those exceptions whose name matches @cite{regexp}.
@end table
@end itemize

@geindex Tasks (in gdb)

@node Ada Tasks,Debugging Generic Units,Stopping When Ada Exceptions Are Raised,Running and Debugging Ada Programs
@anchor{gnat_ugn/gnat_and_program_execution ada-tasks}@anchor{205}@anchor{gnat_ugn/gnat_and_program_execution id10}@anchor{206}
@subsection Ada Tasks


@cite{GDB} allows the following task-related commands:


@itemize *

@item 

@table @asis

@item @emph{info tasks}

This command shows a list of current Ada tasks, as in the following example:

@example
(gdb) info tasks
  ID       TID P-ID   Thread Pri State                 Name
   1   8088000   0   807e000  15 Child Activation Wait main_task
   2   80a4000   1   80ae000  15 Accept/Select Wait    b
   3   809a800   1   80a4800  15 Child Activation Wait a
*  4   80ae800   3   80b8000  15 Running               c
@end example

In this listing, the asterisk before the first task indicates it to be the
currently running task. The first column lists the task ID that is used
to refer to tasks in the following commands.
@end table
@end itemize

@geindex Breakpoints and tasks


@itemize *

@item 
@emph{break `linespec` task `taskid`}, @emph{break `linespec` task `taskid` if ...}

@quotation

These commands are like the @cite{break ... thread ...}.
@cite{linespec} specifies source lines.

Use the qualifier @code{task @emph{taskid}} with a breakpoint command
to specify that you only want @cite{GDB} to stop the program when a
particular Ada task reaches this breakpoint. @cite{taskid} is one of the
numeric task identifiers assigned by @cite{GDB}, shown in the first
column of the @code{info tasks} display.

If you do not specify @code{task @emph{taskid}} when you set a
breakpoint, the breakpoint applies to @emph{all} tasks of your
program.

You can use the @cite{task} qualifier on conditional breakpoints as
well; in this case, place @code{task @emph{taskid}} before the
breakpoint condition (before the @cite{if}).
@end quotation
@end itemize

@geindex Task switching (in gdb)


@itemize *

@item 
@emph{task `taskno`}

@quotation

This command allows switching to the task referred by @cite{taskno}. In
particular, this allows browsing of the backtrace of the specified
task. It is advisable to switch back to the original task before
continuing execution otherwise the scheduling of the program may be
perturbed.
@end quotation
@end itemize

For more detailed information on the tasking support,
see @cite{Debugging with GDB}.

@geindex Debugging Generic Units

@geindex Generics

@node Debugging Generic Units,Remote Debugging with gdbserver,Ada Tasks,Running and Debugging Ada Programs
@anchor{gnat_ugn/gnat_and_program_execution debugging-generic-units}@anchor{207}@anchor{gnat_ugn/gnat_and_program_execution id11}@anchor{208}
@subsection Debugging Generic Units


GNAT always uses code expansion for generic instantiation. This means that
each time an instantiation occurs, a complete copy of the original code is
made, with appropriate substitutions of formals by actuals.

It is not possible to refer to the original generic entities in
@cite{GDB}, but it is always possible to debug a particular instance of
a generic, by using the appropriate expanded names. For example, if we have

@quotation

@example
procedure g is

   generic package k is
      procedure kp (v1 : in out integer);
   end k;

   package body k is
      procedure kp (v1 : in out integer) is
      begin
         v1 := v1 + 1;
      end kp;
   end k;

   package k1 is new k;
   package k2 is new k;

   var : integer := 1;

begin
   k1.kp (var);
   k2.kp (var);
   k1.kp (var);
   k2.kp (var);
end;
@end example
@end quotation

Then to break on a call to procedure kp in the k2 instance, simply
use the command:

@quotation

@example
(gdb) break g.k2.kp
@end example
@end quotation

When the breakpoint occurs, you can step through the code of the
instance in the normal manner and examine the values of local variables, as for
other units.

@geindex Remote Debugging with gdbserver

@node Remote Debugging with gdbserver,GNAT Abnormal Termination or Failure to Terminate,Debugging Generic Units,Running and Debugging Ada Programs
@anchor{gnat_ugn/gnat_and_program_execution remote-debugging-with-gdbserver}@anchor{209}@anchor{gnat_ugn/gnat_and_program_execution id12}@anchor{20a}
@subsection Remote Debugging with gdbserver


On platforms where gdbserver is supported, it is possible to use this tool
to debug your application remotely.  This can be useful in situations
where the program needs to be run on a target host that is different
from the host used for development, particularly when the target has
a limited amount of resources (either CPU and/or memory).

To do so, start your program using gdbserver on the target machine.
gdbserver then automatically suspends the execution of your program
at its entry point, waiting for a debugger to connect to it.  The
following commands starts an application and tells gdbserver to
wait for a connection with the debugger on localhost port 4444.

@quotation

@example
$ gdbserver localhost:4444 program
Process program created; pid = 5685
Listening on port 4444
@end example
@end quotation

Once gdbserver has started listening, we can tell the debugger to establish
a connection with this gdbserver, and then start the same debugging session
as if the program was being debugged on the same host, directly under
the control of GDB.

@quotation

@example
$ gdb program
(gdb) target remote targethost:4444
Remote debugging using targethost:4444
0x00007f29936d0af0 in ?? () from /lib64/ld-linux-x86-64.so.
(gdb) b foo.adb:3
Breakpoint 1 at 0x401f0c: file foo.adb, line 3.
(gdb) continue
Continuing.

Breakpoint 1, foo () at foo.adb:4
4       end foo;
@end example
@end quotation

It is also possible to use gdbserver to attach to an already running
program, in which case the execution of that program is simply suspended
until the connection between the debugger and gdbserver is established.

For more information on how to use gdbserver, see the @emph{Using the gdbserver Program}
section in @cite{Debugging with GDB}.
GNAT provides support for gdbserver on x86-linux, x86-windows and x86_64-linux.

@geindex Abnormal Termination or Failure to Terminate

@node GNAT Abnormal Termination or Failure to Terminate,Naming Conventions for GNAT Source Files,Remote Debugging with gdbserver,Running and Debugging Ada Programs
@anchor{gnat_ugn/gnat_and_program_execution gnat-abnormal-termination-or-failure-to-terminate}@anchor{20b}@anchor{gnat_ugn/gnat_and_program_execution id13}@anchor{20c}
@subsection GNAT Abnormal Termination or Failure to Terminate


When presented with programs that contain serious errors in syntax
or semantics,
GNAT may on rare occasions  experience problems in operation, such
as aborting with a
segmentation fault or illegal memory access, raising an internal
exception, terminating abnormally, or failing to terminate at all.
In such cases, you can activate
various features of GNAT that can help you pinpoint the construct in your
program that is the likely source of the problem.

The following strategies are presented in increasing order of
difficulty, corresponding to your experience in using GNAT and your
familiarity with compiler internals.


@itemize *

@item 
Run @emph{gcc} with the @emph{-gnatf}. This first
switch causes all errors on a given line to be reported. In its absence,
only the first error on a line is displayed.

The @emph{-gnatdO} switch causes errors to be displayed as soon as they
are encountered, rather than after compilation is terminated. If GNAT
terminates prematurely or goes into an infinite loop, the last error
message displayed may help to pinpoint the culprit.

@item 
Run @emph{gcc} with the @emph{-v (verbose)} switch. In this
mode, @emph{gcc} produces ongoing information about the progress of the
compilation and provides the name of each procedure as code is
generated. This switch allows you to find which Ada procedure was being
compiled when it encountered a code generation problem.
@end itemize

@geindex -gnatdc switch


@itemize *

@item 
Run @emph{gcc} with the @emph{-gnatdc} switch. This is a GNAT specific
switch that does for the front-end what @emph{-v} does
for the back end. The system prints the name of each unit,
either a compilation unit or nested unit, as it is being analyzed.

@item 
Finally, you can start
@cite{gdb} directly on the @cite{gnat1} executable. @cite{gnat1} is the
front-end of GNAT, and can be run independently (normally it is just
called from @emph{gcc}). You can use @cite{gdb} on @cite{gnat1} as you
would on a C program (but @ref{1f7,,The GNAT Debugger GDB} for caveats). The
@cite{where} command is the first line of attack; the variable
@cite{lineno} (seen by @cite{print lineno}), used by the second phase of
@cite{gnat1} and by the @emph{gcc} backend, indicates the source line at
which the execution stopped, and @cite{input_file name} indicates the name of
the source file.
@end itemize

@node Naming Conventions for GNAT Source Files,Getting Internal Debugging Information,GNAT Abnormal Termination or Failure to Terminate,Running and Debugging Ada Programs
@anchor{gnat_ugn/gnat_and_program_execution naming-conventions-for-gnat-source-files}@anchor{20d}@anchor{gnat_ugn/gnat_and_program_execution id14}@anchor{20e}
@subsection Naming Conventions for GNAT Source Files


In order to examine the workings of the GNAT system, the following
brief description of its organization may be helpful:


@itemize *

@item 
Files with prefix @code{sc} contain the lexical scanner.

@item 
All files prefixed with @code{par} are components of the parser. The
numbers correspond to chapters of the Ada Reference Manual. For example,
parsing of select statements can be found in @code{par-ch9.adb}.

@item 
All files prefixed with @code{sem} perform semantic analysis. The
numbers correspond to chapters of the Ada standard. For example, all
issues involving context clauses can be found in @code{sem_ch10.adb}. In
addition, some features of the language require sufficient special processing
to justify their own semantic files: sem_aggr for aggregates, sem_disp for
dynamic dispatching, etc.

@item 
All files prefixed with @code{exp} perform normalization and
expansion of the intermediate representation (abstract syntax tree, or AST).
these files use the same numbering scheme as the parser and semantics files.
For example, the construction of record initialization procedures is done in
@code{exp_ch3.adb}.

@item 
The files prefixed with @code{bind} implement the binder, which
verifies the consistency of the compilation, determines an order of
elaboration, and generates the bind file.

@item 
The files @code{atree.ads} and @code{atree.adb} detail the low-level
data structures used by the front-end.

@item 
The files @code{sinfo.ads} and @code{sinfo.adb} detail the structure of
the abstract syntax tree as produced by the parser.

@item 
The files @code{einfo.ads} and @code{einfo.adb} detail the attributes of
all entities, computed during semantic analysis.

@item 
Library management issues are dealt with in files with prefix
@code{lib}.

@geindex Annex A (in Ada Reference Manual)

@item 
Ada files with the prefix @code{a-} are children of @cite{Ada}, as
defined in Annex A.

@geindex Annex B (in Ada reference Manual)

@item 
Files with prefix @code{i-} are children of @cite{Interfaces}, as
defined in Annex B.

@geindex System (package in Ada Reference Manual)

@item 
Files with prefix @code{s-} are children of @cite{System}. This includes
both language-defined children and GNAT run-time routines.

@geindex GNAT (package)

@item 
Files with prefix @code{g-} are children of @cite{GNAT}. These are useful
general-purpose packages, fully documented in their specs. All
the other @code{.c} files are modifications of common @emph{gcc} files.
@end itemize

@node Getting Internal Debugging Information,Stack Traceback,Naming Conventions for GNAT Source Files,Running and Debugging Ada Programs
@anchor{gnat_ugn/gnat_and_program_execution id15}@anchor{20f}@anchor{gnat_ugn/gnat_and_program_execution getting-internal-debugging-information}@anchor{210}
@subsection Getting Internal Debugging Information


Most compilers have internal debugging switches and modes. GNAT
does also, except GNAT internal debugging switches and modes are not
secret. A summary and full description of all the compiler and binder
debug flags are in the file @code{debug.adb}. You must obtain the
sources of the compiler to see the full detailed effects of these flags.

The switches that print the source of the program (reconstructed from
the internal tree) are of general interest for user programs, as are the
options to print
the full internal tree, and the entity table (the symbol table
information). The reconstructed source provides a readable version of the
program after the front-end has completed analysis and  expansion,
and is useful when studying the performance of specific constructs.
For example, constraint checks are indicated, complex aggregates
are replaced with loops and assignments, and tasking primitives
are replaced with run-time calls.

@geindex traceback

@geindex stack traceback

@geindex stack unwinding

@node Stack Traceback,,Getting Internal Debugging Information,Running and Debugging Ada Programs
@anchor{gnat_ugn/gnat_and_program_execution stack-traceback}@anchor{211}@anchor{gnat_ugn/gnat_and_program_execution id16}@anchor{212}
@subsection Stack Traceback


Traceback is a mechanism to display the sequence of subprogram calls that
leads to a specified execution point in a program. Often (but not always)
the execution point is an instruction at which an exception has been raised.
This mechanism is also known as @emph{stack unwinding} because it obtains
its information by scanning the run-time stack and recovering the activation
records of all active subprograms. Stack unwinding is one of the most
important tools for program debugging.

The first entry stored in traceback corresponds to the deepest calling level,
that is to say the subprogram currently executing the instruction
from which we want to obtain the traceback.

Note that there is no runtime performance penalty when stack traceback
is enabled, and no exception is raised during program execution.

@geindex traceback
@geindex non-symbolic

@menu
* Non-Symbolic Traceback:: 
* Symbolic Traceback:: 

@end menu

@node Non-Symbolic Traceback,Symbolic Traceback,,Stack Traceback
@anchor{gnat_ugn/gnat_and_program_execution non-symbolic-traceback}@anchor{213}@anchor{gnat_ugn/gnat_and_program_execution id17}@anchor{214}
@subsubsection Non-Symbolic Traceback


Note: this feature is not supported on all platforms. See
@code{GNAT.Traceback} spec in @code{g-traceb.ads}
for a complete list of supported platforms.

@subsubheading Tracebacks From an Unhandled Exception


A runtime non-symbolic traceback is a list of addresses of call instructions.
To enable this feature you must use the @emph{-E}
@cite{gnatbind}'s option. With this option a stack traceback is stored as part
of exception information. You can retrieve this information using the
@cite{addr2line} tool.

Here is a simple example:

@quotation

@example
procedure STB is

   procedure P1 is
   begin
      raise Constraint_Error;
   end P1;

   procedure P2 is
   begin
      P1;
   end P2;

begin
   P2;
end STB;
@end example

@example
$ gnatmake stb -bargs -E
$ stb

Execution terminated by unhandled exception
Exception name: CONSTRAINT_ERROR
Message: stb.adb:5
Call stack traceback locations:
0x401373 0x40138b 0x40139c 0x401335 0x4011c4 0x4011f1 0x77e892a4
@end example
@end quotation

As we see the traceback lists a sequence of addresses for the unhandled
exception @cite{CONSTRAINT_ERROR} raised in procedure P1. It is easy to
guess that this exception come from procedure P1. To translate these
addresses into the source lines where the calls appear, the
@cite{addr2line} tool, described below, is invaluable. The use of this tool
requires the program to be compiled with debug information.

@quotation

@example
$ gnatmake -g stb -bargs -E
$ stb

Execution terminated by unhandled exception
Exception name: CONSTRAINT_ERROR
Message: stb.adb:5
Call stack traceback locations:
0x401373 0x40138b 0x40139c 0x401335 0x4011c4 0x4011f1 0x77e892a4

$ addr2line --exe=stb 0x401373 0x40138b 0x40139c 0x401335 0x4011c4
   0x4011f1 0x77e892a4

00401373 at d:/stb/stb.adb:5
0040138B at d:/stb/stb.adb:10
0040139C at d:/stb/stb.adb:14
00401335 at d:/stb/b~stb.adb:104
004011C4 at /build/.../crt1.c:200
004011F1 at /build/.../crt1.c:222
77E892A4 in ?? at ??:0
@end example
@end quotation

The @cite{addr2line} tool has several other useful options:

@quotation


@multitable {xxxxxxxxxxxxxxxxxxxxxxxxxx} {xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx} 
@item

@code{--functions}

@tab

to get the function name corresponding to any location

@item

@code{--demangle=gnat}

@tab

to use the gnat decoding mode for the function names.
Note that for binutils version 2.9.x the option is
simply @code{--demangle}.

@end multitable


@example
$ addr2line --exe=stb --functions --demangle=gnat 0x401373 0x40138b
   0x40139c 0x401335 0x4011c4 0x4011f1

00401373 in stb.p1 at d:/stb/stb.adb:5
0040138B in stb.p2 at d:/stb/stb.adb:10
0040139C in stb at d:/stb/stb.adb:14
00401335 in main at d:/stb/b~stb.adb:104
004011C4 in <__mingw_CRTStartup> at /build/.../crt1.c:200
004011F1 in <mainCRTStartup> at /build/.../crt1.c:222
@end example
@end quotation

From this traceback we can see that the exception was raised in
@code{stb.adb} at line 5, which was reached from a procedure call in
@code{stb.adb} at line 10, and so on. The @code{b~std.adb} is the binder file,
which contains the call to the main program.
@ref{120,,Running gnatbind}. The remaining entries are assorted runtime routines,
and the output will vary from platform to platform.

It is also possible to use @cite{GDB} with these traceback addresses to debug
the program. For example, we can break at a given code location, as reported
in the stack traceback:

@quotation

@example
$ gdb -nw stb
@end example
@end quotation

Furthermore, this feature is not implemented inside Windows DLL. Only
the non-symbolic traceback is reported in this case.

@quotation

@example
(gdb) break *0x401373
Breakpoint 1 at 0x401373: file stb.adb, line 5.
@end example
@end quotation

It is important to note that the stack traceback addresses
do not change when debug information is included. This is particularly useful
because it makes it possible to release software without debug information (to
minimize object size), get a field report that includes a stack traceback
whenever an internal bug occurs, and then be able to retrieve the sequence
of calls with the same program compiled with debug information.

@subsubheading Tracebacks From Exception Occurrences


Non-symbolic tracebacks are obtained by using the @emph{-E} binder argument.
The stack traceback is attached to the exception information string, and can
be retrieved in an exception handler within the Ada program, by means of the
Ada facilities defined in @cite{Ada.Exceptions}. Here is a simple example:

@quotation

@example
with Ada.Text_IO;
with Ada.Exceptions;

procedure STB is

   use Ada;
   use Ada.Exceptions;

   procedure P1 is
      K : Positive := 1;
   begin
      K := K - 1;
   exception
      when E : others =>
         Text_IO.Put_Line (Exception_Information (E));
   end P1;

   procedure P2 is
   begin
      P1;
   end P2;

begin
   P2;
end STB;
@end example
@end quotation

This program will output:

@quotation

@example
$ stb

Exception name: CONSTRAINT_ERROR
Message: stb.adb:12
Call stack traceback locations:
0x4015e4 0x401633 0x401644 0x401461 0x4011c4 0x4011f1 0x77e892a4
@end example
@end quotation

@subsubheading Tracebacks From Anywhere in a Program


It is also possible to retrieve a stack traceback from anywhere in a
program. For this you need to
use the @cite{GNAT.Traceback} API. This package includes a procedure called
@cite{Call_Chain} that computes a complete stack traceback, as well as useful
display procedures described below. It is not necessary to use the
@emph{-E gnatbind} option in this case, because the stack traceback mechanism
is invoked explicitly.

In the following example we compute a traceback at a specific location in
the program, and we display it using @cite{GNAT.Debug_Utilities.Image} to
convert addresses to strings:

@quotation

@example
with Ada.Text_IO;
with GNAT.Traceback;
with GNAT.Debug_Utilities;

procedure STB is

   use Ada;
   use GNAT;
   use GNAT.Traceback;

   procedure P1 is
      TB  : Tracebacks_Array (1 .. 10);
      --  We are asking for a maximum of 10 stack frames.
      Len : Natural;
      --  Len will receive the actual number of stack frames returned.
   begin
      Call_Chain (TB, Len);

      Text_IO.Put ("In STB.P1 : ");

      for K in 1 .. Len loop
         Text_IO.Put (Debug_Utilities.Image (TB (K)));
         Text_IO.Put (' ');
      end loop;

      Text_IO.New_Line;
   end P1;

   procedure P2 is
   begin
      P1;
   end P2;

begin
   P2;
end STB;
@end example

@example
$ gnatmake -g stb
$ stb

In STB.P1 : 16#0040_F1E4# 16#0040_14F2# 16#0040_170B# 16#0040_171C#
16#0040_1461# 16#0040_11C4# 16#0040_11F1# 16#77E8_92A4#
@end example
@end quotation

You can then get further information by invoking the @cite{addr2line}
tool as described earlier (note that the hexadecimal addresses
need to be specified in C format, with a leading '0x').

@geindex traceback
@geindex symbolic

@node Symbolic Traceback,,Non-Symbolic Traceback,Stack Traceback
@anchor{gnat_ugn/gnat_and_program_execution id18}@anchor{215}@anchor{gnat_ugn/gnat_and_program_execution symbolic-traceback}@anchor{216}
@subsubsection Symbolic Traceback


A symbolic traceback is a stack traceback in which procedure names are
associated with each code location.

Note that this feature is not supported on all platforms. See
@code{GNAT.Traceback.Symbolic} spec in @code{g-trasym.ads} for a complete
list of currently supported platforms.

Note that the symbolic traceback requires that the program be compiled
with debug information. If it is not compiled with debug information
only the non-symbolic information will be valid.

@subsubheading Tracebacks From Exception Occurrences


Here is an example:

@quotation

@example
with Ada.Text_IO;
with GNAT.Traceback.Symbolic;

procedure STB is

   procedure P1 is
   begin
      raise Constraint_Error;
   end P1;

   procedure P2 is
   begin
      P1;
   end P2;

   procedure P3 is
   begin
      P2;
   end P3;

begin
   P3;
exception
   when E : others =>
      Ada.Text_IO.Put_Line (GNAT.Traceback.Symbolic.Symbolic_Traceback (E));
end STB;
@end example

@example
$ gnatmake -g .\stb -bargs -E
$ stb

0040149F in stb.p1 at stb.adb:8
004014B7 in stb.p2 at stb.adb:13
004014CF in stb.p3 at stb.adb:18
004015DD in ada.stb at stb.adb:22
00401461 in main at b~stb.adb:168
004011C4 in __mingw_CRTStartup at crt1.c:200
004011F1 in mainCRTStartup at crt1.c:222
77E892A4 in ?? at ??:0
@end example
@end quotation

In the above example the @code{.\} syntax in the @emph{gnatmake} command
is currently required by @emph{addr2line} for files that are in
the current working directory.
Moreover, the exact sequence of linker options may vary from platform
to platform.
The above @emph{-largs} section is for Windows platforms. By contrast,
under Unix there is no need for the @emph{-largs} section.
Differences across platforms are due to details of linker implementation.

@subsubheading Tracebacks From Anywhere in a Program


It is possible to get a symbolic stack traceback
from anywhere in a program, just as for non-symbolic tracebacks.
The first step is to obtain a non-symbolic
traceback, and then call @cite{Symbolic_Traceback} to compute the symbolic
information. Here is an example:

@quotation

@example
with Ada.Text_IO;
with GNAT.Traceback;
with GNAT.Traceback.Symbolic;

procedure STB is

   use Ada;
   use GNAT.Traceback;
   use GNAT.Traceback.Symbolic;

   procedure P1 is
      TB  : Tracebacks_Array (1 .. 10);
      --  We are asking for a maximum of 10 stack frames.
      Len : Natural;
      --  Len will receive the actual number of stack frames returned.
   begin
      Call_Chain (TB, Len);
      Text_IO.Put_Line (Symbolic_Traceback (TB (1 .. Len)));
   end P1;

   procedure P2 is
   begin
      P1;
   end P2;

begin
   P2;
end STB;
@end example
@end quotation

@geindex Code Coverage

@geindex Profiling

@node Code Coverage and Profiling,Improving Performance,Running and Debugging Ada Programs,GNAT and Program Execution
@anchor{gnat_ugn/gnat_and_program_execution id19}@anchor{1f1}@anchor{gnat_ugn/gnat_and_program_execution code-coverage-and-profiling}@anchor{27}
@section Code Coverage and Profiling


This section describes how to use the @cite{gcov} coverage testing tool and
the @cite{gprof} profiler tool on Ada programs.

@geindex gcov

@menu
* Code Coverage of Ada Programs with gcov:: 
* Profiling an Ada Program with gprof:: 

@end menu

@node Code Coverage of Ada Programs with gcov,Profiling an Ada Program with gprof,,Code Coverage and Profiling
@anchor{gnat_ugn/gnat_and_program_execution id20}@anchor{217}@anchor{gnat_ugn/gnat_and_program_execution code-coverage-of-ada-programs-with-gcov}@anchor{218}
@subsection Code Coverage of Ada Programs with gcov


@cite{gcov} is a test coverage program: it analyzes the execution of a given
program on selected tests, to help you determine the portions of the program
that are still untested.

@cite{gcov} is part of the GCC suite, and is described in detail in the GCC
User's Guide. You can refer to this documentation for a more complete
description.

This chapter provides a quick startup guide, and
details some GNAT-specific features.

@menu
* Quick startup guide:: 
* GNAT specifics:: 

@end menu

@node Quick startup guide,GNAT specifics,,Code Coverage of Ada Programs with gcov
@anchor{gnat_ugn/gnat_and_program_execution id21}@anchor{219}@anchor{gnat_ugn/gnat_and_program_execution quick-startup-guide}@anchor{21a}
@subsubsection Quick startup guide


In order to perform coverage analysis of a program using @cite{gcov}, several
steps are needed:


@enumerate 

@item 
Instrument the code during the compilation process,

@item 
Execute the instrumented program, and

@item 
Invoke the @cite{gcov} tool to generate the coverage results.
@end enumerate

@geindex -fprofile-arcs (gcc)

@geindex -ftest-coverage (gcc

@geindex -fprofile-arcs (gnatbind)

The code instrumentation needed by gcov is created at the object level.
The source code is not modified in any way, because the instrumentation code is
inserted by gcc during the compilation process. To compile your code with code
coverage activated, you need to recompile your whole project using the
switches
@cite{-fprofile-arcs} and @cite{-ftest-coverage}, and link it using
@cite{-fprofile-arcs}.

@quotation

@example
$ gnatmake -P my_project.gpr -f -cargs -fprofile-arcs -ftest-coverage \\
   -largs -fprofile-arcs
@end example
@end quotation

This compilation process will create @code{.gcno} files together with
the usual object files.

Once the program is compiled with coverage instrumentation, you can
run it as many times as needed -- on portions of a test suite for
example. The first execution will produce @code{.gcda} files at the
same location as the @code{.gcno} files.  Subsequent executions
will update those files, so that a cumulative result of the covered
portions of the program is generated.

Finally, you need to call the @cite{gcov} tool. The different options of
@cite{gcov} are described in the GCC User's Guide, section 'Invoking gcov'.

This will create annotated source files with a @code{.gcov} extension:
@code{my_main.adb} file will be analyzed in @code{my_main.adb.gcov}.

@node GNAT specifics,,Quick startup guide,Code Coverage of Ada Programs with gcov
@anchor{gnat_ugn/gnat_and_program_execution gnat-specifics}@anchor{21b}@anchor{gnat_ugn/gnat_and_program_execution id22}@anchor{21c}
@subsubsection GNAT specifics


Because of Ada semantics, portions of the source code may be shared among
several object files. This is the case for example when generics are
involved, when inlining is active  or when declarations generate  initialisation
calls. In order to take
into account this shared code, you need to call @cite{gcov} on all
source files of the tested program at once.

The list of source files might exceed the system's maximum command line
length. In order to bypass this limitation, a new mechanism has been
implemented in @cite{gcov}: you can now list all your project's files into a
text file, and provide this file to gcov as a parameter,  preceded by a @code{@@}
(e.g. @code{gcov @@mysrclist.txt}).

Note that on AIX compiling a static library with @cite{-fprofile-arcs} is
not supported as there can be unresolved symbols during the final link.

@geindex gprof

@geindex Profiling

@node Profiling an Ada Program with gprof,,Code Coverage of Ada Programs with gcov,Code Coverage and Profiling
@anchor{gnat_ugn/gnat_and_program_execution profiling-an-ada-program-with-gprof}@anchor{21d}@anchor{gnat_ugn/gnat_and_program_execution id23}@anchor{21e}
@subsection Profiling an Ada Program with gprof


This section is not meant to be an exhaustive documentation of @cite{gprof}.
Full documentation for it can be found in the @cite{GNU Profiler User's Guide}
documentation that is part of this GNAT distribution.

Profiling a program helps determine the parts of a program that are executed
most often, and are therefore the most time-consuming.

@cite{gprof} is the standard GNU profiling tool; it has been enhanced to
better handle Ada programs and multitasking.
It is currently supported on the following platforms


@itemize *

@item 
linux x86/x86_64

@item 
solaris sparc/sparc64/x86

@item 
windows x86
@end itemize

In order to profile a program using @cite{gprof}, several steps are needed:


@enumerate 

@item 
Instrument the code, which requires a full recompilation of the project with the
proper switches.

@item 
Execute the program under the analysis conditions, i.e. with the desired
input.

@item 
Analyze the results using the @cite{gprof} tool.
@end enumerate

The following sections detail the different steps, and indicate how
to interpret the results.

@menu
* Compilation for profiling:: 
* Program execution:: 
* Running gprof:: 
* Interpretation of profiling results:: 

@end menu

@node Compilation for profiling,Program execution,,Profiling an Ada Program with gprof
@anchor{gnat_ugn/gnat_and_program_execution id24}@anchor{21f}@anchor{gnat_ugn/gnat_and_program_execution compilation-for-profiling}@anchor{220}
@subsubsection Compilation for profiling


@geindex -pg (gcc)
@geindex for profiling

@geindex -pg (gnatlink)
@geindex for profiling

In order to profile a program the first step is to tell the compiler
to generate the necessary profiling information. The compiler switch to be used
is @code{-pg}, which must be added to other compilation switches. This
switch needs to be specified both during compilation and link stages, and can
be specified once when using gnatmake:

@quotation

@example
$ gnatmake -f -pg -P my_project
@end example
@end quotation

Note that only the objects that were compiled with the @code{-pg} switch will
be profiled; if you need to profile your whole project, use the @code{-f}
gnatmake switch to force full recompilation.

@node Program execution,Running gprof,Compilation for profiling,Profiling an Ada Program with gprof
@anchor{gnat_ugn/gnat_and_program_execution program-execution}@anchor{221}@anchor{gnat_ugn/gnat_and_program_execution id25}@anchor{222}
@subsubsection Program execution


Once the program has been compiled for profiling, you can run it as usual.

The only constraint imposed by profiling is that the program must terminate
normally. An interrupted program (via a Ctrl-C, kill, etc.) will not be
properly analyzed.

Once the program completes execution, a data file called @code{gmon.out} is
generated in the directory where the program was launched from. If this file
already exists, it will be overwritten.

@node Running gprof,Interpretation of profiling results,Program execution,Profiling an Ada Program with gprof
@anchor{gnat_ugn/gnat_and_program_execution running-gprof}@anchor{223}@anchor{gnat_ugn/gnat_and_program_execution id26}@anchor{224}
@subsubsection Running gprof


The @cite{gprof} tool is called as follow:

@quotation

@example
$ gprof my_prog gmon.out
@end example
@end quotation

or simply:

@quotation

@example
$  gprof my_prog
@end example
@end quotation

The complete form of the gprof command line is the following:

@quotation

@example
$ gprof [switches] [executable [data-file]]
@end example
@end quotation

@cite{gprof} supports numerous switches. The order of these
switch does not matter. The full list of options can be found in
the GNU Profiler User's Guide documentation that comes with this documentation.

The following is the subset of those switches that is most relevant:

@geindex --demangle (gprof)


@table @asis

@item @code{--demangle[=@emph{style}]}, @code{--no-demangle}

These options control whether symbol names should be demangled when
printing output.  The default is to demangle C++ symbols.  The
@code{--no-demangle} option may be used to turn off demangling. Different
compilers have different mangling styles.  The optional demangling style
argument can be used to choose an appropriate demangling style for your
compiler, in particular Ada symbols generated by GNAT can be demangled using
@code{--demangle=gnat}.
@end table

@geindex -e (gprof)


@table @asis

@item @code{-e @emph{function_name}}

The @code{-e @emph{function}} option tells @cite{gprof} not to print
information about the function @cite{function_name} (and its
children...) in the call graph.  The function will still be listed
as a child of any functions that call it, but its index number will be
shown as @code{[not printed]}.  More than one @code{-e} option may be
given; only one @cite{function_name} may be indicated with each @code{-e}
option.
@end table

@geindex -E (gprof)


@table @asis

@item @code{-E @emph{function_name}}

The @code{-E @emph{function}} option works like the @code{-e} option, but
execution time spent in the function (and children who were not called from
anywhere else), will not be used to compute the percentages-of-time for
the call graph.  More than one @code{-E} option may be given; only one
@cite{function_name} may be indicated with each @code{-E} option.
@end table

@geindex -f (gprof)


@table @asis

@item @code{-f @emph{function_name}}

The @code{-f @emph{function}} option causes @cite{gprof} to limit the
call graph to the function @cite{function_name} and its children (and
their children...).  More than one @code{-f} option may be given;
only one @cite{function_name} may be indicated with each @code{-f}
option.
@end table

@geindex -F (gprof)


@table @asis

@item @code{-F @emph{function_name}}

The @code{-F @emph{function}} option works like the @code{-f} option, but
only time spent in the function and its children (and their
children...) will be used to determine total-time and
percentages-of-time for the call graph.  More than one @code{-F} option
may be given; only one @cite{function_name} may be indicated with each
@code{-F} option.  The @code{-F} option overrides the @code{-E} option.
@end table

@node Interpretation of profiling results,,Running gprof,Profiling an Ada Program with gprof
@anchor{gnat_ugn/gnat_and_program_execution id27}@anchor{225}@anchor{gnat_ugn/gnat_and_program_execution interpretation-of-profiling-results}@anchor{226}
@subsubsection Interpretation of profiling results


The results of the profiling analysis are represented by two arrays: the
'flat profile' and the 'call graph'. Full documentation of those outputs
can be found in the GNU Profiler User's Guide.

The flat profile shows the time spent in each function of the program, and how
many time it has been called. This allows you to locate easily the most
time-consuming functions.

The call graph shows, for each subprogram, the subprograms that call it,
and the subprograms that it calls. It also provides an estimate of the time
spent in each of those callers/called subprograms.

@node Improving Performance,Overflow Check Handling in GNAT,Code Coverage and Profiling,GNAT and Program Execution
@anchor{gnat_ugn/gnat_and_program_execution improving-performance}@anchor{28}@anchor{gnat_ugn/gnat_and_program_execution id28}@anchor{1f2}
@section Improving Performance


@geindex Improving performance

This section presents several topics related to program performance.
It first describes some of the tradeoffs that need to be considered
and some of the techniques for making your program run faster.


It then documents the unused subprogram/data elimination feature,
which can reduce the size of program executables.

@menu
* Performance Considerations:: 
* Text_IO Suggestions:: 
* Reducing Size of Executables with Unused Subprogram/Data Elimination:: 

@end menu

@node Performance Considerations,Text_IO Suggestions,,Improving Performance
@anchor{gnat_ugn/gnat_and_program_execution id29}@anchor{227}@anchor{gnat_ugn/gnat_and_program_execution performance-considerations}@anchor{228}
@subsection Performance Considerations


The GNAT system provides a number of options that allow a trade-off
between


@itemize *

@item 
performance of the generated code

@item 
speed of compilation

@item 
minimization of dependences and recompilation

@item 
the degree of run-time checking.
@end itemize

The defaults (if no options are selected) aim at improving the speed
of compilation and minimizing dependences, at the expense of performance
of the generated code:


@itemize *

@item 
no optimization

@item 
no inlining of subprogram calls

@item 
all run-time checks enabled except overflow and elaboration checks
@end itemize

These options are suitable for most program development purposes. This
section describes how you can modify these choices, and also provides
some guidelines on debugging optimized code.

@menu
* Controlling Run-Time Checks:: 
* Use of Restrictions:: 
* Optimization Levels:: 
* Debugging Optimized Code:: 
* Inlining of Subprograms:: 
* Floating_Point_Operations:: 
* Vectorization of loops:: 
* Other Optimization Switches:: 
* Optimization and Strict Aliasing:: 
* Aliased Variables and Optimization:: 
* Atomic Variables and Optimization:: 
* Passive Task Optimization:: 

@end menu

@node Controlling Run-Time Checks,Use of Restrictions,,Performance Considerations
@anchor{gnat_ugn/gnat_and_program_execution controlling-run-time-checks}@anchor{229}@anchor{gnat_ugn/gnat_and_program_execution id30}@anchor{22a}
@subsubsection Controlling Run-Time Checks


By default, GNAT generates all run-time checks, except integer overflow
checks, stack overflow checks, and checks for access before elaboration on
subprogram calls. The latter are not required in default mode, because all
necessary checking is done at compile time.

@geindex -gnatp (gcc)

@geindex -gnato (gcc)

Two gnat switches, @emph{-gnatp} and @emph{-gnato} allow this default to
be modified. See @ref{fe,,Run-Time Checks}.

Our experience is that the default is suitable for most development
purposes.

We treat integer overflow specially because these
are quite expensive and in our experience are not as important as other
run-time checks in the development process. Note that division by zero
is not considered an overflow check, and divide by zero checks are
generated where required by default.

Elaboration checks are off by default, and also not needed by default, since
GNAT uses a static elaboration analysis approach that avoids the need for
run-time checking. This manual contains a full chapter discussing the issue
of elaboration checks, and if the default is not satisfactory for your use,
you should read this chapter.

For validity checks, the minimal checks required by the Ada Reference
Manual (for case statements and assignments to array elements) are on
by default. These can be suppressed by use of the @emph{-gnatVn} switch.
Note that in Ada 83, there were no validity checks, so if the Ada 83 mode
is acceptable (or when comparing GNAT performance with an Ada 83 compiler),
it may be reasonable to routinely use @emph{-gnatVn}. Validity checks
are also suppressed entirely if @emph{-gnatp} is used.

@geindex Overflow checks

@geindex Checks
@geindex overflow

@geindex Suppress

@geindex Unsuppress

@geindex pragma Suppress

@geindex pragma Unsuppress

Note that the setting of the switches controls the default setting of
the checks. They may be modified using either @cite{pragma Suppress} (to
remove checks) or @cite{pragma Unsuppress} (to add back suppressed
checks) in the program source.

@node Use of Restrictions,Optimization Levels,Controlling Run-Time Checks,Performance Considerations
@anchor{gnat_ugn/gnat_and_program_execution use-of-restrictions}@anchor{22b}@anchor{gnat_ugn/gnat_and_program_execution id31}@anchor{22c}
@subsubsection Use of Restrictions


The use of pragma Restrictions allows you to control which features are
permitted in your program. Apart from the obvious point that if you avoid
relatively expensive features like finalization (enforceable by the use
of pragma Restrictions (No_Finalization), the use of this pragma does not
affect the generated code in most cases.

One notable exception to this rule is that the possibility of task abort
results in some distributed overhead, particularly if finalization or
exception handlers are used. The reason is that certain sections of code
have to be marked as non-abortable.

If you use neither the @cite{abort} statement, nor asynchronous transfer
of control (@cite{select ... then abort}), then this distributed overhead
is removed, which may have a general positive effect in improving
overall performance.  Especially code involving frequent use of tasking
constructs and controlled types will show much improved performance.
The relevant restrictions pragmas are

@quotation

@example
pragma Restrictions (No_Abort_Statements);
pragma Restrictions (Max_Asynchronous_Select_Nesting => 0);
@end example
@end quotation

It is recommended that these restriction pragmas be used if possible. Note
that this also means that you can write code without worrying about the
possibility of an immediate abort at any point.

@node Optimization Levels,Debugging Optimized Code,Use of Restrictions,Performance Considerations
@anchor{gnat_ugn/gnat_and_program_execution id32}@anchor{22d}@anchor{gnat_ugn/gnat_and_program_execution optimization-levels}@anchor{101}
@subsubsection Optimization Levels


@geindex -O (gcc)

Without any optimization option,
the compiler's goal is to reduce the cost of
compilation and to make debugging produce the expected results.
Statements are independent: if you stop the program with a breakpoint between
statements, you can then assign a new value to any variable or change
the program counter to any other statement in the subprogram and get exactly
the results you would expect from the source code.

Turning on optimization makes the compiler attempt to improve the
performance and/or code size at the expense of compilation time and
possibly the ability to debug the program.

If you use multiple
-O options, with or without level numbers,
the last such option is the one that is effective.

The default is optimization off. This results in the fastest compile
times, but GNAT makes absolutely no attempt to optimize, and the
generated programs are considerably larger and slower than when
optimization is enabled. You can use the
@emph{-O} switch (the permitted forms are @emph{-O0}, @emph{-O1}
@emph{-O2}, @emph{-O3}, and @emph{-Os})
to @emph{gcc} to control the optimization level:


@itemize *

@item 

@table @asis

@item @emph{-O0}

No optimization (the default);
generates unoptimized code but has
the fastest compilation time.

Note that many other compilers do fairly extensive optimization
even if 'no optimization' is specified. With gcc, it is
very unusual to use -O0 for production if
execution time is of any concern, since -O0
really does mean no optimization at all. This difference between
gcc and other compilers should be kept in mind when doing
performance comparisons.
@end table

@item 

@table @asis

@item @emph{-O1}

Moderate optimization;
optimizes reasonably well but does not
degrade compilation time significantly.
@end table

@item 

@table @asis

@item @emph{-O2}

Full optimization;
generates highly optimized code and has
the slowest compilation time.
@end table

@item 

@table @asis

@item @emph{-O3}

Full optimization as in @emph{-O2};
also uses more aggressive automatic inlining of subprograms within a unit
(@ref{114,,Inlining of Subprograms}) and attempts to vectorize loops.
@end table

@item 

@table @asis

@item @emph{-Os}

Optimize space usage (code and data) of resulting program.
@end table
@end itemize

Higher optimization levels perform more global transformations on the
program and apply more expensive analysis algorithms in order to generate
faster and more compact code. The price in compilation time, and the
resulting improvement in execution time,
both depend on the particular application and the hardware environment.
You should experiment to find the best level for your application.

Since the precise set of optimizations done at each level will vary from
release to release (and sometime from target to target), it is best to think
of the optimization settings in general terms.
See the @emph{Options That Control Optimization} section in
@cite{Using the GNU Compiler Collection (GCC)}
for details about
the @emph{-O} settings and a number of @emph{-f} options that
individually enable or disable specific optimizations.

Unlike some other compilation systems, @emph{gcc} has
been tested extensively at all optimization levels. There are some bugs
which appear only with optimization turned on, but there have also been
bugs which show up only in @emph{unoptimized} code. Selecting a lower
level of optimization does not improve the reliability of the code
generator, which in practice is highly reliable at all optimization
levels.

Note regarding the use of @emph{-O3}: The use of this optimization level
is generally discouraged with GNAT, since it often results in larger
executables which may run more slowly. See further discussion of this point
in @ref{114,,Inlining of Subprograms}.

@node Debugging Optimized Code,Inlining of Subprograms,Optimization Levels,Performance Considerations
@anchor{gnat_ugn/gnat_and_program_execution id33}@anchor{22e}@anchor{gnat_ugn/gnat_and_program_execution debugging-optimized-code}@anchor{22f}
@subsubsection Debugging Optimized Code


@geindex Debugging optimized code

@geindex Optimization and debugging

Although it is possible to do a reasonable amount of debugging at
nonzero optimization levels,
the higher the level the more likely that
source-level constructs will have been eliminated by optimization.
For example, if a loop is strength-reduced, the loop
control variable may be completely eliminated and thus cannot be
displayed in the debugger.
This can only happen at @emph{-O2} or @emph{-O3}.
Explicit temporary variables that you code might be eliminated at
level @emph{-O1} or higher.

@geindex -g (gcc)

The use of the @emph{-g} switch,
which is needed for source-level debugging,
affects the size of the program executable on disk,
and indeed the debugging information can be quite large.
However, it has no effect on the generated code (and thus does not
degrade performance)

Since the compiler generates debugging tables for a compilation unit before
it performs optimizations, the optimizing transformations may invalidate some
of the debugging data.  You therefore need to anticipate certain
anomalous situations that may arise while debugging optimized code.
These are the most common cases:


@itemize *

@item 
@emph{The 'hopping Program Counter':}  Repeated @cite{step} or @cite{next}
commands show
the PC bouncing back and forth in the code.  This may result from any of
the following optimizations:


@itemize -

@item 
@emph{Common subexpression elimination:} using a single instance of code for a
quantity that the source computes several times.  As a result you
may not be able to stop on what looks like a statement.

@item 
@emph{Invariant code motion:} moving an expression that does not change within a
loop, to the beginning of the loop.

@item 
@emph{Instruction scheduling:} moving instructions so as to
overlap loads and stores (typically) with other code, or in
general to move computations of values closer to their uses. Often
this causes you to pass an assignment statement without the assignment
happening and then later bounce back to the statement when the
value is actually needed.  Placing a breakpoint on a line of code
and then stepping over it may, therefore, not always cause all the
expected side-effects.
@end itemize

@item 
@emph{The 'big leap':} More commonly known as @emph{cross-jumping}, in which
two identical pieces of code are merged and the program counter suddenly
jumps to a statement that is not supposed to be executed, simply because
it (and the code following) translates to the same thing as the code
that @emph{was} supposed to be executed.  This effect is typically seen in
sequences that end in a jump, such as a @cite{goto}, a @cite{return}, or
a @cite{break} in a C @cite{switch} statement.

@item 
@emph{The 'roving variable':} The symptom is an unexpected value in a variable.
There are various reasons for this effect:


@itemize -

@item 
In a subprogram prologue, a parameter may not yet have been moved to its
'home'.

@item 
A variable may be dead, and its register re-used.  This is
probably the most common cause.

@item 
As mentioned above, the assignment of a value to a variable may
have been moved.

@item 
A variable may be eliminated entirely by value propagation or
other means.  In this case, GCC may incorrectly generate debugging
information for the variable
@end itemize

In general, when an unexpected value appears for a local variable or parameter
you should first ascertain if that value was actually computed by
your program, as opposed to being incorrectly reported by the debugger.
Record fields or
array elements in an object designated by an access value
are generally less of a problem, once you have ascertained that the access
value is sensible.
Typically, this means checking variables in the preceding code and in the
calling subprogram to verify that the value observed is explainable from other
values (one must apply the procedure recursively to those
other values); or re-running the code and stopping a little earlier
(perhaps before the call) and stepping to better see how the variable obtained
the value in question; or continuing to step @emph{from} the point of the
strange value to see if code motion had simply moved the variable's
assignments later.
@end itemize

In light of such anomalies, a recommended technique is to use @emph{-O0}
early in the software development cycle, when extensive debugging capabilities
are most needed, and then move to @emph{-O1} and later @emph{-O2} as
the debugger becomes less critical.
Whether to use the @emph{-g} switch in the release version is
a release management issue.
Note that if you use @emph{-g} you can then use the @emph{strip} program
on the resulting executable,
which removes both debugging information and global symbols.

@node Inlining of Subprograms,Floating_Point_Operations,Debugging Optimized Code,Performance Considerations
@anchor{gnat_ugn/gnat_and_program_execution id34}@anchor{230}@anchor{gnat_ugn/gnat_and_program_execution inlining-of-subprograms}@anchor{114}
@subsubsection Inlining of Subprograms


A call to a subprogram in the current unit is inlined if all the
following conditions are met:


@itemize *

@item 
The optimization level is at least @emph{-O1}.

@item 
The called subprogram is suitable for inlining: It must be small enough
and not contain something that @emph{gcc} cannot support in inlined
subprograms.

@geindex pragma Inline

@geindex Inline

@item 
Any one of the following applies: @cite{pragma Inline} is applied to the
subprogram and the @emph{-gnatn} switch is specified; the
subprogram is local to the unit and called once from within it; the
subprogram is small and optimization level @emph{-O2} is specified;
optimization level @emph{-O3} is specified.
@end itemize

Calls to subprograms in @emph{with}ed units are normally not inlined.
To achieve actual inlining (that is, replacement of the call by the code
in the body of the subprogram), the following conditions must all be true:


@itemize *

@item 
The optimization level is at least @emph{-O1}.

@item 
The called subprogram is suitable for inlining: It must be small enough
and not contain something that @emph{gcc} cannot support in inlined
subprograms.

@item 
The call appears in a body (not in a package spec).

@item 
There is a @cite{pragma Inline} for the subprogram.

@item 
The @emph{-gnatn} switch is used on the command line.
@end itemize

Even if all these conditions are met, it may not be possible for
the compiler to inline the call, due to the length of the body,
or features in the body that make it impossible for the compiler
to do the inlining.

Note that specifying the @emph{-gnatn} switch causes additional
compilation dependencies. Consider the following:

@quotation

@example
package R is
   procedure Q;
   pragma Inline (Q);
end R;
package body R is
   ...
end R;

with R;
procedure Main is
begin
   ...
   R.Q;
end Main;
@end example
@end quotation

With the default behavior (no @emph{-gnatn} switch specified), the
compilation of the @cite{Main} procedure depends only on its own source,
@code{main.adb}, and the spec of the package in file @code{r.ads}. This
means that editing the body of @cite{R} does not require recompiling
@cite{Main}.

On the other hand, the call @cite{R.Q} is not inlined under these
circumstances. If the @emph{-gnatn} switch is present when @cite{Main}
is compiled, the call will be inlined if the body of @cite{Q} is small
enough, but now @cite{Main} depends on the body of @cite{R} in
@code{r.adb} as well as on the spec. This means that if this body is edited,
the main program must be recompiled. Note that this extra dependency
occurs whether or not the call is in fact inlined by @emph{gcc}.

The use of front end inlining with @emph{-gnatN} generates similar
additional dependencies.

@geindex -fno-inline (gcc)

Note: The @emph{-fno-inline} switch overrides all other conditions and ensures that
no inlining occurs, unless requested with pragma Inline_Always for gcc
back-ends. The extra dependences resulting from @emph{-gnatn} will still be active,
even if this switch is used to suppress the resulting inlining actions.

@geindex -fno-inline-functions (gcc)

Note: The @emph{-fno-inline-functions} switch can be used to prevent
automatic inlining of subprograms if @emph{-O3} is used.

@geindex -fno-inline-small-functions (gcc)

Note: The @emph{-fno-inline-small-functions} switch can be used to prevent
automatic inlining of small subprograms if @emph{-O2} is used.

@geindex -fno-inline-functions-called-once (gcc)

Note: The @emph{-fno-inline-functions-called-once} switch
can be used to prevent inlining of subprograms local to the unit
and called once from within it if @emph{-O1} is used.

Note regarding the use of @emph{-O3}: @emph{-gnatn} is made up of two
sub-switches @emph{-gnatn1} and @emph{-gnatn2} that can be directly
specified in lieu of it, @emph{-gnatn} being translated into one of them
based on the optimization level. With @emph{-O2} or below, @emph{-gnatn}
is equivalent to @emph{-gnatn1} which activates pragma @cite{Inline} with
moderate inlining across modules. With @emph{-O3}, @emph{-gnatn} is
equivalent to @emph{-gnatn2} which activates pragma @cite{Inline} with
full inlining across modules. If you have used pragma @cite{Inline} in
appropriate cases, then it is usually much better to use @emph{-O2}
and @emph{-gnatn} and avoid the use of @emph{-O3} which has the additional
effect of inlining subprograms you did not think should be inlined. We have
found that the use of @emph{-O3} may slow down the compilation and increase
the code size by performing excessive inlining, leading to increased
instruction cache pressure from the increased code size and thus minor
performance improvements. So the bottom line here is that you should not
automatically assume that @emph{-O3} is better than @emph{-O2}, and
indeed you should use @emph{-O3} only if tests show that it actually
improves performance for your program.

@node Floating_Point_Operations,Vectorization of loops,Inlining of Subprograms,Performance Considerations
@anchor{gnat_ugn/gnat_and_program_execution floating-point-operations}@anchor{231}@anchor{gnat_ugn/gnat_and_program_execution id35}@anchor{232}
@subsubsection Floating_Point_Operations


@geindex Floating-Point Operations

On almost all targets, GNAT maps Float and Long_Float to the 32-bit and
64-bit standard IEEE floating-point representations, and operations will
use standard IEEE arithmetic as provided by the processor. On most, but
not all, architectures, the attribute Machine_Overflows is False for these
types, meaning that the semantics of overflow is implementation-defined.
In the case of GNAT, these semantics correspond to the normal IEEE
treatment of infinities and NaN (not a number) values. For example,
1.0 / 0.0 yields plus infinitiy and 0.0 / 0.0 yields a NaN. By
avoiding explicit overflow checks, the performance is greatly improved
on many targets. However, if required, floating-point overflow can be
enabled by the use of the pragma Check_Float_Overflow.

Another consideration that applies specifically to x86 32-bit
architectures is which form of floating-point arithmetic is used.
By default the operations use the old style x86 floating-point,
which implements an 80-bit extended precision form (on these
architectures the type Long_Long_Float corresponds to that form).
In addition, generation of efficient code in this mode means that
the extended precision form will be used for intermediate results.
This may be helpful in improving the final precision of a complex
expression. However it means that the results obtained on the x86
will be different from those on other architectures, and for some
algorithms, the extra intermediate precision can be detrimental.

In addition to this old-style floating-point, all modern x86 chips
implement an alternative floating-point operation model referred
to as SSE2. In this model there is no extended form, and furthermore
execution performance is significantly enhanced. To force GNAT to use
this more modern form, use both of the switches:

@quotation

-msse2 -mfpmath=sse
@end quotation

A unit compiled with these switches will automatically use the more
efficient SSE2 instruction set for Float and Long_Float operations.
Note that the ABI has the same form for both floating-point models,
so it is permissible to mix units compiled with and without these
switches.

@node Vectorization of loops,Other Optimization Switches,Floating_Point_Operations,Performance Considerations
@anchor{gnat_ugn/gnat_and_program_execution id36}@anchor{233}@anchor{gnat_ugn/gnat_and_program_execution vectorization-of-loops}@anchor{234}
@subsubsection Vectorization of loops


@geindex Optimization Switches

You can take advantage of the auto-vectorizer present in the @emph{gcc}
back end to vectorize loops with GNAT.  The corresponding command line switch
is @emph{-ftree-vectorize} but, as it is enabled by default at @emph{-O3}
and other aggressive optimizations helpful for vectorization also are enabled
by default at this level, using @emph{-O3} directly is recommended.

You also need to make sure that the target architecture features a supported
SIMD instruction set.  For example, for the x86 architecture, you should at
least specify @emph{-msse2} to get significant vectorization (but you don't
need to specify it for x86-64 as it is part of the base 64-bit architecture).
Similarly, for the PowerPC architecture, you should specify @emph{-maltivec}.

The preferred loop form for vectorization is the @cite{for} iteration scheme.
Loops with a @cite{while} iteration scheme can also be vectorized if they are
very simple, but the vectorizer will quickly give up otherwise.  With either
iteration scheme, the flow of control must be straight, in particular no
@cite{exit} statement may appear in the loop body.  The loop may however
contain a single nested loop, if it can be vectorized when considered alone:

@quotation

@example
A : array (1..4, 1..4) of Long_Float;
S : array (1..4) of Long_Float;

procedure Sum is
begin
   for I in A'Range(1) loop
      for J in A'Range(2) loop
         S (I) := S (I) + A (I, J);
      end loop;
   end loop;
end Sum;
@end example
@end quotation

The vectorizable operations depend on the targeted SIMD instruction set, but
the adding and some of the multiplying operators are generally supported, as
well as the logical operators for modular types.  Note that, in the former
case, enabling overflow checks, for example with @emph{-gnato}, totally
disables vectorization.  The other checks are not supposed to have the same
definitive effect, although compiling with @emph{-gnatp} might well reveal
cases where some checks do thwart vectorization.

Type conversions may also prevent vectorization if they involve semantics that
are not directly supported by the code generator or the SIMD instruction set.
A typical example is direct conversion from floating-point to integer types.
The solution in this case is to use the following idiom:

@quotation

@example
Integer (S'Truncation (F))
@end example
@end quotation

if @cite{S} is the subtype of floating-point object @cite{F}.

In most cases, the vectorizable loops are loops that iterate over arrays.
All kinds of array types are supported, i.e. constrained array types with
static bounds:

@quotation

@example
type Array_Type is array (1 .. 4) of Long_Float;
@end example
@end quotation

constrained array types with dynamic bounds:

@quotation

@example
type Array_Type is array (1 .. Q.N) of Long_Float;

type Array_Type is array (Q.K .. 4) of Long_Float;

type Array_Type is array (Q.K .. Q.N) of Long_Float;
@end example
@end quotation

or unconstrained array types:

@quotation

@example
type Array_Type is array (Positive range <>) of Long_Float;
@end example
@end quotation

The quality of the generated code decreases when the dynamic aspect of the
array type increases, the worst code being generated for unconstrained array
types.  This is so because, the less information the compiler has about the
bounds of the array, the more fallback code it needs to generate in order to
fix things up at run time.

It is possible to specify that a given loop should be subject to vectorization
preferably to other optimizations by means of pragma @cite{Loop_Optimize}:

@quotation

@example
pragma Loop_Optimize (Vector);
@end example
@end quotation

placed immediately within the loop will convey the appropriate hint to the
compiler for this loop.

It is also possible to help the compiler generate better vectorized code
for a given loop by asserting that there are no loop-carried dependencies
in the loop.  Consider for example the procedure:

@quotation

@example
type Arr is array (1 .. 4) of Long_Float;

procedure Add (X, Y : not null access Arr; R : not null access Arr) is
begin
  for I in Arr'Range loop
    R(I) := X(I) + Y(I);
  end loop;
end;
@end example
@end quotation

By default, the compiler cannot unconditionally vectorize the loop because
assigning to a component of the array designated by R in one iteration could
change the value read from the components of the array designated by X or Y
in a later iteration.  As a result, the compiler will generate two versions
of the loop in the object code, one vectorized and the other not vectorized,
as well as a test to select the appropriate version at run time.  This can
be overcome by another hint:

@quotation

@example
pragma Loop_Optimize (Ivdep);
@end example
@end quotation

placed immediately within the loop will tell the compiler that it can safely
omit the non-vectorized version of the loop as well as the run-time test.

@node Other Optimization Switches,Optimization and Strict Aliasing,Vectorization of loops,Performance Considerations
@anchor{gnat_ugn/gnat_and_program_execution id37}@anchor{235}@anchor{gnat_ugn/gnat_and_program_execution other-optimization-switches}@anchor{236}
@subsubsection Other Optimization Switches


@geindex Optimization Switches

Since @cite{GNAT} uses the @emph{gcc} back end, all the specialized
@emph{gcc} optimization switches are potentially usable. These switches
have not been extensively tested with GNAT but can generally be expected
to work. Examples of switches in this category are @emph{-funroll-loops}
and the various target-specific @emph{-m} options (in particular, it has
been observed that @emph{-march=xxx} can significantly improve performance
on appropriate machines). For full details of these switches, see
the @cite{Submodel Options} section in the @cite{Hardware Models and Configurations}
chapter of @cite{Using the GNU Compiler Collection (GCC)}.

@node Optimization and Strict Aliasing,Aliased Variables and Optimization,Other Optimization Switches,Performance Considerations
@anchor{gnat_ugn/gnat_and_program_execution optimization-and-strict-aliasing}@anchor{f8}@anchor{gnat_ugn/gnat_and_program_execution id38}@anchor{237}
@subsubsection Optimization and Strict Aliasing


@geindex Aliasing

@geindex Strict Aliasing

@geindex No_Strict_Aliasing

The strong typing capabilities of Ada allow an optimizer to generate
efficient code in situations where other languages would be forced to
make worst case assumptions preventing such optimizations. Consider
the following example:

@quotation

@example
procedure R is
   type Int1 is new Integer;
   type Int2 is new Integer;
   type Int1A is access Int1;
   type Int2A is access Int2;
   Int1V : Int1A;
   Int2V : Int2A;
   ...

begin
   ...
   for J in Data'Range loop
      if Data (J) = Int1V.all then
         Int2V.all := Int2V.all + 1;
      end if;
   end loop;
   ...
end R;
@end example
@end quotation

In this example, since the variable @cite{Int1V} can only access objects
of type @cite{Int1}, and @cite{Int2V} can only access objects of type
@cite{Int2}, there is no possibility that the assignment to
@cite{Int2V.all} affects the value of @cite{Int1V.all}. This means that
the compiler optimizer can "know" that the value @cite{Int1V.all} is constant
for all iterations of the loop and avoid the extra memory reference
required to dereference it each time through the loop.

This kind of optimization, called strict aliasing analysis, is
triggered by specifying an optimization level of @emph{-O2} or
higher or @emph{-Os} and allows @cite{GNAT} to generate more efficient code
when access values are involved.

However, although this optimization is always correct in terms of
the formal semantics of the Ada Reference Manual, difficulties can
arise if features like @cite{Unchecked_Conversion} are used to break
the typing system. Consider the following complete program example:

@quotation

@example
package p1 is
   type int1 is new integer;
   type int2 is new integer;
   type a1 is access int1;
   type a2 is access int2;
end p1;

with p1; use p1;
package p2 is
   function to_a2 (Input : a1) return a2;
end p2;

with Unchecked_Conversion;
package body p2 is
   function to_a2 (Input : a1) return a2 is
      function to_a2u is
        new Unchecked_Conversion (a1, a2);
   begin
      return to_a2u (Input);
   end to_a2;
end p2;

with p2; use p2;
with p1; use p1;
with Text_IO; use Text_IO;
procedure m is
   v1 : a1 := new int1;
   v2 : a2 := to_a2 (v1);
begin
   v1.all := 1;
   v2.all := 0;
   put_line (int1'image (v1.all));
end;
@end example
@end quotation

This program prints out 0 in @emph{-O0} or @emph{-O1}
mode, but it prints out 1 in @emph{-O2} mode. That's
because in strict aliasing mode, the compiler can and
does assume that the assignment to @cite{v2.all} could not
affect the value of @cite{v1.all}, since different types
are involved.

This behavior is not a case of non-conformance with the standard, since
the Ada RM specifies that an unchecked conversion where the resulting
bit pattern is not a correct value of the target type can result in an
abnormal value and attempting to reference an abnormal value makes the
execution of a program erroneous.  That's the case here since the result
does not point to an object of type @cite{int2}.  This means that the
effect is entirely unpredictable.

However, although that explanation may satisfy a language
lawyer, in practice an applications programmer expects an
unchecked conversion involving pointers to create true
aliases and the behavior of printing 1 seems plain wrong.
In this case, the strict aliasing optimization is unwelcome.

Indeed the compiler recognizes this possibility, and the
unchecked conversion generates a warning:

@quotation

@example
p2.adb:5:07: warning: possible aliasing problem with type "a2"
p2.adb:5:07: warning: use -fno-strict-aliasing switch for references
p2.adb:5:07: warning:  or use "pragma No_Strict_Aliasing (a2);"
@end example
@end quotation

Unfortunately the problem is recognized when compiling the body of
package @cite{p2}, but the actual "bad" code is generated while
compiling the body of @cite{m} and this latter compilation does not see
the suspicious @cite{Unchecked_Conversion}.

As implied by the warning message, there are approaches you can use to
avoid the unwanted strict aliasing optimization in a case like this.

One possibility is to simply avoid the use of @emph{-O2}, but
that is a bit drastic, since it throws away a number of useful
optimizations that do not involve strict aliasing assumptions.

A less drastic approach is to compile the program using the
option @emph{-fno-strict-aliasing}. Actually it is only the
unit containing the dereferencing of the suspicious pointer
that needs to be compiled. So in this case, if we compile
unit @cite{m} with this switch, then we get the expected
value of zero printed. Analyzing which units might need
the switch can be painful, so a more reasonable approach
is to compile the entire program with options @emph{-O2}
and @emph{-fno-strict-aliasing}. If the performance is
satisfactory with this combination of options, then the
advantage is that the entire issue of possible "wrong"
optimization due to strict aliasing is avoided.

To avoid the use of compiler switches, the configuration
pragma @cite{No_Strict_Aliasing} with no parameters may be
used to specify that for all access types, the strict
aliasing optimization should be suppressed.

However, these approaches are still overkill, in that they causes
all manipulations of all access values to be deoptimized. A more
refined approach is to concentrate attention on the specific
access type identified as problematic.

First, if a careful analysis of uses of the pointer shows
that there are no possible problematic references, then
the warning can be suppressed by bracketing the
instantiation of @cite{Unchecked_Conversion} to turn
the warning off:

@quotation

@example
pragma Warnings (Off);
function to_a2u is
  new Unchecked_Conversion (a1, a2);
pragma Warnings (On);
@end example
@end quotation

Of course that approach is not appropriate for this particular
example, since indeed there is a problematic reference. In this
case we can take one of two other approaches.

The first possibility is to move the instantiation of unchecked
conversion to the unit in which the type is declared. In
this example, we would move the instantiation of
@cite{Unchecked_Conversion} from the body of package
@cite{p2} to the spec of package @cite{p1}. Now the
warning disappears. That's because any use of the
access type knows there is a suspicious unchecked
conversion, and the strict aliasing optimization
is automatically suppressed for the type.

If it is not practical to move the unchecked conversion to the same unit
in which the destination access type is declared (perhaps because the
source type is not visible in that unit), you may use pragma
@cite{No_Strict_Aliasing} for the type. This pragma must occur in the
same declarative sequence as the declaration of the access type:

@quotation

@example
type a2 is access int2;
pragma No_Strict_Aliasing (a2);
@end example
@end quotation

Here again, the compiler now knows that the strict aliasing optimization
should be suppressed for any reference to type @cite{a2} and the
expected behavior is obtained.

Finally, note that although the compiler can generate warnings for
simple cases of unchecked conversions, there are tricker and more
indirect ways of creating type incorrect aliases which the compiler
cannot detect. Examples are the use of address overlays and unchecked
conversions involving composite types containing access types as
components. In such cases, no warnings are generated, but there can
still be aliasing problems. One safe coding practice is to forbid the
use of address clauses for type overlaying, and to allow unchecked
conversion only for primitive types. This is not really a significant
restriction since any possible desired effect can be achieved by
unchecked conversion of access values.

The aliasing analysis done in strict aliasing mode can certainly
have significant benefits. We have seen cases of large scale
application code where the time is increased by up to 5% by turning
this optimization off. If you have code that includes significant
usage of unchecked conversion, you might want to just stick with
@emph{-O1} and avoid the entire issue. If you get adequate
performance at this level of optimization level, that's probably
the safest approach. If tests show that you really need higher
levels of optimization, then you can experiment with @emph{-O2}
and @emph{-O2 -fno-strict-aliasing} to see how much effect this
has on size and speed of the code. If you really need to use
@emph{-O2} with strict aliasing in effect, then you should
review any uses of unchecked conversion of access types,
particularly if you are getting the warnings described above.

@node Aliased Variables and Optimization,Atomic Variables and Optimization,Optimization and Strict Aliasing,Performance Considerations
@anchor{gnat_ugn/gnat_and_program_execution aliased-variables-and-optimization}@anchor{238}@anchor{gnat_ugn/gnat_and_program_execution id39}@anchor{239}
@subsubsection Aliased Variables and Optimization


@geindex Aliasing

There are scenarios in which programs may
use low level techniques to modify variables
that otherwise might be considered to be unassigned. For example,
a variable can be passed to a procedure by reference, which takes
the address of the parameter and uses the address to modify the
variable's value, even though it is passed as an IN parameter.
Consider the following example:

@quotation

@example
procedure P is
   Max_Length : constant Natural := 16;
   type Char_Ptr is access all Character;

   procedure Get_String(Buffer: Char_Ptr; Size : Integer);
   pragma Import (C, Get_String, "get_string");

   Name : aliased String (1 .. Max_Length) := (others => ' ');
   Temp : Char_Ptr;

   function Addr (S : String) return Char_Ptr is
      function To_Char_Ptr is
        new Ada.Unchecked_Conversion (System.Address, Char_Ptr);
   begin
      return To_Char_Ptr (S (S'First)'Address);
   end;

begin
   Temp := Addr (Name);
   Get_String (Temp, Max_Length);
end;
@end example
@end quotation

where Get_String is a C function that uses the address in Temp to
modify the variable @cite{Name}. This code is dubious, and arguably
erroneous, and the compiler would be entitled to assume that
@cite{Name} is never modified, and generate code accordingly.

However, in practice, this would cause some existing code that
seems to work with no optimization to start failing at high
levels of optimzization.

What the compiler does for such cases is to assume that marking
a variable as aliased indicates that some "funny business" may
be going on. The optimizer recognizes the aliased keyword and
inhibits optimizations that assume the value cannot be assigned.
This means that the above example will in fact "work" reliably,
that is, it will produce the expected results.

@node Atomic Variables and Optimization,Passive Task Optimization,Aliased Variables and Optimization,Performance Considerations
@anchor{gnat_ugn/gnat_and_program_execution atomic-variables-and-optimization}@anchor{23a}@anchor{gnat_ugn/gnat_and_program_execution id40}@anchor{23b}
@subsubsection Atomic Variables and Optimization


@geindex Atomic

There are two considerations with regard to performance when
atomic variables are used.

First, the RM only guarantees that access to atomic variables
be atomic, it has nothing to say about how this is achieved,
though there is a strong implication that this should not be
achieved by explicit locking code. Indeed GNAT will never
generate any locking code for atomic variable access (it will
simply reject any attempt to make a variable or type atomic
if the atomic access cannot be achieved without such locking code).

That being said, it is important to understand that you cannot
assume that the entire variable will always be accessed. Consider
this example:

@quotation

@example
type R is record
   A,B,C,D : Character;
end record;
for R'Size use 32;
for R'Alignment use 4;

RV : R;
pragma Atomic (RV);
X : Character;
...
X := RV.B;
@end example
@end quotation

You cannot assume that the reference to @cite{RV.B}
will read the entire 32-bit
variable with a single load instruction. It is perfectly legitimate if
the hardware allows it to do a byte read of just the B field. This read
is still atomic, which is all the RM requires. GNAT can and does take
advantage of this, depending on the architecture and optimization level.
Any assumption to the contrary is non-portable and risky. Even if you
examine the assembly language and see a full 32-bit load, this might
change in a future version of the compiler.

If your application requires that all accesses to @cite{RV} in this
example be full 32-bit loads, you need to make a copy for the access
as in:

@quotation

@example
declare
   RV_Copy : constant R := RV;
begin
   X := RV_Copy.B;
end;
@end example
@end quotation

Now the reference to RV must read the whole variable.
Actually one can imagine some compiler which figures
out that the whole copy is not required (because only
the B field is actually accessed), but GNAT
certainly won't do that, and we don't know of any
compiler that would not handle this right, and the
above code will in practice work portably across
all architectures (that permit the Atomic declaration).

The second issue with atomic variables has to do with
the possible requirement of generating synchronization
code. For more details on this, consult the sections on
the pragmas Enable/Disable_Atomic_Synchronization in the
GNAT Reference Manual. If performance is critical, and
such synchronization code is not required, it may be
useful to disable it.

@node Passive Task Optimization,,Atomic Variables and Optimization,Performance Considerations
@anchor{gnat_ugn/gnat_and_program_execution id41}@anchor{23c}@anchor{gnat_ugn/gnat_and_program_execution passive-task-optimization}@anchor{23d}
@subsubsection Passive Task Optimization


@geindex Passive Task

A passive task is one which is sufficiently simple that
in theory a compiler could recognize it an implement it
efficiently without creating a new thread. The original design
of Ada 83 had in mind this kind of passive task optimization, but
only a few Ada 83 compilers attempted it. The problem was that
it was difficult to determine the exact conditions under which
the optimization was possible. The result is a very fragile
optimization where a very minor change in the program can
suddenly silently make a task non-optimizable.

With the revisiting of this issue in Ada 95, there was general
agreement that this approach was fundamentally flawed, and the
notion of protected types was introduced. When using protected
types, the restrictions are well defined, and you KNOW that the
operations will be optimized, and furthermore this optimized
performance is fully portable.

Although it would theoretically be possible for GNAT to attempt to
do this optimization, but it really doesn't make sense in the
context of Ada 95, and none of the Ada 95 compilers implement
this optimization as far as we know. In particular GNAT never
attempts to perform this optimization.

In any new Ada 95 code that is written, you should always
use protected types in place of tasks that might be able to
be optimized in this manner.
Of course this does not help if you have legacy Ada 83 code
that depends on this optimization, but it is unusual to encounter
a case where the performance gains from this optimization
are significant.

Your program should work correctly without this optimization. If
you have performance problems, then the most practical
approach is to figure out exactly where these performance problems
arise, and update those particular tasks to be protected types. Note
that typically clients of the tasks who call entries, will not have
to be modified, only the task definition itself.

@node Text_IO Suggestions,Reducing Size of Executables with Unused Subprogram/Data Elimination,Performance Considerations,Improving Performance
@anchor{gnat_ugn/gnat_and_program_execution text-io-suggestions}@anchor{23e}@anchor{gnat_ugn/gnat_and_program_execution id42}@anchor{23f}
@subsection @cite{Text_IO} Suggestions


@geindex Text_IO and performance

The @cite{Ada.Text_IO} package has fairly high overheads due in part to
the requirement of maintaining page and line counts. If performance
is critical, a recommendation is to use @cite{Stream_IO} instead of
@cite{Text_IO} for volume output, since this package has less overhead.

If @cite{Text_IO} must be used, note that by default output to the standard
output and standard error files is unbuffered (this provides better
behavior when output statements are used for debugging, or if the
progress of a program is observed by tracking the output, e.g. by
using the Unix @emph{tail -f} command to watch redirected output.

If you are generating large volumes of output with @cite{Text_IO} and
performance is an important factor, use a designated file instead
of the standard output file, or change the standard output file to
be buffered using @cite{Interfaces.C_Streams.setvbuf}.

@node Reducing Size of Executables with Unused Subprogram/Data Elimination,,Text_IO Suggestions,Improving Performance
@anchor{gnat_ugn/gnat_and_program_execution id43}@anchor{240}@anchor{gnat_ugn/gnat_and_program_execution reducing-size-of-executables-with-unused-subprogram-data-elimination}@anchor{241}
@subsection Reducing Size of Executables with Unused Subprogram/Data Elimination


@geindex Uunused subprogram/data elimination

This section describes how you can eliminate unused subprograms and data from
your executable just by setting options at compilation time.

@menu
* About unused subprogram/data elimination:: 
* Compilation options:: 
* Example of unused subprogram/data elimination:: 

@end menu

@node About unused subprogram/data elimination,Compilation options,,Reducing Size of Executables with Unused Subprogram/Data Elimination
@anchor{gnat_ugn/gnat_and_program_execution id44}@anchor{242}@anchor{gnat_ugn/gnat_and_program_execution about-unused-subprogram-data-elimination}@anchor{243}
@subsubsection About unused subprogram/data elimination


By default, an executable contains all code and data of its composing objects
(directly linked or coming from statically linked libraries), even data or code
never used by this executable.

This feature will allow you to eliminate such unused code from your
executable, making it smaller (in disk and in memory).

This functionality is available on all Linux platforms except for the IA-64
architecture and on all cross platforms using the ELF binary file format.
In both cases GNU binutils version 2.16 or later are required to enable it.

@node Compilation options,Example of unused subprogram/data elimination,About unused subprogram/data elimination,Reducing Size of Executables with Unused Subprogram/Data Elimination
@anchor{gnat_ugn/gnat_and_program_execution id45}@anchor{244}@anchor{gnat_ugn/gnat_and_program_execution compilation-options}@anchor{245}
@subsubsection Compilation options


The operation of eliminating the unused code and data from the final executable
is directly performed by the linker.

@geindex -ffunction-sections (gcc)

@geindex -fdata-sections (gcc)

In order to do this, it has to work with objects compiled with the
following options:
@emph{-ffunction-sections} @emph{-fdata-sections}.

These options are usable with C and Ada files.
They will place respectively each
function or data in a separate section in the resulting object file.

Once the objects and static libraries are created with these options, the
linker can perform the dead code elimination. You can do this by setting
the @emph{-Wl,--gc-sections} option to gcc command or in the
@emph{-largs} section of @emph{gnatmake}. This will perform a
garbage collection of code and data never referenced.

If the linker performs a partial link (@emph{-r} linker option), then you
will need to provide the entry point using the @emph{-e} / @emph{--entry}
linker option.

Note that objects compiled without the @emph{-ffunction-sections} and
@emph{-fdata-sections} options can still be linked with the executable.
However, no dead code elimination will be performed on those objects (they will
be linked as is).

The GNAT static library is now compiled with -ffunction-sections and
-fdata-sections on some platforms. This allows you to eliminate the unused code
and data of the GNAT library from your executable.

@node Example of unused subprogram/data elimination,,Compilation options,Reducing Size of Executables with Unused Subprogram/Data Elimination
@anchor{gnat_ugn/gnat_and_program_execution id46}@anchor{246}@anchor{gnat_ugn/gnat_and_program_execution example-of-unused-subprogram-data-elimination}@anchor{247}
@subsubsection Example of unused subprogram/data elimination


Here is a simple example:

@quotation

@example
with Aux;

procedure Test is
begin
   Aux.Used (10);
end Test;

package Aux is
   Used_Data   : Integer;
   Unused_Data : Integer;

   procedure Used   (Data : Integer);
   procedure Unused (Data : Integer);
end Aux;

package body Aux is
   procedure Used (Data : Integer) is
   begin
      Used_Data := Data;
   end Used;

   procedure Unused (Data : Integer) is
   begin
      Unused_Data := Data;
   end Unused;
end Aux;
@end example
@end quotation

@cite{Unused} and @cite{Unused_Data} are never referenced in this code
excerpt, and hence they may be safely removed from the final executable.

@quotation

@example
$ gnatmake test

$ nm test | grep used
020015f0 T aux__unused
02005d88 B aux__unused_data
020015cc T aux__used
02005d84 B aux__used_data

$ gnatmake test -cargs -fdata-sections -ffunction-sections \\
     -largs -Wl,--gc-sections

$ nm test | grep used
02005350 T aux__used
0201ffe0 B aux__used_data
@end example
@end quotation

It can be observed that the procedure @cite{Unused} and the object
@cite{Unused_Data} are removed by the linker when using the
appropriate options.

@geindex Overflow checks

@geindex Checks (overflow)


@node Overflow Check Handling in GNAT,Performing Dimensionality Analysis in GNAT,Improving Performance,GNAT and Program Execution
@anchor{gnat_ugn/gnat_and_program_execution id54}@anchor{1f3}@anchor{gnat_ugn/gnat_and_program_execution overflow-check-handling-in-gnat}@anchor{29}
@section Overflow Check Handling in GNAT


This section explains how to control the handling of overflow checks.

@menu
* Background:: 
* Overflow Checking Modes in GNAT:: 
* Specifying the Desired Mode:: 
* Default Settings:: 
* Implementation Notes:: 

@end menu

@node Background,Overflow Checking Modes in GNAT,,Overflow Check Handling in GNAT
@anchor{gnat_ugn/gnat_and_program_execution id55}@anchor{248}@anchor{gnat_ugn/gnat_and_program_execution background}@anchor{249}
@subsection Background


Overflow checks are checks that the compiler may make to ensure
that intermediate results are not out of range. For example:

@quotation

@example
A : Integer;
...
A := A + 1;
@end example
@end quotation

If @cite{A} has the value @cite{Integer'Last}, then the addition may cause
overflow since the result is out of range of the type @cite{Integer}.
In this case @cite{Constraint_Error} will be raised if checks are
enabled.

A trickier situation arises in examples like the following:

@quotation

@example
A, C : Integer;
...
A := (A + 1) + C;
@end example
@end quotation

where @cite{A} is @cite{Integer'Last} and @cite{C} is @cite{-1}.
Now the final result of the expression on the right hand side is
@cite{Integer'Last} which is in range, but the question arises whether the
intermediate addition of @cite{(A + 1)} raises an overflow error.

The (perhaps surprising) answer is that the Ada language
definition does not answer this question. Instead it leaves
it up to the implementation to do one of two things if overflow
checks are enabled.


@itemize *

@item 
raise an exception (@cite{Constraint_Error}), or

@item 
yield the correct mathematical result which is then used in
subsequent operations.
@end itemize

If the compiler chooses the first approach, then the assignment of this
example will indeed raise @cite{Constraint_Error} if overflow checking is
enabled, or result in erroneous execution if overflow checks are suppressed.

But if the compiler
chooses the second approach, then it can perform both additions yielding
the correct mathematical result, which is in range, so no exception
will be raised, and the right result is obtained, regardless of whether
overflow checks are suppressed.

Note that in the first example an
exception will be raised in either case, since if the compiler
gives the correct mathematical result for the addition, it will
be out of range of the target type of the assignment, and thus
fails the range check.

This lack of specified behavior in the handling of overflow for
intermediate results is a source of non-portability, and can thus
be problematic when programs are ported. Most typically this arises
in a situation where the original compiler did not raise an exception,
and then the application is moved to a compiler where the check is
performed on the intermediate result and an unexpected exception is
raised.

Furthermore, when using Ada 2012's preconditions and other
assertion forms, another issue arises. Consider:

@quotation

@example
procedure P (A, B : Integer) with
  Pre => A + B <= Integer'Last;
@end example
@end quotation

One often wants to regard arithmetic in a context like this from
a mathematical point of view. So for example, if the two actual parameters
for a call to @cite{P} are both @cite{Integer'Last}, then
the precondition should be regarded as False. If we are executing
in a mode with run-time checks enabled for preconditions, then we would
like this precondition to fail, rather than raising an exception
because of the intermediate overflow.

However, the language definition leaves the specification of
whether the above condition fails (raising @cite{Assert_Error}) or
causes an intermediate overflow (raising @cite{Constraint_Error})
up to the implementation.

The situation is worse in a case such as the following:

@quotation

@example
procedure Q (A, B, C : Integer) with
  Pre => A + B + C <= Integer'Last;
@end example
@end quotation

Consider the call

@quotation

@example
Q (A => Integer'Last, B => 1, C => -1);
@end example
@end quotation

From a mathematical point of view the precondition
is True, but at run time we may (but are not guaranteed to) get an
exception raised because of the intermediate overflow (and we really
would prefer this precondition to be considered True at run time).

@node Overflow Checking Modes in GNAT,Specifying the Desired Mode,Background,Overflow Check Handling in GNAT
@anchor{gnat_ugn/gnat_and_program_execution id56}@anchor{24a}@anchor{gnat_ugn/gnat_and_program_execution overflow-checking-modes-in-gnat}@anchor{24b}
@subsection Overflow Checking Modes in GNAT


To deal with the portability issue, and with the problem of
mathematical versus run-time interpretation of the expressions in
assertions, GNAT provides comprehensive control over the handling
of intermediate overflow. GNAT can operate in three modes, and
furthemore, permits separate selection of operating modes for
the expressions within assertions (here the term 'assertions'
is used in the technical sense, which includes preconditions and so forth)
and for expressions appearing outside assertions.

The three modes are:


@itemize *

@item 
@emph{Use base type for intermediate operations} (@cite{STRICT})

In this mode, all intermediate results for predefined arithmetic
operators are computed using the base type, and the result must
be in range of the base type. If this is not the
case then either an exception is raised (if overflow checks are
enabled) or the execution is erroneous (if overflow checks are suppressed).
This is the normal default mode.

@item 
@emph{Most intermediate overflows avoided} (@cite{MINIMIZED})

In this mode, the compiler attempts to avoid intermediate overflows by
using a larger integer type, typically @cite{Long_Long_Integer},
as the type in which arithmetic is
performed for predefined arithmetic operators. This may be slightly more
expensive at
run time (compared to suppressing intermediate overflow checks), though
the cost is negligible on modern 64-bit machines. For the examples given
earlier, no intermediate overflows would have resulted in exceptions,
since the intermediate results are all in the range of
@cite{Long_Long_Integer} (typically 64-bits on nearly all implementations
of GNAT). In addition, if checks are enabled, this reduces the number of
checks that must be made, so this choice may actually result in an
improvement in space and time behavior.

However, there are cases where @cite{Long_Long_Integer} is not large
enough, consider the following example:

@quotation

@example
procedure R (A, B, C, D : Integer) with
  Pre => (A**2 * B**2) / (C**2 * D**2) <= 10;
@end example
@end quotation

where @cite{A} = @cite{B} = @cite{C} = @cite{D} = @cite{Integer'Last}.
Now the intermediate results are
out of the range of @cite{Long_Long_Integer} even though the final result
is in range and the precondition is True (from a mathematical point
of view). In such a case, operating in this mode, an overflow occurs
for the intermediate computation (which is why this mode
says @emph{most} intermediate overflows are avoided). In this case,
an exception is raised if overflow checks are enabled, and the
execution is erroneous if overflow checks are suppressed.

@item 
@emph{All intermediate overflows avoided} (@cite{ELIMINATED})

In this mode, the compiler  avoids all intermediate overflows
by using arbitrary precision arithmetic as required. In this
mode, the above example with @cite{A**2 * B**2} would
not cause intermediate overflow, because the intermediate result
would be evaluated using sufficient precision, and the result
of evaluating the precondition would be True.

This mode has the advantage of avoiding any intermediate
overflows, but at the expense of significant run-time overhead,
including the use of a library (included automatically in this
mode) for multiple-precision arithmetic.

This mode provides cleaner semantics for assertions, since now
the run-time behavior emulates true arithmetic behavior for the
predefined arithmetic operators, meaning that there is never a
conflict between the mathematical view of the assertion, and its
run-time behavior.

Note that in this mode, the behavior is unaffected by whether or
not overflow checks are suppressed, since overflow does not occur.
It is possible for gigantic intermediate expressions to raise
@cite{Storage_Error} as a result of attempting to compute the
results of such expressions (e.g. @cite{Integer'Last ** Integer'Last})
but overflow is impossible.
@end itemize

Note that these modes apply only to the evaluation of predefined
arithmetic, membership, and comparison operators for signed integer
aritmetic.

For fixed-point arithmetic, checks can be suppressed. But if checks
are enabled
then fixed-point values are always checked for overflow against the
base type for intermediate expressions (that is such checks always
operate in the equivalent of @cite{STRICT} mode).

For floating-point, on nearly all architectures, @cite{Machine_Overflows}
is False, and IEEE infinities are generated, so overflow exceptions
are never raised. If you want to avoid infinities, and check that
final results of expressions are in range, then you can declare a
constrained floating-point type, and range checks will be carried
out in the normal manner (with infinite values always failing all
range checks).

@node Specifying the Desired Mode,Default Settings,Overflow Checking Modes in GNAT,Overflow Check Handling in GNAT
@anchor{gnat_ugn/gnat_and_program_execution specifying-the-desired-mode}@anchor{fd}@anchor{gnat_ugn/gnat_and_program_execution id57}@anchor{24c}
@subsection Specifying the Desired Mode


@geindex pragma Overflow_Mode

The desired mode of for handling intermediate overflow can be specified using
either the @cite{Overflow_Mode} pragma or an equivalent compiler switch.
The pragma has the form

@quotation

@example
pragma Overflow_Mode ([General =>] MODE [, [Assertions =>] MODE]);
@end example
@end quotation

where @cite{MODE} is one of


@itemize *

@item 
@cite{STRICT}:  intermediate overflows checked (using base type)

@item 
@cite{MINIMIZED}: minimize intermediate overflows

@item 
@cite{ELIMINATED}: eliminate intermediate overflows
@end itemize

The case is ignored, so @cite{MINIMIZED}, @cite{Minimized} and
@cite{minimized} all have the same effect.

If only the @cite{General} parameter is present, then the given @cite{MODE}
applies
to expressions both within and outside assertions. If both arguments
are present, then @cite{General} applies to expressions outside assertions,
and @cite{Assertions} applies to expressions within assertions. For example:

@quotation

@example
pragma Overflow_Mode
  (General => Minimized, Assertions => Eliminated);
@end example
@end quotation

specifies that general expressions outside assertions be evaluated
in 'minimize intermediate overflows' mode, and expressions within
assertions be evaluated in 'eliminate intermediate overflows' mode.
This is often a reasonable choice, avoiding excessive overhead
outside assertions, but assuring a high degree of portability
when importing code from another compiler, while incurring
the extra overhead for assertion expressions to ensure that
the behavior at run time matches the expected mathematical
behavior.

The @cite{Overflow_Mode} pragma has the same scoping and placement
rules as pragma @cite{Suppress}, so it can occur either as a
configuration pragma, specifying a default for the whole
program, or in a declarative scope, where it applies to the
remaining declarations and statements in that scope.

Note that pragma @cite{Overflow_Mode} does not affect whether
overflow checks are enabled or suppressed. It only controls the
method used to compute intermediate values. To control whether
overflow checking is enabled or suppressed, use pragma @cite{Suppress}
or @cite{Unsuppress} in the usual manner

@geindex -gnato? (gcc)

@geindex -gnato?? (gcc)

Additionally, a compiler switch @emph{-gnato?} or @emph{-gnato??}
can be used to control the checking mode default (which can be subsequently
overridden using pragmas).

Here @code{?} is one of the digits @code{1} through @code{3}:

@quotation


@multitable {xxxxxxxx} {xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx} 
@item

@code{1}

@tab

use base type for intermediate operations (@cite{STRICT})

@item

@code{2}

@tab

minimize intermediate overflows (@cite{MINIMIZED})

@item

@code{3}

@tab

eliminate intermediate overflows (@cite{ELIMINATED})

@end multitable

@end quotation

As with the pragma, if only one digit appears then it applies to all
cases; if two digits are given, then the first applies outside
assertions, and the second within assertions. Thus the equivalent
of the example pragma above would be
@emph{-gnato23}.

If no digits follow the @emph{-gnato}, then it is equivalent to
@emph{-gnato11},
causing all intermediate operations to be computed using the base
type (@cite{STRICT} mode).

In addition to setting the mode used for computation of intermediate
results, the @cite{-gnato} switch also enables overflow checking (which
is suppressed by default). It thus combines the effect of using
a pragma @cite{Overflow_Mode} and pragma @cite{Unsuppress}.

@node Default Settings,Implementation Notes,Specifying the Desired Mode,Overflow Check Handling in GNAT
@anchor{gnat_ugn/gnat_and_program_execution id58}@anchor{24d}@anchor{gnat_ugn/gnat_and_program_execution default-settings}@anchor{24e}
@subsection Default Settings


The default mode for overflow checks is

@quotation

@example
General => Strict
@end example
@end quotation

which causes all computations both inside and outside assertions to use
the base type. In addition overflow checks are suppressed.

This retains compatibility with previous versions of
GNAT which suppressed overflow checks by default and always
used the base type for computation of intermediate results.

The switch @emph{-gnato} (with no digits following) is equivalent to
.. index:: -gnato (gcc)

@quotation

@example
General => Strict
@end example
@end quotation

which causes overflow checking of all intermediate overflows
both inside and outside assertions against the base type.
This provides compatibility
with this switch as implemented in previous versions of GNAT.

The pragma @cite{Suppress (Overflow_Check)} disables overflow
checking, but it has no effect on the method used for computing
intermediate results.

The pragma @cite{Unsuppress (Overflow_Check)} enables overflow
checking, but it has no effect on the method used for computing
intermediate results.

@node Implementation Notes,,Default Settings,Overflow Check Handling in GNAT
@anchor{gnat_ugn/gnat_and_program_execution implementation-notes}@anchor{24f}@anchor{gnat_ugn/gnat_and_program_execution id59}@anchor{250}
@subsection Implementation Notes


In practice on typical 64-bit machines, the @cite{MINIMIZED} mode is
reasonably efficient, and can be generally used. It also helps
to ensure compatibility with code imported from some other
compiler to GNAT.

Setting all intermediate overflows checking (@cite{CHECKED} mode)
makes sense if you want to
make sure that your code is compatible with any other possible
Ada implementation. This may be useful in ensuring portability
for code that is to be exported to some other compiler than GNAT.

The Ada standard allows the reassociation of expressions at
the same precedence level if no parentheses are present. For
example, @cite{A+B+C} parses as though it were @cite{(A+B)+C}, but
the compiler can reintepret this as @cite{A+(B+C)}, possibly
introducing or eliminating an overflow exception. The GNAT
compiler never takes advantage of this freedom, and the
expression @cite{A+B+C} will be evaluated as @cite{(A+B)+C}.
If you need the other order, you can write the parentheses
explicitly @cite{A+(B+C)} and GNAT will respect this order.

The use of @cite{ELIMINATED} mode will cause the compiler to
automatically include an appropriate arbitrary precision
integer arithmetic package. The compiler will make calls
to this package, though only in cases where it cannot be
sure that @cite{Long_Long_Integer} is sufficient to guard against
intermediate overflows. This package does not use dynamic
alllocation, but it does use the secondary stack, so an
appropriate secondary stack package must be present (this
is always true for standard full Ada, but may require
specific steps for restricted run times such as ZFP).

Although @cite{ELIMINATED} mode causes expressions to use arbitrary
precision arithmetic, avoiding overflow, the final result
must be in an appropriate range. This is true even if the
final result is of type @cite{[Long_[Long_]]Integer'Base}, which
still has the same bounds as its associated constrained
type at run-time.

Currently, the @cite{ELIMINATED} mode is only available on target
platforms for which @cite{Long_Long_Integer} is 64-bits (nearly all GNAT
platforms).

@node Performing Dimensionality Analysis in GNAT,Stack Related Facilities,Overflow Check Handling in GNAT,GNAT and Program Execution
@anchor{gnat_ugn/gnat_and_program_execution performing-dimensionality-analysis-in-gnat}@anchor{2a}@anchor{gnat_ugn/gnat_and_program_execution id60}@anchor{1f4}
@section Performing Dimensionality Analysis in GNAT


@geindex Dimensionality analysis

The GNAT compiler supports dimensionality checking. The user can
specify physical units for objects, and the compiler will verify that uses
of these objects are compatible with their dimensions, in a fashion that is
familiar to engineering practice. The dimensions of algebraic expressions
(including powers with static exponents) are computed from their constituents.

@geindex Dimension_System aspect

@geindex Dimension aspect

This feature depends on Ada 2012 aspect specifications, and is available from
version 7.0.1 of GNAT onwards.
The GNAT-specific aspect @cite{Dimension_System}
allows you to define a system of units; the aspect @cite{Dimension}
then allows the user to declare dimensioned quantities within a given system.
(These aspects are described in the @emph{Implementation Defined Aspects}
chapter of the @emph{GNAT Reference Manual}).

The major advantage of this model is that it does not require the declaration of
multiple operators for all possible combinations of types: it is only necessary
to use the proper subtypes in object declarations.

@geindex System.Dim.Mks package (GNAT library)

@geindex MKS_Type type

The simplest way to impose dimensionality checking on a computation is to make
use of the package @cite{System.Dim.Mks},
which is part of the GNAT library. This
package defines a floating-point type @cite{MKS_Type},
for which a sequence of
dimension names are specified, together with their conventional abbreviations.
The following should be read together with the full specification of the
package, in file @code{s-dimmks.ads}.

@quotation

@geindex s-dimmks.ads file

@example
type Mks_Type is new Long_Long_Float
  with
   Dimension_System => (
     (Unit_Name => Meter,    Unit_Symbol => 'm',   Dim_Symbol => 'L'),
     (Unit_Name => Kilogram, Unit_Symbol => "kg",  Dim_Symbol => 'M'),
     (Unit_Name => Second,   Unit_Symbol => 's',   Dim_Symbol => 'T'),
     (Unit_Name => Ampere,   Unit_Symbol => 'A',   Dim_Symbol => 'I'),
     (Unit_Name => Kelvin,   Unit_Symbol => 'K',   Dim_Symbol => "Theta"),
     (Unit_Name => Mole,     Unit_Symbol => "mol", Dim_Symbol => 'N'),
     (Unit_Name => Candela,  Unit_Symbol => "cd",  Dim_Symbol => 'J'));
@end example
@end quotation

The package then defines a series of subtypes that correspond to these
conventional units. For example:

@quotation

@example
subtype Length is Mks_Type
  with
   Dimension => (Symbol => 'm', Meter  => 1, others => 0);
@end example
@end quotation

and similarly for @cite{Mass}, @cite{Time}, @cite{Electric_Current},
@cite{Thermodynamic_Temperature}, @cite{Amount_Of_Substance}, and
@cite{Luminous_Intensity} (the standard set of units of the SI system).

The package also defines conventional names for values of each unit, for
example:

@quotation

@c code-block":: ada
@c 
@c m   : constant Length           := 1.0;
@c kg  : constant Mass             := 1.0;
@c s   : constant Time             := 1.0;
@c A   : constant Electric_Current := 1.0;
@end quotation

as well as useful multiples of these units:

@quotation

@example
 cm  : constant Length := 1.0E-02;
 g   : constant Mass   := 1.0E-03;
 min : constant Time   := 60.0;
 day : constant Time   := 60.0 * 24.0 * min;
...
@end example
@end quotation

Using this package, you can then define a derived unit by
providing the aspect that
specifies its dimensions within the MKS system, as well as the string to
be used for output of a value of that unit:

@quotation

@example
subtype Acceleration is Mks_Type
  with Dimension => ("m/sec^2",
                     Meter => 1,
                     Second => -2,
                     others => 0);
@end example
@end quotation

Here is a complete example of use:

@quotation

@example
with System.Dim.MKS; use System.Dim.Mks;
with System.Dim.Mks_IO; use System.Dim.Mks_IO;
with Text_IO; use Text_IO;
procedure Free_Fall is
  subtype Acceleration is Mks_Type
    with Dimension => ("m/sec^2", 1, 0, -2, others => 0);
  G : constant acceleration := 9.81 * m / (s ** 2);
  T : Time := 10.0*s;
  Distance : Length;

begin
  Put ("Gravitational constant: ");
  Put (G, Aft => 2, Exp => 0); Put_Line ("");
  Distance := 0.5 * G * T ** 2;
  Put ("distance travelled in 10 seconds of free fall ");
  Put (Distance, Aft => 2, Exp => 0);
  Put_Line ("");
end Free_Fall;
@end example
@end quotation

Execution of this program yields:

@quotation

@example
Gravitational constant:  9.81 m/sec^2
distance travelled in 10 seconds of free fall 490.50 m
@end example
@end quotation

However, incorrect assignments such as:

@quotation

@example
Distance := 5.0;
Distance := 5.0 * kg:
@end example
@end quotation

are rejected with the following diagnoses:

@quotation

@example
Distance := 5.0;
   >>> dimensions mismatch in assignment
   >>> left-hand side has dimension [L]
   >>> right-hand side is dimensionless

Distance := 5.0 * kg:
   >>> dimensions mismatch in assignment
   >>> left-hand side has dimension [L]
   >>> right-hand side has dimension [M]
@end example
@end quotation

The dimensions of an expression are properly displayed, even if there is
no explicit subtype for it. If we add to the program:

@quotation

@example
Put ("Final velocity: ");
Put (G * T, Aft =>2, Exp =>0);
Put_Line ("");
@end example
@end quotation

then the output includes:

@quotation

@example
Final velocity: 98.10 m.s**(-1)
@end example
@end quotation

@node Stack Related Facilities,Memory Management Issues,Performing Dimensionality Analysis in GNAT,GNAT and Program Execution
@anchor{gnat_ugn/gnat_and_program_execution id61}@anchor{1f5}@anchor{gnat_ugn/gnat_and_program_execution stack-related-facilities}@anchor{2b}
@section Stack Related Facilities


This section describes some useful tools associated with stack
checking and analysis. In
particular, it deals with dynamic and static stack usage measurements.

@menu
* Stack Overflow Checking:: 
* Static Stack Usage Analysis:: 
* Dynamic Stack Usage Analysis:: 

@end menu

@node Stack Overflow Checking,Static Stack Usage Analysis,,Stack Related Facilities
@anchor{gnat_ugn/gnat_and_program_execution id62}@anchor{251}@anchor{gnat_ugn/gnat_and_program_execution stack-overflow-checking}@anchor{f9}
@subsection Stack Overflow Checking


@geindex Stack Overflow Checking

@geindex -fstack-check (gcc)

For most operating systems, @emph{gcc} does not perform stack overflow
checking by default. This means that if the main environment task or
some other task exceeds the available stack space, then unpredictable
behavior will occur. Most native systems offer some level of protection by
adding a guard page at the end of each task stack. This mechanism is usually
not enough for dealing properly with stack overflow situations because
a large local variable could "jump" above the guard page.
Furthermore, when the
guard page is hit, there may not be any space left on the stack for executing
the exception propagation code. Enabling stack checking avoids
such situations.

To activate stack checking, compile all units with the gcc option
@cite{-fstack-check}. For example:

@quotation

@example
$ gcc -c -fstack-check package1.adb
@end example
@end quotation

Units compiled with this option will generate extra instructions to check
that any use of the stack (for procedure calls or for declaring local
variables in declare blocks) does not exceed the available stack space.
If the space is exceeded, then a @cite{Storage_Error} exception is raised.

For declared tasks, the stack size is controlled by the size
given in an applicable @cite{Storage_Size} pragma or by the value specified
at bind time with @code{-d} (@ref{123,,Switches for gnatbind}) or is set to
the default size as defined in the GNAT runtime otherwise.

@geindex GNAT_STACK_LIMIT

For the environment task, the stack size depends on
system defaults and is unknown to the compiler. Stack checking
may still work correctly if a fixed
size stack is allocated, but this cannot be guaranteed.
To ensure that a clean exception is signalled for stack
overflow, set the environment variable
@geindex GNAT_STACK_LIMIT
@geindex environment variable; GNAT_STACK_LIMIT
@code{GNAT_STACK_LIMIT} to indicate the maximum
stack area that can be used, as in:

@quotation

@example
$ SET GNAT_STACK_LIMIT 1600
@end example
@end quotation

The limit is given in kilobytes, so the above declaration would
set the stack limit of the environment task to 1.6 megabytes.
Note that the only purpose of this usage is to limit the amount
of stack used by the environment task. If it is necessary to
increase the amount of stack for the environment task, then this
is an operating systems issue, and must be addressed with the
appropriate operating systems commands.

@node Static Stack Usage Analysis,Dynamic Stack Usage Analysis,Stack Overflow Checking,Stack Related Facilities
@anchor{gnat_ugn/gnat_and_program_execution static-stack-usage-analysis}@anchor{fa}@anchor{gnat_ugn/gnat_and_program_execution id63}@anchor{252}
@subsection Static Stack Usage Analysis


@geindex Static Stack Usage Analysis

@geindex -fstack-usage

A unit compiled with @code{-fstack-usage} will generate an extra file
that specifies
the maximum amount of stack used, on a per-function basis.
The file has the same
basename as the target object file with a @code{.su} extension.
Each line of this file is made up of three fields:


@itemize *

@item 
The name of the function.

@item 
A number of bytes.

@item 
One or more qualifiers: @cite{static}, @cite{dynamic}, @cite{bounded}.
@end itemize

The second field corresponds to the size of the known part of the function
frame.

The qualifier @cite{static} means that the function frame size
is purely static.
It usually means that all local variables have a static size.
In this case, the second field is a reliable measure of the function stack
utilization.

The qualifier @cite{dynamic} means that the function frame size is not static.
It happens mainly when some local variables have a dynamic size. When this
qualifier appears alone, the second field is not a reliable measure
of the function stack analysis. When it is qualified with  @cite{bounded}, it
means that the second field is a reliable maximum of the function stack
utilization.

A unit compiled with @code{-Wstack-usage} will issue a warning for each
subprogram whose stack usage might be larger than the specified amount of
bytes.  The wording is in keeping with the qualifier documented above.

@node Dynamic Stack Usage Analysis,,Static Stack Usage Analysis,Stack Related Facilities
@anchor{gnat_ugn/gnat_and_program_execution id64}@anchor{253}@anchor{gnat_ugn/gnat_and_program_execution dynamic-stack-usage-analysis}@anchor{125}
@subsection Dynamic Stack Usage Analysis


It is possible to measure the maximum amount of stack used by a task, by
adding a switch to @emph{gnatbind}, as:

@quotation

@example
$ gnatbind -u0 file
@end example
@end quotation

With this option, at each task termination, its stack usage is  output on
@code{stderr}.
It is not always convenient to output the stack usage when the program
is still running. Hence, it is possible to delay this output until program
termination. for a given number of tasks specified as the argument of the
@code{-u} option. For instance:

@quotation

@example
$ gnatbind -u100 file
@end example
@end quotation

will buffer the stack usage information of the first 100 tasks to terminate and
output this info at program termination. Results are displayed in four
columns:

@quotation

@example
Index | Task Name | Stack Size | Stack Usage
@end example
@end quotation

where:


@itemize *

@item 
@emph{Index} is a number associated with each task.

@item 
@emph{Task Name} is the name of the task analyzed.

@item 
@emph{Stack Size} is the maximum size for the stack.

@item 
@emph{Stack Usage} is the measure done by the stack analyzer.
In order to prevent overflow, the stack
is not entirely analyzed, and it's not possible to know exactly how
much has actually been used.
@end itemize

The environment task stack, e.g., the stack that contains the main unit, is
only processed when the environment variable GNAT_STACK_LIMIT is set.

The package @cite{GNAT.Task_Stack_Usage} provides facilities to get
stack usage reports at run-time. See its body for the details.

@node Memory Management Issues,,Stack Related Facilities,GNAT and Program Execution
@anchor{gnat_ugn/gnat_and_program_execution id65}@anchor{1f6}@anchor{gnat_ugn/gnat_and_program_execution memory-management-issues}@anchor{2c}
@section Memory Management Issues


This section describes some useful memory pools provided in the GNAT library
and in particular the GNAT Debug Pool facility, which can be used to detect
incorrect uses of access values (including 'dangling references').


@menu
* Some Useful Memory Pools:: 
* The GNAT Debug Pool Facility:: 

@end menu

@node Some Useful Memory Pools,The GNAT Debug Pool Facility,,Memory Management Issues
@anchor{gnat_ugn/gnat_and_program_execution id66}@anchor{254}@anchor{gnat_ugn/gnat_and_program_execution some-useful-memory-pools}@anchor{255}
@subsection Some Useful Memory Pools


@geindex Memory Pool

@geindex storage
@geindex pool

The @cite{System.Pool_Global} package offers the Unbounded_No_Reclaim_Pool
storage pool. Allocations use the standard system call @cite{malloc} while
deallocations use the standard system call @cite{free}. No reclamation is
performed when the pool goes out of scope. For performance reasons, the
standard default Ada allocators/deallocators do not use any explicit storage
pools but if they did, they could use this storage pool without any change in
behavior. That is why this storage pool is used  when the user
manages to make the default implicit allocator explicit as in this example:

@quotation

@example
type T1 is access Something;
 -- no Storage pool is defined for T2

type T2 is access Something_Else;
for T2'Storage_Pool use T1'Storage_Pool;
-- the above is equivalent to
for T2'Storage_Pool use System.Pool_Global.Global_Pool_Object;
@end example
@end quotation

The @cite{System.Pool_Local} package offers the Unbounded_Reclaim_Pool storage
pool. The allocation strategy is similar to @cite{Pool_Local}'s
except that the all
storage allocated with this pool is reclaimed when the pool object goes out of
scope. This pool provides a explicit mechanism similar to the implicit one
provided by several Ada 83 compilers for allocations performed through a local
access type and whose purpose was to reclaim memory when exiting the
scope of a given local access. As an example, the following program does not
leak memory even though it does not perform explicit deallocation:

@quotation

@example
with System.Pool_Local;
procedure Pooloc1 is
   procedure Internal is
      type A is access Integer;
      X : System.Pool_Local.Unbounded_Reclaim_Pool;
      for A'Storage_Pool use X;
      v : A;
   begin
      for I in  1 .. 50 loop
         v := new Integer;
      end loop;
   end Internal;
begin
   for I in  1 .. 100 loop
      Internal;
   end loop;
end Pooloc1;
@end example
@end quotation

The @cite{System.Pool_Size} package implements the Stack_Bounded_Pool used when
@cite{Storage_Size} is specified for an access type.
The whole storage for the pool is
allocated at once, usually on the stack at the point where the access type is
elaborated. It is automatically reclaimed when exiting the scope where the
access type is defined. This package is not intended to be used directly by the
user and it is implicitly used for each such declaration:

@quotation

@example
type T1 is access Something;
for T1'Storage_Size use 10_000;
@end example
@end quotation

@node The GNAT Debug Pool Facility,,Some Useful Memory Pools,Memory Management Issues
@anchor{gnat_ugn/gnat_and_program_execution id67}@anchor{256}@anchor{gnat_ugn/gnat_and_program_execution the-gnat-debug-pool-facility}@anchor{257}
@subsection The GNAT Debug Pool Facility


@geindex Debug Pool

@geindex storage
@geindex pool
@geindex memory corruption

The use of unchecked deallocation and unchecked conversion can easily
lead to incorrect memory references. The problems generated by such
references are usually difficult to tackle because the symptoms can be
very remote from the origin of the problem. In such cases, it is
very helpful to detect the problem as early as possible. This is the
purpose of the Storage Pool provided by @cite{GNAT.Debug_Pools}.

In order to use the GNAT specific debugging pool, the user must
associate a debug pool object with each of the access types that may be
related to suspected memory problems. See Ada Reference Manual 13.11.

@quotation

@example
type Ptr is access Some_Type;
Pool : GNAT.Debug_Pools.Debug_Pool;
for Ptr'Storage_Pool use Pool;
@end example
@end quotation

@cite{GNAT.Debug_Pools} is derived from a GNAT-specific kind of
pool: the @cite{Checked_Pool}. Such pools, like standard Ada storage pools,
allow the user to redefine allocation and deallocation strategies. They
also provide a checkpoint for each dereference, through the use of
the primitive operation @cite{Dereference} which is implicitly called at
each dereference of an access value.

Once an access type has been associated with a debug pool, operations on
values of the type may raise four distinct exceptions,
which correspond to four potential kinds of memory corruption:


@itemize *

@item 
@cite{GNAT.Debug_Pools.Accessing_Not_Allocated_Storage}

@item 
@cite{GNAT.Debug_Pools.Accessing_Deallocated_Storage}

@item 
@cite{GNAT.Debug_Pools.Freeing_Not_Allocated_Storage}

@item 
@cite{GNAT.Debug_Pools.Freeing_Deallocated_Storage}
@end itemize

For types associated with a Debug_Pool, dynamic allocation is performed using
the standard GNAT allocation routine. References to all allocated chunks of
memory are kept in an internal dictionary. Several deallocation strategies are
provided, whereupon the user can choose to release the memory to the system,
keep it allocated for further invalid access checks, or fill it with an easily
recognizable pattern for debug sessions. The memory pattern is the old IBM
hexadecimal convention: @cite{16#DEADBEEF#}.

See the documentation in the file g-debpoo.ads for more information on the
various strategies.

Upon each dereference, a check is made that the access value denotes a
properly allocated memory location. Here is a complete example of use of
@cite{Debug_Pools}, that includes typical instances of  memory corruption:

@quotation

@example
with Gnat.Io; use Gnat.Io;
with Unchecked_Deallocation;
with Unchecked_Conversion;
with GNAT.Debug_Pools;
with System.Storage_Elements;
with Ada.Exceptions; use Ada.Exceptions;
procedure Debug_Pool_Test is

   type T is access Integer;
   type U is access all T;

   P : GNAT.Debug_Pools.Debug_Pool;
   for T'Storage_Pool use P;

   procedure Free is new Unchecked_Deallocation (Integer, T);
   function UC is new Unchecked_Conversion (U, T);
   A, B : aliased T;

   procedure Info is new GNAT.Debug_Pools.Print_Info(Put_Line);

begin
   Info (P);
   A := new Integer;
   B := new Integer;
   B := A;
   Info (P);
   Free (A);
   begin
      Put_Line (Integer'Image(B.all));
   exception
      when E : others => Put_Line ("raised: " & Exception_Name (E));
   end;
   begin
      Free (B);
   exception
      when E : others => Put_Line ("raised: " & Exception_Name (E));
   end;
   B := UC(A'Access);
   begin
      Put_Line (Integer'Image(B.all));
   exception
      when E : others => Put_Line ("raised: " & Exception_Name (E));
   end;
   begin
      Free (B);
   exception
      when E : others => Put_Line ("raised: " & Exception_Name (E));
   end;
   Info (P);
end Debug_Pool_Test;
@end example
@end quotation

The debug pool mechanism provides the following precise diagnostics on the
execution of this erroneous program:

@quotation

@example
Debug Pool info:
  Total allocated bytes :  0
  Total deallocated bytes :  0
  Current Water Mark:  0
  High Water Mark:  0

Debug Pool info:
  Total allocated bytes :  8
  Total deallocated bytes :  0
  Current Water Mark:  8
  High Water Mark:  8

raised: GNAT.DEBUG_POOLS.ACCESSING_DEALLOCATED_STORAGE
raised: GNAT.DEBUG_POOLS.FREEING_DEALLOCATED_STORAGE
raised: GNAT.DEBUG_POOLS.ACCESSING_NOT_ALLOCATED_STORAGE
raised: GNAT.DEBUG_POOLS.FREEING_NOT_ALLOCATED_STORAGE
Debug Pool info:
  Total allocated bytes :  8
  Total deallocated bytes :  4
  Current Water Mark:  4
  High Water Mark:  8
@end example
@end quotation


@c -- Non-breaking space in running text
@c -- E.g. Ada |nbsp| 95

@node Platform-Specific Information,Example of Binder Output File,GNAT and Program Execution,Top
@anchor{gnat_ugn/platform_specific_information platform-specific-information}@anchor{f}@anchor{gnat_ugn/platform_specific_information doc}@anchor{258}@anchor{gnat_ugn/platform_specific_information id1}@anchor{259}
@chapter Platform-Specific Information


This appendix contains information relating to the implementation
of run-time libraries on various platforms and also covers
topics related to the GNAT implementation on Windows and Mac OS.

@menu
* Run-Time Libraries:: 
* Specifying a Run-Time Library:: 
* Microsoft Windows Topics:: 
* Mac OS Topics:: 

@end menu

@node Run-Time Libraries,Specifying a Run-Time Library,,Platform-Specific Information
@anchor{gnat_ugn/platform_specific_information id2}@anchor{25a}@anchor{gnat_ugn/platform_specific_information run-time-libraries}@anchor{2d}
@section Run-Time Libraries


@geindex Tasking and threads libraries

@geindex Threads libraries and tasking

@geindex Run-time libraries (platform-specific information)

The GNAT run-time implementation may vary with respect to both the
underlying threads library and the exception handling scheme.
For threads support, one or more of the following are supplied:


@itemize *

@item 
@strong{native threads library}, a binding to the thread package from
the underlying operating system

@item 
@strong{pthreads library} (Sparc Solaris only), a binding to the Solaris
POSIX thread package
@end itemize

For exception handling, either or both of two models are supplied:

@quotation

@geindex Zero-Cost Exceptions

@geindex ZCX (Zero-Cost Exceptions)
@end quotation


@itemize *

@item 
@strong{Zero-Cost Exceptions} ("ZCX"),
which uses binder-generated tables that
are interrogated at run time to locate a handler.

@geindex setjmp/longjmp Exception Model

@geindex SJLJ (setjmp/longjmp Exception Model)

@item 
@strong{setjmp / longjmp} ('SJLJ'),
which uses dynamically-set data to establish
the set of handlers
@end itemize

Most programs should experience a substantial speed improvement by
being compiled with a ZCX run-time.
This is especially true for
tasking applications or applications with many exception handlers.@}

This section summarizes which combinations of threads and exception support
are supplied on various GNAT platforms.
It then shows how to select a particular library either
permanently or temporarily,
explains the properties of (and tradeoffs among) the various threads
libraries, and provides some additional
information about several specific platforms.

@menu
* Summary of Run-Time Configurations:: 

@end menu

@node Summary of Run-Time Configurations,,,Run-Time Libraries
@anchor{gnat_ugn/platform_specific_information summary-of-run-time-configurations}@anchor{25b}@anchor{gnat_ugn/platform_specific_information id3}@anchor{25c}
@subsection Summary of Run-Time Configurations



@multitable {xxxxxxxxxxxxxxxxxxx} {xxxxxxxxxxxxxxxx} {xxxxxxxxxxxxxxxxxxxxxxxxxxx} {xxxxxxxxxxxxxx} 
@headitem

Platform

@tab

Run-Time

@tab

Tasking

@tab

Exceptions

@item

ppc-aix

@tab

rts-native
(default)

@tab

native AIX threads

@tab

ZCX

@item

rts-sjlj

@tab

native AIX threads

@tab

SJLJ

@item

sparc-solaris

@tab

rts-native
(default)

@tab

native Solaris
threads library

@tab

ZCX

@item

rts-pthread

@tab

pthread library

@tab

ZCX

@item

rts-sjlj

@tab

native Solaris
threads library

@tab

SJLJ

@item

sparc64-solaris

@tab

rts-native
(default)

@tab

native Solaris
threads library

@tab

ZCX

@item

x86-linux

@tab

rts-native
(default)

@tab

pthread library

@tab

ZCX

@item

rts-sjlj

@tab

pthread library

@tab

SJLJ

@item

x86-lynx

@tab

rts-native
(default)

@tab

native LynxOS threads

@tab

SJLJ

@item

x86-solaris

@tab

rts-native
(default)

@tab

native Solaris
threads library

@tab

ZCX

@item

rts-sjlj

@tab

native Solaris
threads library

@tab

SJLJ

@item

x86-windows

@tab

rts-native
(default)

@tab

native Win32 threads

@tab

ZCX

@item

rts-sjlj

@tab

native Win32 threads

@tab

SJLJ

@item

x86_64-linux

@tab

rts-native
(default)

@tab

pthread library

@tab

ZCX

@item

rts-sjlj

@tab

pthread library

@tab

SJLJ

@end multitable


@node Specifying a Run-Time Library,Microsoft Windows Topics,Run-Time Libraries,Platform-Specific Information
@anchor{gnat_ugn/platform_specific_information specifying-a-run-time-library}@anchor{25d}@anchor{gnat_ugn/platform_specific_information id4}@anchor{25e}
@section Specifying a Run-Time Library


The @code{adainclude} subdirectory containing the sources of the GNAT
run-time library, and the @code{adalib} subdirectory containing the
@code{ALI} files and the static and/or shared GNAT library, are located
in the gcc target-dependent area:

@quotation

@example
target=$prefix/lib/gcc/gcc-*dumpmachine*/gcc-*dumpversion*/
@end example
@end quotation

As indicated above, on some platforms several run-time libraries are supplied.
These libraries are installed in the target dependent area and
contain a complete source and binary subdirectory. The detailed description
below explains the differences between the different libraries in terms of
their thread support.

The default run-time library (when GNAT is installed) is @emph{rts-native}.
This default run time is selected by the means of soft links.
For example on x86-linux:

@example
--
--  $(target-dir)
--      |
--      +--- adainclude----------+
--      |                        |
--      +--- adalib-----------+  |
--      |                     |  |
--      +--- rts-native       |  |
--      |    |                |  |
--      |    +--- adainclude <---+
--      |    |                |
--      |    +--- adalib <----+
--      |
--      +--- rts-sjlj
--           |
--           +--- adainclude
--           |
--           +--- adalib
@end example

If the @emph{rts-sjlj} library is to be selected on a permanent basis,
these soft links can be modified with the following commands:

@quotation

@example
$ cd $target
$ rm -f adainclude adalib
$ ln -s rts-sjlj/adainclude adainclude
$ ln -s rts-sjlj/adalib adalib
@end example
@end quotation

Alternatively, you can specify @code{rts-sjlj/adainclude} in the file
@code{$target/ada_source_path} and @code{rts-sjlj/adalib} in
@code{$target/ada_object_path}.

@geindex --RTS option

Selecting another run-time library temporarily can be
achieved by using the @emph{--RTS} switch, e.g., @emph{--RTS=sjlj}
@anchor{gnat_ugn/platform_specific_information choosing-the-scheduling-policy}@anchor{25f}
@geindex SCHED_FIFO scheduling policy

@geindex SCHED_RR scheduling policy

@geindex SCHED_OTHER scheduling policy

@menu
* Choosing the Scheduling Policy:: 
* Solaris-Specific Considerations:: 
* Solaris Threads Issues:: 
* AIX-Specific Considerations:: 

@end menu

@node Choosing the Scheduling Policy,Solaris-Specific Considerations,,Specifying a Run-Time Library
@anchor{gnat_ugn/platform_specific_information id5}@anchor{260}
@subsection Choosing the Scheduling Policy


When using a POSIX threads implementation, you have a choice of several
scheduling policies: @cite{SCHED_FIFO}, @cite{SCHED_RR} and @cite{SCHED_OTHER}.

Typically, the default is @cite{SCHED_OTHER}, while using @cite{SCHED_FIFO}
or @cite{SCHED_RR} requires special (e.g., root) privileges.

@geindex pragma Time_Slice

@geindex -T0 option

@geindex pragma Task_Dispatching_Policy

By default, GNAT uses the @cite{SCHED_OTHER} policy. To specify
@cite{SCHED_FIFO},
you can use one of the following:


@itemize *

@item 
@cite{pragma Time_Slice (0.0)}

@item 
the corresponding binder option @emph{-T0}

@item 
@cite{pragma Task_Dispatching_Policy (FIFO_Within_Priorities)}
@end itemize

To specify @cite{SCHED_RR},
you should use @cite{pragma Time_Slice} with a
value greater than 0.0, or else use the corresponding @emph{-T}
binder option.

@geindex Solaris Sparc threads libraries

@node Solaris-Specific Considerations,Solaris Threads Issues,Choosing the Scheduling Policy,Specifying a Run-Time Library
@anchor{gnat_ugn/platform_specific_information id6}@anchor{261}@anchor{gnat_ugn/platform_specific_information solaris-specific-considerations}@anchor{262}
@subsection Solaris-Specific Considerations


This section addresses some topics related to the various threads libraries
on Sparc Solaris.

@geindex rts-pthread threads library

@node Solaris Threads Issues,AIX-Specific Considerations,Solaris-Specific Considerations,Specifying a Run-Time Library
@anchor{gnat_ugn/platform_specific_information id7}@anchor{263}@anchor{gnat_ugn/platform_specific_information solaris-threads-issues}@anchor{264}
@subsection Solaris Threads Issues


GNAT under Solaris/Sparc 32 bits comes with an alternate tasking run-time
library based on POSIX threads --- @emph{rts-pthread}.

@geindex PTHREAD_PRIO_INHERIT policy (under rts-pthread)

@geindex PTHREAD_PRIO_PROTECT policy (under rts-pthread)

@geindex pragma Locking_Policy (under rts-pthread)

@geindex Inheritance_Locking (under rts-pthread)

@geindex Ceiling_Locking (under rts-pthread)

This run-time library has the advantage of being mostly shared across all
POSIX-compliant thread implementations, and it also provides under
Solaris 8 the @cite{PTHREAD_PRIO_INHERIT}
and @cite{PTHREAD_PRIO_PROTECT}
semantics that can be selected using the predefined pragma
@cite{Locking_Policy}
with respectively
@cite{Inheritance_Locking} and @cite{Ceiling_Locking} as the policy.

As explained above, the native run-time library is based on the Solaris thread
library (@cite{libthread}) and is the default library.

@geindex GNAT_PROCESSOR environment variable (on Sparc Solaris)

When the Solaris threads library is used (this is the default), programs
compiled with GNAT can automatically take advantage of
and can thus execute on multiple processors.
The user can alternatively specify a processor on which the program should run
to emulate a single-processor system. The multiprocessor / uniprocessor choice
is made by
setting the environment variable 
@geindex GNAT_PROCESSOR
@geindex environment variable; GNAT_PROCESSOR
@code{GNAT_PROCESSOR}
to one of the following:

@quotation


@multitable {xxxxxxxxxxxxxxxxxxxxxxxxxxx} {xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx} 
@headitem

@code{GNAT_PROCESSOR} Value

@tab

Effect

@item

@emph{-2}

@tab

Use the default configuration (run the program on all
available processors) - this is the same as having @cite{GNAT_PROCESSOR}
unset

@item

@emph{-1}

@tab

Let the run-time implementation choose one processor and run the
program on that processor

@item

@emph{0 .. Last_Proc}

@tab

Run the program on the specified processor.
@cite{Last_Proc} is equal to @cite{_SC_NPROCESSORS_CONF - 1}
(where @cite{_SC_NPROCESSORS_CONF} is a system variable).

@end multitable

@end quotation

@node AIX-Specific Considerations,,Solaris Threads Issues,Specifying a Run-Time Library
@anchor{gnat_ugn/platform_specific_information aix-specific-considerations}@anchor{265}@anchor{gnat_ugn/platform_specific_information id8}@anchor{266}
@subsection AIX-Specific Considerations


@geindex AIX resolver library

On AIX, the resolver library initializes some internal structure on
the first call to @cite{get*by*} functions, which are used to implement
@cite{GNAT.Sockets.Get_Host_By_Name} and
@cite{GNAT.Sockets.Get_Host_By_Address}.
If such initialization occurs within an Ada task, and the stack size for
the task is the default size, a stack overflow may occur.

To avoid this overflow, the user should either ensure that the first call
to @cite{GNAT.Sockets.Get_Host_By_Name} or
@cite{GNAT.Sockets.Get_Host_By_Addrss}
occurs in the environment task, or use @cite{pragma Storage_Size} to
specify a sufficiently large size for the stack of the task that contains
this call.

@geindex Windows NT

@geindex Windows 95

@geindex Windows 98

@node Microsoft Windows Topics,Mac OS Topics,Specifying a Run-Time Library,Platform-Specific Information
@anchor{gnat_ugn/platform_specific_information microsoft-windows-topics}@anchor{2e}@anchor{gnat_ugn/platform_specific_information id9}@anchor{267}
@section Microsoft Windows Topics


This section describes topics that are specific to the Microsoft Windows
platforms.





@menu
* Using GNAT on Windows:: 
* Using a network installation of GNAT:: 
* CONSOLE and WINDOWS subsystems:: 
* Temporary Files:: 
* Mixed-Language Programming on Windows:: 

@end menu

@node Using GNAT on Windows,Using a network installation of GNAT,,Microsoft Windows Topics
@anchor{gnat_ugn/platform_specific_information using-gnat-on-windows}@anchor{268}@anchor{gnat_ugn/platform_specific_information id10}@anchor{269}
@subsection Using GNAT on Windows


One of the strengths of the GNAT technology is that its tool set
(@emph{gcc}, @emph{gnatbind}, @emph{gnatlink}, @emph{gnatmake}, the
@cite{gdb} debugger, etc.) is used in the same way regardless of the
platform.

On Windows this tool set is complemented by a number of Microsoft-specific
tools that have been provided to facilitate interoperability with Windows
when this is required. With these tools:


@itemize *

@item 
You can build applications using the @cite{CONSOLE} or @cite{WINDOWS}
subsystems.

@item 
You can use any Dynamically Linked Library (DLL) in your Ada code (both
relocatable and non-relocatable DLLs are supported).

@item 
You can build Ada DLLs for use in other applications. These applications
can be written in a language other than Ada (e.g., C, C++, etc). Again both
relocatable and non-relocatable Ada DLLs are supported.

@item 
You can include Windows resources in your Ada application.

@item 
You can use or create COM/DCOM objects.
@end itemize

Immediately below are listed all known general GNAT-for-Windows restrictions.
Other restrictions about specific features like Windows Resources and DLLs
are listed in separate sections below.


@itemize *

@item 
It is not possible to use @cite{GetLastError} and @cite{SetLastError}
when tasking, protected records, or exceptions are used. In these
cases, in order to implement Ada semantics, the GNAT run-time system
calls certain Win32 routines that set the last error variable to 0 upon
success. It should be possible to use @cite{GetLastError} and
@cite{SetLastError} when tasking, protected record, and exception
features are not used, but it is not guaranteed to work.

@item 
It is not possible to link against Microsoft C++ libraries except for
import libraries. Interfacing must be done by the mean of DLLs.

@item 
It is possible to link against Microsoft C libraries. Yet the preferred
solution is to use C/C++ compiler that comes with GNAT, since it
doesn't require having two different development environments and makes the
inter-language debugging experience smoother.

@item 
When the compilation environment is located on FAT32 drives, users may
experience recompilations of the source files that have not changed if
Daylight Saving Time (DST) state has changed since the last time files
were compiled. NTFS drives do not have this problem.

@item 
No components of the GNAT toolset use any entries in the Windows
registry. The only entries that can be created are file associations and
PATH settings, provided the user has chosen to create them at installation
time, as well as some minimal book-keeping information needed to correctly
uninstall or integrate different GNAT products.
@end itemize

@node Using a network installation of GNAT,CONSOLE and WINDOWS subsystems,Using GNAT on Windows,Microsoft Windows Topics
@anchor{gnat_ugn/platform_specific_information id11}@anchor{26a}@anchor{gnat_ugn/platform_specific_information using-a-network-installation-of-gnat}@anchor{26b}
@subsection Using a network installation of GNAT


Make sure the system on which GNAT is installed is accessible from the
current machine, i.e., the install location is shared over the network.
Shared resources are accessed on Windows by means of UNC paths, which
have the format @cite{\\server\sharename\path}

In order to use such a network installation, simply add the UNC path of the
@code{bin} directory of your GNAT installation in front of your PATH. For
example, if GNAT is installed in @code{\GNAT} directory of a share location
called @code{c-drive} on a machine @code{LOKI}, the following command will
make it available:

@quotation

@example
$ path \\loki\c-drive\gnat\bin;%path%`
@end example
@end quotation

Be aware that every compilation using the network installation results in the
transfer of large amounts of data across the network and will likely cause
serious performance penalty.

@node CONSOLE and WINDOWS subsystems,Temporary Files,Using a network installation of GNAT,Microsoft Windows Topics
@anchor{gnat_ugn/platform_specific_information id12}@anchor{26c}@anchor{gnat_ugn/platform_specific_information console-and-windows-subsystems}@anchor{26d}
@subsection CONSOLE and WINDOWS subsystems


@geindex CONSOLE Subsystem

@geindex WINDOWS Subsystem

@geindex -mwindows

There are two main subsystems under Windows. The @cite{CONSOLE} subsystem
(which is the default subsystem) will always create a console when
launching the application. This is not something desirable when the
application has a Windows GUI. To get rid of this console the
application must be using the @cite{WINDOWS} subsystem. To do so
the @emph{-mwindows} linker option must be specified.

@quotation

@example
$ gnatmake winprog -largs -mwindows
@end example
@end quotation

@node Temporary Files,Mixed-Language Programming on Windows,CONSOLE and WINDOWS subsystems,Microsoft Windows Topics
@anchor{gnat_ugn/platform_specific_information id13}@anchor{26e}@anchor{gnat_ugn/platform_specific_information temporary-files}@anchor{26f}
@subsection Temporary Files


@geindex Temporary files

It is possible to control where temporary files gets created by setting
the 
@geindex TMP
@geindex environment variable; TMP
@code{TMP} environment variable. The file will be created:


@itemize *

@item 
Under the directory pointed to by the 
@geindex TMP
@geindex environment variable; TMP
@code{TMP} environment variable if
this directory exists.

@item 
Under @code{c:\temp}, if the 
@geindex TMP
@geindex environment variable; TMP
@code{TMP} environment variable is not
set (or not pointing to a directory) and if this directory exists.

@item 
Under the current working directory otherwise.
@end itemize

This allows you to determine exactly where the temporary
file will be created. This is particularly useful in networked
environments where you may not have write access to some
directories.

@node Mixed-Language Programming on Windows,,Temporary Files,Microsoft Windows Topics
@anchor{gnat_ugn/platform_specific_information mixed-language-programming-on-windows}@anchor{270}@anchor{gnat_ugn/platform_specific_information id14}@anchor{271}
@subsection Mixed-Language Programming on Windows


Developing pure Ada applications on Windows is no different than on
other GNAT-supported platforms. However, when developing or porting an
application that contains a mix of Ada and C/C++, the choice of your
Windows C/C++ development environment conditions your overall
interoperability strategy.

If you use @emph{gcc} or Microsoft C to compile the non-Ada part of
your application, there are no Windows-specific restrictions that
affect the overall interoperability with your Ada code. If you do want
to use the Microsoft tools for your C++ code, you have two choices:


@itemize *

@item 
Encapsulate your C++ code in a DLL to be linked with your Ada
application. In this case, use the Microsoft or whatever environment to
build the DLL and use GNAT to build your executable
(@ref{272,,Using DLLs with GNAT}).

@item 
Or you can encapsulate your Ada code in a DLL to be linked with the
other part of your application. In this case, use GNAT to build the DLL
(@ref{273,,Building DLLs with GNAT Project files}) and use the Microsoft
or whatever environment to build your executable.
@end itemize

In addition to the description about C main in
@ref{46,,Mixed Language Programming} section, if the C main uses a
stand-alone library it is required on x86-windows to
setup the SEH context. For this the C main must looks like this:

@quotation

@example
/* main.c */
extern void adainit (void);
extern void adafinal (void);
extern void __gnat_initialize(void*);
extern void call_to_ada (void);

int main (int argc, char *argv[])
@{
  int SEH [2];

  /* Initialize the SEH context */
  __gnat_initialize (&SEH);

  adainit();

  /* Then call Ada services in the stand-alone library */

  call_to_ada();

  adafinal();
@}
@end example
@end quotation

Note that this is not needed on x86_64-windows where the Windows
native SEH support is used.

@menu
* Windows Calling Conventions:: 
* Introduction to Dynamic Link Libraries (DLLs): Introduction to Dynamic Link Libraries DLLs. 
* Using DLLs with GNAT:: 
* Building DLLs with GNAT Project files:: 
* Building DLLs with GNAT:: 
* Building DLLs with gnatdll:: 
* Ada DLLs and Finalization:: 
* Creating a Spec for Ada DLLs:: 
* GNAT and Windows Resources:: 
* Debugging a DLL:: 
* Setting Stack Size from gnatlink:: 
* Setting Heap Size from gnatlink:: 

@end menu

@node Windows Calling Conventions,Introduction to Dynamic Link Libraries DLLs,,Mixed-Language Programming on Windows
@anchor{gnat_ugn/platform_specific_information windows-calling-conventions}@anchor{274}@anchor{gnat_ugn/platform_specific_information id15}@anchor{275}
@subsubsection Windows Calling Conventions


@geindex Stdcall

@geindex APIENTRY

This section pertain only to Win32. On Win64 there is a single native
calling convention. All convention specifiers are ignored on this
platform.

When a subprogram @cite{F} (caller) calls a subprogram @cite{G}
(callee), there are several ways to push @cite{G}'s parameters on the
stack and there are several possible scenarios to clean up the stack
upon @cite{G}'s return. A calling convention is an agreed upon software
protocol whereby the responsibilities between the caller (@cite{F}) and
the callee (@cite{G}) are clearly defined. Several calling conventions
are available for Windows:


@itemize *

@item 
@cite{C} (Microsoft defined)

@item 
@cite{Stdcall} (Microsoft defined)

@item 
@cite{Win32} (GNAT specific)

@item 
@cite{DLL} (GNAT specific)
@end itemize

@menu
* C Calling Convention:: 
* Stdcall Calling Convention:: 
* Win32 Calling Convention:: 
* DLL Calling Convention:: 

@end menu

@node C Calling Convention,Stdcall Calling Convention,,Windows Calling Conventions
@anchor{gnat_ugn/platform_specific_information c-calling-convention}@anchor{276}@anchor{gnat_ugn/platform_specific_information id16}@anchor{277}
@subsubsection @cite{C} Calling Convention


This is the default calling convention used when interfacing to C/C++
routines compiled with either @emph{gcc} or Microsoft Visual C++.

In the @cite{C} calling convention subprogram parameters are pushed on the
stack by the caller from right to left. The caller itself is in charge of
cleaning up the stack after the call. In addition, the name of a routine
with @cite{C} calling convention is mangled by adding a leading underscore.

The name to use on the Ada side when importing (or exporting) a routine
with @cite{C} calling convention is the name of the routine. For
instance the C function:

@quotation

@example
int get_val (long);
@end example
@end quotation

should be imported from Ada as follows:

@quotation

@example
function Get_Val (V : Interfaces.C.long) return Interfaces.C.int;
pragma Import (C, Get_Val, External_Name => "get_val");
@end example
@end quotation

Note that in this particular case the @cite{External_Name} parameter could
have been omitted since, when missing, this parameter is taken to be the
name of the Ada entity in lower case. When the @cite{Link_Name} parameter
is missing, as in the above example, this parameter is set to be the
@cite{External_Name} with a leading underscore.

When importing a variable defined in C, you should always use the @cite{C}
calling convention unless the object containing the variable is part of a
DLL (in which case you should use the @cite{Stdcall} calling
convention, @ref{278,,Stdcall Calling Convention}).

@node Stdcall Calling Convention,Win32 Calling Convention,C Calling Convention,Windows Calling Conventions
@anchor{gnat_ugn/platform_specific_information stdcall-calling-convention}@anchor{278}@anchor{gnat_ugn/platform_specific_information id17}@anchor{279}
@subsubsection @cite{Stdcall} Calling Convention


This convention, which was the calling convention used for Pascal
programs, is used by Microsoft for all the routines in the Win32 API for
efficiency reasons. It must be used to import any routine for which this
convention was specified.

In the @cite{Stdcall} calling convention subprogram parameters are pushed
on the stack by the caller from right to left. The callee (and not the
caller) is in charge of cleaning the stack on routine exit. In addition,
the name of a routine with @cite{Stdcall} calling convention is mangled by
adding a leading underscore (as for the @cite{C} calling convention) and a
trailing @code{@@@emph{nn}}, where @cite{nn} is the overall size (in
bytes) of the parameters passed to the routine.

The name to use on the Ada side when importing a C routine with a
@cite{Stdcall} calling convention is the name of the C routine. The leading
underscore and trailing @code{@@@emph{nn}} are added automatically by
the compiler. For instance the Win32 function:

@quotation

@example
APIENTRY int get_val (long);
@end example
@end quotation

should be imported from Ada as follows:

@quotation

@example
function Get_Val (V : Interfaces.C.long) return Interfaces.C.int;
pragma Import (Stdcall, Get_Val);
--  On the x86 a long is 4 bytes, so the Link_Name is "_get_val@@4"
@end example
@end quotation

As for the @cite{C} calling convention, when the @cite{External_Name}
parameter is missing, it is taken to be the name of the Ada entity in lower
case. If instead of writing the above import pragma you write:

@quotation

@example
function Get_Val (V : Interfaces.C.long) return Interfaces.C.int;
pragma Import (Stdcall, Get_Val, External_Name => "retrieve_val");
@end example
@end quotation

then the imported routine is @cite{_retrieve_val@@4}. However, if instead
of specifying the @cite{External_Name} parameter you specify the
@cite{Link_Name} as in the following example:

@quotation

@example
function Get_Val (V : Interfaces.C.long) return Interfaces.C.int;
pragma Import (Stdcall, Get_Val, Link_Name => "retrieve_val");
@end example
@end quotation

then the imported routine is @cite{retrieve_val}, that is, there is no
decoration at all. No leading underscore and no Stdcall suffix
@code{@@@emph{nn}}.

This is especially important as in some special cases a DLL's entry
point name lacks a trailing @code{@@@emph{nn}} while the exported
name generated for a call has it.

It is also possible to import variables defined in a DLL by using an
import pragma for a variable. As an example, if a DLL contains a
variable defined as:

@quotation

@example
int my_var;
@end example
@end quotation

then, to access this variable from Ada you should write:

@quotation

@example
My_Var : Interfaces.C.int;
pragma Import (Stdcall, My_Var);
@end example
@end quotation

Note that to ease building cross-platform bindings this convention
will be handled as a @cite{C} calling convention on non-Windows platforms.

@node Win32 Calling Convention,DLL Calling Convention,Stdcall Calling Convention,Windows Calling Conventions
@anchor{gnat_ugn/platform_specific_information id18}@anchor{27a}@anchor{gnat_ugn/platform_specific_information win32-calling-convention}@anchor{27b}
@subsubsection @cite{Win32} Calling Convention


This convention, which is GNAT-specific is fully equivalent to the
@cite{Stdcall} calling convention described above.

@node DLL Calling Convention,,Win32 Calling Convention,Windows Calling Conventions
@anchor{gnat_ugn/platform_specific_information id19}@anchor{27c}@anchor{gnat_ugn/platform_specific_information dll-calling-convention}@anchor{27d}
@subsubsection @cite{DLL} Calling Convention


This convention, which is GNAT-specific is fully equivalent to the
@cite{Stdcall} calling convention described above.

@node Introduction to Dynamic Link Libraries DLLs,Using DLLs with GNAT,Windows Calling Conventions,Mixed-Language Programming on Windows
@anchor{gnat_ugn/platform_specific_information id20}@anchor{27e}@anchor{gnat_ugn/platform_specific_information introduction-to-dynamic-link-libraries-dlls}@anchor{27f}
@subsubsection Introduction to Dynamic Link Libraries (DLLs)


@geindex DLL

A Dynamically Linked Library (DLL) is a library that can be shared by
several applications running under Windows. A DLL can contain any number of
routines and variables.

One advantage of DLLs is that you can change and enhance them without
forcing all the applications that depend on them to be relinked or
recompiled. However, you should be aware than all calls to DLL routines are
slower since, as you will understand below, such calls are indirect.

To illustrate the remainder of this section, suppose that an application
wants to use the services of a DLL @code{API.dll}. To use the services
provided by @code{API.dll} you must statically link against the DLL or
an import library which contains a jump table with an entry for each
routine and variable exported by the DLL. In the Microsoft world this
import library is called @code{API.lib}. When using GNAT this import
library is called either @code{libAPI.dll.a}, @code{libapi.dll.a},
@code{libAPI.a} or @code{libapi.a} (names are case insensitive).

After you have linked your application with the DLL or the import library
and you run your application, here is what happens:


@itemize *

@item 
Your application is loaded into memory.

@item 
The DLL @code{API.dll} is mapped into the address space of your
application. This means that:


@itemize -

@item 
The DLL will use the stack of the calling thread.

@item 
The DLL will use the virtual address space of the calling process.

@item 
The DLL will allocate memory from the virtual address space of the calling
process.

@item 
Handles (pointers) can be safely exchanged between routines in the DLL
routines and routines in the application using the DLL.
@end itemize

@item 
The entries in the jump table (from the import library @code{libAPI.dll.a}
or @code{API.lib} or automatically created when linking against a DLL)
which is part of your application are initialized with the addresses
of the routines and variables in @code{API.dll}.

@item 
If present in @code{API.dll}, routines @cite{DllMain} or
@cite{DllMainCRTStartup} are invoked. These routines typically contain
the initialization code needed for the well-being of the routines and
variables exported by the DLL.
@end itemize

There is an additional point which is worth mentioning. In the Windows
world there are two kind of DLLs: relocatable and non-relocatable
DLLs. Non-relocatable DLLs can only be loaded at a very specific address
in the target application address space. If the addresses of two
non-relocatable DLLs overlap and these happen to be used by the same
application, a conflict will occur and the application will run
incorrectly. Hence, when possible, it is always preferable to use and
build relocatable DLLs. Both relocatable and non-relocatable DLLs are
supported by GNAT. Note that the @emph{-s} linker option (see GNU Linker
User's Guide) removes the debugging symbols from the DLL but the DLL can
still be relocated.

As a side note, an interesting difference between Microsoft DLLs and
Unix shared libraries, is the fact that on most Unix systems all public
routines are exported by default in a Unix shared library, while under
Windows it is possible (but not required) to list exported routines in
a definition file (see @ref{280,,The Definition File}).

@node Using DLLs with GNAT,Building DLLs with GNAT Project files,Introduction to Dynamic Link Libraries DLLs,Mixed-Language Programming on Windows
@anchor{gnat_ugn/platform_specific_information id21}@anchor{281}@anchor{gnat_ugn/platform_specific_information using-dlls-with-gnat}@anchor{272}
@subsubsection Using DLLs with GNAT


To use the services of a DLL, say @code{API.dll}, in your Ada application
you must have:


@itemize *

@item 
The Ada spec for the routines and/or variables you want to access in
@code{API.dll}. If not available this Ada spec must be built from the C/C++
header files provided with the DLL.

@item 
The import library (@code{libAPI.dll.a} or @code{API.lib}). As previously
mentioned an import library is a statically linked library containing the
import table which will be filled at load time to point to the actual
@code{API.dll} routines. Sometimes you don't have an import library for the
DLL you want to use. The following sections will explain how to build
one. Note that this is optional.

@item 
The actual DLL, @code{API.dll}.
@end itemize

Once you have all the above, to compile an Ada application that uses the
services of @code{API.dll} and whose main subprogram is @cite{My_Ada_App},
you simply issue the command

@quotation

@example
$ gnatmake my_ada_app -largs -lAPI
@end example
@end quotation

The argument @emph{-largs -lAPI} at the end of the @emph{gnatmake} command
tells the GNAT linker to look for an import library. The linker will
look for a library name in this specific order:


@itemize *

@item 
@code{libAPI.dll.a}

@item 
@code{API.dll.a}

@item 
@code{libAPI.a}

@item 
@code{API.lib}

@item 
@code{libAPI.dll}

@item 
@code{API.dll}
@end itemize

The first three are the GNU style import libraries. The third is the
Microsoft style import libraries. The last two are the actual DLL names.

Note that if the Ada package spec for @code{API.dll} contains the
following pragma

@quotation

@example
pragma Linker_Options ("-lAPI");
@end example
@end quotation

you do not have to add @emph{-largs -lAPI} at the end of the
@emph{gnatmake} command.

If any one of the items above is missing you will have to create it
yourself. The following sections explain how to do so using as an
example a fictitious DLL called @code{API.dll}.

@menu
* Creating an Ada Spec for the DLL Services:: 
* Creating an Import Library:: 

@end menu

@node Creating an Ada Spec for the DLL Services,Creating an Import Library,,Using DLLs with GNAT
@anchor{gnat_ugn/platform_specific_information creating-an-ada-spec-for-the-dll-services}@anchor{282}@anchor{gnat_ugn/platform_specific_information id22}@anchor{283}
@subsubsection Creating an Ada Spec for the DLL Services


A DLL typically comes with a C/C++ header file which provides the
definitions of the routines and variables exported by the DLL. The Ada
equivalent of this header file is a package spec that contains definitions
for the imported entities. If the DLL you intend to use does not come with
an Ada spec you have to generate one such spec yourself. For example if
the header file of @code{API.dll} is a file @code{api.h} containing the
following two definitions:

@quotation

@example
int some_var;
int get (char *);
@end example
@end quotation

then the equivalent Ada spec could be:

@quotation

@example
with Interfaces.C.Strings;
package API is
   use Interfaces;

   Some_Var : C.int;
   function Get (Str : C.Strings.Chars_Ptr) return C.int;

private
   pragma Import (C, Get);
   pragma Import (DLL, Some_Var);
end API;
@end example
@end quotation

@node Creating an Import Library,,Creating an Ada Spec for the DLL Services,Using DLLs with GNAT
@anchor{gnat_ugn/platform_specific_information id23}@anchor{284}@anchor{gnat_ugn/platform_specific_information creating-an-import-library}@anchor{285}
@subsubsection Creating an Import Library


@geindex Import library

If a Microsoft-style import library @code{API.lib} or a GNAT-style
import library @code{libAPI.dll.a} or @code{libAPI.a} is available
with @code{API.dll} you can skip this section. You can also skip this
section if @code{API.dll} or @code{libAPI.dll} is built with GNU tools
as in this case it is possible to link directly against the
DLL. Otherwise read on.

@geindex Definition file
@anchor{gnat_ugn/platform_specific_information the-definition-file}@anchor{280}
@subsubheading The Definition File


As previously mentioned, and unlike Unix systems, the list of symbols
that are exported from a DLL must be provided explicitly in Windows.
The main goal of a definition file is precisely that: list the symbols
exported by a DLL. A definition file (usually a file with a @cite{.def}
suffix) has the following structure:

@quotation

@example
[LIBRARY `name`]
[DESCRIPTION `string`]
EXPORTS
   `symbol1`
   `symbol2`
   ...
@end example
@end quotation


@table @asis

@item @emph{LIBRARY `name`}

This section, which is optional, gives the name of the DLL.

@item @emph{DESCRIPTION `string`}

This section, which is optional, gives a description string that will be
embedded in the import library.

@item @emph{EXPORTS}

This section gives the list of exported symbols (procedures, functions or
variables). For instance in the case of @code{API.dll} the @cite{EXPORTS}
section of @code{API.def} looks like:

@example
EXPORTS
   some_var
   get
@end example
@end table

Note that you must specify the correct suffix (@code{@@@emph{nn}})
(see @ref{274,,Windows Calling Conventions}) for a Stdcall
calling convention function in the exported symbols list.

There can actually be other sections in a definition file, but these
sections are not relevant to the discussion at hand.

@subsubheading GNAT-Style Import Library

@anchor{gnat_ugn/platform_specific_information gnat-style-import-library}@anchor{286}
To create a static import library from @code{API.dll} with the GNAT tools
you should proceed as follows:


@itemize *

@item 
Create the definition file @code{API.def}
(see @ref{280,,The Definition File}).
For that use the @cite{dll2def} tool as follows:

@example
$ dll2def API.dll > API.def
@end example

@cite{dll2def} is a very simple tool: it takes as input a DLL and prints
to standard output the list of entry points in the DLL. Note that if
some routines in the DLL have the @cite{Stdcall} convention
(@ref{274,,Windows Calling Conventions}) with stripped @code{@@@emph{nn}}
suffix then you'll have to edit @code{api.def} to add it, and specify
@emph{-k} to @emph{gnatdll} when creating the import library.

Here are some hints to find the right @code{@@@emph{nn}} suffix.


@itemize -

@item 
If you have the Microsoft import library (.lib), it is possible to get
the right symbols by using Microsoft @cite{dumpbin} tool (see the
corresponding Microsoft documentation for further details).

@example
$ dumpbin /exports api.lib
@end example

@item 
If you have a message about a missing symbol at link time the compiler
tells you what symbol is expected. You just have to go back to the
definition file and add the right suffix.
@end itemize

@item 
Build the import library @cite{libAPI.dll.a}, using @cite{gnatdll}
(see @ref{287,,Using gnatdll}) as follows:

@example
$ gnatdll -e API.def -d API.dll
@end example

@cite{gnatdll} takes as input a definition file @code{API.def} and the
name of the DLL containing the services listed in the definition file
@code{API.dll}. The name of the static import library generated is
computed from the name of the definition file as follows: if the
definition file name is @cite{xyz`}.def`, the import library name will
be @cite{lib`@w{`}xyz`}.a`. Note that in the previous example option
@emph{-e} could have been removed because the name of the definition
file (before the '@cite{.def}' suffix) is the same as the name of the
DLL (@ref{287,,Using gnatdll} for more information about @cite{gnatdll}).
@end itemize

@subsubheading Microsoft-Style Import Library


With GNAT you can either use a GNAT-style or Microsoft-style import
library. A Microsoft import library is needed only if you plan to make an
Ada DLL available to applications developed with Microsoft
tools (@ref{270,,Mixed-Language Programming on Windows}).

To create a Microsoft-style import library for @code{API.dll} you
should proceed as follows:


@itemize *

@item 
Create the definition file @code{API.def} from the DLL. For this use either
the @cite{dll2def} tool as described above or the Microsoft @cite{dumpbin}
tool (see the corresponding Microsoft documentation for further details).

@item 
Build the actual import library using Microsoft's @cite{lib} utility:

@example
$ lib -machine:IX86 -def:API.def -out:API.lib
@end example

If you use the above command the definition file @code{API.def} must
contain a line giving the name of the DLL:

@example
LIBRARY      "API"
@end example

See the Microsoft documentation for further details about the usage of
@cite{lib}.
@end itemize

@node Building DLLs with GNAT Project files,Building DLLs with GNAT,Using DLLs with GNAT,Mixed-Language Programming on Windows
@anchor{gnat_ugn/platform_specific_information id24}@anchor{288}@anchor{gnat_ugn/platform_specific_information building-dlls-with-gnat-project-files}@anchor{273}
@subsubsection Building DLLs with GNAT Project files


@geindex DLLs
@geindex building

There is nothing specific to Windows in the build process.
@ref{8a,,Library Projects}.

Due to a system limitation, it is not possible under Windows to create threads
when inside the @cite{DllMain} routine which is used for auto-initialization
of shared libraries, so it is not possible to have library level tasks in SALs.

@node Building DLLs with GNAT,Building DLLs with gnatdll,Building DLLs with GNAT Project files,Mixed-Language Programming on Windows
@anchor{gnat_ugn/platform_specific_information building-dlls-with-gnat}@anchor{289}@anchor{gnat_ugn/platform_specific_information id25}@anchor{28a}
@subsubsection Building DLLs with GNAT


@geindex DLLs
@geindex building

This section explain how to build DLLs using the GNAT built-in DLL
support. With the following procedure it is straight forward to build
and use DLLs with GNAT.


@itemize *

@item 
Building object files.
The first step is to build all objects files that are to be included
into the DLL. This is done by using the standard @emph{gnatmake} tool.

@item 
Building the DLL.
To build the DLL you must use @emph{gcc}'s @emph{-shared} and
@emph{-shared-libgcc} options. It is quite simple to use this method:

@example
$ gcc -shared -shared-libgcc -o api.dll obj1.o obj2.o ...
@end example

It is important to note that in this case all symbols found in the
object files are automatically exported. It is possible to restrict
the set of symbols to export by passing to @emph{gcc} a definition
file (see @ref{280,,The Definition File}).
For example:

@example
$ gcc -shared -shared-libgcc -o api.dll api.def obj1.o obj2.o ...
@end example

If you use a definition file you must export the elaboration procedures
for every package that required one. Elaboration procedures are named
using the package name followed by "_E".

@item 
Preparing DLL to be used.
For the DLL to be used by client programs the bodies must be hidden
from it and the .ali set with read-only attribute. This is very important
otherwise GNAT will recompile all packages and will not actually use
the code in the DLL. For example:

@example
$ mkdir apilib
$ copy *.ads *.ali api.dll apilib
$ attrib +R apilib\\*.ali
@end example
@end itemize

At this point it is possible to use the DLL by directly linking
against it. Note that you must use the GNAT shared runtime when using
GNAT shared libraries. This is achieved by using @emph{-shared} binder's
option.

@quotation

@example
$ gnatmake main -Iapilib -bargs -shared -largs -Lapilib -lAPI
@end example
@end quotation

@node Building DLLs with gnatdll,Ada DLLs and Finalization,Building DLLs with GNAT,Mixed-Language Programming on Windows
@anchor{gnat_ugn/platform_specific_information building-dlls-with-gnatdll}@anchor{28b}@anchor{gnat_ugn/platform_specific_information id26}@anchor{28c}
@subsubsection Building DLLs with gnatdll


@geindex DLLs
@geindex building

Note that it is preferred to use GNAT Project files
(@ref{273,,Building DLLs with GNAT Project files}) or the built-in GNAT
DLL support (@ref{289,,Building DLLs with GNAT}) or to build DLLs.

This section explains how to build DLLs containing Ada code using
@cite{gnatdll}. These DLLs will be referred to as Ada DLLs in the
remainder of this section.

The steps required to build an Ada DLL that is to be used by Ada as well as
non-Ada applications are as follows:


@itemize *

@item 
You need to mark each Ada @emph{entity} exported by the DLL with a @cite{C} or
@cite{Stdcall} calling convention to avoid any Ada name mangling for the
entities exported by the DLL
(see @ref{28d,,Exporting Ada Entities}). You can
skip this step if you plan to use the Ada DLL only from Ada applications.

@item 
Your Ada code must export an initialization routine which calls the routine
@cite{adainit} generated by @emph{gnatbind} to perform the elaboration of
the Ada code in the DLL (@ref{28e,,Ada DLLs and Elaboration}). The initialization
routine exported by the Ada DLL must be invoked by the clients of the DLL
to initialize the DLL.

@item 
When useful, the DLL should also export a finalization routine which calls
routine @cite{adafinal} generated by @emph{gnatbind} to perform the
finalization of the Ada code in the DLL (@ref{28f,,Ada DLLs and Finalization}).
The finalization routine exported by the Ada DLL must be invoked by the
clients of the DLL when the DLL services are no further needed.

@item 
You must provide a spec for the services exported by the Ada DLL in each
of the programming languages to which you plan to make the DLL available.

@item 
You must provide a definition file listing the exported entities
(@ref{280,,The Definition File}).

@item 
Finally you must use @cite{gnatdll} to produce the DLL and the import
library (@ref{287,,Using gnatdll}).
@end itemize

Note that a relocatable DLL stripped using the @cite{strip}
binutils tool will not be relocatable anymore. To build a DLL without
debug information pass @cite{-largs -s} to @cite{gnatdll}. This
restriction does not apply to a DLL built using a Library Project.
See @ref{8a,,Library Projects}.

@c Limitations_When_Using_Ada_DLLs_from Ada:

@menu
* Limitations When Using Ada DLLs from Ada:: 
* Exporting Ada Entities:: 
* Ada DLLs and Elaboration:: 

@end menu

@node Limitations When Using Ada DLLs from Ada,Exporting Ada Entities,,Building DLLs with gnatdll
@anchor{gnat_ugn/platform_specific_information limitations-when-using-ada-dlls-from-ada}@anchor{290}
@subsubsection Limitations When Using Ada DLLs from Ada


When using Ada DLLs from Ada applications there is a limitation users
should be aware of. Because on Windows the GNAT run time is not in a DLL of
its own, each Ada DLL includes a part of the GNAT run time. Specifically,
each Ada DLL includes the services of the GNAT run time that are necessary
to the Ada code inside the DLL. As a result, when an Ada program uses an
Ada DLL there are two independent GNAT run times: one in the Ada DLL and
one in the main program.

It is therefore not possible to exchange GNAT run-time objects between the
Ada DLL and the main Ada program. Example of GNAT run-time objects are file
handles (e.g., @cite{Text_IO.File_Type}), tasks types, protected objects
types, etc.

It is completely safe to exchange plain elementary, array or record types,
Windows object handles, etc.

@node Exporting Ada Entities,Ada DLLs and Elaboration,Limitations When Using Ada DLLs from Ada,Building DLLs with gnatdll
@anchor{gnat_ugn/platform_specific_information exporting-ada-entities}@anchor{28d}@anchor{gnat_ugn/platform_specific_information id27}@anchor{291}
@subsubsection Exporting Ada Entities


@geindex Export table

Building a DLL is a way to encapsulate a set of services usable from any
application. As a result, the Ada entities exported by a DLL should be
exported with the @cite{C} or @cite{Stdcall} calling conventions to avoid
any Ada name mangling. As an example here is an Ada package
@cite{API}, spec and body, exporting two procedures, a function, and a
variable:

@quotation

@example
with Interfaces.C; use Interfaces;
package API is
   Count : C.int := 0;
   function Factorial (Val : C.int) return C.int;

   procedure Initialize_API;
   procedure Finalize_API;
   --  Initialization & Finalization routines. More in the next section.
private
   pragma Export (C, Initialize_API);
   pragma Export (C, Finalize_API);
   pragma Export (C, Count);
   pragma Export (C, Factorial);
end API;
@end example

@example
package body API is
   function Factorial (Val : C.int) return C.int is
      Fact : C.int := 1;
   begin
      Count := Count + 1;
      for K in 1 .. Val loop
         Fact := Fact * K;
      end loop;
      return Fact;
   end Factorial;

   procedure Initialize_API is
      procedure Adainit;
      pragma Import (C, Adainit);
   begin
      Adainit;
   end Initialize_API;

   procedure Finalize_API is
      procedure Adafinal;
      pragma Import (C, Adafinal);
   begin
      Adafinal;
   end Finalize_API;
end API;
@end example
@end quotation

If the Ada DLL you are building will only be used by Ada applications
you do not have to export Ada entities with a @cite{C} or @cite{Stdcall}
convention. As an example, the previous package could be written as
follows:

@quotation

@example
package API is
   Count : Integer := 0;
   function Factorial (Val : Integer) return Integer;

   procedure Initialize_API;
   procedure Finalize_API;
   --  Initialization and Finalization routines.
end API;
@end example

@example
package body API is
   function Factorial (Val : Integer) return Integer is
      Fact : Integer := 1;
   begin
      Count := Count + 1;
      for K in 1 .. Val loop
         Fact := Fact * K;
      end loop;
      return Fact;
   end Factorial;

   ...
   --  The remainder of this package body is unchanged.
end API;
@end example
@end quotation

Note that if you do not export the Ada entities with a @cite{C} or
@cite{Stdcall} convention you will have to provide the mangled Ada names
in the definition file of the Ada DLL
(@ref{292,,Creating the Definition File}).

@node Ada DLLs and Elaboration,,Exporting Ada Entities,Building DLLs with gnatdll
@anchor{gnat_ugn/platform_specific_information ada-dlls-and-elaboration}@anchor{28e}@anchor{gnat_ugn/platform_specific_information id28}@anchor{293}
@subsubsection Ada DLLs and Elaboration


@geindex DLLs and elaboration

The DLL that you are building contains your Ada code as well as all the
routines in the Ada library that are needed by it. The first thing a
user of your DLL must do is elaborate the Ada code
(@ref{11,,Elaboration Order Handling in GNAT}).

To achieve this you must export an initialization routine
(@cite{Initialize_API} in the previous example), which must be invoked
before using any of the DLL services. This elaboration routine must call
the Ada elaboration routine @cite{adainit} generated by the GNAT binder
(@ref{ba,,Binding with Non-Ada Main Programs}). See the body of
@cite{Initialize_Api} for an example. Note that the GNAT binder is
automatically invoked during the DLL build process by the @cite{gnatdll}
tool (@ref{287,,Using gnatdll}).

When a DLL is loaded, Windows systematically invokes a routine called
@cite{DllMain}. It would therefore be possible to call @cite{adainit}
directly from @cite{DllMain} without having to provide an explicit
initialization routine. Unfortunately, it is not possible to call
@cite{adainit} from the @cite{DllMain} if your program has library level
tasks because access to the @cite{DllMain} entry point is serialized by
the system (that is, only a single thread can execute 'through' it at a
time), which means that the GNAT run time will deadlock waiting for the
newly created task to complete its initialization.

@node Ada DLLs and Finalization,Creating a Spec for Ada DLLs,Building DLLs with gnatdll,Mixed-Language Programming on Windows
@anchor{gnat_ugn/platform_specific_information id29}@anchor{294}@anchor{gnat_ugn/platform_specific_information ada-dlls-and-finalization}@anchor{28f}
@subsubsection Ada DLLs and Finalization


@geindex DLLs and finalization

When the services of an Ada DLL are no longer needed, the client code should
invoke the DLL finalization routine, if available. The DLL finalization
routine is in charge of releasing all resources acquired by the DLL. In the
case of the Ada code contained in the DLL, this is achieved by calling
routine @cite{adafinal} generated by the GNAT binder
(@ref{ba,,Binding with Non-Ada Main Programs}).
See the body of @cite{Finalize_Api} for an
example. As already pointed out the GNAT binder is automatically invoked
during the DLL build process by the @cite{gnatdll} tool
(@ref{287,,Using gnatdll}).

@node Creating a Spec for Ada DLLs,GNAT and Windows Resources,Ada DLLs and Finalization,Mixed-Language Programming on Windows
@anchor{gnat_ugn/platform_specific_information id30}@anchor{295}@anchor{gnat_ugn/platform_specific_information creating-a-spec-for-ada-dlls}@anchor{296}
@subsubsection Creating a Spec for Ada DLLs


To use the services exported by the Ada DLL from another programming
language (e.g., C), you have to translate the specs of the exported Ada
entities in that language. For instance in the case of @cite{API.dll},
the corresponding C header file could look like:

@quotation

@example
extern int *_imp__count;
#define count (*_imp__count)
int factorial (int);
@end example
@end quotation

It is important to understand that when building an Ada DLL to be used by
other Ada applications, you need two different specs for the packages
contained in the DLL: one for building the DLL and the other for using
the DLL. This is because the @cite{DLL} calling convention is needed to
use a variable defined in a DLL, but when building the DLL, the variable
must have either the @cite{Ada} or @cite{C} calling convention. As an
example consider a DLL comprising the following package @cite{API}:

@quotation

@example
package API is
   Count : Integer := 0;
   ...
   --  Remainder of the package omitted.
end API;
@end example
@end quotation

After producing a DLL containing package @cite{API}, the spec that
must be used to import @cite{API.Count} from Ada code outside of the
DLL is:

@quotation

@example
package API is
   Count : Integer;
   pragma Import (DLL, Count);
end API;
@end example
@end quotation

@menu
* Creating the Definition File:: 
* Using gnatdll:: 

@end menu

@node Creating the Definition File,Using gnatdll,,Creating a Spec for Ada DLLs
@anchor{gnat_ugn/platform_specific_information creating-the-definition-file}@anchor{292}@anchor{gnat_ugn/platform_specific_information id31}@anchor{297}
@subsubsection Creating the Definition File


The definition file is the last file needed to build the DLL. It lists
the exported symbols. As an example, the definition file for a DLL
containing only package @cite{API} (where all the entities are exported
with a @cite{C} calling convention) is:

@quotation

@example
EXPORTS
    count
    factorial
    finalize_api
    initialize_api
@end example
@end quotation

If the @cite{C} calling convention is missing from package @cite{API},
then the definition file contains the mangled Ada names of the above
entities, which in this case are:

@quotation

@example
EXPORTS
    api__count
    api__factorial
    api__finalize_api
    api__initialize_api
@end example
@end quotation

@node Using gnatdll,,Creating the Definition File,Creating a Spec for Ada DLLs
@anchor{gnat_ugn/platform_specific_information using-gnatdll}@anchor{287}@anchor{gnat_ugn/platform_specific_information id32}@anchor{298}
@subsubsection Using @cite{gnatdll}


@geindex gnatdll

@cite{gnatdll} is a tool to automate the DLL build process once all the Ada
and non-Ada sources that make up your DLL have been compiled.
@cite{gnatdll} is actually in charge of two distinct tasks: build the
static import library for the DLL and the actual DLL. The form of the
@cite{gnatdll} command is

@quotation

@example
$ gnatdll [`switches`] `list-of-files` [-largs `opts`]
@end example
@end quotation

where @cite{list-of-files} is a list of ALI and object files. The object
file list must be the exact list of objects corresponding to the non-Ada
sources whose services are to be included in the DLL. The ALI file list
must be the exact list of ALI files for the corresponding Ada sources
whose services are to be included in the DLL. If @cite{list-of-files} is
missing, only the static import library is generated.

You may specify any of the following switches to @cite{gnatdll}:

@quotation

@geindex -a (gnatdll)
@end quotation


@table @asis

@item @code{-a[@emph{address}]}

Build a non-relocatable DLL at @cite{address}. If @cite{address} is not
specified the default address @cite{0x11000000} will be used. By default,
when this switch is missing, @cite{gnatdll} builds relocatable DLL. We
advise the reader to build relocatable DLL.

@geindex -b (gnatdll)

@item @code{-b @emph{address}}

Set the relocatable DLL base address. By default the address is
@cite{0x11000000}.

@geindex -bargs (gnatdll)

@item @code{-bargs @emph{opts}}

Binder options. Pass @cite{opts} to the binder.

@geindex -d (gnatdll)

@item @code{-d @emph{dllfile}}

@cite{dllfile} is the name of the DLL. This switch must be present for
@cite{gnatdll} to do anything. The name of the generated import library is
obtained algorithmically from @cite{dllfile} as shown in the following
example: if @cite{dllfile} is @cite{xyz.dll}, the import library name is
@cite{libxyz.dll.a}. The name of the definition file to use (if not specified
by option @emph{-e}) is obtained algorithmically from @cite{dllfile}
as shown in the following example:
if @cite{dllfile} is @cite{xyz.dll}, the definition
file used is @cite{xyz.def}.

@geindex -e (gnatdll)

@item @code{-e @emph{deffile}}

@cite{deffile} is the name of the definition file.

@geindex -g (gnatdll)

@item @code{-g}

Generate debugging information. This information is stored in the object
file and copied from there to the final DLL file by the linker,
where it can be read by the debugger. You must use the
@emph{-g} switch if you plan on using the debugger or the symbolic
stack traceback.

@geindex -h (gnatdll)

@item @code{-h}

Help mode. Displays @cite{gnatdll} switch usage information.

@geindex -I (gnatdll)

@item @code{-I@emph{dir}}

Direct @cite{gnatdll} to search the @cite{dir} directory for source and
object files needed to build the DLL.
(@ref{8e,,Search Paths and the Run-Time Library (RTL)}).

@geindex -k (gnatdll)

@item @code{-k}

Removes the @code{@@@emph{nn}} suffix from the import library's exported
names, but keeps them for the link names. You must specify this
option if you want to use a @cite{Stdcall} function in a DLL for which
the @code{@@@emph{nn}} suffix has been removed. This is the case for most
of the Windows NT DLL for example. This option has no effect when
@emph{-n} option is specified.

@geindex -l (gnatdll)

@item @code{-l @emph{file}}

The list of ALI and object files used to build the DLL are listed in
@cite{file}, instead of being given in the command line. Each line in
@cite{file} contains the name of an ALI or object file.

@geindex -n (gnatdll)

@item @code{-n}

No Import. Do not create the import library.

@geindex -q (gnatdll)

@item @code{-q}

Quiet mode. Do not display unnecessary messages.

@geindex -v (gnatdll)

@item @code{-v}

Verbose mode. Display extra information.

@geindex -largs (gnatdll)

@item @code{-largs @emph{opts}}

Linker options. Pass @cite{opts} to the linker.
@end table

@subsubheading @cite{gnatdll} Example


As an example the command to build a relocatable DLL from @code{api.adb}
once @code{api.adb} has been compiled and @code{api.def} created is

@quotation

@example
$ gnatdll -d api.dll api.ali
@end example
@end quotation

The above command creates two files: @code{libapi.dll.a} (the import
library) and @code{api.dll} (the actual DLL). If you want to create
only the DLL, just type:

@quotation

@example
$ gnatdll -d api.dll -n api.ali
@end example
@end quotation

Alternatively if you want to create just the import library, type:

@quotation

@example
$ gnatdll -d api.dll
@end example
@end quotation

@subsubheading @cite{gnatdll} behind the Scenes


This section details the steps involved in creating a DLL. @cite{gnatdll}
does these steps for you. Unless you are interested in understanding what
goes on behind the scenes, you should skip this section.

We use the previous example of a DLL containing the Ada package @cite{API},
to illustrate the steps necessary to build a DLL. The starting point is a
set of objects that will make up the DLL and the corresponding ALI
files. In the case of this example this means that @code{api.o} and
@code{api.ali} are available. To build a relocatable DLL, @cite{gnatdll} does
the following:


@itemize *

@item 
@cite{gnatdll} builds the base file (@code{api.base}). A base file gives
the information necessary to generate relocation information for the
DLL.

@example
$ gnatbind -n api
$ gnatlink api -o api.jnk -mdll -Wl,--base-file,api.base
@end example

In addition to the base file, the @emph{gnatlink} command generates an
output file @code{api.jnk} which can be discarded. The @emph{-mdll} switch
asks @emph{gnatlink} to generate the routines @cite{DllMain} and
@cite{DllMainCRTStartup} that are called by the Windows loader when the DLL
is loaded into memory.

@item 
@cite{gnatdll} uses @cite{dlltool} (see @ref{299,,Using dlltool}) to build the
export table (@code{api.exp}). The export table contains the relocation
information in a form which can be used during the final link to ensure
that the Windows loader is able to place the DLL anywhere in memory.

@example
$ dlltool --dllname api.dll --def api.def --base-file api.base \\
          --output-exp api.exp
@end example

@item 
@cite{gnatdll} builds the base file using the new export table. Note that
@emph{gnatbind} must be called once again since the binder generated file
has been deleted during the previous call to @emph{gnatlink}.

@example
$ gnatbind -n api
$ gnatlink api -o api.jnk api.exp -mdll
      -Wl,--base-file,api.base
@end example

@item 
@cite{gnatdll} builds the new export table using the new base file and
generates the DLL import library @code{libAPI.dll.a}.

@example
$ dlltool --dllname api.dll --def api.def --base-file api.base \\
          --output-exp api.exp --output-lib libAPI.a
@end example

@item 
Finally @cite{gnatdll} builds the relocatable DLL using the final export
table.

@example
$ gnatbind -n api
$ gnatlink api api.exp -o api.dll -mdll
@end example
@end itemize
@anchor{gnat_ugn/platform_specific_information using-dlltool}@anchor{299}
@subsubheading Using @cite{dlltool}


@cite{dlltool} is the low-level tool used by @cite{gnatdll} to build
DLLs and static import libraries. This section summarizes the most
common @cite{dlltool} switches. The form of the @cite{dlltool} command
is

@quotation

@example
$ dlltool [`switches`]
@end example
@end quotation

@cite{dlltool} switches include:

@geindex --base-file (dlltool)


@table @asis

@item @code{--base-file @emph{basefile}}

Read the base file @cite{basefile} generated by the linker. This switch
is used to create a relocatable DLL.
@end table

@geindex --def (dlltool)


@table @asis

@item @code{--def @emph{deffile}}

Read the definition file.
@end table

@geindex --dllname (dlltool)


@table @asis

@item @code{--dllname @emph{name}}

Gives the name of the DLL. This switch is used to embed the name of the
DLL in the static import library generated by @cite{dlltool} with switch
@emph{--output-lib}.
@end table

@geindex -k (dlltool)


@table @asis

@item @code{-k}

Kill @code{@@@emph{nn}} from exported names
(@ref{274,,Windows Calling Conventions}
for a discussion about @cite{Stdcall}-style symbols.
@end table

@geindex --help (dlltool)


@table @asis

@item @code{--help}

Prints the @cite{dlltool} switches with a concise description.
@end table

@geindex --output-exp (dlltool)


@table @asis

@item @code{--output-exp @emph{exportfile}}

Generate an export file @cite{exportfile}. The export file contains the
export table (list of symbols in the DLL) and is used to create the DLL.
@end table

@geindex --output-lib (dlltool)


@table @asis

@item @code{--output-lib @emph{libfile}}

Generate a static import library @cite{libfile}.
@end table

@geindex -v (dlltool)


@table @asis

@item @code{-v}

Verbose mode.
@end table

@geindex --as (dlltool)


@table @asis

@item @code{--as @emph{assembler-name}}

Use @cite{assembler-name} as the assembler. The default is @cite{as}.
@end table

@node GNAT and Windows Resources,Debugging a DLL,Creating a Spec for Ada DLLs,Mixed-Language Programming on Windows
@anchor{gnat_ugn/platform_specific_information gnat-and-windows-resources}@anchor{29a}@anchor{gnat_ugn/platform_specific_information id33}@anchor{29b}
@subsubsection GNAT and Windows Resources


@geindex Resources
@geindex windows

Resources are an easy way to add Windows specific objects to your
application. The objects that can be added as resources include:


@itemize *

@item 
menus

@item 
accelerators

@item 
dialog boxes

@item 
string tables

@item 
bitmaps

@item 
cursors

@item 
icons

@item 
fonts

@item 
version information
@end itemize

For example, a version information resource can be defined as follow and
embedded into an executable or DLL:

A version information resource can be used to embed information into an
executable or a DLL. These information can be viewed using the file properties
from the Windows Explorer. Here is an example of a version information
resource:

@quotation

@example
1 VERSIONINFO
FILEVERSION     1,0,0,0
PRODUCTVERSION  1,0,0,0
BEGIN
  BLOCK "StringFileInfo"
  BEGIN
    BLOCK "080904E4"
    BEGIN
      VALUE "CompanyName", "My Company Name"
      VALUE "FileDescription", "My application"
      VALUE "FileVersion", "1.0"
      VALUE "InternalName", "my_app"
      VALUE "LegalCopyright", "My Name"
      VALUE "OriginalFilename", "my_app.exe"
      VALUE "ProductName", "My App"
      VALUE "ProductVersion", "1.0"
    END
  END

  BLOCK "VarFileInfo"
  BEGIN
    VALUE "Translation", 0x809, 1252
  END
END
@end example
@end quotation

The value @cite{0809} (langID) is for the U.K English language and
@cite{04E4} (charsetID), which is equal to @cite{1252} decimal, for
multilingual.

This section explains how to build, compile and use resources. Note that this
section does not cover all resource objects, for a complete description see
the corresponding Microsoft documentation.

@menu
* Building Resources:: 
* Compiling Resources:: 
* Using Resources:: 

@end menu

@node Building Resources,Compiling Resources,,GNAT and Windows Resources
@anchor{gnat_ugn/platform_specific_information building-resources}@anchor{29c}@anchor{gnat_ugn/platform_specific_information id34}@anchor{29d}
@subsubsection Building Resources


@geindex Resources
@geindex building

A resource file is an ASCII file. By convention resource files have an
@code{.rc} extension.
The easiest way to build a resource file is to use Microsoft tools
such as @cite{imagedit.exe} to build bitmaps, icons and cursors and
@cite{dlgedit.exe} to build dialogs.
It is always possible to build an @code{.rc} file yourself by writing a
resource script.

It is not our objective to explain how to write a resource file. A
complete description of the resource script language can be found in the
Microsoft documentation.

@node Compiling Resources,Using Resources,Building Resources,GNAT and Windows Resources
@anchor{gnat_ugn/platform_specific_information compiling-resources}@anchor{29e}@anchor{gnat_ugn/platform_specific_information id35}@anchor{29f}
@subsubsection Compiling Resources


@geindex rc

@geindex windres

@geindex Resources
@geindex compiling

This section describes how to build a GNAT-compatible (COFF) object file
containing the resources. This is done using the Resource Compiler
@cite{windres} as follows:

@quotation

@example
$ windres -i myres.rc -o myres.o
@end example
@end quotation

By default @cite{windres} will run @emph{gcc} to preprocess the @code{.rc}
file. You can specify an alternate preprocessor (usually named
@code{cpp.exe}) using the @cite{windres} @emph{--preprocessor}
parameter. A list of all possible options may be obtained by entering
the command @cite{windres} @emph{--help}.

It is also possible to use the Microsoft resource compiler @cite{rc.exe}
to produce a @code{.res} file (binary resource file). See the
corresponding Microsoft documentation for further details. In this case
you need to use @cite{windres} to translate the @code{.res} file to a
GNAT-compatible object file as follows:

@quotation

@example
$ windres -i myres.res -o myres.o
@end example
@end quotation

@node Using Resources,,Compiling Resources,GNAT and Windows Resources
@anchor{gnat_ugn/platform_specific_information id36}@anchor{2a0}@anchor{gnat_ugn/platform_specific_information using-resources}@anchor{2a1}
@subsubsection Using Resources


@geindex Resources
@geindex using

To include the resource file in your program just add the
GNAT-compatible object file for the resource(s) to the linker
arguments. With @emph{gnatmake} this is done by using the @emph{-largs}
option:

@quotation

@example
$ gnatmake myprog -largs myres.o
@end example
@end quotation

@node Debugging a DLL,Setting Stack Size from gnatlink,GNAT and Windows Resources,Mixed-Language Programming on Windows
@anchor{gnat_ugn/platform_specific_information id37}@anchor{2a2}@anchor{gnat_ugn/platform_specific_information debugging-a-dll}@anchor{2a3}
@subsubsection Debugging a DLL


@geindex DLL debugging

Debugging a DLL is similar to debugging a standard program. But
we have to deal with two different executable parts: the DLL and the
program that uses it. We have the following four possibilities:


@itemize *

@item 
The program and the DLL are built with @cite{GCC/GNAT}.

@item 
The program is built with foreign tools and the DLL is built with
@cite{GCC/GNAT}.

@item 
The program is built with @cite{GCC/GNAT} and the DLL is built with
foreign tools.
@end itemize

In this section we address only cases one and two above.
There is no point in trying to debug
a DLL with @cite{GNU/GDB}, if there is no GDB-compatible debugging
information in it. To do so you must use a debugger compatible with the
tools suite used to build the DLL.

@menu
* Program and DLL Both Built with GCC/GNAT:: 
* Program Built with Foreign Tools and DLL Built with GCC/GNAT:: 

@end menu

@node Program and DLL Both Built with GCC/GNAT,Program Built with Foreign Tools and DLL Built with GCC/GNAT,,Debugging a DLL
@anchor{gnat_ugn/platform_specific_information program-and-dll-both-built-with-gcc-gnat}@anchor{2a4}@anchor{gnat_ugn/platform_specific_information id38}@anchor{2a5}
@subsubsection Program and DLL Both Built with GCC/GNAT


This is the simplest case. Both the DLL and the program have @cite{GDB}
compatible debugging information. It is then possible to break anywhere in
the process. Let's suppose here that the main procedure is named
@cite{ada_main} and that in the DLL there is an entry point named
@cite{ada_dll}.

The DLL (@ref{27f,,Introduction to Dynamic Link Libraries (DLLs)}) and
program must have been built with the debugging information (see GNAT -g
switch). Here are the step-by-step instructions for debugging it:


@itemize *

@item 
Launch @cite{GDB} on the main program.

@example
$ gdb -nw ada_main
@end example

@item 
Start the program and stop at the beginning of the main procedure

@example
(gdb) start
@end example

This step is required to be able to set a breakpoint inside the DLL. As long
as the program is not run, the DLL is not loaded. This has the
consequence that the DLL debugging information is also not loaded, so it is not
possible to set a breakpoint in the DLL.

@item 
Set a breakpoint inside the DLL

@example
(gdb) break ada_dll
(gdb) cont
@end example
@end itemize

At this stage a breakpoint is set inside the DLL. From there on
you can use the standard approach to debug the whole program
(@ref{26,,Running and Debugging Ada Programs}).

@node Program Built with Foreign Tools and DLL Built with GCC/GNAT,,Program and DLL Both Built with GCC/GNAT,Debugging a DLL
@anchor{gnat_ugn/platform_specific_information program-built-with-foreign-tools-and-dll-built-with-gcc-gnat}@anchor{2a6}@anchor{gnat_ugn/platform_specific_information id39}@anchor{2a7}
@subsubsection Program Built with Foreign Tools and DLL Built with GCC/GNAT


In this case things are slightly more complex because it is not possible to
start the main program and then break at the beginning to load the DLL and the
associated DLL debugging information. It is not possible to break at the
beginning of the program because there is no @cite{GDB} debugging information,
and therefore there is no direct way of getting initial control. This
section addresses this issue by describing some methods that can be used
to break somewhere in the DLL to debug it.

First suppose that the main procedure is named @cite{main} (this is for
example some C code built with Microsoft Visual C) and that there is a
DLL named @cite{test.dll} containing an Ada entry point named
@cite{ada_dll}.

The DLL (see @ref{27f,,Introduction to Dynamic Link Libraries (DLLs)}) must have
been built with debugging information (see GNAT @cite{-g} option).

@subsubheading Debugging the DLL Directly



@itemize *

@item 
Find out the executable starting address

@example
$ objdump --file-header main.exe
@end example

The starting address is reported on the last line. For example:

@example
main.exe:     file format pei-i386
architecture: i386, flags 0x0000010a:
EXEC_P, HAS_DEBUG, D_PAGED
start address 0x00401010
@end example

@item 
Launch the debugger on the executable.

@example
$ gdb main.exe
@end example

@item 
Set a breakpoint at the starting address, and launch the program.

@example
$ (gdb) break *0x00401010
$ (gdb) run
@end example

The program will stop at the given address.

@item 
Set a breakpoint on a DLL subroutine.

@example
(gdb) break ada_dll.adb:45
@end example

Or if you want to break using a symbol on the DLL, you need first to
select the Ada language (language used by the DLL).

@example
(gdb) set language ada
(gdb) break ada_dll
@end example

@item 
Continue the program.

@example
(gdb) cont
@end example

This will run the program until it reaches the breakpoint that has been
set. From that point you can use the standard way to debug a program
as described in (@ref{26,,Running and Debugging Ada Programs}).
@end itemize

It is also possible to debug the DLL by attaching to a running process.

@subsubheading Attaching to a Running Process


@geindex DLL debugging
@geindex attach to process

With @cite{GDB} it is always possible to debug a running process by
attaching to it. It is possible to debug a DLL this way. The limitation
of this approach is that the DLL must run long enough to perform the
attach operation. It may be useful for instance to insert a time wasting
loop in the code of the DLL to meet this criterion.


@itemize *

@item 
Launch the main program @code{main.exe}.

@example
$ main
@end example

@item 
Use the Windows @emph{Task Manager} to find the process ID. Let's say
that the process PID for @code{main.exe} is 208.

@item 
Launch gdb.

@example
$ gdb
@end example

@item 
Attach to the running process to be debugged.

@example
(gdb) attach 208
@end example

@item 
Load the process debugging information.

@example
(gdb) symbol-file main.exe
@end example

@item 
Break somewhere in the DLL.

@example
(gdb) break ada_dll
@end example

@item 
Continue process execution.

@example
(gdb) cont
@end example
@end itemize

This last step will resume the process execution, and stop at
the breakpoint we have set. From there you can use the standard
approach to debug a program as described in
@ref{26,,Running and Debugging Ada Programs}.

@node Setting Stack Size from gnatlink,Setting Heap Size from gnatlink,Debugging a DLL,Mixed-Language Programming on Windows
@anchor{gnat_ugn/platform_specific_information setting-stack-size-from-gnatlink}@anchor{13a}@anchor{gnat_ugn/platform_specific_information id40}@anchor{2a8}
@subsubsection Setting Stack Size from @emph{gnatlink}


It is possible to specify the program stack size at link time. On modern
versions of Windows, starting with XP, this is mostly useful to set the size of
the main stack (environment task). The other task stacks are set with pragma
Storage_Size or with the @emph{gnatbind -d} command.

Since older versions of Windows (2000, NT4, etc.) do not allow setting the
reserve size of individual tasks, the link-time stack size applies to all
tasks, and pragma Storage_Size has no effect.
In particular, Stack Overflow checks are made against this
link-time specified size.

This setting can be done with @emph{gnatlink} using either of the following:


@itemize *

@item 
@emph{-Xlinker} linker option

@example
$ gnatlink hello -Xlinker --stack=0x10000,0x1000
@end example

This sets the stack reserve size to 0x10000 bytes and the stack commit
size to 0x1000 bytes.

@item 
@emph{-Wl} linker option

@example
$ gnatlink hello -Wl,--stack=0x1000000
@end example

This sets the stack reserve size to 0x1000000 bytes. Note that with
@emph{-Wl} option it is not possible to set the stack commit size
because the coma is a separator for this option.
@end itemize

@node Setting Heap Size from gnatlink,,Setting Stack Size from gnatlink,Mixed-Language Programming on Windows
@anchor{gnat_ugn/platform_specific_information setting-heap-size-from-gnatlink}@anchor{13b}@anchor{gnat_ugn/platform_specific_information id41}@anchor{2a9}
@subsubsection Setting Heap Size from @emph{gnatlink}


Under Windows systems, it is possible to specify the program heap size from
@emph{gnatlink} using either of the following:


@itemize *

@item 
@emph{-Xlinker} linker option

@example
$ gnatlink hello -Xlinker --heap=0x10000,0x1000
@end example

This sets the heap reserve size to 0x10000 bytes and the heap commit
size to 0x1000 bytes.

@item 
@emph{-Wl} linker option

@example
$ gnatlink hello -Wl,--heap=0x1000000
@end example

This sets the heap reserve size to 0x1000000 bytes. Note that with
@emph{-Wl} option it is not possible to set the heap commit size
because the coma is a separator for this option.
@end itemize

@node Mac OS Topics,,Microsoft Windows Topics,Platform-Specific Information
@anchor{gnat_ugn/platform_specific_information mac-os-topics}@anchor{2f}@anchor{gnat_ugn/platform_specific_information id42}@anchor{2aa}
@section Mac OS Topics


@geindex OS X

This section describes topics that are specific to Apple's OS X
platform.

@menu
* Codesigning the Debugger:: 

@end menu

@node Codesigning the Debugger,,,Mac OS Topics
@anchor{gnat_ugn/platform_specific_information codesigning-the-debugger}@anchor{2ab}
@subsection Codesigning the Debugger


The Darwin Kernel requires the debugger to have special permissions
before it is allowed to control other processes. These permissions
are granted by codesigning the GDB executable. Without these
permissions, the debugger will report error messages such as:

@example
Starting program: /x/y/foo
Unable to find Mach task port for process-id 28885: (os/kern) failure (0x5).
(please check gdb is codesigned - see taskgated(8))
@end example

Codesigning requires a certificate.  The following procedure explains
how to create one:


@itemize *

@item 
Start the Keychain Access application (in
/Applications/Utilities/Keychain Access.app)

@item 
Select the Keychain Access -> Certificate Assistant ->
Create a Certificate... menu

@item 
Then:


@itemize *

@item 
Choose a name for the new certificate (this procedure will use
"gdb-cert" as an example)

@item 
Set "Identity Type" to "Self Signed Root"

@item 
Set "Certificate Type" to "Code Signing"

@item 
Activate the "Let me override defaults" option
@end itemize

@item 
Click several times on "Continue" until the "Specify a Location
For The Certificate" screen appears, then set "Keychain" to "System"

@item 
Click on "Continue" until the certificate is created

@item 
Finally, in the view, double-click on the new certificate,
and set "When using this certificate" to "Always Trust"

@item 
Exit the Keychain Access application and restart the computer
(this is unfortunately required)
@end itemize

Once a certificate has been created, the debugger can be codesigned
as follow. In a Terminal, run the following command:

@quotation

@example
$ codesign -f -s  "gdb-cert"  <gnat_install_prefix>/bin/gdb
@end example
@end quotation

where "gdb-cert" should be replaced by the actual certificate
name chosen above, and <gnat_install_prefix> should be replaced by
the location where you installed GNAT.  Also, be sure that users are
in the Unix group @code{_developer}.

@node Example of Binder Output File,Elaboration Order Handling in GNAT,Platform-Specific Information,Top
@anchor{gnat_ugn/example_of_binder_output example-of-binder-output-file}@anchor{10}@anchor{gnat_ugn/example_of_binder_output doc}@anchor{2ac}@anchor{gnat_ugn/example_of_binder_output id1}@anchor{2ad}
@chapter Example of Binder Output File


@geindex Binder output (example)

This Appendix displays the source code for the output file
generated by @emph{gnatbind} for a simple 'Hello World' program.
Comments have been added for clarification purposes.

@example
--  The package is called Ada_Main unless this name is actually used
--  as a unit name in the partition, in which case some other unique
--  name is used.

pragma Ada_95;
with System;
package ada_main is
   pragma Warnings (Off);

   --  The main program saves the parameters (argument count,
   --  argument values, environment pointer) in global variables
   --  for later access by other units including
   --  Ada.Command_Line.

   gnat_argc : Integer;
   gnat_argv : System.Address;
   gnat_envp : System.Address;

   --  The actual variables are stored in a library routine. This
   --  is useful for some shared library situations, where there
   --  are problems if variables are not in the library.

   pragma Import (C, gnat_argc);
   pragma Import (C, gnat_argv);
   pragma Import (C, gnat_envp);

   --  The exit status is similarly an external location

   gnat_exit_status : Integer;
   pragma Import (C, gnat_exit_status);

   GNAT_Version : constant String :=
                    "GNAT Version: Pro 7.4.0w (20141119-49)" & ASCII.NUL;
   pragma Export (C, GNAT_Version, "__gnat_version");

   Ada_Main_Program_Name : constant String := "_ada_hello" & ASCII.NUL;
   pragma Export (C, Ada_Main_Program_Name, "__gnat_ada_main_program_name");

   --  This is the generated adainit routine that performs
   --  initialization at the start of execution. In the case
   --  where Ada is the main program, this main program makes
   --  a call to adainit at program startup.

   procedure adainit;
   pragma Export (C, adainit, "adainit");

   --  This is the generated adafinal routine that performs
   --  finalization at the end of execution. In the case where
   --  Ada is the main program, this main program makes a call
   --  to adafinal at program termination.

   procedure adafinal;
   pragma Export (C, adafinal, "adafinal");

   --  This routine is called at the start of execution. It is
   --  a dummy routine that is used by the debugger to breakpoint
   --  at the start of execution.

   --  This is the actual generated main program (it would be
   --  suppressed if the no main program switch were used). As
   --  required by standard system conventions, this program has
   --  the external name main.

   function main
     (argc : Integer;
      argv : System.Address;
      envp : System.Address)
      return Integer;
   pragma Export (C, main, "main");

   --  The following set of constants give the version
   --  identification values for every unit in the bound
   --  partition. This identification is computed from all
   --  dependent semantic units, and corresponds to the
   --  string that would be returned by use of the
   --  Body_Version or Version attributes.

   --  The following Export pragmas export the version numbers
   --  with symbolic names ending in B (for body) or S
   --  (for spec) so that they can be located in a link. The
   --  information provided here is sufficient to track down
   --  the exact versions of units used in a given build.

   type Version_32 is mod 2 ** 32;
   u00001 : constant Version_32 := 16#8ad6e54a#;
   pragma Export (C, u00001, "helloB");
   u00002 : constant Version_32 := 16#fbff4c67#;
   pragma Export (C, u00002, "system__standard_libraryB");
   u00003 : constant Version_32 := 16#1ec6fd90#;
   pragma Export (C, u00003, "system__standard_libraryS");
   u00004 : constant Version_32 := 16#3ffc8e18#;
   pragma Export (C, u00004, "adaS");
   u00005 : constant Version_32 := 16#28f088c2#;
   pragma Export (C, u00005, "ada__text_ioB");
   u00006 : constant Version_32 := 16#f372c8ac#;
   pragma Export (C, u00006, "ada__text_ioS");
   u00007 : constant Version_32 := 16#2c143749#;
   pragma Export (C, u00007, "ada__exceptionsB");
   u00008 : constant Version_32 := 16#f4f0cce8#;
   pragma Export (C, u00008, "ada__exceptionsS");
   u00009 : constant Version_32 := 16#a46739c0#;
   pragma Export (C, u00009, "ada__exceptions__last_chance_handlerB");
   u00010 : constant Version_32 := 16#3aac8c92#;
   pragma Export (C, u00010, "ada__exceptions__last_chance_handlerS");
   u00011 : constant Version_32 := 16#1d274481#;
   pragma Export (C, u00011, "systemS");
   u00012 : constant Version_32 := 16#a207fefe#;
   pragma Export (C, u00012, "system__soft_linksB");
   u00013 : constant Version_32 := 16#467d9556#;
   pragma Export (C, u00013, "system__soft_linksS");
   u00014 : constant Version_32 := 16#b01dad17#;
   pragma Export (C, u00014, "system__parametersB");
   u00015 : constant Version_32 := 16#630d49fe#;
   pragma Export (C, u00015, "system__parametersS");
   u00016 : constant Version_32 := 16#b19b6653#;
   pragma Export (C, u00016, "system__secondary_stackB");
   u00017 : constant Version_32 := 16#b6468be8#;
   pragma Export (C, u00017, "system__secondary_stackS");
   u00018 : constant Version_32 := 16#39a03df9#;
   pragma Export (C, u00018, "system__storage_elementsB");
   u00019 : constant Version_32 := 16#30e40e85#;
   pragma Export (C, u00019, "system__storage_elementsS");
   u00020 : constant Version_32 := 16#41837d1e#;
   pragma Export (C, u00020, "system__stack_checkingB");
   u00021 : constant Version_32 := 16#93982f69#;
   pragma Export (C, u00021, "system__stack_checkingS");
   u00022 : constant Version_32 := 16#393398c1#;
   pragma Export (C, u00022, "system__exception_tableB");
   u00023 : constant Version_32 := 16#b33e2294#;
   pragma Export (C, u00023, "system__exception_tableS");
   u00024 : constant Version_32 := 16#ce4af020#;
   pragma Export (C, u00024, "system__exceptionsB");
   u00025 : constant Version_32 := 16#75442977#;
   pragma Export (C, u00025, "system__exceptionsS");
   u00026 : constant Version_32 := 16#37d758f1#;
   pragma Export (C, u00026, "system__exceptions__machineS");
   u00027 : constant Version_32 := 16#b895431d#;
   pragma Export (C, u00027, "system__exceptions_debugB");
   u00028 : constant Version_32 := 16#aec55d3f#;
   pragma Export (C, u00028, "system__exceptions_debugS");
   u00029 : constant Version_32 := 16#570325c8#;
   pragma Export (C, u00029, "system__img_intB");
   u00030 : constant Version_32 := 16#1ffca443#;
   pragma Export (C, u00030, "system__img_intS");
   u00031 : constant Version_32 := 16#b98c3e16#;
   pragma Export (C, u00031, "system__tracebackB");
   u00032 : constant Version_32 := 16#831a9d5a#;
   pragma Export (C, u00032, "system__tracebackS");
   u00033 : constant Version_32 := 16#9ed49525#;
   pragma Export (C, u00033, "system__traceback_entriesB");
   u00034 : constant Version_32 := 16#1d7cb2f1#;
   pragma Export (C, u00034, "system__traceback_entriesS");
   u00035 : constant Version_32 := 16#8c33a517#;
   pragma Export (C, u00035, "system__wch_conB");
   u00036 : constant Version_32 := 16#065a6653#;
   pragma Export (C, u00036, "system__wch_conS");
   u00037 : constant Version_32 := 16#9721e840#;
   pragma Export (C, u00037, "system__wch_stwB");
   u00038 : constant Version_32 := 16#2b4b4a52#;
   pragma Export (C, u00038, "system__wch_stwS");
   u00039 : constant Version_32 := 16#92b797cb#;
   pragma Export (C, u00039, "system__wch_cnvB");
   u00040 : constant Version_32 := 16#09eddca0#;
   pragma Export (C, u00040, "system__wch_cnvS");
   u00041 : constant Version_32 := 16#6033a23f#;
   pragma Export (C, u00041, "interfacesS");
   u00042 : constant Version_32 := 16#ece6fdb6#;
   pragma Export (C, u00042, "system__wch_jisB");
   u00043 : constant Version_32 := 16#899dc581#;
   pragma Export (C, u00043, "system__wch_jisS");
   u00044 : constant Version_32 := 16#10558b11#;
   pragma Export (C, u00044, "ada__streamsB");
   u00045 : constant Version_32 := 16#2e6701ab#;
   pragma Export (C, u00045, "ada__streamsS");
   u00046 : constant Version_32 := 16#db5c917c#;
   pragma Export (C, u00046, "ada__io_exceptionsS");
   u00047 : constant Version_32 := 16#12c8cd7d#;
   pragma Export (C, u00047, "ada__tagsB");
   u00048 : constant Version_32 := 16#ce72c228#;
   pragma Export (C, u00048, "ada__tagsS");
   u00049 : constant Version_32 := 16#c3335bfd#;
   pragma Export (C, u00049, "system__htableB");
   u00050 : constant Version_32 := 16#99e5f76b#;
   pragma Export (C, u00050, "system__htableS");
   u00051 : constant Version_32 := 16#089f5cd0#;
   pragma Export (C, u00051, "system__string_hashB");
   u00052 : constant Version_32 := 16#3bbb9c15#;
   pragma Export (C, u00052, "system__string_hashS");
   u00053 : constant Version_32 := 16#807fe041#;
   pragma Export (C, u00053, "system__unsigned_typesS");
   u00054 : constant Version_32 := 16#d27be59e#;
   pragma Export (C, u00054, "system__val_lluB");
   u00055 : constant Version_32 := 16#fa8db733#;
   pragma Export (C, u00055, "system__val_lluS");
   u00056 : constant Version_32 := 16#27b600b2#;
   pragma Export (C, u00056, "system__val_utilB");
   u00057 : constant Version_32 := 16#b187f27f#;
   pragma Export (C, u00057, "system__val_utilS");
   u00058 : constant Version_32 := 16#d1060688#;
   pragma Export (C, u00058, "system__case_utilB");
   u00059 : constant Version_32 := 16#392e2d56#;
   pragma Export (C, u00059, "system__case_utilS");
   u00060 : constant Version_32 := 16#84a27f0d#;
   pragma Export (C, u00060, "interfaces__c_streamsB");
   u00061 : constant Version_32 := 16#8bb5f2c0#;
   pragma Export (C, u00061, "interfaces__c_streamsS");
   u00062 : constant Version_32 := 16#6db6928f#;
   pragma Export (C, u00062, "system__crtlS");
   u00063 : constant Version_32 := 16#4e6a342b#;
   pragma Export (C, u00063, "system__file_ioB");
   u00064 : constant Version_32 := 16#ba56a5e4#;
   pragma Export (C, u00064, "system__file_ioS");
   u00065 : constant Version_32 := 16#b7ab275c#;
   pragma Export (C, u00065, "ada__finalizationB");
   u00066 : constant Version_32 := 16#19f764ca#;
   pragma Export (C, u00066, "ada__finalizationS");
   u00067 : constant Version_32 := 16#95817ed8#;
   pragma Export (C, u00067, "system__finalization_rootB");
   u00068 : constant Version_32 := 16#52d53711#;
   pragma Export (C, u00068, "system__finalization_rootS");
   u00069 : constant Version_32 := 16#769e25e6#;
   pragma Export (C, u00069, "interfaces__cB");
   u00070 : constant Version_32 := 16#4a38bedb#;
   pragma Export (C, u00070, "interfaces__cS");
   u00071 : constant Version_32 := 16#07e6ee66#;
   pragma Export (C, u00071, "system__os_libB");
   u00072 : constant Version_32 := 16#d7b69782#;
   pragma Export (C, u00072, "system__os_libS");
   u00073 : constant Version_32 := 16#1a817b8e#;
   pragma Export (C, u00073, "system__stringsB");
   u00074 : constant Version_32 := 16#639855e7#;
   pragma Export (C, u00074, "system__stringsS");
   u00075 : constant Version_32 := 16#e0b8de29#;
   pragma Export (C, u00075, "system__file_control_blockS");
   u00076 : constant Version_32 := 16#b5b2aca1#;
   pragma Export (C, u00076, "system__finalization_mastersB");
   u00077 : constant Version_32 := 16#69316dc1#;
   pragma Export (C, u00077, "system__finalization_mastersS");
   u00078 : constant Version_32 := 16#57a37a42#;
   pragma Export (C, u00078, "system__address_imageB");
   u00079 : constant Version_32 := 16#bccbd9bb#;
   pragma Export (C, u00079, "system__address_imageS");
   u00080 : constant Version_32 := 16#7268f812#;
   pragma Export (C, u00080, "system__img_boolB");
   u00081 : constant Version_32 := 16#e8fe356a#;
   pragma Export (C, u00081, "system__img_boolS");
   u00082 : constant Version_32 := 16#d7aac20c#;
   pragma Export (C, u00082, "system__ioB");
   u00083 : constant Version_32 := 16#8365b3ce#;
   pragma Export (C, u00083, "system__ioS");
   u00084 : constant Version_32 := 16#6d4d969a#;
   pragma Export (C, u00084, "system__storage_poolsB");
   u00085 : constant Version_32 := 16#e87cc305#;
   pragma Export (C, u00085, "system__storage_poolsS");
   u00086 : constant Version_32 := 16#e34550ca#;
   pragma Export (C, u00086, "system__pool_globalB");
   u00087 : constant Version_32 := 16#c88d2d16#;
   pragma Export (C, u00087, "system__pool_globalS");
   u00088 : constant Version_32 := 16#9d39c675#;
   pragma Export (C, u00088, "system__memoryB");
   u00089 : constant Version_32 := 16#445a22b5#;
   pragma Export (C, u00089, "system__memoryS");
   u00090 : constant Version_32 := 16#6a859064#;
   pragma Export (C, u00090, "system__storage_pools__subpoolsB");
   u00091 : constant Version_32 := 16#e3b008dc#;
   pragma Export (C, u00091, "system__storage_pools__subpoolsS");
   u00092 : constant Version_32 := 16#63f11652#;
   pragma Export (C, u00092, "system__storage_pools__subpools__finalizationB");
   u00093 : constant Version_32 := 16#fe2f4b3a#;
   pragma Export (C, u00093, "system__storage_pools__subpools__finalizationS");

   --  BEGIN ELABORATION ORDER
   --  ada%s
   --  interfaces%s
   --  system%s
   --  system.case_util%s
   --  system.case_util%b
   --  system.htable%s
   --  system.img_bool%s
   --  system.img_bool%b
   --  system.img_int%s
   --  system.img_int%b
   --  system.io%s
   --  system.io%b
   --  system.parameters%s
   --  system.parameters%b
   --  system.crtl%s
   --  interfaces.c_streams%s
   --  interfaces.c_streams%b
   --  system.standard_library%s
   --  system.exceptions_debug%s
   --  system.exceptions_debug%b
   --  system.storage_elements%s
   --  system.storage_elements%b
   --  system.stack_checking%s
   --  system.stack_checking%b
   --  system.string_hash%s
   --  system.string_hash%b
   --  system.htable%b
   --  system.strings%s
   --  system.strings%b
   --  system.os_lib%s
   --  system.traceback_entries%s
   --  system.traceback_entries%b
   --  ada.exceptions%s
   --  system.soft_links%s
   --  system.unsigned_types%s
   --  system.val_llu%s
   --  system.val_util%s
   --  system.val_util%b
   --  system.val_llu%b
   --  system.wch_con%s
   --  system.wch_con%b
   --  system.wch_cnv%s
   --  system.wch_jis%s
   --  system.wch_jis%b
   --  system.wch_cnv%b
   --  system.wch_stw%s
   --  system.wch_stw%b
   --  ada.exceptions.last_chance_handler%s
   --  ada.exceptions.last_chance_handler%b
   --  system.address_image%s
   --  system.exception_table%s
   --  system.exception_table%b
   --  ada.io_exceptions%s
   --  ada.tags%s
   --  ada.streams%s
   --  ada.streams%b
   --  interfaces.c%s
   --  system.exceptions%s
   --  system.exceptions%b
   --  system.exceptions.machine%s
   --  system.finalization_root%s
   --  system.finalization_root%b
   --  ada.finalization%s
   --  ada.finalization%b
   --  system.storage_pools%s
   --  system.storage_pools%b
   --  system.finalization_masters%s
   --  system.storage_pools.subpools%s
   --  system.storage_pools.subpools.finalization%s
   --  system.storage_pools.subpools.finalization%b
   --  system.memory%s
   --  system.memory%b
   --  system.standard_library%b
   --  system.pool_global%s
   --  system.pool_global%b
   --  system.file_control_block%s
   --  system.file_io%s
   --  system.secondary_stack%s
   --  system.file_io%b
   --  system.storage_pools.subpools%b
   --  system.finalization_masters%b
   --  interfaces.c%b
   --  ada.tags%b
   --  system.soft_links%b
   --  system.os_lib%b
   --  system.secondary_stack%b
   --  system.address_image%b
   --  system.traceback%s
   --  ada.exceptions%b
   --  system.traceback%b
   --  ada.text_io%s
   --  ada.text_io%b
   --  hello%b
   --  END ELABORATION ORDER

end ada_main;
@end example

@example
pragma Ada_95;
--  The following source file name pragmas allow the generated file
--  names to be unique for different main programs. They are needed
--  since the package name will always be Ada_Main.

pragma Source_File_Name (ada_main, Spec_File_Name => "b~hello.ads");
pragma Source_File_Name (ada_main, Body_File_Name => "b~hello.adb");

pragma Suppress (Overflow_Check);
with Ada.Exceptions;

--  Generated package body for Ada_Main starts here

package body ada_main is
   pragma Warnings (Off);

   --  These values are reference counter associated to units which have
   --  been elaborated. It is also used to avoid elaborating the
   --  same unit twice.

   E72 : Short_Integer; pragma Import (Ada, E72, "system__os_lib_E");
   E13 : Short_Integer; pragma Import (Ada, E13, "system__soft_links_E");
   E23 : Short_Integer; pragma Import (Ada, E23, "system__exception_table_E");
   E46 : Short_Integer; pragma Import (Ada, E46, "ada__io_exceptions_E");
   E48 : Short_Integer; pragma Import (Ada, E48, "ada__tags_E");
   E45 : Short_Integer; pragma Import (Ada, E45, "ada__streams_E");
   E70 : Short_Integer; pragma Import (Ada, E70, "interfaces__c_E");
   E25 : Short_Integer; pragma Import (Ada, E25, "system__exceptions_E");
   E68 : Short_Integer; pragma Import (Ada, E68, "system__finalization_root_E");
   E66 : Short_Integer; pragma Import (Ada, E66, "ada__finalization_E");
   E85 : Short_Integer; pragma Import (Ada, E85, "system__storage_pools_E");
   E77 : Short_Integer; pragma Import (Ada, E77, "system__finalization_masters_E");
   E91 : Short_Integer; pragma Import (Ada, E91, "system__storage_pools__subpools_E");
   E87 : Short_Integer; pragma Import (Ada, E87, "system__pool_global_E");
   E75 : Short_Integer; pragma Import (Ada, E75, "system__file_control_block_E");
   E64 : Short_Integer; pragma Import (Ada, E64, "system__file_io_E");
   E17 : Short_Integer; pragma Import (Ada, E17, "system__secondary_stack_E");
   E06 : Short_Integer; pragma Import (Ada, E06, "ada__text_io_E");

   Local_Priority_Specific_Dispatching : constant String := "";
   Local_Interrupt_States : constant String := "";

   Is_Elaborated : Boolean := False;

   procedure finalize_library is
   begin
      E06 := E06 - 1;
      declare
         procedure F1;
         pragma Import (Ada, F1, "ada__text_io__finalize_spec");
      begin
         F1;
      end;
      E77 := E77 - 1;
      E91 := E91 - 1;
      declare
         procedure F2;
         pragma Import (Ada, F2, "system__file_io__finalize_body");
      begin
         E64 := E64 - 1;
         F2;
      end;
      declare
         procedure F3;
         pragma Import (Ada, F3, "system__file_control_block__finalize_spec");
      begin
         E75 := E75 - 1;
         F3;
      end;
      E87 := E87 - 1;
      declare
         procedure F4;
         pragma Import (Ada, F4, "system__pool_global__finalize_spec");
      begin
         F4;
      end;
      declare
         procedure F5;
         pragma Import (Ada, F5, "system__storage_pools__subpools__finalize_spec");
      begin
         F5;
      end;
      declare
         procedure F6;
         pragma Import (Ada, F6, "system__finalization_masters__finalize_spec");
      begin
         F6;
      end;
      declare
         procedure Reraise_Library_Exception_If_Any;
         pragma Import (Ada, Reraise_Library_Exception_If_Any, "__gnat_reraise_library_exception_if_any");
      begin
         Reraise_Library_Exception_If_Any;
      end;
   end finalize_library;

   -------------
   -- adainit --
   -------------

   procedure adainit is

      Main_Priority : Integer;
      pragma Import (C, Main_Priority, "__gl_main_priority");
      Time_Slice_Value : Integer;
      pragma Import (C, Time_Slice_Value, "__gl_time_slice_val");
      WC_Encoding : Character;
      pragma Import (C, WC_Encoding, "__gl_wc_encoding");
      Locking_Policy : Character;
      pragma Import (C, Locking_Policy, "__gl_locking_policy");
      Queuing_Policy : Character;
      pragma Import (C, Queuing_Policy, "__gl_queuing_policy");
      Task_Dispatching_Policy : Character;
      pragma Import (C, Task_Dispatching_Policy, "__gl_task_dispatching_policy");
      Priority_Specific_Dispatching : System.Address;
      pragma Import (C, Priority_Specific_Dispatching, "__gl_priority_specific_dispatching");
      Num_Specific_Dispatching : Integer;
      pragma Import (C, Num_Specific_Dispatching, "__gl_num_specific_dispatching");
      Main_CPU : Integer;
      pragma Import (C, Main_CPU, "__gl_main_cpu");
      Interrupt_States : System.Address;
      pragma Import (C, Interrupt_States, "__gl_interrupt_states");
      Num_Interrupt_States : Integer;
      pragma Import (C, Num_Interrupt_States, "__gl_num_interrupt_states");
      Unreserve_All_Interrupts : Integer;
      pragma Import (C, Unreserve_All_Interrupts, "__gl_unreserve_all_interrupts");
      Detect_Blocking : Integer;
      pragma Import (C, Detect_Blocking, "__gl_detect_blocking");
      Default_Stack_Size : Integer;
      pragma Import (C, Default_Stack_Size, "__gl_default_stack_size");
      Leap_Seconds_Support : Integer;
      pragma Import (C, Leap_Seconds_Support, "__gl_leap_seconds_support");

      procedure Runtime_Initialize;
      pragma Import (C, Runtime_Initialize, "__gnat_runtime_initialize");

      Finalize_Library_Objects : No_Param_Proc;
      pragma Import (C, Finalize_Library_Objects, "__gnat_finalize_library_objects");

   --  Start of processing for adainit

   begin

      --  Record various information for this partition.  The values
      --  are derived by the binder from information stored in the ali
      --  files by the compiler.

      if Is_Elaborated then
         return;
      end if;
      Is_Elaborated := True;
      Main_Priority := -1;
      Time_Slice_Value := -1;
      WC_Encoding := 'b';
      Locking_Policy := ' ';
      Queuing_Policy := ' ';
      Task_Dispatching_Policy := ' ';
      Priority_Specific_Dispatching :=
        Local_Priority_Specific_Dispatching'Address;
      Num_Specific_Dispatching := 0;
      Main_CPU := -1;
      Interrupt_States := Local_Interrupt_States'Address;
      Num_Interrupt_States := 0;
      Unreserve_All_Interrupts := 0;
      Detect_Blocking := 0;
      Default_Stack_Size := -1;
      Leap_Seconds_Support := 0;

      Runtime_Initialize;

      Finalize_Library_Objects := finalize_library'access;

      --  Now we have the elaboration calls for all units in the partition.
      --  The Elab_Spec and Elab_Body attributes generate references to the
      --  implicit elaboration procedures generated by the compiler for
      --  each unit that requires elaboration. Increment a counter of
      --  reference for each unit.

      System.Soft_Links'Elab_Spec;
      System.Exception_Table'Elab_Body;
      E23 := E23 + 1;
      Ada.Io_Exceptions'Elab_Spec;
      E46 := E46 + 1;
      Ada.Tags'Elab_Spec;
      Ada.Streams'Elab_Spec;
      E45 := E45 + 1;
      Interfaces.C'Elab_Spec;
      System.Exceptions'Elab_Spec;
      E25 := E25 + 1;
      System.Finalization_Root'Elab_Spec;
      E68 := E68 + 1;
      Ada.Finalization'Elab_Spec;
      E66 := E66 + 1;
      System.Storage_Pools'Elab_Spec;
      E85 := E85 + 1;
      System.Finalization_Masters'Elab_Spec;
      System.Storage_Pools.Subpools'Elab_Spec;
      System.Pool_Global'Elab_Spec;
      E87 := E87 + 1;
      System.File_Control_Block'Elab_Spec;
      E75 := E75 + 1;
      System.File_Io'Elab_Body;
      E64 := E64 + 1;
      E91 := E91 + 1;
      System.Finalization_Masters'Elab_Body;
      E77 := E77 + 1;
      E70 := E70 + 1;
      Ada.Tags'Elab_Body;
      E48 := E48 + 1;
      System.Soft_Links'Elab_Body;
      E13 := E13 + 1;
      System.Os_Lib'Elab_Body;
      E72 := E72 + 1;
      System.Secondary_Stack'Elab_Body;
      E17 := E17 + 1;
      Ada.Text_Io'Elab_Spec;
      Ada.Text_Io'Elab_Body;
      E06 := E06 + 1;
   end adainit;

   --------------
   -- adafinal --
   --------------

   procedure adafinal is
      procedure s_stalib_adafinal;
      pragma Import (C, s_stalib_adafinal, "system__standard_library__adafinal");

      procedure Runtime_Finalize;
      pragma Import (C, Runtime_Finalize, "__gnat_runtime_finalize");

   begin
      if not Is_Elaborated then
         return;
      end if;
      Is_Elaborated := False;
      Runtime_Finalize;
      s_stalib_adafinal;
   end adafinal;

   --  We get to the main program of the partition by using
   --  pragma Import because if we try to with the unit and
   --  call it Ada style, then not only do we waste time
   --  recompiling it, but also, we don't really know the right
   --  switches (e.g.@@: identifier character set) to be used
   --  to compile it.

   procedure Ada_Main_Program;
   pragma Import (Ada, Ada_Main_Program, "_ada_hello");

   ----------
   -- main --
   ----------

   --  main is actually a function, as in the ANSI C standard,
   --  defined to return the exit status. The three parameters
   --  are the argument count, argument values and environment
   --  pointer.

   function main
     (argc : Integer;
      argv : System.Address;
      envp : System.Address)
      return Integer
   is
      --  The initialize routine performs low level system
      --  initialization using a standard library routine which
      --  sets up signal handling and performs any other
      --  required setup. The routine can be found in file
      --  a-init.c.

      procedure initialize;
      pragma Import (C, initialize, "__gnat_initialize");

      --  The finalize routine performs low level system
      --  finalization using a standard library routine. The
      --  routine is found in file a-final.c and in the standard
      --  distribution is a dummy routine that does nothing, so
      --  really this is a hook for special user finalization.

      procedure finalize;
      pragma Import (C, finalize, "__gnat_finalize");

      --  The following is to initialize the SEH exceptions

      SEH : aliased array (1 .. 2) of Integer;

      Ensure_Reference : aliased System.Address := Ada_Main_Program_Name'Address;
      pragma Volatile (Ensure_Reference);

   --  Start of processing for main

   begin
      --  Save global variables

      gnat_argc := argc;
      gnat_argv := argv;
      gnat_envp := envp;

      --  Call low level system initialization

      Initialize (SEH'Address);

      --  Call our generated Ada initialization routine

      adainit;

      --  Now we call the main program of the partition

      Ada_Main_Program;

      --  Perform Ada finalization

      adafinal;

      --  Perform low level system finalization

      Finalize;

      --  Return the proper exit status
      return (gnat_exit_status);
   end;

--  This section is entirely comments, so it has no effect on the
--  compilation of the Ada_Main package. It provides the list of
--  object files and linker options, as well as some standard
--  libraries needed for the link. The gnatlink utility parses
--  this b~hello.adb file to read these comment lines to generate
--  the appropriate command line arguments for the call to the
--  system linker. The BEGIN/END lines are used for sentinels for
--  this parsing operation.

--  The exact file names will of course depend on the environment,
--  host/target and location of files on the host system.

-- BEGIN Object file/option list
   --   ./hello.o
   --   -L./
   --   -L/usr/local/gnat/lib/gcc-lib/i686-pc-linux-gnu/2.8.1/adalib/
   --   /usr/local/gnat/lib/gcc-lib/i686-pc-linux-gnu/2.8.1/adalib/libgnat.a
-- END Object file/option list

end ada_main;
@end example

The Ada code in the above example is exactly what is generated by the
binder. We have added comments to more clearly indicate the function
of each part of the generated @cite{Ada_Main} package.

The code is standard Ada in all respects, and can be processed by any
tools that handle Ada. In particular, it is possible to use the debugger
in Ada mode to debug the generated @cite{Ada_Main} package. For example,
suppose that for reasons that you do not understand, your program is crashing
during elaboration of the body of @cite{Ada.Text_IO}. To locate this bug,
you can place a breakpoint on the call:

@quotation

@example
Ada.Text_Io'Elab_Body;
@end example
@end quotation

and trace the elaboration routine for this package to find out where
the problem might be (more usually of course you would be debugging
elaboration code in your own application).

@c -- Example: A |withing| unit has a |with| clause, it |withs| a |withed| unit

@node Elaboration Order Handling in GNAT,Inline Assembler,Example of Binder Output File,Top
@anchor{gnat_ugn/elaboration_order_handling_in_gnat elaboration-order-handling-in-gnat}@anchor{11}@anchor{gnat_ugn/elaboration_order_handling_in_gnat doc}@anchor{2ae}@anchor{gnat_ugn/elaboration_order_handling_in_gnat id1}@anchor{2af}
@chapter Elaboration Order Handling in GNAT


@geindex Order of elaboration

@geindex Elaboration control

This appendix describes the handling of elaboration code in Ada and
in GNAT, and discusses how the order of elaboration of program units can
be controlled in GNAT, either automatically or with explicit programming
features.

@menu
* Elaboration Code:: 
* Checking the Elaboration Order:: 
* Controlling the Elaboration Order:: 
* Controlling Elaboration in GNAT - Internal Calls:: 
* Controlling Elaboration in GNAT - External Calls:: 
* Default Behavior in GNAT - Ensuring Safety:: 
* Treatment of Pragma Elaborate:: 
* Elaboration Issues for Library Tasks:: 
* Mixing Elaboration Models:: 
* What to Do If the Default Elaboration Behavior Fails:: 
* Elaboration for Indirect Calls:: 
* Summary of Procedures for Elaboration Control:: 
* Other Elaboration Order Considerations:: 
* Determining the Chosen Elaboration Order:: 

@end menu

@node Elaboration Code,Checking the Elaboration Order,,Elaboration Order Handling in GNAT
@anchor{gnat_ugn/elaboration_order_handling_in_gnat elaboration-code}@anchor{2b0}@anchor{gnat_ugn/elaboration_order_handling_in_gnat id2}@anchor{2b1}
@section Elaboration Code


Ada provides rather general mechanisms for executing code at elaboration
time, that is to say before the main program starts executing. Such code arises
in three contexts:


@itemize *

@item 
@emph{Initializers for variables}

Variables declared at the library level, in package specs or bodies, can
require initialization that is performed at elaboration time, as in:

@example
Sqrt_Half : Float := Sqrt (0.5);
@end example

@item 
@emph{Package initialization code}

Code in a @cite{BEGIN-END} section at the outer level of a package body is
executed as part of the package body elaboration code.

@item 
@emph{Library level task allocators}

Tasks that are declared using task allocators at the library level
start executing immediately and hence can execute at elaboration time.
@end itemize

Subprogram calls are possible in any of these contexts, which means that
any arbitrary part of the program may be executed as part of the elaboration
code. It is even possible to write a program which does all its work at
elaboration time, with a null main program, although stylistically this
would usually be considered an inappropriate way to structure
a program.

An important concern arises in the context of elaboration code:
we have to be sure that it is executed in an appropriate order. What we
have is a series of elaboration code sections, potentially one section
for each unit in the program. It is important that these execute
in the correct order. Correctness here means that, taking the above
example of the declaration of @cite{Sqrt_Half},
if some other piece of
elaboration code references @cite{Sqrt_Half},
then it must run after the
section of elaboration code that contains the declaration of
@cite{Sqrt_Half}.

There would never be any order of elaboration problem if we made a rule
that whenever you @emph{with} a unit, you must elaborate both the spec and body
of that unit before elaborating the unit doing the @emph{with}ing:

@example
with Unit_1;
package Unit_2 is ...
@end example

would require that both the body and spec of @cite{Unit_1} be elaborated
before the spec of @cite{Unit_2}. However, a rule like that would be far too
restrictive. In particular, it would make it impossible to have routines
in separate packages that were mutually recursive.

You might think that a clever enough compiler could look at the actual
elaboration code and determine an appropriate correct order of elaboration,
but in the general case, this is not possible. Consider the following
example.

In the body of @cite{Unit_1}, we have a procedure @cite{Func_1}
that references
the variable @cite{Sqrt_1}, which is declared in the elaboration code
of the body of @cite{Unit_1}:

@example
Sqrt_1 : Float := Sqrt (0.1);
@end example

The elaboration code of the body of @cite{Unit_1} also contains:

@example
if expression_1 = 1 then
   Q := Unit_2.Func_2;
end if;
@end example

@cite{Unit_2} is exactly parallel,
it has a procedure @cite{Func_2} that references
the variable @cite{Sqrt_2}, which is declared in the elaboration code of
the body @cite{Unit_2}:

@example
Sqrt_2 : Float := Sqrt (0.1);
@end example

The elaboration code of the body of @cite{Unit_2} also contains:

@example
if expression_2 = 2 then
   Q := Unit_1.Func_1;
end if;
@end example

Now the question is, which of the following orders of elaboration is
acceptable:

@example
Spec of Unit_1
Spec of Unit_2
Body of Unit_1
Body of Unit_2
@end example

or

@example
Spec of Unit_2
Spec of Unit_1
Body of Unit_2
Body of Unit_1
@end example

If you carefully analyze the flow here, you will see that you cannot tell
at compile time the answer to this question.
If @cite{expression_1} is not equal to 1,
and @cite{expression_2} is not equal to 2,
then either order is acceptable, because neither of the function calls is
executed. If both tests evaluate to true, then neither order is acceptable
and in fact there is no correct order.

If one of the two expressions is true, and the other is false, then one
of the above orders is correct, and the other is incorrect. For example,
if @cite{expression_1} /= 1 and @cite{expression_2} = 2,
then the call to @cite{Func_1}
will occur, but not the call to @cite{Func_2.}
This means that it is essential
to elaborate the body of @cite{Unit_1} before
the body of @cite{Unit_2}, so the first
order of elaboration is correct and the second is wrong.

By making @cite{expression_1} and @cite{expression_2}
depend on input data, or perhaps
the time of day, we can make it impossible for the compiler or binder
to figure out which of these expressions will be true, and hence it
is impossible to guarantee a safe order of elaboration at run time.

@node Checking the Elaboration Order,Controlling the Elaboration Order,Elaboration Code,Elaboration Order Handling in GNAT
@anchor{gnat_ugn/elaboration_order_handling_in_gnat checking-the-elaboration-order}@anchor{2b2}@anchor{gnat_ugn/elaboration_order_handling_in_gnat id3}@anchor{2b3}
@section Checking the Elaboration Order


In some languages that involve the same kind of elaboration problems,
e.g., Java and C++, the programmer needs to take these
ordering problems into account, and it is common to
write a program in which an incorrect elaboration order  gives
surprising results, because it references variables before they
are initialized.
Ada is designed to be a safe language, and a programmer-beware approach is
clearly not sufficient. Consequently, the language provides three lines
of defense:


@itemize *

@item 
@emph{Standard rules}

Some standard rules restrict the possible choice of elaboration
order. In particular, if you @emph{with} a unit, then its spec is always
elaborated before the unit doing the @emph{with}. Similarly, a parent
spec is always elaborated before the child spec, and finally
a spec is always elaborated before its corresponding body.
@end itemize

@geindex Elaboration checks

@geindex Checks
@geindex elaboration


@itemize *

@item 
@emph{Dynamic elaboration checks}

Dynamic checks are made at run time, so that if some entity is accessed
before it is elaborated (typically  by means of a subprogram call)
then the exception (@cite{Program_Error}) is raised.

@item 
@emph{Elaboration control}

Facilities are provided for the programmer to specify the desired order
of elaboration.
@end itemize

Let's look at these facilities in more detail. First, the rules for
dynamic checking. One possible rule would be simply to say that the
exception is raised if you access a variable which has not yet been
elaborated. The trouble with this approach is that it could require
expensive checks on every variable reference. Instead Ada has two
rules which are a little more restrictive, but easier to check, and
easier to state:


@itemize *

@item 
@emph{Restrictions on calls}

A subprogram can only be called at elaboration time if its body
has been elaborated. The rules for elaboration given above guarantee
that the spec of the subprogram has been elaborated before the
call, but not the body. If this rule is violated, then the
exception @cite{Program_Error} is raised.

@item 
@emph{Restrictions on instantiations}

A generic unit can only be instantiated if the body of the generic
unit has been elaborated. Again, the rules for elaboration given above
guarantee that the spec of the generic unit has been elaborated
before the instantiation, but not the body. If this rule is
violated, then the exception @cite{Program_Error} is raised.
@end itemize

The idea is that if the body has been elaborated, then any variables
it references must have been elaborated; by checking for the body being
elaborated we guarantee that none of its references causes any
trouble. As we noted above, this is a little too restrictive, because a
subprogram that has no non-local references in its body may in fact be safe
to call. However, it really would be unsafe to rely on this, because
it would mean that the caller was aware of details of the implementation
in the body. This goes against the basic tenets of Ada.

A plausible implementation can be described as follows.
A Boolean variable is associated with each subprogram
and each generic unit. This variable is initialized to False, and is set to
True at the point body is elaborated. Every call or instantiation checks the
variable, and raises @cite{Program_Error} if the variable is False.

Note that one might think that it would be good enough to have one Boolean
variable for each package, but that would not deal with cases of trying
to call a body in the same package as the call
that has not been elaborated yet.
Of course a compiler may be able to do enough analysis to optimize away
some of the Boolean variables as unnecessary, and @cite{GNAT} indeed
does such optimizations, but still the easiest conceptual model is to
think of there being one variable per subprogram.

@node Controlling the Elaboration Order,Controlling Elaboration in GNAT - Internal Calls,Checking the Elaboration Order,Elaboration Order Handling in GNAT
@anchor{gnat_ugn/elaboration_order_handling_in_gnat id4}@anchor{2b4}@anchor{gnat_ugn/elaboration_order_handling_in_gnat controlling-the-elaboration-order}@anchor{2b5}
@section Controlling the Elaboration Order


In the previous section we discussed the rules in Ada which ensure
that @cite{Program_Error} is raised if an incorrect elaboration order is
chosen. This prevents erroneous executions, but we need mechanisms to
specify a correct execution and avoid the exception altogether.
To achieve this, Ada provides a number of features for controlling
the order of elaboration. We discuss these features in this section.

First, there are several ways of indicating to the compiler that a given
unit has no elaboration problems:


@itemize *

@item 
@emph{packages that do not require a body}

A library package that does not require a body does not permit
a body (this rule was introduced in Ada 95).
Thus if we have a such a package, as in:

@example
package Definitions is
   generic
      type m is new integer;
   package Subp is
      type a is array (1 .. 10) of m;
      type b is array (1 .. 20) of m;
   end Subp;
end Definitions;
@end example

A package that @emph{with}s @cite{Definitions} may safely instantiate
@cite{Definitions.Subp} because the compiler can determine that there
definitely is no package body to worry about in this case
@end itemize

@geindex pragma Pure


@itemize *

@item 
@emph{pragma Pure}

This pragma places sufficient restrictions on a unit to guarantee that
no call to any subprogram in the unit can result in an
elaboration problem. This means that the compiler does not need
to worry about the point of elaboration of such units, and in
particular, does not need to check any calls to any subprograms
in this unit.
@end itemize

@geindex pragma Preelaborate


@itemize *

@item 
@emph{pragma Preelaborate}

This pragma places slightly less stringent restrictions on a unit than
does pragma Pure,
but these restrictions are still sufficient to ensure that there
are no elaboration problems with any calls to the unit.
@end itemize

@geindex pragma Elaborate_Body


@itemize *

@item 
@emph{pragma Elaborate_Body}

This pragma requires that the body of a unit be elaborated immediately
after its spec. Suppose a unit @cite{A} has such a pragma,
and unit @cite{B} does
a @emph{with} of unit @cite{A}. Recall that the standard rules require
the spec of unit @cite{A}
to be elaborated before the @emph{with}ing unit; given the pragma in
@cite{A}, we also know that the body of @cite{A}
will be elaborated before @cite{B}, so
that calls to @cite{A} are safe and do not need a check.

Note that, unlike pragma @cite{Pure} and pragma @cite{Preelaborate},
the use of @cite{Elaborate_Body} does not guarantee that the program is
free of elaboration problems, because it may not be possible
to satisfy the requested elaboration order.
Let's go back to the example with @cite{Unit_1} and @cite{Unit_2}.
If a programmer marks @cite{Unit_1} as @cite{Elaborate_Body},
and not @cite{Unit_2@comma{}} then the order of
elaboration will be:

@example
Spec of Unit_2
Spec of Unit_1
Body of Unit_1
Body of Unit_2
@end example

Now that means that the call to @cite{Func_1} in @cite{Unit_2}
need not be checked,
it must be safe. But the call to @cite{Func_2} in
@cite{Unit_1} may still fail if
@cite{Expression_1} is equal to 1,
and the programmer must still take
responsibility for this not being the case.

If all units carry a pragma @cite{Elaborate_Body}, then all problems are
eliminated, except for calls entirely within a body, which are
in any case fully under programmer control. However, using the pragma
everywhere is not always possible.
In particular, for our @cite{Unit_1}/@cite{Unit_2} example, if
we marked both of them as having pragma @cite{Elaborate_Body}, then
clearly there would be no possible elaboration order.
@end itemize

The above pragmas allow a server to guarantee safe use by clients, and
clearly this is the preferable approach. Consequently a good rule
is to mark units as @cite{Pure} or @cite{Preelaborate} if possible,
and if this is not possible,
mark them as @cite{Elaborate_Body} if possible.
As we have seen, there are situations where neither of these
three pragmas can be used.
So we also provide methods for clients to control the
order of elaboration of the servers on which they depend:

@geindex pragma Elaborate


@itemize *

@item 
@emph{pragma Elaborate (unit)}

This pragma is placed in the context clause, after a @emph{with} clause,
and it requires that the body of the named unit be elaborated before
the unit in which the pragma occurs. The idea is to use this pragma
if the current unit calls at elaboration time, directly or indirectly,
some subprogram in the named unit.
@end itemize

@geindex pragma Elaborate_All


@itemize *

@item 
@emph{pragma Elaborate_All (unit)}

This is a stronger version of the Elaborate pragma. Consider the
following example:

@example
Unit A |withs| unit B and calls B.Func in elab code
Unit B |withs| unit C, and B.Func calls C.Func
@end example

Now if we put a pragma @cite{Elaborate (B)}
in unit @cite{A}, this ensures that the
body of @cite{B} is elaborated before the call, but not the
body of @cite{C}, so
the call to @cite{C.Func} could still cause @cite{Program_Error} to
be raised.

The effect of a pragma @cite{Elaborate_All} is stronger, it requires
not only that the body of the named unit be elaborated before the
unit doing the @emph{with}, but also the bodies of all units that the
named unit uses, following @emph{with} links transitively. For example,
if we put a pragma @cite{Elaborate_All (B)} in unit @cite{A},
then it requires not only that the body of @cite{B} be elaborated before @cite{A},
but also the body of @cite{C}, because @cite{B} @emph{with}s @cite{C}.
@end itemize

We are now in a position to give a usage rule in Ada for avoiding
elaboration problems, at least if dynamic dispatching and access to
subprogram values are not used. We will handle these cases separately
later.

The rule is simple:

@emph{If a unit has elaboration code that can directly or
indirectly make a call to a subprogram in a |withed| unit, or instantiate
a generic package in a |withed| unit,
then if the |withed| unit does not have
pragma `Pure` or `Preelaborate`, then the client should have
a pragma `Elaborate_All`for the |withed| unit.*}

By following this rule a client is
assured that calls can be made without risk of an exception.

For generic subprogram instantiations, the rule can be relaxed to
require only a pragma @cite{Elaborate} since elaborating the body
of a subprogram cannot cause any transitive elaboration (we are
not calling the subprogram in this case, just elaborating its
declaration).

If this rule is not followed, then a program may be in one of four
states:


@itemize *

@item 
@emph{No order exists}

No order of elaboration exists which follows the rules, taking into
account any @cite{Elaborate}, @cite{Elaborate_All},
or @cite{Elaborate_Body} pragmas. In
this case, an Ada compiler must diagnose the situation at bind
time, and refuse to build an executable program.

@item 
@emph{One or more orders exist, all incorrect}

One or more acceptable elaboration orders exist, and all of them
generate an elaboration order problem. In this case, the binder
can build an executable program, but @cite{Program_Error} will be raised
when the program is run.

@item 
@emph{Several orders exist, some right, some incorrect}

One or more acceptable elaboration orders exists, and some of them
work, and some do not. The programmer has not controlled
the order of elaboration, so the binder may or may not pick one of
the correct orders, and the program may or may not raise an
exception when it is run. This is the worst case, because it means
that the program may fail when moved to another compiler, or even
another version of the same compiler.

@item 
@emph{One or more orders exists, all correct}

One ore more acceptable elaboration orders exist, and all of them
work. In this case the program runs successfully. This state of
affairs can be guaranteed by following the rule we gave above, but
may be true even if the rule is not followed.
@end itemize

Note that one additional advantage of following our rules on the use
of @cite{Elaborate} and @cite{Elaborate_All}
is that the program continues to stay in the ideal (all orders OK) state
even if maintenance
changes some bodies of some units. Conversely, if a program that does
not follow this rule happens to be safe at some point, this state of affairs
may deteriorate silently as a result of maintenance changes.

You may have noticed that the above discussion did not mention
the use of @cite{Elaborate_Body}. This was a deliberate omission. If you
@emph{with} an @cite{Elaborate_Body} unit, it still may be the case that
code in the body makes calls to some other unit, so it is still necessary
to use @cite{Elaborate_All} on such units.

@node Controlling Elaboration in GNAT - Internal Calls,Controlling Elaboration in GNAT - External Calls,Controlling the Elaboration Order,Elaboration Order Handling in GNAT
@anchor{gnat_ugn/elaboration_order_handling_in_gnat id5}@anchor{2b6}@anchor{gnat_ugn/elaboration_order_handling_in_gnat controlling-elaboration-in-gnat-internal-calls}@anchor{2b7}
@section Controlling Elaboration in GNAT - Internal Calls


In the case of internal calls, i.e., calls within a single package, the
programmer has full control over the order of elaboration, and it is up
to the programmer to elaborate declarations in an appropriate order. For
example writing:

@example
function One return Float;

Q : Float := One;

function One return Float is
begin
     return 1.0;
end One;
@end example

will obviously raise @cite{Program_Error} at run time, because function
One will be called before its body is elaborated. In this case GNAT will
generate a warning that the call will raise @cite{Program_Error}:

@example
 1. procedure y is
 2.    function One return Float;
 3.
 4.    Q : Float := One;
                    |
    >>> warning: cannot call "One" before body is elaborated
    >>> warning: Program_Error will be raised at run time

 5.
 6.    function One return Float is
 7.    begin
 8.         return 1.0;
 9.    end One;
10.
11. begin
12.    null;
13. end;
@end example

Note that in this particular case, it is likely that the call is safe, because
the function @cite{One} does not access any global variables.
Nevertheless in Ada, we do not want the validity of the check to depend on
the contents of the body (think about the separate compilation case), so this
is still wrong, as we discussed in the previous sections.

The error is easily corrected by rearranging the declarations so that the
body of @cite{One} appears before the declaration containing the call
(note that in Ada 95 as well as later versions of the Ada standard,
declarations can appear in any order, so there is no restriction that
would prevent this reordering, and if we write:

@example
function One return Float;

function One return Float is
begin
     return 1.0;
end One;

Q : Float := One;
@end example

then all is well, no warning is generated, and no
@cite{Program_Error} exception
will be raised.
Things are more complicated when a chain of subprograms is executed:

@example
function A return Integer;
function B return Integer;
function C return Integer;

function B return Integer is begin return A; end;
function C return Integer is begin return B; end;

X : Integer := C;

function A return Integer is begin return 1; end;
@end example

Now the call to @cite{C}
at elaboration time in the declaration of @cite{X} is correct, because
the body of @cite{C} is already elaborated,
and the call to @cite{B} within the body of
@cite{C} is correct, but the call
to @cite{A} within the body of @cite{B} is incorrect, because the body
of @cite{A} has not been elaborated, so @cite{Program_Error}
will be raised on the call to @cite{A}.
In this case GNAT will generate a
warning that @cite{Program_Error} may be
raised at the point of the call. Let's look at the warning:

@example
 1. procedure x is
 2.    function A return Integer;
 3.    function B return Integer;
 4.    function C return Integer;
 5.
 6.    function B return Integer is begin return A; end;
                                                    |
    >>> warning: call to "A" before body is elaborated may
                 raise Program_Error
    >>> warning: "B" called at line 7
    >>> warning: "C" called at line 9

 7.    function C return Integer is begin return B; end;
 8.
 9.    X : Integer := C;
10.
11.    function A return Integer is begin return 1; end;
12.
13. begin
14.    null;
15. end;
@end example

Note that the message here says 'may raise', instead of the direct case,
where the message says 'will be raised'. That's because whether
@cite{A} is
actually called depends in general on run-time flow of control.
For example, if the body of @cite{B} said

@example
function B return Integer is
begin
   if some-condition-depending-on-input-data then
      return A;
   else
      return 1;
   end if;
end B;
@end example

then we could not know until run time whether the incorrect call to A would
actually occur, so @cite{Program_Error} might
or might not be raised. It is possible for a compiler to
do a better job of analyzing bodies, to
determine whether or not @cite{Program_Error}
might be raised, but it certainly
couldn't do a perfect job (that would require solving the halting problem
and is provably impossible), and because this is a warning anyway, it does
not seem worth the effort to do the analysis. Cases in which it
would be relevant are rare.

In practice, warnings of either of the forms given
above will usually correspond to
real errors, and should be examined carefully and eliminated.
In the rare case where a warning is bogus, it can be suppressed by any of
the following methods:


@itemize *

@item 
Compile with the @emph{-gnatws} switch set

@item 
Suppress @cite{Elaboration_Check} for the called subprogram

@item 
Use pragma @cite{Warnings_Off} to turn warnings off for the call
@end itemize

For the internal elaboration check case,
GNAT by default generates the
necessary run-time checks to ensure
that @cite{Program_Error} is raised if any
call fails an elaboration check. Of course this can only happen if a
warning has been issued as described above. The use of pragma
@cite{Suppress (Elaboration_Check)} may (but is not guaranteed to) suppress
some of these checks, meaning that it may be possible (but is not
guaranteed) for a program to be able to call a subprogram whose body
is not yet elaborated, without raising a @cite{Program_Error} exception.

@node Controlling Elaboration in GNAT - External Calls,Default Behavior in GNAT - Ensuring Safety,Controlling Elaboration in GNAT - Internal Calls,Elaboration Order Handling in GNAT
@anchor{gnat_ugn/elaboration_order_handling_in_gnat id6}@anchor{2b8}@anchor{gnat_ugn/elaboration_order_handling_in_gnat controlling-elaboration-in-gnat-external-calls}@anchor{2b9}
@section Controlling Elaboration in GNAT - External Calls


The previous section discussed the case in which the execution of a
particular thread of elaboration code occurred entirely within a
single unit. This is the easy case to handle, because a programmer
has direct and total control over the order of elaboration, and
furthermore, checks need only be generated in cases which are rare
and which the compiler can easily detect.
The situation is more complex when separate compilation is taken into account.
Consider the following:

@example
package Math is
   function Sqrt (Arg : Float) return Float;
end Math;

package body Math is
   function Sqrt (Arg : Float) return Float is
   begin
         ...
   end Sqrt;
end Math;

with Math;
package Stuff is
   X : Float := Math.Sqrt (0.5);
end Stuff;

with Stuff;
procedure Main is
begin
   ...
end Main;
@end example

where @cite{Main} is the main program. When this program is executed, the
elaboration code must first be executed, and one of the jobs of the
binder is to determine the order in which the units of a program are
to be elaborated. In this case we have four units: the spec and body
of @cite{Math},
the spec of @cite{Stuff} and the body of @cite{Main}).
In what order should the four separate sections of elaboration code
be executed?

There are some restrictions in the order of elaboration that the binder
can choose. In particular, if unit U has a @emph{with}
for a package @cite{X}, then you
are assured that the spec of @cite{X}
is elaborated before U , but you are
not assured that the body of @cite{X}
is elaborated before U.
This means that in the above case, the binder is allowed to choose the
order:

@example
spec of Math
spec of Stuff
body of Math
body of Main
@end example

but that's not good, because now the call to @cite{Math.Sqrt}
that happens during
the elaboration of the @cite{Stuff}
spec happens before the body of @cite{Math.Sqrt} is
elaborated, and hence causes @cite{Program_Error} exception to be raised.
At first glance, one might say that the binder is misbehaving, because
obviously you want to elaborate the body of something you @emph{with} first, but
that is not a general rule that can be followed in all cases. Consider

@example
package X is ...

package Y is ...

with X;
package body Y is ...

with Y;
package body X is ...
@end example

This is a common arrangement, and, apart from the order of elaboration
problems that might arise in connection with elaboration code, this works fine.
A rule that says that you must first elaborate the body of anything you
@emph{with} cannot work in this case:
the body of @cite{X} @emph{with}s @cite{Y},
which means you would have to
elaborate the body of @cite{Y} first, but that @emph{with}s @cite{X},
which means
you have to elaborate the body of @cite{X} first, but ... and we have a
loop that cannot be broken.

It is true that the binder can in many cases guess an order of elaboration
that is unlikely to cause a @cite{Program_Error}
exception to be raised, and it tries to do so (in the
above example of @cite{Math/Stuff/Spec}, the GNAT binder will
by default
elaborate the body of @cite{Math} right after its spec, so all will be well).

However, a program that blindly relies on the binder to be helpful can
get into trouble, as we discussed in the previous sections, so GNAT
provides a number of facilities for assisting the programmer in
developing programs that are robust with respect to elaboration order.

@node Default Behavior in GNAT - Ensuring Safety,Treatment of Pragma Elaborate,Controlling Elaboration in GNAT - External Calls,Elaboration Order Handling in GNAT
@anchor{gnat_ugn/elaboration_order_handling_in_gnat id7}@anchor{2ba}@anchor{gnat_ugn/elaboration_order_handling_in_gnat default-behavior-in-gnat-ensuring-safety}@anchor{2bb}
@section Default Behavior in GNAT - Ensuring Safety


The default behavior in GNAT ensures elaboration safety. In its
default mode GNAT implements the
rule we previously described as the right approach. Let's restate it:

@emph{If a unit has elaboration code that can directly or indirectly make a
call to a subprogram in a |withed| unit, or instantiate a generic
package in a |withed| unit, then if the |withed| unit
does not have pragma `Pure` or `Preelaborate`, then the client should have an
`Elaborate_All` pragma for the |withed| unit.}

@emph{In the case of instantiating a generic subprogram, it is always
sufficient to have only an `Elaborate` pragma for the
|withed| unit.}

By following this rule a client is assured that calls and instantiations
can be made without risk of an exception.

In this mode GNAT traces all calls that are potentially made from
elaboration code, and puts in any missing implicit @cite{Elaborate}
and @cite{Elaborate_All} pragmas.
The advantage of this approach is that no elaboration problems
are possible if the binder can find an elaboration order that is
consistent with these implicit @cite{Elaborate} and
@cite{Elaborate_All} pragmas. The
disadvantage of this approach is that no such order may exist.

If the binder does not generate any diagnostics, then it means that it has
found an elaboration order that is guaranteed to be safe. However, the binder
may still be relying on implicitly generated @cite{Elaborate} and
@cite{Elaborate_All} pragmas so portability to other compilers than GNAT is not
guaranteed.

If it is important to guarantee portability, then the compilations should
use the @emph{-gnatel}
(info messages for elaboration pragmas) switch. This will cause info messages
to be generated indicating the missing @cite{Elaborate} and
@cite{Elaborate_All} pragmas.
Consider the following source program:

@example
with k;
package j is
  m : integer := k.r;
end;
@end example

where it is clear that there
should be a pragma @cite{Elaborate_All}
for unit @cite{k}. An implicit pragma will be generated, and it is
likely that the binder will be able to honor it. However, if you want
to port this program to some other Ada compiler than GNAT.
it is safer to include the pragma explicitly in the source. If this
unit is compiled with the @emph{-gnatel}
switch, then the compiler outputs an information message:

@example
1. with k;
2. package j is
3.   m : integer := k.r;
                     |
   >>> info: call to "r" may raise Program_Error
   >>> info: missing pragma Elaborate_All for "k"

4. end;
@end example

and these messages can be used as a guide for supplying manually
the missing pragmas. It is usually a bad idea to use this
option during development. That's because it will tell you when
you need to put in a pragma, but cannot tell you when it is time
to take it out. So the use of pragma @cite{Elaborate_All} may lead to
unnecessary dependencies and even false circularities.

This default mode is more restrictive than the Ada Reference
Manual, and it is possible to construct programs which will compile
using the dynamic model described there, but will run into a
circularity using the safer static model we have described.

Of course any Ada compiler must be able to operate in a mode
consistent with the requirements of the Ada Reference Manual,
and in particular must have the capability of implementing the
standard dynamic model of elaboration with run-time checks.

In GNAT, this standard mode can be achieved either by the use of
the @emph{-gnatE} switch on the compiler (@emph{gcc} or
@emph{gnatmake}) command, or by the use of the configuration pragma:

@example
pragma Elaboration_Checks (DYNAMIC);
@end example

Either approach will cause the unit affected to be compiled using the
standard dynamic run-time elaboration checks described in the Ada
Reference Manual. The static model is generally preferable, since it
is clearly safer to rely on compile and link time checks rather than
run-time checks. However, in the case of legacy code, it may be
difficult to meet the requirements of the static model. This
issue is further discussed in
@ref{2bc,,What to Do If the Default Elaboration Behavior Fails}.

Note that the static model provides a strict subset of the allowed
behavior and programs of the Ada Reference Manual, so if you do
adhere to the static model and no circularities exist,
then you are assured that your program will
work using the dynamic model, providing that you remove any
pragma Elaborate statements from the source.

@node Treatment of Pragma Elaborate,Elaboration Issues for Library Tasks,Default Behavior in GNAT - Ensuring Safety,Elaboration Order Handling in GNAT
@anchor{gnat_ugn/elaboration_order_handling_in_gnat treatment-of-pragma-elaborate}@anchor{2bd}@anchor{gnat_ugn/elaboration_order_handling_in_gnat id8}@anchor{2be}
@section Treatment of Pragma Elaborate


@geindex Pragma Elaborate

The use of @cite{pragma Elaborate}
should generally be avoided in Ada 95 and Ada 2005 programs,
since there is no guarantee that transitive calls
will be properly handled. Indeed at one point, this pragma was placed
in Annex J (Obsolescent Features), on the grounds that it is never useful.

Now that's a bit restrictive. In practice, the case in which
@cite{pragma Elaborate} is useful is when the caller knows that there
are no transitive calls, or that the called unit contains all necessary
transitive @cite{pragma Elaborate} statements, and legacy code often
contains such uses.

Strictly speaking the static mode in GNAT should ignore such pragmas,
since there is no assurance at compile time that the necessary safety
conditions are met. In practice, this would cause GNAT to be incompatible
with correctly written Ada 83 code that had all necessary
@cite{pragma Elaborate} statements in place. Consequently, we made the
decision that GNAT in its default mode will believe that if it encounters
a @cite{pragma Elaborate} then the programmer knows what they are doing,
and it will trust that no elaboration errors can occur.

The result of this decision is two-fold. First to be safe using the
static mode, you should remove all @cite{pragma Elaborate} statements.
Second, when fixing circularities in existing code, you can selectively
use @cite{pragma Elaborate} statements to convince the static mode of
GNAT that it need not generate an implicit @cite{pragma Elaborate_All}
statement.

When using the static mode with @emph{-gnatwl}, any use of
@cite{pragma Elaborate} will generate a warning about possible
problems.

@node Elaboration Issues for Library Tasks,Mixing Elaboration Models,Treatment of Pragma Elaborate,Elaboration Order Handling in GNAT
@anchor{gnat_ugn/elaboration_order_handling_in_gnat elaboration-issues-for-library-tasks}@anchor{2bf}@anchor{gnat_ugn/elaboration_order_handling_in_gnat id9}@anchor{2c0}
@section Elaboration Issues for Library Tasks


@geindex Library tasks
@geindex elaboration issues

@geindex Elaboration of library tasks

In this section we examine special elaboration issues that arise for
programs that declare library level tasks.

Generally the model of execution of an Ada program is that all units are
elaborated, and then execution of the program starts. However, the
declaration of library tasks definitely does not fit this model. The
reason for this is that library tasks start as soon as they are declared
(more precisely, as soon as the statement part of the enclosing package
body is reached), that is to say before elaboration
of the program is complete. This means that if such a task calls a
subprogram, or an entry in another task, the callee may or may not be
elaborated yet, and in the standard
Reference Manual model of dynamic elaboration checks, you can even
get timing dependent Program_Error exceptions, since there can be
a race between the elaboration code and the task code.

The static model of elaboration in GNAT seeks to avoid all such
dynamic behavior, by being conservative, and the conservative
approach in this particular case is to assume that all the code
in a task body is potentially executed at elaboration time if
a task is declared at the library level.

This can definitely result in unexpected circularities. Consider
the following example

@example
package Decls is
  task Lib_Task is
     entry Start;
  end Lib_Task;

  type My_Int is new Integer;

  function Ident (M : My_Int) return My_Int;
end Decls;

with Utils;
package body Decls is
  task body Lib_Task is
  begin
     accept Start;
     Utils.Put_Val (2);
  end Lib_Task;

  function Ident (M : My_Int) return My_Int is
  begin
     return M;
  end Ident;
end Decls;

with Decls;
package Utils is
  procedure Put_Val (Arg : Decls.My_Int);
end Utils;

with Text_IO;
package body Utils is
  procedure Put_Val (Arg : Decls.My_Int) is
  begin
     Text_IO.Put_Line (Decls.My_Int'Image (Decls.Ident (Arg)));
  end Put_Val;
end Utils;

with Decls;
procedure Main is
begin
   Decls.Lib_Task.Start;
end;
@end example

If the above example is compiled in the default static elaboration
mode, then a circularity occurs. The circularity comes from the call
@cite{Utils.Put_Val} in the task body of @cite{Decls.Lib_Task}. Since
this call occurs in elaboration code, we need an implicit pragma
@cite{Elaborate_All} for @cite{Utils}. This means that not only must
the spec and body of @cite{Utils} be elaborated before the body
of @cite{Decls}, but also the spec and body of any unit that is
@emph{with}ed by the body of @cite{Utils} must also be elaborated before
the body of @cite{Decls}. This is the transitive implication of
pragma @cite{Elaborate_All} and it makes sense, because in general
the body of @cite{Put_Val} might have a call to something in a
@emph{with}ed unit.

In this case, the body of Utils (actually its spec) @emph{with}s
@cite{Decls}. Unfortunately this means that the body of @cite{Decls}
must be elaborated before itself, in case there is a call from the
body of @cite{Utils}.

Here is the exact chain of events we are worrying about:


@itemize *

@item 
In the body of @cite{Decls} a call is made from within the body of a library
task to a subprogram in the package @cite{Utils}. Since this call may
occur at elaboration time (given that the task is activated at elaboration
time), we have to assume the worst, i.e., that the
call does happen at elaboration time.

@item 
This means that the body and spec of @cite{Util} must be elaborated before
the body of @cite{Decls} so that this call does not cause an access before
elaboration.

@item 
Within the body of @cite{Util}, specifically within the body of
@cite{Util.Put_Val} there may be calls to any unit @emph{with}ed
by this package.

@item 
One such @emph{with}ed package is package @cite{Decls}, so there
might be a call to a subprogram in @cite{Decls} in @cite{Put_Val}.
In fact there is such a call in this example, but we would have to
assume that there was such a call even if it were not there, since
we are not supposed to write the body of @cite{Decls} knowing what
is in the body of @cite{Utils}; certainly in the case of the
static elaboration model, the compiler does not know what is in
other bodies and must assume the worst.

@item 
This means that the spec and body of @cite{Decls} must also be
elaborated before we elaborate the unit containing the call, but
that unit is @cite{Decls}! This means that the body of @cite{Decls}
must be elaborated before itself, and that's a circularity.
@end itemize

Indeed, if you add an explicit pragma @cite{Elaborate_All} for @cite{Utils} in
the body of @cite{Decls} you will get a true Ada Reference Manual
circularity that makes the program illegal.

In practice, we have found that problems with the static model of
elaboration in existing code often arise from library tasks, so
we must address this particular situation.

Note that if we compile and run the program above, using the dynamic model of
elaboration (that is to say use the @emph{-gnatE} switch),
then it compiles, binds,
links, and runs, printing the expected result of 2. Therefore in some sense
the circularity here is only apparent, and we need to capture
the properties of this program that  distinguish it from other library-level
tasks that have real elaboration problems.

We have four possible answers to this question:


@itemize *

@item 
Use the dynamic model of elaboration.

If we use the @emph{-gnatE} switch, then as noted above, the program works.
Why is this? If we examine the task body, it is apparent that the task cannot
proceed past the
@cite{accept} statement until after elaboration has been completed, because
the corresponding entry call comes from the main program, not earlier.
This is why the dynamic model works here. But that's really giving
up on a precise analysis, and we prefer to take this approach only if we cannot
solve the
problem in any other manner. So let us examine two ways to reorganize
the program to avoid the potential elaboration problem.

@item 
Split library tasks into separate packages.

Write separate packages, so that library tasks are isolated from
other declarations as much as possible. Let us look at a variation on
the above program.

@example
package Decls1 is
  task Lib_Task is
     entry Start;
  end Lib_Task;
end Decls1;

with Utils;
package body Decls1 is
  task body Lib_Task is
  begin
     accept Start;
     Utils.Put_Val (2);
  end Lib_Task;
end Decls1;

package Decls2 is
  type My_Int is new Integer;
  function Ident (M : My_Int) return My_Int;
end Decls2;

with Utils;
package body Decls2 is
  function Ident (M : My_Int) return My_Int is
  begin
     return M;
  end Ident;
end Decls2;

with Decls2;
package Utils is
  procedure Put_Val (Arg : Decls2.My_Int);
end Utils;

with Text_IO;
package body Utils is
  procedure Put_Val (Arg : Decls2.My_Int) is
  begin
     Text_IO.Put_Line (Decls2.My_Int'Image (Decls2.Ident (Arg)));
  end Put_Val;
end Utils;

with Decls1;
procedure Main is
begin
   Decls1.Lib_Task.Start;
end;
@end example

All we have done is to split @cite{Decls} into two packages, one
containing the library task, and one containing everything else. Now
there is no cycle, and the program compiles, binds, links and executes
using the default static model of elaboration.

@item 
Declare separate task types.

A significant part of the problem arises because of the use of the
single task declaration form. This means that the elaboration of
the task type, and the elaboration of the task itself (i.e., the
creation of the task) happen at the same time. A good rule
of style in Ada is to always create explicit task types. By
following the additional step of placing task objects in separate
packages from the task type declaration, many elaboration problems
are avoided. Here is another modified example of the example program:

@example
package Decls is
  task type Lib_Task_Type is
     entry Start;
  end Lib_Task_Type;

  type My_Int is new Integer;

  function Ident (M : My_Int) return My_Int;
end Decls;

with Utils;
package body Decls is
  task body Lib_Task_Type is
  begin
     accept Start;
     Utils.Put_Val (2);
  end Lib_Task_Type;

  function Ident (M : My_Int) return My_Int is
  begin
     return M;
  end Ident;
end Decls;

with Decls;
package Utils is
  procedure Put_Val (Arg : Decls.My_Int);
end Utils;

with Text_IO;
package body Utils is
  procedure Put_Val (Arg : Decls.My_Int) is
  begin
     Text_IO.Put_Line (Decls.My_Int'Image (Decls.Ident (Arg)));
  end Put_Val;
end Utils;

with Decls;
package Declst is
   Lib_Task : Decls.Lib_Task_Type;
end Declst;

with Declst;
procedure Main is
begin
   Declst.Lib_Task.Start;
end;
@end example

What we have done here is to replace the @cite{task} declaration in
package @cite{Decls} with a @cite{task type} declaration. Then we
introduce a separate package @cite{Declst} to contain the actual
task object. This separates the elaboration issues for
the @cite{task type}
declaration, which causes no trouble, from the elaboration issues
of the task object, which is also unproblematic, since it is now independent
of the elaboration of  @cite{Utils}.
This separation of concerns also corresponds to
a generally sound engineering principle of separating declarations
from instances. This version of the program also compiles, binds, links,
and executes, generating the expected output.
@end itemize

@geindex No_Entry_Calls_In_Elaboration_Code restriction


@itemize *

@item 
Use No_Entry_Calls_In_Elaboration_Code restriction.

The previous two approaches described how a program can be restructured
to avoid the special problems caused by library task bodies. in practice,
however, such restructuring may be difficult to apply to existing legacy code,
so we must consider solutions that do not require massive rewriting.

Let us consider more carefully why our original sample program works
under the dynamic model of elaboration. The reason is that the code
in the task body blocks immediately on the @cite{accept}
statement. Now of course there is nothing to prohibit elaboration
code from making entry calls (for example from another library level task),
so we cannot tell in isolation that
the task will not execute the accept statement  during elaboration.

However, in practice it is very unusual to see elaboration code
make any entry calls, and the pattern of tasks starting
at elaboration time and then immediately blocking on @cite{accept} or
@cite{select} statements is very common. What this means is that
the compiler is being too pessimistic when it analyzes the
whole package body as though it might be executed at elaboration
time.

If we know that the elaboration code contains no entry calls, (a very safe
assumption most of the time, that could almost be made the default
behavior), then we can compile all units of the program under control
of the following configuration pragma:

@example
pragma Restrictions (No_Entry_Calls_In_Elaboration_Code);
@end example

This pragma can be placed in the @code{gnat.adc} file in the usual
manner. If we take our original unmodified program and compile it
in the presence of a @code{gnat.adc} containing the above pragma,
then once again, we can compile, bind, link, and execute, obtaining
the expected result. In the presence of this pragma, the compiler does
not trace calls in a task body, that appear after the first @cite{accept}
or @cite{select} statement, and therefore does not report a potential
circularity in the original program.

The compiler will check to the extent it can that the above
restriction is not violated, but it is not always possible to do a
complete check at compile time, so it is important to use this
pragma only if the stated restriction is in fact met, that is to say
no task receives an entry call before elaboration of all units is completed.
@end itemize

@node Mixing Elaboration Models,What to Do If the Default Elaboration Behavior Fails,Elaboration Issues for Library Tasks,Elaboration Order Handling in GNAT
@anchor{gnat_ugn/elaboration_order_handling_in_gnat id10}@anchor{2c1}@anchor{gnat_ugn/elaboration_order_handling_in_gnat mixing-elaboration-models}@anchor{2c2}
@section Mixing Elaboration Models


So far, we have assumed that the entire program is either compiled
using the dynamic model or static model, ensuring consistency. It
is possible to mix the two models, but rules have to be followed
if this mixing is done to ensure that elaboration checks are not
omitted.

The basic rule is that
@strong{a unit compiled with the static model cannot
be |withed| by a unit compiled with the dynamic model}.
The reason for this is that in the static model, a unit assumes that
its clients guarantee to use (the equivalent of) pragma
@cite{Elaborate_All} so that no elaboration checks are required
in inner subprograms, and this assumption is violated if the
client is compiled with dynamic checks.

The precise rule is as follows. A unit that is compiled with dynamic
checks can only @emph{with} a unit that meets at least one of the
following criteria:


@itemize *

@item 
The @emph{with}ed unit is itself compiled with dynamic elaboration
checks (that is with the @emph{-gnatE} switch.

@item 
The @emph{with}ed unit is an internal GNAT implementation unit from
the System, Interfaces, Ada, or GNAT hierarchies.

@item 
The @emph{with}ed unit has pragma Preelaborate or pragma Pure.

@item 
The @emph{with}ing unit (that is the client) has an explicit pragma
@cite{Elaborate_All} for the @emph{with}ed unit.
@end itemize

If this rule is violated, that is if a unit with dynamic elaboration
checks @emph{with}s a unit that does not meet one of the above four
criteria, then the binder (@cite{gnatbind}) will issue a warning
similar to that in the following example:

@example
warning: "x.ads" has dynamic elaboration checks and with's
warning:   "y.ads" which has static elaboration checks
@end example

These warnings indicate that the rule has been violated, and that as a result
elaboration checks may be missed in the resulting executable file.
This warning may be suppressed using the @emph{-ws} binder switch
in the usual manner.

One useful application of this mixing rule is in the case of a subsystem
which does not itself @emph{with} units from the remainder of the
application. In this case, the entire subsystem can be compiled with
dynamic checks to resolve a circularity in the subsystem, while
allowing the main application that uses this subsystem to be compiled
using the more reliable default static model.

@node What to Do If the Default Elaboration Behavior Fails,Elaboration for Indirect Calls,Mixing Elaboration Models,Elaboration Order Handling in GNAT
@anchor{gnat_ugn/elaboration_order_handling_in_gnat id11}@anchor{2c3}@anchor{gnat_ugn/elaboration_order_handling_in_gnat what-to-do-if-the-default-elaboration-behavior-fails}@anchor{2bc}
@section What to Do If the Default Elaboration Behavior Fails


If the binder cannot find an acceptable order, it outputs detailed
diagnostics. For example:

@example
error: elaboration circularity detected
info:   "proc (body)" must be elaborated before "pack (body)"
info:     reason: Elaborate_All probably needed in unit "pack (body)"
info:     recompile "pack (body)" with -gnatel
info:                             for full details
info:       "proc (body)"
info:         is needed by its spec:
info:       "proc (spec)"
info:         which is withed by:
info:       "pack (body)"
info:  "pack (body)" must be elaborated before "proc (body)"
info:     reason: pragma Elaborate in unit "proc (body)"
@end example

In this case we have a cycle that the binder cannot break. On the one
hand, there is an explicit pragma Elaborate in @cite{proc} for
@cite{pack}. This means that the body of @cite{pack} must be elaborated
before the body of @cite{proc}. On the other hand, there is elaboration
code in @cite{pack} that calls a subprogram in @cite{proc}. This means
that for maximum safety, there should really be a pragma
Elaborate_All in @cite{pack} for @cite{proc} which would require that
the body of @cite{proc} be elaborated before the body of
@cite{pack}. Clearly both requirements cannot be satisfied.
Faced with a circularity of this kind, you have three different options.


@itemize *

@item 
@emph{Fix the program}

The most desirable option from the point of view of long-term maintenance
is to rearrange the program so that the elaboration problems are avoided.
One useful technique is to place the elaboration code into separate
child packages. Another is to move some of the initialization code to
explicitly called subprograms, where the program controls the order
of initialization explicitly. Although this is the most desirable option,
it may be impractical and involve too much modification, especially in
the case of complex legacy code.

@item 
@emph{Perform dynamic checks}

If the compilations are done using the @emph{-gnatE}
(dynamic elaboration check) switch, then GNAT behaves in a quite different
manner. Dynamic checks are generated for all calls that could possibly result
in raising an exception. With this switch, the compiler does not generate
implicit @cite{Elaborate} or @cite{Elaborate_All} pragmas. The behavior then is
exactly as specified in the @cite{Ada Reference Manual}.
The binder will generate
an executable program that may or may not raise @cite{Program_Error}, and then
it is the programmer's job to ensure that it does not raise an exception. Note
that it is important to compile all units with the switch, it cannot be used
selectively.

@item 
@emph{Suppress checks}

The drawback of dynamic checks is that they generate a
significant overhead at run time, both in space and time. If you
are absolutely sure that your program cannot raise any elaboration
exceptions, and you still want to use the dynamic elaboration model,
then you can use the configuration pragma
@cite{Suppress (Elaboration_Check)} to suppress all such checks. For
example this pragma could be placed in the @code{gnat.adc} file.

@item 
@emph{Suppress checks selectively}

When you know that certain calls or instantiations in elaboration code cannot
possibly lead to an elaboration error, and the binder nevertheless complains
about implicit @cite{Elaborate} and @cite{Elaborate_All} pragmas that lead to
elaboration circularities, it is possible to remove those warnings locally and
obtain a program that will bind. Clearly this can be unsafe, and it is the
responsibility of the programmer to make sure that the resulting program has no
elaboration anomalies. The pragma @cite{Suppress (Elaboration_Check)} can be
used with different granularity to suppress warnings and break elaboration
circularities:


@itemize *

@item 
Place the pragma that names the called subprogram in the declarative part
that contains the call.

@item 
Place the pragma in the declarative part, without naming an entity. This
disables warnings on all calls in the corresponding  declarative region.

@item 
Place the pragma in the package spec that declares the called subprogram,
and name the subprogram. This disables warnings on all elaboration calls to
that subprogram.

@item 
Place the pragma in the package spec that declares the called subprogram,
without naming any entity. This disables warnings on all elaboration calls to
all subprograms declared in this spec.

@item 
Use Pragma Elaborate.

As previously described in section @ref{2bd,,Treatment of Pragma Elaborate},
GNAT in static mode assumes that a @cite{pragma} Elaborate indicates correctly
that no elaboration checks are required on calls to the designated unit.
There may be cases in which the caller knows that no transitive calls
can occur, so that a @cite{pragma Elaborate} will be sufficient in a
case where @cite{pragma Elaborate_All} would cause a circularity.
@end itemize

These five cases are listed in order of decreasing safety, and therefore
require increasing programmer care in their application. Consider the
following program:

@example
package Pack1 is
  function F1 return Integer;
  X1 : Integer;
end Pack1;

package Pack2 is
  function F2 return Integer;
  function Pure (x : integer) return integer;
  --  pragma Suppress (Elaboration_Check, On => Pure);  -- (3)
  --  pragma Suppress (Elaboration_Check);              -- (4)
end Pack2;

with Pack2;
package body Pack1 is
  function F1 return Integer is
  begin
    return 100;
  end F1;
  Val : integer := Pack2.Pure (11);    --  Elab. call (1)
begin
  declare
    --  pragma Suppress(Elaboration_Check, Pack2.F2);   -- (1)
    --  pragma Suppress(Elaboration_Check);             -- (2)
  begin
    X1 := Pack2.F2 + 1;                --  Elab. call (2)
  end;
end Pack1;

with Pack1;
package body Pack2 is
  function F2 return Integer is
  begin
     return Pack1.F1;
  end F2;
  function Pure (x : integer) return integer is
  begin
     return x ** 3 - 3 * x;
  end;
end Pack2;

with Pack1, Ada.Text_IO;
procedure Proc3 is
begin
  Ada.Text_IO.Put_Line(Pack1.X1'Img); -- 101
end Proc3;
@end example

In the absence of any pragmas, an attempt to bind this program produces
the following diagnostics:

@example
error: elaboration circularity detected
info:    "pack1 (body)" must be elaborated before "pack1 (body)"
info:       reason: Elaborate_All probably needed in unit "pack1 (body)"
info:       recompile "pack1 (body)" with -gnatel for full details
info:          "pack1 (body)"
info:             must be elaborated along with its spec:
info:          "pack1 (spec)"
info:             which is withed by:
info:          "pack2 (body)"
info:             which must be elaborated along with its spec:
info:          "pack2 (spec)"
info:             which is withed by:
info:          "pack1 (body)"
@end example

The sources of the circularity are the two calls to @cite{Pack2.Pure} and
@cite{Pack2.F2} in the body of @cite{Pack1}. We can see that the call to
F2 is safe, even though F2 calls F1, because the call appears after the
elaboration of the body of F1. Therefore the pragma (1) is safe, and will
remove the warning on the call. It is also possible to use pragma (2)
because there are no other potentially unsafe calls in the block.

The call to @cite{Pure} is safe because this function does not depend on the
state of @cite{Pack2}. Therefore any call to this function is safe, and it
is correct to place pragma (3) in the corresponding package spec.

Finally, we could place pragma (4) in the spec of @cite{Pack2} to disable
warnings on all calls to functions declared therein. Note that this is not
necessarily safe, and requires more detailed examination of the subprogram
bodies involved. In particular, a call to @cite{F2} requires that @cite{F1}
be already elaborated.
@end itemize

It is hard to generalize on which of these four approaches should be
taken. Obviously if it is possible to fix the program so that the default
treatment works, this is preferable, but this may not always be practical.
It is certainly simple enough to use @emph{-gnatE}
but the danger in this case is that, even if the GNAT binder
finds a correct elaboration order, it may not always do so,
and certainly a binder from another Ada compiler might not. A
combination of testing and analysis (for which the
information messages generated with the @emph{-gnatel}
switch can be useful) must be used to ensure that the program is free
of errors. One switch that is useful in this testing is the
@emph{-p (pessimistic elaboration order)} switch for @cite{gnatbind}.
Normally the binder tries to find an order that has the best chance
of avoiding elaboration problems. However, if this switch is used, the binder
plays a devil's advocate role, and tries to choose the order that
has the best chance of failing. If your program works even with this
switch, then it has a better chance of being error free, but this is still
not a guarantee.

For an example of this approach in action, consider the C-tests (executable
tests) from the ACATS suite. If these are compiled and run with the default
treatment, then all but one of them succeed without generating any error
diagnostics from the binder. However, there is one test that fails, and
this is not surprising, because the whole point of this test is to ensure
that the compiler can handle cases where it is impossible to determine
a correct order statically, and it checks that an exception is indeed
raised at run time.

This one test must be compiled and run using the @emph{-gnatE}
switch, and then it passes. Alternatively, the entire suite can
be run using this switch. It is never wrong to run with the dynamic
elaboration switch if your code is correct, and we assume that the
C-tests are indeed correct (it is less efficient, but efficiency is
not a factor in running the ACATS tests.)

@node Elaboration for Indirect Calls,Summary of Procedures for Elaboration Control,What to Do If the Default Elaboration Behavior Fails,Elaboration Order Handling in GNAT
@anchor{gnat_ugn/elaboration_order_handling_in_gnat id12}@anchor{2c4}@anchor{gnat_ugn/elaboration_order_handling_in_gnat elaboration-for-indirect-calls}@anchor{2c5}
@section Elaboration for Indirect Calls


@geindex Dispatching calls

@geindex Indirect calls

In rare cases, the static elaboration model fails to prevent
dispatching calls to not-yet-elaborated subprograms. In such cases, we
fall back to run-time checks; premature calls to any primitive
operation of a tagged type before the body of the operation has been
elaborated will raise @cite{Program_Error}.

Access-to-subprogram types, however, are handled conservatively, and
do not require run-time checks. This was not true in earlier versions
of the compiler; you can use the @emph{-gnatd.U} debug switch to
revert to the old behavior if the new conservative behavior causes
elaboration cycles. Here, 'conservative' means that if you do
@cite{P'Access} during elaboration, the compiler will assume that you
might call @cite{P} indirectly during elaboration, so it adds an
implicit @cite{pragma Elaborate_All} on the library unit containing
@cite{P}. The @emph{-gnatd.U} switch is safe if you know there are
no such calls. If the program worked before, it will continue to work
with @emph{-gnatd.U}. But beware that code modifications such as
adding an indirect call can cause erroneous behavior in the presence
of @emph{-gnatd.U}.

@node Summary of Procedures for Elaboration Control,Other Elaboration Order Considerations,Elaboration for Indirect Calls,Elaboration Order Handling in GNAT
@anchor{gnat_ugn/elaboration_order_handling_in_gnat id13}@anchor{2c6}@anchor{gnat_ugn/elaboration_order_handling_in_gnat summary-of-procedures-for-elaboration-control}@anchor{2c7}
@section Summary of Procedures for Elaboration Control


@geindex Elaboration control

First, compile your program with the default options, using none of
the special elaboration control switches. If the binder successfully
binds your program, then you can be confident that, apart from issues
raised by the use of access-to-subprogram types and dynamic dispatching,
the program is free of elaboration errors. If it is important that the
program be portable to other compilers than GNAT, then use the
@emph{-gnatel}
switch to generate messages about missing @cite{Elaborate} or
@cite{Elaborate_All} pragmas, and supply the missing pragmas.

If the program fails to bind using the default static elaboration
handling, then you can fix the program to eliminate the binder
message, or recompile the entire program with the
@emph{-gnatE} switch to generate dynamic elaboration checks,
and, if you are sure there really are no elaboration problems,
use a global pragma @cite{Suppress (Elaboration_Check)}.

@node Other Elaboration Order Considerations,Determining the Chosen Elaboration Order,Summary of Procedures for Elaboration Control,Elaboration Order Handling in GNAT
@anchor{gnat_ugn/elaboration_order_handling_in_gnat id14}@anchor{2c8}@anchor{gnat_ugn/elaboration_order_handling_in_gnat other-elaboration-order-considerations}@anchor{2c9}
@section Other Elaboration Order Considerations


This section has been entirely concerned with the issue of finding a valid
elaboration order, as defined by the Ada Reference Manual. In a case
where several elaboration orders are valid, the task is to find one
of the possible valid elaboration orders (and the static model in GNAT
will ensure that this is achieved).

The purpose of the elaboration rules in the Ada Reference Manual is to
make sure that no entity is accessed before it has been elaborated. For
a subprogram, this means that the spec and body must have been elaborated
before the subprogram is called. For an object, this means that the object
must have been elaborated before its value is read or written. A violation
of either of these two requirements is an access before elaboration order,
and this section has been all about avoiding such errors.

In the case where more than one order of elaboration is possible, in the
sense that access before elaboration errors are avoided, then any one of
the orders is 'correct' in the sense that it meets the requirements of
the Ada Reference Manual, and no such error occurs.

However, it may be the case for a given program, that there are
constraints on the order of elaboration that come not from consideration
of avoiding elaboration errors, but rather from extra-lingual logic
requirements. Consider this example:

@example
with Init_Constants;
package Constants is
   X : Integer := 0;
   Y : Integer := 0;
end Constants;

package Init_Constants is
   procedure P; --* require a body*
end Init_Constants;

with Constants;
package body Init_Constants is
   procedure P is begin null; end;
begin
   Constants.X := 3;
   Constants.Y := 4;
end Init_Constants;

with Constants;
package Calc is
   Z : Integer := Constants.X + Constants.Y;
end Calc;

with Calc;
with Text_IO; use Text_IO;
procedure Main is
begin
   Put_Line (Calc.Z'Img);
end Main;
@end example

In this example, there is more than one valid order of elaboration. For
example both the following are correct orders:

@example
Init_Constants spec
Constants spec
Calc spec
Init_Constants body
Main body
@end example

and

@example
Init_Constants spec
Init_Constants body
Constants spec
Calc spec
Main body
@end example

There is no language rule to prefer one or the other, both are correct
from an order of elaboration point of view. But the programmatic effects
of the two orders are very different. In the first, the elaboration routine
of @cite{Calc} initializes @cite{Z} to zero, and then the main program
runs with this value of zero. But in the second order, the elaboration
routine of @cite{Calc} runs after the body of Init_Constants has set
@cite{X} and @cite{Y} and thus @cite{Z} is set to 7 before @cite{Main} runs.

One could perhaps by applying pretty clever non-artificial intelligence
to the situation guess that it is more likely that the second order of
elaboration is the one desired, but there is no formal linguistic reason
to prefer one over the other. In fact in this particular case, GNAT will
prefer the second order, because of the rule that bodies are elaborated
as soon as possible, but it's just luck that this is what was wanted
(if indeed the second order was preferred).

If the program cares about the order of elaboration routines in a case like
this, it is important to specify the order required. In this particular
case, that could have been achieved by adding to the spec of Calc:

@example
pragma Elaborate_All (Constants);
@end example

which requires that the body (if any) and spec of @cite{Constants},
as well as the body and spec of any unit @emph{with}ed by
@cite{Constants} be elaborated before @cite{Calc} is elaborated.

Clearly no automatic method can always guess which alternative you require,
and if you are working with legacy code that had constraints of this kind
which were not properly specified by adding @cite{Elaborate} or
@cite{Elaborate_All} pragmas, then indeed it is possible that two different
compilers can choose different orders.

However, GNAT does attempt to diagnose the common situation where there
are uninitialized variables in the visible part of a package spec, and the
corresponding package body has an elaboration block that directly or
indirectly initialized one or more of these variables. This is the situation
in which a pragma Elaborate_Body is usually desirable, and GNAT will generate
a warning that suggests this addition if it detects this situation.

The @cite{gnatbind} @emph{-p} switch may be useful in smoking
out problems. This switch causes bodies to be elaborated as late as possible
instead of as early as possible. In the example above, it would have forced
the choice of the first elaboration order. If you get different results
when using this switch, and particularly if one set of results is right,
and one is wrong as far as you are concerned, it shows that you have some
missing @cite{Elaborate} pragmas. For the example above, we have the
following output:

@example
$ gnatmake -f -q main
$ main
 7
$ gnatmake -f -q main -bargs -p
$ main
 0
@end example

It is of course quite unlikely that both these results are correct, so
it is up to you in a case like this to investigate the source of the
difference, by looking at the two elaboration orders that are chosen,
and figuring out which is correct, and then adding the necessary
@cite{Elaborate} or @cite{Elaborate_All} pragmas to ensure the desired order.

@node Determining the Chosen Elaboration Order,,Other Elaboration Order Considerations,Elaboration Order Handling in GNAT
@anchor{gnat_ugn/elaboration_order_handling_in_gnat determining-the-chosen-elaboration-order}@anchor{2ca}@anchor{gnat_ugn/elaboration_order_handling_in_gnat id15}@anchor{2cb}
@section Determining the Chosen Elaboration Order


To see the elaboration order that the binder chooses, you can look at
the last part of the file:@cite{b~xxx.adb} binder output file. Here is an example:

@example
System.Soft_Links'Elab_Body;
E14 := True;
System.Secondary_Stack'Elab_Body;
E18 := True;
System.Exception_Table'Elab_Body;
E24 := True;
Ada.Io_Exceptions'Elab_Spec;
E67 := True;
Ada.Tags'Elab_Spec;
Ada.Streams'Elab_Spec;
E43 := True;
Interfaces.C'Elab_Spec;
E69 := True;
System.Finalization_Root'Elab_Spec;
E60 := True;
System.Os_Lib'Elab_Body;
E71 := True;
System.Finalization_Implementation'Elab_Spec;
System.Finalization_Implementation'Elab_Body;
E62 := True;
Ada.Finalization'Elab_Spec;
E58 := True;
Ada.Finalization.List_Controller'Elab_Spec;
E76 := True;
System.File_Control_Block'Elab_Spec;
E74 := True;
System.File_Io'Elab_Body;
E56 := True;
Ada.Tags'Elab_Body;
E45 := True;
Ada.Text_Io'Elab_Spec;
Ada.Text_Io'Elab_Body;
E07 := True;
@end example

Here Elab_Spec elaborates the spec
and Elab_Body elaborates the body. The assignments to the @code{E@emph{xx}} flags
flag that the corresponding body is now elaborated.

You can also ask the binder to generate a more
readable list of the elaboration order using the
@cite{-l} switch when invoking the binder. Here is
an example of the output generated by this switch:

@example
ada (spec)
interfaces (spec)
system (spec)
system.case_util (spec)
system.case_util (body)
system.concat_2 (spec)
system.concat_2 (body)
system.concat_3 (spec)
system.concat_3 (body)
system.htable (spec)
system.parameters (spec)
system.parameters (body)
system.crtl (spec)
interfaces.c_streams (spec)
interfaces.c_streams (body)
system.restrictions (spec)
system.restrictions (body)
system.standard_library (spec)
system.exceptions (spec)
system.exceptions (body)
system.storage_elements (spec)
system.storage_elements (body)
system.secondary_stack (spec)
system.stack_checking (spec)
system.stack_checking (body)
system.string_hash (spec)
system.string_hash (body)
system.htable (body)
system.strings (spec)
system.strings (body)
system.traceback (spec)
system.traceback (body)
system.traceback_entries (spec)
system.traceback_entries (body)
ada.exceptions (spec)
ada.exceptions.last_chance_handler (spec)
system.soft_links (spec)
system.soft_links (body)
ada.exceptions.last_chance_handler (body)
system.secondary_stack (body)
system.exception_table (spec)
system.exception_table (body)
ada.io_exceptions (spec)
ada.tags (spec)
ada.streams (spec)
interfaces.c (spec)
interfaces.c (body)
system.finalization_root (spec)
system.finalization_root (body)
system.memory (spec)
system.memory (body)
system.standard_library (body)
system.os_lib (spec)
system.os_lib (body)
system.unsigned_types (spec)
system.stream_attributes (spec)
system.stream_attributes (body)
system.finalization_implementation (spec)
system.finalization_implementation (body)
ada.finalization (spec)
ada.finalization (body)
ada.finalization.list_controller (spec)
ada.finalization.list_controller (body)
system.file_control_block (spec)
system.file_io (spec)
system.file_io (body)
system.val_uns (spec)
system.val_util (spec)
system.val_util (body)
system.val_uns (body)
system.wch_con (spec)
system.wch_con (body)
system.wch_cnv (spec)
system.wch_jis (spec)
system.wch_jis (body)
system.wch_cnv (body)
system.wch_stw (spec)
system.wch_stw (body)
ada.tags (body)
ada.exceptions (body)
ada.text_io (spec)
ada.text_io (body)
text_io (spec)
gdbstr (body)
@end example

@node Inline Assembler,GNU Free Documentation License,Elaboration Order Handling in GNAT,Top
@anchor{gnat_ugn/inline_assembler inline-assembler}@anchor{12}@anchor{gnat_ugn/inline_assembler doc}@anchor{2cc}@anchor{gnat_ugn/inline_assembler id1}@anchor{2cd}
@chapter Inline Assembler


@geindex Inline Assembler

If you need to write low-level software that interacts directly
with the hardware, Ada provides two ways to incorporate assembly
language code into your program.  First, you can import and invoke
external routines written in assembly language, an Ada feature fully
supported by GNAT.  However, for small sections of code it may be simpler
or more efficient to include assembly language statements directly
in your Ada source program, using the facilities of the implementation-defined
package @cite{System.Machine_Code}, which incorporates the gcc
Inline Assembler.  The Inline Assembler approach offers a number of advantages,
including the following:


@itemize *

@item 
No need to use non-Ada tools

@item 
Consistent interface over different targets

@item 
Automatic usage of the proper calling conventions

@item 
Access to Ada constants and variables

@item 
Definition of intrinsic routines

@item 
Possibility of inlining a subprogram comprising assembler code

@item 
Code optimizer can take Inline Assembler code into account
@end itemize

This appendix presents a series of examples to show you how to use
the Inline Assembler.  Although it focuses on the Intel x86,
the general approach applies also to other processors.
It is assumed that you are familiar with Ada
and with assembly language programming.

@menu
* Basic Assembler Syntax:: 
* A Simple Example of Inline Assembler:: 
* Output Variables in Inline Assembler:: 
* Input Variables in Inline Assembler:: 
* Inlining Inline Assembler Code:: 
* Other Asm Functionality:: 

@end menu

@node Basic Assembler Syntax,A Simple Example of Inline Assembler,,Inline Assembler
@anchor{gnat_ugn/inline_assembler id2}@anchor{2ce}@anchor{gnat_ugn/inline_assembler basic-assembler-syntax}@anchor{2cf}
@section Basic Assembler Syntax


The assembler used by GNAT and gcc is based not on the Intel assembly
language, but rather on a language that descends from the AT&T Unix
assembler @emph{as} (and which is often referred to as 'AT&T syntax').
The following table summarizes the main features of @emph{as} syntax
and points out the differences from the Intel conventions.
See the gcc @emph{as} and @emph{gas} (an @emph{as} macro
pre-processor) documentation for further information.


@display
@emph{Register names}@w{ }
@display
gcc / @emph{as}: Prefix with '%'; for example @cite{%eax}@w{ }
Intel: No extra punctuation; for example @cite{eax}@w{ }
@end display
@end display




@display
@emph{Immediate operand}@w{ }
@display
gcc / @emph{as}: Prefix with '$'; for example @cite{$4}@w{ }
Intel: No extra punctuation; for example @cite{4}@w{ }
@end display
@end display




@display
@emph{Address}@w{ }
@display
gcc / @emph{as}: Prefix with '$'; for example @cite{$loc}@w{ }
Intel: No extra punctuation; for example @cite{loc}@w{ }
@end display
@end display




@display
@emph{Memory contents}@w{ }
@display
gcc / @emph{as}: No extra punctuation; for example @cite{loc}@w{ }
Intel: Square brackets; for example @cite{[loc]}@w{ }
@end display
@end display




@display
@emph{Register contents}@w{ }
@display
gcc / @emph{as}: Parentheses; for example @cite{(%eax)}@w{ }
Intel: Square brackets; for example @cite{[eax]}@w{ }
@end display
@end display




@display
@emph{Hexadecimal numbers}@w{ }
@display
gcc / @emph{as}: Leading '0x' (C language syntax); for example @cite{0xA0}@w{ }
Intel: Trailing 'h'; for example @cite{A0h}@w{ }
@end display
@end display




@display
@emph{Operand size}@w{ }
@display
gcc / @emph{as}: Explicit in op code; for example @cite{movw} to move a 16-bit word@w{ }
Intel: Implicit, deduced by assembler; for example @cite{mov}@w{ }
@end display
@end display




@display
@emph{Instruction repetition}@w{ }
@display
gcc / @emph{as}: Split into two lines; for example@w{ }
@display
@cite{rep}@w{ }
@cite{stosl}@w{ }
@end display
Intel: Keep on one line; for example @cite{rep stosl}@w{ }
@end display
@end display




@display
@emph{Order of operands}@w{ }
@display
gcc / @emph{as}: Source first; for example @cite{movw $4@comma{} %eax}@w{ }
Intel: Destination first; for example @cite{mov eax@comma{} 4}@w{ }
@end display
@end display



@node A Simple Example of Inline Assembler,Output Variables in Inline Assembler,Basic Assembler Syntax,Inline Assembler
@anchor{gnat_ugn/inline_assembler a-simple-example-of-inline-assembler}@anchor{2d0}@anchor{gnat_ugn/inline_assembler id3}@anchor{2d1}
@section A Simple Example of Inline Assembler


The following example will generate a single assembly language statement,
@cite{nop}, which does nothing.  Despite its lack of run-time effect,
the example will be useful in illustrating the basics of
the Inline Assembler facility.

@quotation

@example
with System.Machine_Code; use System.Machine_Code;
procedure Nothing is
begin
   Asm ("nop");
end Nothing;
@end example
@end quotation

@cite{Asm} is a procedure declared in package @cite{System.Machine_Code};
here it takes one parameter, a @emph{template string} that must be a static
expression and that will form the generated instruction.
@cite{Asm} may be regarded as a compile-time procedure that parses
the template string and additional parameters (none here),
from which it generates a sequence of assembly language instructions.

The examples in this chapter will illustrate several of the forms
for invoking @cite{Asm}; a complete specification of the syntax
is found in the @cite{Machine_Code_Insertions} section of the
@cite{GNAT Reference Manual}.

Under the standard GNAT conventions, the @cite{Nothing} procedure
should be in a file named @code{nothing.adb}.
You can build the executable in the usual way:

@quotation

@example
$ gnatmake nothing
@end example
@end quotation

However, the interesting aspect of this example is not its run-time behavior
but rather the generated assembly code.
To see this output, invoke the compiler as follows:

@quotation

@example
$  gcc -c -S -fomit-frame-pointer -gnatp nothing.adb
@end example
@end quotation

where the options are:


@itemize *

@item 

@table @asis

@item @code{-c}

compile only (no bind or link)
@end table

@item 

@table @asis

@item @code{-S}

generate assembler listing
@end table

@item 

@table @asis

@item @code{-fomit-frame-pointer}

do not set up separate stack frames
@end table

@item 

@table @asis

@item @code{-gnatp}

do not add runtime checks
@end table
@end itemize

This gives a human-readable assembler version of the code. The resulting
file will have the same name as the Ada source file, but with a @cite{.s}
extension. In our example, the file @code{nothing.s} has the following
contents:

@quotation

@example
.file "nothing.adb"
gcc2_compiled.:
___gnu_compiled_ada:
.text
   .align 4
.globl __ada_nothing
__ada_nothing:
#APP
   nop
#NO_APP
   jmp L1
   .align 2,0x90
L1:
   ret
@end example
@end quotation

The assembly code you included is clearly indicated by
the compiler, between the @cite{#APP} and @cite{#NO_APP}
delimiters. The character before the 'APP' and 'NOAPP'
can differ on different targets. For example, GNU/Linux uses '#APP' while
on NT you will see '/APP'.

If you make a mistake in your assembler code (such as using the
wrong size modifier, or using a wrong operand for the instruction) GNAT
will report this error in a temporary file, which will be deleted when
the compilation is finished.  Generating an assembler file will help
in such cases, since you can assemble this file separately using the
@emph{as} assembler that comes with gcc.

Assembling the file using the command

@quotation

@example
$ as nothing.s
@end example
@end quotation

will give you error messages whose lines correspond to the assembler
input file, so you can easily find and correct any mistakes you made.
If there are no errors, @emph{as} will generate an object file
@code{nothing.out}.

@node Output Variables in Inline Assembler,Input Variables in Inline Assembler,A Simple Example of Inline Assembler,Inline Assembler
@anchor{gnat_ugn/inline_assembler id4}@anchor{2d2}@anchor{gnat_ugn/inline_assembler output-variables-in-inline-assembler}@anchor{2d3}
@section Output Variables in Inline Assembler


The examples in this section, showing how to access the processor flags,
illustrate how to specify the destination operands for assembly language
statements.

@quotation

@example
with Interfaces; use Interfaces;
with Ada.Text_IO; use Ada.Text_IO;
with System.Machine_Code; use System.Machine_Code;
procedure Get_Flags is
   Flags : Unsigned_32;
   use ASCII;
begin
   Asm ("pushfl"          & LF & HT & -- push flags on stack
        "popl %%eax"      & LF & HT & -- load eax with flags
        "movl %%eax, %0",             -- store flags in variable
        Outputs => Unsigned_32'Asm_Output ("=g", Flags));
   Put_Line ("Flags register:" & Flags'Img);
end Get_Flags;
@end example
@end quotation

In order to have a nicely aligned assembly listing, we have separated
multiple assembler statements in the Asm template string with linefeed
(ASCII.LF) and horizontal tab (ASCII.HT) characters.
The resulting section of the assembly output file is:

@quotation

@example
#APP
   pushfl
   popl %eax
   movl %eax, -40(%ebp)
#NO_APP
@end example
@end quotation

It would have been legal to write the Asm invocation as:

@quotation

@example
Asm ("pushfl popl %%eax movl %%eax, %0")
@end example
@end quotation

but in the generated assembler file, this would come out as:

@quotation

@example
#APP
   pushfl popl %eax movl %eax, -40(%ebp)
#NO_APP
@end example
@end quotation

which is not so convenient for the human reader.

We use Ada comments
at the end of each line to explain what the assembler instructions
actually do.  This is a useful convention.

When writing Inline Assembler instructions, you need to precede each register
and variable name with a percent sign.  Since the assembler already requires
a percent sign at the beginning of a register name, you need two consecutive
percent signs for such names in the Asm template string, thus @cite{%%eax}.
In the generated assembly code, one of the percent signs will be stripped off.

Names such as @cite{%0}, @cite{%1}, @cite{%2}, etc., denote input or output
variables: operands you later define using @cite{Input} or @cite{Output}
parameters to @cite{Asm}.
An output variable is illustrated in
the third statement in the Asm template string:

@quotation

@example
movl %%eax, %0
@end example
@end quotation

The intent is to store the contents of the eax register in a variable that can
be accessed in Ada.  Simply writing @cite{movl %%eax@comma{} Flags} would not
necessarily work, since the compiler might optimize by using a register
to hold Flags, and the expansion of the @cite{movl} instruction would not be
aware of this optimization.  The solution is not to store the result directly
but rather to advise the compiler to choose the correct operand form;
that is the purpose of the @cite{%0} output variable.

Information about the output variable is supplied in the @cite{Outputs}
parameter to @cite{Asm}:

@quotation

@example
Outputs => Unsigned_32'Asm_Output ("=g", Flags));
@end example
@end quotation

The output is defined by the @cite{Asm_Output} attribute of the target type;
the general format is

@quotation

@example
Type'Asm_Output (constraint_string, variable_name)
@end example
@end quotation

The constraint string directs the compiler how
to store/access the associated variable.  In the example

@quotation

@example
Unsigned_32'Asm_Output ("=m", Flags);
@end example
@end quotation

the @cite{"m"} (memory) constraint tells the compiler that the variable
@cite{Flags} should be stored in a memory variable, thus preventing
the optimizer from keeping it in a register.  In contrast,

@quotation

@example
Unsigned_32'Asm_Output ("=r", Flags);
@end example
@end quotation

uses the @cite{"r"} (register) constraint, telling the compiler to
store the variable in a register.

If the constraint is preceded by the equal character '=', it tells
the compiler that the variable will be used to store data into it.

In the @cite{Get_Flags} example, we used the @cite{"g"} (global) constraint,
allowing the optimizer to choose whatever it deems best.

There are a fairly large number of constraints, but the ones that are
most useful (for the Intel x86 processor) are the following:

@quotation


@multitable {xxxxxxxx} {xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx} 
@item

@emph{=}

@tab

output constraint

@item

@emph{g}

@tab

global (i.e., can be stored anywhere)

@item

@emph{m}

@tab

in memory

@item

@emph{I}

@tab

a constant

@item

@emph{a}

@tab

use eax

@item

@emph{b}

@tab

use ebx

@item

@emph{c}

@tab

use ecx

@item

@emph{d}

@tab

use edx

@item

@emph{S}

@tab

use esi

@item

@emph{D}

@tab

use edi

@item

@emph{r}

@tab

use one of eax, ebx, ecx or edx

@item

@emph{q}

@tab

use one of eax, ebx, ecx, edx, esi or edi

@end multitable

@end quotation

The full set of constraints is described in the gcc and @emph{as}
documentation; note that it is possible to combine certain constraints
in one constraint string.

You specify the association of an output variable with an assembler operand
through the @code{%@emph{n}} notation, where @emph{n} is a non-negative
integer.  Thus in

@quotation

@example
Asm ("pushfl"          & LF & HT & -- push flags on stack
     "popl %%eax"      & LF & HT & -- load eax with flags
     "movl %%eax, %0",             -- store flags in variable
     Outputs => Unsigned_32'Asm_Output ("=g", Flags));
@end example
@end quotation

@cite{%0} will be replaced in the expanded code by the appropriate operand,
whatever
the compiler decided for the @cite{Flags} variable.

In general, you may have any number of output variables:


@itemize *

@item 
Count the operands starting at 0; thus @cite{%0}, @cite{%1}, etc.

@item 
Specify the @cite{Outputs} parameter as a parenthesized comma-separated list
of @cite{Asm_Output} attributes
@end itemize

For example:

@quotation

@example
Asm ("movl %%eax, %0" & LF & HT &
     "movl %%ebx, %1" & LF & HT &
     "movl %%ecx, %2",
     Outputs => (Unsigned_32'Asm_Output ("=g", Var_A),   --  %0 = Var_A
                 Unsigned_32'Asm_Output ("=g", Var_B),   --  %1 = Var_B
                 Unsigned_32'Asm_Output ("=g", Var_C))); --  %2 = Var_C
@end example
@end quotation

where @cite{Var_A}, @cite{Var_B}, and @cite{Var_C} are variables
in the Ada program.

As a variation on the @cite{Get_Flags} example, we can use the constraints
string to direct the compiler to store the eax register into the @cite{Flags}
variable, instead of including the store instruction explicitly in the
@cite{Asm} template string:

@quotation

@example
with Interfaces; use Interfaces;
with Ada.Text_IO; use Ada.Text_IO;
with System.Machine_Code; use System.Machine_Code;
procedure Get_Flags_2 is
   Flags : Unsigned_32;
   use ASCII;
begin
   Asm ("pushfl"      & LF & HT & -- push flags on stack
        "popl %%eax",             -- save flags in eax
        Outputs => Unsigned_32'Asm_Output ("=a", Flags));
   Put_Line ("Flags register:" & Flags'Img);
end Get_Flags_2;
@end example
@end quotation

The @cite{"a"} constraint tells the compiler that the @cite{Flags}
variable will come from the eax register. Here is the resulting code:

@quotation

@example
#APP
   pushfl
   popl %eax
#NO_APP
   movl %eax,-40(%ebp)
@end example
@end quotation

The compiler generated the store of eax into Flags after
expanding the assembler code.

Actually, there was no need to pop the flags into the eax register;
more simply, we could just pop the flags directly into the program variable:

@quotation

@example
with Interfaces; use Interfaces;
with Ada.Text_IO; use Ada.Text_IO;
with System.Machine_Code; use System.Machine_Code;
procedure Get_Flags_3 is
   Flags : Unsigned_32;
   use ASCII;
begin
   Asm ("pushfl"  & LF & HT & -- push flags on stack
        "pop %0",             -- save flags in Flags
        Outputs => Unsigned_32'Asm_Output ("=g", Flags));
   Put_Line ("Flags register:" & Flags'Img);
end Get_Flags_3;
@end example
@end quotation

@node Input Variables in Inline Assembler,Inlining Inline Assembler Code,Output Variables in Inline Assembler,Inline Assembler
@anchor{gnat_ugn/inline_assembler id5}@anchor{2d4}@anchor{gnat_ugn/inline_assembler input-variables-in-inline-assembler}@anchor{2d5}
@section Input Variables in Inline Assembler


The example in this section illustrates how to specify the source operands
for assembly language statements.
The program simply increments its input value by 1:

@quotation

@example
with Interfaces; use Interfaces;
with Ada.Text_IO; use Ada.Text_IO;
with System.Machine_Code; use System.Machine_Code;
procedure Increment is

   function Incr (Value : Unsigned_32) return Unsigned_32 is
      Result : Unsigned_32;
   begin
      Asm ("incl %0",
           Outputs => Unsigned_32'Asm_Output ("=a", Result),
           Inputs  => Unsigned_32'Asm_Input ("a", Value));
      return Result;
   end Incr;

   Value : Unsigned_32;

begin
   Value := 5;
   Put_Line ("Value before is" & Value'Img);
   Value := Incr (Value);
  Put_Line ("Value after is" & Value'Img);
end Increment;
@end example
@end quotation

The @cite{Outputs} parameter to @cite{Asm} specifies
that the result will be in the eax register and that it is to be stored
in the @cite{Result} variable.

The @cite{Inputs} parameter looks much like the @cite{Outputs} parameter,
but with an @cite{Asm_Input} attribute.
The @cite{"="} constraint, indicating an output value, is not present.

You can have multiple input variables, in the same way that you can have more
than one output variable.

The parameter count (%0, %1) etc, still starts at the first output statement,
and continues with the input statements.

Just as the @cite{Outputs} parameter causes the register to be stored into the
target variable after execution of the assembler statements, so does the
@cite{Inputs} parameter cause its variable to be loaded into the register
before execution of the assembler statements.

Thus the effect of the @cite{Asm} invocation is:


@itemize *

@item 
load the 32-bit value of @cite{Value} into eax

@item 
execute the @cite{incl %eax} instruction

@item 
store the contents of eax into the @cite{Result} variable
@end itemize

The resulting assembler file (with @emph{-O2} optimization) contains:

@quotation

@example
_increment__incr.1:
   subl $4,%esp
   movl 8(%esp),%eax
#APP
   incl %eax
#NO_APP
   movl %eax,%edx
   movl %ecx,(%esp)
   addl $4,%esp
   ret
@end example
@end quotation

@node Inlining Inline Assembler Code,Other Asm Functionality,Input Variables in Inline Assembler,Inline Assembler
@anchor{gnat_ugn/inline_assembler id6}@anchor{2d6}@anchor{gnat_ugn/inline_assembler inlining-inline-assembler-code}@anchor{2d7}
@section Inlining Inline Assembler Code


For a short subprogram such as the @cite{Incr} function in the previous
section, the overhead of the call and return (creating / deleting the stack
frame) can be significant, compared to the amount of code in the subprogram
body.  A solution is to apply Ada's @cite{Inline} pragma to the subprogram,
which directs the compiler to expand invocations of the subprogram at the
point(s) of call, instead of setting up a stack frame for out-of-line calls.
Here is the resulting program:

@quotation

@example
with Interfaces; use Interfaces;
with Ada.Text_IO; use Ada.Text_IO;
with System.Machine_Code; use System.Machine_Code;
procedure Increment_2 is

   function Incr (Value : Unsigned_32) return Unsigned_32 is
      Result : Unsigned_32;
   begin
      Asm ("incl %0",
           Outputs => Unsigned_32'Asm_Output ("=a", Result),
           Inputs  => Unsigned_32'Asm_Input ("a", Value));
      return Result;
   end Incr;
   pragma Inline (Increment);

   Value : Unsigned_32;

begin
   Value := 5;
   Put_Line ("Value before is" & Value'Img);
   Value := Increment (Value);
   Put_Line ("Value after is" & Value'Img);
end Increment_2;
@end example
@end quotation

Compile the program with both optimization (@emph{-O2}) and inlining
(@emph{-gnatn}) enabled.

The @cite{Incr} function is still compiled as usual, but at the
point in @cite{Increment} where our function used to be called:

@quotation

@example
pushl %edi
call _increment__incr.1
@end example
@end quotation

the code for the function body directly appears:

@quotation

@example
movl %esi,%eax
#APP
   incl %eax
#NO_APP
   movl %eax,%edx
@end example
@end quotation

thus saving the overhead of stack frame setup and an out-of-line call.

@node Other Asm Functionality,,Inlining Inline Assembler Code,Inline Assembler
@anchor{gnat_ugn/inline_assembler other-asm-functionality}@anchor{2d8}@anchor{gnat_ugn/inline_assembler id7}@anchor{2d9}
@section Other @cite{Asm} Functionality


This section describes two important parameters to the @cite{Asm}
procedure: @cite{Clobber}, which identifies register usage;
and @cite{Volatile}, which inhibits unwanted optimizations.

@menu
* The Clobber Parameter:: 
* The Volatile Parameter:: 

@end menu

@node The Clobber Parameter,The Volatile Parameter,,Other Asm Functionality
@anchor{gnat_ugn/inline_assembler the-clobber-parameter}@anchor{2da}@anchor{gnat_ugn/inline_assembler id8}@anchor{2db}
@subsection The @cite{Clobber} Parameter


One of the dangers of intermixing assembly language and a compiled language
such as Ada is that the compiler needs to be aware of which registers are
being used by the assembly code.  In some cases, such as the earlier examples,
the constraint string is sufficient to indicate register usage (e.g.,
@cite{"a"} for
the eax register).  But more generally, the compiler needs an explicit
identification of the registers that are used by the Inline Assembly
statements.

Using a register that the compiler doesn't know about
could be a side effect of an instruction (like @cite{mull}
storing its result in both eax and edx).
It can also arise from explicit register usage in your
assembly code; for example:

@quotation

@example
Asm ("movl %0, %%ebx" & LF & HT &
     "movl %%ebx, %1",
     Outputs => Unsigned_32'Asm_Output ("=g", Var_Out),
     Inputs  => Unsigned_32'Asm_Input  ("g", Var_In));
@end example
@end quotation

where the compiler (since it does not analyze the @cite{Asm} template string)
does not know you are using the ebx register.

In such cases you need to supply the @cite{Clobber} parameter to @cite{Asm},
to identify the registers that will be used by your assembly code:

@quotation

@example
Asm ("movl %0, %%ebx" & LF & HT &
     "movl %%ebx, %1",
     Outputs => Unsigned_32'Asm_Output ("=g", Var_Out),
     Inputs  => Unsigned_32'Asm_Input  ("g", Var_In),
     Clobber => "ebx");
@end example
@end quotation

The Clobber parameter is a static string expression specifying the
register(s) you are using.  Note that register names are @emph{not} prefixed
by a percent sign. Also, if more than one register is used then their names
are separated by commas; e.g., @cite{"eax@comma{} ebx"}

The @cite{Clobber} parameter has several additional uses:


@itemize *

@item 
Use 'register' name @cite{cc} to indicate that flags might have changed

@item 
Use 'register' name @cite{memory} if you changed a memory location
@end itemize

@node The Volatile Parameter,,The Clobber Parameter,Other Asm Functionality
@anchor{gnat_ugn/inline_assembler the-volatile-parameter}@anchor{2dc}@anchor{gnat_ugn/inline_assembler id9}@anchor{2dd}
@subsection The @cite{Volatile} Parameter


@geindex Volatile parameter

Compiler optimizations in the presence of Inline Assembler may sometimes have
unwanted effects.  For example, when an @cite{Asm} invocation with an input
variable is inside a loop, the compiler might move the loading of the input
variable outside the loop, regarding it as a one-time initialization.

If this effect is not desired, you can disable such optimizations by setting
the @cite{Volatile} parameter to @cite{True}; for example:

@quotation

@example
Asm ("movl %0, %%ebx" & LF & HT &
     "movl %%ebx, %1",
     Outputs  => Unsigned_32'Asm_Output ("=g", Var_Out),
     Inputs   => Unsigned_32'Asm_Input  ("g", Var_In),
     Clobber  => "ebx",
     Volatile => True);
@end example
@end quotation

By default, @cite{Volatile} is set to @cite{False} unless there is no
@cite{Outputs} parameter.

Although setting @cite{Volatile} to @cite{True} prevents unwanted
optimizations, it will also disable other optimizations that might be
important for efficiency. In general, you should set @cite{Volatile}
to @cite{True} only if the compiler's optimizations have created
problems.

@node GNU Free Documentation License,Index,Inline Assembler,Top
@anchor{share/gnu_free_documentation_license gnu-fdl}@anchor{1}@anchor{share/gnu_free_documentation_license doc}@anchor{2de}@anchor{share/gnu_free_documentation_license gnu-free-documentation-license}@anchor{2df}
@chapter GNU Free Documentation License


Version 1.3, 3 November 2008

Copyright  2000, 2001, 2002, 2007, 2008  Free Software Foundation, Inc
@indicateurl{http://fsf.org/}

Everyone is permitted to copy and distribute verbatim copies of this
license document, but changing it is not allowed.

@strong{Preamble}

The purpose of this License is to make a manual, textbook, or other
functional and useful document "free" in the sense of freedom: to
assure everyone the effective freedom to copy and redistribute it,
with or without modifying it, either commercially or noncommercially.
Secondarily, this License preserves for the author and publisher a way
to get credit for their work, while not being considered responsible
for modifications made by others.

This License is a kind of "copyleft", which means that derivative
works of the document must themselves be free in the same sense.  It
complements the GNU General Public License, which is a copyleft
license designed for free software.

We have designed this License in order to use it for manuals for free
software, because free software needs free documentation: a free
program should come with manuals providing the same freedoms that the
software does.  But this License is not limited to software manuals;
it can be used for any textual work, regardless of subject matter or
whether it is published as a printed book.  We recommend this License
principally for works whose purpose is instruction or reference.

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This License applies to any manual or other work, in any medium, that
contains a notice placed by the copyright holder saying it can be
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A "@strong{Secondary Section}" is a named appendix or a front-matter section of
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a computer-network location from which the general network-using
public has access to download using public-standard network protocols
a complete Transparent copy of the Document, free of added material.
If you use the latter option, you must take reasonably prudent steps,
when you begin distribution of Opaque copies in quantity, to ensure
that this Transparent copy will remain thus accessible at the stated
location until at least one year after the last time you distribute an
Opaque copy (directly or through your agents or retailers) of that
edition to the public.

It is requested, but not required, that you contact the authors of the
Document well before redistributing any large number of copies, to give
them a chance to provide you with an updated version of the Document.

@strong{4. MODIFICATIONS}

You may copy and distribute a Modified Version of the Document under
the conditions of sections 2 and 3 above, provided that you release
the Modified Version under precisely this License, with the Modified
Version filling the role of the Document, thus licensing distribution
and modification of the Modified Version to whoever possesses a copy
of it.  In addition, you must do these things in the Modified Version:


@enumerate A

@item 
Use in the Title Page (and on the covers, if any) a title distinct
from that of the Document, and from those of previous versions
(which should, if there were any, be listed in the History section
of the Document).  You may use the same title as a previous version
if the original publisher of that version gives permission.

@item 
List on the Title Page, as authors, one or more persons or entities
responsible for authorship of the modifications in the Modified
Version, together with at least five of the principal authors of the
Document (all of its principal authors, if it has fewer than five),
unless they release you from this requirement.

@item 
State on the Title page the name of the publisher of the
Modified Version, as the publisher.

@item 
Preserve all the copyright notices of the Document.

@item 
Add an appropriate copyright notice for your modifications
adjacent to the other copyright notices.

@item 
Include, immediately after the copyright notices, a license notice
giving the public permission to use the Modified Version under the
terms of this License, in the form shown in the Addendum below.

@item 
Preserve in that license notice the full lists of Invariant Sections
and required Cover Texts given in the Document's license notice.

@item 
Include an unaltered copy of this License.

@item 
Preserve the section Entitled "History", Preserve its Title, and add
to it an item stating at least the title, year, new authors, and
publisher of the Modified Version as given on the Title Page.  If
there is no section Entitled "History" in the Document, create one
stating the title, year, authors, and publisher of the Document as
given on its Title Page, then add an item describing the Modified
Version as stated in the previous sentence.

@item 
Preserve the network location, if any, given in the Document for
public access to a Transparent copy of the Document, and likewise
the network locations given in the Document for previous versions
it was based on.  These may be placed in the "History" section.
You may omit a network location for a work that was published at
least four years before the Document itself, or if the original
publisher of the version it refers to gives permission.

@item 
For any section Entitled "Acknowledgements" or "Dedications",
Preserve the Title of the section, and preserve in the section all
the substance and tone of each of the contributor acknowledgements
and/or dedications given therein.

@item 
Preserve all the Invariant Sections of the Document,
unaltered in their text and in their titles.  Section numbers
or the equivalent are not considered part of the section titles.

@item 
Delete any section Entitled "Endorsements".  Such a section
may not be included in the Modified Version.

@item 
Do not retitle any existing section to be Entitled "Endorsements"
or to conflict in title with any Invariant Section.

@item 
Preserve any Warranty Disclaimers.
@end enumerate

If the Modified Version includes new front-matter sections or
appendices that qualify as Secondary Sections and contain no material
copied from the Document, you may at your option designate some or all
of these sections as invariant.  To do this, add their titles to the
list of Invariant Sections in the Modified Version's license notice.
These titles must be distinct from any other section titles.

You may add a section Entitled "Endorsements", provided it contains
nothing but endorsements of your Modified Version by various
parties---for example, statements of peer review or that the text has
been approved by an organization as the authoritative definition of a
standard.

You may add a passage of up to five words as a Front-Cover Text, and a
passage of up to 25 words as a Back-Cover Text, to the end of the list
of Cover Texts in the Modified Version.  Only one passage of
Front-Cover Text and one of Back-Cover Text may be added by (or
through arrangements made by) any one entity.  If the Document already
includes a cover text for the same cover, previously added by you or
by arrangement made by the same entity you are acting on behalf of,
you may not add another; but you may replace the old one, on explicit
permission from the previous publisher that added the old one.

The author(s) and publisher(s) of the Document do not by this License
give permission to use their names for publicity for or to assert or
imply endorsement of any Modified Version.

@strong{5. COMBINING DOCUMENTS}

You may combine the Document with other documents released under this
License, under the terms defined in section 4 above for modified
versions, provided that you include in the combination all of the
Invariant Sections of all of the original documents, unmodified, and
list them all as Invariant Sections of your combined work in its
license notice, and that you preserve all their Warranty Disclaimers.

The combined work need only contain one copy of this License, and
multiple identical Invariant Sections may be replaced with a single
copy.  If there are multiple Invariant Sections with the same name but
different contents, make the title of each such section unique by
adding at the end of it, in parentheses, the name of the original
author or publisher of that section if known, or else a unique number.
Make the same adjustment to the section titles in the list of
Invariant Sections in the license notice of the combined work.

In the combination, you must combine any sections Entitled "History"
in the various original documents, forming one section Entitled
"History"; likewise combine any sections Entitled "Acknowledgements",
and any sections Entitled "Dedications".  You must delete all sections
Entitled "Endorsements".

@strong{6. COLLECTIONS OF DOCUMENTS}

You may make a collection consisting of the Document and other documents
released under this License, and replace the individual copies of this
License in the various documents with a single copy that is included in
the collection, provided that you follow the rules of this License for
verbatim copying of each of the documents in all other respects.

You may extract a single document from such a collection, and distribute
it individually under this License, provided you insert a copy of this
License into the extracted document, and follow this License in all
other respects regarding verbatim copying of that document.

@strong{7. AGGREGATION WITH INDEPENDENT WORKS}

A compilation of the Document or its derivatives with other separate
and independent documents or works, in or on a volume of a storage or
distribution medium, is called an "aggregate" if the copyright
resulting from the compilation is not used to limit the legal rights
of the compilation's users beyond what the individual works permit.
When the Document is included in an aggregate, this License does not
apply to the other works in the aggregate which are not themselves
derivative works of the Document.

If the Cover Text requirement of section 3 is applicable to these
copies of the Document, then if the Document is less than one half of
the entire aggregate, the Document's Cover Texts may be placed on
covers that bracket the Document within the aggregate, or the
electronic equivalent of covers if the Document is in electronic form.
Otherwise they must appear on printed covers that bracket the whole
aggregate.

@strong{8. TRANSLATION}

Translation is considered a kind of modification, so you may
distribute translations of the Document under the terms of section 4.
Replacing Invariant Sections with translations requires special
permission from their copyright holders, but you may include
translations of some or all Invariant Sections in addition to the
original versions of these Invariant Sections.  You may include a
translation of this License, and all the license notices in the
Document, and any Warranty Disclaimers, provided that you also include
the original English version of this License and the original versions
of those notices and disclaimers.  In case of a disagreement between
the translation and the original version of this License or a notice
or disclaimer, the original version will prevail.

If a section in the Document is Entitled "Acknowledgements",
"Dedications", or "History", the requirement (section 4) to Preserve
its Title (section 1) will typically require changing the actual
title.

@strong{9. TERMINATION}

You may not copy, modify, sublicense, or distribute the Document
except as expressly provided under this License.  Any attempt
otherwise to copy, modify, sublicense, or distribute it is void, and
will automatically terminate your rights under this License.

However, if you cease all violation of this License, then your license
from a particular copyright holder is reinstated (a) provisionally,
unless and until the copyright holder explicitly and finally
terminates your license, and (b) permanently, if the copyright holder
fails to notify you of the violation by some reasonable means prior to
60 days after the cessation.

Moreover, your license from a particular copyright holder is
reinstated permanently if the copyright holder notifies you of the
violation by some reasonable means, this is the first time you have
received notice of violation of this License (for any work) from that
copyright holder, and you cure the violation prior to 30 days after
your receipt of the notice.

Termination of your rights under this section does not terminate the
licenses of parties who have received copies or rights from you under
this License.  If your rights have been terminated and not permanently
reinstated, receipt of a copy of some or all of the same material does
not give you any rights to use it.

@strong{10. FUTURE REVISIONS OF THIS LICENSE}

The Free Software Foundation may publish new, revised versions
of the GNU Free Documentation License from time to time.  Such new
versions will be similar in spirit to the present version, but may
differ in detail to address new problems or concerns.  See
@indicateurl{http://www.gnu.org/copyleft/}.

Each version of the License is given a distinguishing version number.
If the Document specifies that a particular numbered version of this
License "or any later version" applies to it, you have the option of
following the terms and conditions either of that specified version or
of any later version that has been published (not as a draft) by the
Free Software Foundation.  If the Document does not specify a version
number of this License, you may choose any version ever published (not
as a draft) by the Free Software Foundation.  If the Document
specifies that a proxy can decide which future versions of this
License can be used, that proxy's public statement of acceptance of a
version permanently authorizes you to choose that version for the
Document.

@strong{11. RELICENSING}

"Massive Multiauthor Collaboration Site" (or "MMC Site") means any
World Wide Web server that publishes copyrightable works and also
provides prominent facilities for anybody to edit those works.  A
public wiki that anybody can edit is an example of such a server.  A
"Massive Multiauthor Collaboration" (or "MMC") contained in the
site means any set of copyrightable works thus published on the MMC
site.

"CC-BY-SA" means the Creative Commons Attribution-Share Alike 3.0
license published by Creative Commons Corporation, a not-for-profit
corporation with a principal place of business in San Francisco,
California, as well as future copyleft versions of that license
published by that same organization.

"Incorporate" means to publish or republish a Document, in whole or
in part, as part of another Document.

An MMC is "eligible for relicensing" if it is licensed under this
License, and if all works that were first published under this License
somewhere other than this MMC, and subsequently incorporated in whole
or in part into the MMC, (1) had no cover texts or invariant sections,
and (2) were thus incorporated prior to November 1, 2008.

The operator of an MMC Site may republish an MMC contained in the site
under CC-BY-SA on the same site at any time before August 1, 2009,
provided the MMC is eligible for relicensing.

@strong{ADDENDUM: How to use this License for your documents}

To use this License in a document you have written, include a copy of
the License in the document and put the following copyright and
license notices just after the title page:

@quotation

Copyright © YEAR  YOUR NAME.
Permission is granted to copy, distribute and/or modify this document
under the terms of the GNU Free Documentation License, Version 1.3
or any later version published by the Free Software Foundation;
with no Invariant Sections, no Front-Cover Texts, and no Back-Cover Texts.
A copy of the license is included in the section entitled "GNU
Free Documentation License".
@end quotation

If you have Invariant Sections, Front-Cover Texts and Back-Cover Texts,
replace the "with ... Texts." line with this:

@quotation

with the Invariant Sections being LIST THEIR TITLES, with the
Front-Cover Texts being LIST, and with the Back-Cover Texts being LIST.
@end quotation

If you have Invariant Sections without Cover Texts, or some other
combination of the three, merge those two alternatives to suit the
situation.

If your document contains nontrivial examples of program code, we
recommend releasing these examples in parallel under your choice of
free software license, such as the GNU General Public License,
to permit their use in free software.

@node Index,,GNU Free Documentation License,Top
@unnumbered Index


@printindex ge


@c %**end of body
@bye