@c Copyright (C) 1995-1997 Free Software Foundation, Inc.
@c This is part of the G77 manual.
@c For copying conditions, see the file g77.tex.

@c The text of this file appears in the file INSTALL
@c in the G77 distribution, as well as in the G77 manual.

@c 1998-03-15

@set version-g77 0.5.22
@set version-gcc 2.7.2.3
@set version-gcc-patched 2.7.2.3.f.2
@set version-gzip 1.2.4
@set version-tar 1.12
@set version-patch 2.5
@set version-make 3.76.1
@set version-bison 1.25
@set version-makeinfo 1.68
@set version-texinfo 3.11
@set version-sed 2.05

@ifclear INSTALLONLY
@node Installation
@chapter Installing GNU Fortran
@end ifclear
@cindex installing GNU Fortran

The following information describes how to install @code{g77}.

The information in this file generally pertains to dealing
with @emph{source} distributions of @code{g77} and @code{gcc}.
It is possible that some of this information will be applicable
to some @emph{binary} distributions of these products---however,
since these distributions are not made by the maintainers of
@code{g77}, responsibility for binary distributions rests with
whoever built and first distributed them.

Nevertheless, efforts to make @code{g77} easier to both build
and install from source and package up as a binary distribution
are ongoing.

@menu
* Prerequisites::          Make sure your system is ready for @code{g77}.
* Problems Installing::    Known trouble areas.
* Settings::               Changing @code{g77} internals before building.
* Quick Start::            The easier procedure for non-experts.
* Complete Installation::  For experts, or those who want to be: the details.
* Distributing Binaries::  If you plan on distributing your @code{g77}.
@end menu

@node Prerequisites
@section Prerequisites
@cindex prerequisites

The procedures described to unpack, configure, build, and
install @code{g77} assume your system has certain programs
already installed.

The following prerequisites should be met by your
system before you follow the @code{g77} installation instructions:

@table @asis
@item @code{gzip}
To unpack the @code{gcc} and @code{g77} distributions,
you'll need the @code{gunzip} utility in the @code{gzip}
distribution.
Most UNIX systems already have @code{gzip} installed.
If yours doesn't, you can get it from the FSF.

Note that you'll need @code{tar} and other utilities
as well, but all UNIX systems have these.
There are GNU versions of all these available---in fact,
a complete GNU UNIX system can be put together on
most systems, if desired.

The version of GNU @code{gzip} used to package this release
is @value{version-gzip}.
(The version of GNU @code{tar} used to package this release
is @value{version-tar}.)

@item @file{gcc-@value{version-gcc}.tar.gz}
You need to have this, or some other applicable, version
of @code{gcc} on your system.
The version should be an exact copy of a distribution
from the FSF.
Its size is approximately 7.1MB.

If you've already unpacked @file{gcc-@value{version-gcc}.tar.gz} into a
directory (named @file{gcc-@value{version-gcc}}) called the @dfn{source tree}
for @code{gcc}, you can delete the distribution
itself, but you'll need to remember to skip any instructions to unpack
this distribution.

Without an applicable @code{gcc} source tree, you cannot
build @code{g77}.
You can obtain an FSF distribution of @code{gcc} from the FSF.

@item @file{g77-@value{version-g77}.tar.gz}
You probably have already unpacked this package,
or you are reading an advance copy of these installation instructions,
which are contained in this distribution.
The size of this package is approximately 1.5MB.

You can obtain an FSF distribution of @code{g77} from the FSF,
the same way you obtained @code{gcc}.

@item Enough disk space
The amount of disk space needed to unpack, build, install,
and use @code{g77} depends on the type of system you're
using, how you build @code{g77}, and how much of it you
install (primarily, which languages you install).

The sizes shown below assume all languages distributed
in @code{gcc-@value{version-gcc}}, plus @code{g77}, will be built
and installed.
These sizes are indicative of GNU/Linux systems on
Intel x86 running COFF and on Digital Alpha (AXP) systems
running ELF.
These should be fairly representative of 32-bit and 64-bit
systems, respectively.

Note that all sizes are approximate and subject to change without
notice!
They are based on preliminary releases of g77 made shortly
before the public beta release.

@itemize ---
@item
@code{gcc} and @code{g77} distributions occupy 8.6MB
packed, 35MB unpacked.
These consist of the source code and documentation,
plus some derived files (mostly documentation), for
@code{gcc} and @code{g77}.
Any deviations from these numbers for different
kinds of systems are likely to be very minor.

@item
A ``bootstrap'' build requires an additional 67.3MB
for a total of 102MB on an ix86, and an additional
98MB for a total of 165MB on an Alpha.

@item
Removing @file{gcc/stage1} after the build recovers
10.7MB for a total of 91MB on an ix86, and recovers
??MB for a total of ??MB on an Alpha.

After doing this, the integrity of the build can
still be verified via @samp{make compare}, and the
@code{gcc} compiler modified and used to build itself for
testing fairly quickly, using the copy of the compiler
kept in @code{gcc/stage2}.

@item
Removing @file{gcc/stage2} after the build further
recovers 27.3MB for a total of 64.3MB, and recovers
??MB for a total of ??MB on an Alpha.

After doing this, the compiler can still be installed,
especially if GNU @code{make} is used to avoid
gratuitous rebuilds (or, the installation can be done
by hand).

@item
Installing @code{gcc} and @code{g77} copies
14.9MB onto the @samp{--prefix} disk for a total of 79.2MB
on an ix86, and copies ??MB onto the @samp{--prefix}
disk for a total of ??MB on an Alpha.
@end itemize

After installation, if no further modifications and
builds of @code{gcc} or @code{g77} are planned, the
source and build directory may be removed, leaving
the total impact on a system's disk storage as
that of the amount copied during installation.

Systems with the appropriate version of @code{gcc}
installed don't require the complete
bootstrap build.
Doing a ``straight build'' requires about as much
space as does a bootstrap build followed by removing
both the @file{gcc/stage1} and @file{gcc/stage2}
directories.

Installing @code{gcc} and @code{g77} over existing
versions might require less @emph{new} disk space,
but note that, unlike many products, @code{gcc}
installs itself in a way that avoids overwriting other
installed versions of itself, so that other versions may
easily be invoked (via @samp{gcc -V @var{version}}).

So, the amount of space saved as a result of having
an existing version of @code{gcc} and @code{g77}
already installed is not much---typically only the
command drivers (@code{gcc}, @code{g77}, @code{g++},
and so on, which are small) and the documentation
is overwritten by the new installation.
The rest of the new installation is done without
replacing existing installed versions (assuming
they have different version numbers).

@item @code{patch}
Although you can do everything @code{patch} does yourself,
by hand, without much trouble, having @code{patch} installed
makes installation of new versions of GNU utilities such as
@code{g77} so much easier that it is worth getting.
You can obtain @code{patch} the same way you obtained
@code{gcc} and @code{g77}.

In any case, you can apply patches by hand---patch files
are designed for humans to read them.

The version of GNU @code{patch} used to develop this release
is @value{version-patch}.

@item @code{make}
Your system must have @code{make}, and you will probably save
yourself a lot of trouble if it is GNU @code{make} (sometimes
referred to as @code{gmake}).

The version of GNU @code{make} used to develop this release
is @value{version-make}.

@item @code{cc}
Your system must have a working C compiler.

@xref{Installation,,Installing GNU CC,gcc,Using and Porting GNU CC},
for more information on prerequisites for installing @code{gcc}.

@item @code{bison}
If you do not have @code{bison} installed, you can usually
work around any need for it, since @code{g77} itself does
not use it, and @code{gcc} normally includes all files
generated by running it in its distribution.
You can obtain @code{bison} the same way you obtained
@code{gcc} and @code{g77}.

The version of GNU @code{bison} used to develop this release
is @value{version-bison}.

@xref{Missing bison?},
for information on how to work around not having @code{bison}.

@item @code{makeinfo}
If you are missing @code{makeinfo}, you can usually work
around any need for it.
You can obtain @code{makeinfo} the same way you obtained
@code{gcc} and @code{g77}.

The version of GNU @code{makeinfo} used to develop this release
is @value{version-makeinfo}, from
GNU @code{texinfo} version @value{version-texinfo}.

@xref{Missing makeinfo?},
for information on getting around the lack of @code{makeinfo}.

@item @code{sed}
All UNIX systems have @code{sed}, but some have a broken
version that cannot handle configuring, building, or
installing @code{gcc} or @code{g77}.

The version of GNU @code{sed} used to develop this release
is @value{version-sed}.
(Note that GNU @code{sed} version 3.0 was withdrawn by the
FSF---if you happen to have this version installed, replace
it with version @value{version-sed} immediately.
See a GNU distribution site for further explanation.)

@item @code{root} access or equivalent
To perform the complete installation procedures on a system,
you need to have @code{root} access to that system, or
equivalent access to the @samp{--prefix} directory tree
specified on the @code{configure} command line.

Portions of the procedure (such as configuring and building
@code{g77}) can be performed by any user with enough disk
space and virtual memory.

However, these instructions are oriented towards less-experienced
users who want to install @code{g77} on their own personal
systems.

System administrators with more experience will want to
determine for themselves how they want to modify the
procedures described below to suit the needs of their
installation.
@end table

@node Problems Installing
@section Problems Installing
@cindex problems installing
@cindex installation problems

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.

@xref{Installation Problems,,,gcc,Using and Porting GNU CC},
for more information on installation problems that can afflict
either @code{gcc} or @code{g77}.

@menu
* General Problems::         Problems afflicting most or all systems.
* System-specific Problems:: Problems afflicting particular systems.
* Cross-compiler Problems::  Problems afflicting cross-compilation setups.
@end menu

@node General Problems
@subsection General Problems

These problems can occur on most or all systems.

@menu
* GNU C Required::             Why even ANSI C is not enough.
* Patching GNU CC Necessary::  Why @code{gcc} must be patched first.
* Building GNU CC Necessary::  Why you can't build @emph{just} Fortran.
* Missing strtoul::            If linking @code{f771} fails due to an
                                unresolved reference to @code{strtoul}.
* Object File Differences::    It's okay that @samp{make compare} will
                                flag @file{f/zzz.o}.
* Cleanup Kills Stage Directories::  A minor nit for @code{g77} developers.
* Missing gperf?::             When building requires @code{gperf}.
@end menu

@node GNU C Required
@subsubsection GNU C Required
@cindex GNU C required
@cindex requirements, GNU C

Compiling @code{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 @code{gcc}
installed to build @code{g77}.
As long as you have a working C compiler, you can use a
bootstrap build to automate the process of first building
@code{gcc} using the working C compiler you have, then building
@code{g77} and rebuilding @code{gcc} using that just-built @code{gcc},
and so on.

@node Patching GNU CC Necessary
@subsubsection Patching GNU CC Necessary
@cindex patch files
@cindex GBE

@code{g77} currently requires application of a patch file to the gcc compiler
tree.
The necessary patches should be folded in to the mainline gcc distribution.

Some combinations
of versions of @code{g77} and @code{gcc} might actually @emph{require} no
patches, but the patch files will be provided anyway as long as
there are more changes expected in subsequent releases.
These patch files might contain
unnecessary, but possibly helpful, patches.
As a result, it is possible this issue might never be
resolved, except by eliminating the need for the person
configuring @code{g77} to apply a patch by hand, by going
to a more automated approach (such as configure-time patching).

@node Building GNU CC Necessary
@subsubsection Building GNU CC Necessary
@cindex gcc, building
@cindex building gcc

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

@node Missing strtoul
@subsubsection Missing strtoul
@cindex strtoul
@cindex _strtoul
@cindex undefined reference (_strtoul)
@cindex f771, linking error for
@cindex linking error for f771
@cindex ld error for f771
@cindex ld can't find _strtoul
@cindex SunOS4

On SunOS4 systems, linking the @code{f771} program produces
an error message concerning an undefined symbol named
@samp{_strtoul}.

This is not a @code{g77} bug.
@xref{Patching GNU Fortran}, for information on
a workaround provided by @code{g77}.

The proper fix is either to upgrade your system to one that
provides a complete ANSI C environment, or improve @code{gcc} so
that it provides one for all the languages and configurations it supports.

@emph{Note:} In earlier versions of @code{g77}, an automated
workaround for this problem was attempted.
It worked for systems without @samp{_strtoul}, substituting
the incomplete-yet-sufficient version supplied with @code{g77}
for those systems.
However, the automated workaround failed mysteriously for systems
that appeared to have conforming ANSI C environments, and it
was decided that, lacking resources to more fully investigate
the problem, it was better to not punish users of those systems
either by requiring them to work around the problem by hand or
by always substituting an incomplete @code{strtoul()} implementation
when their systems had a complete, working one.
Unfortunately, this meant inconveniencing users of systems not
having @code{strtoul()}, but they're using obsolete (and generally
unsupported) systems anyway.

@node Object File Differences
@subsubsection Object File Differences
@cindex zzz.o
@cindex zzz.c
@cindex object file, differences
@cindex differences between object files
@cindex make compare

A comparison of object files after building Stage 3 during a
bootstrap build will result in @file{gcc/f/zzz.o} being flagged
as different from the Stage 2 version.
That is because it
contains a string with an expansion of the @code{__TIME__} macro,
which expands to the current time of day.
It is nothing to worry about, since
@file{gcc/f/zzz.c} doesn't contain any actual code.
It does allow you to override its use of @code{__DATE__} and
@code{__TIME__} by defining macros for the compilation---see the
source code for details.

@node Cleanup Kills Stage Directories
@subsubsection Cleanup Kills Stage Directories
@cindex stage directories
@cindex make clean

It'd be helpful if @code{g77}'s @file{Makefile.in} or @file{Make-lang.in}
would create the various @file{stage@var{n}} directories and their
subdirectories, so developers and expert installers wouldn't have to
reconfigure after cleaning up.

@node Missing gperf?
@subsubsection Missing @code{gperf}?
@cindex @code{gperf}
@cindex missing @code{gperf}

If a build aborts trying to invoke @code{gperf}, that
strongly suggests an improper method was used to
create the @code{gcc} source directory,
such as the UNIX @samp{cp -r} command instead
of @samp{cp -pr}, since this problem very likely
indicates that the date-time-modified information on
the @code{gcc} source files is incorrect.

The proper solution is to recreate the @code{gcc} source
directory from a @code{gcc} distribution known to be
provided by the FSF.

It is possible you might be able to temporarily
work around the problem, however, by trying these
commands:

@example
sh# @kbd{cd gcc}
sh# @kbd{touch c-gperf.h}
sh#
@end example

These commands update the date-time-modified information for
the file produced by the invocation of @code{gperf}
in the current versions of @code{gcc}, so that @code{make} no
longer believes it needs to update it.
This file should already exist in a @code{gcc}
distribution, but mistakes made when copying the @code{gcc}
directory can leave the modification information
set such that the @code{gperf} input files look more ``recent''
than the corresponding output files.

If the above does not work, definitely start from scratch
and avoid copying the @code{gcc} using any method that does
not reliably preserve date-time-modified information, such
as the UNIX @samp{cp -r} command (use @samp{cp -pr} instead).

@node System-specific Problems
@subsection System-specific Problems

@cindex Digital Alpha
@cindex Alpha, Digital
@cindex DEC Alpha
@cindex AXP
If your system is based on a Digital Alpha (AXP) architecture
and employs a 64-bit operating system (such as GNU/Linux),
you might consider using @code{egcs} instead of versions
of @code{g77} based on versions of @code{gcc} prior to 2.8.
@uref{http://www.cygnus.com/egcs} for information on @code{egcs},
or obtain a copy from @uref{ftp://egcs.cygnus.com/pub/egcs}.

@cindex Irix 6
@cindex SGI
If your system is Irix 6, to obtain a working version of @code{gcc},
@uref{http://reality.sgi.com/knobi/gcc-2.7.2.x-on-irix-6.2-6.3}.

@node Cross-compiler Problems
@subsection Cross-compiler Problems
@cindex cross-compiler, problems

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

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

@itemize @bullet
@item
There is one known bug
(a design bug to be fixed in 0.6) that prevents configuration of
@code{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.

@item
@code{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.

@item
Improvements to the way @code{libf2c} is built could make
building @code{g77} as a cross-compiler easier---for example,
passing and using @samp{$(LD)} and @samp{$(AR)} in the appropriate
ways.

@item
There are still some challenges putting together the right
run-time libraries (needed by @code{libf2c}) for a target
system, depending on the systems involved in the configuration.
(This is a general problem with cross-compilation, and with
@code{gcc} in particular.)
@end itemize

@node Settings
@section Changing Settings Before Building

Here are some internal @code{g77} settings that can be changed
by editing source files in @file{gcc/f/} before building.

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

@menu
* Larger File Unit Numbers::     Raising @samp{MXUNIT}.
* Always Flush Output::          Synchronizing write errors.
* Maximum Stackable Size::       Large arrays forced off the stack.
* Floating-point Bit Patterns::  Possible programs building @code{g77}
                                   as a cross-compiler.
* Large Initialization::         Large arrays with @code{DATA}
                                   initialization.
* Alpha Problems Fixed::         Problems with 64-bit systems like
                                   Alphas now fixed?
@end menu

@node Larger File Unit Numbers
@subsection Larger File Unit Numbers
@cindex MXUNIT
@cindex unit numbers
@cindex maximum unit number
@cindex illegal unit number
@cindex increasing maximum unit number

As distributed, whether as part of @code{f2c} or @code{g77},
@code{libf2c} accepts file unit numbers only in the range
0 through 99.
For example, a statement such as @samp{WRITE (UNIT=100)} causes
a run-time crash in @code{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 @samp{MXUNIT} macro, which represents the maximum unit
number, to an appropriately higher value.

To do this, edit the file @file{f/runtime/libI77/fio.h} in your
@code{g77} source tree, changing the following line:

@example
#define MXUNIT 100
@end example

Change the line so that the value of @samp{MXUNIT} is defined to be
at least one @emph{greater} than the maximum unit number used by
the Fortran programs on your system.

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

Then build or rebuild @code{g77} as appropriate.

@emph{Note:} Changing this macro has @emph{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 @samp{WRITE (UNIT=100)},
but the library and operating system underlying @code{libf2c} might
disallow it if many other files have already been opened (via @code{OPEN} or
implicitly via @code{READ}, @code{WRITE}, and so on).
Information on how to increase these other limits should be found
in your system's documentation.

@node Always Flush Output
@subsection Always Flush Output
@cindex ALWAYS_FLUSH
@cindex synchronous write errors
@cindex disk full
@cindex flushing output
@cindex fflush()
@cindex I/O, flushing
@cindex output, flushing
@cindex writes, flushing
@cindex NFS
@cindex network file system

Some Fortran programs require output
(writes) to be flushed to the operating system (under UNIX,
via the @code{fflush()} library call) so that errors,
such as disk full, are immediately flagged via the relevant
@code{ERR=} and @code{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).

@code{libf2c} supports flagging write errors immediately when
it is built with the @samp{ALWAYS_FLUSH} macro defined.
This results in a @code{libf2c} 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 @code{g77} you are building, you might wish to
modify the @code{g77} source tree so that the version of
@code{libf2c} is built with the @samp{ALWAYS_FLUSH} macro
defined, enabling this behavior.

To do this, find this line in @file{f/runtime/configure.in} in
your @code{g77} source tree:

@example
dnl AC_DEFINE(ALWAYS_FLUSH)
@end example

Remove the leading @samp{dnl@w{ }}, so the line begins with
@samp{AC_DEFINE(}, and run @code{autoconf} in that file's directory.
(Or, if you don't have @code{autoconf}, you can modify @file{f2c.h.in}
in the same directory to include the line @samp{#define ALWAYS_FLUSH}
after @samp{#define F2C_INCLUDE}.)

Then build or rebuild @code{g77} as appropriate.

@node Maximum Stackable Size
@subsection Maximum Stackable Size
@vindex FFECOM_sizeMAXSTACKITEM
@cindex code, stack variables
@cindex maximum stackable size
@cindex stack allocation
@cindex segmentation violation
@code{g77}, on most machines, puts many variables and arrays on the stack
where possible, and can be configured (by changing
@samp{FFECOM_sizeMAXSTACKITEM} in @file{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).

@emph{Note:} Putting more variables and arrays on the stack
might cause problems due to system-dependent limits on stack size.
Also, the value of @samp{FFECOM_sizeMAXSTACKITEM} has no
effect on automatic variables and arrays.
@xref{But-bugs}, for more information.

@node Floating-point Bit Patterns
@subsection Floating-point Bit Patterns

@cindex cross-compiler, building
@cindex floating-point bit patterns
@cindex bit patterns
The @code{g77} build will crash if an attempt is made to build
it as a cross-compiler
for a target when @code{g77} cannot reliably determine the bit pattern of
floating-point constants for the target.
Planned improvements for version 0.6 of @code{g77}
will give it the capabilities it needs to not have to crash the build
but rather generate correct code for the target.
(Currently, @code{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 @samp{EQUIVALENCE (I,R)} and @samp{DATA R/9.43578/}.)

@node Large Initialization
@subsection Initialization of Large Aggregate Areas

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

This size currently is quite small, since @code{g77}
currently has a known bug requiring too much memory
and time to handle such cases.
In @file{gcc/f/data.c}, the macro
@samp{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 @code{g77} for
the change to take effect.

Note that, as of version 0.5.18, improvements have
reduced the scope of the problem for @emph{sparse}
initialization of large arrays, especially those
with large, contiguous uninitialized areas.
However, the warning is issued at a point prior to
when @code{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.

@node Alpha Problems Fixed
@subsection Alpha Problems Fixed

@cindex Alpha, support
@cindex 64-bit systems
@code{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 @code{g77} was known to not work
properly on such configurations.

As of version 0.5.20, @code{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.

@node Quick Start
@section Quick Start
@cindex quick start

This procedure configures, builds, and installs @code{g77}
``out of the box'' and works on most UNIX systems.
Each command is identified by a unique number,
used in the explanatory text that follows.
For the most part, the output of each command is not shown,
though indications of the types of responses are given in a
few cases.

To perform this procedure, the installer must be logged
in as user @code{root}.
Much of it can be done while not logged in as @code{root},
and users experienced with UNIX administration should be
able to modify the procedure properly to do so.

Following traditional UNIX conventions, it is assumed that
the source trees for @code{g77} and @code{gcc} will be
placed in @file{/usr/src}.
It also is assumed that the source distributions themselves
already reside in @file{/usr/FSF}, a naming convention
used by the author of @code{g77} on his own system:

@example
/usr/FSF/gcc-@value{version-gcc}.tar.gz
/usr/FSF/g77-@value{version-g77}.tar.gz
@end example

@c (You can use @file{gcc-2.7.2.1.tar.gz} instead, or
@c the equivalent of it obtained by applying the
@c patch distributed as @file{gcc-2.7.2-2.7.2.1.diff.gz}
@c to version 2.7.2 of @code{gcc},
@c if you remember to make the appropriate adjustments in the
@c instructions below.)

@cindex SunOS4
Users of the following systems should not blindly follow
these quick-start instructions, because of problems their
systems have coping with straightforward installation of
@code{g77}:

@itemize @bullet
@item
SunOS4
@end itemize

Instead, see @ref{Complete Installation}, for detailed information
on how to configure, build, and install @code{g77} for your
particular system.
Also, see @ref{Trouble,,Known Causes of Trouble with GNU Fortran},
for information on bugs and other problems known to afflict the
installation process, and how to report newly discovered ones.

If your system is @emph{not} on the above list, and @emph{is}
a UNIX system or one of its variants, you should be able to
follow the instructions below.
If you vary @emph{any} of the steps below, you might run into
trouble, including possibly breaking existing programs for
other users of your system.
Before doing so, it is wise to review the explanations of some
of the steps.
These explanations follow this list of steps.

@example
sh[ 1]# @kbd{cd /usr/src}
@set source-dir 1
sh[ 2]# @kbd{gunzip -c < /usr/FSF/gcc-@value{version-gcc}.tar.gz | tar xf -}
[Might say "Broken pipe"...that is normal on some systems.]
@set unpack-gcc 2
sh[ 3]# @kbd{gunzip -c < /usr/FSF/g77-@value{version-g77}.tar.gz | tar xf -}
["Broken pipe" again possible.]
@set unpack-g77 3
sh[ 4]# @kbd{ln -s gcc-@value{version-gcc} gcc}
@set link-gcc 4
sh[ 5]# @kbd{ln -s g77-@value{version-g77} g77}
@set link-g77 5
sh[ 6]# @kbd{mv -i g77/* gcc}
[No questions should be asked by mv here; or, you made a mistake.]
@set merge-g77 6
sh[ 7]# @kbd{patch -p1 -E -V t -d gcc < gcc/f/gbe/@value{version-gcc}.diff}
[Unless patch complains about rejected patches, this step worked.]
@set apply-patch 7
sh[ 8]# @kbd{cd gcc}
sh[ 9]# @kbd{touch f77-install-ok}
[Do not do the above if your system already has an f77
command, unless you've checked that overwriting it
is okay.]
@set f77-install-ok 9
sh[10]# @kbd{touch f2c-install-ok}
[Do not do the above if your system already has an f2c
command, unless you've checked that overwriting it
is okay.  Else, @kbd{touch f2c-exists-ok}.]
@set f2c-install-ok 10
sh[11]# @kbd{./configure --prefix=/usr}
[Do not do the above if gcc is not installed in /usr/bin.
You might need a different @kbd{--prefix=@dots{}}, as
described below.]
@set configure-gcc 11
sh[12]# @kbd{make bootstrap}
[This takes a long time, and is where most problems occur.]
@set build-gcc 12
sh[13]# @kbd{make compare}
[This verifies that the compiler is `sane'.  Only
the file `f/zzz.o' (aka `tmp-foo1' and `tmp-foo2')
should be in the list of object files this command
prints as having different contents.  If other files
are printed, you have likely found a g77 bug.]
@set compare-gcc 13
sh[14]# @kbd{rm -fr stage1}
@set rm-stage1 14
sh[15]# @kbd{make -k install}
[The actual installation.]
@set install-g77 15
sh[16]# @kbd{g77 -v}
[Verify that g77 is installed, obtain version info.]
@set show-version 16
sh[17]#
@set end-procedure 17
@end example

@xref{Updating Documentation,,Updating Your Info Directory}, for
information on how to update your system's top-level @code{info}
directory to contain a reference to this manual, so that
users of @code{g77} can easily find documentation instead
of having to ask you for it.

Elaborations of many of the above steps follows:

@table @asis
@item Step @value{source-dir}: @kbd{cd /usr/src}
You can build @code{g77} pretty much anyplace.
By convention, this manual assumes @file{/usr/src}.
It might be helpful if other users on your system
knew where to look for the source code for the
installed version of @code{g77} and @code{gcc} in any case.

@c @item Step @value{unpack-gcc}: @kbd{gunzip -d @dots{}}
@c Here, you might wish to use @file{gcc-2.7.2.1.tar.gz}
@c instead, or apply @file{gcc-2.7.2-2.7.2.1.diff.gz} to achieve
@c similar results.

@item Step @value{unpack-g77}: @kbd{gunzip -d < /usr/FSF/g77-@value{version-g77}.tar.gz | tar xf -}
It is not always necessary to obtain the latest version of
@code{g77} as a complete @file{.tar.gz} file if you have
a complete, earlier distribution of @code{g77}.
If appropriate, you can unpack that earlier
version of @code{g77}, and then apply the appropriate patches
to achieve the same result---a source tree containing version
@value{version-g77} of @code{g77}.

@item Step @value{link-gcc}: @kbd{ln -s gcc-@value{version-gcc} gcc}
@item Step @value{link-g77}: @kbd{ln -s g77-@value{version-g77} g77}
These commands mainly help reduce typing,
and help reduce visual clutter in examples
in this manual showing what to type to install @code{g77}.

@c Of course, if appropriate, @kbd{ln -s gcc-2.7.2.1 gcc} or
@c similar.

@xref{Unpacking}, for information on
using distributions of @code{g77} made by organizations
other than the FSF.

@item Step @value{merge-g77}: @kbd{mv -i g77/* gcc}
After doing this, you can, if you like, type
@samp{rm g77} and @samp{rmdir g77-@value{version-g77}} to remove
the empty directory and the symbol link to it.
But, it might be helpful to leave them around as
quick reminders of which version(s) of @code{g77} are
installed on your system.

@xref{Unpacking}, for information
on the contents of the @file{g77} directory (as merged
into the @file{gcc} directory).

@item Step @value{apply-patch}: @kbd{patch -p1 @dots{}}
@c (Or `@kbd{@dots{} < gcc/f/gbe/2.7.2.1.diff}', if appropriate.)
@c
If you are using
GNU @code{patch} version @value{version-patch} or later,
this should produce a list of files patched.
(Other versions of @code{patch} might not work
properly.)

If messages about ``fuzz'', ``offset'', or
especially ``reject files'' are printed, it might
mean you applied the wrong patch file.
If you believe this is the case, it is best to restart
the sequence after deleting (or at least renaming to unused
names) the top-level directories for @code{g77} and @code{gcc}
and their symbolic links.

After this command finishes, the @code{gcc} directory might
have old versions of several files as saved by @code{patch}.
To remove these, after @kbd{cd gcc}, type @kbd{rm -i *.~*~}.

@xref{Merging Distributions}, for more information.

@emph{Note:} @code{gcc} versions circa 2.7.2.2 and 2.7.2.3
are known to have slightly differing versions of the
@code{gcc/ChangeLog} file,
depending on how they are obtained.
You can safely ignore diagnostics @code{patch} reports
when patching this particular file,
since it is purely a documentation file for implementors.
See @file{gcc/f/gbe/2.7.2.3.diff} for more information.

@item Step @value{f77-install-ok}: @kbd{touch f77-install-ok}
Don't do this if you don't want to overwrite an existing
version of @code{f77} (such as a native compiler, or a
script that invokes @code{f2c}).
Otherwise, installation will overwrite the @code{f77} command
and the @code{f77} man pages with copies of the corresponding
@code{g77} material.

@xref{Installing f77,,Installing @code{f77}}, for more
information.

@item Step @value{f2c-install-ok}: @kbd{touch f2c-install-ok}
Don't do this if you don't want to overwrite an existing
installation of @code{libf2c} (though, chances are, you do).
Instead, @kbd{touch f2c-exists-ok} to allow the installation
to continue without any error messages about @file{/usr/lib/libf2c.a}
already existing.

@xref{Installing f2c,,Installing @code{f2c}}, for more
information.

@item Step @value{configure-gcc}: @kbd{./configure --prefix=/usr}
This is where you specify that the @file{g77} executable is to be
installed in @file{/usr/bin/}, the @file{libf2c.a} library is
to be installed in @file{/usr/lib/}, and so on.

You should ensure that any existing installation of the @file{gcc}
executable is in @file{/usr/bin/}.
Otherwise, installing @code{g77} so that it does not fully
replace the existing installation of @code{gcc} is likely
to result in the inability to compile Fortran programs.

@xref{Where to Install,,Where in the World Does Fortran (and GNU CC) Go?},
for more information on determining where to install @code{g77}.
@xref{Configuring gcc}, for more information on the
configuration process triggered by invoking the @file{./configure}
script.

@item Step @value{build-gcc}: @kbd{make bootstrap}
@xref{Installation,,Installing GNU CC,
gcc,Using and Porting GNU CC}, for information
on the kinds of diagnostics you should expect during
this procedure.

@xref{Building gcc}, for complete @code{g77}-specific
information on this step.

@item Step @value{compare-gcc}: @kbd{make compare}
@xref{Bug Lists,,Where to Port Bugs}, for information
on where to report that you observed more than
@file{f/zzz.o} having different contents during this
phase.

@xref{Bug Reporting,,How to Report Bugs}, for
information on @emph{how} to report bugs like this.

@item Step @value{rm-stage1}: @kbd{rm -fr stage1}
You don't need to do this, but it frees up disk space.

@item Step @value{install-g77}: @kbd{make -k install}
If this doesn't seem to work, try:

@example
make -k install install-libf77 install-f2c-all
@end example

@xref{Installation of Binaries}, for more information.

@xref{Updating Documentation,,Updating Your Info Directory},
for information on entering this manual into your
system's list of texinfo manuals.

@item Step @value{show-version}: @kbd{g77 -v}
If this command prints approximately 25 lines of output,
including the GNU Fortran Front End version number (which
should be the same as the version number for the version
of @code{g77} you just built and installed) and the
version numbers for the three parts of the @code{libf2c}
library (@code{libF77}, @code{libI77}, @code{libU77}), and
those version numbers are all in agreement, then there is
a high likelihood that the installation has been successfully
completed.

You might consider doing further testing.
For example, log in as a non-privileged user, then create
a small Fortran program, such as:

@example
      PROGRAM SMTEST
      DO 10 I=1, 10
         PRINT *, 'Hello World #', I
10    CONTINUE
      END
@end example

Compile, link, and run the above program, and, assuming you named
the source file @file{smtest.f}, the session should look like this:

@example
sh# @kbd{g77 -o smtest smtest.f}
sh# @kbd{./smtest}
 Hello World # 1
 Hello World # 2
 Hello World # 3
 Hello World # 4
 Hello World # 5
 Hello World # 6
 Hello World # 7
 Hello World # 8
 Hello World # 9
 Hello World # 10
sh#
@end example

After proper installation, you don't
need to keep your gcc and g77 source and build directories
around anymore.
Removing them can free up a lot of disk space.
@end table

@node Complete Installation
@section Complete Installation

Here is the complete @code{g77}-specific information on how
to configure, build, and install @code{g77}.

@menu
* Unpacking::
* Merging Distributions::
* f77: Installing f77.
* f2c: Installing f2c.
* Patching GNU Fortran::
* Where to Install::
* Configuring gcc::
* Building gcc::
* Pre-installation Checks::
* Installation of Binaries::
* Updating Documentation::
* bison: Missing bison?.
* makeinfo: Missing makeinfo?.
@end menu

@node Unpacking
@subsection Unpacking
@cindex unpacking distributions
@cindex distributions, unpacking
@cindex code, source
@cindex source code
@cindex source tree
@cindex packages

The @code{gcc} source distribution is a stand-alone distribution.
It is designed to be unpacked (producing the @code{gcc}
source tree) and built as is, assuming certain
prerequisites are met (including the availability of compatible
UNIX programs such as @code{make}, @code{cc}, and so on).

However, before building @code{gcc}, you will want to unpack
and merge the @code{g77} distribution in with it, so that you
build a Fortran-capable version of @code{gcc}, which includes
the @code{g77} command, the necessary run-time libraries,
and this manual.

Unlike @code{gcc}, the @code{g77} source distribution
is @emph{not} a stand-alone distribution.
It is designed to be unpacked and, afterwards, immediately merged
into an applicable @code{gcc} source tree.
That is, the @code{g77} distribution @emph{augments} a
@code{gcc} distribution---without @code{gcc}, generally
only the documentation is immediately usable.

A sequence of commands typically used to unpack @code{gcc}
and @code{g77} is:

@example
sh# @kbd{cd /usr/src}
sh# @kbd{gunzip -c /usr/FSF/gcc-@value{version-gcc}.tar.gz | tar xf -}
sh# @kbd{gunzip -c /usr/FSF/g77-@value{version-g77}.tar.gz | tar xf -}
sh# @kbd{ln -s gcc-@value{version-gcc} gcc}
sh# @kbd{ln -s g77-@value{version-g77} g77}
sh# @kbd{mv -i g77/* gcc}
@end example

@emph{Notes:} The commands beginning with @samp{gunzip@dots{}} might
print @samp{Broken pipe@dots{}} as they complete.
That is nothing to worry about, unless you actually
@emph{hear} a pipe breaking.
The @code{ln} commands are helpful in reducing typing
and clutter in installation examples in this manual.
Hereafter, the top level of @code{gcc} source tree is referred to
as @file{gcc}, and the top level of just the @code{g77}
source tree (prior to issuing the @code{mv} command, above)
is referred to as @file{g77}.

There are three top-level names in a @code{g77} distribution:

@example
g77/COPYING.g77
g77/README.g77
g77/f
@end example

All three entries should be moved (or copied) into a @code{gcc}
source tree (typically named after its version number and
as it appears in the FSF distributions---e.g. @file{gcc-@value{version-gcc}}).

@file{g77/f} is the subdirectory containing all of the
code, documentation, and other information that is specific
to @code{g77}.
The other two files exist to provide information on @code{g77}
to someone encountering a @code{gcc} source tree with @code{g77}
already present, who has not yet read these installation
instructions and thus needs help understanding that the
source tree they are looking at does not come from a single
FSF distribution.
They also help people encountering an unmerged @code{g77} source
tree for the first time.

@cindex modifying @code{g77}
@cindex code, modifying
@cindex Pentium optimizations
@cindex optimizations, Pentium
@emph{Note:} Please use @strong{only} @code{gcc} and @code{g77}
source trees as distributed by the FSF.
Use of modified versions, such as the Pentium-specific-optimization
port of @code{gcc}, is likely to result in problems that appear to be
in the @code{g77} code but, in fact, are not.
Do not use such modified versions
unless you understand all the differences between them and the versions
the FSF distributes---in which case you should be able to modify the
@code{g77} (or @code{gcc}) source trees appropriately so @code{g77}
and @code{gcc} can coexist as they do in the stock FSF distributions.

@node Merging Distributions
@subsection Merging Distributions
@cindex merging distributions
@cindex @code{gcc} versions supported by @code{g77}
@cindex versions of @code{gcc}
@cindex support for @code{gcc} versions

After merging the @code{g77} source tree into the @code{gcc}
source tree, the final merge step is done by applying the
pertinent patches the @code{g77} distribution provides for
the @code{gcc} source tree.

Read the file @file{gcc/f/gbe/README}, and apply the appropriate
patch file for the version of the GNU CC compiler you have, if
that exists.
If the directory exists but the appropriate file
does not exist, you are using either an old, unsupported version,
or a release one that is newer than the newest @code{gcc} version
supported by the version of @code{g77} you have.

@cindex gcc version numbering
@cindex version numbering
@cindex g77 version number
@cindex GNU version numbering
As of version 0.5.18, @code{g77} modifies the version number
of @code{gcc} via the pertinent patches.
This is done because the resulting version of @code{gcc} is
deemed sufficiently different from the vanilla distribution
to make it worthwhile to present, to the user, information
signaling the fact that there are some differences.

GNU version numbers make it easy to figure out whether a
particular version of a distribution is newer or older than
some other version of that distribution.
The format is,
generally, @var{major}.@var{minor}.@var{patch}, with
each field being a decimal number.
(You can safely ignore
leading zeros; for example, 1.5.3 is the same as 1.5.03.)@ 
The @var{major} field only increases with time.
The other two fields are reset to 0 when the field to
their left is incremented; otherwise, they, too, only
increase with time.
So, version 2.6.2 is newer than version 2.5.8, and
version 3.0 is newer than both.
(Trailing @samp{.0} fields often are omitted in
announcements and in names for distributions and
the directories they create.)

If your version of @code{gcc} is older than the oldest version
supported by @code{g77} (as casually determined by listing
the contents of @file{gcc/f/gbe/}), you should obtain a newer,
supported version of @code{gcc}.
(You could instead obtain an older version of @code{g77},
or try and get your @code{g77} to work with the old
@code{gcc}, but neither approach is recommended, and
you shouldn't bother reporting any bugs you find if you
take either approach, because they're probably already
fixed in the newer versions you're not using.)

If your version of @code{gcc} is newer than the newest version
supported by @code{g77}, it is possible that your @code{g77}
will work with it anyway.
If the version number for @code{gcc} differs only in the
@var{patch} field, you might as well try applying the @code{g77} patch
that is for the newest version of @code{gcc} having the same
@var{major} and @var{minor} fields, as this is likely to work.

So, for example, if a particular version of @code{g77} has support for
@code{gcc} versions 2.7.0 and 2.7.1,
it is likely that @file{gcc-2.7.2} would work well with @code{g77}
by using the @file{2.7.1.diff} patch file provided
with @code{g77} (aside from some offsets reported by @code{patch},
which usually are harmless).

However, @file{gcc-2.8.0} would almost certainly
not work with that version of @code{g77} no matter which patch file was
used, so a new version of @code{g77} would be needed (and you should
wait for it rather than bothering the maintainers---@pxref{Changes,,
User-Visible Changes}).

@cindex distributions, why separate
@cindex separate distributions
@cindex why separate distributions
This complexity is the result of @code{gcc} and @code{g77} being
separate distributions.
By keeping them separate, each product is able to be independently
improved and distributed to its user base more frequently.

However, @code{g77} often requires changes to contemporary
versions of @code{gcc}.
Also, the GBE interface defined by @code{gcc} typically
undergoes some incompatible changes at least every time the
@var{minor} field of the version number is incremented,
and such changes require corresponding changes to
the @code{g77} front end (FFE).

It is hoped that the GBE interface, and the @code{gcc} and
@code{g77} products in general, will stabilize sufficiently
for the need for hand-patching to disappear.

If you are using
GNU @code{patch} version @value{version-patch} or later,
this should produce a list of files patched.
(Other versions of @code{patch} might not work
properly.)

If messages about ``fuzz'', ``offset'', or
especially ``reject files'' are printed, it might
mean you applied the wrong patch file.
If you believe this is the case, it is best to restart
the sequence after deleting (or at least renaming to unused
names) the top-level directories for @code{g77} and @code{gcc}
and their symbolic links.
That is because @code{patch} might have partially patched
some @code{gcc} source files, so reapplying the correct
patch file might result in the correct patches being
applied incorrectly (due to the way @code{patch} necessarily
works).

After @code{patch} finishes, the @code{gcc} directory might
have old versions of several files as saved by @code{patch}.
To remove these, after @kbd{cd gcc}, type @kbd{rm -i *.~*~}.

@emph{Note:} @code{gcc} versions circa 2.7.2.2 and 2.7.2.3
are known to have slightly differing versions of the
@code{gcc/ChangeLog} file,
depending on how they are obtained.
You can safely ignore diagnostics @code{patch} reports
when patching this particular file,
since it is purely a documentation file for implementors.
See @file{gcc/f/gbe/2.7.2.3.diff} for more information.

@pindex config-lang.in
@emph{Note:} @code{g77}'s configuration file @file{gcc/f/config-lang.in}
ensures that the source code for the version of @code{gcc}
being configured has at least one indication of being patched
as required specifically by @code{g77}.
This configuration-time
checking should catch failure to apply the correct patch and,
if so caught, should abort the configuration with an explanation.
@emph{Please} do not try to disable the check,
otherwise @code{g77} might well appear to build
and install correctly, and even appear to compile correctly,
but could easily produce broken code.

@cindex creating patch files
@cindex patch files, creating
@pindex gcc/f/gbe/
@samp{LC_ALL=C TZ=UTC0 diff -rcp2N} is used to create the patch files
in @file{gcc/f/gbe/}.

@node Installing f77
@subsection Installing @code{f77}
@cindex f77 command
@cindex commands, f77
@cindex native compiler

You should decide whether you want installation of @code{g77}
to also install an @code{f77} command.
On systems with a native @code{f77}, this is not
normally desired, so @code{g77} does not do this by
default.

@pindex f77-install-ok
@vindex F77_INSTALL_FLAG
If you want @code{f77} installed, create the file @file{f77-install-ok}
(e.g. via the UNIX command @samp{touch f77-install-ok}) in the
source or build top-level directory (the same directory in
which the @code{g77} @file{f} directory resides, not the @file{f} directory
itself), or edit @file{gcc/f/Make-lang.in} and change the definition
of the @samp{F77_INSTALL_FLAG} macro appropriately.

Usually, this means that, after typing @samp{cd gcc}, you
would type @samp{touch f77-install-ok}.

When you enable installation of @code{f77}, either a link to or a
direct copy of the @code{g77} command is made.
Similarly, @file{f77.1} is installed as a man page.

(The @code{uninstall} target in the @file{gcc/Makefile} also tests
this macro and file, when invoked, to determine whether to delete the
installed copies of @code{f77} and @file{f77.1}.)

@emph{Note:} No attempt is yet made
to install a program (like a shell script) that provides
compatibility with any other @code{f77} programs.
Only the most rudimentary invocations of @code{f77} will
work the same way with @code{g77}.

@node Installing f2c
@subsection Installing @code{f2c}

Currently, @code{g77} does not include @code{f2c} itself in its
distribution.
However, it does include a modified version of the @code{libf2c}.
This version is normally compatible with @code{f2c}, but has been
modified to meet the needs of @code{g77} in ways that might possibly
be incompatible with some versions or configurations of @code{f2c}.

Decide how installation of @code{g77} should affect any existing installation
of @code{f2c} on your system.

@pindex f2c
@pindex f2c.h
@pindex libf2c.a
@pindex libF77.a
@pindex libI77.a
If you do not have @code{f2c} on your system (e.g. no @file{/usr/bin/f2c},
no @file{/usr/include/f2c.h}, and no @file{/usr/lib/libf2c.a},
@file{/usr/lib/libF77.a}, or @file{/usr/lib/libI77.a}), you don't need to
be concerned with this item.

If you do have @code{f2c} on your system, you need to decide how users
of @code{f2c} will be affected by your installing @code{g77}.
Since @code{g77} is
currently designed to be object-code-compatible with @code{f2c} (with
very few, clear exceptions), users of @code{f2c} might want to combine
@code{f2c}-compiled object files with @code{g77}-compiled object files in a
single executable.

To do this, users of @code{f2c} should use the same copies of @file{f2c.h} and
@file{libf2c.a} that @code{g77} uses (and that get built as part of
@code{g77}).

If you do nothing here, the @code{g77} installation process will not
overwrite the @file{include/f2c.h} and @file{lib/libf2c.a} files with its
own versions, and in fact will not even install @file{libf2c.a} for use
with the newly installed versions of @code{gcc} and @code{g77} if it sees
that @file{lib/libf2c.a} exists---instead, it will print an explanatory
message and skip this part of the installation.

@pindex f2c-install-ok
@vindex F2C_INSTALL_FLAG
To install @code{g77}'s versions of @file{f2c.h} and @file{libf2c.a}
in the appropriate
places, create the file @file{f2c-install-ok} (e.g. via the UNIX
command @samp{touch f2c-install-ok}) in the source or build top-level
directory (the same directory in which the @code{g77} @file{f} directory
resides, not the @file{f} directory itself), or edit @file{gcc/f/Make-lang.in}
and change the definition of the @samp{F2C_INSTALL_FLAG} macro appropriately.

Usually, this means that, after typing @samp{cd gcc}, you
would type @samp{touch f2c-install-ok}.

Make sure that when you enable the overwriting of @file{f2c.h}
and @file{libf2c.a}
as used by @code{f2c}, you have a recent and properly configured version of
@file{bin/f2c} so that it generates code that is compatible with @code{g77}.

@pindex f2c-exists-ok
@vindex F2CLIBOK
If you don't want installation of @code{g77} to overwrite @code{f2c}'s existing
installation, but you do want @code{g77} installation to proceed with
installation of its own versions of @file{f2c.h} and @file{libf2c.a} in places
where @code{g77} will pick them up (even when linking @code{f2c}-compiled
object files---which might lead to incompatibilities), create
the file @file{f2c-exists-ok} (e.g. via the UNIX command
@samp{touch f2c-exists-ok}) in the source or build top-level directory,
or edit @file{gcc/f/Make-lang.in} and change the definition of the
@samp{F2CLIBOK} macro appropriately.

@node Patching GNU Fortran
@subsection Patching GNU Fortran

If you're using a SunOS4 system, you'll need to make the following
change to @file{gcc/f/proj.h}: edit the line reading

@example
#define FFEPROJ_STRTOUL 1  @dots{}
@end example

@noindent
by replacing the @samp{1} with @samp{0}.
Or, you can avoid editing the source by adding
@example
CFLAGS='-DFFEPROJ_STRTOUL=0 -g -O'
@end example
to the command line for @code{make} when you invoke it.
(@samp{-g} is the default for @samp{CFLAGS}.)

This causes a minimal version of @code{strtoul()} provided
as part of the @code{g77} distribution to be compiled and
linked into whatever @code{g77} programs need it, since
some systems (like SunOS4 with only the bundled compiler and its
runtime) do not provide this function in their system libraries.

Similarly, a minimal version of @code{bsearch()} is available
and can be enabled by editing a line similar to the one
for @code{strtoul()} above in @file{gcc/f/proj.h}, if
your system libraries lack @code{bsearch()}.
The method of overriding @samp{X_CFLAGS} may also be used.

These are not problems with @code{g77}, which requires an
ANSI C environment.
You should upgrade your system to one that provides
a full ANSI C environment, or encourage the maintainers
of @code{gcc} to provide one to all @code{gcc}-based
compilers in future @code{gcc} distributions.

@xref{Problems Installing}, for more information on
why @code{strtoul()} comes up missing and on approaches
to dealing with this problem that have already been tried.

@node Where to Install
@subsection Where in the World Does Fortran (and GNU CC) Go?
@cindex language f77 not recognized
@cindex gcc will not compile Fortran programs

Before configuring, you should make sure you know
where you want the @code{g77} and @code{gcc}
binaries to be installed after they're built,
because this information is given to the configuration
tool and used during the build itself.

A @code{g77} installation necessarily requires installation of
a @code{g77}-aware version of @code{gcc}, so that the @code{gcc}
command recognizes Fortran source files and knows how to compile
them.

For this to work, the version of @code{gcc} that you will be building
as part of @code{g77} @strong{must} be installed as the ``active''
version of @code{gcc} on the system.

Sometimes people make the mistake of installing @code{gcc} as
@file{/usr/local/bin/gcc},
leaving an older, non-Fortran-aware version in @file{/usr/bin/gcc}.
(Or, the opposite happens.)@ 
This can result in @code{g77} being unable to compile Fortran
source files, because when it calls on @code{gcc} to do the
actual compilation, @code{gcc} complains that it does not
recognize the language, or the file name suffix.

So, determine whether @code{gcc} already is installed on your system,
and, if so, @emph{where} it is installed, and prepare to configure the
new version of @code{gcc} you'll be building so that it installs
over the existing version of @code{gcc}.

You might want to back up your existing copy of @file{bin/gcc}, and
the entire @file{lib/} directory, before
you perform the actual installation (as described in this manual).

Existing @code{gcc} installations typically are
found in @file{/usr} or @file{/usr/local}.
If you aren't certain where the currently
installed version of @code{gcc} and its
related programs reside, look at the output
of this command:

@example
gcc -v -o /tmp/delete-me -xc /dev/null -xnone
@end example

All sorts of interesting information on the locations of various
@code{gcc}-related programs and data files should be visible
in the output of the above command.
(The output also is likely to include a diagnostic from
the linker, since there's no @samp{main_()} function.)
However, you do have to sift through it yourself; @code{gcc}
currently provides no easy way to ask it where it is installed
and where it looks for the various programs and data files it
calls on to do its work.

Just @emph{building} @code{g77} should not overwrite any installed
programs---but, usually, after you build @code{g77}, you will want
to install it, so backing up anything it might overwrite is
a good idea.
(This is true for any package, not just @code{g77},
though in this case it is intentional that @code{g77} overwrites
@code{gcc} if it is already installed---it is unusual that
the installation process for one distribution intentionally
overwrites a program or file installed by another distribution.)

Another reason to back up the existing version first,
or make sure you can restore it easily, is that it might be
an older version on which other users have come to depend
for certain behaviors.
However, even the new version of @code{gcc} you install
will offer users the ability to specify an older version of
the actual compilation programs if desired, and these
older versions need not include any @code{g77} components.
@xref{Target Options,,Specifying Target Machine and Compiler Version,
gcc,Using and Porting GNU CC}, for information on the @samp{-V}
option of @code{gcc}.

@node Configuring gcc
@subsection Configuring GNU CC

@code{g77} is configured automatically when you configure
@code{gcc}.
There are two parts of @code{g77} that are configured in two
different ways---@code{g77}, which ``camps on'' to the
@code{gcc} configuration mechanism, and @code{libf2c}, which
uses a variation of the GNU @code{autoconf} configuration
system.

Generally, you shouldn't have to be concerned with
either @code{g77} or @code{libf2c} configuration, unless
you're configuring @code{g77} as a cross-compiler.
In this case, the @code{libf2c} configuration, and possibly the
@code{g77} and @code{gcc} configurations as well,
might need special attention.
(This also might be the case if you're porting @code{gcc} to
a whole new system---even if it is just a new operating system
on an existing, supported CPU.)

To configure the system, see
@ref{Installation,,Installing GNU CC,gcc,Using and Porting GNU CC},
following the instructions for running @file{./configure}.
Pay special attention to the @samp{--prefix=} option, which
you almost certainly will need to specify.

(Note that @code{gcc} installation information is provided
as a straight text file in @file{gcc/INSTALL}.)

The information printed by the invocation of @file{./configure}
should show that the @file{f} directory (the Fortran language)
has been configured.
If it does not, there is a problem.

@emph{Note:} Configuring with the @samp{--srcdir} argument is known
to work with GNU @code{make}, but it is not known to work with
other variants of @code{make}.
Irix5.2 and SunOS4.1 versions of @code{make} definitely
won't work outside the source directory at present.
@code{g77}'s
portion of the @file{configure} script issues a warning message
about this when you configure for building binaries outside
the source directory.

@node Building gcc
@subsection Building GNU CC
@cindex building @code{gcc}
@cindex building @code{g77}

@vindex LANGUAGES
Building @code{g77} requires building enough of @code{gcc} that
these instructions assume you're going to build all of
@code{gcc}, including @code{g++}, @code{protoize}, and so on.
You can save a little time and disk space by changes the
@samp{LANGUAGES} macro definition in @code{gcc/Makefile.in}
or @code{gcc/Makefile}, but if you do that, you're on your own.
One change is almost @emph{certainly} going to cause failures:
removing @samp{c} or @samp{f77} from the definition of the
@samp{LANGUAGES} macro.

After configuring @code{gcc}, which configures @code{g77} and
@code{libf2c} automatically, you're ready to start the actual
build by invoking @code{make}.

@pindex configure
@emph{Note:} You @strong{must} have run @file{./configure}
before you run @code{make}, even if you're
using an already existing @code{gcc} development directory, because
@file{./configure} does the work to recognize that you've added
@code{g77} to the configuration.

There are two general approaches to building GNU CC from
scratch:

@table @dfn
@item bootstrap
This method uses minimal native system facilities to
build a barebones, unoptimized @code{gcc}, that is then
used to compile (``bootstrap'') the entire system.

@item straight
This method assumes a more complete native system
exists, and uses that just once to build the entire
system.
@end table

On all systems without a recent version of @code{gcc}
already installed, the @i{bootstrap} method must be
used.
In particular, @code{g77} uses extensions to the C
language offered, apparently, only by @code{gcc}.

On most systems with a recent version of @code{gcc}
already installed, the @i{straight} method can be
used.
This is an advantage, because it takes less CPU time
and disk space for the build.
However, it does require that the system have fairly
recent versions of many GNU programs and other
programs, which are not enumerated here.

@menu
* Bootstrap Build::  For all systems.
* Straight Build::   For systems with a recent version of @code{gcc}.
@end menu

@node Bootstrap Build
@subsubsection Bootstrap Build
@cindex bootstrap build
@cindex build, bootstrap

A complete bootstrap build is done by issuing a command
beginning with @samp{make bootstrap @dots{}}, as
described in @ref{Installation,,Installing GNU CC,
gcc,Using and Porting GNU CC}.
This is the most reliable form of build, but it does require
the most disk space and CPU time, since the complete system
is built twice (in Stages 2 and 3), after an initial build
(during Stage 1) of a minimal @code{gcc} compiler using
the native compiler and libraries.

You might have to, or want to, control the way a bootstrap
build is done by entering the @code{make} commands to build
each stage one at a time, as described in the @code{gcc}
manual.
For example, to save time or disk space, you might want
to not bother doing the Stage 3 build, in which case you
are assuming that the @code{gcc} compiler you have built
is basically sound (because you are giving up the opportunity
to compare a large number of object files to ensure they're
identical).

To save some disk space during installation, after Stage 2
is built, you can type @samp{rm -fr stage1} to remove the
binaries built during Stage 1.

@emph{Note:} @xref{Object File Differences}, for information on
expected differences in object files produced during Stage 2 and
Stage 3 of a bootstrap build.
These differences will be encountered as a result of using
the @samp{make compare} or similar command sequence recommended
by the GNU CC installation documentation.

Also, @xref{Installation,,Installing GNU CC,gcc,Using and Porting GNU CC},
for important information on building @code{gcc} that is
not described in this @code{g77} manual.
For example, explanations of diagnostic messages
and whether they're expected, or indicate trouble,
are found there.

@node Straight Build
@subsubsection Straight Build
@cindex straight build
@cindex build, straight

If you have a recent version of @code{gcc}
already installed on your system, and if you're
reasonably certain it produces code that is
object-compatible with the version of @code{gcc}
you want to build as part of building @code{g77},
you can save time and disk space by doing a straight
build.

To build just the C and Fortran compilers and the
necessary run-time libraries, issue the following
command:

@example
make -k CC=gcc LANGUAGES=f77 all g77
@end example

(The @samp{g77} target is necessary because the @code{gcc}
build procedures apparently do not automatically build
command drivers for languages in subdirectories.
It's the @samp{all} target that triggers building
everything except, apparently, the @code{g77} command
itself.)

If you run into problems using this method, you have
two options:

@itemize @bullet
@item
Abandon this approach and do a bootstrap build.

@item
Try to make this approach work by diagnosing the
problems you're running into and retrying.
@end itemize

Especially if you do the latter, you might consider
submitting any solutions as bug/fix reports.
@xref{Trouble,,Known Causes of Trouble with GNU Fortran}.

However, understand that many problems preventing a
straight build from working are not @code{g77} problems,
and, in such cases, are not likely to be addressed in
future versions of @code{g77}.

@node Pre-installation Checks
@subsection Pre-installation Checks
@cindex pre-installation checks
@cindex installing, checking before

Before installing the system, which includes installing
@code{gcc}, you might want to do some minimum checking
to ensure that some basic things work.

Here are some commands you can try, and output typically
printed by them when they work:

@example
sh# @kbd{cd /usr/src/gcc}
sh# @kbd{./g77 --driver=./xgcc -B./ -v}
g77 version @value{version-g77}
 ./xgcc -B./ -v -fnull-version -o /tmp/gfa18047 @dots{}
Reading specs from ./specs
gcc version @value{version-gcc-patched}
 ./cpp -lang-c -v -isystem ./include -undef @dots{}
GNU CPP version @value{version-gcc-patched} (Linux/Alpha)
#include "..." search starts here:
#include <...> search starts here:
 ./include
 /usr/local/include
 /usr/alpha-unknown-linux/include
 /usr/lib/gcc-lib/alpha-unknown-linux/@value{version-gcc-patched}/include
 /usr/include
End of search list.
 ./f771 /tmp/cca18048.i -fset-g77-defaults -quiet -dumpbase @dots{}
GNU F77 version @value{version-gcc-patched} (Linux/Alpha) compiled @dots{}
GNU Fortran Front End version @value{version-g77} compiled: @dots{}
 as -nocpp -o /tmp/cca180481.o /tmp/cca18048.s
 ld -G 8 -O1 -o /tmp/gfa18047 /usr/lib/crt0.o -L. @dots{}
__G77_LIBF77_VERSION__: @value{version-g77}
@@(#)LIBF77 VERSION 19970404
__G77_LIBI77_VERSION__: @value{version-g77}
@@(#) LIBI77 VERSION pjw,dmg-mods 19970816
__G77_LIBU77_VERSION__: @value{version-g77}
@@(#) LIBU77 VERSION 19970609
sh# @kbd{./xgcc -B./ -v -o /tmp/delete-me -xc /dev/null -xnone}
Reading specs from ./specs
gcc version @value{version-gcc-patched}
 ./cpp -lang-c -v -isystem ./include -undef @dots{}
GNU CPP version @value{version-gcc-patched} (Linux/Alpha)
#include "..." search starts here:
#include <...> search starts here:
 ./include
 /usr/local/include
 /usr/alpha-unknown-linux/include
 /usr/lib/gcc-lib/alpha-unknown-linux/@value{version-gcc-patched}/include
 /usr/include
End of search list.
 ./cc1 /tmp/cca18063.i -quiet -dumpbase null.c -version @dots{}
GNU C version @value{version-gcc-patched} (Linux/Alpha) compiled @dots{}
 as -nocpp -o /tmp/cca180631.o /tmp/cca18063.s
 ld -G 8 -O1 -o /tmp/delete-me /usr/lib/crt0.o -L. @dots{}
/usr/lib/crt0.o: In function `__start':
crt0.S:110: undefined reference to `main'
/usr/lib/crt0.o(.lita+0x28): undefined reference to `main'
sh#
@end example

(Note that long lines have been truncated, and @samp{@dots{}}
used to indicate such truncations.)

The above two commands test whether @code{g77} and @code{gcc},
respectively, are able to compile empty (null) source files,
whether invocation of the C preprocessor works, whether libraries
can be linked, and so on.

If the output you get from either of the above two commands
is noticeably different, especially if it is shorter or longer
in ways that do not look consistent with the above sample
output, you probably should not install @code{gcc} and @code{g77}
until you have investigated further.

For example, you could try compiling actual applications and
seeing how that works.
(You might want to do that anyway, even if the above tests
work.)

To compile using the not-yet-installed versions of @code{gcc}
and @code{g77}, use the following commands to invoke them.

To invoke @code{g77}, type:

@example
/usr/src/gcc/g77 --driver=/usr/src/gcc/xgcc -B/usr/src/gcc/ @dots{}
@end example

To invoke @code{gcc}, type:

@example
/usr/src/gcc/xgcc -B/usr/src/gcc/ @dots{}
@end example

@node Installation of Binaries
@subsection Installation of Binaries
@cindex installation of binaries
@cindex @code{g77}, installation of
@cindex @code{gcc}, installation of

After configuring, building, and testing @code{g77} and @code{gcc},
when you are ready to install them on your system, type:

@example
make -k CC=gcc LANGUAGES=f77 install
@end example

As described in @ref{Installation,,Installing GNU CC,
gcc,Using and Porting GNU CC}, the values for
the @samp{CC} and @samp{LANGUAGES} macros should
be the same as those you supplied for the build
itself.

So, the details of the above command might vary
if you used a bootstrap build (where you might be
able to omit both definitions, or might have to
supply the same definitions you used when building
the final stage) or if you deviated from the
instructions for a straight build.

If the above command does not install @file{libf2c.a}
as expected, try this:

@example
make -k @dots{} install install-libf77 install-f2c-all
@end example

We don't know why some non-GNU versions of @code{make} sometimes
require this alternate command, but they do.
(Remember to supply the appropriate definitions for @samp{CC} and
@samp{LANGUAGES} where you see @samp{@dots{}} in the above command.)

Note that using the @samp{-k} option tells @code{make} to
continue after some installation problems, like not having
@code{makeinfo} installed on your system.
It might not be necessary for your system.

@node Updating Documentation
@subsection Updating Your Info Directory
@cindex updating info directory
@cindex info, updating directory
@cindex directory, updating info
@pindex /usr/info/dir
@pindex g77.info
@cindex texinfo
@cindex documentation

As part of installing @code{g77}, you should make sure users
of @code{info} can easily access this manual on-line.
Do this by making sure a line such as the following exists
in @file{/usr/info/dir}, or in whatever file is the top-level
file in the @code{info} directory on your system (perhaps
@file{/usr/local/info/dir}:

@example
* g77: (g77).           The GNU Fortran programming language.
@end example

If the menu in @file{dir} is organized into sections, @code{g77}
probably belongs in a section with a name such as one of
the following:

@itemize @bullet
@item
Fortran Programming

@item
Writing Programs

@item
Programming Languages

@item
Languages Other Than C

@item
Scientific/Engineering Tools

@item
GNU Compilers
@end itemize

@node Missing bison?
@subsection Missing @code{bison}?
@cindex @code{bison}
@cindex missing @code{bison}

If you cannot install @code{bison}, make sure you have started
with a @emph{fresh} distribution of @code{gcc}, do @emph{not}
do @samp{make maintainer-clean} (in other versions of @code{gcc},
this was called @samp{make realclean}), and, to ensure that
@code{bison} is not invoked by @code{make} during the build,
type these commands:

@example
sh# @kbd{cd gcc}
sh# @kbd{touch bi-parser.c bi-parser.h c-parse.c c-parse.h cexp.c}
sh# @kbd{touch cp/parse.c cp/parse.h objc-parse.c}
sh#
@end example

These commands update the date-time-modified information for
all the files produced by the various invocations of @code{bison}
in the current versions of @code{gcc}, so that @code{make} no
longer believes it needs to update them.
All of these files should already exist in a @code{gcc}
distribution, but the application of patches to upgrade
to a newer version can leave the modification information
set such that the @code{bison} input files look more ``recent''
than the corresponding output files.

@emph{Note:} New versions of @code{gcc} might change the set of
files it generates by invoking @code{bison}---if you cannot figure
out for yourself how to handle such a situation, try an
older version of @code{gcc} until you find someone who can
(or until you obtain and install @code{bison}).

@node Missing makeinfo?
@subsection Missing @code{makeinfo}?
@cindex @code{makeinfo}
@cindex missing @code{makeinfo}

If you cannot install @code{makeinfo}, either use the @code{-k} option when
invoking make to specify any of the @samp{install} or related targets,
or specify @samp{MAKEINFO=echo} on the @code{make} command line.

If you fail to do one of these things, some files, like @file{libf2c.a},
might not be installed, because the failed attempt by @code{make} to
invoke @code{makeinfo} causes it to cancel any further processing.

@node Distributing Binaries
@section Distributing Binaries
@cindex binaries, distributing
@cindex code, distributing

If you are building @code{g77} for distribution to others in binary form,
first make sure you are aware of your legal responsibilities (read
the file @file{gcc/COPYING} thoroughly).

Then, consider your target audience and decide where @code{g77} should
be installed.

For systems like GNU/Linux that have no native Fortran compiler (or
where @code{g77} could be considered the native compiler for Fortran and
@code{gcc} for C, etc.), you should definitely configure
@code{g77} for installation
in @file{/usr/bin} instead of @file{/usr/local/bin}.
Specify the
@samp{--prefix=/usr} option when running @file{./configure}.
You might
also want to set up the distribution so the @code{f77} command is a
link to @code{g77}---just make an empty file named @file{f77-install-ok} in
the source or build directory (the one in which the @file{f} directory
resides, not the @file{f} directory itself) when you specify one of the
@file{install} or @file{uninstall} targets in a @code{make} command.

For a system that might already have @code{f2c} installed, you definitely
will want to make another empty file (in the same directory) named
either @file{f2c-exists-ok} or @file{f2c-install-ok}.
Use the former if you
don't want your distribution to overwrite @code{f2c}-related files in existing
systems; use the latter if you want to improve the likelihood that
users will be able to use both @code{f2c} and @code{g77} to compile code for a
single program without encountering link-time or run-time
incompatibilities.

(Make sure you clearly document, in the ``advertising'' for
your distribution, how installation of your distribution will
affect existing installations of @code{gcc}, @code{f2c},
@code{f77}, @file{libf2c.a}, and so on.
Similarly, you should clearly document any requirements
you assume are met by users of your distribution.)

For other systems with native @code{f77} (and @code{cc}) compilers,
configure @code{g77} as you (or most of your audience) would
configure @code{gcc} for their installations.
Typically this is for installation in
@file{/usr/local}, and would not include a copy of
@code{g77} named @code{f77}, so
users could still use the native @code{f77}.

In any case, for @code{g77} to work properly, you @strong{must} ensure
that the binaries you distribute include:

@table @file
@item bin/g77
This is the command most users use to compile Fortran.

@item bin/gcc
This is the command all users use to compile Fortran, either
directly or indirectly via the @code{g77} command.
The @file{bin/gcc} executable file must have been built
from a @code{gcc} source tree into which a @code{g77} source
tree was merged and configured, or it will not know how
to compile Fortran programs.

@item bin/f77
In installations with no non-GNU native Fortran
compiler, this is the same as @file{bin/g77}.
Otherwise, it should be omitted from the distribution,
so the one on already on a particular system does
not get overwritten.

@item info/g77.info*
This is the documentation for @code{g77}.
If it is not included, users will have trouble understanding
diagnostics messages and other such things, and will send
you a lot of email asking questions.

Please edit this documentation (by editing @file{gcc/f/*.tex}
and doing @samp{make doc} from the @file{/usr/src/gcc} directory)
to reflect any changes you've made to @code{g77}, or at
least to encourage users of your binary distribution to
report bugs to you first.

Also, whether you distribute binaries or install @code{g77}
on your own system, it might be helpful for everyone to
add a line listing this manual by name and topic to the
top-level @code{info} node in @file{/usr/info/dir}.
That way, users can find @code{g77} documentation more
easily.
@xref{Updating Documentation,,Updating Your Info Directory}.

@item man/man1/g77.1
This is the short man page for @code{g77}.
It is out of date, but you might as well include it
for people who really like man pages.

@item man/man1/f77.1
In installations where @code{f77} is the same as @code{g77},
this is the same as @file{man/man1/g77.1}.
Otherwise, it should be omitted from the distribution,
so the one already on a particular system does not
get overwritten.

@item lib/gcc-lib/@dots{}/f771
This is the actual Fortran compiler.

@item lib/gcc-lib/@dots{}/libf2c.a
This is the run-time library for @code{g77}-compiled programs.
@end table

Whether you want to include the slightly updated (and possibly
improved) versions of @code{cc1}, @code{cc1plus}, and whatever other
binaries get rebuilt with the changes the GNU Fortran distribution
makes to the GNU back end, is up to you.
These changes are
highly unlikely to break any compilers, and it is possible
they'll fix back-end bugs that can be demonstrated using front
ends other than GNU Fortran's.

Please assure users that unless
they have a specific need for their existing,
older versions of @code{gcc} command,
they are unlikely to experience any problems by overwriting
it with your version---though they could certainly protect
themselves by making backup copies first!
Otherwise, users might try and install your binaries
in a ``safe'' place, find they cannot compile Fortran
programs with your distribution (because, perhaps, they're
picking up their old version of the @code{gcc} command,
which does not recognize Fortran programs), and assume
that your binaries (or, more generally, GNU Fortran
distributions in general) are broken, at least for their
system.

Finally, @strong{please} ask for bug reports to go to you first, at least
until you're sure your distribution is widely used and has been
well tested.
This especially goes for those of you making any
changes to the @code{g77} sources to port @code{g77}, e.g. to OS/2.
@email{fortran@@gnu.org} has received a fair number of bug
reports that turned out to be problems with other peoples' ports
and distributions, about which nothing could be done for the
user.
Once you are quite certain a bug report does not involve
your efforts, you can forward it to us.
