Use new tail-calling mechanism on ARM.

[official-gcc.git] / gcc / f / INSTALL

*Note:* This file is automatically generated from the files
`install0.texi' and `g77install.texi'.  `INSTALL' is *not* a source
file, although it is normally included within source distributions.

   This file contains installation information for the GNU Fortran
compiler.  Copyright (C) {No Value For "copyrights-install"} Free
Software Foundation, Inc.  You may copy, distribute, and modify it
freely as long as you preserve this copyright notice and permission
notice.

Installing GNU Fortran
**********************

   The following information describes how to install `g77'.

   Note that, for users of the GCC-2.95 version of `g77', much of the
information is obsolete, and is superceded by the GCC installation
procedures.  Such information is accordingly omitted and flagged as
such.

   *Warning:* The information below is still under development, and
might not accurately reflect the `g77' code base of which it is a part.
Efforts are made to keep it somewhat up-to-date, but they are
particularly concentrated on any version of this information that is
distributed as part of a *released* `g77'.

   In particular, while this information is intended to apply to the
GCC-2.95 version of `g77', only an official *release* of that version
is expected to contain documentation that is most consistent with the
`g77' product in that version.

   The following information was last updated on 1999-07-17:

Prerequisites
=============

   For users of the GCC-2.95 version of `g77', this information is
superceded by the GCC installation instructions.

Problems Installing
===================

   This is a list of problems (and some apparent problems which don't
really mean anything is wrong) that show up when configuring, building,
installing, or porting GNU Fortran.

   *Note Installation Problems: (gcc)Installation Problems, for more
information on installation problems that can afflict either `gcc' or
`g77'.

General Problems
----------------

   These problems can occur on most or all systems.

GNU C Required
..............

   Compiling `g77' requires GNU C, not just ANSI C.  Fixing this
wouldn't be very hard (just tedious), but the code using GNU extensions
to the C language is expected to be rewritten for 0.6 anyway, so there
are no plans for an interim fix.

   This requirement does not mean you must already have `gcc' installed
to build `g77'.  As long as you have a working C compiler, you can use a
"bootstrap" build to automate the process of first building `gcc' using
the working C compiler you have, then building `g77' and rebuilding
`gcc' using that just-built `gcc', and so on.

Patching GNU CC
...............

   `g77' no longer requires application of a patch file to the `gcc'
compiler tree.  In fact, no such patch file is distributed with `g77'.
This is as of version 0.5.23 and `egcs' version 1.0.

Building GNU CC Necessary
.........................

   It should be possible to build the runtime without building `cc1'
and other non-Fortran items, but, for now, an easy way to do that is
not yet established.

Missing strtoul or bsearch
..........................

   This information does not apply to the GCC-2.95 version of `g77',

Cleanup Kills Stage Directories
...............................

   It'd be helpful if `g77''s `Makefile.in' or `Make-lang.in' would
create the various `stageN' directories and their subdirectories, so
developers and expert installers wouldn't have to reconfigure after
cleaning up.

   That help has arrived as of version 0.5.23 of `g77' and version 1.1
of `egcs'.  Configuration itself no longer creates any particular
directories that are unique to `g77'.  The build procedures in
`Make-lang.in' take care of that, on demand.

LANGUAGES Macro Ignored
.......................

   Prior to version 0.5.23 of `g77' and version 1.1 of `egcs', `g77'
would sometimes ignore the absence of `f77' and `F77' in the
`LANGUAGES' macro definition used for the `make' command being
processed.

   As of `g77' version 0.5.23 and `egcs' version 1.1, `g77' now obeys
this macro in all relevant situations.

   However, in versions of `gcc' through 2.8.1, non-`g77' portions of
`gcc', such as `g++', are known to go ahead and perform various
language-specific activities when their respective language strings do
not appear in the `LANGUAGES' macro in effect during that invocation of
`make'.

   It is expected that these remaining problems will be fixed in a
future version of `gcc'.

System-specific Problems
------------------------

   A linker bug on some versions of AIX 4.1 might prevent building when
`g77' is built within `gcc'.  It might also occur when building within
`egcs'.

Cross-compiler Problems
-----------------------

   `g77' has been in alpha testing since September of 1992, and in
public beta testing since February of 1995.  Alpha testing was done by
a small number of people worldwide on a fairly wide variety of
machines, involving self-compilation in most or all cases.  Beta
testing has been done primarily via self-compilation, but in more and
more cases, cross-compilation (and "criss-cross compilation", where a
version of a compiler is built on one machine to run on a second and
generate code that runs on a third) has been tried and has succeeded,
to varying extents.

   Generally, `g77' can be ported to any configuration to which `gcc',
`f2c', and `libf2c' can be ported and made to work together, aside from
the known problems described in this manual.  If you want to port `g77'
to a particular configuration, you should first make sure `gcc' and
`libf2c' can be ported to that configuration before focusing on `g77',
because `g77' is so dependent on them.

   Even for cases where `gcc' and `libf2c' work, you might run into
problems with cross-compilation on certain machines, for several
reasons.

   * There is one known bug (a design bug to be fixed in 0.6) that
     prevents configuration of `g77' as a cross-compiler in some cases,
     though there are assumptions made during configuration that
     probably make doing non-self-hosting builds a hassle, requiring
     manual intervention.

   * `gcc' might still have some trouble being configured for certain
     combinations of machines.  For example, it might not know how to
     handle floating-point constants.

   * Improvements to the way `libg2c' is built could make building
     `g77' as a cross-compiler easier--for example, passing and using
     `$(LD)' and `$(AR)' in the appropriate ways.  (This is improved in
     the `egcs' version of `g77', especially as of version 1.1.)

   * There are still some challenges putting together the right
     run-time libraries (needed by `libg2c') for a target system,
     depending on the systems involved in the configuration.  (This is
     a general problem with cross-compilation, and with `gcc' in
     particular.)

Changing Settings Before Building
=================================

   Here are some internal `g77' settings that can be changed by editing
source files in `egcs/gcc/f/' before building.

   This information, and perhaps even these settings, represent
stop-gap solutions to problems people doing various ports of `g77' have
encountered.  As such, none of the following information is expected to
be pertinent in future versions of `g77'.

Larger File Unit Numbers
------------------------

   As distributed, whether as part of `f2c' or `g77', `libf2c' accepts
file unit numbers only in the range 0 through 99.  For example, a
statement such as `WRITE (UNIT=100)' causes a run-time crash in
`libf2c', because the unit number, 100, is out of range.

   If you know that Fortran programs at your installation require the
use of unit numbers higher than 99, you can change the value of the
`MXUNIT' macro, which represents the maximum unit number, to an
appropriately higher value.

   To do this, edit the file `egcs/libf2c/libI77/fio.h' in your `g77'
source tree, changing the following line:

     #define MXUNIT 100

   Change the line so that the value of `MXUNIT' is defined to be at
least one *greater* than the maximum unit number used by the Fortran
programs on your system.

   (For example, a program that does `WRITE (UNIT=255)' would require
`MXUNIT' set to at least 256 to avoid crashing.)

   Then build or rebuild `g77' as appropriate.

   *Note:* Changing this macro has *no* effect on other limits your
system might place on the number of files open at the same time.  That
is, the macro might allow a program to do `WRITE (UNIT=100)', but the
library and operating system underlying `libf2c' might disallow it if
many other files have already been opened (via `OPEN' or implicitly via
`READ', `WRITE', and so on).  Information on how to increase these
other limits should be found in your system's documentation.

Always Flush Output
-------------------

   Some Fortran programs require output (writes) to be flushed to the
operating system (under UNIX, via the `fflush()' library call) so that
errors, such as disk full, are immediately flagged via the relevant
`ERR=' and `IOSTAT=' mechanism, instead of such errors being flagged
later as subsequent writes occur, forcing the previously written data
to disk, or when the file is closed.

   Essentially, the difference can be viewed as synchronous error
reporting (immediate flagging of errors during writes) versus
asynchronous, or, more precisely, buffered error reporting (detection
of errors might be delayed).

   `libg2c' supports flagging write errors immediately when it is built
with the `ALWAYS_FLUSH' macro defined.  This results in a `libg2c' that
runs slower, sometimes quite a bit slower, under certain
circumstances--for example, accessing files via the networked file
system NFS--but the effect can be more reliable, robust file I/O.

   If you know that Fortran programs requiring this level of precision
of error reporting are to be compiled using the version of `g77' you
are building, you might wish to modify the `g77' source tree so that
the version of `libg2c' is built with the `ALWAYS_FLUSH' macro defined,
enabling this behavior.

   To do this, find this line in `egcs/libf2c/f2c.h' in your `g77'
source tree:

     /* #define ALWAYS_FLUSH */

   Remove the leading `/* ', so the line begins with `#define', and the
trailing ` */'.

   Then build or rebuild `g77' as appropriate.

Maximum Stackable Size
----------------------

   `g77', on most machines, puts many variables and arrays on the stack
where possible, and can be configured (by changing
`FFECOM_sizeMAXSTACKITEM' in `egcs/gcc/f/com.c') to force smaller-sized
entities into static storage (saving on stack space) or permit
larger-sized entities to be put on the stack (which can improve
run-time performance, as it presents more opportunities for the GBE to
optimize the generated code).

   *Note:* Putting more variables and arrays on the stack might cause
problems due to system-dependent limits on stack size.  Also, the value
of `FFECOM_sizeMAXSTACKITEM' has no effect on automatic variables and
arrays.  *Note But-bugs::, for more information.

Floating-point Bit Patterns
---------------------------

   The `g77' build will crash if an attempt is made to build it as a
cross-compiler for a target when `g77' cannot reliably determine the
bit pattern of floating-point constants for the target.  Planned
improvements for version 0.6 of `g77' will give it the capabilities it
needs to not have to crash the build but rather generate correct code
for the target.  (Currently, `g77' would generate bad code under such
circumstances if it didn't crash during the build, e.g. when compiling
a source file that does something like `EQUIVALENCE (I,R)' and `DATA
R/9.43578/'.)

Initialization of Large Aggregate Areas
---------------------------------------

   A warning message is issued when `g77' sees code that provides
initial values (e.g. via `DATA') to an aggregate area (`COMMON' or
`EQUIVALENCE', or even a large enough array or `CHARACTER' variable)
that is large enough to increase `g77''s compile time by roughly a
factor of 10.

   This size currently is quite small, since `g77' currently has a
known bug requiring too much memory and time to handle such cases.  In
`egcs/gcc/f/data.c', the macro `FFEDATA_sizeTOO_BIG_INIT_' is defined
to the minimum size for the warning to appear.  The size is specified
in storage units, which can be bytes, words, or whatever, on a
case-by-case basis.

   After changing this macro definition, you must (of course) rebuild
and reinstall `g77' for the change to take effect.

   Note that, as of version 0.5.18, improvements have reduced the scope
of the problem for *sparse* initialization of large arrays, especially
those with large, contiguous uninitialized areas.  However, the warning
is issued at a point prior to when `g77' knows whether the
initialization is sparse, and delaying the warning could mean it is
produced too late to be helpful.

   Therefore, the macro definition should not be adjusted to reflect
sparse cases.  Instead, adjust it to generate the warning when densely
initialized arrays begin to cause responses noticeably slower than
linear performance would suggest.

Alpha Problems Fixed
--------------------

   `g77' used to warn when it was used to compile Fortran code for a
target configuration that is not basically a 32-bit machine (such as an
Alpha, which is a 64-bit machine, especially if it has a 64-bit
operating system running on it).  That was because `g77' was known to
not work properly on such configurations.

   As of version 0.5.20, `g77' is believed to work well enough on such
systems.  So, the warning is no longer needed or provided.

   However, support for 64-bit systems, especially in areas such as
cross-compilation and handling of intrinsics, is still incomplete.  The
symptoms are believed to be compile-time diagnostics rather than the
generation of bad code.  It is hoped that version 0.6 will completely
support 64-bit systems.

Quick Start
===========

   For users of the GCC-2.95 version of `g77', this information is
superceded by the GCC installation instructions.

Complete Installation
=====================

   For users of the GCC-2.95 version of `g77', this information is
superceded by the GCC installation instructions.

Distributing Binaries
=====================

   For users of the GCC-2.95 version of `g77', this information is
superceded by the GCC installation instructions.