Add a super-simple pseudo 'ldd'

[msysgit.git] / mingw / info / gdbint.info-1

This is gdbint.info, produced by makeinfo version 4.8 from
../.././gdb/doc/gdbint.texinfo.

INFO-DIR-SECTION Software development
START-INFO-DIR-ENTRY
* Gdb-Internals: (gdbint).      The GNU debugger's internals.
END-INFO-DIR-ENTRY

   This file documents the internals of the GNU debugger GDB.
Copyright (C) 1990, 1991, 1992, 1993, 1994, 1996, 1998, 1999, 2000,
2001,    2002, 2003, 2004, 2005, 2006    Free Software Foundation, Inc.
Contributed by Cygnus Solutions.  Written by John Gilmore.  Second
Edition by Stan Shebs.

   Permission is granted to copy, distribute and/or modify this document
under the terms of the GNU Free Documentation License, Version 1.1 or
any later version published by the Free Software Foundation; with no
Invariant Sections, with no Front-Cover Texts, and with no Back-Cover
Texts.  A copy of the license is included in the section entitled "GNU
Free Documentation License".

\x1f
File: gdbint.info,  Node: Top,  Next: Requirements,  Up: (dir)

Scope of this Document
**********************

This document documents the internals of the GNU debugger, GDB.  It
includes description of GDB's key algorithms and operations, as well as
the mechanisms that adapt GDB to specific hosts and targets.

* Menu:

* Requirements::
* Overall Structure::
* Algorithms::
* User Interface::
* libgdb::
* Symbol Handling::
* Language Support::
* Host Definition::
* Target Architecture Definition::
* Target Descriptions::
* Target Vector Definition::
* Native Debugging::
* Support Libraries::
* Coding::
* Porting GDB::
* Versions and Branches::
* Start of New Year Procedure::
* Releasing GDB::
* Testsuite::
* Hints::

* GDB Observers::  GDB Currently available observers
* GNU Free Documentation License::  The license for this documentation
* Index::

\x1f
File: gdbint.info,  Node: Requirements,  Next: Overall Structure,  Prev: Top,  Up: Top

1 Requirements
**************

Before diving into the internals, you should understand the formal
requirements and other expectations for GDB.  Although some of these
may seem obvious, there have been proposals for GDB that have run
counter to these requirements.

   First of all, GDB is a debugger.  It's not designed to be a front
panel for embedded systems.  It's not a text editor.  It's not a shell.
It's not a programming environment.

   GDB is an interactive tool.  Although a batch mode is available,
GDB's primary role is to interact with a human programmer.

   GDB should be responsive to the user.  A programmer hot on the trail
of a nasty bug, and operating under a looming deadline, is going to be
very impatient of everything, including the response time to debugger
commands.

   GDB should be relatively permissive, such as for expressions.  While
the compiler should be picky (or have the option to be made picky),
since source code lives for a long time usually, the programmer doing
debugging shouldn't be spending time figuring out to mollify the
debugger.

   GDB will be called upon to deal with really large programs.
Executable sizes of 50 to 100 megabytes occur regularly, and we've
heard reports of programs approaching 1 gigabyte in size.

   GDB should be able to run everywhere.  No other debugger is
available for even half as many configurations as GDB supports.

\x1f
File: gdbint.info,  Node: Overall Structure,  Next: Algorithms,  Prev: Requirements,  Up: Top

2 Overall Structure
*******************

GDB consists of three major subsystems: user interface, symbol handling
(the "symbol side"), and target system handling (the "target side").

   The user interface consists of several actual interfaces, plus
supporting code.

   The symbol side consists of object file readers, debugging info
interpreters, symbol table management, source language expression
parsing, type and value printing.

   The target side consists of execution control, stack frame analysis,
and physical target manipulation.

   The target side/symbol side division is not formal, and there are a
number of exceptions.  For instance, core file support involves symbolic
elements (the basic core file reader is in BFD) and target elements (it
supplies the contents of memory and the values of registers).  Instead,
this division is useful for understanding how the minor subsystems
should fit together.

2.1 The Symbol Side
===================

The symbolic side of GDB can be thought of as "everything you can do in
GDB without having a live program running".  For instance, you can look
at the types of variables, and evaluate many kinds of expressions.

2.2 The Target Side
===================

The target side of GDB is the "bits and bytes manipulator".  Although
it may make reference to symbolic info here and there, most of the
target side will run with only a stripped executable available--or even
no executable at all, in remote debugging cases.

   Operations such as disassembly, stack frame crawls, and register
display, are able to work with no symbolic info at all.  In some cases,
such as disassembly, GDB will use symbolic info to present addresses
relative to symbols rather than as raw numbers, but it will work either
way.

2.3 Configurations
==================

"Host" refers to attributes of the system where GDB runs.  "Target"
refers to the system where the program being debugged executes.  In
most cases they are the same machine, in which case a third type of
"Native" attributes come into play.

   Defines and include files needed to build on the host are host
support.  Examples are tty support, system defined types, host byte
order, host float format.

   Defines and information needed to handle the target format are target
dependent.  Examples are the stack frame format, instruction set,
breakpoint instruction, registers, and how to set up and tear down the
stack to call a function.

   Information that is only needed when the host and target are the
same, is native dependent.  One example is Unix child process support;
if the host and target are not the same, doing a fork to start the
target process is a bad idea.  The various macros needed for finding the
registers in the `upage', running `ptrace', and such are all in the
native-dependent files.

   Another example of native-dependent code is support for features that
are really part of the target environment, but which require `#include'
files that are only available on the host system.  Core file handling
and `setjmp' handling are two common cases.

   When you want to make GDB work "native" on a particular machine, you
have to include all three kinds of information.

2.4 Source Tree Structure
=========================

The GDB source directory has a mostly flat structure--there are only a
few subdirectories.  A file's name usually gives a hint as to what it
does; for example, `stabsread.c' reads stabs, `dwarf2read.c' reads
DWARF 2, etc.

   Files that are related to some common task have names that share
common substrings.  For example, `*-thread.c' files deal with debugging
threads on various platforms; `*read.c' files deal with reading various
kinds of symbol and object files; `inf*.c' files deal with direct
control of the "inferior program" (GDB parlance for the program being
debugged).

   There are several dozens of files in the `*-tdep.c' family.  `tdep'
stands for "target-dependent code"--each of these files implements
debug support for a specific target architecture (sparc, mips, etc).
Usually, only one of these will be used in a specific GDB configuration
(sometimes two, closely related).

   Similarly, there are many `*-nat.c' files, each one for native
debugging on a specific system (e.g., `sparc-linux-nat.c' is for native
debugging of Sparc machines running the Linux kernel).

   The few subdirectories of the source tree are:

`cli'
     Code that implements "CLI", the GDB Command-Line Interpreter.
     *Note Command Interpreter: User Interface.

`gdbserver'
     Code for the GDB remote server.

`gdbtk'
     Code for Insight, the GDB TK-based GUI front-end.

`mi'
     The "GDB/MI", the GDB Machine Interface interpreter.

`signals'
     Target signal translation code.

`tui'
     Code for "TUI", the GDB Text-mode full-screen User Interface.
     *Note TUI: User Interface.

\x1f
File: gdbint.info,  Node: Algorithms,  Next: User Interface,  Prev: Overall Structure,  Up: Top

3 Algorithms
************

GDB uses a number of debugging-specific algorithms.  They are often not
very complicated, but get lost in the thicket of special cases and
real-world issues.  This chapter describes the basic algorithms and
mentions some of the specific target definitions that they use.

3.1 Frames
==========

A frame is a construct that GDB uses to keep track of calling and
called functions.

   GDB's frame model, a fresh design, was implemented with the need to
support DWARF's Call Frame Information in mind.  In fact, the term
"unwind" is taken directly from that specification.  Developers wishing
to learn more about unwinders, are encouraged to read the DWARF
specification.

   GDB's model is that you find a frame's registers by "unwinding" them
from the next younger frame.  That is, `get_frame_register' which
returns the value of a register in frame #1 (the next-to-youngest
frame), is implemented by calling frame #0's `frame_register_unwind'
(the youngest frame).  But then the obvious question is: how do you
access the registers of the youngest frame itself?

   To answer this question, GDB has the "sentinel" frame, the "-1st"
frame.  Unwinding registers from the sentinel frame gives you the
current values of the youngest real frame's registers.  If F is a
sentinel frame, then `get_frame_type (F) == SENTINEL_FRAME'.

3.2 Prologue Analysis
=====================

To produce a backtrace and allow the user to manipulate older frames'
variables and arguments, GDB needs to find the base addresses of older
frames, and discover where those frames' registers have been saved.
Since a frame's "callee-saves" registers get saved by younger frames if
and when they're reused, a frame's registers may be scattered
unpredictably across younger frames.  This means that changing the
value of a register-allocated variable in an older frame may actually
entail writing to a save slot in some younger frame.

   Modern versions of GCC emit Dwarf call frame information ("CFI"),
which describes how to find frame base addresses and saved registers.
But CFI is not always available, so as a fallback GDB uses a technique
called "prologue analysis" to find frame sizes and saved registers.  A
prologue analyzer disassembles the function's machine code starting
from its entry point, and looks for instructions that allocate frame
space, save the stack pointer in a frame pointer register, save
registers, and so on.  Obviously, this can't be done accurately in
general, but it's tractable to do well enough to be very helpful.
Prologue analysis predates the GNU toolchain's support for CFI; at one
time, prologue analysis was the only mechanism GDB used for stack
unwinding at all, when the function calling conventions didn't specify
a fixed frame layout.

   In the olden days, function prologues were generated by hand-written,
target-specific code in GCC, and treated as opaque and untouchable by
optimizers.  Looking at this code, it was usually straightforward to
write a prologue analyzer for GDB that would accurately understand all
the prologues GCC would generate.  However, over time GCC became more
aggressive about instruction scheduling, and began to understand more
about the semantics of the prologue instructions themselves; in
response, GDB's analyzers became more complex and fragile.  Keeping the
prologue analyzers working as GCC (and the instruction sets themselves)
evolved became a substantial task.

   To try to address this problem, the code in `prologue-value.h' and
`prologue-value.c' provides a general framework for writing prologue
analyzers that are simpler and more robust than ad-hoc analyzers.  When
we analyze a prologue using the prologue-value framework, we're really
doing "abstract interpretation" or "pseudo-evaluation": running the
function's code in simulation, but using conservative approximations of
the values registers and memory would hold when the code actually runs.
For example, if our function starts with the instruction:

     addi r1, 42     # add 42 to r1
   we don't know exactly what value will be in `r1' after executing
this instruction, but we do know it'll be 42 greater than its original
value.

   If we then see an instruction like:

     addi r1, 22     # add 22 to r1
   we still don't know what `r1's' value is, but again, we can say it
is now 64 greater than its original value.

   If the next instruction were:

     mov r2, r1      # set r2 to r1's value
   then we can say that `r2's' value is now the original value of `r1'
plus 64.

   It's common for prologues to save registers on the stack, so we'll
need to track the values of stack frame slots, as well as the
registers.  So after an instruction like this:

     mov (fp+4), r2
   then we'd know that the stack slot four bytes above the frame pointer
holds the original value of `r1' plus 64.

   And so on.

   Of course, this can only go so far before it gets unreasonable.  If
we wanted to be able to say anything about the value of `r1' after the
instruction:

     xor r1, r3      # exclusive-or r1 and r3, place result in r1
   then things would get pretty complex.  But remember, we're just doing
a conservative approximation; if exclusive-or instructions aren't
relevant to prologues, we can just say `r1''s value is now "unknown".
We can ignore things that are too complex, if that loss of information
is acceptable for our application.

   So when we say "conservative approximation" here, what we mean is an
approximation that is either accurate, or marked "unknown", but never
inaccurate.

   Using this framework, a prologue analyzer is simply an interpreter
for machine code, but one that uses conservative approximations for the
contents of registers and memory instead of actual values.  Starting
from the function's entry point, you simulate instructions up to the
current PC, or an instruction that you don't know how to simulate.  Now
you can examine the state of the registers and stack slots you've kept
track of.

   * To see how large your stack frame is, just check the value of the
     stack pointer register; if it's the original value of the SP minus
     a constant, then that constant is the stack frame's size.  If the
     SP's value has been marked as "unknown", then that means the
     prologue has done something too complex for us to track, and we
     don't know the frame size.

   * To see where we've saved the previous frame's registers, we just
     search the values we've tracked -- stack slots, usually, but
     registers, too, if you want -- for something equal to the
     register's original value.  If the calling conventions suggest a
     standard place to save a given register, then we can check there
     first, but really, anything that will get us back the original
     value will probably work.

   This does take some work.  But prologue analyzers aren't
quick-and-simple pattern patching to recognize a few fixed prologue
forms any more; they're big, hairy functions.  Along with inferior
function calls, prologue analysis accounts for a substantial portion of
the time needed to stabilize a GDB port.  So it's worthwhile to look
for an approach that will be easier to understand and maintain.  In the
approach described above:

   * It's easier to see that the analyzer is correct: you just see
     whether the analyzer properly (albeit conservatively) simulates
     the effect of each instruction.

   * It's easier to extend the analyzer: you can add support for new
     instructions, and know that you haven't broken anything that
     wasn't already broken before.

   * It's orthogonal: to gather new information, you don't need to
     complicate the code for each instruction.  As long as your domain
     of conservative values is already detailed enough to tell you what
     you need, then all the existing instruction simulations are
     already gathering the right data for you.


   The file `prologue-value.h' contains detailed comments explaining
the framework and how to use it.

3.3 Breakpoint Handling
=======================

In general, a breakpoint is a user-designated location in the program
where the user wants to regain control if program execution ever reaches
that location.

   There are two main ways to implement breakpoints; either as
"hardware" breakpoints or as "software" breakpoints.

   Hardware breakpoints are sometimes available as a builtin debugging
features with some chips.  Typically these work by having dedicated
register into which the breakpoint address may be stored.  If the PC
(shorthand for "program counter") ever matches a value in a breakpoint
registers, the CPU raises an exception and reports it to GDB.

   Another possibility is when an emulator is in use; many emulators
include circuitry that watches the address lines coming out from the
processor, and force it to stop if the address matches a breakpoint's
address.

   A third possibility is that the target already has the ability to do
breakpoints somehow; for instance, a ROM monitor may do its own
software breakpoints.  So although these are not literally "hardware
breakpoints", from GDB's point of view they work the same; GDB need not
do anything more than set the breakpoint and wait for something to
happen.

   Since they depend on hardware resources, hardware breakpoints may be
limited in number; when the user asks for more, GDB will start trying
to set software breakpoints.  (On some architectures, notably the
32-bit x86 platforms, GDB cannot always know whether there's enough
hardware resources to insert all the hardware breakpoints and
watchpoints.  On those platforms, GDB prints an error message only when
the program being debugged is continued.)

   Software breakpoints require GDB to do somewhat more work.  The
basic theory is that GDB will replace a program instruction with a
trap, illegal divide, or some other instruction that will cause an
exception, and then when it's encountered, GDB will take the exception
and stop the program.  When the user says to continue, GDB will restore
the original instruction, single-step, re-insert the trap, and continue
on.

   Since it literally overwrites the program being tested, the program
area must be writable, so this technique won't work on programs in ROM.
It can also distort the behavior of programs that examine themselves,
although such a situation would be highly unusual.

   Also, the software breakpoint instruction should be the smallest
size of instruction, so it doesn't overwrite an instruction that might
be a jump target, and cause disaster when the program jumps into the
middle of the breakpoint instruction.  (Strictly speaking, the
breakpoint must be no larger than the smallest interval between
instructions that may be jump targets; perhaps there is an architecture
where only even-numbered instructions may jumped to.)  Note that it's
possible for an instruction set not to have any instructions usable for
a software breakpoint, although in practice only the ARC has failed to
define such an instruction.

   The basic definition of the software breakpoint is the macro
`BREAKPOINT'.

   Basic breakpoint object handling is in `breakpoint.c'.  However,
much of the interesting breakpoint action is in `infrun.c'.

`target_remove_breakpoint (BP_TGT)'
`target_insert_breakpoint (BP_TGT)'
     Insert or remove a software breakpoint at address
     `BP_TGT->placed_address'.  Returns zero for success, non-zero for
     failure.  On input, BP_TGT contains the address of the breakpoint,
     and is otherwise initialized to zero.  The fields of the `struct
     bp_target_info' pointed to by BP_TGT are updated to contain other
     information about the breakpoint on output.  The field
     `placed_address' may be updated if the breakpoint was placed at a
     related address; the field `shadow_contents' contains the real
     contents of the bytes where the breakpoint has been inserted, if
     reading memory would return the breakpoint instead of the
     underlying memory; the field `shadow_len' is the length of memory
     cached in `shadow_contents', if any; and the field `placed_size'
     is optionally set and used by the target, if it could differ from
     `shadow_len'.

     For example, the remote target `Z0' packet does not require
     shadowing memory, so `shadow_len' is left at zero.  However, the
     length reported by `gdbarch_breakpoint_from_pc' is cached in
     `placed_size', so that a matching `z0' packet can be used to
     remove the breakpoint.

`target_remove_hw_breakpoint (BP_TGT)'
`target_insert_hw_breakpoint (BP_TGT)'
     Insert or remove a hardware-assisted breakpoint at address
     `BP_TGT->placed_address'.  Returns zero for success, non-zero for
     failure.  See `target_insert_breakpoint' for a description of the
     `struct bp_target_info' pointed to by BP_TGT; the
     `shadow_contents' and `shadow_len' members are not used for
     hardware breakpoints, but `placed_size' may be.

3.4 Single Stepping
===================

3.5 Signal Handling
===================

3.6 Thread Handling
===================

3.7 Inferior Function Calls
===========================

3.8 Longjmp Support
===================

GDB has support for figuring out that the target is doing a `longjmp'
and for stopping at the target of the jump, if we are stepping.  This
is done with a few specialized internal breakpoints, which are visible
in the output of the `maint info breakpoint' command.

   To make this work, you need to define a function called
`gdbarch_get_longjmp_target', which will examine the `jmp_buf'
structure and extract the longjmp target address.  Since `jmp_buf' is
target specific, you will need to define it in the appropriate
`tm-TARGET.h' file.  Look in `tm-sun4os4.h' and `sparc-tdep.c' for
examples of how to do this.

3.9 Watchpoints
===============

Watchpoints are a special kind of breakpoints (*note breakpoints:
Algorithms.) which break when data is accessed rather than when some
instruction is executed.  When you have data which changes without your
knowing what code does that, watchpoints are the silver bullet to hunt
down and kill such bugs.

   Watchpoints can be either hardware-assisted or not; the latter type
is known as "software watchpoints."  GDB always uses hardware-assisted
watchpoints if they are available, and falls back on software
watchpoints otherwise.  Typical situations where GDB will use software
watchpoints are:

   * The watched memory region is too large for the underlying hardware
     watchpoint support.  For example, each x86 debug register can
     watch up to 4 bytes of memory, so trying to watch data structures
     whose size is more than 16 bytes will cause GDB to use software
     watchpoints.

   * The value of the expression to be watched depends on data held in
     registers (as opposed to memory).

   * Too many different watchpoints requested.  (On some architectures,
     this situation is impossible to detect until the debugged program
     is resumed.)  Note that x86 debug registers are used both for
     hardware breakpoints and for watchpoints, so setting too many
     hardware breakpoints might cause watchpoint insertion to fail.

   * No hardware-assisted watchpoints provided by the target
     implementation.

   Software watchpoints are very slow, since GDB needs to single-step
the program being debugged and test the value of the watched
expression(s) after each instruction.  The rest of this section is
mostly irrelevant for software watchpoints.

   When the inferior stops, GDB tries to establish, among other
possible reasons, whether it stopped due to a watchpoint being hit.  It
first uses `STOPPED_BY_WATCHPOINT' to see if any watchpoint was hit.
If not, all watchpoint checking is skipped.

   Then GDB calls `target_stopped_data_address' exactly once.  This
method returns the address of the watchpoint which triggered, if the
target can determine it.  If the triggered address is available, GDB
compares the address returned by this method with each watched memory
address in each active watchpoint.  For data-read and data-access
watchpoints, GDB announces every watchpoint that watches the triggered
address as being hit.  For this reason, data-read and data-access
watchpoints _require_ that the triggered address be available; if not,
read and access watchpoints will never be considered hit.  For
data-write watchpoints, if the triggered address is available, GDB
considers only those watchpoints which match that address; otherwise,
GDB considers all data-write watchpoints.  For each data-write
watchpoint that GDB considers, it evaluates the expression whose value
is being watched, and tests whether the watched value has changed.
Watchpoints whose watched values have changed are announced as hit.

   GDB uses several macros and primitives to support hardware
watchpoints:

`TARGET_HAS_HARDWARE_WATCHPOINTS'
     If defined, the target supports hardware watchpoints.

`TARGET_CAN_USE_HARDWARE_WATCHPOINT (TYPE, COUNT, OTHER)'
     Return the number of hardware watchpoints of type TYPE that are
     possible to be set.  The value is positive if COUNT watchpoints of
     this type can be set, zero if setting watchpoints of this type is
     not supported, and negative if COUNT is more than the maximum
     number of watchpoints of type TYPE that can be set.  OTHER is
     non-zero if other types of watchpoints are currently enabled (there
     are architectures which cannot set watchpoints of different types
     at the same time).

`TARGET_REGION_OK_FOR_HW_WATCHPOINT (ADDR, LEN)'
     Return non-zero if hardware watchpoints can be used to watch a
     region whose address is ADDR and whose length in bytes is LEN.

`target_insert_watchpoint (ADDR, LEN, TYPE)'
`target_remove_watchpoint (ADDR, LEN, TYPE)'
     Insert or remove a hardware watchpoint starting at ADDR, for LEN
     bytes.  TYPE is the watchpoint type, one of the possible values of
     the enumerated data type `target_hw_bp_type', defined by
     `breakpoint.h' as follows:

           enum target_hw_bp_type
             {
               hw_write   = 0, /* Common (write) HW watchpoint */
               hw_read    = 1, /* Read    HW watchpoint */
               hw_access  = 2, /* Access (read or write) HW watchpoint */
               hw_execute = 3  /* Execute HW breakpoint */
             };

     These two macros should return 0 for success, non-zero for failure.

`target_stopped_data_address (ADDR_P)'
     If the inferior has some watchpoint that triggered, place the
     address associated with the watchpoint at the location pointed to
     by ADDR_P and return non-zero.  Otherwise, return zero.  This is
     required for data-read and data-access watchpoints.  It is not
     required for data-write watchpoints, but GDB uses it to improve
     handling of those also.

     GDB will only call this method once per watchpoint stop,
     immediately after calling `STOPPED_BY_WATCHPOINT'.  If the
     target's watchpoint indication is sticky, i.e., stays set after
     resuming, this method should clear it.  For instance, the x86 debug
     control register has sticky triggered flags.

`HAVE_STEPPABLE_WATCHPOINT'
     If defined to a non-zero value, it is not necessary to disable a
     watchpoint to step over it.    Like
     `gdbarch_have_nonsteppable_watchpoint', this is usually set when
     watchpoints trigger at the instruction which will perform an
     interesting read or write.  It should be set if there is a
     temporary disable bit which allows the processor to step over the
     interesting instruction without raising the watchpoint exception
     again.

`int gdbarch_have_nonsteppable_watchpoint (GDBARCH)'
     If it returns a non-zero value, GDB should disable a watchpoint to
     step the inferior over it.  This is usually set when watchpoints
     trigger at the instruction which will perform an interesting read
     or write.

`HAVE_CONTINUABLE_WATCHPOINT'
     If defined to a non-zero value, it is possible to continue the
     inferior after a watchpoint has been hit.  This is usually set
     when watchpoints trigger at the instruction following an
     interesting read or write.

`CANNOT_STEP_HW_WATCHPOINTS'
     If this is defined to a non-zero value, GDB will remove all
     watchpoints before stepping the inferior.

`STOPPED_BY_WATCHPOINT (WAIT_STATUS)'
     Return non-zero if stopped by a watchpoint.  WAIT_STATUS is of the
     type `struct target_waitstatus', defined by `target.h'.  Normally,
     this macro is defined to invoke the function pointed to by the
     `to_stopped_by_watchpoint' member of the structure (of the type
     `target_ops', defined on `target.h') that describes the
     target-specific operations; `to_stopped_by_watchpoint' ignores the
     WAIT_STATUS argument.

     GDB does not require the non-zero value returned by
     `STOPPED_BY_WATCHPOINT' to be 100% correct, so if a target cannot
     determine for sure whether the inferior stopped due to a
     watchpoint, it could return non-zero "just in case".

3.9.1 Watchpoints and Threads
-----------------------------

GDB only supports process-wide watchpoints, which trigger in all
threads.  GDB uses the thread ID to make watchpoints act as if they
were thread-specific, but it cannot set hardware watchpoints that only
trigger in a specific thread.  Therefore, even if the target supports
threads, per-thread debug registers, and watchpoints which only affect
a single thread, it should set the per-thread debug registers for all
threads to the same value.  On GNU/Linux native targets, this is
accomplished by using `ALL_LWPS' in `target_insert_watchpoint' and
`target_remove_watchpoint' and by using `linux_set_new_thread' to
register a handler for newly created threads.

   GDB's GNU/Linux support only reports a single event at a time,
although multiple events can trigger simultaneously for multi-threaded
programs.  When multiple events occur, `linux-nat.c' queues subsequent
events and returns them the next time the program is resumed.  This
means that `STOPPED_BY_WATCHPOINT' and `target_stopped_data_address'
only need to consult the current thread's state--the thread indicated
by `inferior_ptid'.  If two threads have hit watchpoints
simultaneously, those routines will be called a second time for the
second thread.

3.9.2 x86 Watchpoints
---------------------

The 32-bit Intel x86 (a.k.a. ia32) processors feature special debug
registers designed to facilitate debugging.  GDB provides a generic
library of functions that x86-based ports can use to implement support
for watchpoints and hardware-assisted breakpoints.  This subsection
documents the x86 watchpoint facilities in GDB.

   To use the generic x86 watchpoint support, a port should do the
following:

   * Define the macro `I386_USE_GENERIC_WATCHPOINTS' somewhere in the
     target-dependent headers.

   * Include the `config/i386/nm-i386.h' header file _after_ defining
     `I386_USE_GENERIC_WATCHPOINTS'.

   * Add `i386-nat.o' to the value of the Make variable `NATDEPFILES'
     (*note NATDEPFILES: Native Debugging.) or `TDEPFILES' (*note
     TDEPFILES: Target Architecture Definition.).

   * Provide implementations for the `I386_DR_LOW_*' macros described
     below.  Typically, each macro should call a target-specific
     function which does the real work.

   The x86 watchpoint support works by maintaining mirror images of the
debug registers.  Values are copied between the mirror images and the
real debug registers via a set of macros which each target needs to
provide:

`I386_DR_LOW_SET_CONTROL (VAL)'
     Set the Debug Control (DR7) register to the value VAL.

`I386_DR_LOW_SET_ADDR (IDX, ADDR)'
     Put the address ADDR into the debug register number IDX.

`I386_DR_LOW_RESET_ADDR (IDX)'
     Reset (i.e. zero out) the address stored in the debug register
     number IDX.

`I386_DR_LOW_GET_STATUS'
     Return the value of the Debug Status (DR6) register.  This value is
     used immediately after it is returned by `I386_DR_LOW_GET_STATUS',
     so as to support per-thread status register values.

   For each one of the 4 debug registers (whose indices are from 0 to 3)
that store addresses, a reference count is maintained by GDB, to allow
sharing of debug registers by several watchpoints.  This allows users
to define several watchpoints that watch the same expression, but with
different conditions and/or commands, without wasting debug registers
which are in short supply.  GDB maintains the reference counts
internally, targets don't have to do anything to use this feature.

   The x86 debug registers can each watch a region that is 1, 2, or 4
bytes long.  The ia32 architecture requires that each watched region be
appropriately aligned: 2-byte region on 2-byte boundary, 4-byte region
on 4-byte boundary.  However, the x86 watchpoint support in GDB can
watch unaligned regions and regions larger than 4 bytes (up to 16
bytes) by allocating several debug registers to watch a single region.
This allocation of several registers per a watched region is also done
automatically without target code intervention.

   The generic x86 watchpoint support provides the following API for the
GDB's application code:

`i386_region_ok_for_watchpoint (ADDR, LEN)'
     The macro `TARGET_REGION_OK_FOR_HW_WATCHPOINT' is set to call this
     function.  It counts the number of debug registers required to
     watch a given region, and returns a non-zero value if that number
     is less than 4, the number of debug registers available to x86
     processors.

`i386_stopped_data_address (ADDR_P)'
     The target function `target_stopped_data_address' is set to call
     this function.  This function examines the breakpoint condition
     bits in the DR6 Debug Status register, as returned by the
     `I386_DR_LOW_GET_STATUS' macro, and returns the address associated
     with the first bit that is set in DR6.

`i386_stopped_by_watchpoint (void)'
     The macro `STOPPED_BY_WATCHPOINT' is set to call this function.
     The argument passed to `STOPPED_BY_WATCHPOINT' is ignored.  This
     function examines the breakpoint condition bits in the DR6 Debug
     Status register, as returned by the `I386_DR_LOW_GET_STATUS'
     macro, and returns true if any bit is set.  Otherwise, false is
     returned.

`i386_insert_watchpoint (ADDR, LEN, TYPE)'
`i386_remove_watchpoint (ADDR, LEN, TYPE)'
     Insert or remove a watchpoint.  The macros
     `target_insert_watchpoint' and `target_remove_watchpoint' are set
     to call these functions.  `i386_insert_watchpoint' first looks for
     a debug register which is already set to watch the same region for
     the same access types; if found, it just increments the reference
     count of that debug register, thus implementing debug register
     sharing between watchpoints.  If no such register is found, the
     function looks for a vacant debug register, sets its mirrored
     value to ADDR, sets the mirrored value of DR7 Debug Control
     register as appropriate for the LEN and TYPE parameters, and then
     passes the new values of the debug register and DR7 to the
     inferior by calling `I386_DR_LOW_SET_ADDR' and
     `I386_DR_LOW_SET_CONTROL'.  If more than one debug register is
     required to cover the given region, the above process is repeated
     for each debug register.

     `i386_remove_watchpoint' does the opposite: it resets the address
     in the mirrored value of the debug register and its read/write and
     length bits in the mirrored value of DR7, then passes these new
     values to the inferior via `I386_DR_LOW_RESET_ADDR' and
     `I386_DR_LOW_SET_CONTROL'.  If a register is shared by several
     watchpoints, each time a `i386_remove_watchpoint' is called, it
     decrements the reference count, and only calls
     `I386_DR_LOW_RESET_ADDR' and `I386_DR_LOW_SET_CONTROL' when the
     count goes to zero.

`i386_insert_hw_breakpoint (BP_TGT)'
`i386_remove_hw_breakpoint (BP_TGT)'
     These functions insert and remove hardware-assisted breakpoints.
     The macros `target_insert_hw_breakpoint' and
     `target_remove_hw_breakpoint' are set to call these functions.
     The argument is a `struct bp_target_info *', as described in the
     documentation for `target_insert_breakpoint'.  These functions
     work like `i386_insert_watchpoint' and `i386_remove_watchpoint',
     respectively, except that they set up the debug registers to watch
     instruction execution, and each hardware-assisted breakpoint
     always requires exactly one debug register.

`i386_stopped_by_hwbp (void)'
     This function returns non-zero if the inferior has some watchpoint
     or hardware breakpoint that triggered.  It works like
     `i386_stopped_data_address', except that it doesn't record the
     address whose watchpoint triggered.

`i386_cleanup_dregs (void)'
     This function clears all the reference counts, addresses, and
     control bits in the mirror images of the debug registers.  It
     doesn't affect the actual debug registers in the inferior process.

*Notes:*
  1. x86 processors support setting watchpoints on I/O reads or writes.
     However, since no target supports this (as of March 2001), and
     since `enum target_hw_bp_type' doesn't even have an enumeration
     for I/O watchpoints, this feature is not yet available to GDB
     running on x86.

  2. x86 processors can enable watchpoints locally, for the current task
     only, or globally, for all the tasks.  For each debug register,
     there's a bit in the DR7 Debug Control register that determines
     whether the associated address is watched locally or globally.  The
     current implementation of x86 watchpoint support in GDB always
     sets watchpoints to be locally enabled, since global watchpoints
     might interfere with the underlying OS and are probably
     unavailable in many platforms.

3.10 Checkpoints
================

In the abstract, a checkpoint is a point in the execution history of
the program, which the user may wish to return to at some later time.

   Internally, a checkpoint is a saved copy of the program state,
including whatever information is required in order to restore the
program to that state at a later time.  This can be expected to include
the state of registers and memory, and may include external state such
as the state of open files and devices.

   There are a number of ways in which checkpoints may be implemented
in gdb, e.g. as corefiles, as forked processes, and as some opaque
method implemented on the target side.

   A corefile can be used to save an image of target memory and register
state, which can in principle be restored later -- but corefiles do not
typically include information about external entities such as open
files.  Currently this method is not implemented in gdb.

   A forked process can save the state of user memory and registers, as
well as some subset of external (kernel) state.  This method is used to
implement checkpoints on Linux, and in principle might be used on other
systems.

   Some targets, e.g. simulators, might have their own built-in method
for saving checkpoints, and gdb might be able to take advantage of that
capability without necessarily knowing any details of how it is done.

3.11 Observing changes in GDB internals
=======================================

In order to function properly, several modules need to be notified when
some changes occur in the GDB internals.  Traditionally, these modules
have relied on several paradigms, the most common ones being hooks and
gdb-events.  Unfortunately, none of these paradigms was versatile
enough to become the standard notification mechanism in GDB.  The fact
that they only supported one "client" was also a strong limitation.

   A new paradigm, based on the Observer pattern of the `Design
Patterns' book, has therefore been implemented.  The goal was to provide
a new interface overcoming the issues with the notification mechanisms
previously available.  This new interface needed to be strongly typed,
easy to extend, and versatile enough to be used as the standard
interface when adding new notifications.

   See *Note GDB Observers:: for a brief description of the observers
currently implemented in GDB. The rationale for the current
implementation is also briefly discussed.

\x1f
File: gdbint.info,  Node: User Interface,  Next: libgdb,  Prev: Algorithms,  Up: Top

4 User Interface
****************

GDB has several user interfaces.  Although the command-line interface
is the most common and most familiar, there are others.

4.1 Command Interpreter
=======================

The command interpreter in GDB is fairly simple.  It is designed to
allow for the set of commands to be augmented dynamically, and also has
a recursive subcommand capability, where the first argument to a
command may itself direct a lookup on a different command list.

   For instance, the `set' command just starts a lookup on the
`setlist' command list, while `set thread' recurses to the
`set_thread_cmd_list'.

   To add commands in general, use `add_cmd'.  `add_com' adds to the
main command list, and should be used for those commands.  The usual
place to add commands is in the `_initialize_XYZ' routines at the ends
of most source files.

   To add paired `set' and `show' commands, use `add_setshow_cmd' or
`add_setshow_cmd_full'.  The former is a slightly simpler interface
which is useful when you don't need to further modify the new command
structures, while the latter returns the new command structures for
manipulation.

   Before removing commands from the command set it is a good idea to
deprecate them for some time.  Use `deprecate_cmd' on commands or
aliases to set the deprecated flag.  `deprecate_cmd' takes a `struct
cmd_list_element' as it's first argument.  You can use the return value
from `add_com' or `add_cmd' to deprecate the command immediately after
it is created.

   The first time a command is used the user will be warned and offered
a replacement (if one exists). Note that the replacement string passed
to `deprecate_cmd' should be the full name of the command, i.e., the
entire string the user should type at the command line.

4.2 UI-Independent Output--the `ui_out' Functions
=================================================

The `ui_out' functions present an abstraction level for the GDB output
code.  They hide the specifics of different user interfaces supported
by GDB, and thus free the programmer from the need to write several
versions of the same code, one each for every UI, to produce output.

4.2.1 Overview and Terminology
------------------------------

In general, execution of each GDB command produces some sort of output,
and can even generate an input request.

   Output can be generated for the following purposes:

   * to display a _result_ of an operation;

   * to convey _info_ or produce side-effects of a requested operation;

   * to provide a _notification_ of an asynchronous event (including
     progress indication of a prolonged asynchronous operation);

   * to display _error messages_ (including warnings);

   * to show _debug data_;

   * to _query_ or prompt a user for input (a special case).

This section mainly concentrates on how to build result output,
although some of it also applies to other kinds of output.

   Generation of output that displays the results of an operation
involves one or more of the following:

   * output of the actual data

   * formatting the output as appropriate for console output, to make it
     easily readable by humans

   * machine oriented formatting-a more terse formatting to allow for
     easy parsing by programs which read GDB's output

   * annotation, whose purpose is to help legacy GUIs to identify
     interesting parts in the output

   The `ui_out' routines take care of the first three aspects.
Annotations are provided by separate annotation routines.  Note that use
of annotations for an interface between a GUI and GDB is deprecated.

   Output can be in the form of a single item, which we call a "field";
a "list" consisting of identical fields; a "tuple" consisting of
non-identical fields; or a "table", which is a tuple consisting of a
header and a body.  In a BNF-like form:

`<table> ==>'
     `<header> <body>'

`<header> ==>'
     `{ <column> }'

`<column> ==>'
     `<width> <alignment> <title>'

`<body> ==>'
     `{<row>}'

4.2.2 General Conventions
-------------------------

Most `ui_out' routines are of type `void', the exceptions are
`ui_out_stream_new' (which returns a pointer to the newly created
object) and the `make_cleanup' routines.

   The first parameter is always the `ui_out' vector object, a pointer
to a `struct ui_out'.

   The FORMAT parameter is like in `printf' family of functions.  When
it is present, there must also be a variable list of arguments
sufficient used to satisfy the `%' specifiers in the supplied format.

   When a character string argument is not used in a `ui_out' function
call, a `NULL' pointer has to be supplied instead.

4.2.3 Table, Tuple and List Functions
-------------------------------------

This section introduces `ui_out' routines for building lists, tuples
and tables.  The routines to output the actual data items (fields) are
presented in the next section.

   To recap: A "tuple" is a sequence of "fields", each field containing
information about an object; a "list" is a sequence of fields where
each field describes an identical object.

   Use the "table" functions when your output consists of a list of
rows (tuples) and the console output should include a heading.  Use this
even when you are listing just one object but you still want the header.

   Tables can not be nested.  Tuples and lists can be nested up to a
maximum of five levels.

   The overall structure of the table output code is something like
this:

       ui_out_table_begin
         ui_out_table_header
         ...
         ui_out_table_body
           ui_out_tuple_begin
             ui_out_field_*
             ...
           ui_out_tuple_end
           ...
       ui_out_table_end

   Here is the description of table-, tuple- and list-related `ui_out'
functions:

 -- Function: void ui_out_table_begin (struct ui_out *UIOUT, int
          NBROFCOLS, int NR_ROWS, const char *TBLID)
     The function `ui_out_table_begin' marks the beginning of the output
     of a table.  It should always be called before any other `ui_out'
     function for a given table.  NBROFCOLS is the number of columns in
     the table. NR_ROWS is the number of rows in the table.  TBLID is
     an optional string identifying the table.  The string pointed to
     by TBLID is copied by the implementation of `ui_out_table_begin',
     so the application can free the string if it was `malloc'ed.

     The companion function `ui_out_table_end', described below, marks
     the end of the table's output.

 -- Function: void ui_out_table_header (struct ui_out *UIOUT, int
          WIDTH, enum ui_align ALIGNMENT, const char *COLHDR)
     `ui_out_table_header' provides the header information for a single
     table column.  You call this function several times, one each for
     every column of the table, after `ui_out_table_begin', but before
     `ui_out_table_body'.

     The value of WIDTH gives the column width in characters.  The
     value of ALIGNMENT is one of `left', `center', and `right', and it
     specifies how to align the header: left-justify, center, or
     right-justify it.  COLHDR points to a string that specifies the
     column header; the implementation copies that string, so column
     header strings in `malloc'ed storage can be freed after the call.

 -- Function: void ui_out_table_body (struct ui_out *UIOUT)
     This function delimits the table header from the table body.

 -- Function: void ui_out_table_end (struct ui_out *UIOUT)
     This function signals the end of a table's output.  It should be
     called after the table body has been produced by the list and
     field output functions.

     There should be exactly one call to `ui_out_table_end' for each
     call to `ui_out_table_begin', otherwise the `ui_out' functions
     will signal an internal error.

   The output of the tuples that represent the table rows must follow
the call to `ui_out_table_body' and precede the call to
`ui_out_table_end'.  You build a tuple by calling `ui_out_tuple_begin'
and `ui_out_tuple_end', with suitable calls to functions which actually
output fields between them.

 -- Function: void ui_out_tuple_begin (struct ui_out *UIOUT, const char
          *ID)
     This function marks the beginning of a tuple output.  ID points to
     an optional string that identifies the tuple; it is copied by the
     implementation, and so strings in `malloc'ed storage can be freed
     after the call.

 -- Function: void ui_out_tuple_end (struct ui_out *UIOUT)
     This function signals an end of a tuple output.  There should be
     exactly one call to `ui_out_tuple_end' for each call to
     `ui_out_tuple_begin', otherwise an internal GDB error will be
     signaled.

 -- Function: struct cleanup *make_cleanup_ui_out_tuple_begin_end
          (struct ui_out *UIOUT, const char *ID)
     This function first opens the tuple and then establishes a cleanup
     (*note Cleanups: Coding.) to close the tuple.  It provides a
     convenient and correct implementation of the non-portable(1) code
     sequence:
          struct cleanup *old_cleanup;
          ui_out_tuple_begin (uiout, "...");
          old_cleanup = make_cleanup ((void(*)(void *)) ui_out_tuple_end,
                                      uiout);

 -- Function: void ui_out_list_begin (struct ui_out *UIOUT, const char
          *ID)
     This function marks the beginning of a list output.  ID points to
     an optional string that identifies the list; it is copied by the
     implementation, and so strings in `malloc'ed storage can be freed
     after the call.

 -- Function: void ui_out_list_end (struct ui_out *UIOUT)
     This function signals an end of a list output.  There should be
     exactly one call to `ui_out_list_end' for each call to
     `ui_out_list_begin', otherwise an internal GDB error will be
     signaled.

 -- Function: struct cleanup *make_cleanup_ui_out_list_begin_end
          (struct ui_out *UIOUT, const char *ID)
     Similar to `make_cleanup_ui_out_tuple_begin_end', this function
     opens a list and then establishes cleanup (*note Cleanups: Coding.)
     that will close the list.

4.2.4 Item Output Functions
---------------------------

The functions described below produce output for the actual data items,
or fields, which contain information about the object.

   Choose the appropriate function accordingly to your particular needs.

 -- Function: void ui_out_field_fmt (struct ui_out *UIOUT, char
          *FLDNAME, char *FORMAT, ...)
     This is the most general output function.  It produces the
     representation of the data in the variable-length argument list
     according to formatting specifications in FORMAT, a `printf'-like
     format string.  The optional argument FLDNAME supplies the name of
     the field.  The data items themselves are supplied as additional
     arguments after FORMAT.

     This generic function should be used only when it is not possible
     to use one of the specialized versions (see below).

 -- Function: void ui_out_field_int (struct ui_out *UIOUT, const char
          *FLDNAME, int VALUE)
     This function outputs a value of an `int' variable.  It uses the
     `"%d"' output conversion specification.  FLDNAME specifies the
     name of the field.

 -- Function: void ui_out_field_fmt_int (struct ui_out *UIOUT, int
          WIDTH, enum ui_align ALIGNMENT, const char *FLDNAME, int
          VALUE)
     This function outputs a value of an `int' variable.  It differs
     from `ui_out_field_int' in that the caller specifies the desired
     WIDTH and ALIGNMENT of the output.  FLDNAME specifies the name of
     the field.

 -- Function: void ui_out_field_core_addr (struct ui_out *UIOUT, const
          char *FLDNAME, CORE_ADDR ADDRESS)
     This function outputs an address.

 -- Function: void ui_out_field_string (struct ui_out *UIOUT, const
          char *FLDNAME, const char *STRING)
     This function outputs a string using the `"%s"' conversion
     specification.

   Sometimes, there's a need to compose your output piece by piece using
functions that operate on a stream, such as `value_print' or
`fprintf_symbol_filtered'.  These functions accept an argument of the
type `struct ui_file *', a pointer to a `ui_file' object used to store
the data stream used for the output.  When you use one of these
functions, you need a way to pass their results stored in a `ui_file'
object to the `ui_out' functions.  To this end, you first create a
`ui_stream' object by calling `ui_out_stream_new', pass the `stream'
member of that `ui_stream' object to `value_print' and similar
functions, and finally call `ui_out_field_stream' to output the field
you constructed.  When the `ui_stream' object is no longer needed, you
should destroy it and free its memory by calling `ui_out_stream_delete'.

 -- Function: struct ui_stream *ui_out_stream_new (struct ui_out *UIOUT)
     This function creates a new `ui_stream' object which uses the same
     output methods as the `ui_out' object whose pointer is passed in
     UIOUT.  It returns a pointer to the newly created `ui_stream'
     object.

 -- Function: void ui_out_stream_delete (struct ui_stream *STREAMBUF)
     This functions destroys a `ui_stream' object specified by
     STREAMBUF.

 -- Function: void ui_out_field_stream (struct ui_out *UIOUT, const
          char *FIELDNAME, struct ui_stream *STREAMBUF)
     This function consumes all the data accumulated in
     `streambuf->stream' and outputs it like `ui_out_field_string'
     does.  After a call to `ui_out_field_stream', the accumulated data
     no longer exists, but the stream is still valid and may be used
     for producing more fields.

   *Important:* If there is any chance that your code could bail out
before completing output generation and reaching the point where
`ui_out_stream_delete' is called, it is necessary to set up a cleanup,
to avoid leaking memory and other resources.  Here's a skeleton code to
do that:

      struct ui_stream *mybuf = ui_out_stream_new (uiout);
      struct cleanup *old = make_cleanup (ui_out_stream_delete, mybuf);
      ...
      do_cleanups (old);

   If the function already has the old cleanup chain set (for other
kinds of cleanups), you just have to add your cleanup to it:

       mybuf = ui_out_stream_new (uiout);
       make_cleanup (ui_out_stream_delete, mybuf);

   Note that with cleanups in place, you should not call
`ui_out_stream_delete' directly, or you would attempt to free the same
buffer twice.

4.2.5 Utility Output Functions
------------------------------

 -- Function: void ui_out_field_skip (struct ui_out *UIOUT, const char
          *FLDNAME)
     This function skips a field in a table.  Use it if you have to
     leave an empty field without disrupting the table alignment.  The
     argument FLDNAME specifies a name for the (missing) filed.

 -- Function: void ui_out_text (struct ui_out *UIOUT, const char
          *STRING)
     This function outputs the text in STRING in a way that makes it
     easy to be read by humans.  For example, the console
     implementation of this method filters the text through a built-in
     pager, to prevent it from scrolling off the visible portion of the
     screen.

     Use this function for printing relatively long chunks of text
     around the actual field data: the text it produces is not aligned
     according to the table's format.  Use `ui_out_field_string' to
     output a string field, and use `ui_out_message', described below,
     to output short messages.

 -- Function: void ui_out_spaces (struct ui_out *UIOUT, int NSPACES)
     This function outputs NSPACES spaces.  It is handy to align the
     text produced by `ui_out_text' with the rest of the table or list.

 -- Function: void ui_out_message (struct ui_out *UIOUT, int VERBOSITY,
          const char *FORMAT, ...)
     This function produces a formatted message, provided that the
     current verbosity level is at least as large as given by
     VERBOSITY.  The current verbosity level is specified by the user
     with the `set verbositylevel' command.(2)

 -- Function: void ui_out_wrap_hint (struct ui_out *UIOUT, char *INDENT)
     This function gives the console output filter (a paging filter) a
     hint of where to break lines which are too long.  Ignored for all
     other output consumers.  INDENT, if non-`NULL', is the string to
     be printed to indent the wrapped text on the next line; it must
     remain accessible until the next call to `ui_out_wrap_hint', or
     until an explicit newline is produced by one of the other
     functions.  If INDENT is `NULL', the wrapped text will not be
     indented.

 -- Function: void ui_out_flush (struct ui_out *UIOUT)
     This function flushes whatever output has been accumulated so far,
     if the UI buffers output.

4.2.6 Examples of Use of `ui_out' functions
-------------------------------------------

This section gives some practical examples of using the `ui_out'
functions to generalize the old console-oriented code in GDB.  The
examples all come from functions defined on the `breakpoints.c' file.

   This example, from the `breakpoint_1' function, shows how to produce
a table.

   The original code was:

      if (!found_a_breakpoint++)
        {
          annotate_breakpoints_headers ();

          annotate_field (0);
          printf_filtered ("Num ");
          annotate_field (1);
          printf_filtered ("Type           ");
          annotate_field (2);
          printf_filtered ("Disp ");
          annotate_field (3);
          printf_filtered ("Enb ");
          if (addressprint)
            {
              annotate_field (4);
              printf_filtered ("Address    ");
            }
          annotate_field (5);
          printf_filtered ("What\n");

          annotate_breakpoints_table ();
        }

   Here's the new version:

       nr_printable_breakpoints = ...;

       if (addressprint)
         ui_out_table_begin (ui, 6, nr_printable_breakpoints, "BreakpointTable");
       else
         ui_out_table_begin (ui, 5, nr_printable_breakpoints, "BreakpointTable");

       if (nr_printable_breakpoints > 0)
         annotate_breakpoints_headers ();
       if (nr_printable_breakpoints > 0)
         annotate_field (0);
       ui_out_table_header (uiout, 3, ui_left, "number", "Num");                /* 1 */
       if (nr_printable_breakpoints > 0)
         annotate_field (1);
       ui_out_table_header (uiout, 14, ui_left, "type", "Type");                /* 2 */
       if (nr_printable_breakpoints > 0)
         annotate_field (2);
       ui_out_table_header (uiout, 4, ui_left, "disp", "Disp");         /* 3 */
       if (nr_printable_breakpoints > 0)
         annotate_field (3);
       ui_out_table_header (uiout, 3, ui_left, "enabled", "Enb");       /* 4 */
       if (addressprint)
         {
          if (nr_printable_breakpoints > 0)
            annotate_field (4);
          if (gdbarch_addr_bit (current_gdbarch) <= 32)
            ui_out_table_header (uiout, 10, ui_left, "addr", "Address");/* 5 */
          else
            ui_out_table_header (uiout, 18, ui_left, "addr", "Address");/* 5 */
         }
       if (nr_printable_breakpoints > 0)
         annotate_field (5);
       ui_out_table_header (uiout, 40, ui_noalign, "what", "What");     /* 6 */
       ui_out_table_body (uiout);
       if (nr_printable_breakpoints > 0)
         annotate_breakpoints_table ();

   This example, from the `print_one_breakpoint' function, shows how to
produce the actual data for the table whose structure was defined in
the above example.  The original code was:

        annotate_record ();
        annotate_field (0);
        printf_filtered ("%-3d ", b->number);
        annotate_field (1);
        if ((int)b->type > (sizeof(bptypes)/sizeof(bptypes[0]))
            || ((int) b->type != bptypes[(int) b->type].type))
          internal_error ("bptypes table does not describe type #%d.",
                          (int)b->type);
        printf_filtered ("%-14s ", bptypes[(int)b->type].description);
        annotate_field (2);
        printf_filtered ("%-4s ", bpdisps[(int)b->disposition]);
        annotate_field (3);
        printf_filtered ("%-3c ", bpenables[(int)b->enable]);
        ...

   This is the new version:

        annotate_record ();
        ui_out_tuple_begin (uiout, "bkpt");
        annotate_field (0);
        ui_out_field_int (uiout, "number", b->number);
        annotate_field (1);
        if (((int) b->type > (sizeof (bptypes) / sizeof (bptypes[0])))
            || ((int) b->type != bptypes[(int) b->type].type))
          internal_error ("bptypes table does not describe type #%d.",
                          (int) b->type);
        ui_out_field_string (uiout, "type", bptypes[(int)b->type].description);
        annotate_field (2);
        ui_out_field_string (uiout, "disp", bpdisps[(int)b->disposition]);
        annotate_field (3);
        ui_out_field_fmt (uiout, "enabled", "%c", bpenables[(int)b->enable]);
        ...

   This example, also from `print_one_breakpoint', shows how to produce
a complicated output field using the `print_expression' functions which
requires a stream to be passed.  It also shows how to automate stream
destruction with cleanups.  The original code was:

         annotate_field (5);
         print_expression (b->exp, gdb_stdout);

   The new version is:

       struct ui_stream *stb = ui_out_stream_new (uiout);
       struct cleanup *old_chain = make_cleanup_ui_out_stream_delete (stb);
       ...
       annotate_field (5);
       print_expression (b->exp, stb->stream);
       ui_out_field_stream (uiout, "what", local_stream);

   This example, also from `print_one_breakpoint', shows how to use
`ui_out_text' and `ui_out_field_string'.  The original code was:

       annotate_field (5);
       if (b->dll_pathname == NULL)
         printf_filtered ("<any library> ");
       else
         printf_filtered ("library \"%s\" ", b->dll_pathname);

   It became:

       annotate_field (5);
       if (b->dll_pathname == NULL)
         {
           ui_out_field_string (uiout, "what", "<any library>");
           ui_out_spaces (uiout, 1);
         }
       else
         {
           ui_out_text (uiout, "library \"");
           ui_out_field_string (uiout, "what", b->dll_pathname);
           ui_out_text (uiout, "\" ");
         }

   The following example from `print_one_breakpoint' shows how to use
`ui_out_field_int' and `ui_out_spaces'.  The original code was:

       annotate_field (5);
       if (b->forked_inferior_pid != 0)
         printf_filtered ("process %d ", b->forked_inferior_pid);

   It became:

       annotate_field (5);
       if (b->forked_inferior_pid != 0)
         {
           ui_out_text (uiout, "process ");
           ui_out_field_int (uiout, "what", b->forked_inferior_pid);
           ui_out_spaces (uiout, 1);
         }

   Here's an example of using `ui_out_field_string'.  The original code
was:

       annotate_field (5);
       if (b->exec_pathname != NULL)
         printf_filtered ("program \"%s\" ", b->exec_pathname);

   It became:

       annotate_field (5);
       if (b->exec_pathname != NULL)
         {
           ui_out_text (uiout, "program \"");
           ui_out_field_string (uiout, "what", b->exec_pathname);
           ui_out_text (uiout, "\" ");
         }

   Finally, here's an example of printing an address.  The original
code:

       annotate_field (4);
       printf_filtered ("%s ",
             hex_string_custom ((unsigned long) b->address, 8));

   It became:

       annotate_field (4);
       ui_out_field_core_addr (uiout, "Address", b->address);

4.3 Console Printing
====================

4.4 TUI
=======

---------- Footnotes ----------

   (1) The function cast is not portable ISO C.

   (2) As of this writing (April 2001), setting verbosity level is not
yet implemented, and is always returned as zero.  So calling
`ui_out_message' with a VERBOSITY argument more than zero will cause
the message to never be printed.

\x1f
File: gdbint.info,  Node: libgdb,  Next: Symbol Handling,  Prev: User Interface,  Up: Top

5 libgdb
********

5.1 libgdb 1.0
==============

`libgdb' 1.0 was an abortive project of years ago.  The theory was to
provide an API to GDB's functionality.

5.2 libgdb 2.0
==============

`libgdb' 2.0 is an ongoing effort to update GDB so that is better able
to support graphical and other environments.

   Since `libgdb' development is on-going, its architecture is still
evolving.  The following components have so far been identified:

   * Observer - `gdb-events.h'.

   * Builder - `ui-out.h'

   * Event Loop - `event-loop.h'

   * Library - `gdb.h'

   The model that ties these components together is described below.

5.3 The `libgdb' Model
======================

A client of `libgdb' interacts with the library in two ways.

   * As an observer (using `gdb-events') receiving notifications from
     `libgdb' of any internal state changes (break point changes, run
     state, etc).

   * As a client querying `libgdb' (using the `ui-out' builder) to
     obtain various status values from GDB.

   Since `libgdb' could have multiple clients (e.g., a GUI supporting
the existing GDB CLI), those clients must co-operate when controlling
`libgdb'.  In particular, a client must ensure that `libgdb' is idle
(i.e. no other client is using `libgdb') before responding to a
`gdb-event' by making a query.

5.4 CLI support
===============

At present GDB's CLI is very much entangled in with the core of
`libgdb'.  Consequently, a client wishing to include the CLI in their
interface needs to carefully co-ordinate its own and the CLI's
requirements.

   It is suggested that the client set `libgdb' up to be bi-modal
(alternate between CLI and client query modes).  The notes below sketch
out the theory:

   * The client registers itself as an observer of `libgdb'.

   * The client create and install `cli-out' builder using its own
     versions of the `ui-file' `gdb_stderr', `gdb_stdtarg' and
     `gdb_stdout' streams.

   * The client creates a separate custom `ui-out' builder that is only
     used while making direct queries to `libgdb'.

   When the client receives input intended for the CLI, it simply
passes it along.  Since the `cli-out' builder is installed by default,
all the CLI output in response to that command is routed (pronounced
rooted) through to the client controlled `gdb_stdout' et. al. streams.
At the same time, the client is kept abreast of internal changes by
virtue of being a `libgdb' observer.

   The only restriction on the client is that it must wait until
`libgdb' becomes idle before initiating any queries (using the client's
custom builder).

5.5 `libgdb' components
=======================

Observer - `gdb-events.h'
-------------------------

`gdb-events' provides the client with a very raw mechanism that can be
used to implement an observer.  At present it only allows for one
observer and that observer must, internally, handle the need to delay
the processing of any event notifications until after `libgdb' has
finished the current command.

Builder - `ui-out.h'
--------------------

`ui-out' provides the infrastructure necessary for a client to create a
builder.  That builder is then passed down to `libgdb' when doing any
queries.

Event Loop - `event-loop.h'
---------------------------

`event-loop', currently non-re-entrant, provides a simple event loop.
A client would need to either plug its self into this loop or,
implement a new event-loop that GDB would use.

   The event-loop will eventually be made re-entrant.  This is so that
GDB can better handle the problem of some commands blocking instead of
returning.

Library - `gdb.h'
-----------------

`libgdb' is the most obvious component of this system.  It provides the
query interface.  Each function is parameterized by a `ui-out' builder.
The result of the query is constructed using that builder before the
query function returns.

\x1f
File: gdbint.info,  Node: Symbol Handling,  Next: Language Support,  Prev: libgdb,  Up: Top

6 Symbol Handling
*****************

Symbols are a key part of GDB's operation.  Symbols include variables,
functions, and types.

6.1 Symbol Reading
==================

GDB reads symbols from "symbol files".  The usual symbol file is the
file containing the program which GDB is debugging.  GDB can be
directed to use a different file for symbols (with the `symbol-file'
command), and it can also read more symbols via the `add-file' and
`load' commands, or while reading symbols from shared libraries.

   Symbol files are initially opened by code in `symfile.c' using the
BFD library (*note Support Libraries::).  BFD identifies the type of
the file by examining its header.  `find_sym_fns' then uses this
identification to locate a set of symbol-reading functions.

   Symbol-reading modules identify themselves to GDB by calling
`add_symtab_fns' during their module initialization.  The argument to
`add_symtab_fns' is a `struct sym_fns' which contains the name (or name
prefix) of the symbol format, the length of the prefix, and pointers to
four functions.  These functions are called at various times to process
symbol files whose identification matches the specified prefix.

   The functions supplied by each module are:

`XYZ_symfile_init(struct sym_fns *sf)'
     Called from `symbol_file_add' when we are about to read a new
     symbol file.  This function should clean up any internal state
     (possibly resulting from half-read previous files, for example)
     and prepare to read a new symbol file.  Note that the symbol file
     which we are reading might be a new "main" symbol file, or might
     be a secondary symbol file whose symbols are being added to the
     existing symbol table.

     The argument to `XYZ_symfile_init' is a newly allocated `struct
     sym_fns' whose `bfd' field contains the BFD for the new symbol
     file being read.  Its `private' field has been zeroed, and can be
     modified as desired.  Typically, a struct of private information
     will be `malloc''d, and a pointer to it will be placed in the
     `private' field.

     There is no result from `XYZ_symfile_init', but it can call
     `error' if it detects an unavoidable problem.

`XYZ_new_init()'
     Called from `symbol_file_add' when discarding existing symbols.
     This function needs only handle the symbol-reading module's
     internal state; the symbol table data structures visible to the
     rest of GDB will be discarded by `symbol_file_add'.  It has no
     arguments and no result.  It may be called after
     `XYZ_symfile_init', if a new symbol table is being read, or may be
     called alone if all symbols are simply being discarded.

`XYZ_symfile_read(struct sym_fns *sf, CORE_ADDR addr, int mainline)'
     Called from `symbol_file_add' to actually read the symbols from a
     symbol-file into a set of psymtabs or symtabs.

     `sf' points to the `struct sym_fns' originally passed to
     `XYZ_sym_init' for possible initialization.  `addr' is the offset
     between the file's specified start address and its true address in
     memory.  `mainline' is 1 if this is the main symbol table being
     read, and 0 if a secondary symbol file (e.g., shared library or
     dynamically loaded file) is being read.

   In addition, if a symbol-reading module creates psymtabs when
XYZ_symfile_read is called, these psymtabs will contain a pointer to a
function `XYZ_psymtab_to_symtab', which can be called from any point in
the GDB symbol-handling code.

`XYZ_psymtab_to_symtab (struct partial_symtab *pst)'
     Called from `psymtab_to_symtab' (or the `PSYMTAB_TO_SYMTAB' macro)
     if the psymtab has not already been read in and had its
     `pst->symtab' pointer set.  The argument is the psymtab to be
     fleshed-out into a symtab.  Upon return, `pst->readin' should have
     been set to 1, and `pst->symtab' should contain a pointer to the
     new corresponding symtab, or zero if there were no symbols in that
     part of the symbol file.

6.2 Partial Symbol Tables
=========================

GDB has three types of symbol tables:

   * Full symbol tables ("symtabs").  These contain the main
     information about symbols and addresses.

   * Partial symbol tables ("psymtabs").  These contain enough
     information to know when to read the corresponding part of the full
     symbol table.

   * Minimal symbol tables ("msymtabs").  These contain information
     gleaned from non-debugging symbols.

   This section describes partial symbol tables.

   A psymtab is constructed by doing a very quick pass over an
executable file's debugging information.  Small amounts of information
are extracted--enough to identify which parts of the symbol table will
need to be re-read and fully digested later, when the user needs the
information.  The speed of this pass causes GDB to start up very
quickly.  Later, as the detailed rereading occurs, it occurs in small
pieces, at various times, and the delay therefrom is mostly invisible to
the user.

   The symbols that show up in a file's psymtab should be, roughly,
those visible to the debugger's user when the program is not running
code from that file.  These include external symbols and types, static
symbols and types, and `enum' values declared at file scope.

   The psymtab also contains the range of instruction addresses that the
full symbol table would represent.

   The idea is that there are only two ways for the user (or much of the
code in the debugger) to reference a symbol:

   * By its address (e.g., execution stops at some address which is
     inside a function in this file).  The address will be noticed to
     be in the range of this psymtab, and the full symtab will be read
     in.  `find_pc_function', `find_pc_line', and other `find_pc_...'
     functions handle this.

   * By its name (e.g., the user asks to print a variable, or set a
     breakpoint on a function).  Global names and file-scope names will
     be found in the psymtab, which will cause the symtab to be pulled
     in.  Local names will have to be qualified by a global name, or a
     file-scope name, in which case we will have already read in the
     symtab as we evaluated the qualifier.  Or, a local symbol can be
     referenced when we are "in" a local scope, in which case the first
     case applies.  `lookup_symbol' does most of the work here.

   The only reason that psymtabs exist is to cause a symtab to be read
in at the right moment.  Any symbol that can be elided from a psymtab,
while still causing that to happen, should not appear in it.  Since
psymtabs don't have the idea of scope, you can't put local symbols in
them anyway.  Psymtabs don't have the idea of the type of a symbol,
either, so types need not appear, unless they will be referenced by
name.

   It is a bug for GDB to behave one way when only a psymtab has been
read, and another way if the corresponding symtab has been read in.
Such bugs are typically caused by a psymtab that does not contain all
the visible symbols, or which has the wrong instruction address ranges.

   The psymtab for a particular section of a symbol file (objfile)
could be thrown away after the symtab has been read in.  The symtab
should always be searched before the psymtab, so the psymtab will never
be used (in a bug-free environment).  Currently, psymtabs are allocated
on an obstack, and all the psymbols themselves are allocated in a pair
of large arrays on an obstack, so there is little to be gained by
trying to free them unless you want to do a lot more work.

6.3 Types
=========

Fundamental Types (e.g., `FT_VOID', `FT_BOOLEAN').
--------------------------------------------------

These are the fundamental types that GDB uses internally.  Fundamental
types from the various debugging formats (stabs, ELF, etc) are mapped
into one of these.  They are basically a union of all fundamental types
that GDB knows about for all the languages that GDB knows about.

Type Codes (e.g., `TYPE_CODE_PTR', `TYPE_CODE_ARRAY').
------------------------------------------------------

Each time GDB builds an internal type, it marks it with one of these
types.  The type may be a fundamental type, such as `TYPE_CODE_INT', or
a derived type, such as `TYPE_CODE_PTR' which is a pointer to another
type.  Typically, several `FT_*' types map to one `TYPE_CODE_*' type,
and are distinguished by other members of the type struct, such as
whether the type is signed or unsigned, and how many bits it uses.

Builtin Types (e.g., `builtin_type_void', `builtin_type_char').
---------------------------------------------------------------

These are instances of type structs that roughly correspond to
fundamental types and are created as global types for GDB to use for
various ugly historical reasons.  We eventually want to eliminate
these.  Note for example that `builtin_type_int' initialized in
`gdbtypes.c' is basically the same as a `TYPE_CODE_INT' type that is
initialized in `c-lang.c' for an `FT_INTEGER' fundamental type.  The
difference is that the `builtin_type' is not associated with any
particular objfile, and only one instance exists, while `c-lang.c'
builds as many `TYPE_CODE_INT' types as needed, with each one
associated with some particular objfile.

6.4 Object File Formats
=======================

6.4.1 a.out
-----------

The `a.out' format is the original file format for Unix.  It consists
of three sections: `text', `data', and `bss', which are for program
code, initialized data, and uninitialized data, respectively.

   The `a.out' format is so simple that it doesn't have any reserved
place for debugging information.  (Hey, the original Unix hackers used
`adb', which is a machine-language debugger!)  The only debugging
format for `a.out' is stabs, which is encoded as a set of normal
symbols with distinctive attributes.

   The basic `a.out' reader is in `dbxread.c'.

6.4.2 COFF
----------

The COFF format was introduced with System V Release 3 (SVR3) Unix.
COFF files may have multiple sections, each prefixed by a header.  The
number of sections is limited.

   The COFF specification includes support for debugging.  Although this
was a step forward, the debugging information was woefully limited.  For
instance, it was not possible to represent code that came from an
included file.

   The COFF reader is in `coffread.c'.

6.4.3 ECOFF
-----------

ECOFF is an extended COFF originally introduced for Mips and Alpha
workstations.

   The basic ECOFF reader is in `mipsread.c'.

6.4.4 XCOFF
-----------

The IBM RS/6000 running AIX uses an object file format called XCOFF.
The COFF sections, symbols, and line numbers are used, but debugging
symbols are `dbx'-style stabs whose strings are located in the `.debug'
section (rather than the string table).  For more information, see
*Note Top: (stabs)Top.

   The shared library scheme has a clean interface for figuring out what
shared libraries are in use, but the catch is that everything which
refers to addresses (symbol tables and breakpoints at least) needs to be
relocated for both shared libraries and the main executable.  At least
using the standard mechanism this can only be done once the program has
been run (or the core file has been read).

6.4.5 PE
--------

Windows 95 and NT use the PE ("Portable Executable") format for their
executables.  PE is basically COFF with additional headers.

   While BFD includes special PE support, GDB needs only the basic COFF
reader.

6.4.6 ELF
---------

The ELF format came with System V Release 4 (SVR4) Unix.  ELF is similar
to COFF in being organized into a number of sections, but it removes
many of COFF's limitations.

   The basic ELF reader is in `elfread.c'.

6.4.7 SOM
---------

SOM is HP's object file and debug format (not to be confused with IBM's
SOM, which is a cross-language ABI).

   The SOM reader is in `somread.c'.

6.5 Debugging File Formats
==========================

This section describes characteristics of debugging information that
are independent of the object file format.

6.5.1 stabs
-----------

`stabs' started out as special symbols within the `a.out' format.
Since then, it has been encapsulated into other file formats, such as
COFF and ELF.

   While `dbxread.c' does some of the basic stab processing, including
for encapsulated versions, `stabsread.c' does the real work.

6.5.2 COFF
----------

The basic COFF definition includes debugging information.  The level of
support is minimal and non-extensible, and is not often used.

6.5.3 Mips debug (Third Eye)
----------------------------

ECOFF includes a definition of a special debug format.

   The file `mdebugread.c' implements reading for this format.

6.5.4 DWARF 2
-------------

DWARF 2 is an improved but incompatible version of DWARF 1.

   The DWARF 2 reader is in `dwarf2read.c'.

6.5.5 SOM
---------

Like COFF, the SOM definition includes debugging information.

6.6 Adding a New Symbol Reader to GDB
=====================================

If you are using an existing object file format (`a.out', COFF, ELF,
etc), there is probably little to be done.

   If you need to add a new object file format, you must first add it to
BFD.  This is beyond the scope of this document.

   You must then arrange for the BFD code to provide access to the
debugging symbols.  Generally GDB will have to call swapping routines
from BFD and a few other BFD internal routines to locate the debugging
information.  As much as possible, GDB should not depend on the BFD
internal data structures.

   For some targets (e.g., COFF), there is a special transfer vector
used to call swapping routines, since the external data structures on
various platforms have different sizes and layouts.  Specialized
routines that will only ever be implemented by one object file format
may be called directly.  This interface should be described in a file
`bfd/libXYZ.h', which is included by GDB.

6.7 Memory Management for Symbol Files
======================================

Most memory associated with a loaded symbol file is stored on its
`objfile_obstack'.  This includes symbols, types, namespace data, and
other information produced by the symbol readers.

   Because this data lives on the objfile's obstack, it is automatically
released when the objfile is unloaded or reloaded.  Therefore one
objfile must not reference symbol or type data from another objfile;
they could be unloaded at different times.

   User convenience variables, et cetera, have associated types.
Normally these types live in the associated objfile.  However, when the
objfile is unloaded, those types are deep copied to global memory, so
that the values of the user variables and history items are not lost.

\x1f
File: gdbint.info,  Node: Language Support,  Next: Host Definition,  Prev: Symbol Handling,  Up: Top

7 Language Support
******************

GDB's language support is mainly driven by the symbol reader, although
it is possible for the user to set the source language manually.

   GDB chooses the source language by looking at the extension of the
file recorded in the debug info; `.c' means C, `.f' means Fortran, etc.
It may also use a special-purpose language identifier if the debug
format supports it, like with DWARF.

7.1 Adding a Source Language to GDB
===================================

To add other languages to GDB's expression parser, follow the following
steps:

_Create the expression parser._
     This should reside in a file `LANG-exp.y'.  Routines for building
     parsed expressions into a `union exp_element' list are in
     `parse.c'.

     Since we can't depend upon everyone having Bison, and YACC produces
     parsers that define a bunch of global names, the following lines
     *must* be included at the top of the YACC parser, to prevent the
     various parsers from defining the same global names:

          #define yyparse         LANG_parse
          #define yylex           LANG_lex
          #define yyerror         LANG_error
          #define yylval          LANG_lval
          #define yychar          LANG_char
          #define yydebug         LANG_debug
          #define yypact          LANG_pact
          #define yyr1            LANG_r1
          #define yyr2            LANG_r2
          #define yydef           LANG_def
          #define yychk           LANG_chk
          #define yypgo           LANG_pgo
          #define yyact           LANG_act
          #define yyexca          LANG_exca
          #define yyerrflag       LANG_errflag
          #define yynerrs         LANG_nerrs

     At the bottom of your parser, define a `struct language_defn' and
     initialize it with the right values for your language.  Define an
     `initialize_LANG' routine and have it call
     `add_language(LANG_language_defn)' to tell the rest of GDB that
     your language exists.  You'll need some other supporting variables
     and functions, which will be used via pointers from your
     `LANG_language_defn'.  See the declaration of `struct
     language_defn' in `language.h', and the other `*-exp.y' files, for
     more information.

_Add any evaluation routines, if necessary_
     If you need new opcodes (that represent the operations of the
     language), add them to the enumerated type in `expression.h'.  Add
     support code for these operations in the `evaluate_subexp' function
     defined in the file `eval.c'.  Add cases for new opcodes in two
     functions from `parse.c': `prefixify_subexp' and
     `length_of_subexp'.  These compute the number of `exp_element's
     that a given operation takes up.

_Update some existing code_
     Add an enumerated identifier for your language to the enumerated
     type `enum language' in `defs.h'.

     Update the routines in `language.c' so your language is included.
     These routines include type predicates and such, which (in some
     cases) are language dependent.  If your language does not appear
     in the switch statement, an error is reported.

     Also included in `language.c' is the code that updates the variable
     `current_language', and the routines that translate the
     `language_LANG' enumerated identifier into a printable string.

     Update the function `_initialize_language' to include your
     language.  This function picks the default language upon startup,
     so is dependent upon which languages that GDB is built for.

     Update `allocate_symtab' in `symfile.c' and/or symbol-reading code
     so that the language of each symtab (source file) is set properly.
     This is used to determine the language to use at each stack frame
     level.  Currently, the language is set based upon the extension of
     the source file.  If the language can be better inferred from the
     symbol information, please set the language of the symtab in the
     symbol-reading code.

     Add helper code to `print_subexp' (in `expprint.c') to handle any
     new expression opcodes you have added to `expression.h'.  Also,
     add the printed representations of your operators to
     `op_print_tab'.

_Add a place of call_
     Add a call to `LANG_parse()' and `LANG_error' in `parse_exp_1'
     (defined in `parse.c').

_Use macros to trim code_
     The user has the option of building GDB for some or all of the
     languages.  If the user decides to build GDB for the language
     LANG, then every file dependent on `language.h' will have the
     macro `_LANG_LANG' defined in it.  Use `#ifdef's to leave out
     large routines that the user won't need if he or she is not using
     your language.

     Note that you do not need to do this in your YACC parser, since if
     GDB is not build for LANG, then `LANG-exp.tab.o' (the compiled
     form of your parser) is not linked into GDB at all.

     See the file `configure.in' for how GDB is configured for
     different languages.

_Edit `Makefile.in'_
     Add dependencies in `Makefile.in'.  Make sure you update the macro
     variables such as `HFILES' and `OBJS', otherwise your code may not
     get linked in, or, worse yet, it may not get `tar'red into the
     distribution!

\x1f
File: gdbint.info,  Node: Host Definition,  Next: Target Architecture Definition,  Prev: Language Support,  Up: Top

8 Host Definition
*****************

With the advent of Autoconf, it's rarely necessary to have host
definition machinery anymore.  The following information is provided,
mainly, as an historical reference.

8.1 Adding a New Host
=====================

GDB's host configuration support normally happens via Autoconf.  New
host-specific definitions should not be needed.  Older hosts GDB still
use the host-specific definitions and files listed below, but these
mostly exist for historical reasons, and will eventually disappear.

`gdb/config/ARCH/XYZ.mh'
     This file once contained both host and native configuration
     information (*note Native Debugging::) for the machine XYZ.  The
     host configuration information is now handed by Autoconf.

     Host configuration information included a definition of
     `XM_FILE=xm-XYZ.h' and possibly definitions for `CC',
     `SYSV_DEFINE', `XM_CFLAGS', `XM_ADD_FILES', `XM_CLIBS',
     `XM_CDEPS', etc.; see `Makefile.in'.

     New host only configurations do not need this file.

`gdb/config/ARCH/xm-XYZ.h'
     This file once contained definitions and includes required when
     hosting gdb on machine XYZ.  Those definitions and includes are now
     handled by Autoconf.

     New host and native configurations do not need this file.

     _Maintainer's note: Some hosts continue to use the `xm-xyz.h' file
     to define the macros HOST_FLOAT_FORMAT, HOST_DOUBLE_FORMAT and
     HOST_LONG_DOUBLE_FORMAT.  That code also needs to be replaced with
     either an Autoconf or run-time test._


Generic Host Support Files
--------------------------

There are some "generic" versions of routines that can be used by
various systems.  These can be customized in various ways by macros
defined in your `xm-XYZ.h' file.  If these routines work for the XYZ
host, you can just include the generic file's name (with `.o', not
`.c') in `XDEPFILES'.

   Otherwise, if your machine needs custom support routines, you will
need to write routines that perform the same functions as the generic
file.  Put them into `XYZ-xdep.c', and put `XYZ-xdep.o' into
`XDEPFILES'.

`ser-unix.c'
     This contains serial line support for Unix systems.  This is always
     included, via the makefile variable `SER_HARDWIRE'; override this
     variable in the `.mh' file to avoid it.

`ser-go32.c'
     This contains serial line support for 32-bit programs running
     under DOS, using the DJGPP (a.k.a. GO32) execution environment.

`ser-tcp.c'
     This contains generic TCP support using sockets.

8.2 Host Conditionals
=====================

When GDB is configured and compiled, various macros are defined or left
undefined, to control compilation based on the attributes of the host
system.  These macros and their meanings (or if the meaning is not
documented here, then one of the source files where they are used is
indicated) are:

`GDBINIT_FILENAME'
     The default name of GDB's initialization file (normally
     `.gdbinit').

`NO_STD_REGS'
     This macro is deprecated.

`SIGWINCH_HANDLER'
     If your host defines `SIGWINCH', you can define this to be the name
     of a function to be called if `SIGWINCH' is received.

`SIGWINCH_HANDLER_BODY'
     Define this to expand into code that will define the function
     named by the expansion of `SIGWINCH_HANDLER'.

`CRLF_SOURCE_FILES'
     Define this if host files use `\r\n' rather than `\n' as a line
     terminator.  This will cause source file listings to omit `\r'
     characters when printing and it will allow `\r\n' line endings of
     files which are "sourced" by gdb.  It must be possible to open
     files in binary mode using `O_BINARY' or, for fopen, `"rb"'.

`DEFAULT_PROMPT'
     The default value of the prompt string (normally `"(gdb) "').

`DEV_TTY'
     The name of the generic TTY device, defaults to `"/dev/tty"'.

`FOPEN_RB'
     Define this if binary files are opened the same way as text files.

`HAVE_MMAP'
     In some cases, use the system call `mmap' for reading symbol
     tables.  For some machines this allows for sharing and quick
     updates.

`HAVE_TERMIO'
     Define this if the host system has `termio.h'.

`INT_MAX'
`INT_MIN'
`LONG_MAX'
`UINT_MAX'
`ULONG_MAX'
     Values for host-side constants.

`ISATTY'
     Substitute for isatty, if not available.

`LONGEST'
     This is the longest integer type available on the host.  If not
     defined, it will default to `long long' or `long', depending on
     `CC_HAS_LONG_LONG'.

`CC_HAS_LONG_LONG'
     Define this if the host C compiler supports `long long'.  This is
     set by the `configure' script.

`PRINTF_HAS_LONG_LONG'
     Define this if the host can handle printing of long long integers
     via the printf format conversion specifier `ll'.  This is set by
     the `configure' script.

`HAVE_LONG_DOUBLE'
     Define this if the host C compiler supports `long double'.  This is
     set by the `configure' script.

`PRINTF_HAS_LONG_DOUBLE'
     Define this if the host can handle printing of long double
     float-point numbers via the printf format conversion specifier
     `Lg'.  This is set by the `configure' script.

`SCANF_HAS_LONG_DOUBLE'
     Define this if the host can handle the parsing of long double
     float-point numbers via the scanf format conversion specifier
     `Lg'.  This is set by the `configure' script.

`LSEEK_NOT_LINEAR'
     Define this if `lseek (n)' does not necessarily move to byte number
     `n' in the file.  This is only used when reading source files.  It
     is normally faster to define `CRLF_SOURCE_FILES' when possible.

`L_SET'
     This macro is used as the argument to `lseek' (or, most commonly,
     `bfd_seek').  FIXME, should be replaced by SEEK_SET instead, which
     is the POSIX equivalent.

`NORETURN'
     If defined, this should be one or more tokens, such as `volatile',
     that can be used in both the declaration and definition of
     functions to indicate that they never return.  The default is
     already set correctly if compiling with GCC.  This will almost
     never need to be defined.

`ATTR_NORETURN'
     If defined, this should be one or more tokens, such as
     `__attribute__ ((noreturn))', that can be used in the declarations
     of functions to indicate that they never return.  The default is
     already set correctly if compiling with GCC.  This will almost
     never need to be defined.

`SEEK_CUR'
`SEEK_SET'
     Define these to appropriate value for the system `lseek', if not
     already defined.

`STOP_SIGNAL'
     This is the signal for stopping GDB.  Defaults to `SIGTSTP'.
     (Only redefined for the Convex.)

`USG'
     Means that System V (prior to SVR4) include files are in use.
     (FIXME: This symbol is abused in `infrun.c', `regex.c', and
     `utils.c' for other things, at the moment.)

`lint'
     Define this to help placate `lint' in some situations.

`volatile'
     Define this to override the defaults of `__volatile__' or `/**/'.

\x1f
File: gdbint.info,  Node: Target Architecture Definition,  Next: Target Descriptions,  Prev: Host Definition,  Up: Top

9 Target Architecture Definition
********************************

GDB's target architecture defines what sort of machine-language
programs GDB can work with, and how it works with them.

   The target architecture object is implemented as the C structure
`struct gdbarch *'.  The structure, and its methods, are generated
using the Bourne shell script `gdbarch.sh'.

* Menu:

* OS ABI Variant Handling::
* Initialize New Architecture::
* Registers and Memory::
* Pointers and Addresses::
* Address Classes::
* Raw and Virtual Registers::
* Register and Memory Data::
* Frame Interpretation::
* Inferior Call Setup::
* Compiler Characteristics::
* Target Conditionals::
* Adding a New Target::

\x1f
File: gdbint.info,  Node: OS ABI Variant Handling,  Next: Initialize New Architecture,  Up: Target Architecture Definition

9.1 Operating System ABI Variant Handling
=========================================

GDB provides a mechanism for handling variations in OS ABIs.  An OS ABI
variant may have influence over any number of variables in the target
architecture definition.  There are two major components in the OS ABI
mechanism: sniffers and handlers.

   A "sniffer" examines a file matching a BFD architecture/flavour pair
(the architecture may be wildcarded) in an attempt to determine the OS
ABI of that file.  Sniffers with a wildcarded architecture are
considered to be "generic", while sniffers for a specific architecture
are considered to be "specific".  A match from a specific sniffer
overrides a match from a generic sniffer.  Multiple sniffers for an
architecture/flavour may exist, in order to differentiate between two
different operating systems which use the same basic file format.  The
OS ABI framework provides a generic sniffer for ELF-format files which
examines the `EI_OSABI' field of the ELF header, as well as note
sections known to be used by several operating systems.

   A "handler" is used to fine-tune the `gdbarch' structure for the
selected OS ABI.  There may be only one handler for a given OS ABI for
each BFD architecture.

   The following OS ABI variants are defined in `defs.h':

`GDB_OSABI_UNINITIALIZED'
     Used for struct gdbarch_info if ABI is still uninitialized.

`GDB_OSABI_UNKNOWN'
     The ABI of the inferior is unknown.  The default `gdbarch'
     settings for the architecture will be used.

`GDB_OSABI_SVR4'
     UNIX System V Release 4.

`GDB_OSABI_HURD'
     GNU using the Hurd kernel.

`GDB_OSABI_SOLARIS'
     Sun Solaris.

`GDB_OSABI_OSF1'
     OSF/1, including Digital UNIX and Compaq Tru64 UNIX.

`GDB_OSABI_LINUX'
     GNU using the Linux kernel.

`GDB_OSABI_FREEBSD_AOUT'
     FreeBSD using the `a.out' executable format.

`GDB_OSABI_FREEBSD_ELF'
     FreeBSD using the ELF executable format.

`GDB_OSABI_NETBSD_AOUT'
     NetBSD using the `a.out' executable format.

`GDB_OSABI_NETBSD_ELF'
     NetBSD using the ELF executable format.

`GDB_OSABI_OPENBSD_ELF'
     OpenBSD using the ELF executable format.

`GDB_OSABI_WINCE'
     Windows CE.

`GDB_OSABI_GO32'
     DJGPP.

`GDB_OSABI_IRIX'
     Irix.

`GDB_OSABI_INTERIX'
     Interix (Posix layer for MS-Windows systems).

`GDB_OSABI_HPUX_ELF'
     HP/UX using the ELF executable format.

`GDB_OSABI_HPUX_SOM'
     HP/UX using the SOM executable format.

`GDB_OSABI_QNXNTO'
     QNX Neutrino.

`GDB_OSABI_CYGWIN'
     Cygwin.

`GDB_OSABI_AIX'
     AIX.


   Here are the functions that make up the OS ABI framework:

 -- Function: const char *gdbarch_osabi_name (enum gdb_osabi OSABI)
     Return the name of the OS ABI corresponding to OSABI.

 -- Function: void gdbarch_register_osabi (enum bfd_architecture ARCH,
          unsigned long MACHINE, enum gdb_osabi OSABI, void
          (*INIT_OSABI)(struct gdbarch_info INFO, struct gdbarch
          *GDBARCH))
     Register the OS ABI handler specified by INIT_OSABI for the
     architecture, machine type and OS ABI specified by ARCH, MACHINE
     and OSABI.  In most cases, a value of zero for the machine type,
     which implies the architecture's default machine type, will
     suffice.

 -- Function: void gdbarch_register_osabi_sniffer (enum
          bfd_architecture ARCH, enum bfd_flavour FLAVOUR, enum
          gdb_osabi (*SNIFFER)(bfd *ABFD))
     Register the OS ABI file sniffer specified by SNIFFER for the BFD
     architecture/flavour pair specified by ARCH and FLAVOUR.  If ARCH
     is `bfd_arch_unknown', the sniffer is considered to be generic,
     and is allowed to examine FLAVOUR-flavoured files for any
     architecture.

 -- Function: enum gdb_osabi gdbarch_lookup_osabi (bfd *ABFD)
     Examine the file described by ABFD to determine its OS ABI.  The
     value `GDB_OSABI_UNKNOWN' is returned if the OS ABI cannot be
     determined.

 -- Function: void gdbarch_init_osabi (struct gdbarch info INFO, struct
          gdbarch *GDBARCH, enum gdb_osabi OSABI)
     Invoke the OS ABI handler corresponding to OSABI to fine-tune the
     `gdbarch' structure specified by GDBARCH.  If a handler
     corresponding to OSABI has not been registered for GDBARCH's
     architecture, a warning will be issued and the debugging session
     will continue with the defaults already established for GDBARCH.

 -- Function: void generic_elf_osabi_sniff_abi_tag_sections (bfd *ABFD,
          asection *SECT, void *OBJ)
     Helper routine for ELF file sniffers.  Examine the file described
     by ABFD and look at ABI tag note sections to determine the OS ABI
     from the note.  This function should be called via
     `bfd_map_over_sections'.

\x1f
File: gdbint.info,  Node: Initialize New Architecture,  Next: Registers and Memory,  Prev: OS ABI Variant Handling,  Up: Target Architecture Definition

9.2 Initializing a New Architecture
===================================

Each `gdbarch' is associated with a single BFD architecture, via a
`bfd_arch_ARCH' constant.  The `gdbarch' is registered by a call to
`register_gdbarch_init', usually from the file's `_initialize_FILENAME'
routine, which will be automatically called during GDB startup.  The
arguments are a BFD architecture constant and an initialization
function.

   The initialization function has this type:

     static struct gdbarch *
     ARCH_gdbarch_init (struct gdbarch_info INFO,
                              struct gdbarch_list *ARCHES)

   The INFO argument contains parameters used to select the correct
architecture, and ARCHES is a list of architectures which have already
been created with the same `bfd_arch_ARCH' value.

   The initialization function should first make sure that INFO is
acceptable, and return `NULL' if it is not.  Then, it should search
through ARCHES for an exact match to INFO, and return one if found.
Lastly, if no exact match was found, it should create a new
architecture based on INFO and return it.

   Only information in INFO should be used to choose the new
architecture.  Historically, INFO could be sparse, and defaults would
be collected from the first element on ARCHES.  However, GDB now fills
in INFO more thoroughly, so new `gdbarch' initialization functions
should not take defaults from ARCHES.

\x1f
File: gdbint.info,  Node: Registers and Memory,  Next: Pointers and Addresses,  Prev: Initialize New Architecture,  Up: Target Architecture Definition

9.3 Registers and Memory
========================

GDB's model of the target machine is rather simple.  GDB assumes the
machine includes a bank of registers and a block of memory.  Each
register may have a different size.

   GDB does not have a magical way to match up with the compiler's idea
of which registers are which; however, it is critical that they do
match up accurately.  The only way to make this work is to get accurate
information about the order that the compiler uses, and to reflect that
in the `gdbarch_register_name' and related functions.

   GDB can handle big-endian, little-endian, and bi-endian
architectures.

\x1f
File: gdbint.info,  Node: Pointers and Addresses,  Next: Address Classes,  Prev: Registers and Memory,  Up: Target Architecture Definition

9.4 Pointers Are Not Always Addresses
=====================================

On almost all 32-bit architectures, the representation of a pointer is
indistinguishable from the representation of some fixed-length number
whose value is the byte address of the object pointed to.  On such
machines, the words "pointer" and "address" can be used interchangeably.
However, architectures with smaller word sizes are often cramped for
address space, so they may choose a pointer representation that breaks
this identity, and allows a larger code address space.

   For example, the Renesas D10V is a 16-bit VLIW processor whose
instructions are 32 bits long(1).  If the D10V used ordinary byte
addresses to refer to code locations, then the processor would only be
able to address 64kb of instructions.  However, since instructions must
be aligned on four-byte boundaries, the low two bits of any valid
instruction's byte address are always zero--byte addresses waste two
bits.  So instead of byte addresses, the D10V uses word addresses--byte
addresses shifted right two bits--to refer to code.  Thus, the D10V can
use 16-bit words to address 256kb of code space.

   However, this means that code pointers and data pointers have
different forms on the D10V.  The 16-bit word `0xC020' refers to byte
address `0xC020' when used as a data address, but refers to byte address
`0x30080' when used as a code address.

   (The D10V also uses separate code and data address spaces, which also
affects the correspondence between pointers and addresses, but we're
going to ignore that here; this example is already too long.)

   To cope with architectures like this--the D10V is not the only
one!--GDB tries to distinguish between "addresses", which are byte
numbers, and "pointers", which are the target's representation of an
address of a particular type of data.  In the example above, `0xC020'
is the pointer, which refers to one of the addresses `0xC020' or
`0x30080', depending on the type imposed upon it.  GDB provides
functions for turning a pointer into an address and vice versa, in the
appropriate way for the current architecture.

   Unfortunately, since addresses and pointers are identical on almost
all processors, this distinction tends to bit-rot pretty quickly.  Thus,
each time you port GDB to an architecture which does distinguish
between pointers and addresses, you'll probably need to clean up some
architecture-independent code.

   Here are functions which convert between pointers and addresses:

 -- Function: CORE_ADDR extract_typed_address (void *BUF, struct type
          *TYPE)
     Treat the bytes at BUF as a pointer or reference of type TYPE, and
     return the address it represents, in a manner appropriate for the
     current architecture.  This yields an address GDB can use to read
     target memory, disassemble, etc.  Note that BUF refers to a buffer
     in GDB's memory, not the inferior's.

     For example, if the current architecture is the Intel x86, this
     function extracts a little-endian integer of the appropriate
     length from BUF and returns it.  However, if the current
     architecture is the D10V, this function will return a 16-bit
     integer extracted from BUF, multiplied by four if TYPE is a
     pointer to a function.

     If TYPE is not a pointer or reference type, then this function
     will signal an internal error.

 -- Function: CORE_ADDR store_typed_address (void *BUF, struct type
          *TYPE, CORE_ADDR ADDR)
     Store the address ADDR in BUF, in the proper format for a pointer
     of type TYPE in the current architecture.  Note that BUF refers to
     a buffer in GDB's memory, not the inferior's.

     For example, if the current architecture is the Intel x86, this
     function stores ADDR unmodified as a little-endian integer of the
     appropriate length in BUF.  However, if the current architecture
     is the D10V, this function divides ADDR by four if TYPE is a
     pointer to a function, and then stores it in BUF.

     If TYPE is not a pointer or reference type, then this function
     will signal an internal error.

 -- Function: CORE_ADDR value_as_address (struct value *VAL)
     Assuming that VAL is a pointer, return the address it represents,
     as appropriate for the current architecture.

     This function actually works on integral values, as well as
     pointers.  For pointers, it performs architecture-specific
     conversions as described above for `extract_typed_address'.

 -- Function: CORE_ADDR value_from_pointer (struct type *TYPE,
          CORE_ADDR ADDR)
     Create and return a value representing a pointer of type TYPE to
     the address ADDR, as appropriate for the current architecture.
     This function performs architecture-specific conversions as
     described above for `store_typed_address'.

   Here are two functions which architectures can define to indicate the
relationship between pointers and addresses.  These have default
definitions, appropriate for architectures on which all pointers are
simple unsigned byte addresses.

 -- Function: CORE_ADDR gdbarch_pointer_to_address (struct gdbarch
          *CURRENT_GDBARCH, struct type *TYPE, char *BUF)
     Assume that BUF holds a pointer of type TYPE, in the appropriate
     format for the current architecture.  Return the byte address the
     pointer refers to.

     This function may safely assume that TYPE is either a pointer or a
     C++ reference type.

 -- Function: void gdbarch_address_to_pointer (struct gdbarch
          *CURRENT_GDBARCH, struct type *TYPE, char *BUF, CORE_ADDR
          ADDR)
     Store in BUF a pointer of type TYPE representing the address ADDR,
     in the appropriate format for the current architecture.

     This function may safely assume that TYPE is either a pointer or a
     C++ reference type.

   ---------- Footnotes ----------

   (1) Some D10V instructions are actually pairs of 16-bit
sub-instructions.  However, since you can't jump into the middle of
such a pair, code addresses can only refer to full 32 bit instructions,
which is what matters in this explanation.

\x1f
File: gdbint.info,  Node: Address Classes,  Next: Raw and Virtual Registers,  Prev: Pointers and Addresses,  Up: Target Architecture Definition

9.5 Address Classes
===================

Sometimes information about different kinds of addresses is available
via the debug information.  For example, some programming environments
define addresses of several different sizes.  If the debug information
distinguishes these kinds of address classes through either the size
info (e.g, `DW_AT_byte_size' in DWARF 2) or through an explicit address
class attribute (e.g, `DW_AT_address_class' in DWARF 2), the following
macros should be defined in order to disambiguate these types within
GDB as well as provide the added information to a GDB user when
printing type expressions.

 -- Function: int gdbarch_address_class_type_flags (struct gdbarch
          *CURRENT_GDBARCH, int BYTE_SIZE, int DWARF2_ADDR_CLASS)
     Returns the type flags needed to construct a pointer type whose
     size is BYTE_SIZE and whose address class is DWARF2_ADDR_CLASS.
     This function is normally called from within a symbol reader.  See
     `dwarf2read.c'.

 -- Function: char *gdbarch_address_class_type_flags_to_name (struct
          gdbarch *CURRENT_GDBARCH, int TYPE_FLAGS)
     Given the type flags representing an address class qualifier,
     return its name.

 -- Function: int gdbarch_address_class_name_to_type_flags (struct
          gdbarch *CURRENT_GDBARCH, int NAME, int *vartype_flags_ptr)
     Given an address qualifier name, set the `int' referenced by
     TYPE_FLAGS_PTR to the type flags for that address class qualifier.

   Since the need for address classes is rather rare, none of the
address class functions are defined by default.  Predicate functions
are provided to detect when they are defined.

   Consider a hypothetical architecture in which addresses are normally
32-bits wide, but 16-bit addresses are also supported.  Furthermore,
suppose that the DWARF 2 information for this architecture simply uses
a `DW_AT_byte_size' value of 2 to indicate the use of one of these
"short" pointers.  The following functions could be defined to
implement the address class functions:

     somearch_address_class_type_flags (int byte_size,
                                        int dwarf2_addr_class)
     {
       if (byte_size == 2)
         return TYPE_FLAG_ADDRESS_CLASS_1;
       else
         return 0;
     }

     static char *
     somearch_address_class_type_flags_to_name (int type_flags)
     {
       if (type_flags & TYPE_FLAG_ADDRESS_CLASS_1)
         return "short";
       else
         return NULL;
     }

     int
     somearch_address_class_name_to_type_flags (char *name,
                                                int *type_flags_ptr)
     {
       if (strcmp (name, "short") == 0)
         {
           *type_flags_ptr = TYPE_FLAG_ADDRESS_CLASS_1;
           return 1;
         }
       else
         return 0;
     }

   The qualifier `@short' is used in GDB's type expressions to indicate
the presence of one of these "short" pointers.  E.g, if the debug
information indicates that `short_ptr_var' is one of these short
pointers, GDB might show the following behavior:

     (gdb) ptype short_ptr_var
     type = int * @short

\x1f
File: gdbint.info,  Node: Raw and Virtual Registers,  Next: Register and Memory Data,  Prev: Address Classes,  Up: Target Architecture Definition

9.6 Raw and Virtual Register Representations
============================================

_Maintainer note: This section is pretty much obsolete.  The
functionality described here has largely been replaced by
pseudo-registers and the mechanisms described in *Note Using Different
Register and Memory Data Representations: Target Architecture
Definition.  See also Bug Tracking Database
(http://www.gnu.org/software/gdb/bugs/) and ARI Index
(http://sources.redhat.com/gdb/current/ari/) for more up-to-date
information._

   Some architectures use one representation for a value when it lives
in a register, but use a different representation when it lives in
memory.  In GDB's terminology, the "raw" representation is the one used
in the target registers, and the "virtual" representation is the one
used in memory, and within GDB `struct value' objects.

   _Maintainer note: Notice that the same mechanism is being used to
both convert a register to a `struct value' and alternative register
forms._

   For almost all data types on almost all architectures, the virtual
and raw representations are identical, and no special handling is
needed.  However, they do occasionally differ.  For example:

   * The x86 architecture supports an 80-bit `long double' type.
     However, when we store those values in memory, they occupy twelve
     bytes: the floating-point number occupies the first ten, and the
     final two bytes are unused.  This keeps the values aligned on
     four-byte boundaries, allowing more efficient access.  Thus, the
     x86 80-bit floating-point type is the raw representation, and the
     twelve-byte loosely-packed arrangement is the virtual
     representation.

   * Some 64-bit MIPS targets present 32-bit registers to GDB as 64-bit
     registers, with garbage in their upper bits.  GDB ignores the top
     32 bits.  Thus, the 64-bit form, with garbage in the upper 32
     bits, is the raw representation, and the trimmed 32-bit
     representation is the virtual representation.

   In general, the raw representation is determined by the
architecture, or GDB's interface to the architecture, while the virtual
representation can be chosen for GDB's convenience.  GDB's register
file, `registers', holds the register contents in raw format, and the
GDB remote protocol transmits register values in raw format.

   Your architecture may define the following macros to request
conversions between the raw and virtual format:

 -- Target Macro: int REGISTER_CONVERTIBLE (int REG)
     Return non-zero if register number REG's value needs different raw
     and virtual formats.

     You should not use `REGISTER_CONVERT_TO_VIRTUAL' for a register
     unless this macro returns a non-zero value for that register.

 -- Target Macro: int DEPRECATED_REGISTER_RAW_SIZE (int REG)
     The size of register number REG's raw value.  This is the number
     of bytes the register will occupy in `registers', or in a GDB
     remote protocol packet.

 -- Target Macro: int DEPRECATED_REGISTER_VIRTUAL_SIZE (int REG)
     The size of register number REG's value, in its virtual format.
     This is the size a `struct value''s buffer will have, holding that
     register's value.

 -- Target Macro: struct type *DEPRECATED_REGISTER_VIRTUAL_TYPE (int
          REG)
     This is the type of the virtual representation of register number
     REG.  Note that there is no need for a macro giving a type for the
     register's raw form; once the register's value has been obtained,
     GDB always uses the virtual form.

 -- Target Macro: void REGISTER_CONVERT_TO_VIRTUAL (int REG, struct
          type *TYPE, char *FROM, char *TO)
     Convert the value of register number REG to TYPE, which should
     always be `DEPRECATED_REGISTER_VIRTUAL_TYPE (REG)'.  The buffer at
     FROM holds the register's value in raw format; the macro should
     convert the value to virtual format, and place it at TO.

     Note that `REGISTER_CONVERT_TO_VIRTUAL' and
     `REGISTER_CONVERT_TO_RAW' take their REG and TYPE arguments in
     different orders.

     You should only use `REGISTER_CONVERT_TO_VIRTUAL' with registers
     for which the `REGISTER_CONVERTIBLE' macro returns a non-zero
     value.

 -- Target Macro: void REGISTER_CONVERT_TO_RAW (struct type *TYPE, int
          REG, char *FROM, char *TO)
     Convert the value of register number REG to TYPE, which should
     always be `DEPRECATED_REGISTER_VIRTUAL_TYPE (REG)'.  The buffer at
     FROM holds the register's value in raw format; the macro should
     convert the value to virtual format, and place it at TO.

     Note that REGISTER_CONVERT_TO_VIRTUAL and REGISTER_CONVERT_TO_RAW
     take their REG and TYPE arguments in different orders.

\x1f
File: gdbint.info,  Node: Register and Memory Data,  Next: Frame Interpretation,  Prev: Raw and Virtual Registers,  Up: Target Architecture Definition

9.7 Using Different Register and Memory Data Representations
============================================================

_Maintainer's note: The way GDB manipulates registers is undergoing
significant change.  Many of the macros and functions referred to in
this section are likely to be subject to further revision.  See A.R.
Index (http://sources.redhat.com/gdb/current/ari/) and Bug Tracking
Database (http://www.gnu.org/software/gdb/bugs) for further
information.  cagney/2002-05-06._

   Some architectures can represent a data object in a register using a
form that is different to the objects more normal memory representation.
For example:

   * The Alpha architecture can represent 32 bit integer values in
     floating-point registers.

   * The x86 architecture supports 80-bit floating-point registers.  The
     `long double' data type occupies 96 bits in memory but only 80 bits
     when stored in a register.


   In general, the register representation of a data type is determined
by the architecture, or GDB's interface to the architecture, while the
memory representation is determined by the Application Binary Interface.

   For almost all data types on almost all architectures, the two
representations are identical, and no special handling is needed.
However, they do occasionally differ.  Your architecture may define the
following macros to request conversions between the register and memory
representations of a data type:

 -- Function: int gdbarch_convert_register_p (struct gdbarch *GDBARCH,
          int REG)
     Return non-zero if the representation of a data value stored in
     this register may be different to the representation of that same
     data value when stored in memory.

     When non-zero, the macros `gdbarch_register_to_value' and
     `value_to_register' are used to perform any necessary conversion.

     This function should return zero for the register's native type,
     when no conversion is necessary.

 -- Function: void gdbarch_register_to_value (struct gdbarch *GDBARCH,
          int REG, struct type *TYPE, char *FROM, char *TO)
     Convert the value of register number REG to a data object of type
     TYPE.  The buffer at FROM holds the register's value in raw
     format; the converted value should be placed in the buffer at TO.

     Note that `gdbarch_register_to_value' and
     `gdbarch_value_to_register' take their REG and TYPE arguments in
     different orders.

     You should only use `gdbarch_register_to_value' with registers for
     which the `gdbarch_convert_register_p' function returns a non-zero
     value.

 -- Function: void gdbarch_value_to_register (struct gdbarch *GDBARCH,
          struct type *TYPE, int REG, char *FROM, char *TO)
     Convert a data value of type TYPE to register number REG' raw
     format.

     Note that `gdbarch_register_to_value' and
     `gdbarch_value_to_register' take their REG and TYPE arguments in
     different orders.

     You should only use `gdbarch_value_to_register' with registers for
     which the `gdbarch_convert_register_p' function returns a non-zero
     value.

 -- Target Macro: void REGISTER_CONVERT_TO_TYPE (int REGNUM, struct
          type *TYPE, char *BUF)
     See `mips-tdep.c'.  It does not do what you want.

\x1f
File: gdbint.info,  Node: Frame Interpretation,  Next: Inferior Call Setup,  Prev: Register and Memory Data,  Up: Target Architecture Definition

9.8 Frame Interpretation
========================

\x1f
File: gdbint.info,  Node: Inferior Call Setup,  Next: Compiler Characteristics,  Prev: Frame Interpretation,  Up: Target Architecture Definition

9.9 Inferior Call Setup
=======================

\x1f
File: gdbint.info,  Node: Compiler Characteristics,  Next: Target Conditionals,  Prev: Inferior Call Setup,  Up: Target Architecture Definition

9.10 Compiler Characteristics
=============================

\x1f
File: gdbint.info,  Node: Target Conditionals,  Next: Adding a New Target,  Prev: Compiler Characteristics,  Up: Target Architecture Definition

9.11 Target Conditionals
========================

This section describes the macros and functions that you can use to
define the target machine.

`CORE_ADDR gdbarch_addr_bits_remove (GDBARCH, ADDR)'
     If a raw machine instruction address includes any bits that are not
     really part of the address, then this function is used to zero
     those bits in ADDR.  This is only used for addresses of
     instructions, and even then not in all contexts.

     For example, the two low-order bits of the PC on the
     Hewlett-Packard PA 2.0 architecture contain the privilege level of
     the corresponding instruction.  Since instructions must always be
     aligned on four-byte boundaries, the processor masks out these
     bits to generate the actual address of the instruction.
     `gdbarch_addr_bits_remove' would then for example look like that:
          arch_addr_bits_remove (CORE_ADDR addr)
          {
            return (addr &= ~0x3);
          }

`int address_class_name_to_type_flags (GDBARCH, NAME, TYPE_FLAGS_PTR)'
     If NAME is a valid address class qualifier name, set the `int'
     referenced by TYPE_FLAGS_PTR to the mask representing the qualifier
     and return 1.  If NAME is not a valid address class qualifier name,
     return 0.

     The value for TYPE_FLAGS_PTR should be one of
     `TYPE_FLAG_ADDRESS_CLASS_1', `TYPE_FLAG_ADDRESS_CLASS_2', or
     possibly some combination of these values or'd together.  *Note
     Address Classes: Target Architecture Definition.

`int address_class_name_to_type_flags_p (GDBARCH)'
     Predicate which indicates whether
     `address_class_name_to_type_flags' has been defined.

`int gdbarch_address_class_type_flags (GDBARCH, BYTE_SIZE, DWARF2_ADDR_CLASS)'
     Given a pointers byte size (as described by the debug information)
     and the possible `DW_AT_address_class' value, return the type flags
     used by GDB to represent this address class.  The value returned
     should be one of `TYPE_FLAG_ADDRESS_CLASS_1',
     `TYPE_FLAG_ADDRESS_CLASS_2', or possibly some combination of these
     values or'd together.  *Note Address Classes: Target Architecture
     Definition.

`int gdbarch_address_class_type_flags_p (GDBARCH)'
     Predicate which indicates whether
     `gdbarch_address_class_type_flags_p' has been defined.

`const char *gdbarch_address_class_type_flags_to_name (GDBARCH, TYPE_FLAGS)'
     Return the name of the address class qualifier associated with the
     type flags given by TYPE_FLAGS.

`int gdbarch_address_class_type_flags_to_name_p (GDBARCH)'
     Predicate which indicates whether
     `gdbarch_address_class_type_flags_to_name' has been defined.
     *Note Address Classes: Target Architecture Definition.

`void gdbarch_address_to_pointer (GDBARCH, TYPE, BUF, ADDR)'
     Store in BUF a pointer of type TYPE representing the address ADDR,
     in the appropriate format for the current architecture.  This
     function may safely assume that TYPE is either a pointer or a C++
     reference type.  *Note Pointers Are Not Always Addresses: Target
     Architecture Definition.

`int gdbarch_believe_pcc_promotion (GDBARCH)'
     Used to notify if the compiler promotes a `short' or `char'
     parameter to an `int', but still reports the parameter as its
     original type, rather than the promoted type.

`gdbarch_bits_big_endian (GDBARCH)'
     This is used if the numbering of bits in the targets does *not*
     match the endianness of the target byte order.  A value of 1 means
     that the bits are numbered in a big-endian bit order, 0 means
     little-endian.

`set_gdbarch_bits_big_endian (GDBARCH, BITS_BIG_ENDIAN)'
     Calling set_gdbarch_bits_big_endian with a value of 1 indicates
     that the bits in the target are numbered in a big-endian bit
     order, 0 indicates little-endian.

`BREAKPOINT'
     This is the character array initializer for the bit pattern to put
     into memory where a breakpoint is set.  Although it's common to
     use a trap instruction for a breakpoint, it's not required; for
     instance, the bit pattern could be an invalid instruction.  The
     breakpoint must be no longer than the shortest instruction of the
     architecture.

     `BREAKPOINT' has been deprecated in favor of
     `gdbarch_breakpoint_from_pc'.

`BIG_BREAKPOINT'
`LITTLE_BREAKPOINT'
     Similar to BREAKPOINT, but used for bi-endian targets.

     `BIG_BREAKPOINT' and `LITTLE_BREAKPOINT' have been deprecated in
     favor of `gdbarch_breakpoint_from_pc'.

`const gdb_byte *gdbarch_breakpoint_from_pc (GDBARCH, PCPTR, LENPTR)'
     Use the program counter to determine the contents and size of a
     breakpoint instruction.  It returns a pointer to a string of bytes
     that encode a breakpoint instruction, stores the length of the
     string to `*LENPTR', and adjusts the program counter (if
     necessary) to point to the actual memory location where the
     breakpoint should be inserted.

     Although it is common to use a trap instruction for a breakpoint,
     it's not required; for instance, the bit pattern could be an
     invalid instruction.  The breakpoint must be no longer than the
     shortest instruction of the architecture.

     Replaces all the other BREAKPOINT macros.

`int gdbarch_memory_insert_breakpoint (GDBARCH, BP_TGT)'
`gdbarch_memory_remove_breakpoint (GDBARCH, BP_TGT)'
     Insert or remove memory based breakpoints.  Reasonable defaults
     (`default_memory_insert_breakpoint' and
     `default_memory_remove_breakpoint' respectively) have been
     provided so that it is not necessary to set these for most
     architectures.  Architectures which may want to set
     `gdbarch_memory_insert_breakpoint' and
     `gdbarch_memory_remove_breakpoint' will likely have instructions
     that are oddly sized or are not stored in a conventional manner.

     It may also be desirable (from an efficiency standpoint) to define
     custom breakpoint insertion and removal routines if
     `gdbarch_breakpoint_from_pc' needs to read the target's memory for
     some reason.

`CORE_ADDR gdbarch_adjust_breakpoint_address (GDBARCH, BPADDR)'
     Given an address at which a breakpoint is desired, return a
     breakpoint address adjusted to account for architectural
     constraints on breakpoint placement.  This method is not needed by
     most targets.

     The FR-V target (see `frv-tdep.c') requires this method.  The FR-V
     is a VLIW architecture in which a number of RISC-like instructions
     are grouped (packed) together into an aggregate instruction or
     instruction bundle.  When the processor executes one of these
     bundles, the component instructions are executed in parallel.

     In the course of optimization, the compiler may group instructions
     from distinct source statements into the same bundle.  The line
     number information associated with one of the latter statements
     will likely refer to some instruction other than the first one in
     the bundle.  So, if the user attempts to place a breakpoint on one
     of these latter statements, GDB must be careful to _not_ place the
     break instruction on any instruction other than the first one in
     the bundle.  (Remember though that the instructions within a
     bundle execute in parallel, so the _first_ instruction is the
     instruction at the lowest address and has nothing to do with
     execution order.)

     The FR-V's `gdbarch_adjust_breakpoint_address' method will adjust a
     breakpoint's address by scanning backwards for the beginning of
     the bundle, returning the address of the bundle.

     Since the adjustment of a breakpoint may significantly alter a
     user's expectation, GDB prints a warning when an adjusted
     breakpoint is initially set and each time that that breakpoint is
     hit.

`int gdbarch_call_dummy_location (GDBARCH)'
     See the file `inferior.h'.

     This method has been replaced by `gdbarch_push_dummy_code' (*note
     gdbarch_push_dummy_code::).

`int gdbarch_cannot_fetch_register (GDBARCH, REGUM)'
     This function should return nonzero if REGNO cannot be fetched
     from an inferior process.  This is only relevant if
     `FETCH_INFERIOR_REGISTERS' is not defined.

`int gdbarch_cannot_store_register (GDBARCH, REGNUM)'
     This function should return nonzero if REGNO should not be written
     to the target.  This is often the case for program counters,
     status words, and other special registers.  This function returns
     0 as default so that GDB will assume that all registers may be
     written.

`int gdbarch_convert_register_p (GDBARCH, REGNUM, struct type *TYPE)'
     Return non-zero if register REGNUM represents data values of type
     TYPE in a non-standard form.  *Note Using Different Register and
     Memory Data Representations: Target Architecture Definition.

`CORE_ADDR gdbarch_decr_pc_after_break (GDBARCH)'
     This function shall return the amount by which to decrement the PC
     after the program encounters a breakpoint.  This is often the
     number of bytes in `BREAKPOINT', though not always.  For most
     targets this value will be 0.

`DISABLE_UNSETTABLE_BREAK (ADDR)'
     If defined, this should evaluate to 1 if ADDR is in a shared
     library in which breakpoints cannot be set and so should be
     disabled.

`void gdbarch_print_float_info (GDBARCH, FILE, FRAME, ARGS)'
     If defined, then the `info float' command will print information
     about the processor's floating point unit.

`void gdbarch_print_registers_info (GDBARCH, FRAME, REGNUM, ALL)'
     If defined, pretty print the value of the register REGNUM for the
     specified FRAME.  If the value of REGNUM is -1, pretty print
     either all registers (ALL is non zero) or a select subset of
     registers (ALL is zero).

     The default method prints one register per line, and if ALL is
     zero omits floating-point registers.

`int gdbarch_print_vector_info (GDBARCH, FILE, FRAME, ARGS)'
     If defined, then the `info vector' command will call this function
     to print information about the processor's vector unit.

     By default, the `info vector' command will print all vector
     registers (the register's type having the vector attribute).

`int gdbarch_dwarf_reg_to_regnum (GDBARCH, DWARF_REGNR)'
     Convert DWARF register number DWARF_REGNR into GDB regnum.  If not
     defined, no conversion will be performed.

`int gdbarch_dwarf2_reg_to_regnum (GDBARCH, DWARF2_REGNR)'
     Convert DWARF2 register number DWARF2_REGNR into GDB regnum.  If
     not defined, no conversion will be performed.

`int gdbarch_ecoff_reg_to_regnum (GDBARCH, ECOFF_REGNR)'
     Convert ECOFF register number  ECOFF_REGNR into GDB regnum.  If
     not defined, no conversion will be performed.

`DEPRECATED_FP_REGNUM'
     If the virtual frame pointer is kept in a register, then define
     this macro to be the number (greater than or equal to zero) of
     that register.

     This should only need to be defined if `DEPRECATED_TARGET_READ_FP'
     is not defined.

`DEPRECATED_FRAMELESS_FUNCTION_INVOCATION(FI)'
     Define this to an expression that returns 1 if the function
     invocation represented by FI does not have a stack frame
     associated with it.  Otherwise return 0.

`CORE_ADDR frame_align (GDBARCH, ADDRESS)'
     Define this to adjust ADDRESS so that it meets the alignment
     requirements for the start of a new stack frame.  A stack frame's
     alignment requirements are typically stronger than a target
     processors stack alignment requirements.

     This function is used to ensure that, when creating a dummy frame,
     both the initial stack pointer and (if needed) the address of the
     return value are correctly aligned.

     This function always adjusts the address in the direction of stack
     growth.

     By default, no frame based stack alignment is performed.

`int gdbarch_frame_red_zone_size (GDBARCH)'
     The number of bytes, beyond the innermost-stack-address, reserved
     by the ABI.  A function is permitted to use this scratch area
     (instead of allocating extra stack space).

     When performing an inferior function call, to ensure that it does
     not modify this area, GDB adjusts the innermost-stack-address by
     GDBARCH_FRAME_RED_ZONE_SIZE bytes before pushing parameters onto
     the stack.

     By default, zero bytes are allocated.  The value must be aligned
     (*note frame_align::).

     The AMD64 (nee x86-64) ABI documentation refers to the _red zone_
     when describing this scratch area.  

`DEPRECATED_FRAME_CHAIN(FRAME)'
     Given FRAME, return a pointer to the calling frame.

`DEPRECATED_FRAME_CHAIN_VALID(CHAIN, THISFRAME)'
     Define this to be an expression that returns zero if the given
     frame is an outermost frame, with no caller, and nonzero
     otherwise.  Most normal situations can be handled without defining
     this macro, including `NULL' chain pointers, dummy frames, and
     frames whose PC values are inside the startup file (e.g.
     `crt0.o'), inside `main', or inside `_start'.

`DEPRECATED_FRAME_INIT_SAVED_REGS(FRAME)'
     See `frame.h'.  Determines the address of all registers in the
     current stack frame storing each in `frame->saved_regs'.  Space for
     `frame->saved_regs' shall be allocated by
     `DEPRECATED_FRAME_INIT_SAVED_REGS' using `frame_saved_regs_zalloc'.

     `FRAME_FIND_SAVED_REGS' is deprecated.

`int gdbarch_frame_num_args (GDBARCH, FRAME)'
     For the frame described by FRAME return the number of arguments
     that are being passed.  If the number of arguments is not known,
     return `-1'.

`DEPRECATED_FRAME_SAVED_PC(FRAME)'
     Given FRAME, return the pc saved there.  This is the return
     address.

     This method is deprecated. *Note gdbarch_unwind_pc::.

`CORE_ADDR gdbarch_unwind_pc (NEXT_FRAME)'
     Return the instruction address, in NEXT_FRAME's caller, at which
     execution will resume after NEXT_FRAME returns.  This is commonly
     referred to as the return address.

     The implementation, which must be frame agnostic (work with any
     frame), is typically no more than:

          ULONGEST pc;
          pc = frame_unwind_register_unsigned (next_frame, S390_PC_REGNUM);
          return gdbarch_addr_bits_remove (gdbarch, pc);

     *Note DEPRECATED_FRAME_SAVED_PC::, which this method replaces.

`CORE_ADDR gdbarch_unwind_sp (GDBARCH, NEXT_FRAME)'
     Return the frame's inner most stack address.  This is commonly
     referred to as the frame's "stack pointer".

     The implementation, which must be frame agnostic (work with any
     frame), is typically no more than:

          ULONGEST sp;
          sp = frame_unwind_register_unsigned (next_frame, S390_SP_REGNUM);
          return gdbarch_addr_bits_remove (gdbarch, sp);

     *Note TARGET_READ_SP::, which this method replaces.

`FUNCTION_EPILOGUE_SIZE'
     For some COFF targets, the `x_sym.x_misc.x_fsize' field of the
     function end symbol is 0.  For such targets, you must define
     `FUNCTION_EPILOGUE_SIZE' to expand into the standard size of a
     function's epilogue.

`DEPRECATED_FUNCTION_START_OFFSET'
     An integer, giving the offset in bytes from a function's address
     (as used in the values of symbols, function pointers, etc.), and
     the function's first genuine instruction.

     This is zero on almost all machines: the function's address is
     usually the address of its first instruction.  However, on the
     VAX, for example, each function starts with two bytes containing a
     bitmask indicating which registers to save upon entry to the
     function.  The VAX `call' instructions check this value, and save
     the appropriate registers automatically.  Thus, since the offset
     from the function's address to its first instruction is two bytes,
     `DEPRECATED_FUNCTION_START_OFFSET' would be 2 on the VAX.

`GCC_COMPILED_FLAG_SYMBOL'
`GCC2_COMPILED_FLAG_SYMBOL'
     If defined, these are the names of the symbols that GDB will look
     for to detect that GCC compiled the file.  The default symbols are
     `gcc_compiled.' and `gcc2_compiled.', respectively.  (Currently
     only defined for the Delta 68.)

`gdbarch_get_longjmp_target'
     For most machines, this is a target-dependent parameter.  On the
     DECstation and the Iris, this is a native-dependent parameter,
     since the header file `setjmp.h' is needed to define it.

     This macro determines the target PC address that `longjmp' will
     jump to, assuming that we have just stopped at a `longjmp'
     breakpoint.  It takes a `CORE_ADDR *' as argument, and stores the
     target PC value through this pointer.  It examines the current
     state of the machine as needed.

`DEPRECATED_IBM6000_TARGET'
     Shows that we are configured for an IBM RS/6000 system.  This
     conditional should be eliminated (FIXME) and replaced by
     feature-specific macros.  It was introduced in a haste and we are
     repenting at leisure.

`I386_USE_GENERIC_WATCHPOINTS'
     An x86-based target can define this to use the generic x86
     watchpoint support; see *Note I386_USE_GENERIC_WATCHPOINTS:
     Algorithms.

`int gdbarch_inner_than (GDBARCH, LHS, RHS)'
     Returns non-zero if stack address LHS is inner than (nearer to the
     stack top) stack address RHS.  Let the function return `lhs < rhs'
     if the target's stack grows downward in memory, or `lhs > rsh' if
     the stack grows upward.

`gdbarch_in_function_epilogue_p (GDBARCH, ADDR)'
     Returns non-zero if the given ADDR is in the epilogue of a
     function.  The epilogue of a function is defined as the part of a
     function where the stack frame of the function already has been
     destroyed up to the final `return from function call' instruction.

`int gdbarch_in_solib_return_trampoline (GDBARCH, PC, NAME)'
     Define this function to return nonzero if the program is stopped
     in the trampoline that returns from a shared library.

`IN_SOLIB_DYNSYM_RESOLVE_CODE (PC)'
     Define this to return nonzero if the program is stopped in the
     dynamic linker.

`SKIP_SOLIB_RESOLVER (PC)'
     Define this to evaluate to the (nonzero) address at which execution
     should continue to get past the dynamic linker's symbol resolution
     function.  A zero value indicates that it is not important or
     necessary to set a breakpoint to get through the dynamic linker
     and that single stepping will suffice.

`CORE_ADDR gdbarch_integer_to_address (GDBARCH, TYPE, BUF)'
     Define this when the architecture needs to handle non-pointer to
     address conversions specially.  Converts that value to an address
     according to the current architectures conventions.

     _Pragmatics: When the user copies a well defined expression from
     their source code and passes it, as a parameter, to GDB's `print'
     command, they should get the same value as would have been
     computed by the target program.  Any deviation from this rule can
     cause major confusion and annoyance, and needs to be justified
     carefully.  In other words, GDB doesn't really have the freedom to
     do these conversions in clever and useful ways.  It has, however,
     been pointed out that users aren't complaining about how GDB casts
     integers to pointers; they are complaining that they can't take an
     address from a disassembly listing and give it to `x/i'.  Adding
     an architecture method like `gdbarch_integer_to_address' certainly
     makes it possible for GDB to "get it right" in all circumstances._

     *Note Pointers Are Not Always Addresses: Target Architecture
     Definition.

`CORE_ADDR gdbarch_pointer_to_address (GDBARCH, TYPE, BUF)'
     Assume that BUF holds a pointer of type TYPE, in the appropriate
     format for the current architecture.  Return the byte address the
     pointer refers to.  *Note Pointers Are Not Always Addresses:
     Target Architecture Definition.

`void gdbarch_register_to_value(GDBARCH, FRAME, REGNUM, TYPE, FUR)'
     Convert the raw contents of register REGNUM into a value of type
     TYPE.  *Note Using Different Register and Memory Data
     Representations: Target Architecture Definition.

`register_reggroup_p (GDBARCH, REGNUM, REGGROUP)'
     Return non-zero if register REGNUM is a member of the register
     group REGGROUP.

     By default, registers are grouped as follows:

    `float_reggroup'
          Any register with a valid name and a floating-point type.

    `vector_reggroup'
          Any register with a valid name and a vector type.

    `general_reggroup'
          Any register with a valid name and a type other than vector or
          floating-point.  `float_reggroup'.

    `save_reggroup'
    `restore_reggroup'
    `all_reggroup'
          Any register with a valid name.

`DEPRECATED_REGISTER_VIRTUAL_SIZE (REG)'
     Return the virtual size of REG; defaults to the size of the
     register's virtual type.  Return the virtual size of REG.  *Note
     Raw and Virtual Register Representations: Target Architecture
     Definition.

`DEPRECATED_REGISTER_VIRTUAL_TYPE (REG)'
     Return the virtual type of REG.  *Note Raw and Virtual Register
     Representations: Target Architecture Definition.

`struct type *register_type (GDBARCH, REG)'
     If defined, return the type of register REG.  This function
     supersedes `DEPRECATED_REGISTER_VIRTUAL_TYPE'.  *Note Raw and
     Virtual Register Representations: Target Architecture Definition.

`REGISTER_CONVERT_TO_VIRTUAL(REG, TYPE, FROM, TO)'
     Convert the value of register REG from its raw form to its virtual
     form.  *Note Raw and Virtual Register Representations: Target
     Architecture Definition.

`REGISTER_CONVERT_TO_RAW(TYPE, REG, FROM, TO)'
     Convert the value of register REG from its virtual form to its raw
     form.  *Note Raw and Virtual Register Representations: Target
     Architecture Definition.

`const struct regset *regset_from_core_section (struct gdbarch * GDBARCH, const char * SECT_NAME, size_t SECT_SIZE)'
     Return the appropriate register set for a core file section with
     name SECT_NAME and size SECT_SIZE.

`SOFTWARE_SINGLE_STEP_P()'
     Define this as 1 if the target does not have a hardware single-step
     mechanism.  The macro `SOFTWARE_SINGLE_STEP' must also be defined.

`SOFTWARE_SINGLE_STEP(SIGNAL, INSERT_BREAKPOINTS_P)'
     A function that inserts or removes (depending on
     INSERT_BREAKPOINTS_P) breakpoints at each possible destinations of
     the next instruction. See `sparc-tdep.c' and `rs6000-tdep.c' for
     examples.

`set_gdbarch_sofun_address_maybe_missing (GDBARCH, SET)'
     Somebody clever observed that, the more actual addresses you have
     in the debug information, the more time the linker has to spend
     relocating them.  So whenever there's some other way the debugger
     could find the address it needs, you should omit it from the debug
     info, to make linking faster.

     Calling `set_gdbarch_sofun_address_maybe_missing' with a non-zero
     argument SET indicates that a particular set of hacks of this sort
     are in use, affecting `N_SO' and `N_FUN' entries in stabs-format
     debugging information.  `N_SO' stabs mark the beginning and ending
     addresses of compilation units in the text segment.  `N_FUN' stabs
     mark the starts and ends of functions.

     In this case, GDB assumes two things:

        * `N_FUN' stabs have an address of zero.  Instead of using those
          addresses, you should find the address where the function
          starts by taking the function name from the stab, and then
          looking that up in the minsyms (the linker/assembler symbol
          table).  In other words, the stab has the name, and the
          linker/assembler symbol table is the only place that carries
          the address.

        * `N_SO' stabs have an address of zero, too.  You just look at
          the `N_FUN' stabs that appear before and after the `N_SO'
          stab, and guess the starting and ending addresses of the
          compilation unit from them.

`int gdbarch_pc_regnum (GDBARCH)'
     If the program counter is kept in a register, then let this
     function return the number (greater than or equal to zero) of that
     register.

     This should only need to be defined if `gdbarch_read_pc' and
     `gdbarch_write_pc' are not defined.

`int gdbarch_stabs_argument_has_addr (GDBARCH, TYPE)'
     Define this function to return nonzero if a function argument of
     type TYPE is passed by reference instead of value.

`PROCESS_LINENUMBER_HOOK'
     A hook defined for XCOFF reading.

`gdbarch_ps_regnum (GDBARCH'
     If defined, this function returns the number of the processor
     status register.  (This definition is only used in generic code
     when parsing "$ps".)

`CORE_ADDR gdbarch_push_dummy_call (GDBARCH, FUNCTION, REGCACHE, BP_ADDR, NARGS, ARGS, SP, STRUCT_RETURN, STRUCT_ADDR)'
     Define this to push the dummy frame's call to the inferior
     function onto the stack.  In addition to pushing NARGS, the code
     should push STRUCT_ADDR (when STRUCT_RETURN is non-zero), and the
     return address (BP_ADDR).

     FUNCTION is a pointer to a `struct value'; on architectures that
     use function descriptors, this contains the function descriptor
     value.

     Returns the updated top-of-stack pointer.

     This method replaces `DEPRECATED_PUSH_ARGUMENTS'.

`CORE_ADDR gdbarch_push_dummy_code (GDBARCH, SP, FUNADDR, USING_GCC, ARGS, NARGS, VALUE_TYPE, REAL_PC, BP_ADDR, REGCACHE)'
     Given a stack based call dummy, push the instruction sequence
     (including space for a breakpoint) to which the called function
     should return.

     Set BP_ADDR to the address at which the breakpoint instruction
     should be inserted, REAL_PC to the resume address when starting
     the call sequence, and return the updated inner-most stack address.

     By default, the stack is grown sufficient to hold a frame-aligned
     (*note frame_align::) breakpoint, BP_ADDR is set to the address
     reserved for that breakpoint, and REAL_PC set to FUNADDR.

     This method replaces `gdbarch_call_dummy_location (GDBARCH)' and
     `DEPRECATED_REGISTER_SIZE'.

`const char *gdbarch_register_name (GDBARCH, REGNR)'
     Return the name of register REGNR as a string.  May return `NULL'
     to indicate that REGNR is not a valid register.

`SAVE_DUMMY_FRAME_TOS (SP)'
     Used in `call_function_by_hand' to notify the target dependent
     code of the top-of-stack value that will be passed to the inferior
     code.  This is the value of the `SP' after both the dummy frame
     and space for parameters/results have been allocated on the stack.
     *Note gdbarch_unwind_dummy_id::.

`int gdbarch_sdb_reg_to_regnum (GDBARCH, SDB_REGNR)'
     Use this function to convert sdb register SDB_REGNR into GDB
     regnum.  If not defined, no conversion will be done.

`enum return_value_convention gdbarch_return_value (struct gdbarch *GDBARCH, struct type *VALTYPE, struct regcache *REGCACHE, void *READBUF, const void *WRITEBUF)'
     Given a function with a return-value of type RETTYPE, return which
     return-value convention that function would use.

     GDB currently recognizes two function return-value conventions:
     `RETURN_VALUE_REGISTER_CONVENTION' where the return value is found
     in registers; and `RETURN_VALUE_STRUCT_CONVENTION' where the return
     value is found in memory and the address of that memory location is
     passed in as the function's first parameter.

     If the register convention is being used, and WRITEBUF is
     non-`NULL', also copy the return-value in WRITEBUF into REGCACHE.

     If the register convention is being used, and READBUF is
     non-`NULL', also copy the return value from REGCACHE into READBUF
     (REGCACHE contains a copy of the registers from the just returned
     function).

     _Maintainer note: This method replaces separate predicate, extract,
     store methods.  By having only one method, the logic needed to
     determine the return-value convention need only be implemented in
     one place.  If GDB were written in an OO language, this method
     would instead return an object that knew how to perform the
     register return-value extract and store._

     _Maintainer note: This method does not take a GCC_P parameter, and
     such a parameter should not be added.  If an architecture that
     requires per-compiler or per-function information be identified,
     then the replacement of RETTYPE with `struct value' FUNCTION
     should be pursued._

     _Maintainer note: The REGCACHE parameter limits this methods to
     the inner most frame.  While replacing REGCACHE with a `struct
     frame_info' FRAME parameter would remove that limitation there has
     yet to be a demonstrated need for such a change._

`void gdbarch_skip_permanent_breakpoint (GDBARCH, REGCACHE)'
     Advance the inferior's PC past a permanent breakpoint.  GDB
     normally steps over a breakpoint by removing it, stepping one
     instruction, and re-inserting the breakpoint.  However, permanent
     breakpoints are hardwired into the inferior, and can't be removed,
     so this strategy doesn't work.  Calling
     `gdbarch_skip_permanent_breakpoint' adjusts the processor's state
     so that execution will resume just after the breakpoint.  This
     function does the right thing even when the breakpoint is in the
     delay slot of a branch or jump.

`CORE_ADDR gdbarch_skip_prologue (GDBARCH, IP)'
     A function that returns the address of the "real" code beyond the
     function entry prologue found at IP.

`CORE_ADDR gdbarch_skip_trampoline_code (GDBARCH, FRAME, PC)'
     If the target machine has trampoline code that sits between
     callers and the functions being called, then define this function
     to return a new PC that is at the start of the real function.

`int gdbarch_sp_regnum (GDBARCH)'
     If the stack-pointer is kept in a register, then use this function
     to return the number (greater than or equal to zero) of that
     register, or -1 if there is no such register.

`int gdbarch_stab_reg_to_regnum (GDBARCH, STAB_REGNR)'
     Use this function to convert stab register STAB_REGNR into GDB
     regnum.  If not defined, no conversion will be done.

`SYMBOL_RELOADING_DEFAULT'
     The default value of the "symbol-reloading" variable.  (Never
     defined in current sources.)

`TARGET_CHAR_BIT'
     Number of bits in a char; defaults to 8.

`int gdbarch_char_signed (GDBARCH)'
     Non-zero if `char' is normally signed on this architecture; zero if
     it should be unsigned.

     The ISO C standard requires the compiler to treat `char' as
     equivalent to either `signed char' or `unsigned char'; any
     character in the standard execution set is supposed to be positive.
     Most compilers treat `char' as signed, but `char' is unsigned on
     the IBM S/390, RS6000, and PowerPC targets.

`int gdbarch_double_bit (GDBARCH)'
     Number of bits in a double float; defaults to
     `8 * TARGET_CHAR_BIT'.

`int gdbarch_float_bit (GDBARCH)'
     Number of bits in a float; defaults to `4 * TARGET_CHAR_BIT'.

`int gdbarch_int_bit (GDBARCH)'
     Number of bits in an integer; defaults to `4 * TARGET_CHAR_BIT'.

`int gdbarch_long_bit (GDBARCH)'
     Number of bits in a long integer; defaults to
     `4 * TARGET_CHAR_BIT'.

`int gdbarch_long_double_bit (GDBARCH)'
     Number of bits in a long double float; defaults to
     `2 * gdbarch_double_bit (GDBARCH)'.

`int gdbarch_long_long_bit (GDBARCH)'
     Number of bits in a long long integer; defaults to
     `2 * gdbarch_long_bit (GDBARCH)'.

`int gdbarch_ptr_bit (GDBARCH)'
     Number of bits in a pointer; defaults to
     `gdbarch_int_bit (GDBARCH)'.

`int gdbarch_short_bit (GDBARCH)'
     Number of bits in a short integer; defaults to
     `2 * TARGET_CHAR_BIT'.

`CORE_ADDR gdbarch_read_pc (GDBARCH, REGCACHE)'
`gdbarch_write_pc (GDBARCH, REGCACHE, VAL)'
`TARGET_READ_SP'
`TARGET_READ_FP'
     These change the behavior of `gdbarch_read_pc',
     `gdbarch_write_pc', and `read_sp'.  For most targets, these may be
     left undefined.  GDB will call the read and write register
     functions with the relevant `_REGNUM' argument.

     These macros and functions are useful when a target keeps one of
     these registers in a hard to get at place; for example, part in a
     segment register and part in an ordinary register.

     *Note gdbarch_unwind_sp::, which replaces `TARGET_READ_SP'.

`void gdbarch_virtual_frame_pointer (GDBARCH, PC, FRAME_REGNUM, FRAME_OFFSET)'
     Returns a `(register, offset)' pair representing the virtual frame
     pointer in use at the code address PC.  If virtual frame pointers
     are not used, a default definition simply returns
     `DEPRECATED_FP_REGNUM', with an offset of zero.

`TARGET_HAS_HARDWARE_WATCHPOINTS'
     If non-zero, the target has support for hardware-assisted
     watchpoints.  *Note watchpoints: Algorithms, for more details and
     other related macros.

`int gdbarch_print_insn (GDBARCH, VMA, INFO)'
     This is the function used by GDB to print an assembly instruction.
     It prints the instruction at address VMA in debugged memory and
     returns the length of the instruction, in bytes.  If a target
     doesn't define its own printing routine, it defaults to an
     accessor function for the global pointer
     `deprecated_tm_print_insn'.  This usually points to a function in
     the `opcodes' library (*note Opcodes: Support Libraries.).  INFO
     is a structure (of type `disassemble_info') defined in
     `include/dis-asm.h' used to pass information to the instruction
     decoding routine.

`frame_id gdbarch_unwind_dummy_id (GDBARCH, FRAME)'
     Given FRAME return a `struct frame_id' that uniquely identifies an
     inferior function call's dummy frame.  The value returned must
     match the dummy frame stack value previously saved using
     `SAVE_DUMMY_FRAME_TOS'.  *Note SAVE_DUMMY_FRAME_TOS::.

`DEPRECATED_USE_STRUCT_CONVENTION (GCC_P, TYPE)'
     If defined, this must be an expression that is nonzero if a value
     of the given TYPE being returned from a function must have space
     allocated for it on the stack.  GCC_P is true if the function
     being considered is known to have been compiled by GCC; this is
     helpful for systems where GCC is known to use different calling
     convention than other compilers.

     This method has been deprecated in favour of `gdbarch_return_value'
     (*note gdbarch_return_value::).

`void gdbarch_value_to_register (GDBARCH, FRAME, TYPE, BUF)'
     Convert a value of type TYPE into the raw contents of a register.
     *Note Using Different Register and Memory Data Representations:
     Target Architecture Definition.


   Motorola M68K target conditionals.

`BPT_VECTOR'
     Define this to be the 4-bit location of the breakpoint trap
     vector.  If not defined, it will default to `0xf'.

`REMOTE_BPT_VECTOR'
     Defaults to `1'.

`const char *gdbarch_name_of_malloc (GDBARCH)'
     A string containing the name of the function to call in order to
     allocate some memory in the inferior. The default value is
     "malloc".


\x1f
File: gdbint.info,  Node: Adding a New Target,  Prev: Target Conditionals,  Up: Target Architecture Definition

9.12 Adding a New Target
========================

The following files add a target to GDB:

`gdb/config/ARCH/TTT.mt'
     Contains a Makefile fragment specific to this target.  Specifies
     what object files are needed for target TTT, by defining
     `TDEPFILES=...' and `TDEPLIBS=...'.  Also specifies the header
     file which describes TTT, by defining `TM_FILE= tm-TTT.h'.

     You can also define `TM_CFLAGS', `TM_CLIBS', `TM_CDEPS', but these
     are now deprecated, replaced by autoconf, and may go away in
     future versions of GDB.

`gdb/TTT-tdep.c'
     Contains any miscellaneous code required for this target machine.
     On some machines it doesn't exist at all.  Sometimes the macros in
     `tm-TTT.h' become very complicated, so they are implemented as
     functions here instead, and the macro is simply defined to call the
     function.  This is vastly preferable, since it is easier to
     understand and debug.

`gdb/ARCH-tdep.c'
`gdb/ARCH-tdep.h'
     This often exists to describe the basic layout of the target
     machine's processor chip (registers, stack, etc.).  If used, it is
     included by `TTT-tdep.h'.  It can be shared among many targets
     that use the same processor.

`gdb/config/ARCH/tm-TTT.h'
     (`tm.h' is a link to this file, created by `configure').  Contains
     macro definitions about the target machine's registers, stack frame
     format and instructions.

     New targets do not need this file and should not create it.

`gdb/config/ARCH/tm-ARCH.h'
     This often exists to describe the basic layout of the target
     machine's processor chip (registers, stack, etc.).  If used, it is
     included by `tm-TTT.h'.  It can be shared among many targets that
     use the same processor.

     New targets do not need this file and should not create it.


   If you are adding a new operating system for an existing CPU chip,
add a `config/tm-OS.h' file that describes the operating system
facilities that are unusual (extra symbol table info; the breakpoint
instruction needed; etc.).  Then write a `ARCH/tm-OS.h' that just
`#include's `tm-ARCH.h' and `config/tm-OS.h'.

\x1f
File: gdbint.info,  Node: Target Descriptions,  Next: Target Vector Definition,  Prev: Target Architecture Definition,  Up: Top

10 Target Descriptions
**********************

The target architecture definition (*note Target Architecture
Definition::) contains GDB's hard-coded knowledge about an
architecture.  For some platforms, it is handy to have more flexible
knowledge about a specific instance of the architecture--for instance,
a processor or development board.  "Target descriptions" provide a
mechanism for the user to tell GDB more about what their target
supports, or for the target to tell GDB directly.

   For details on writing, automatically supplying, and manually
selecting target descriptions, see *Note Target Descriptions:
(gdb)Target Descriptions.  This section will cover some related topics
about the GDB internals.

* Menu:

* Target Descriptions Implementation::
* Adding Target Described Register Support::

\x1f
File: gdbint.info,  Node: Target Descriptions Implementation,  Next: Adding Target Described Register Support,  Up: Target Descriptions

10.1 Target Descriptions Implementation
=======================================

Before GDB connects to a new target, or runs a new program on an
existing target, it discards any existing target description and
reverts to a default gdbarch.  Then, after connecting, it looks for a
new target description by calling `target_find_description'.

   A description may come from a user specified file (XML), the remote
`qXfer:features:read' packet (also XML), or from any custom
`to_read_description' routine in the target vector.  For instance, the
remote target supports guessing whether a MIPS target is 32-bit or
64-bit based on the size of the `g' packet.

   If any target description is found, GDB creates a new gdbarch
incorporating the description by calling `gdbarch_update_p'.  Any
`<architecture>' element is handled first, to determine which
architecture's gdbarch initialization routine is called to create the
new architecture.  Then the initialization routine is called, and has a
chance to adjust the constructed architecture based on the contents of
the target description.  For instance, it can recognize any properties
set by a `to_read_description' routine.  Also see *Note Adding Target
Described Register Support::.

\x1f
File: gdbint.info,  Node: Adding Target Described Register Support,  Prev: Target Descriptions Implementation,  Up: Target Descriptions

10.2 Adding Target Described Register Support
=============================================

Target descriptions can report additional registers specific to an
instance of the target.  But it takes a little work in the architecture
specific routines to support this.

   A target description must either have no registers or a complete
set--this avoids complexity in trying to merge standard registers with
the target defined registers.  It is the architecture's responsibility
to validate that a description with registers has everything it needs.
To keep architecture code simple, the same mechanism is used to assign
fixed internal register numbers to standard registers.

   If `tdesc_has_registers' returns 1, the description contains
registers.  The architecture's `gdbarch_init' routine should:

   * Call `tdesc_data_alloc' to allocate storage, early, before
     searching for a matching gdbarch or allocating a new one.

   * Use `tdesc_find_feature' to locate standard features by name.

   * Use `tdesc_numbered_register' and `tdesc_numbered_register_choices'
     to locate the expected registers in the standard features.

   * Return `NULL' if a required feature is missing, or if any standard
     feature is missing expected registers.  This will produce a
     warning that the description was incomplete.

   * Free the allocated data before returning, unless
     `tdesc_use_registers' is called.

   * Call `set_gdbarch_num_regs' as usual, with a number higher than any
     fixed number passed to `tdesc_numbered_register'.

   * Call `tdesc_use_registers' after creating a new gdbarch, before
     returning it.


   After `tdesc_use_registers' has been called, the architecture's
`register_name', `register_type', and `register_reggroup_p' routines
will not be called; that information will be taken from the target
description.  `num_regs' may be increased to account for any additional
registers in the description.

   Pseudo-registers require some extra care:

   * Using `tdesc_numbered_register' allows the architecture to give
     constant register numbers to standard architectural registers, e.g.
     as an `enum' in `ARCH-tdep.h'.  But because pseudo-registers are
     always numbered above `num_regs', which may be increased by the
     description, constant numbers can not be used for pseudos.  They
     must be numbered relative to `num_regs' instead.

   * The description will not describe pseudo-registers, so the
     architecture must call `set_tdesc_pseudo_register_name',
     `set_tdesc_pseudo_register_type', and
     `set_tdesc_pseudo_register_reggroup_p' to supply routines
     describing pseudo registers.  These routines will be passed
     internal register numbers, so the same routines used for the
     gdbarch equivalents are usually suitable.


\x1f
File: gdbint.info,  Node: Target Vector Definition,  Next: Native Debugging,  Prev: Target Descriptions,  Up: Top

11 Target Vector Definition
***************************

The target vector defines the interface between GDB's abstract handling
of target systems, and the nitty-gritty code that actually exercises
control over a process or a serial port.  GDB includes some 30-40
different target vectors; however, each configuration of GDB includes
only a few of them.

* Menu:

* Managing Execution State::
* Existing Targets::

\x1f
File: gdbint.info,  Node: Managing Execution State,  Next: Existing Targets,  Up: Target Vector Definition

11.1 Managing Execution State
=============================

A target vector can be completely inactive (not pushed on the target
stack), active but not running (pushed, but not connected to a fully
manifested inferior), or completely active (pushed, with an accessible
inferior).  Most targets are only completely inactive or completely
active, but some support persistent connections to a target even when
the target has exited or not yet started.

   For example, connecting to the simulator using `target sim' does not
create a running program.  Neither registers nor memory are accessible
until `run'.  Similarly, after `kill', the program can not continue
executing.  But in both cases GDB remains connected to the simulator,
and target-specific commands are directed to the simulator.

   A target which only supports complete activation should push itself
onto the stack in its `to_open' routine (by calling `push_target'), and
unpush itself from the stack in its `to_mourn_inferior' routine (by
calling `unpush_target').

   A target which supports both partial and complete activation should
still call `push_target' in `to_open', but not call `unpush_target' in
`to_mourn_inferior'.  Instead, it should call either
`target_mark_running' or `target_mark_exited' in its `to_open',
depending on whether the target is fully active after connection.  It
should also call `target_mark_running' any time the inferior becomes
fully active (e.g. in `to_create_inferior' and `to_attach'), and
`target_mark_exited' when the inferior becomes inactive (in
`to_mourn_inferior').  The target should also make sure to call
`target_mourn_inferior' from its `to_kill', to return the target to
inactive state.

\x1f
File: gdbint.info,  Node: Existing Targets,  Prev: Managing Execution State,  Up: Target Vector Definition

11.2 Existing Targets
=====================

11.2.1 File Targets
-------------------

Both executables and core files have target vectors.

11.2.2 Standard Protocol and Remote Stubs
-----------------------------------------

GDB's file `remote.c' talks a serial protocol to code that runs in the
target system.  GDB provides several sample "stubs" that can be
integrated into target programs or operating systems for this purpose;
they are named `*-stub.c'.

   The GDB user's manual describes how to put such a stub into your
target code.  What follows is a discussion of integrating the SPARC
stub into a complicated operating system (rather than a simple
program), by Stu Grossman, the author of this stub.

   The trap handling code in the stub assumes the following upon entry
to `trap_low':

  1. %l1 and %l2 contain pc and npc respectively at the time of the
     trap;

  2. traps are disabled;

  3. you are in the correct trap window.

   As long as your trap handler can guarantee those conditions, then
there is no reason why you shouldn't be able to "share" traps with the
stub.  The stub has no requirement that it be jumped to directly from
the hardware trap vector.  That is why it calls `exceptionHandler()',
which is provided by the external environment.  For instance, this could
set up the hardware traps to actually execute code which calls the stub
first, and then transfers to its own trap handler.

   For the most point, there probably won't be much of an issue with
"sharing" traps, as the traps we use are usually not used by the kernel,
and often indicate unrecoverable error conditions.  Anyway, this is all
controlled by a table, and is trivial to modify.  The most important
trap for us is for `ta 1'.  Without that, we can't single step or do
breakpoints.  Everything else is unnecessary for the proper operation
of the debugger/stub.

   From reading the stub, it's probably not obvious how breakpoints
work.  They are simply done by deposit/examine operations from GDB.

11.2.3 ROM Monitor Interface
----------------------------

11.2.4 Custom Protocols
-----------------------

11.2.5 Transport Layer
----------------------

11.2.6 Builtin Simulator
------------------------

\x1f
File: gdbint.info,  Node: Native Debugging,  Next: Support Libraries,  Prev: Target Vector Definition,  Up: Top

12 Native Debugging
*******************

Several files control GDB's configuration for native support:

`gdb/config/ARCH/XYZ.mh'
     Specifies Makefile fragments needed by a _native_ configuration on
     machine XYZ.  In particular, this lists the required
     native-dependent object files, by defining `NATDEPFILES=...'.
     Also specifies the header file which describes native support on
     XYZ, by defining `NAT_FILE= nm-XYZ.h'.  You can also define
     `NAT_CFLAGS', `NAT_ADD_FILES', `NAT_CLIBS', `NAT_CDEPS', etc.; see
     `Makefile.in'.

     _Maintainer's note: The `.mh' suffix is because this file
     originally contained `Makefile' fragments for hosting GDB on
     machine XYZ.  While the file is no longer used for this purpose,
     the `.mh' suffix remains.  Perhaps someone will eventually rename
     these fragments so that they have a `.mn' suffix._

`gdb/config/ARCH/nm-XYZ.h'
     (`nm.h' is a link to this file, created by `configure').  Contains
     C macro definitions describing the native system environment, such
     as child process control and core file support.

`gdb/XYZ-nat.c'
     Contains any miscellaneous C code required for this native support
     of this machine.  On some machines it doesn't exist at all.

   There are some "generic" versions of routines that can be used by
various systems.  These can be customized in various ways by macros
defined in your `nm-XYZ.h' file.  If these routines work for the XYZ
host, you can just include the generic file's name (with `.o', not
`.c') in `NATDEPFILES'.

   Otherwise, if your machine needs custom support routines, you will
need to write routines that perform the same functions as the generic
file.  Put them into `XYZ-nat.c', and put `XYZ-nat.o' into
`NATDEPFILES'.

`inftarg.c'
     This contains the _target_ops vector_ that supports Unix child
     processes on systems which use ptrace and wait to control the
     child.

`procfs.c'
     This contains the _target_ops vector_ that supports Unix child
     processes on systems which use /proc to control the child.

`fork-child.c'
     This does the low-level grunge that uses Unix system calls to do a
     "fork and exec" to start up a child process.

`infptrace.c'
     This is the low level interface to inferior processes for systems
     using the Unix `ptrace' call in a vanilla way.

12.1 Native core file Support
=============================

`core-aout.c::fetch_core_registers()'
     Support for reading registers out of a core file.  This routine
     calls `register_addr()', see below.  Now that BFD is used to read
     core files, virtually all machines should use `core-aout.c', and
     should just provide `fetch_core_registers' in `XYZ-nat.c' (or
     `REGISTER_U_ADDR' in `nm-XYZ.h').

`core-aout.c::register_addr()'
     If your `nm-XYZ.h' file defines the macro `REGISTER_U_ADDR(addr,
     blockend, regno)', it should be defined to set `addr' to the
     offset within the `user' struct of GDB register number `regno'.
     `blockend' is the offset within the "upage" of `u.u_ar0'.  If
     `REGISTER_U_ADDR' is defined, `core-aout.c' will define the
     `register_addr()' function and use the macro in it.  If you do not
     define `REGISTER_U_ADDR', but you are using the standard
     `fetch_core_registers()', you will need to define your own version
     of `register_addr()', put it into your `XYZ-nat.c' file, and be
     sure `XYZ-nat.o' is in the `NATDEPFILES' list.  If you have your
     own `fetch_core_registers()', you may not need a separate
     `register_addr()'.  Many custom `fetch_core_registers()'
     implementations simply locate the registers themselves.

   When making GDB run native on a new operating system, to make it
possible to debug core files, you will need to either write specific
code for parsing your OS's core files, or customize `bfd/trad-core.c'.
First, use whatever `#include' files your machine uses to define the
struct of registers that is accessible (possibly in the u-area) in a
core file (rather than `machine/reg.h'), and an include file that
defines whatever header exists on a core file (e.g., the u-area or a
`struct core').  Then modify `trad_unix_core_file_p' to use these
values to set up the section information for the data segment, stack
segment, any other segments in the core file (perhaps shared library
contents or control information), "registers" segment, and if there are
two discontiguous sets of registers (e.g., integer and float), the
"reg2" segment.  This section information basically delimits areas in
the core file in a standard way, which the section-reading routines in
BFD know how to seek around in.

   Then back in GDB, you need a matching routine called
`fetch_core_registers'.  If you can use the generic one, it's in
`core-aout.c'; if not, it's in your `XYZ-nat.c' file.  It will be
passed a char pointer to the entire "registers" segment, its length,
and a zero; or a char pointer to the entire "regs2" segment, its
length, and a 2.  The routine should suck out the supplied register
values and install them into GDB's "registers" array.

   If your system uses `/proc' to control processes, and uses ELF
format core files, then you may be able to use the same routines for
reading the registers out of processes and out of core files.

12.2 ptrace
===========

12.3 /proc
==========

12.4 win32
==========

12.5 shared libraries
=====================

12.6 Native Conditionals
========================

When GDB is configured and compiled, various macros are defined or left
undefined, to control compilation when the host and target systems are
the same.  These macros should be defined (or left undefined) in
`nm-SYSTEM.h'.

`CHILD_PREPARE_TO_STORE'
     If the machine stores all registers at once in the child process,
     then define this to ensure that all values are correct.  This
     usually entails a read from the child.

     [Note that this is incorrectly defined in `xm-SYSTEM.h' files
     currently.]

`FETCH_INFERIOR_REGISTERS'
     Define this if the native-dependent code will provide its own
     routines `fetch_inferior_registers' and `store_inferior_registers'
     in `HOST-nat.c'.  If this symbol is _not_ defined, and
     `infptrace.c' is included in this configuration, the default
     routines in `infptrace.c' are used for these functions.

`int gdbarch_fp0_regnum (GDBARCH)'
     This functions normally returns the number of the first floating
     point register, if the machine has such registers.  As such, it
     would appear only in target-specific code.  However, `/proc'
     support uses this to decide whether floats are in use on this
     target.

`int gdbarch_get_longjmp_target (GDBARCH)'
     For most machines, this is a target-dependent parameter.  On the
     DECstation and the Iris, this is a native-dependent parameter,
     since `setjmp.h' is needed to define it.

     This function determines the target PC address that `longjmp' will
     jump to, assuming that we have just stopped at a longjmp
     breakpoint.  It takes a `CORE_ADDR *' as argument, and stores the
     target PC value through this pointer.  It examines the current
     state of the machine as needed.

`I386_USE_GENERIC_WATCHPOINTS'
     An x86-based machine can define this to use the generic x86
     watchpoint support; see *Note I386_USE_GENERIC_WATCHPOINTS:
     Algorithms.

`ONE_PROCESS_WRITETEXT'
     Define this to be able to, when a breakpoint insertion fails, warn
     the user that another process may be running with the same
     executable.

`PROC_NAME_FMT'
     Defines the format for the name of a `/proc' device.  Should be
     defined in `nm.h' _only_ in order to override the default
     definition in `procfs.c'.

`SOLIB_ADD (FILENAME, FROM_TTY, TARG, READSYMS)'
     Define this to expand into an expression that will cause the
     symbols in FILENAME to be added to GDB's symbol table. If READSYMS
     is zero symbols are not read but any necessary low level
     processing for FILENAME is still done.

`SOLIB_CREATE_INFERIOR_HOOK'
     Define this to expand into any shared-library-relocation code that
     you want to be run just after the child process has been forked.

`START_INFERIOR_TRAPS_EXPECTED'
     When starting an inferior, GDB normally expects to trap twice;
     once when the shell execs, and once when the program itself execs.
     If the actual number of traps is something other than 2, then
     define this macro to expand into the number expected.


\x1f
File: gdbint.info,  Node: Support Libraries,  Next: Coding,  Prev: Native Debugging,  Up: Top

13 Support Libraries
********************

13.1 BFD
========

BFD provides support for GDB in several ways:

_identifying executable and core files_
     BFD will identify a variety of file types, including a.out, coff,
     and several variants thereof, as well as several kinds of core
     files.

_access to sections of files_
     BFD parses the file headers to determine the names, virtual
     addresses, sizes, and file locations of all the various named
     sections in files (such as the text section or the data section).
     GDB simply calls BFD to read or write section X at byte offset Y
     for length Z.

_specialized core file support_
     BFD provides routines to determine the failing command name stored
     in a core file, the signal with which the program failed, and
     whether a core file matches (i.e. could be a core dump of) a
     particular executable file.

_locating the symbol information_
     GDB uses an internal interface of BFD to determine where to find
     the symbol information in an executable file or symbol-file.  GDB
     itself handles the reading of symbols, since BFD does not
     "understand" debug symbols, but GDB uses BFD's cached information
     to find the symbols, string table, etc.

13.2 opcodes
============

The opcodes library provides GDB's disassembler.  (It's a separate
library because it's also used in binutils, for `objdump').

13.3 readline
=============

The `readline' library provides a set of functions for use by
applications that allow users to edit command lines as they are typed
in.

13.4 libiberty
==============

The `libiberty' library provides a set of functions and features that
integrate and improve on functionality found in modern operating
systems.  Broadly speaking, such features can be divided into three
groups: supplemental functions (functions that may be missing in some
environments and operating systems), replacement functions (providing a
uniform and easier to use interface for commonly used standard
functions), and extensions (which provide additional functionality
beyond standard functions).

   GDB uses various features provided by the `libiberty' library, for
instance the C++ demangler, the IEEE floating format support functions,
the input options parser `getopt', the `obstack' extension, and other
functions.

13.4.1 `obstacks' in GDB
------------------------

The obstack mechanism provides a convenient way to allocate and free
chunks of memory.  Each obstack is a pool of memory that is managed
like a stack.  Objects (of any nature, size and alignment) are
allocated and freed in a LIFO fashion on an obstack (see `libiberty''s
documentation for a more detailed explanation of `obstacks').

   The most noticeable use of the `obstacks' in GDB is in object files.
There is an obstack associated with each internal representation of an
object file.  Lots of things get allocated on these `obstacks':
dictionary entries, blocks, blockvectors, symbols, minimal symbols,
types, vectors of fundamental types, class fields of types, object
files section lists, object files section offset lists, line tables,
symbol tables, partial symbol tables, string tables, symbol table
private data, macros tables, debug information sections and entries,
import and export lists (som), unwind information (hppa), dwarf2
location expressions data.  Plus various strings such as directory
names strings, debug format strings, names of types.

   An essential and convenient property of all data on `obstacks' is
that memory for it gets allocated (with `obstack_alloc') at various
times during a debugging session, but it is released all at once using
the `obstack_free' function.  The `obstack_free' function takes a
pointer to where in the stack it must start the deletion from (much
like the cleanup chains have a pointer to where to start the cleanups).
Because of the stack like structure of the `obstacks', this allows to
free only a top portion of the obstack.  There are a few instances in
GDB where such thing happens.  Calls to `obstack_free' are done after
some local data is allocated to the obstack.  Only the local data is
deleted from the obstack.  Of course this assumes that nothing between
the `obstack_alloc' and the `obstack_free' allocates anything else on
the same obstack.  For this reason it is best and safest to use
temporary `obstacks'.

   Releasing the whole obstack is also not safe per se.  It is safe only
under the condition that we know the `obstacks' memory is no longer
needed.  In GDB we get rid of the `obstacks' only when we get rid of
the whole objfile(s), for instance upon reading a new symbol file.

13.5 gnu-regex
==============

Regex conditionals.

`C_ALLOCA'

`NFAILURES'

`RE_NREGS'

`SIGN_EXTEND_CHAR'

`SWITCH_ENUM_BUG'

`SYNTAX_TABLE'

`Sword'

`sparc'

13.6 Array Containers
=====================

Often it is necessary to manipulate a dynamic array of a set of
objects.  C forces some bookkeeping on this, which can get cumbersome
and repetitive.  The `vec.h' file contains macros for defining and
using a typesafe vector type.  The functions defined will be inlined
when compiling, and so the abstraction cost should be zero.  Domain
checks are added to detect programming errors.

   An example use would be an array of symbols or section information.
The array can be grown as symbols are read in (or preallocated), and
the accessor macros provided keep care of all the necessary
bookkeeping.  Because the arrays are type safe, there is no danger of
accidentally mixing up the contents.  Think of these as C++ templates,
but implemented in C.

   Because of the different behavior of structure objects, scalar
objects and of pointers, there are three flavors of vector, one for
each of these variants.  Both the structure object and pointer variants
pass pointers to objects around -- in the former case the pointers are
stored into the vector and in the latter case the pointers are
dereferenced and the objects copied into the vector.  The scalar object
variant is suitable for `int'-like objects, and the vector elements are
returned by value.

   There are both `index' and `iterate' accessors.  The iterator
returns a boolean iteration condition and updates the iteration
variable passed by reference.  Because the iterator will be inlined,
the address-of can be optimized away.

   The vectors are implemented using the trailing array idiom, thus they
are not resizeable without changing the address of the vector object
itself.  This means you cannot have variables or fields of vector type
-- always use a pointer to a vector.  The one exception is the final
field of a structure, which could be a vector type.  You will have to
use the `embedded_size' & `embedded_init' calls to create such objects,
and they will probably not be resizeable (so don't use the "safe"
allocation variants).  The trailing array idiom is used (rather than a
pointer to an array of data), because, if we allow `NULL' to also
represent an empty vector, empty vectors occupy minimal space in the
structure containing them.

   Each operation that increases the number of active elements is
available in "quick" and "safe" variants.  The former presumes that
there is sufficient allocated space for the operation to succeed (it
dies if there is not).  The latter will reallocate the vector, if
needed.  Reallocation causes an exponential increase in vector size.
If you know you will be adding N elements, it would be more efficient
to use the reserve operation before adding the elements with the
"quick" operation.  This will ensure there are at least as many
elements as you ask for, it will exponentially increase if there are
too few spare slots.  If you want reserve a specific number of slots,
but do not want the exponential increase (for instance, you know this
is the last allocation), use a negative number for reservation.  You
can also create a vector of a specific size from the get go.

   You should prefer the push and pop operations, as they append and
remove from the end of the vector. If you need to remove several items
in one go, use the truncate operation.  The insert and remove
operations allow you to change elements in the middle of the vector.
There are two remove operations, one which preserves the element
ordering `ordered_remove', and one which does not `unordered_remove'.
The latter function copies the end element into the removed slot,
rather than invoke a memmove operation.  The `lower_bound' function
will determine where to place an item in the array using insert that
will maintain sorted order.

   If you need to directly manipulate a vector, then the `address'
accessor will return the address of the start of the vector.  Also the
`space' predicate will tell you whether there is spare capacity in the
vector.  You will not normally need to use these two functions.

   Vector types are defined using a `DEF_VEC_{O,P,I}(TYPENAME)' macro.
Variables of vector type are declared using a `VEC(TYPENAME)' macro.
The characters `O', `P' and `I' indicate whether TYPENAME is an object
(`O'), pointer (`P') or integral (`I') type.  Be careful to pick the
correct one, as you'll get an awkward and inefficient API if you use
the wrong one.  There is a check, which results in a compile-time
warning, for the `P' and `I' versions, but there is no check for the
`O' versions, as that is not possible in plain C.

   An example of their use would be,

     DEF_VEC_P(tree);   // non-managed tree vector.

     struct my_struct {
       VEC(tree) *v;      // A (pointer to) a vector of tree pointers.
     };

     struct my_struct *s;

     if (VEC_length(tree, s->v)) { we have some contents }
     VEC_safe_push(tree, s->v, decl); // append some decl onto the end
     for (ix = 0; VEC_iterate(tree, s->v, ix, elt); ix++)
       { do something with elt }

   The `vec.h' file provides details on how to invoke the various
accessors provided.  They are enumerated here:

`VEC_length'
     Return the number of items in the array,

`VEC_empty'
     Return true if the array has no elements.

`VEC_last'
`VEC_index'
     Return the last or arbitrary item in the array.

`VEC_iterate'
     Access an array element and indicate whether the array has been
     traversed.

`VEC_alloc'
`VEC_free'
     Create and destroy an array.

`VEC_embedded_size'
`VEC_embedded_init'
     Helpers for embedding an array as the final element of another
     struct.

`VEC_copy'
     Duplicate an array.

`VEC_space'
     Return the amount of free space in an array.

`VEC_reserve'
     Ensure a certain amount of free space.

`VEC_quick_push'
`VEC_safe_push'
     Append to an array, either assuming the space is available, or
     making sure that it is.

`VEC_pop'
     Remove the last item from an array.

`VEC_truncate'
     Remove several items from the end of an array.

`VEC_safe_grow'
     Add several items to the end of an array.

`VEC_replace'
     Overwrite an item in the array.

`VEC_quick_insert'
`VEC_safe_insert'
     Insert an item into the middle of the array.  Either the space must
     already exist, or the space is created.

`VEC_ordered_remove'
`VEC_unordered_remove'
     Remove an item from the array, preserving order or not.

`VEC_block_remove'
     Remove a set of items from the array.

`VEC_address'
     Provide the address of the first element.

`VEC_lower_bound'
     Binary search the array.


13.7 include
============

\x1f
File: gdbint.info,  Node: Coding,  Next: Porting GDB,  Prev: Support Libraries,  Up: Top

14 Coding
*********

This chapter covers topics that are lower-level than the major
algorithms of GDB.

14.1 Cleanups
=============

Cleanups are a structured way to deal with things that need to be done
later.

   When your code does something (e.g., `xmalloc' some memory, or
`open' a file) that needs to be undone later (e.g., `xfree' the memory
or `close' the file), it can make a cleanup.  The cleanup will be done
at some future point: when the command is finished and control returns
to the top level; when an error occurs and the stack is unwound; or
when your code decides it's time to explicitly perform cleanups.
Alternatively you can elect to discard the cleanups you created.

   Syntax:

`struct cleanup *OLD_CHAIN;'
     Declare a variable which will hold a cleanup chain handle.

`OLD_CHAIN = make_cleanup (FUNCTION, ARG);'
     Make a cleanup which will cause FUNCTION to be called with ARG (a
     `char *') later.  The result, OLD_CHAIN, is a handle that can
     later be passed to `do_cleanups' or `discard_cleanups'.  Unless
     you are going to call `do_cleanups' or `discard_cleanups', you can
     ignore the result from `make_cleanup'.

`do_cleanups (OLD_CHAIN);'
     Do all cleanups added to the chain since the corresponding
     `make_cleanup' call was made.

`discard_cleanups (OLD_CHAIN);'
     Same as `do_cleanups' except that it just removes the cleanups from
     the chain and does not call the specified functions.

   Cleanups are implemented as a chain.  The handle returned by
`make_cleanups' includes the cleanup passed to the call and any later
cleanups appended to the chain (but not yet discarded or performed).
E.g.:

     make_cleanup (a, 0);
     {
       struct cleanup *old = make_cleanup (b, 0);
       make_cleanup (c, 0)
       ...
       do_cleanups (old);
     }

will call `c()' and `b()' but will not call `a()'.  The cleanup that
calls `a()' will remain in the cleanup chain, and will be done later
unless otherwise discarded.

   Your function should explicitly do or discard the cleanups it
creates.  Failing to do this leads to non-deterministic behavior since
the caller will arbitrarily do or discard your functions cleanups.
This need leads to two common cleanup styles.

   The first style is try/finally.  Before it exits, your code-block
calls `do_cleanups' with the old cleanup chain and thus ensures that
your code-block's cleanups are always performed.  For instance, the
following code-segment avoids a memory leak problem (even when `error'
is called and a forced stack unwind occurs) by ensuring that the
`xfree' will always be called:

     struct cleanup *old = make_cleanup (null_cleanup, 0);
     data = xmalloc (sizeof blah);
     make_cleanup (xfree, data);
     ... blah blah ...
     do_cleanups (old);

   The second style is try/except.  Before it exits, your code-block
calls `discard_cleanups' with the old cleanup chain and thus ensures
that any created cleanups are not performed.  For instance, the
following code segment, ensures that the file will be closed but only
if there is an error:

     FILE *file = fopen ("afile", "r");
     struct cleanup *old = make_cleanup (close_file, file);
     ... blah blah ...
     discard_cleanups (old);
     return file;

   Some functions, e.g., `fputs_filtered()' or `error()', specify that
they "should not be called when cleanups are not in place".  This means
that any actions you need to reverse in the case of an error or
interruption must be on the cleanup chain before you call these
functions, since they might never return to your code (they `longjmp'
instead).

14.2 Per-architecture module data
=================================

The multi-arch framework includes a mechanism for adding module
specific per-architecture data-pointers to the `struct gdbarch'
architecture object.

   A module registers one or more per-architecture data-pointers using:

 -- Function: struct gdbarch_data *gdbarch_data_register_pre_init
          (gdbarch_data_pre_init_ftype *PRE_INIT)
     PRE_INIT is used to, on-demand, allocate an initial value for a
     per-architecture data-pointer using the architecture's obstack
     (passed in as a parameter).  Since PRE_INIT can be called during
     architecture creation, it is not parameterized with the
     architecture.  and must not call modules that use per-architecture
     data.

 -- Function: struct gdbarch_data *gdbarch_data_register_post_init
          (gdbarch_data_post_init_ftype *POST_INIT)
     POST_INIT is used to obtain an initial value for a
     per-architecture data-pointer _after_.  Since POST_INIT is always
     called after architecture creation, it both receives the fully
     initialized architecture and is free to call modules that use
     per-architecture data (care needs to be taken to ensure that those
     other modules do not try to call back to this module as that will
     create in cycles in the initialization call graph).

   These functions return a `struct gdbarch_data' that is used to
identify the per-architecture data-pointer added for that module.

   The per-architecture data-pointer is accessed using the function:

 -- Function: void *gdbarch_data (struct gdbarch *GDBARCH, struct
          gdbarch_data *DATA_HANDLE)
     Given the architecture ARCH and module data handle DATA_HANDLE
     (returned by `gdbarch_data_register_pre_init' or
     `gdbarch_data_register_post_init'), this function returns the
     current value of the per-architecture data-pointer.  If the data
     pointer is `NULL', it is first initialized by calling the
     corresponding PRE_INIT or POST_INIT method.

   The examples below assume the following definitions:

     struct nozel { int total; };
     static struct gdbarch_data *nozel_handle;

   A module can extend the architecture vector, adding additional
per-architecture data, using the PRE_INIT method.  The module's
per-architecture data is then initialized during architecture creation.

   In the below, the module's per-architecture _nozel_ is added.  An
architecture can specify its nozel by calling `set_gdbarch_nozel' from
`gdbarch_init'.

     static void *
     nozel_pre_init (struct obstack *obstack)
     {
       struct nozel *data = OBSTACK_ZALLOC (obstack, struct nozel);
       return data;
     }

     extern void
     set_gdbarch_nozel (struct gdbarch *gdbarch, int total)
     {
       struct nozel *data = gdbarch_data (gdbarch, nozel_handle);
       data->total = nozel;
     }

   A module can on-demand create architecture dependant data structures
using `post_init'.

   In the below, the nozel's total is computed on-demand by
`nozel_post_init' using information obtained from the architecture.

     static void *
     nozel_post_init (struct gdbarch *gdbarch)
     {
       struct nozel *data = GDBARCH_OBSTACK_ZALLOC (gdbarch, struct nozel);
       nozel->total = gdbarch... (gdbarch);
       return data;
     }

     extern int
     nozel_total (struct gdbarch *gdbarch)
     {
       struct nozel *data = gdbarch_data (gdbarch, nozel_handle);
       return data->total;
     }

14.3 Wrapping Output Lines
==========================

Output that goes through `printf_filtered' or `fputs_filtered' or
`fputs_demangled' needs only to have calls to `wrap_here' added in
places that would be good breaking points.  The utility routines will
take care of actually wrapping if the line width is exceeded.

   The argument to `wrap_here' is an indentation string which is
printed _only_ if the line breaks there.  This argument is saved away
and used later.  It must remain valid until the next call to
`wrap_here' or until a newline has been printed through the
`*_filtered' functions.  Don't pass in a local variable and then return!

   It is usually best to call `wrap_here' after printing a comma or
space.  If you call it before printing a space, make sure that your
indentation properly accounts for the leading space that will print if
the line wraps there.

   Any function or set of functions that produce filtered output must
finish by printing a newline, to flush the wrap buffer, before switching
to unfiltered (`printf') output.  Symbol reading routines that print
warnings are a good example.

14.4 GDB Coding Standards
=========================

GDB follows the GNU coding standards, as described in
`etc/standards.texi'.  This file is also available for anonymous FTP
from GNU archive sites.  GDB takes a strict interpretation of the
standard; in general, when the GNU standard recommends a practice but
does not require it, GDB requires it.

   GDB follows an additional set of coding standards specific to GDB,
as described in the following sections.

14.4.1 ISO C
------------

GDB assumes an ISO/IEC 9899:1990 (a.k.a. ISO C90) compliant compiler.

   GDB does not assume an ISO C or POSIX compliant C library.

14.4.2 Memory Management
------------------------

GDB does not use the functions `malloc', `realloc', `calloc', `free'
and `asprintf'.

   GDB uses the functions `xmalloc', `xrealloc' and `xcalloc' when
allocating memory.  Unlike `malloc' et.al.  these functions do not
return when the memory pool is empty.  Instead, they unwind the stack
using cleanups.  These functions return `NULL' when requested to
allocate a chunk of memory of size zero.

   _Pragmatics: By using these functions, the need to check every
memory allocation is removed.  These functions provide portable
behavior._

   GDB does not use the function `free'.

   GDB uses the function `xfree' to return memory to the memory pool.
Consistent with ISO-C, this function ignores a request to free a `NULL'
pointer.

   _Pragmatics: On some systems `free' fails when passed a `NULL'
pointer._

   GDB can use the non-portable function `alloca' for the allocation of
small temporary values (such as strings).

   _Pragmatics: This function is very non-portable.  Some systems
restrict the memory being allocated to no more than a few kilobytes._

   GDB uses the string function `xstrdup' and the print function
`xstrprintf'.

   _Pragmatics: `asprintf' and `strdup' can fail.  Print functions such
as `sprintf' are very prone to buffer overflow errors._

14.4.3 Compiler Warnings
------------------------

With few exceptions, developers should avoid the configuration option
`--disable-werror' when building GDB.  The exceptions are listed in the
file `gdb/MAINTAINERS'.  The default, when building with GCC, is
`--enable-werror'.

   This option causes GDB (when built using GCC) to be compiled with a
carefully selected list of compiler warning flags.  Any warnings from
those flags are treated as errors.

   The current list of warning flags includes:

`-Wall'
     Recommended GCC warnings.

`-Wdeclaration-after-statement'
     GCC 3.x (and later) and C99 allow declarations mixed with code,
     but GCC 2.x and C89 do not.

`-Wpointer-arith'

`-Wformat-nonliteral'
     Non-literal format strings, with a few exceptions, are bugs - they
     might contain unintended user-supplied format specifiers.  Since
     GDB uses the `format printf' attribute on all `printf' like
     functions this checks not just `printf' calls but also calls to
     functions such as `fprintf_unfiltered'.

`-Wno-pointer-sign'
     In version 4.0, GCC began warning about pointer argument passing or
     assignment even when the source and destination differed only in
     signedness.  However, most GDB code doesn't distinguish carefully
     between `char' and `unsigned char'.  In early 2006 the GDB
     developers decided correcting these warnings wasn't worth the time
     it would take.

`-Wno-unused-parameter'
     Due to the way that GDB is implemented many functions have unused
     parameters.  Consequently this warning is avoided.  The macro
     `ATTRIBUTE_UNUSED' is not used as it leads to false negatives --
     it is not an error to have `ATTRIBUTE_UNUSED' on a parameter that
     is being used.

`-Wno-unused'
`-Wno-switch'
`-Wno-char-subscripts'
     These are warnings which might be useful for GDB, but are
     currently too noisy to enable with `-Werror'.


14.4.4 Formatting
-----------------

The standard GNU recommendations for formatting must be followed
strictly.

   A function declaration should not have its name in column zero.  A
function definition should have its name in column zero.

     /* Declaration */
     static void foo (void);
     /* Definition */
     void
     foo (void)
     {
     }

   _Pragmatics: This simplifies scripting.  Function definitions can be
found using `^function-name'._

   There must be a space between a function or macro name and the
opening parenthesis of its argument list (except for macro definitions,
as required by C).  There must not be a space after an open
paren/bracket or before a close paren/bracket.

   While additional whitespace is generally helpful for reading, do not
use more than one blank line to separate blocks, and avoid adding
whitespace after the end of a program line (as of 1/99, some 600 lines
had whitespace after the semicolon).  Excess whitespace causes
difficulties for `diff' and `patch' utilities.

   Pointers are declared using the traditional K&R C style:

     void *foo;

and not:

     void * foo;
     void* foo;

14.4.5 Comments
---------------

The standard GNU requirements on comments must be followed strictly.

   Block comments must appear in the following form, with no `/*'- or
`*/'-only lines, and no leading `*':

     /* Wait for control to return from inferior to debugger.  If inferior
        gets a signal, we may decide to start it up again instead of
        returning.  That is why there is a loop in this function.  When
        this function actually returns it means the inferior should be left
        stopped and GDB should read more commands.  */

   (Note that this format is encouraged by Emacs; tabbing for a
multi-line comment works correctly, and `M-q' fills the block
consistently.)

   Put a blank line between the block comments preceding function or
variable definitions, and the definition itself.

   In general, put function-body comments on lines by themselves, rather
than trying to fit them into the 20 characters left at the end of a
line, since either the comment or the code will inevitably get longer
than will fit, and then somebody will have to move it anyhow.

14.4.6 C Usage
--------------

Code must not depend on the sizes of C data types, the format of the
host's floating point numbers, the alignment of anything, or the order
of evaluation of expressions.

   Use functions freely.  There are only a handful of compute-bound
areas in GDB that might be affected by the overhead of a function call,
mainly in symbol reading.  Most of GDB's performance is limited by the
target interface (whether serial line or system call).

   However, use functions with moderation.  A thousand one-line
functions are just as hard to understand as a single thousand-line
function.

   _Macros are bad, M'kay._ (But if you have to use a macro, make sure
that the macro arguments are protected with parentheses.)

   Declarations like `struct foo *' should be used in preference to
declarations like `typedef struct foo { ... } *foo_ptr'.

14.4.7 Function Prototypes
--------------------------

Prototypes must be used when both _declaring_ and _defining_ a
function.  Prototypes for GDB functions must include both the argument
type and name, with the name matching that used in the actual function
definition.

   All external functions should have a declaration in a header file
that callers include, except for `_initialize_*' functions, which must
be external so that `init.c' construction works, but shouldn't be
visible to random source files.

   Where a source file needs a forward declaration of a static function,
that declaration must appear in a block near the top of the source file.

14.4.8 Internal Error Recovery
------------------------------

During its execution, GDB can encounter two types of errors.  User
errors and internal errors.  User errors include not only a user
entering an incorrect command but also problems arising from corrupt
object files and system errors when interacting with the target.
Internal errors include situations where GDB has detected, at run time,
a corrupt or erroneous situation.

   When reporting an internal error, GDB uses `internal_error' and
`gdb_assert'.

   GDB must not call `abort' or `assert'.

   _Pragmatics: There is no `internal_warning' function.  Either the
code detected a user error, recovered from it and issued a `warning' or
the code failed to correctly recover from the user error and issued an
`internal_error'._

14.4.9 File Names
-----------------

Any file used when building the core of GDB must be in lower case. Any
file used when building the core of GDB must be 8.3 unique.  These
requirements apply to both source and generated files.

   _Pragmatics: The core of GDB must be buildable on many platforms
including DJGPP and MacOS/HFS.  Every time an unfriendly file is
introduced to the build process both `Makefile.in' and `configure.in'
need to be modified accordingly.  Compare the convoluted conversion
process needed to transform `COPYING' into `copying.c' with the
conversion needed to transform `version.in' into `version.c'._

   Any file non 8.3 compliant file (that is not used when building the
core of GDB) must be added to `gdb/config/djgpp/fnchange.lst'.

   _Pragmatics: This is clearly a compromise._

   When GDB has a local version of a system header file (ex `string.h')
the file name based on the POSIX header prefixed with `gdb_'
(`gdb_string.h').  These headers should be relatively independent: they
should use only macros defined by `configure', the compiler, or the
host; they should include only system headers; they should refer only
to system types.  They may be shared between multiple programs, e.g.
GDB and GDBSERVER.

   For other files `-' is used as the separator.

14.4.10 Include Files
---------------------

A `.c' file should include `defs.h' first.

   A `.c' file should directly include the `.h' file of every
declaration and/or definition it directly refers to.  It cannot rely on
indirect inclusion.

   A `.h' file should directly include the `.h' file of every
declaration and/or definition it directly refers to.  It cannot rely on
indirect inclusion.  Exception: The file `defs.h' does not need to be
directly included.

   An external declaration should only appear in one include file.

   An external declaration should never appear in a `.c' file.
Exception: a declaration for the `_initialize' function that pacifies
`-Wmissing-declaration'.

   A `typedef' definition should only appear in one include file.

   An opaque `struct' declaration can appear in multiple `.h' files.
Where possible, a `.h' file should use an opaque `struct' declaration
instead of an include.

   All `.h' files should be wrapped in:

     #ifndef INCLUDE_FILE_NAME_H
     #define INCLUDE_FILE_NAME_H
     header body
     #endif

14.4.11 Clean Design and Portable Implementation
------------------------------------------------

In addition to getting the syntax right, there's the little question of
semantics.  Some things are done in certain ways in GDB because long
experience has shown that the more obvious ways caused various kinds of
trouble.

   You can't assume the byte order of anything that comes from a target
(including VALUEs, object files, and instructions).  Such things must
be byte-swapped using `SWAP_TARGET_AND_HOST' in GDB, or one of the swap
routines defined in `bfd.h', such as `bfd_get_32'.

   You can't assume that you know what interface is being used to talk
to the target system.  All references to the target must go through the
current `target_ops' vector.

   You can't assume that the host and target machines are the same
machine (except in the "native" support modules).  In particular, you
can't assume that the target machine's header files will be available
on the host machine.  Target code must bring along its own header files
- written from scratch or explicitly donated by their owner, to avoid
copyright problems.

   Insertion of new `#ifdef''s will be frowned upon.  It's much better
to write the code portably than to conditionalize it for various
systems.

   New `#ifdef''s which test for specific compilers or manufacturers or
operating systems are unacceptable.  All `#ifdef''s should test for
features.  The information about which configurations contain which
features should be segregated into the configuration files.  Experience
has proven far too often that a feature unique to one particular system
often creeps into other systems; and that a conditional based on some
predefined macro for your current system will become worthless over
time, as new versions of your system come out that behave differently
with regard to this feature.

   Adding code that handles specific architectures, operating systems,
target interfaces, or hosts, is not acceptable in generic code.

   One particularly notorious area where system dependencies tend to
creep in is handling of file names.  The mainline GDB code assumes
Posix semantics of file names: absolute file names begin with a forward
slash `/', slashes are used to separate leading directories,
case-sensitive file names.  These assumptions are not necessarily true
on non-Posix systems such as MS-Windows.  To avoid system-dependent
code where you need to take apart or construct a file name, use the
following portable macros:

`HAVE_DOS_BASED_FILE_SYSTEM'
     This preprocessing symbol is defined to a non-zero value on hosts
     whose filesystems belong to the MS-DOS/MS-Windows family.  Use this
     symbol to write conditional code which should only be compiled for
     such hosts.

`IS_DIR_SEPARATOR (C)'
     Evaluates to a non-zero value if C is a directory separator
     character.  On Unix and GNU/Linux systems, only a slash `/' is
     such a character, but on Windows, both `/' and `\' will pass.

`IS_ABSOLUTE_PATH (FILE)'
     Evaluates to a non-zero value if FILE is an absolute file name.
     For Unix and GNU/Linux hosts, a name which begins with a slash `/'
     is absolute.  On DOS and Windows, `d:/foo' and `x:\bar' are also
     absolute file names.

`FILENAME_CMP (F1, F2)'
     Calls a function which compares file names F1 and F2 as
     appropriate for the underlying host filesystem.  For Posix systems,
     this simply calls `strcmp'; on case-insensitive filesystems it
     will call `strcasecmp' instead.

`DIRNAME_SEPARATOR'
     Evaluates to a character which separates directories in
     `PATH'-style lists, typically held in environment variables.  This
     character is `:' on Unix, `;' on DOS and Windows.

`SLASH_STRING'
     This evaluates to a constant string you should use to produce an
     absolute filename from leading directories and the file's basename.
     `SLASH_STRING' is `"/"' on most systems, but might be `"\\"' for
     some Windows-based ports.

   In addition to using these macros, be sure to use portable library
functions whenever possible.  For example, to extract a directory or a
basename part from a file name, use the `dirname' and `basename'
library functions (available in `libiberty' for platforms which don't
provide them), instead of searching for a slash with `strrchr'.

   Another way to generalize GDB along a particular interface is with an
attribute struct.  For example, GDB has been generalized to handle
multiple kinds of remote interfaces--not by `#ifdef's everywhere, but
by defining the `target_ops' structure and having a current target (as
well as a stack of targets below it, for memory references).  Whenever
something needs to be done that depends on which remote interface we are
using, a flag in the current target_ops structure is tested (e.g.,
`target_has_stack'), or a function is called through a pointer in the
current target_ops structure.  In this way, when a new remote interface
is added, only one module needs to be touched--the one that actually
implements the new remote interface.  Other examples of
attribute-structs are BFD access to multiple kinds of object file
formats, or GDB's access to multiple source languages.

   Please avoid duplicating code.  For example, in GDB 3.x all the code
interfacing between `ptrace' and the rest of GDB was duplicated in
`*-dep.c', and so changing something was very painful.  In GDB 4.x,
these have all been consolidated into `infptrace.c'.  `infptrace.c' can
deal with variations between systems the same way any system-independent
file would (hooks, `#if defined', etc.), and machines which are
radically different don't need to use `infptrace.c' at all.

   All debugging code must be controllable using the `set debug MODULE'
command.  Do not use `printf' to print trace messages.  Use
`fprintf_unfiltered(gdb_stdlog, ...'.  Do not use `#ifdef DEBUG'.

\x1f
File: gdbint.info,  Node: Porting GDB,  Next: Versions and Branches,  Prev: Coding,  Up: Top

15 Porting GDB
**************

Most of the work in making GDB compile on a new machine is in
specifying the configuration of the machine.  This is done in a
dizzying variety of header files and configuration scripts, which we
hope to make more sensible soon.  Let's say your new host is called an
XYZ (e.g.,  `sun4'), and its full three-part configuration name is
`ARCH-XVEND-XOS' (e.g., `sparc-sun-sunos4').  In particular:

   * In the top level directory, edit `config.sub' and add ARCH, XVEND,
     and XOS to the lists of supported architectures, vendors, and
     operating systems near the bottom of the file.  Also, add XYZ as
     an alias that maps to `ARCH-XVEND-XOS'.  You can test your changes
     by running

          ./config.sub XYZ

     and

          ./config.sub `ARCH-XVEND-XOS'

     which should both respond with `ARCH-XVEND-XOS' and no error
     messages.

     You need to port BFD, if that hasn't been done already.  Porting
     BFD is beyond the scope of this manual.

   * To configure GDB itself, edit `gdb/configure.host' to recognize
     your system and set `gdb_host' to XYZ, and (unless your desired
     target is already available) also edit `gdb/configure.tgt',
     setting `gdb_target' to something appropriate (for instance, XYZ).

     _Maintainer's note: Work in progress.  The file
     `gdb/configure.host' originally needed to be modified when either a
     new native target or a new host machine was being added to GDB.
     Recent changes have removed this requirement.  The file now only
     needs to be modified when adding a new native configuration.  This
     will likely changed again in the future._

   * Finally, you'll need to specify and define GDB's host-, native-,
     and target-dependent `.h' and `.c' files used for your
     configuration.

\x1f
File: gdbint.info,  Node: Versions and Branches,  Next: Start of New Year Procedure,  Prev: Porting GDB,  Up: Top

16 Versions and Branches
************************

16.1 Versions
=============

GDB's version is determined by the file `gdb/version.in' and takes one
of the following forms:

MAJOR.MINOR
MAJOR.MINOR.PATCHLEVEL
     an official release (e.g., 6.2 or 6.2.1)

MAJOR.MINOR.PATCHLEVEL.YYYYMMDD
     a snapshot taken at YYYY-MM-DD-gmt (e.g., 6.1.50.20020302,
     6.1.90.20020304, or 6.1.0.20020308)

MAJOR.MINOR.PATCHLEVEL.YYYYMMDD-cvs
     a CVS check out drawn on YYYY-MM-DD (e.g., 6.1.50.20020302-cvs,
     6.1.90.20020304-cvs, or 6.1.0.20020308-cvs)

MAJOR.MINOR.PATCHLEVEL.YYYYMMDD (VENDOR)
     a vendor specific release of GDB, that while based on
     MAJOR.MINOR.PATCHLEVEL.YYYYMMDD, may include additional changes

   GDB's mainline uses the MAJOR and MINOR version numbers from the
most recent release branch, with a PATCHLEVEL of 50.  At the time each
new release branch is created, the mainline's MAJOR and MINOR version
numbers are updated.

   GDB's release branch is similar.  When the branch is cut, the
PATCHLEVEL is changed from 50 to 90.  As draft releases are drawn from
the branch, the PATCHLEVEL is incremented.  Once the first release
(MAJOR.MINOR) has been made, the PATCHLEVEL is set to 0 and updates
have an incremented PATCHLEVEL.

   For snapshots, and CVS check outs, it is also possible to identify
the CVS origin:

MAJOR.MINOR.50.YYYYMMDD
     drawn from the HEAD of mainline CVS (e.g., 6.1.50.20020302)

MAJOR.MINOR.90.YYYYMMDD
MAJOR.MINOR.91.YYYYMMDD ...
     drawn from a release branch prior to the release (e.g.,
     6.1.90.20020304)

MAJOR.MINOR.0.YYYYMMDD
MAJOR.MINOR.1.YYYYMMDD ...
     drawn from a release branch after the release (e.g.,
     6.2.0.20020308)

   If the previous GDB version is 6.1 and the current version is 6.2,
then, substituting 6 for MAJOR and 1 or 2 for MINOR, here's an
illustration of a typical sequence:

          <HEAD>
             |
     6.1.50.20020302-cvs
             |
             +--------------------------.
             |                    <gdb_6_2-branch>
             |                          |
     6.2.50.20020303-cvs        6.1.90 (draft #1)
             |                          |
     6.2.50.20020304-cvs        6.1.90.20020304-cvs
             |                          |
     6.2.50.20020305-cvs        6.1.91 (draft #2)
             |                          |
     6.2.50.20020306-cvs        6.1.91.20020306-cvs
             |                          |
     6.2.50.20020307-cvs        6.2 (release)
             |                          |
     6.2.50.20020308-cvs        6.2.0.20020308-cvs
             |                          |
     6.2.50.20020309-cvs        6.2.1 (update)
             |                          |
     6.2.50.20020310-cvs         <branch closed>
             |
     6.2.50.20020311-cvs
             |
             +--------------------------.
             |                     <gdb_6_3-branch>
             |                          |
     6.3.50.20020312-cvs        6.2.90 (draft #1)
             |                          |

16.2 Release Branches
=====================

GDB draws a release series (6.2, 6.2.1, ...) from a single release
branch, and identifies that branch using the CVS branch tags:

     gdb_MAJOR_MINOR-YYYYMMDD-branchpoint
     gdb_MAJOR_MINOR-branch
     gdb_MAJOR_MINOR-YYYYMMDD-release

   _Pragmatics: To help identify the date at which a branch or release
is made, both the branchpoint and release tags include the date that
they are cut (YYYYMMDD) in the tag.  The branch tag, denoting the head
of the branch, does not need this._

16.3 Vendor Branches
====================

To avoid version conflicts, vendors are expected to modify the file
`gdb/version.in' to include a vendor unique alphabetic identifier (an
official GDB release never uses alphabetic characters in its version
identifier).  E.g., `6.2widgit2', or `6.2 (Widgit Inc Patch 2)'.

16.4 Experimental Branches
==========================

16.4.1 Guidelines
-----------------

GDB permits the creation of branches, cut from the CVS repository, for
experimental development.  Branches make it possible for developers to
share preliminary work, and maintainers to examine significant new
developments.

   The following are a set of guidelines for creating such branches:

_a branch has an owner_
     The owner can set further policy for a branch, but may not change
     the ground rules.  In particular, they can set a policy for
     commits (be it adding more reviewers or deciding who can commit).

_all commits are posted_
     All changes committed to a branch shall also be posted to the GDB
     patches mailing list <gdb-patches@sources.redhat.com>.  While
     commentary on such changes are encouraged, people should remember
     that the changes only apply to a branch.

_all commits are covered by an assignment_
     This ensures that all changes belong to the Free Software
     Foundation, and avoids the possibility that the branch may become
     contaminated.

_a branch is focused_
     A focused branch has a single objective or goal, and does not
     contain unnecessary or irrelevant changes.  Cleanups, where
     identified, being be pushed into the mainline as soon as possible.

_a branch tracks mainline_
     This keeps the level of divergence under control.  It also keeps
     the pressure on developers to push cleanups and other stuff into
     the mainline.

_a branch shall contain the entire GDB module_
     The GDB module `gdb' should be specified when creating a branch
     (branches of individual files should be avoided).  *Note Tags::.

_a branch shall be branded using `version.in'_
     The file `gdb/version.in' shall be modified so that it identifies
     the branch OWNER and branch NAME, e.g.,
     `6.2.50.20030303_owner_name' or `6.2 (Owner Name)'.


16.4.2 Tags
-----------

To simplify the identification of GDB branches, the following branch
tagging convention is strongly recommended:

`OWNER_NAME-YYYYMMDD-branchpoint'
`OWNER_NAME-YYYYMMDD-branch'
     The branch point and corresponding branch tag.  YYYYMMDD is the
     date that the branch was created.  A branch is created using the
     sequence:
          cvs rtag OWNER_NAME-YYYYMMDD-branchpoint gdb
          cvs rtag -b -r OWNER_NAME-YYYYMMDD-branchpoint \
             OWNER_NAME-YYYYMMDD-branch gdb

`OWNER_NAME-YYYYMMDD-mergepoint'
     The tagged point, on the mainline, that was used when merging the
     branch on YYYYMMDD.  To merge in all changes since the branch was
     cut, use a command sequence like:
          cvs rtag OWNER_NAME-YYYYMMDD-mergepoint gdb
          cvs update \
             -jOWNER_NAME-YYYYMMDD-branchpoint
             -jOWNER_NAME-YYYYMMDD-mergepoint
     Similar sequences can be used to just merge in changes since the
     last merge.


For further information on CVS, see Concurrent Versions System
(http://www.gnu.org/software/cvs/).

\x1f
File: gdbint.info,  Node: Start of New Year Procedure,  Next: Releasing GDB,  Prev: Versions and Branches,  Up: Top

17 Start of New Year Procedure
******************************

At the start of each new year, the following actions should be
performed:

   * Rotate the ChangeLog file

     The current `ChangeLog' file should be renamed into
     `ChangeLog-YYYY' where YYYY is the year that has just passed.  A
     new `ChangeLog' file should be created, and its contents should
     contain a reference to the previous ChangeLog.  The following
     should also be preserved at the end of the new ChangeLog, in order
     to provide the appropriate settings when editing this file with
     Emacs:
          Local Variables:
          mode: change-log
          left-margin: 8
          fill-column: 74
          version-control: never
          End:

   * Add an entry for the newly created ChangeLog file
     (`ChangeLog-YYYY') in `gdb/config/djgpp/fnchange.lst'.

   * Update the copyright year in the startup message

     Update the copyright year in file `top.c', function
     `print_gdb_version'.

   * Add the new year in the copyright notices of all source and
     documentation files.  This can be done semi-automatically by
     running the `copyright.sh' script.  This script requires Emacs 22
     or later to be installed.


\x1f
File: gdbint.info,  Node: Releasing GDB,  Next: Testsuite,  Prev: Start of New Year Procedure,  Up: Top

18 Releasing GDB
****************

18.1 Branch Commit Policy
=========================

The branch commit policy is pretty slack.  GDB releases 5.0, 5.1 and
5.2 all used the below:

   * The `gdb/MAINTAINERS' file still holds.

   * Don't fix something on the branch unless/until it is also fixed in
     the trunk.  If this isn't possible, mentioning it in the
     `gdb/PROBLEMS' file is better than committing a hack.

   * When considering a patch for the branch, suggested criteria
     include: Does it fix a build?  Does it fix the sequence `break
     main; run' when debugging a static binary?

   * The further a change is from the core of GDB, the less likely the
     change will worry anyone (e.g., target specific code).

   * Only post a proposal to change the core of GDB after you've sent
     individual bribes to all the people listed in the `MAINTAINERS'
     file ;-)

   _Pragmatics: Provided updates are restricted to non-core
functionality there is little chance that a broken change will be fatal.
This means that changes such as adding a new architectures or (within
reason) support for a new host are considered acceptable._

18.2 Obsoleting code
====================

Before anything else, poke the other developers (and around the source
code) to see if there is anything that can be removed from GDB (an old
target, an unused file).

   Obsolete code is identified by adding an `OBSOLETE' prefix to every
line.  Doing this means that it is easy to identify something that has
been obsoleted when greping through the sources.

   The process is done in stages -- this is mainly to ensure that the
wider GDB community has a reasonable opportunity to respond.  Remember,
everything on the Internet takes a week.

  1. Post the proposal on the GDB mailing list <gdb@sources.redhat.com>
     Creating a bug report to track the task's state, is also highly
     recommended.

  2. Wait a week or so.

  3. Post the proposal on the GDB Announcement mailing list
     <gdb-announce@sources.redhat.com>.

  4. Wait a week or so.

  5. Go through and edit all relevant files and lines so that they are
     prefixed with the word `OBSOLETE'.

  6. Wait until the next GDB version, containing this obsolete code,
     has been released.

  7. Remove the obsolete code.

_Maintainer note: While removing old code is regrettable it is
hopefully better for GDB's long term development.  Firstly it helps the
developers by removing code that is either no longer relevant or simply
wrong.  Secondly since it removes any history associated with the file
(effectively clearing the slate) the developer has a much freer hand
when it comes to fixing broken files._

18.3 Before the Branch
======================

The most important objective at this stage is to find and fix simple
changes that become a pain to track once the branch is created.  For
instance, configuration problems that stop GDB from even building.  If
you can't get the problem fixed, document it in the `gdb/PROBLEMS' file.

Prompt for `gdb/NEWS'
---------------------

People always forget.  Send a post reminding them but also if you know
something interesting happened add it yourself.  The `schedule' script
will mention this in its e-mail.

Review `gdb/README'
-------------------

Grab one of the nightly snapshots and then walk through the
`gdb/README' looking for anything that can be improved.  The `schedule'
script will mention this in its e-mail.

Refresh any imported files.
---------------------------

A number of files are taken from external repositories.  They include:

   * `texinfo/texinfo.tex'

   * `config.guess' et. al. (see the top-level `MAINTAINERS' file)

   * `etc/standards.texi', `etc/make-stds.texi'

Check the ARI
-------------

A.R.I. is an `awk' script (Awk Regression Index ;-) that checks for a
number of errors and coding conventions.  The checks include things
like using `malloc' instead of `xmalloc' and file naming problems.
There shouldn't be any regressions.

18.3.1 Review the bug data base
-------------------------------

Close anything obviously fixed.

18.3.2 Check all cross targets build
------------------------------------

The targets are listed in `gdb/MAINTAINERS'.

18.4 Cut the Branch
===================

Create the branch
-----------------

     $  u=5.1
     $  v=5.2
     $  V=`echo $v | sed 's/\./_/g'`
     $  D=`date -u +%Y-%m-%d`
     $  echo $u $V $D
     5.1 5_2 2002-03-03
     $  echo cvs -f -d :ext:sources.redhat.com:/cvs/src rtag \
     -D $D-gmt gdb_$V-$D-branchpoint insight
     cvs -f -d :ext:sources.redhat.com:/cvs/src rtag
     -D 2002-03-03-gmt gdb_5_2-2002-03-03-branchpoint insight
     $  ^echo ^^
     ...
     $  echo cvs -f -d :ext:sources.redhat.com:/cvs/src rtag \
     -b -r gdb_$V-$D-branchpoint gdb_$V-branch insight
     cvs -f -d :ext:sources.redhat.com:/cvs/src rtag \
     -b -r gdb_5_2-2002-03-03-branchpoint gdb_5_2-branch insight
     $  ^echo ^^
     ...
     $

   * By using `-D YYYY-MM-DD-gmt', the branch is forced to an exact
     date/time.

   * The trunk is first tagged so that the branch point can easily be
     found.

   * Insight, which includes GDB, is tagged at the same time.

   * `version.in' gets bumped to avoid version number conflicts.

   * The reading of `.cvsrc' is disabled using `-f'.

Update `version.in'
-------------------

     $  u=5.1
     $  v=5.2
     $  V=`echo $v | sed 's/\./_/g'`
     $  echo $u $v$V
     5.1 5_2
     $  cd /tmp
     $  echo cvs -f -d :ext:sources.redhat.com:/cvs/src co \
     -r gdb_$V-branch src/gdb/version.in
     cvs -f -d :ext:sources.redhat.com:/cvs/src co
      -r gdb_5_2-branch src/gdb/version.in
     $  ^echo ^^
     U src/gdb/version.in
     $  cd src/gdb
     $  echo $u.90-0000-00-00-cvs > version.in
     $  cat version.in
     5.1.90-0000-00-00-cvs
     $  cvs -f commit version.in

   * `0000-00-00' is used as a date to pump prime the version.in update
     mechanism.

   * `.90' and the previous branch version are used as fairly arbitrary
     initial branch version number.

Update the web and news pages
-----------------------------

Something?

Tweak cron to track the new branch
----------------------------------

The file `gdbadmin/cron/crontab' contains gdbadmin's cron table.  This
file needs to be updated so that:

   * A daily timestamp is added to the file `version.in'.

   * The new branch is included in the snapshot process.

See the file `gdbadmin/cron/README' for how to install the updated cron
table.

   The file `gdbadmin/ss/README' should also be reviewed to reflect any
changes.  That file is copied to both the branch/ and current/ snapshot
directories.

Update the NEWS and README files
--------------------------------

The `NEWS' file needs to be updated so that on the branch it refers to
_changes in the current release_ while on the trunk it also refers to
_changes since the current release_.

   The `README' file needs to be updated so that it refers to the
current release.

Post the branch info
--------------------

Send an announcement to the mailing lists:

   * GDB Announcement mailing list <gdb-announce@sources.redhat.com>

   * GDB Discussion mailing list <gdb@sources.redhat.com> and GDB
     Testers mailing list <gdb-testers@sources.redhat.com>

   _Pragmatics: The branch creation is sent to the announce list to
ensure that people people not subscribed to the higher volume discussion
list are alerted._

   The announcement should include:

   * The branch tag.

   * How to check out the branch using CVS.

   * The date/number of weeks until the release.

   * The branch commit policy still holds.

18.5 Stabilize the branch
=========================

Something goes here.

18.6 Create a Release
=====================

The process of creating and then making available a release is broken
down into a number of stages.  The first part addresses the technical
process of creating a releasable tar ball.  The later stages address the
process of releasing that tar ball.

   When making a release candidate just the first section is needed.

18.6.1 Create a release candidate
---------------------------------

The objective at this stage is to create a set of tar balls that can be
made available as a formal release (or as a less formal release
candidate).

Freeze the branch
.................

Send out an e-mail notifying everyone that the branch is frozen to
<gdb-patches@sources.redhat.com>.

Establish a few defaults.
.........................

     $  b=gdb_5_2-branch
     $  v=5.2
     $  t=/sourceware/snapshot-tmp/gdbadmin-tmp
     $  echo $t/$b/$v
     /sourceware/snapshot-tmp/gdbadmin-tmp/gdb_5_2-branch/5.2
     $  mkdir -p $t/$b/$v
     $  cd $t/$b/$v
     $  pwd
     /sourceware/snapshot-tmp/gdbadmin-tmp/gdb_5_2-branch/5.2
     $  which autoconf
     /home/gdbadmin/bin/autoconf
     $

Notes:

   * Check the `autoconf' version carefully.  You want to be using the
     version taken from the `binutils' snapshot directory, which can be
     found at `ftp://sources.redhat.com/pub/binutils/'. It is very
     unlikely that a system installed version of `autoconf' (e.g.,
     `/usr/bin/autoconf') is correct.

Check out the relevant modules:
...............................

     $  for m in gdb insight
     do
     ( mkdir -p $m && cd $m && cvs -q -f -d /cvs/src co -P -r $b $m )
     done
     $

Note:

   * The reading of `.cvsrc' is disabled (`-f') so that there isn't any
     confusion between what is written here and what your local `cvs'
     really does.

Update relevant files.
......................

`gdb/NEWS'
     Major releases get their comments added as part of the mainline.
     Minor releases should probably mention any significant bugs that
     were fixed.

     Don't forget to include the `ChangeLog' entry.

          $  emacs gdb/src/gdb/NEWS
          ...
          c-x 4 a
          ...
          c-x c-s c-x c-c
          $  cp gdb/src/gdb/NEWS insight/src/gdb/NEWS
          $  cp gdb/src/gdb/ChangeLog insight/src/gdb/ChangeLog

`gdb/README'
     You'll need to update:

        * The version.

        * The update date.

        * Who did it.

          $  emacs gdb/src/gdb/README
          ...
          c-x 4 a
          ...
          c-x c-s c-x c-c
          $  cp gdb/src/gdb/README insight/src/gdb/README
          $  cp gdb/src/gdb/ChangeLog insight/src/gdb/ChangeLog

     _Maintainer note: Hopefully the `README' file was reviewed before
     the initial branch was cut so just a simple substitute is needed
     to get it updated._

     _Maintainer note: Other projects generate `README' and `INSTALL'
     from the core documentation.  This might be worth pursuing._

`gdb/version.in'
          $  echo $v > gdb/src/gdb/version.in
          $  cat gdb/src/gdb/version.in
          5.2
          $  emacs gdb/src/gdb/version.in
          ...
          c-x 4 a
          ... Bump to version ...
          c-x c-s c-x c-c
          $  cp gdb/src/gdb/version.in insight/src/gdb/version.in
          $  cp gdb/src/gdb/ChangeLog insight/src/gdb/ChangeLog


Do the dirty work
.................

This is identical to the process used to create the daily snapshot.

     $  for m in gdb insight
     do
     ( cd $m/src && gmake -f src-release $m.tar )
     done

   If the top level source directory does not have `src-release' (GDB
version 5.3.1 or earlier), try these commands instead:

     $  for m in gdb insight
     do
     ( cd $m/src && gmake -f Makefile.in $m.tar )
     done

Check the source files
......................

You're looking for files that have mysteriously disappeared.
`distclean' has the habit of deleting files it shouldn't.  Watch out
for the `version.in' update `cronjob'.

     $  ( cd gdb/src && cvs -f -q -n update )
     M djunpack.bat
     ? gdb-5.1.91.tar
     ? proto-toplev
     ... lots of generated files ...
     M gdb/ChangeLog
     M gdb/NEWS
     M gdb/README
     M gdb/version.in
     ... lots of generated files ...
     $

_Don't worry about the `gdb.info-??' or `gdb/p-exp.tab.c'.  They were
generated (and yes `gdb.info-1' was also generated only something
strange with CVS means that they didn't get suppressed).  Fixing it
would be nice though._

Create compressed versions of the release
.........................................

     $  cp */src/*.tar .
     $  cp */src/*.bz2 .
     $  ls -F
     gdb/ gdb-5.2.tar insight/ insight-5.2.tar
     $  for m in gdb insight
     do
     bzip2 -v -9 -c $m-$v.tar > $m-$v.tar.bz2
     gzip -v -9 -c $m-$v.tar > $m-$v.tar.gz
     done
     $

Note:

   * A pipe such as `bunzip2 < xxx.bz2 | gzip -9 > xxx.gz' is not since,
     in that mode, `gzip' does not know the name of the file and, hence,
     can not include it in the compressed file.  This is also why the
     release process runs `tar' and `bzip2' as separate passes.

18.6.2 Sanity check the tar ball
--------------------------------

Pick a popular machine (Solaris/PPC?) and try the build on that.

     $  bunzip2 < gdb-5.2.tar.bz2 | tar xpf -
     $  cd gdb-5.2
     $  ./configure
     $  make
     ...
     $  ./gdb/gdb ./gdb/gdb
     GNU gdb 5.2
     ...
     (gdb)  b main
     Breakpoint 1 at 0x80732bc: file main.c, line 734.
     (gdb)  run
     Starting program: /tmp/gdb-5.2/gdb/gdb

     Breakpoint 1, main (argc=1, argv=0xbffff8b4) at main.c:734
     734       catch_errors (captured_main, &args, "", RETURN_MASK_ALL);
     (gdb)  print args
     $1 = {argc = 136426532, argv = 0x821b7f0}
     (gdb)

18.6.3 Make a release candidate available
-----------------------------------------

If this is a release candidate then the only remaining steps are:

  1. Commit `version.in' and `ChangeLog'

  2. Tweak `version.in' (and `ChangeLog' to read L.M.N-0000-00-00-cvs
     so that the version update process can restart.

  3. Make the release candidate available in
     `ftp://sources.redhat.com/pub/gdb/snapshots/branch'

  4. Notify the relevant mailing lists ( <gdb@sources.redhat.com> and
     <gdb-testers@sources.redhat.com> that the candidate is available.

18.6.4 Make a formal release available
--------------------------------------

(And you thought all that was required was to post an e-mail.)

Install on sware
................

Copy the new files to both the release and the old release directory:

     $  cp *.bz2 *.gz ~ftp/pub/gdb/old-releases/
     $  cp *.bz2 *.gz ~ftp/pub/gdb/releases

Clean up the releases directory so that only the most recent releases
are available (e.g. keep 5.2 and 5.2.1 but remove 5.1):

     $  cd ~ftp/pub/gdb/releases
     $  rm ...

Update the file `README' and `.message' in the releases directory:

     $  vi README
     ...
     $  rm -f .message
     $  ln README .message

Update the web pages.
.....................

`htdocs/download/ANNOUNCEMENT'
     This file, which is posted as the official announcement, includes:
        * General announcement.

        * News.  If making an M.N.1 release, retain the news from
          earlier M.N release.

        * Errata.

`htdocs/index.html'
`htdocs/news/index.html'
`htdocs/download/index.html'
     These files include:
        * Announcement of the most recent release.

        * News entry (remember to update both the top level and the
          news directory).
     These pages also need to be regenerate using `index.sh'.

`download/onlinedocs/'
     You need to find the magic command that is used to generate the
     online docs from the `.tar.bz2'.  The best way is to look in the
     output from one of the nightly `cron' jobs and then just edit
     accordingly.  Something like:

          $  ~/ss/update-web-docs \
           ~ftp/pub/gdb/releases/gdb-5.2.tar.bz2 \
           $PWD/www \
           /www/sourceware/htdocs/gdb/download/onlinedocs \
           gdb

`download/ari/'
     Just like the online documentation.  Something like:

          $  /bin/sh ~/ss/update-web-ari \
           ~ftp/pub/gdb/releases/gdb-5.2.tar.bz2 \
           $PWD/www \
           /www/sourceware/htdocs/gdb/download/ari \
           gdb


Shadow the pages onto gnu
.........................

Something goes here.

Install the GDB tar ball on GNU
...............................

At the time of writing, the GNU machine was `gnudist.gnu.org' in
`~ftp/gnu/gdb'.

Make the `ANNOUNCEMENT'
.......................

Post the `ANNOUNCEMENT' file you created above to:

   * GDB Announcement mailing list <gdb-announce@sources.redhat.com>

   * General GNU Announcement list <info-gnu@gnu.org> (but delay it a
     day or so to let things get out)

   * GDB Bug Report mailing list <bug-gdb@gnu.org>

18.6.5 Cleanup
--------------

The release is out but you're still not finished.

Commit outstanding changes
..........................

In particular you'll need to commit any changes to:

   * `gdb/ChangeLog'

   * `gdb/version.in'

   * `gdb/NEWS'

   * `gdb/README'

Tag the release
...............

Something like:

     $  d=`date -u +%Y-%m-%d`
     $  echo $d
     2002-01-24
     $  ( cd insight/src/gdb && cvs -f -q update )
     $  ( cd insight/src && cvs -f -q tag gdb_5_2-$d-release )

   Insight is used since that contains more of the release than GDB.

Mention the release on the trunk
................................

Just put something in the `ChangeLog' so that the trunk also indicates
when the release was made.

Restart `gdb/version.in'
........................

If `gdb/version.in' does not contain an ISO date such as `2002-01-24'
then the daily `cronjob' won't update it.  Having committed all the
release changes it can be set to `5.2.0_0000-00-00-cvs' which will
restart things (yes the `_' is important - it affects the snapshot
process).

   Don't forget the `ChangeLog'.

Merge into trunk
................

The files committed to the branch may also need changes merged into the
trunk.

Revise the release schedule
...........................

Post a revised release schedule to GDB Discussion List
<gdb@sources.redhat.com> with an updated announcement.  The schedule
can be generated by running:

     $  ~/ss/schedule `date +%s` schedule

The first parameter is approximate date/time in seconds (from the epoch)
of the most recent release.

   Also update the schedule `cronjob'.

18.7 Post release
=================

Remove any `OBSOLETE' code.

\x1f
File: gdbint.info,  Node: Testsuite,  Next: Hints,  Prev: Releasing GDB,  Up: Top

19 Testsuite
************

The testsuite is an important component of the GDB package.  While it
is always worthwhile to encourage user testing, in practice this is
rarely sufficient; users typically use only a small subset of the
available commands, and it has proven all too common for a change to
cause a significant regression that went unnoticed for some time.

   The GDB testsuite uses the DejaGNU testing framework.  The tests
themselves are calls to various `Tcl' procs; the framework runs all the
procs and summarizes the passes and fails.

19.1 Using the Testsuite
========================

To run the testsuite, simply go to the GDB object directory (or to the
testsuite's objdir) and type `make check'.  This just sets up some
environment variables and invokes DejaGNU's `runtest' script.  While
the testsuite is running, you'll get mentions of which test file is in
use, and a mention of any unexpected passes or fails.  When the
testsuite is finished, you'll get a summary that looks like this:

                     === gdb Summary ===

     # of expected passes            6016
     # of unexpected failures        58
     # of unexpected successes       5
     # of expected failures          183
     # of unresolved testcases       3
     # of untested testcases         5

   To run a specific test script, type:
     make check RUNTESTFLAGS='TESTS'
   where TESTS is a list of test script file names, separated by spaces.

   The ideal test run consists of expected passes only; however, reality
conspires to keep us from this ideal.  Unexpected failures indicate
real problems, whether in GDB or in the testsuite.  Expected failures
are still failures, but ones which have been decided are too hard to
deal with at the time; for instance, a test case might work everywhere
except on AIX, and there is no prospect of the AIX case being fixed in
the near future.  Expected failures should not be added lightly, since
you may be masking serious bugs in GDB.  Unexpected successes are
expected fails that are passing for some reason, while unresolved and
untested cases often indicate some minor catastrophe, such as the
compiler being unable to deal with a test program.

   When making any significant change to GDB, you should run the
testsuite before and after the change, to confirm that there are no
regressions.  Note that truly complete testing would require that you
run the testsuite with all supported configurations and a variety of
compilers; however this is more than really necessary.  In many cases
testing with a single configuration is sufficient.  Other useful
options are to test one big-endian (Sparc) and one little-endian (x86)
host, a cross config with a builtin simulator (powerpc-eabi, mips-elf),
or a 64-bit host (Alpha).

   If you add new functionality to GDB, please consider adding tests
for it as well; this way future GDB hackers can detect and fix their
changes that break the functionality you added.  Similarly, if you fix
a bug that was not previously reported as a test failure, please add a
test case for it.  Some cases are extremely difficult to test, such as
code that handles host OS failures or bugs in particular versions of
compilers, and it's OK not to try to write tests for all of those.

   DejaGNU supports separate build, host, and target machines.  However,
some GDB test scripts do not work if the build machine and the host
machine are not the same.  In such an environment, these scripts will
give a result of "UNRESOLVED", like this:

     UNRESOLVED: gdb.base/example.exp: This test script does not work on a remote host.

19.2 Testsuite Organization
===========================

The testsuite is entirely contained in `gdb/testsuite'.  While the
testsuite includes some makefiles and configury, these are very minimal,
and used for little besides cleaning up, since the tests themselves
handle the compilation of the programs that GDB will run.  The file
`testsuite/lib/gdb.exp' contains common utility procs useful for all
GDB tests, while the directory `testsuite/config' contains
configuration-specific files, typically used for special-purpose
definitions of procs like `gdb_load' and `gdb_start'.

   The tests themselves are to be found in `testsuite/gdb.*' and
subdirectories of those.  The names of the test files must always end
with `.exp'.  DejaGNU collects the test files by wildcarding in the
test directories, so both subdirectories and individual files get
chosen and run in alphabetical order.

   The following table lists the main types of subdirectories and what
they are for.  Since DejaGNU finds test files no matter where they are
located, and since each test file sets up its own compilation and
execution environment, this organization is simply for convenience and
intelligibility.

`gdb.base'
     This is the base testsuite.  The tests in it should apply to all
     configurations of GDB (but generic native-only tests may live
     here).  The test programs should be in the subset of C that is
     valid K&R, ANSI/ISO, and C++ (`#ifdef's are allowed if necessary,
     for instance for prototypes).

`gdb.LANG'
     Language-specific tests for any language LANG besides C.  Examples
     are `gdb.cp' and `gdb.java'.

`gdb.PLATFORM'
     Non-portable tests.  The tests are specific to a specific
     configuration (host or target), such as HP-UX or eCos.  Example is
     `gdb.hp', for HP-UX.

`gdb.COMPILER'
     Tests specific to a particular compiler.  As of this writing (June
     1999), there aren't currently any groups of tests in this category
     that couldn't just as sensibly be made platform-specific, but one
     could imagine a `gdb.gcc', for tests of GDB's handling of GCC
     extensions.

`gdb.SUBSYSTEM'
     Tests that exercise a specific GDB subsystem in more depth.  For
     instance, `gdb.disasm' exercises various disassemblers, while
     `gdb.stabs' tests pathways through the stabs symbol reader.

19.3 Writing Tests
==================

In many areas, the GDB tests are already quite comprehensive; you
should be able to copy existing tests to handle new cases.

   You should try to use `gdb_test' whenever possible, since it
includes cases to handle all the unexpected errors that might happen.
However, it doesn't cost anything to add new test procedures; for
instance, `gdb.base/exprs.exp' defines a `test_expr' that calls
`gdb_test' multiple times.

   Only use `send_gdb' and `gdb_expect' when absolutely necessary.
Even if GDB has several valid responses to a command, you can use
`gdb_test_multiple'.  Like `gdb_test', `gdb_test_multiple' recognizes
internal errors and unexpected prompts.

   Do not write tests which expect a literal tab character from GDB.
On some operating systems (e.g. OpenBSD) the TTY layer expands tabs to
spaces, so by the time GDB's output reaches expect the tab is gone.

   The source language programs do _not_ need to be in a consistent
style.  Since GDB is used to debug programs written in many different
styles, it's worth having a mix of styles in the testsuite; for
instance, some GDB bugs involving the display of source lines would
never manifest themselves if the programs used GNU coding style
uniformly.

\x1f
File: gdbint.info,  Node: Hints,  Next: GDB Observers,  Prev: Testsuite,  Up: Top

20 Hints
********

Check the `README' file, it often has useful information that does not
appear anywhere else in the directory.

* Menu:

* Getting Started::             Getting started working on GDB
* Debugging GDB::               Debugging GDB with itself

\x1f
File: gdbint.info,  Node: Getting Started,  Up: Hints

20.1 Getting Started
====================

GDB is a large and complicated program, and if you first starting to
work on it, it can be hard to know where to start.  Fortunately, if you
know how to go about it, there are ways to figure out what is going on.

   This manual, the GDB Internals manual, has information which applies
generally to many parts of GDB.

   Information about particular functions or data structures are
located in comments with those functions or data structures.  If you
run across a function or a global variable which does not have a
comment correctly explaining what is does, this can be thought of as a
bug in GDB; feel free to submit a bug report, with a suggested comment
if you can figure out what the comment should say.  If you find a
comment which is actually wrong, be especially sure to report that.

   Comments explaining the function of macros defined in host, target,
or native dependent files can be in several places.  Sometimes they are
repeated every place the macro is defined.  Sometimes they are where the
macro is used.  Sometimes there is a header file which supplies a
default definition of the macro, and the comment is there.  This manual
also documents all the available macros.

   Start with the header files.  Once you have some idea of how GDB's
internal symbol tables are stored (see `symtab.h', `gdbtypes.h'), you
will find it much easier to understand the code which uses and creates
those symbol tables.

   You may wish to process the information you are getting somehow, to
enhance your understanding of it.  Summarize it, translate it to another
language, add some (perhaps trivial or non-useful) feature to GDB, use
the code to predict what a test case would do and write the test case
and verify your prediction, etc.  If you are reading code and your eyes
are starting to glaze over, this is a sign you need to use a more active
approach.

   Once you have a part of GDB to start with, you can find more
specifically the part you are looking for by stepping through each
function with the `next' command.  Do not use `step' or you will
quickly get distracted; when the function you are stepping through
calls another function try only to get a big-picture understanding
(perhaps using the comment at the beginning of the function being
called) of what it does.  This way you can identify which of the
functions being called by the function you are stepping through is the
one which you are interested in.  You may need to examine the data
structures generated at each stage, with reference to the comments in
the header files explaining what the data structures are supposed to
look like.

   Of course, this same technique can be used if you are just reading
the code, rather than actually stepping through it.  The same general
principle applies--when the code you are looking at calls something
else, just try to understand generally what the code being called does,
rather than worrying about all its details.

   A good place to start when tracking down some particular area is with
a command which invokes that feature.  Suppose you want to know how
single-stepping works.  As a GDB user, you know that the `step' command
invokes single-stepping.  The command is invoked via command tables
(see `command.h'); by convention the function which actually performs
the command is formed by taking the name of the command and adding
`_command', or in the case of an `info' subcommand, `_info'.  For
example, the `step' command invokes the `step_command' function and the
`info display' command invokes `display_info'.  When this convention is
not followed, you might have to use `grep' or `M-x tags-search' in
emacs, or run GDB on itself and set a breakpoint in `execute_command'.

   If all of the above fail, it may be appropriate to ask for
information on `bug-gdb'.  But _never_ post a generic question like "I
was wondering if anyone could give me some tips about understanding
GDB"--if we had some magic secret we would put it in this manual.
Suggestions for improving the manual are always welcome, of course.

\x1f
File: gdbint.info,  Node: Debugging GDB,  Up: Hints

20.2 Debugging GDB with itself
==============================

If GDB is limping on your machine, this is the preferred way to get it
fully functional.  Be warned that in some ancient Unix systems, like
Ultrix 4.2, a program can't be running in one process while it is being
debugged in another.  Rather than typing the command `./gdb ./gdb',
which works on Suns and such, you can copy `gdb' to `gdb2' and then
type `./gdb ./gdb2'.

   When you run GDB in the GDB source directory, it will read a
`.gdbinit' file that sets up some simple things to make debugging gdb
easier.  The `info' command, when executed without a subcommand in a
GDB being debugged by gdb, will pop you back up to the top level gdb.
See `.gdbinit' for details.

   If you use emacs, you will probably want to do a `make TAGS' after
you configure your distribution; this will put the machine dependent
routines for your local machine where they will be accessed first by
`M-.'

   Also, make sure that you've either compiled GDB with your local cc,
or have run `fixincludes' if you are compiling with gcc.

20.3 Submitting Patches
=======================

Thanks for thinking of offering your changes back to the community of
GDB users.  In general we like to get well designed enhancements.
Thanks also for checking in advance about the best way to transfer the
changes.

   The GDB maintainers will only install "cleanly designed" patches.
This manual summarizes what we believe to be clean design for GDB.

   If the maintainers don't have time to put the patch in when it
arrives, or if there is any question about a patch, it goes into a
large queue with everyone else's patches and bug reports.

   The legal issue is that to incorporate substantial changes requires a
copyright assignment from you and/or your employer, granting ownership
of the changes to the Free Software Foundation.  You can get the
standard documents for doing this by sending mail to `gnu@gnu.org' and
asking for it.  We recommend that people write in "All programs owned
by the Free Software Foundation" as "NAME OF PROGRAM", so that changes
in many programs (not just GDB, but GAS, Emacs, GCC, etc) can be
contributed with only one piece of legalese pushed through the
bureaucracy and filed with the FSF.  We can't start merging changes
until this paperwork is received by the FSF (their rules, which we
follow since we maintain it for them).

   Technically, the easiest way to receive changes is to receive each
feature as a small context diff or unidiff, suitable for `patch'.  Each
message sent to me should include the changes to C code and header
files for a single feature, plus `ChangeLog' entries for each directory
where files were modified, and diffs for any changes needed to the
manuals (`gdb/doc/gdb.texinfo' or `gdb/doc/gdbint.texinfo').  If there
are a lot of changes for a single feature, they can be split down into
multiple messages.

   In this way, if we read and like the feature, we can add it to the
sources with a single patch command, do some testing, and check it in.
If you leave out the `ChangeLog', we have to write one.  If you leave
out the doc, we have to puzzle out what needs documenting.  Etc., etc.

   The reason to send each change in a separate message is that we will
not install some of the changes.  They'll be returned to you with
questions or comments.  If we're doing our job correctly, the message
back to you will say what you have to fix in order to make the change
acceptable.  The reason to have separate messages for separate features
is so that the acceptable changes can be installed while one or more
changes are being reworked.  If multiple features are sent in a single
message, we tend to not put in the effort to sort out the acceptable
changes from the unacceptable, so none of the features get installed
until all are acceptable.

   If this sounds painful or authoritarian, well, it is.  But we get a
lot of bug reports and a lot of patches, and many of them don't get
installed because we don't have the time to finish the job that the bug
reporter or the contributor could have done.  Patches that arrive
complete, working, and well designed, tend to get installed on the day
they arrive.  The others go into a queue and get installed as time
permits, which, since the maintainers have many demands to meet, may not
be for quite some time.

   Please send patches directly to the GDB maintainers
<gdb-patches@sources.redhat.com>.

20.4 Obsolete Conditionals
==========================

Fragments of old code in GDB sometimes reference or set the following
configuration macros.  They should not be used by new code, and old uses
should be removed as those parts of the debugger are otherwise touched.

`STACK_END_ADDR'
     This macro used to define where the end of the stack appeared, for
     use in interpreting core file formats that don't record this
     address in the core file itself.  This information is now
     configured in BFD, and GDB gets the info portably from there.  The
     values in GDB's configuration files should be moved into BFD
     configuration files (if needed there), and deleted from all of
     GDB's config files.

     Any `FOO-xdep.c' file that references STACK_END_ADDR is so old
     that it has never been converted to use BFD.  Now that's old!


20.5 Build Script
=================

The script `gdb_buildall.sh' builds GDB with flag
`--enable-targets=all' set.  This builds GDB with all supported targets
activated.  This helps testing GDB when doing changes that affect more
than one architecture and is much faster than using `gdb_mbuild.sh'.

   After building GDB the script checks which architectures are
supported and then switches the current architecture to each of those
to get information about the architecture.  The test results are stored
in log files in the directory the script was called from.

\x1f
File: gdbint.info,  Node: GDB Observers,  Next: GNU Free Documentation License,  Prev: Hints,  Up: Top

Appendix A GDB Currently available observers
********************************************

A.1 Implementation rationale
============================

An "observer" is an entity which is interested in being notified when
GDB reaches certain states, or certain events occur in GDB.  The entity
being observed is called the "subject".  To receive notifications, the
observer attaches a callback to the subject.  One subject can have
several observers.

   `observer.c' implements an internal generic low-level event
notification mechanism.  This generic event notification mechanism is
then re-used to implement the exported high-level notification
management routines for all possible notifications.

   The current implementation of the generic observer provides support
for contextual data.  This contextual data is given to the subject when
attaching the callback.  In return, the subject will provide this
contextual data back to the observer as a parameter of the callback.

   Note that the current support for the contextual data is only
partial, as it lacks a mechanism that would deallocate this data when
the callback is detached.  This is not a problem so far, as this
contextual data is only used internally to hold a function pointer.
Later on, if a certain observer needs to provide support for user-level
contextual data, then the generic notification mechanism will need to be
enhanced to allow the observer to provide a routine to deallocate the
data when attaching the callback.

   The observer implementation is also currently not reentrant.  In
particular, it is therefore not possible to call the attach or detach
routines during a notification.

A.2 Debugging
=============

Observer notifications can be traced using the command `set debug
observer 1' (*note Optional messages about internal happenings:
(gdb)Debugging Output.).

A.3 `normal_stop' Notifications
===============================

GDB notifies all `normal_stop' observers when the inferior execution
has just stopped, the associated messages and annotations have been
printed, and the control is about to be returned to the user.

   Note that the `normal_stop' notification is not emitted when the
execution stops due to a breakpoint, and this breakpoint has a
condition that is not met.  If the breakpoint has any associated
commands list, the commands are executed after the notification is
emitted.

   The following interfaces are available to manage observers:

 -- Function: extern struct observer *observer_attach_EVENT
          (observer_EVENT_ftype *F)
     Using the function F, create an observer that is notified when
     ever EVENT occurs, return the observer.

 -- Function: extern void observer_detach_EVENT (struct observer
          *OBSERVER);
     Remove OBSERVER from the list of observers to be notified when
     EVENT occurs.

 -- Function: extern void observer_notify_EVENT (void);
     Send a notification to all EVENT observers.

   The following observable events are defined:

 -- Function: void normal_stop (struct bpstats *BS)
     The inferior has stopped for real.

 -- Function: void target_changed (struct target_ops *TARGET)
     The target's register contents have changed.

 -- Function: void executable_changed (void *UNUSED_ARGS)
     The executable being debugged by GDB has changed: The user decided
     to debug a different program, or the program he was debugging has
     been modified since being loaded by the debugger (by being
     recompiled, for instance).

 -- Function: void inferior_created (struct target_ops *OBJFILE, int
          FROM_TTY)
     GDB has just connected to an inferior.  For `run', GDB calls this
     observer while the inferior is still stopped at the entry-point
     instruction.  For `attach' and `core', GDB calls this observer
     immediately after connecting to the inferior, and before any
     information on the inferior has been printed.

 -- Function: void solib_loaded (struct so_list *SOLIB)
     The shared library specified by SOLIB has been loaded.  Note that
     when GDB calls this observer, the library's symbols probably
     haven't been loaded yet.

 -- Function: void solib_unloaded (struct so_list *SOLIB)
     The shared library specified by SOLIB has been unloaded.

 -- Function: void new_objfile (struct objfile *OBJFILE)
     The symbol file specified by OBJFILE has been loaded.  Called with
     OBJFILE equal to `NULL' to indicate previously loaded symbol table
     data has now been invalidated.

\x1f
File: gdbint.info,  Node: GNU Free Documentation License,  Next: Index,  Prev: GDB Observers,  Up: Top

Appendix B GNU Free Documentation License
*****************************************

                      Version 1.2, November 2002

     Copyright (C) 2000,2001,2002 Free Software Foundation, Inc.
     51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.

     Everyone is permitted to copy and distribute verbatim copies
     of this license document, but changing it is not allowed.

  0. 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.

  1. APPLICABILITY AND DEFINITIONS

     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 distributed under the terms of this License.  Such a notice
     grants a world-wide, royalty-free license, unlimited in duration,
     to use that work under the conditions stated herein.  The
     "Document", below, refers to any such manual or work.  Any member
     of the public is a licensee, and is addressed as "you".  You
     accept the license if you copy, modify or distribute the work in a
     way requiring permission under copyright law.

     A "Modified Version" of the Document means any work containing the
     Document or a portion of it, either copied verbatim, or with
     modifications and/or translated into another language.

     A "Secondary Section" is a named appendix or a front-matter section
     of the Document that deals exclusively with the relationship of the
     publishers or authors of the Document to the Document's overall
     subject (or to related matters) and contains nothing that could
     fall directly within that overall subject.  (Thus, if the Document
     is in part a textbook of mathematics, a Secondary Section may not
     explain any mathematics.)  The relationship could be a matter of
     historical connection with the subject or with related matters, or
     of legal, commercial, philosophical, ethical or political position
     regarding them.

     The "Invariant Sections" are certain Secondary Sections whose
     titles are designated, as being those of Invariant Sections, in
     the notice that says that the Document is released under this
     License.  If a section does not fit the above definition of
     Secondary then it is not allowed to be designated as Invariant.
     The Document may contain zero Invariant Sections.  If the Document
     does not identify any Invariant Sections then there are none.

     The "Cover Texts" are certain short passages of text that are
     listed, as Front-Cover Texts or Back-Cover Texts, in the notice
     that says that the Document is released under this License.  A
     Front-Cover Text may be at most 5 words, and a Back-Cover Text may
     be at most 25 words.

     A "Transparent" copy of the Document means a machine-readable copy,
     represented in a format whose specification is available to the
     general public, that is suitable for revising the document
     straightforwardly with generic text editors or (for images
     composed of pixels) generic paint programs or (for drawings) some
     widely available drawing editor, and that is suitable for input to
     text formatters or for automatic translation to a variety of
     formats suitable for input to text formatters.  A copy made in an
     otherwise Transparent file format whose markup, or absence of
     markup, has been arranged to thwart or discourage subsequent
     modification by readers is not Transparent.  An image format is
     not Transparent if used for any substantial amount of text.  A
     copy that is not "Transparent" is called "Opaque".

     Examples of suitable formats for Transparent copies include plain
     ASCII without markup, Texinfo input format, LaTeX input format,
     SGML or XML using a publicly available DTD, and
     standard-conforming simple HTML, PostScript or PDF designed for
     human modification.  Examples of transparent image formats include
     PNG, XCF and JPG.  Opaque formats include proprietary formats that
     can be read and edited only by proprietary word processors, SGML or
     XML for which the DTD and/or processing tools are not generally
     available, and the machine-generated HTML, PostScript or PDF
     produced by some word processors for output purposes only.

     The "Title Page" means, for a printed book, the title page itself,
     plus such following pages as are needed to hold, legibly, the
     material this License requires to appear in the title page.  For
     works in formats which do not have any title page as such, "Title
     Page" means the text near the most prominent appearance of the
     work's title, preceding the beginning of the body of the text.

     A section "Entitled XYZ" means a named subunit of the Document
     whose title either is precisely XYZ or contains XYZ in parentheses
     following text that translates XYZ in another language.  (Here XYZ
     stands for a specific section name mentioned below, such as
     "Acknowledgements", "Dedications", "Endorsements", or "History".)
     To "Preserve the Title" of such a section when you modify the
     Document means that it remains a section "Entitled XYZ" according
     to this definition.

     The Document may include Warranty Disclaimers next to the notice
     which states that this License applies to the Document.  These
     Warranty Disclaimers are considered to be included by reference in
     this License, but only as regards disclaiming warranties: any other
     implication that these Warranty Disclaimers may have is void and
     has no effect on the meaning of this License.

  2. VERBATIM COPYING

     You may copy and distribute the Document in any medium, either
     commercially or noncommercially, provided that this License, the
     copyright notices, and the license notice saying this License
     applies to the Document are reproduced in all copies, and that you
     add no other conditions whatsoever to those of this License.  You
     may not use technical measures to obstruct or control the reading
     or further copying of the copies you make or distribute.  However,
     you may accept compensation in exchange for copies.  If you
     distribute a large enough number of copies you must also follow
     the conditions in section 3.

     You may also lend copies, under the same conditions stated above,
     and you may publicly display copies.

  3. COPYING IN QUANTITY

     If you publish printed copies (or copies in media that commonly
     have printed covers) of the Document, numbering more than 100, and
     the Document's license notice requires Cover Texts, you must
     enclose the copies in covers that carry, clearly and legibly, all
     these Cover Texts: Front-Cover Texts on the front cover, and
     Back-Cover Texts on the back cover.  Both covers must also clearly
     and legibly identify you as the publisher of these copies.  The
     front cover must present the full title with all words of the
     title equally prominent and visible.  You may add other material
     on the covers in addition.  Copying with changes limited to the
     covers, as long as they preserve the title of the Document and
     satisfy these conditions, can be treated as verbatim copying in
     other respects.

     If the required texts for either cover are too voluminous to fit
     legibly, you should put the first ones listed (as many as fit
     reasonably) on the actual cover, and continue the rest onto
     adjacent pages.

     If you publish or distribute Opaque copies of the Document
     numbering more than 100, you must either include a
     machine-readable Transparent copy along with each Opaque copy, or
     state in or with each Opaque copy 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.

  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:

       A. 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.

       B. 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.

       C. State on the Title page the name of the publisher of the
          Modified Version, as the publisher.

       D. Preserve all the copyright notices of the Document.

       E. Add an appropriate copyright notice for your modifications
          adjacent to the other copyright notices.

       F. 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.

       G. Preserve in that license notice the full lists of Invariant
          Sections and required Cover Texts given in the Document's
          license notice.

       H. Include an unaltered copy of this License.

       I. 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.

       J. 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.

       K. 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.

       L. 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.

       M. Delete any section Entitled "Endorsements".  Such a section
          may not be included in the Modified Version.

       N. Do not retitle any existing section to be Entitled
          "Endorsements" or to conflict in title with any Invariant
          Section.

       O. Preserve any Warranty Disclaimers.

     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.

  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."

  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.

  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.

  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.

  9. TERMINATION

     You may not copy, modify, sublicense, or distribute the Document
     except as expressly provided for under this License.  Any other
     attempt to copy, modify, sublicense or distribute the Document is
     void, and will automatically terminate your rights under this
     License.  However, parties who have received copies, or rights,
     from you under this License will not have their licenses
     terminated so long as such parties remain in full compliance.

 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
     `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.

B.1 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:

       Copyright (C)  YEAR  YOUR NAME.
       Permission is granted to copy, distribute and/or modify this document
       under the terms of the GNU Free Documentation License, Version 1.2
       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''.

   If you have Invariant Sections, Front-Cover Texts and Back-Cover
Texts, replace the "with...Texts." line with this:

         with the Invariant Sections being LIST THEIR TITLES, with
         the Front-Cover Texts being LIST, and with the Back-Cover Texts
         being LIST.

   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.