This file documents the use and the internals of the GNU compiler.

Published by the Free Software Foundation

59 Temple Place - Suite 330

Boston, MA 02111-1307 USA

Copyright (C) 1988, 1989, 1992, 1993, 1994, 1995, 1996, 1997, 1998, 1999, 2000, 2001 Free Software Foundation, Inc.

Permission is granted to make and distribute verbatim copies of this manual provided the copyright notice and this permission notice are preserved on all copies.

Permission is granted to copy and distribute modified versions of this manual under the conditions for verbatim copying, provided also that the sections entitled ``GNU General Public License'' and ``Funding for Free Software'' are included exactly as in the original, and provided that the entire resulting derived work is distributed under the terms of a permission notice identical to this one.

Permission is granted to copy and distribute translations of this manual into another language, under the above conditions for modified versions, except that the sections entitled ``GNU General Public License'' and ``Funding for Free Software'', and this permission notice, may be included in translations approved by the Free Software Foundation instead of in the original English.

Introduction
************

This manual documents how to run, install and port the GNU compiler, as well as its new features and incompatibilities, and how to report bugs.  It corresponds to GCC version 3.1.

Compile C, C++, Objective C, Fortran, Java or CHILL
***************************************************

Several versions of the compiler (C, C++, Objective C, Fortran, Java and CHILL) are integrated; this is why we use the name ``GNU Compiler Collection''. GCC can compile programs written in any of these languages. The Fortran, CHILL, and Java compilers are described in separate manuals.

``GCC'' is a common shorthand term for the GNU Compiler Collection.  This is both the most general name for the compiler, and the name used when the emphasis is on compiling C programs (as the abbreviation formerly stood for ``GNU C Compiler'').

When referring to C++ compilation, it is usual to call the compiler ``G++''.  Since there is only one compiler, it is also accurate to call it ``GCC'' no matter what the language context; however, the term ``G++'' is more useful when the emphasis is on compiling C++ programs.

We use the name ``GCC'' to refer to the compilation system as a whole, and more specifically to the language-independent part of the compiler.  For example, we refer to the optimization options as affecting the behavior of ``GCC'' or sometimes just ``the compiler''.

Front ends for other languages, such as Ada 95 and Pascal exist but have not yet been integrated into GCC. These front-ends, like that for C++, are built in subdirectories of GCC and link to it.  The result is an integrated compiler that can compile programs written in C, C++, Objective C, or any of the languages for which you have installed front ends.

In this manual, we only discuss the options for the C, Objective-C, and C++ compilers and those of the GCC core.  Consult the documentation of the other front ends for the options to use when compiling programs written in other languages.

G++ is a compiler, not merely a preprocessor.  G++ builds object code directly from your C++ program source.  There is no intermediate C version of the program.  (By contrast, for example, some other implementations use a program that generates a C program from your C++ source.)  Avoiding an intermediate C representation of the program means that you get better object code, and better debugging information.  The GNU debugger, GDB, works with this information in the object code to give you comprehensive C++ source-level editing capabilities (see C and C++ (Debugging with GDB)).

Language Standards Supported by GCC
***********************************

For each language compiled by GCC for which there is a standard, GCC attempts to follow one or more versions of that standard, possibly with some exceptions, and possibly with some extensions.

GCC supports three versions of the C standard, although support for the most recent version is not yet complete.

The original ANSI C standard (X3.159-1989) was ratified in 1989 and published in 1990.  This standard was ratified as an ISO standard (ISO/IEC 9899:1990) later in 1990.  There were no technical differences between these publications, although the sections of the ANSI standard were renumbered and became clauses in the ISO standard. This standard, in both its forms, is commonly known as C89, or occasionally as C90, from the dates of ratification.  The ANSI standard, but not the ISO standard, also came with a Rationale document.  To select this standard in GCC, use one of the options -ansi, -std=c89 or -std=iso9899:1990; to obtain all the diagnostics required by the standard, you should also specify -pedantic (or -pedantic-errors if you want them to be errors rather than warnings).  See Options Controlling C Dialect.

Errors in the 1990 ISO C standard were corrected in two Technical Corrigenda published in 1994 and 1996.  GCC does not support the uncorrected version.

An amendment to the 1990 standard was published in 1995.  This amendment added digraphs and __STDC_VERSION__ to the language, but otherwise concerned the library.  This amendment is commonly known as AMD1; the amended standard is sometimes known as C94 or C95.  To select this standard in GCC, use the option -std=iso9899:199409 (with, as for other standard versions, -pedantic to receive all required diagnostics).

A new edition of the ISO C standard was published in 1999 as ISO/IEC 9899:1999, and is commonly known as C99.  GCC has incomplete support for this standard version; see http://gcc.gnu.org/c99status.html for details.  To select this standard, use -std=c99 or -std=iso9899:1999.  (While in development, drafts of this standard version were referred to as C9X.)

GCC also has some limited support for traditional (pre-ISO) C with the -traditional option.  This support may be of use for compiling some very old programs that have not been updated to ISO C, but should not be used for new programs.  It will not work with some modern C libraries such as the GNU C library.

By default, GCC provides some extensions to the C language that on rare occasions conflict with the C standard.  See Extensions to the C Language Family.  Use of the -std options listed above will disable these extensions where they conflict with the C standard version selected.  You may also select an extended version of the C language explicitly with -std=gnu89 (for C89 with GNU extensions) or -std=gnu99 (for C99 with GNU extensions).  The default, if no C language dialect options are given, is -std=gnu89; this will change to -std=gnu99 in some future release when the C99 support is complete.  Some features that are part of the C99 standard are accepted as extensions in C89 mode.

The ISO C standard defines (in clause 4) two classes of conforming implementation.  A conforming hosted implementation supports the whole standard including all the library facilities; a conforming freestanding implementation is only required to provide certain library facilities: those in <float.h>, <limits.h>, <stdarg.h>, and <stddef.h>; since AMD1, also those in <iso646.h>; and in C99, also those in <stdbool.h> and <stdint.h>.  In addition, complex types, added in C99, are not required for freestanding implementations.  The standard also defines two environments for programs, a freestanding environment, required of all implementations and which may not have library facilities beyond those required of freestanding implementations, where the handling of program startup and termination are implementation-defined, and a hosted environment, which is not required, in which all the library facilities are provided and startup is through a function int main (void) or int main (int, char *[]).  An OS kernel would be a freestanding environment; a program using the facilities of an operating system would normally be in a hosted implementation.

GNU CC aims towards being usable as a conforming freestanding implementation, or as the compiler for a conforming hosted implementation.  By default, it will act as the compiler for a hosted implementation, defining __STDC_HOSTED__ as 1 and presuming that when the names of ISO C functions are used, they have the semantics defined in the standard.  To make it act as a conforming freestanding implementation for a freestanding environment, use the option -ffreestanding; it will then define __STDC_HOSTED__ to 0 and not make assumptions about the meanings of function names from the standard library.  To build an OS kernel, you may well still need to make your own arrangements for linking and startup.  See Options Controlling C Dialect.

GNU CC does not provide the library facilities required only of hosted implementations, nor yet all the facilities required by C99 of freestanding implementations; to use the facilities of a hosted environment, you will need to find them elsewhere (for example, in the GNU C library).  See Standard Libraries.

For references to Technical Corrigenda, Rationale documents and information concerning the history of C that is available online, see http://gcc.gnu.org/readings.html

See The GNU Fortran Language (Using and Porting GNU Fortran), for details of the Fortran language supported by GCC.

See Compatibility with the Java Platform (GNU gcj), for details of compatibility between gcj and the Java Platform.

See Language Definition References (GNU Chill), for details of the CHILL standard.

     [file invoke.texi not included]

     [file install.texi not included]

     [file extend.texi not included]

     [file gcov.texi not included]

Known Causes of Trouble with GCC
********************************

This section describes known problems that affect users of GCC.  Most of these are not GCC bugs per se---if they were, we would fix them. But the result for a user may be like the result of a bug.

Some of these problems are due to bugs in other software, some are missing features that are too much work to add, and some are places where people's opinions differ as to what is best.

Actual Bugs We Haven't Fixed Yet
================================

  * The fixincludes script interacts badly with automounters; if the directory of system header files is automounted, it tends to be unmounted while fixincludes is running.  This would seem to be a bug in the automounter.  We don't know any good way to work around it.

  * The fixproto script will sometimes add prototypes for the sigsetjmp and siglongjmp functions that reference the jmp_buf type before that type is defined.  To work around this, edit the offending file and place the typedef in front of the prototypes.

  * When -pedantic-errors is specified, GCC will incorrectly give an error message when a function name is specified in an expression involving the comma operator.

Installation Problems
=====================

This is a list of problems (and some apparent problems which don't really mean anything is wrong) that show up during installation of GNU CC.

  * On certain systems, defining certain environment variables such as CC can interfere with the functioning of make.

  * If you encounter seemingly strange errors when trying to build the compiler in a directory other than the source directory, it could be because you have previously configured the compiler in the source directory.  Make sure you have done all the necessary preparations. See Other Dir.

  * If you build GCC on a BSD system using a directory stored in a System V file system, problems may occur in running fixincludes if the System V file system doesn't support symbolic links.  These problems result in a failure to fix the declaration of size_t in sys/types.h.  If you find that size_t is a signed type and that type mismatches occur, this could be the cause.

     The solution is not to use such a directory for building GCC.

  * Some commands executed when making the compiler may fail (return a non-zero status) and be ignored by make.  These failures, which are often due to files that were not found, are expected, and can safely be ignored.

  * It is normal to have warnings in compiling certain files about unreachable code and about enumeration type clashes.  These files' names begin with insn-.  Also, real.c may get some warnings that you can ignore.

  * Sometimes make recompiles parts of the compiler when installing the compiler.  In one case, this was traced down to a bug in make.  Either ignore the problem or switch to GNU Make.

  * On GNU/Linux SLS 1.01, there is a problem with libc.a: it does not contain the obstack functions.  However, GCC assumes that the obstack functions are in libc.a when it is the GNU C library.  To work around this problem, change the __GNU_LIBRARY__ conditional around line 31 to #if 1.

  * On SCO systems, when compiling GCC with the system's compiler, do not use -O.  Some versions of the system's compiler miscompile GCC with -O.

  * Sometimes on a Sun 4 you may observe a crash in the program genflags or genoutput while building GCC.  This is said to be due to a bug in sh.  You can probably get around it by running genflags or genoutput manually and then retrying the make.

  * On Solaris 2, executables of GCC version 2.0.2 are commonly available, but they have a bug that shows up when compiling current versions of GCC: undefined symbol errors occur during assembly if you use -g.

     The solution is to compile the current version of GCC without -g.  That makes a working compiler which you can use to recompile with -g.

  * Solaris 2 comes with a number of optional OS packages.  Some of these packages are needed to use GCC fully.  If you did not install all optional packages when installing Solaris, you will need to verify that the packages that GCC needs are installed.

     To check whether an optional package is installed, use the pkginfo command.  To add an optional package, use the pkgadd command.  For further details, see the Solaris documentation.

     For Solaris 2.0 and 2.1, GCC needs six packages: SUNWarc, SUNWbtool, SUNWesu, SUNWhea, SUNWlibm, and SUNWtoo.

     For Solaris 2.2, GCC needs an additional seventh package: SUNWsprot.

  * On Solaris 2, trying to use the linker and other tools in /usr/ucb to install GCC has been observed to cause trouble. For example, the linker may hang indefinitely.  The fix is to remove /usr/ucb from your PATH.

  * If you use the 1.31 version of the MIPS assembler (such as was shipped with Ultrix 3.1), you will need to use the -fno-delayed-branch switch when optimizing floating point code.  Otherwise, the assembler will complain when the GCC compiler fills a branch delay slot with a floating point instruction, such as add.d.

  * If on a MIPS system you get an error message saying ``does not have gp sections for all it's [sic] sectons [sic]'', don't worry about it.  This happens whenever you use GAS with the MIPS linker, but there is not really anything wrong, and it is okay to use the output file.  You can stop such warnings by installing the GNU linker.

     It would be nice to extend GAS to produce the gp tables, but they are optional, and there should not be a warning about their absence.

  * Users have reported some problems with version 2.0 of the MIPS compiler tools that were shipped with Ultrix 4.1.  Version 2.10 which came with Ultrix 4.2 seems to work fine.

     Users have also reported some problems with version 2.20 of the MIPS compiler tools that were shipped with RISC/os 4.x.  The earlier version 2.11 seems to work fine.

  * Some versions of the MIPS linker will issue an assertion failure when linking code that uses alloca against shared libraries on RISC-OS 5.0, and DEC's OSF/1 systems.  This is a bug in the linker, that is supposed to be fixed in future revisions. To protect against this, GCC passes -non_shared to the linker unless you pass an explicit -shared or -call_shared switch.

  * On System V release 3, you may get this error message while linking:

          ld fatal: failed to write symbol name SOMETHING
           in strings table for file WHATEVER

     This probably indicates that the disk is full or your ULIMIT won't allow the file to be as large as it needs to be.

     This problem can also result because the kernel parameter MAXUMEM is too small.  If so, you must regenerate the kernel and make the value much larger.  The default value is reported to be 1024; a value of 32768 is said to work.  Smaller values may also work.

  * On System V, if you get an error like this,

          /usr/local/lib/bison.simple: In function `yyparse':
          /usr/local/lib/bison.simple:625: virtual memory exhausted

     that too indicates a problem with disk space, ULIMIT, or MAXUMEM.

  * Current GCC versions probably do not work on version 2 of the NeXT operating system.

  * On NeXTStep 3.0, the Objective C compiler does not work, due, apparently, to a kernel bug that it happens to trigger.  This problem does not happen on 3.1.

  * On the Tower models 4N0 and 6N0, by default a process is not allowed to have more than one megabyte of memory.  GCC cannot compile itself (or many other programs) with -O in that much memory.

     To solve this problem, reconfigure the kernel adding the following line to the configuration file:

          MAXUMEM = 4096

  * On HP 9000 series 300 or 400 running HP-UX release 8.0, there is a bug in the assembler that must be fixed before GCC can be built.  This bug manifests itself during the first stage of compilation, while building libgcc2.a:

          _floatdisf
          cc1: warning: `-g' option not supported on this version of GCC
          cc1: warning: `-g1' option not supported on this version of GCC
          ./xgcc: Internal compiler error: program as got fatal signal 11

     A patched version of the assembler is available as the file ftp://altdorf.ai.mit.edu/archive/cph/hpux-8.0-assembler.  If you have HP software support, the patch can also be obtained directly from HP, as described in the following note:

          This is the patched assembler, to patch SR#1653-010439, where the assembler aborts on floating point constants.

          The bug is not really in the assembler, but in the shared library version of the function ``cvtnum(3c)''.  The bug on ``cvtnum(3c)'' is SR#4701-078451.  Anyway, the attached assembler uses the archive library version of ``cvtnum(3c)'' and thus does not exhibit the bug.

     This patch is also known as PHCO_4484.

  * On HP-UX version 8.05, but not on 8.07 or more recent versions, the fixproto shell script triggers a bug in the system shell. If you encounter this problem, upgrade your operating system or use BASH (the GNU shell) to run fixproto.

  * There may be similar problems on System V Release 3.1 on 386 systems.

  * On the Intel Paragon (an i860 machine), if you are using operating system version 1.0, you will get warnings or errors about redefinition of va_arg when you build GCC.

     If this happens, then you need to link most programs with the library iclib.a.  You must also modify stdio.h as follows: before the lines

          #if     defined(__i860__) && !defined(_VA_LIST)
          #include <va_list.h>

     insert the line

          #if __PGC__

     and after the lines

          extern int  vprintf(const char *, va_list );
          extern int  vsprintf(char *, const char *, va_list );
          #endif

     insert the line

          #endif /* __PGC__ */

     These problems don't exist in operating system version 1.1.

  * On the Altos 3068, programs compiled with GCC won't work unless you fix a kernel bug.  This happens using system versions V.2.2 1.0gT1 and V.2.2 1.0e and perhaps later versions as well.  See the file README.ALTOS.

  * You will get several sorts of compilation and linking errors on the we32k if you don't follow the special instructions.  See Configurations.

  * A bug in the HP-UX 8.05 (and earlier) shell will cause the fixproto program to report an error of the form:

          ./fixproto: sh internal 1K buffer overflow

     To fix this, change the first line of the fixproto script to look like:

          #!/bin/ksh

Cross-Compiler Problems
=======================

You may run into problems with cross compilation on certain machines, for several reasons.

  * Cross compilation can run into trouble for certain machines because some target machines' assemblers require floating point numbers to be written as integer constants in certain contexts.

     The compiler writes these integer constants by examining the floating point value as an integer and printing that integer, because this is simple to write and independent of the details of the floating point representation.  But this does not work if the compiler is running on a different machine with an incompatible floating point format, or even a different byte-ordering.

     In addition, correct constant folding of floating point values requires representing them in the target machine's format. (The C standard does not quite require this, but in practice it is the only way to win.)

     It is now possible to overcome these problems by defining macros such as REAL_VALUE_TYPE.  But doing so is a substantial amount of work for each target machine. See Cross-compilation.

  * At present, the program mips-tfile which adds debug support to object files on MIPS systems does not work in a cross compile environment.

Interoperation
==============

This section lists various difficulties encountered in using GNU C or GNU C++ together with other compilers or with the assemblers, linkers, libraries and debuggers on certain systems.

  * Objective C does not work on the RS/6000.

  * GNU C++ does not do name mangling in the same way as other C++ compilers.  This means that object files compiled with one compiler cannot be used with another.

     This effect is intentional, to protect you from more subtle problems. Compilers differ as to many internal details of C++ implementation, including: how class instances are laid out, how multiple inheritance is implemented, and how virtual function calls are handled.  If the name encoding were made the same, your programs would link against libraries provided from other compilers---but the programs would then crash when run.  Incompatible libraries are then detected at link time, rather than at run time.

  * Older GDB versions sometimes fail to read the output of GCC version 2.  If you have trouble, get GDB version 4.4 or later.

  * DBX rejects some files produced by GCC, though it accepts similar constructs in output from PCC.  Until someone can supply a coherent description of what is valid DBX input and what is not, there is nothing I can do about these problems.  You are on your own.

  * The GNU assembler (GAS) does not support PIC.  To generate PIC code, you must use some other assembler, such as /bin/as.

  * On some BSD systems, including some versions of Ultrix, use of profiling causes static variable destructors (currently used only in C++) not to be run.

  * Use of -I/usr/include may cause trouble.

     Many systems come with header files that won't work with GCC unless corrected by fixincludes.  The corrected header files go in a new directory; GCC searches this directory before /usr/include. If you use -I/usr/include, this tells GCC to search /usr/include earlier on, before the corrected headers.  The result is that you get the uncorrected header files.

     Instead, you should use these options (when compiling C programs):

          -I/usr/local/lib/gcc-lib/TARGET/VERSION/include -I/usr/include

     For C++ programs, GCC also uses a special directory that defines C++ interfaces to standard C subroutines.  This directory is meant to be searched before other standard include directories, so that it takes precedence.  If you are compiling C++ programs and specifying include directories explicitly, use this option first, then the two options above:

          -I/usr/local/lib/g++-include

  * On some SGI systems, when you use -lgl_s as an option, it gets translated magically to -lgl_s -lX11_s -lc_s. Naturally, this does not happen when you use GCC. You must specify all three options explicitly.

  * On a Sparc, GCC aligns all values of type double on an 8-byte boundary, and it expects every double to be so aligned.  The Sun compiler usually gives double values 8-byte alignment, with one exception: function arguments of type double may not be aligned.

     As a result, if a function compiled with Sun CC takes the address of an argument of type double and passes this pointer of type double * to a function compiled with GCC, dereferencing the pointer may cause a fatal signal.

     One way to solve this problem is to compile your entire program with GNU CC.  Another solution is to modify the function that is compiled with Sun CC to copy the argument into a local variable; local variables are always properly aligned.  A third solution is to modify the function that uses the pointer to dereference it via the following function access_double instead of directly with *:

          inline double
          access_double (double *unaligned_ptr)
          {
            union d2i { double d; int i[2]; };

            union d2i *p = (union d2i *) unaligned_ptr;
            union d2i u;

            u.i[0] = p->i[0];
            u.i[1] = p->i[1];

            return u.d;
          }

     Storing into the pointer can be done likewise with the same union.

  * On Solaris, the malloc function in the libmalloc.a library may allocate memory that is only 4 byte aligned.  Since GCC on the Sparc assumes that doubles are 8 byte aligned, this may result in a fatal signal if doubles are stored in memory allocated by the libmalloc.a library.

     The solution is to not use the libmalloc.a library.  Use instead malloc and related functions from libc.a; they do not have this problem.

  * Sun forgot to include a static version of libdl.a with some versions of SunOS (mainly 4.1).  This results in undefined symbols when linking static binaries (that is, if you use -static).  If you see undefined symbols _dlclose, _dlsym or _dlopen when linking, compile and link against the file mit/util/misc/dlsym.c from the MIT version of X windows.

  * The 128-bit long double format that the Sparc port supports currently works by using the architecturally defined quad-word floating point instructions.  Since there is no hardware that supports these instructions they must be emulated by the operating system.  Long doubles do not work in Sun OS versions 4.0.3 and earlier, because the kernel emulator uses an obsolete and incompatible format.  Long doubles do not work in Sun OS version 4.1.1 due to a problem in a Sun library. Long doubles do work on Sun OS versions 4.1.2 and higher, but GCC does not enable them by default.  Long doubles appear to work in Sun OS 5.x (Solaris 2.x).

  * On HP-UX version 9.01 on the HP PA, the HP compiler cc does not compile GCC correctly.  We do not yet know why.  However, GCC compiled on earlier HP-UX versions works properly on HP-UX 9.01 and can compile itself properly on 9.01.

  * On the HP PA machine, ADB sometimes fails to work on functions compiled with GCC.  Specifically, it fails to work on functions that use alloca or variable-size arrays.  This is because GCC doesn't generate HP-UX unwind descriptors for such functions.  It may even be impossible to generate them.

  * Debugging (-g) is not supported on the HP PA machine, unless you use the preliminary GNU tools (see Installation).

  * Taking the address of a label may generate errors from the HP-UX PA assembler.  GAS for the PA does not have this problem.

  * Using floating point parameters for indirect calls to static functions will not work when using the HP assembler.  There simply is no way for GCC to specify what registers hold arguments for static functions when using the HP assembler.  GAS for the PA does not have this problem.

  * In extremely rare cases involving some very large functions you may receive errors from the HP linker complaining about an out of bounds unconditional branch offset.  This used to occur more often in previous versions of GCC, but is now exceptionally rare.  If you should run into it, you can work around by making your function smaller.

  * GCC compiled code sometimes emits warnings from the HP-UX assembler of the form:

          (warning) Use of GR3 when
            frame >= 8192 may cause conflict.

     These warnings are harmless and can be safely ignored.

  * The current version of the assembler (/bin/as) for the RS/6000 has certain problems that prevent the -g option in GCC from working.  Note that Makefile.in uses -g by default when compiling libgcc2.c.

     IBM has produced a fixed version of the assembler.  The upgraded assembler unfortunately was not included in any of the AIX 3.2 update PTF releases (3.2.2, 3.2.3, or 3.2.3e).  Users of AIX 3.1 should request PTF U403044 from IBM and users of AIX 3.2 should request PTF U416277. See the file README.RS6000 for more details on these updates.

     You can test for the presence of a fixed assembler by using the command

          as -u < /dev/null

     If the command exits normally, the assembler fix already is installed. If the assembler complains that "-u" is an unknown flag, you need to order the fix.

  * On the IBM RS/6000, compiling code of the form

          extern int foo;

          ... foo ...

          static int foo;

     will cause the linker to report an undefined symbol foo. Although this behavior differs from most other systems, it is not a bug because redefining an extern variable as static is undefined in ISO C.

  * AIX on the RS/6000 provides support (NLS) for environments outside of the United States.  Compilers and assemblers use NLS to support locale-specific representations of various objects including floating-point numbers ("." vs "," for separating decimal fractions). There have been problems reported where the library linked with GCC does not produce the same floating-point formats that the assembler accepts. If you have this problem, set the LANG environment variable to "C" or "En_US".

  * Even if you specify -fdollars-in-identifiers, you cannot successfully use $ in identifiers on the RS/6000 due to a restriction in the IBM assembler.  GAS supports these identifiers.

  * On the RS/6000, XLC version 1.3.0.0 will miscompile jump.c.  XLC version 1.3.0.1 or later fixes this problem.  You can obtain XLC-1.3.0.2 by requesting PTF 421749 from IBM.

  * There is an assembler bug in versions of DG/UX prior to 5.4.2.01 that occurs when the fldcr instruction is used.  GCC uses fldcr on the 88100 to serialize volatile memory references.  Use the option -mno-serialize-volatile if your version of the assembler has this bug.

  * On VMS, GAS versions 1.38.1 and earlier may cause spurious warning messages from the linker.  These warning messages complain of mismatched psect attributes.  You can ignore them.  See VMS Install.

  * On NewsOS version 3, if you include both of the files stddef.h and sys/types.h, you get an error because there are two typedefs of size_t.  You should change sys/types.h by adding these lines around the definition of size_t:

          #ifndef _SIZE_T
          #define _SIZE_T
          ACTUAL TYPEDEF HERE
          #endif

  * On the Alliant, the system's own convention for returning structures and unions is unusual, and is not compatible with GCC no matter what options are used.

  * On the IBM RT PC, the MetaWare HighC compiler (hc) uses a different convention for structure and union returning.  Use the option -mhc-struct-return to tell GCC to use a convention compatible with it.

  * On Ultrix, the Fortran compiler expects registers 2 through 5 to be saved by function calls.  However, the C compiler uses conventions compatible with BSD Unix: registers 2 through 5 may be clobbered by function calls.

     GCC uses the same convention as the Ultrix C compiler.  You can use these options to produce code compatible with the Fortran compiler:

          -fcall-saved-r2 -fcall-saved-r3 -fcall-saved-r4 -fcall-saved-r5

  * On the WE32k, you may find that programs compiled with GCC do not work with the standard shared C library.  You may need to link with the ordinary C compiler.  If you do so, you must specify the following options:

          -L/usr/local/lib/gcc-lib/we32k-att-sysv/2.8.1 -lgcc -lc_s

     The first specifies where to find the library libgcc.a specified with the -lgcc option.

     GCC does linking by invoking ld, just as cc does, and there is no reason why it should matter which compilation program you use to invoke ld.  If someone tracks this problem down, it can probably be fixed easily.

  * On the Alpha, you may get assembler errors about invalid syntax as a result of floating point constants.  This is due to a bug in the C library functions ecvt, fcvt and gcvt.  Given valid floating point numbers, they sometimes print NaN.

  * On Irix 4.0.5F (and perhaps in some other versions), an assembler bug sometimes reorders instructions incorrectly when optimization is turned on.  If you think this may be happening to you, try using the GNU assembler; GAS version 2.1 supports ECOFF on Irix.

     Or use the -noasmopt option when you compile GCC with itself, and then again when you compile your program.  (This is a temporary kludge to turn off assembler optimization on Irix.)  If this proves to be what you need, edit the assembler spec in the file specs so that it unconditionally passes -O0 to the assembler, and never passes -O2 or -O3.

Problems Compiling Certain Programs
===================================

Certain programs have problems compiling.

  * Parse errors may occur compiling X11 on a Decstation running Ultrix 4.2 because of problems in DEC's versions of the X11 header files X11/Xlib.h and X11/Xutil.h.  People recommend adding -I/usr/include/mit to use the MIT versions of the header files, using the -traditional switch to turn off ISO C, or fixing the header files by adding this:

          #ifdef __STDC__
          #define NeedFunctionPrototypes 0
          #endif

  * On various 386 Unix systems derived from System V, including SCO, ISC, and ESIX, you may get error messages about running out of virtual memory while compiling certain programs.

     You can prevent this problem by linking GCC with the GNU malloc (which thus replaces the malloc that comes with the system).  GNU malloc is available as a separate package, and also in the file src/gmalloc.c in the GNU Emacs 19 distribution.

     If you have installed GNU malloc as a separate library package, use this option when you relink GCC:

          MALLOC=/usr/local/lib/libgmalloc.a

     Alternatively, if you have compiled gmalloc.c from Emacs 19, copy the object file to gmalloc.o and use this option when you relink GCC:

          MALLOC=gmalloc.o

Incompatibilities of GCC
========================

There are several noteworthy incompatibilities between GNU C and K&R (non-ISO) versions of C.  The -traditional option eliminates many of these incompatibilities, but not all, by telling GNU C to behave like a K&R C compiler.

  * GCC normally makes string constants read-only.  If several identical-looking string constants are used, GCC stores only one copy of the string.

     One consequence is that you cannot call mktemp with a string constant argument.  The function mktemp always alters the string its argument points to.

     Another consequence is that sscanf does not work on some systems when passed a string constant as its format control string or input. This is because sscanf incorrectly tries to write into the string constant.  Likewise fscanf and scanf.

     The best solution to these problems is to change the program to use char-array variables with initialization strings for these purposes instead of string constants.  But if this is not possible, you can use the -fwritable-strings flag, which directs GCC to handle string constants the same way most C compilers do. -traditional also has this effect, among others.

  * -2147483648 is positive.

     This is because 2147483648 cannot fit in the type int, so (following the ISO C rules) its data type is unsigned long int. Negating this value yields 2147483648 again.

  * GCC does not substitute macro arguments when they appear inside of string constants.  For example, the following macro in GCC

          #define foo(a) "a"

     will produce output "a" regardless of what the argument A is.

     The -traditional option directs GCC to handle such cases (among others) in the old-fashioned (non-ISO) fashion.

  * When you use setjmp and longjmp, the only automatic variables guaranteed to remain valid are those declared volatile.  This is a consequence of automatic register allocation.  Consider this function:

          jmp_buf j;

          foo ()
          {
            int a, b;

            a = fun1 ();
            if (setjmp (j))
              return a;

            a = fun2 ();
            /* longjmp (j) may occur in fun3. */
            return a + fun3 ();
          }

     Here a may or may not be restored to its first value when the longjmp occurs.  If a is allocated in a register, then its first value is restored; otherwise, it keeps the last value stored in it.

     If you use the -W option with the -O option, you will get a warning when GCC thinks such a problem might be possible.

     The -traditional option directs GNU C to put variables in the stack by default, rather than in registers, in functions that call setjmp.  This results in the behavior found in traditional C compilers.

  * Programs that use preprocessing directives in the middle of macro arguments do not work with GCC.  For example, a program like this will not work:

          foobar (
          #define luser
                  hack)

     ISO C does not permit such a construct.  It would make sense to support it when -traditional is used, but it is too much work to implement.

  * K&R compilers allow comments to cross over an inclusion boundary (i.e. started in an include file and ended in the including file).  I think this would be quite ugly and can't imagine it could be needed.

  * Declarations of external variables and functions within a block apply only to the block containing the declaration.  In other words, they have the same scope as any other declaration in the same place.

     In some other C compilers, a extern declaration affects all the rest of the file even if it happens within a block.

     The -traditional option directs GNU C to treat all extern declarations as global, like traditional compilers.

  * In traditional C, you can combine long, etc., with a typedef name, as shown here:

          typedef int foo;
          typedef long foo bar;

     In ISO C, this is not allowed: long and other type modifiers require an explicit int.  Because this criterion is expressed by Bison grammar rules rather than C code, the -traditional flag cannot alter it.

  * PCC allows typedef names to be used as function parameters.  The difficulty described immediately above applies here too.

  * When in -traditional mode, GCC allows the following erroneous pair of declarations to appear together in a given scope:

          typedef int foo;
          typedef foo foo;

  * GCC treats all characters of identifiers as significant, even when in -traditional mode.  According to K&R-1 (2.2), ``No more than the first eight characters are significant, although more may be used.''. Also according to K&R-1 (2.2), ``An identifier is a sequence of letters and digits; the first character must be a letter.  The underscore _ counts as a letter.'', but GCC also allows dollar signs in identifiers.

  * PCC allows whitespace in the middle of compound assignment operators such as +=.  GCC, following the ISO standard, does not allow this.  The difficulty described immediately above applies here too.

  * GCC complains about unterminated character constants inside of preprocessing conditionals that fail.  Some programs have English comments enclosed in conditionals that are guaranteed to fail; if these comments contain apostrophes, GCC will probably report an error.  For example, this code would produce an error:

          #if 0
          You can't expect this to work.
          #endif

     The best solution to such a problem is to put the text into an actual C comment delimited by /*...*/.  However, -traditional suppresses these error messages.

  * Many user programs contain the declaration long time ();.  In the past, the system header files on many systems did not actually declare time, so it did not matter what type your program declared it to return.  But in systems with ISO C headers, time is declared to return time_t, and if that is not the same as long, then long time (); is erroneous.

     The solution is to change your program to use appropriate system headers (<time.h> on systems with ISO C headers) and not to declare time if the system header files declare it, or failing that to use time_t as the return type of time.

  * When compiling functions that return float, PCC converts it to a double.  GCC actually returns a float.  If you are concerned with PCC compatibility, you should declare your functions to return double; you might as well say what you mean.

  * When compiling functions that return structures or unions, GCC output code normally uses a method different from that used on most versions of Unix.  As a result, code compiled with GCC cannot call a structure-returning function compiled with PCC, and vice versa.

     The method used by GCC is as follows: a structure or union which is 1, 2, 4 or 8 bytes long is returned like a scalar.  A structure or union with any other size is stored into an address supplied by the caller (usually in a special, fixed register, but on some machines it is passed on the stack).  The machine-description macros STRUCT_VALUE and STRUCT_INCOMING_VALUE tell GCC where to pass this address.

     By contrast, PCC on most target machines returns structures and unions of any size by copying the data into an area of static storage, and then returning the address of that storage as if it were a pointer value. The caller must copy the data from that memory area to the place where the value is wanted.  GCC does not use this method because it is slower and nonreentrant.

     On some newer machines, PCC uses a reentrant convention for all structure and union returning.  GCC on most of these machines uses a compatible convention when returning structures and unions in memory, but still returns small structures and unions in registers.

     You can tell GCC to use a compatible convention for all structure and union returning with the option -fpcc-struct-return.

  * GNU C complains about program fragments such as 0x74ae-0x4000 which appear to be two hexadecimal constants separated by the minus operator.  Actually, this string is a single preprocessing token. Each such token must correspond to one token in C.  Since this does not, GNU C prints an error message.  Although it may appear obvious that what is meant is an operator and two values, the ISO C standard specifically requires that this be treated as erroneous.

     A preprocessing token is a preprocessing number if it begins with a digit and is followed by letters, underscores, digits, periods and e+, e-, E+, E-, p+, p-, P+, or P- character sequences.  (In strict C89 mode, the sequences p+, p-, P+ and P- cannot appear in preprocessing numbers.)

     To make the above program fragment valid, place whitespace in front of the minus sign.  This whitespace will end the preprocessing number.

Fixed Header Files
==================

GCC needs to install corrected versions of some system header files. This is because most target systems have some header files that won't work with GCC unless they are changed.  Some have bugs, some are incompatible with ISO C, and some depend on special features of other compilers.

Installing GCC automatically creates and installs the fixed header files, by running a program called fixincludes (or for certain targets an alternative such as fixinc.svr4).  Normally, you don't need to pay attention to this.  But there are cases where it doesn't do the right thing automatically.

  * If you update the system's header files, such as by installing a new system version, the fixed header files of GCC are not automatically updated.  The easiest way to update them is to reinstall GCC.  (If you want to be clever, look in the makefile and you can find a shortcut.)

  * On some systems, in particular SunOS 4, header file directories contain machine-specific symbolic links in certain places.  This makes it possible to share most of the header files among hosts running the same version of SunOS 4 on different machine models.

     The programs that fix the header files do not understand this special way of using symbolic links; therefore, the directory of fixed header files is good only for the machine model used to build it.

     In SunOS 4, only programs that look inside the kernel will notice the difference between machine models.  Therefore, for most purposes, you need not be concerned about this.

     It is possible to make separate sets of fixed header files for the different machine models, and arrange a structure of symbolic links so as to use the proper set, but you'll have to do this by hand.

  * On Lynxos, GCC by default does not fix the header files.  This is because bugs in the shell cause the fixincludes script to fail.

     This means you will encounter problems due to bugs in the system header files.  It may be no comfort that they aren't GCC's fault, but it does mean that there's nothing for us to do about them.

Standard Libraries
==================

GCC by itself attempts to be a conforming freestanding implementation. See Language Standards Supported by GCC, for details of what this means.  Beyond the library facilities required of such an implementation, the rest of the C library is supplied by the vendor of the operating system.  If that C library doesn't conform to the C standards, then your programs might get warnings (especially when using -Wall) that you don't expect.

For example, the sprintf function on SunOS 4.1.3 returns char * while the C standard says that sprintf returns an int.  The fixincludes program could make the prototype for this function match the Standard, but that would be wrong, since the function will still return char *.

If you need a Standard compliant library, then you need to find one, as GCC does not provide one.  The GNU C library (called glibc) provides ISO C, POSIX, BSD, SystemV and X/Open compatibility for GNU/Linux and HURD-based GNU systems; no recent version of it supports other systems, though some very old versions did.  Version 2.2 of the GNU C library includes nearly complete C99 support.  You could also ask your operating system vendor if newer libraries are available.

Disappointments and Misunderstandings
=====================================

These problems are perhaps regrettable, but we don't know any practical way around them.

  * Certain local variables aren't recognized by debuggers when you compile with optimization.

     This occurs because sometimes GCC optimizes the variable out of existence.  There is no way to tell the debugger how to compute the value such a variable ``would have had'', and it is not clear that would be desirable anyway.  So GCC simply does not mention the eliminated variable when it writes debugging information.

     You have to expect a certain amount of disagreement between the executable and your source code, when you use optimization.

  * Users often think it is a bug when GCC reports an error for code like this:

          int foo (struct mumble *);

          struct mumble { ... };

          int foo (struct mumble *x)
          { ... }

     This code really is erroneous, because the scope of struct mumble in the prototype is limited to the argument list containing it. It does not refer to the struct mumble defined with file scope immediately below---they are two unrelated types with similar names in different scopes.

     But in the definition of foo, the file-scope type is used because that is available to be inherited.  Thus, the definition and the prototype do not match, and you get an error.

     This behavior may seem silly, but it's what the ISO standard specifies. It is easy enough for you to make your code work by moving the definition of struct mumble above the prototype.  It's not worth being incompatible with ISO C just to avoid an error for the example shown above.

  * Accesses to bitfields even in volatile objects works by accessing larger objects, such as a byte or a word.  You cannot rely on what size of object is accessed in order to read or write the bitfield; it may even vary for a given bitfield according to the precise usage.

     If you care about controlling the amount of memory that is accessed, use volatile but do not use bitfields.

  * GCC comes with shell scripts to fix certain known problems in system header files.  They install corrected copies of various header files in a special directory where only GCC will normally look for them.  The scripts adapt to various systems by searching all the system header files for the problem cases that we know about.

     If new system header files are installed, nothing automatically arranges to update the corrected header files.  You will have to reinstall GCC to fix the new header files.  More specifically, go to the build directory and delete the files stmp-fixinc and stmp-headers, and the subdirectory include; then do make install again.

  * On 68000 and x86 systems, for instance, you can get paradoxical results if you test the precise values of floating point numbers.  For example, you can find that a floating point value which is not a NaN is not equal to itself.  This results from the fact that the floating point registers hold a few more bits of precision than fit in a double in memory. Compiled code moves values between memory and floating point registers at its convenience, and moving them into memory truncates them.

     You can partially avoid this problem by using the -ffloat-store option (see Optimize Options).

  * On the MIPS, variable argument functions using varargs.h cannot have a floating point value for the first argument.  The reason for this is that in the absence of a prototype in scope, if the first argument is a floating point, it is passed in a floating point register, rather than an integer register.

     If the code is rewritten to use the ISO standard stdarg.h method of variable arguments, and the prototype is in scope at the time of the call, everything will work fine.

  * On the H8/300 and H8/300H, variable argument functions must be implemented using the ISO standard stdarg.h method of variable arguments.  Furthermore, calls to functions using stdarg.h variable arguments must have a prototype for the called function in scope at the time of the call.

Common Misunderstandings with GNU C++
=====================================

C++ is a complex language and an evolving one, and its standard definition (the ISO C++ standard) was only recently completed.  As a result, your C++ compiler may occasionally surprise you, even when its behavior is correct.  This section discusses some areas that frequently give rise to questions of this sort.

Declare and Define Static Members
---------------------------------

When a class has static data members, it is not enough to declare the static member; you must also define it.  For example:

     class Foo
     {
       ...
       void method();
       static int bar;
     };

This declaration only establishes that the class Foo has an int named Foo::bar, and a member function named Foo::method.  But you still need to define both method and bar elsewhere.  According to the ISO standard, you must supply an initializer in one (and only one) source file, such as:

     int Foo::bar = 0;

Other C++ compilers may not correctly implement the standard behavior. As a result, when you switch to g++ from one of these compilers, you may discover that a program that appeared to work correctly in fact does not conform to the standard: g++ reports as undefined symbols any static data members that lack definitions.

Temporaries May Vanish Before You Expect
----------------------------------------

It is dangerous to use pointers or references to portions of a temporary object.  The compiler may very well delete the object before you expect it to, leaving a pointer to garbage.  The most common place where this problem crops up is in classes like string classes, especially ones that define a conversion function to type char * or const char * -- which is one reason why the standard string class requires you to call the c_str member function.  However, any class that returns a pointer to some internal structure is potentially subject to this problem.

For example, a program may use a function strfunc that returns string objects, and another function charfunc that operates on pointers to char:

     string strfunc ();
     void charfunc (const char *);

     void
     f ()
     {
       const char *p = strfunc().c_str();
       ...
       charfunc (p);
       ...
       charfunc (p);
     }

In this situation, it may seem reasonable to save a pointer to the C string returned by the c_str member function and use that rather than call c_str repeatedly.  However, the temporary string created by the call to strfunc is destroyed after p is initialized, at which point p is left pointing to freed memory.

Code like this may run successfully under some other compilers, particularly obsolete cfront-based compilers that delete temporaries along with normal local variables.  However, the GNU C++ behavior is standard-conforming, so if your program depends on late destruction of temporaries it is not portable.

The safe way to write such code is to give the temporary a name, which forces it to remain until the end of the scope of the name.  For example:

     string& tmp = strfunc ();
     charfunc (tmp.c_str ());

Implicit Copy-Assignment for Virtual Bases
------------------------------------------

When a base class is virtual, only one subobject of the base class belongs to each full object. Also, the constructors and destructors are invoked only once, and called from the most-derived class. However, such objects behave unspecified when being assigned. For example:

     struct Base{
       char *name;
       Base(char *n) : name(strdup(n)){}
       Base& operator= (const Base& other){
        free (name);
        name = strdup (other.name);
       }
     };

     struct A:virtual Base{
       int val;
       A():Base("A"){}
     };

     struct B:virtual Base{
       int bval;
       B():Base("B"){}
     };

     struct Derived:public A, public B{
       Derived():Base("Derived"){}
     };

     void func(Derived &d1, Derived &d2)
     {
       d1 = d2;
     }

The C++ standard specifies that Base::Base is only called once when constructing or copy-constructing a Derived object. It is unspecified whether Base::operator= is called more than once when the implicit copy-assignment for Derived objects is invoked (as it is inside func in the example).

g++ implements the "intuitive" algorithm for copy-assignment: assign all direct bases, then assign all members. In that algorithm, the virtual base subobject can be encountered many times. In the example, copying proceeds in the following order: val, name (via strdup), bval, and name again.

If application code relies on copy-assignment, a user-defined copy-assignment operator removes any uncertainties. With such an operator, the application can define whether and how the virtual base subobject is assigned.

Caveats of using protoize
=========================

The conversion programs protoize and unprotoize can sometimes change a source file in a way that won't work unless you rearrange it.

  * protoize can insert references to a type name or type tag before the definition, or in a file where they are not defined.

     If this happens, compiler error messages should show you where the new references are, so fixing the file by hand is straightforward.

  * There are some C constructs which protoize cannot figure out. For example, it can't determine argument types for declaring a pointer-to-function variable; this you must do by hand.  protoize inserts a comment containing ??? each time it finds such a variable; so you can find all such variables by searching for this string.  ISO C does not require declaring the argument types of pointer-to-function types.

  * Using unprotoize can easily introduce bugs.  If the program relied on prototypes to bring about conversion of arguments, these conversions will not take place in the program without prototypes. One case in which you can be sure unprotoize is safe is when you are removing prototypes that were made with protoize; if the program worked before without any prototypes, it will work again without them.

     You can find all the places where this problem might occur by compiling the program with the -Wconversion option.  It prints a warning whenever an argument is converted.

  * Both conversion programs can be confused if there are macro calls in and around the text to be converted.  In other words, the standard syntax for a declaration or definition must not result from expanding a macro. This problem is inherent in the design of C and cannot be fixed.  If only a few functions have confusing macro calls, you can easily convert them manually.

  * protoize cannot get the argument types for a function whose definition was not actually compiled due to preprocessing conditionals. When this happens, protoize changes nothing in regard to such a function.  protoize tries to detect such instances and warn about them.

     You can generally work around this problem by using protoize step by step, each time specifying a different set of -D options for compilation, until all of the functions have been converted.  There is no automatic way to verify that you have got them all, however.

  * Confusion may result if there is an occasion to convert a function declaration or definition in a region of source code where there is more than one formal parameter list present.  Thus, attempts to convert code containing multiple (conditionally compiled) versions of a single function header (in the same vicinity) may not produce the desired (or expected) results.

     If you plan on converting source files which contain such code, it is recommended that you first make sure that each conditionally compiled region of source code which contains an alternative function header also contains at least one additional follower token (past the final right parenthesis of the function header).  This should circumvent the problem.

  * unprotoize can become confused when trying to convert a function definition or declaration which contains a declaration for a pointer-to-function formal argument which has the same name as the function being defined or declared.  We recommend you avoid such choices of formal parameter names.

  * You might also want to correct some of the indentation by hand and break long lines.  (The conversion programs don't write lines longer than eighty characters in any case.)

Certain Changes We Don't Want to Make
=====================================

This section lists changes that people frequently request, but which we do not make because we think GCC is better without them.

  * Checking the number and type of arguments to a function which has an old-fashioned definition and no prototype.

     Such a feature would work only occasionally---only for calls that appear in the same file as the called function, following the definition.  The only way to check all calls reliably is to add a prototype for the function.  But adding a prototype eliminates the motivation for this feature.  So the feature is not worthwhile.

  * Warning about using an expression whose type is signed as a shift count.

     Shift count operands are probably signed more often than unsigned. Warning about this would cause far more annoyance than good.

  * Warning about assigning a signed value to an unsigned variable.

     Such assignments must be very common; warning about them would cause more annoyance than good.

  * Warning when a non-void function value is ignored.

     Coming as I do from a Lisp background, I balk at the idea that there is something dangerous about discarding a value.  There are functions that return values which some callers may find useful; it makes no sense to clutter the program with a cast to void whenever the value isn't useful.

  * Assuming (for optimization) that the address of an external symbol is never zero.

     This assumption is false on certain systems when #pragma weak is used.

  * Making -fshort-enums the default.

     This would cause storage layout to be incompatible with most other C compilers.  And it doesn't seem very important, given that you can get the same result in other ways.  The case where it matters most is when the enumeration-valued object is inside a structure, and in that case you can specify a field width explicitly.

  * Making bitfields unsigned by default on particular machines where ``the ABI standard'' says to do so.

     The ISO C standard leaves it up to the implementation whether a bitfield declared plain int is signed or not.  This in effect creates two alternative dialects of C.

     The GNU C compiler supports both dialects; you can specify the signed dialect with -fsigned-bitfields and the unsigned dialect with -funsigned-bitfields.  However, this leaves open the question of which dialect to use by default.

     Currently, the preferred dialect makes plain bitfields signed, because this is simplest.  Since int is the same as signed int in every other context, it is cleanest for them to be the same in bitfields as well.

     Some computer manufacturers have published Application Binary Interface standards which specify that plain bitfields should be unsigned.  It is a mistake, however, to say anything about this issue in an ABI.  This is because the handling of plain bitfields distinguishes two dialects of C. Both dialects are meaningful on every type of machine.  Whether a particular object file was compiled using signed bitfields or unsigned is of no concern to other object files, even if they access the same bitfields in the same data structures.

     A given program is written in one or the other of these two dialects. The program stands a chance to work on most any machine if it is compiled with the proper dialect.  It is unlikely to work at all if compiled with the wrong dialect.

     Many users appreciate the GNU C compiler because it provides an environment that is uniform across machines.  These users would be inconvenienced if the compiler treated plain bitfields differently on certain machines.

     Occasionally users write programs intended only for a particular machine type.  On these occasions, the users would benefit if the GNU C compiler were to support by default the same dialect as the other compilers on that machine.  But such applications are rare.  And users writing a program to run on more than one type of machine cannot possibly benefit from this kind of compatibility.

     This is why GCC does and will treat plain bitfields in the same fashion on all types of machines (by default).

     There are some arguments for making bitfields unsigned by default on all machines.  If, for example, this becomes a universal de facto standard, it would make sense for GCC to go along with it.  This is something to be considered in the future.

     (Of course, users strongly concerned about portability should indicate explicitly in each bitfield whether it is signed or not.  In this way, they write programs which have the same meaning in both C dialects.)

  * Undefining __STDC__ when -ansi is not used.

     Currently, GCC defines __STDC__ as long as you don't use -traditional.  This provides good results in practice.

     Programmers normally use conditionals on __STDC__ to ask whether it is safe to use certain features of ISO C, such as function prototypes or ISO token concatenation.  Since plain gcc supports all the features of ISO C, the correct answer to these questions is ``yes''.

     Some users try to use __STDC__ to check for the availability of certain library facilities.  This is actually incorrect usage in an ISO C program, because the ISO C standard says that a conforming freestanding implementation should define __STDC__ even though it does not have the library facilities.  gcc -ansi -pedantic is a conforming freestanding implementation, and it is therefore required to define __STDC__, even though it does not come with an ISO C library.

     Sometimes people say that defining __STDC__ in a compiler that does not completely conform to the ISO C standard somehow violates the standard.  This is illogical.  The standard is a standard for compilers that claim to support ISO C, such as gcc -ansi---not for other compilers such as plain gcc.  Whatever the ISO C standard says is relevant to the design of plain gcc without -ansi only for pragmatic reasons, not as a requirement.

     GCC normally defines __STDC__ to be 1, and in addition defines __STRICT_ANSI__ if you specify the -ansi option, or a -std option for strict conformance to some version of ISO C. On some hosts, system include files use a different convention, where __STDC__ is normally 0, but is 1 if the user specifies strict conformance to the C Standard.  GCC follows the host convention when processing system include files, but when processing user files it follows the usual GNU C convention.

  * Undefining __STDC__ in C++.

     Programs written to compile with C++-to-C translators get the value of __STDC__ that goes with the C compiler that is subsequently used.  These programs must test __STDC__ to determine what kind of C preprocessor that compiler uses: whether they should concatenate tokens in the ISO C fashion or in the traditional fashion.

     These programs work properly with GNU C++ if __STDC__ is defined. They would not work otherwise.

     In addition, many header files are written to provide prototypes in ISO C but not in traditional C.  Many of these header files can work without change in C++ provided __STDC__ is defined.  If __STDC__ is not defined, they will all fail, and will all need to be changed to test explicitly for C++ as well.

  * Deleting ``empty'' loops.

     Historically, GCC has not deleted ``empty'' loops under the assumption that the most likely reason you would put one in a program is to have a delay, so deleting them will not make real programs run any faster.

     However, the rationale here is that optimization of a nonempty loop cannot produce an empty one, which holds for C but is not always the case for C++.

     Moreover, with -funroll-loops small ``empty'' loops are already removed, so the current behavior is both sub-optimal and inconsistent and will change in the future.

  * Making side effects happen in the same order as in some other compiler.

     It is never safe to depend on the order of evaluation of side effects. For example, a function call like this may very well behave differently from one compiler to another:

          void func (int, int);

          int i = 2;
          func (i++, i++);

     There is no guarantee (in either the C or the C++ standard language definitions) that the increments will be evaluated in any particular order.  Either increment might happen first.  func might get the arguments 2, 3, or it might get 3, 2, or even 2, 2.

  * Not allowing structures with volatile fields in registers.

     Strictly speaking, there is no prohibition in the ISO C standard against allowing structures with volatile fields in registers, but it does not seem to make any sense and is probably not what you wanted to do.  So the compiler will give an error message in this case.

  * Making certain warnings into errors by default.

     Some ISO C testsuites report failure when the compiler does not produce an error message for a certain program.

     ISO C requires a ``diagnostic'' message for certain kinds of invalid programs, but a warning is defined by GCC to count as a diagnostic.  If GCC produces a warning but not an error, that is correct ISO C support. If test suites call this ``failure'', they should be run with the GCC option -pedantic-errors, which will turn these warnings into errors.

Warning Messages and Error Messages
===================================

The GNU compiler can produce two kinds of diagnostics: errors and warnings.  Each kind has a different purpose:

  Errors report problems that make it impossible to compile your program.  GCC reports errors with the source file name and line number where the problem is apparent.

  Warnings report other unusual conditions in your code that may indicate a problem, although compilation can (and does) proceed.  Warning messages also report the source file name and line number, but include the text warning: to distinguish them from error messages.

Warnings may indicate danger points where you should check to make sure that your program really does what you intend; or the use of obsolete features; or the use of nonstandard features of GNU C or C++.  Many warnings are issued only if you ask for them, with one of the -W options (for instance, -Wall requests a variety of useful warnings).

GCC always tries to compile your program if possible; it never gratuitously rejects a program whose meaning is clear merely because (for instance) it fails to conform to a standard.  In some cases, however, the C and C++ standards specify that certain extensions are forbidden, and a diagnostic must be issued by a conforming compiler.  The -pedantic option tells GCC to issue warnings in such cases; -pedantic-errors says to make them errors instead. This does not mean that all non-ISO constructs get warnings or errors.

See Options to Request or Suppress Warnings, for more detail on these and related command-line options.

Reporting Bugs
**************

Your bug reports play an essential role in making GCC reliable.

When you encounter a problem, the first thing to do is to see if it is already known.  See Trouble.  If it isn't known, then you should report the problem.

Reporting a bug may help you by bringing a solution to your problem, or it may not.  (If it does not, look in the service directory; see Service.)  In any case, the principal function of a bug report is to help the entire community by making the next version of GCC work better.  Bug reports are your contribution to the maintenance of GCC.

Since the maintainers are very overloaded, we cannot respond to every bug report.  However, if the bug has not been fixed, we are likely to send you a patch and ask you to tell us whether it works.

In order for a bug report to serve its purpose, you must include the information that makes for fixing the bug.

Have You Found a Bug?
=====================

If you are not sure whether you have found a bug, here are some guidelines:

  * If the compiler gets a fatal signal, for any input whatever, that is a compiler bug.  Reliable compilers never crash.

  * If the compiler produces invalid assembly code, for any input whatever (except an asm statement), that is a compiler bug, unless the compiler reports errors (not just warnings) which would ordinarily prevent the assembler from being run.

  * If the compiler produces valid assembly code that does not correctly execute the input source code, that is a compiler bug.

     However, you must double-check to make sure, because you may have run into an incompatibility between GNU C and traditional C (see Incompatibilities).  These incompatibilities might be considered bugs, but they are inescapable consequences of valuable features.

     Or you may have a program whose behavior is undefined, which happened by chance to give the desired results with another C or C++ compiler.

     For example, in many nonoptimizing compilers, you can write x; at the end of a function instead of return x;, with the same results.  But the value of the function is undefined if return is omitted; it is not a bug when GCC produces different results.

     Problems often result from expressions with two increment operators, as in f (*p++, *p++).  Your previous compiler might have interpreted that expression the way you intended; GCC might interpret it another way.  Neither compiler is wrong.  The bug is in your code.

     After you have localized the error to a single source line, it should be easy to check for these things.  If your program is correct and well defined, you have found a compiler bug.

  * If the compiler produces an error message for valid input, that is a compiler bug.

  * If the compiler does not produce an error message for invalid input, that is a compiler bug.  However, you should note that your idea of ``invalid input'' might be my idea of ``an extension'' or ``support for traditional practice''.

  * If you are an experienced user of one of the languages GCC supports, your suggestions for improvement of GCC are welcome in any case.

Where to Report Bugs
====================

Send bug reports for the GNU Compiler Collection to gcc-bugs@gcc.gnu.org.  In accordance with the GNU-wide convention, in which bug reports for tool ``foo'' are sent to bug-foo@gnu.org, the address bug-gcc@gnu.org may also be used; it will forward to the address given above.

Please read http://gcc.gnu.org/bugs.html for additional and/or more up-to-date bug reporting instructions before you post a bug report.

How to Report Bugs
==================

The fundamental principle of reporting bugs usefully is this: report all the facts.  If you are not sure whether to state a fact or leave it out, state it!

Often people omit facts because they think they know what causes the problem and they conclude that some details don't matter.  Thus, you might assume that the name of the variable you use in an example does not matter. Well, probably it doesn't, but one cannot be sure.  Perhaps the bug is a stray memory reference which happens to fetch from the location where that name is stored in memory; perhaps, if the name were different, the contents of that location would fool the compiler into doing the right thing despite the bug.  Play it safe and give a specific, complete example.  That is the easiest thing for you to do, and the most helpful.

Keep in mind that the purpose of a bug report is to enable someone to fix the bug if it is not known.  It isn't very important what happens if the bug is already known.  Therefore, always write your bug reports on the assumption that the bug is not known.

Sometimes people give a few sketchy facts and ask, ``Does this ring a bell?''  This cannot help us fix a bug, so it is basically useless.  We respond by asking for enough details to enable us to investigate. You might as well expedite matters by sending them to begin with.

Try to make your bug report self-contained.  If we have to ask you for more information, it is best if you include all the previous information in your response, as well as the information that was missing.

Please report each bug in a separate message.  This makes it easier for us to track which bugs have been fixed and to forward your bugs reports to the appropriate maintainer.

To enable someone to investigate the bug, you should include all these things:

  * The version of GCC.  You can get this by running it with the -v option.

     Without this, we won't know whether there is any point in looking for the bug in the current version of GCC.

  * A complete input file that will reproduce the bug.  If the bug is in the C preprocessor, send a source file and any header files that it requires.  If the bug is in the compiler proper (cc1), send the preprocessor output generated by adding -save-temps to the compilation command (see Debugging Options).  When you do this, use the same -I, -D or -U options that you used in actual compilation. Then send the INPUT.i or INPUT.ii files generated.

     A single statement is not enough of an example.  In order to compile it, it must be embedded in a complete file of compiler input; and the bug might depend on the details of how this is done.

     Without a real example one can compile, all anyone can do about your bug report is wish you luck.  It would be futile to try to guess how to provoke the bug.  For example, bugs in register allocation and reloading frequently depend on every little detail of the function they happen in.

     Even if the input file that fails comes from a GNU program, you should still send the complete test case.  Don't ask the GCC maintainers to do the extra work of obtaining the program in question---they are all overworked as it is.  Also, the problem may depend on what is in the header files on your system; it is unreliable for the GCC maintainers to try the problem with the header files available to them.  By sending CPP output, you can eliminate this source of uncertainty and save us a certain percentage of wild goose chases.

  * The command arguments you gave GCC to compile that example and observe the bug.  For example, did you use -O?  To guarantee you won't omit something important, list all the options.

     If we were to try to guess the arguments, we would probably guess wrong and then we would not encounter the bug.

  * The type of machine you are using, and the operating system name and version number.

  * The operands you gave to the configure command when you installed the compiler.

  * A complete list of any modifications you have made to the compiler source.  (We don't promise to investigate the bug unless it happens in an unmodified compiler.  But if you've made modifications and don't tell us, then you are sending us on a wild goose chase.)

     Be precise about these changes.  A description in English is not enough---send a context diff for them.

     Adding files of your own (such as a machine description for a machine we don't support) is a modification of the compiler source.

  * Details of any other deviations from the standard procedure for installing GCC.

  * A description of what behavior you observe that you believe is incorrect.  For example, ``The compiler gets a fatal signal,'' or, ``The assembler instruction at line 208 in the output is incorrect.''

     Of course, if the bug is that the compiler gets a fatal signal, then one can't miss it.  But if the bug is incorrect output, the maintainer might not notice unless it is glaringly wrong.  None of us has time to study all the assembler code from a 50-line C program just on the chance that one instruction might be wrong.  We need you to do this part!

     Even if the problem you experience is a fatal signal, you should still say so explicitly.  Suppose something strange is going on, such as, your copy of the compiler is out of synch, or you have encountered a bug in the C library on your system.  (This has happened!)  Your copy might crash and the copy here would not.  If you said to expect a crash, then when the compiler here fails to crash, we would know that the bug was not happening.  If you don't say to expect a crash, then we would not know whether the bug was happening.  We would not be able to draw any conclusion from our observations.

     If the problem is a diagnostic when compiling GCC with some other compiler, say whether it is a warning or an error.

     Often the observed symptom is incorrect output when your program is run. Sad to say, this is not enough information unless the program is short and simple.  None of us has time to study a large program to figure out how it would work if compiled correctly, much less which line of it was compiled wrong.  So you will have to do that.  Tell us which source line it is, and what incorrect result happens when that line is executed.  A person who understands the program can find this as easily as finding a bug in the program itself.

  * If you send examples of assembler code output from GCC, please use -g when you make them.  The debugging information includes source line numbers which are essential for correlating the output with the input.

  * If you wish to mention something in the GCC source, refer to it by context, not by line number.

     The line numbers in the development sources don't match those in your sources.  Your line numbers would convey no useful information to the maintainers.

  * Additional information from a debugger might enable someone to find a problem on a machine which he does not have available.  However, you need to think when you collect this information if you want it to have any chance of being useful.

     For example, many people send just a backtrace, but that is never useful by itself.  A simple backtrace with arguments conveys little about GCC because the compiler is largely data-driven; the same functions are called over and over for different RTL insns, doing different things depending on the details of the insn.

     Most of the arguments listed in the backtrace are useless because they are pointers to RTL list structure.  The numeric values of the pointers, which the debugger prints in the backtrace, have no significance whatever; all that matters is the contents of the objects they point to (and most of the contents are other such pointers).

     In addition, most compiler passes consist of one or more loops that scan the RTL insn sequence.  The most vital piece of information about such a loop---which insn it has reached---is usually in a local variable, not in an argument.

     What you need to provide in addition to a backtrace are the values of the local variables for several stack frames up.  When a local variable or an argument is an RTX, first print its value and then use the GDB command pr to print the RTL expression that it points to.  (If GDB doesn't run on your machine, use your debugger to call the function debug_rtx with the RTX as an argument.)  In general, whenever a variable is a pointer, its value is no use without the data it points to.

Here are some things that are not necessary:

  * A description of the envelope of the bug.

     Often people who encounter a bug spend a lot of time investigating which changes to the input file will make the bug go away and which changes will not affect it.

     This is often time consuming and not very useful, because the way we will find the bug is by running a single example under the debugger with breakpoints, not by pure deduction from a series of examples.  You might as well save your time for something else.

     Of course, if you can find a simpler example to report instead of the original one, that is a convenience.  Errors in the output will be easier to spot, running under the debugger will take less time, etc. Most GCC bugs involve just one function, so the most straightforward way to simplify an example is to delete all the function definitions except the one where the bug occurs.  Those earlier in the file may be replaced by external declarations if the crucial function depends on them.  (Exception: inline functions may affect compilation of functions defined later in the file.)

     However, simplification is not vital; if you don't want to do this, report the bug anyway and send the entire test case you used.

  * In particular, some people insert conditionals #ifdef BUG around a statement which, if removed, makes the bug not happen.  These are just clutter; we won't pay any attention to them anyway.  Besides, you should send us cpp output, and that can't have conditionals.

  * A patch for the bug.

     A patch for the bug is useful if it is a good one.  But don't omit the necessary information, such as the test case, on the assumption that a patch is all we need.  We might see problems with your patch and decide to fix the problem another way, or we might not understand it at all.

     Sometimes with a program as complicated as GCC it is very hard to construct an example that will make the program follow a certain path through the code.  If you don't send the example, we won't be able to construct one, so we won't be able to verify that the bug is fixed.

     And if we can't understand what bug you are trying to fix, or why your patch should be an improvement, we won't install it.  A test case will help us to understand.

     See Sending Patches, for guidelines on how to make it easy for us to understand and install your patches.

  * A guess about what the bug is or what it depends on.

     Such guesses are usually wrong.  Even I can't guess right about such things without first using the debugger to find the facts.

  * A core dump file.

     We have no way of examining a core dump for your type of machine unless we have an identical system---and if we do have one, we should be able to reproduce the crash ourselves.

The gccbug script
=================

To simplify creation of bug reports, and to allow better tracking of reports, we use the GNATS bug tracking system. Part of that system is the gccbug script. This is a Unix shell script, so you need a shell to run it. It is normally installed in the same directory where gcc is installed.

The gccbug script is derived from send-pr, see Creating new Problem Reports (Reporting Problems). When invoked, it starts a text editor so you can fill out the various fields of the report. When the you quit the editor, the report is automatically send to the bug reporting address.

A number of fields in this bug report form are specific to GCC, and are explained here.

>Category:
     The category of a GCC problem can be one of the following:

     c
          A problem with the C compiler proper. driver.

     c++
          A problem with the C++ compiler. driver.

     fortran
          A problem with the Fortran 77.

     java
          A problem with the Java compiler.

     objc
          A problem with the Objective C compiler.

     libstdc++
          A problem with the C++ standard library.

     libf2c
          A problem with the Fortran 77 library.

     libobjc
          A problem with the Objective C library.

     optimization
          The problem occurs only when generating optimized code.

     debug
          The problem occurs only when generating code for debugging.

     target
          The problem is specific to the target architecture.

     middle-end
          The problem is independent from target architecture and programming language.

     other
          It is a problem in some other part of the GCC software.

     web
          There is a problem with the GCC home page.

>Class:
     The class of a problem can be one of the following:

     doc-bug
          A problem with the documentation.

     accepts-illegal
          GCC fails to reject erroneous code.

     rejects-legal
          GCC gives an error message for correct code.

     wrong-code
          The machine code generated by gcc is incorrect.

     ice-on-legal-code
          GCC gives an Internal Compiler Error (ICE) for correct code.

     ice-on-illegal-code
          GCC gives an ICE instead of reporting an error

     pessimizes-code
          GCC misses an important optimization opportunity.

     sw-bug
          A general product problem.  (sw stands for ``software''.)

     change-request
          A request for a change in behavior, etc.

     support
          A support problem or question.

     duplicate (PR-NUMBER)
          Duplicate PR.  PR-NUMBER should be the number of the original PR.

          The default is sw-bug.

Sending Patches for GCC
=======================

If you would like to write bug fixes or improvements for the GNU C compiler, that is very helpful.  Send suggested fixes to the patches mailing list, gcc-patches@gcc.gnu.org.

Please follow these guidelines so we can study your patches efficiently. If you don't follow these guidelines, your information might still be useful, but using it will take extra work.  Maintaining GNU C is a lot of work in the best of circumstances, and we can't keep up unless you do your best to help.

  * Send an explanation with your changes of what problem they fix or what improvement they bring about.  For a bug fix, just include a copy of the bug report, and explain why the change fixes the bug.

     (Referring to a bug report is not as good as including it, because then we will have to look it up, and we have probably already deleted it if we've already fixed the bug.)

  * Always include a proper bug report for the problem you think you have fixed.  We need to convince ourselves that the change is right before installing it.  Even if it is right, we might have trouble judging it if we don't have a way to reproduce the problem.

  * Include all the comments that are appropriate to help people reading the source in the future understand why this change was needed.

  * Don't mix together changes made for different reasons. Send them individually.

     If you make two changes for separate reasons, then we might not want to install them both.  We might want to install just one.  If you send them all jumbled together in a single set of diffs, we have to do extra work to disentangle them---to figure out which parts of the change serve which purpose.  If we don't have time for this, we might have to ignore your changes entirely.

     If you send each change as soon as you have written it, with its own explanation, then the two changes never get tangled up, and we can consider each one properly without any extra work to disentangle them.

     Ideally, each change you send should be impossible to subdivide into parts that we might want to consider separately, because each of its parts gets its motivation from the other parts.

  * Send each change as soon as that change is finished.  Sometimes people think they are helping us by accumulating many changes to send them all together.  As explained above, this is absolutely the worst thing you could do.

     Since you should send each change separately, you might as well send it right away.  That gives us the option of installing it immediately if it is important.

  * Use diff -c to make your diffs.  Diffs without context are hard for us to install reliably.  More than that, they make it hard for us to study the diffs to decide whether we want to install them.  Unidiff format is better than contextless diffs, but not as easy to read as -c format.

     If you have GNU diff, use diff -cp, which shows the name of the function that each change occurs in.

  * Write the change log entries for your changes.  We get lots of changes, and we don't have time to do all the change log writing ourselves.

     Read the ChangeLog file to see what sorts of information to put in, and to learn the style that we use.  The purpose of the change log is to show people where to find what was changed.  So you need to be specific about what functions you changed; in large functions, it's often helpful to indicate where within the function the change was.

     On the other hand, once you have shown people where to find the change, you need not explain its purpose.  Thus, if you add a new function, all you need to say about it is that it is new.  If you feel that the purpose needs explaining, it probably does---but the explanation will be much more useful if you put it in comments in the code.

     If you would like your name to appear in the header line for who made the change, send us the header line.

  * When you write the fix, keep in mind that we can't install a change that would break other systems.

     People often suggest fixing a problem by changing machine-independent files such as toplev.c to do something special that a particular system needs.  Sometimes it is totally obvious that such changes would break GCC for almost all users.  We can't possibly make a change like that.  At best it might tell us how to write another patch that would solve the problem acceptably.

     Sometimes people send fixes that might be an improvement in general---but it is hard to be sure of this.  It's hard to install such changes because we have to study them very carefully.  Of course, a good explanation of the reasoning by which you concluded the change was correct can help convince us.

     The safest changes are changes to the configuration files for a particular machine.  These are safe because they can't create new bugs on other machines.

     Please help us keep up with the workload by designing the patch in a form that is good to install.

How To Get Help with GCC
************************

If you need help installing, using or changing GCC, there are two ways to find it:

  * Send a message to a suitable network mailing list.  First try gcc-help@gcc.gnu.org (for help installing or using GCC), and if that brings no response, try gcc@gcc.gnu.org.  For help changing GCC, ask gcc@gcc.gnu.org.  If you think you have found a bug in GCC, please report it following the instructions at see Bug Reporting.

  * Look in the service directory for someone who might help you for a fee. The service directory is found at http://www.gnu.org/prep/service.html.

Contributing to GCC Development
*******************************

If you would like to help pretest GCC releases to assure they work well, our current development sources are available by CVS (see http://gcc.gnu.org/cvs.html).  Source and binary snapshots are also available for FTP; see http://gcc.gnu.org/snapshots.html.

If you would like to work on improvements to GCC, please read http://gcc.gnu.org/contribute.html and http://gcc.gnu.org/contributewhy.html for information on how to make useful contributions and avoid duplication of effort.  Suggested projects are listed at http://gcc.gnu.org/projects/.

Using GCC on VMS
****************

Here is how to use GCC on VMS.

Include Files and VMS
=====================

Due to the differences between the filesystems of Unix and VMS, GCC attempts to translate file names in #include into names that VMS will understand.  The basic strategy is to prepend a prefix to the specification of the include file, convert the whole filename to a VMS filename, and then try to open the file.  GCC tries various prefixes one by one until one of them succeeds:

 1. The first prefix is the GNU_CC_INCLUDE: logical name: this is where GNU C header files are traditionally stored.  If you wish to store header files in non-standard locations, then you can assign the logical GNU_CC_INCLUDE to be a search list, where each element of the list is suitable for use with a rooted logical.

 2. The next prefix tried is SYS$SYSROOT:[SYSLIB.].  This is where VAX-C header files are traditionally stored.

 3. If the include file specification by itself is a valid VMS filename, the preprocessor then uses this name with no prefix in an attempt to open the include file.

 4. If the file specification is not a valid VMS filename (i.e. does not contain a device or a directory specifier, and contains a / character), the preprocessor tries to convert it from Unix syntax to VMS syntax.

     Conversion works like this: the first directory name becomes a device, and the rest of the directories are converted into VMS-format directory names.  For example, the name X11/foobar.h is translated to X11:[000000]foobar.h or X11:foobar.h, whichever one can be opened.  This strategy allows you to assign a logical name to point to the actual location of the header files.

 5. If none of these strategies succeeds, the #include fails.

Include directives of the form:

     #include foobar

are a common source of incompatibility between VAX-C and GCC.  VAX-C treats this much like a standard #include <foobar.h> directive. That is incompatible with the ISO C behavior implemented by GCC: to expand the name foobar as a macro.  Macro expansion should eventually yield one of the two standard formats for #include:

     #include "FILE"
     #include <FILE>

If you have this problem, the best solution is to modify the source to convert the #include directives to one of the two standard forms. That will work with either compiler.  If you want a quick and dirty fix, define the file names as macros with the proper expansion, like this:

     #define stdio <stdio.h>

This will work, as long as the name doesn't conflict with anything else in the program.

Another source of incompatibility is that VAX-C assumes that:

     #include "foobar"

is actually asking for the file foobar.h.  GCC does not make this assumption, and instead takes what you ask for literally; it tries to read the file foobar.  The best way to avoid this problem is to always specify the desired file extension in your include directives.

GCC for VMS is distributed with a set of include files that is sufficient to compile most general purpose programs.  Even though the GCC distribution does not contain header files to define constants and structures for some VMS system-specific functions, there is no reason why you cannot use GCC with any of these functions.  You first may have to generate or create header files, either by using the public domain utility UNSDL (which can be found on a DECUS tape), or by extracting the relevant modules from one of the system macro libraries, and using an editor to construct a C header file.

A #include file name cannot contain a DECNET node name.  The preprocessor reports an I/O error if you attempt to use a node name, whether explicitly, or implicitly via a logical name.

Global Declarations and VMS
===========================

GCC does not provide the globalref, globaldef and globalvalue keywords of VAX-C.  You can get the same effect with an obscure feature of GAS, the GNU assembler.  (This requires GAS version 1.39 or later.)  The following macros allow you to use this feature in a fairly natural way:

     #ifdef __GNUC__
     #define GLOBALREF(TYPE,NAME)                      \
       TYPE NAME                                       \
       asm ("_$$PsectAttributes_GLOBALSYMBOL$$" #NAME)
     #define GLOBALDEF(TYPE,NAME,VALUE)                \
       TYPE NAME                                       \
       asm ("_$$PsectAttributes_GLOBALSYMBOL$$" #NAME) \
         = VALUE
     #define GLOBALVALUEREF(TYPE,NAME)                 \
       const TYPE NAME[1]                              \
       asm ("_$$PsectAttributes_GLOBALVALUE$$" #NAME)
     #define GLOBALVALUEDEF(TYPE,NAME,VALUE)           \
       const TYPE NAME[1]                              \
       asm ("_$$PsectAttributes_GLOBALVALUE$$" #NAME)  \
         = {VALUE}
     #else
     #define GLOBALREF(TYPE,NAME) \
       globalref TYPE NAME
     #define GLOBALDEF(TYPE,NAME,VALUE) \
       globaldef TYPE NAME = VALUE
     #define GLOBALVALUEDEF(TYPE,NAME,VALUE) \
       globalvalue TYPE NAME = VALUE
     #define GLOBALVALUEREF(TYPE,NAME) \
       globalvalue TYPE NAME
     #endif

(The _$$PsectAttributes_GLOBALSYMBOL prefix at the start of the name is removed by the assembler, after it has modified the attributes of the symbol).  These macros are provided in the VMS binaries distribution in a header file GNU_HACKS.H.  An example of the usage is:

     GLOBALREF (int, ijk);
     GLOBALDEF (int, jkl, 0);

The macros GLOBALREF and GLOBALDEF cannot be used straightforwardly for arrays, since there is no way to insert the array dimension into the declaration at the right place.  However, you can declare an array with these macros if you first define a typedef for the array type, like this:

     typedef int intvector[10];
     GLOBALREF (intvector, foo);

Array and structure initializers will also break the macros; you can define the initializer to be a macro of its own, or you can expand the GLOBALDEF macro by hand.  You may find a case where you wish to use the GLOBALDEF macro with a large array, but you are not interested in explicitly initializing each element of the array.  In such cases you can use an initializer like: {0,}, which will initialize the entire array to 0.

A shortcoming of this implementation is that a variable declared with GLOBALVALUEREF or GLOBALVALUEDEF is always an array.  For example, the declaration:

     GLOBALVALUEREF(int, ijk);

declares the variable ijk as an array of type int [1]. This is done because a globalvalue is actually a constant; its ``value'' is what the linker would normally consider an address.  That is not how an integer value works in C, but it is how an array works.  So treating the symbol as an array name gives consistent results---with the exception that the value seems to have the wrong type.  Don't try to access an element of the array.  It doesn't have any elements. The array ``address'' may not be the address of actual storage.

The fact that the symbol is an array may lead to warnings where the variable is used.  Insert type casts to avoid the warnings.  Here is an example; it takes advantage of the ISO C feature allowing macros that expand to use the same name as the macro itself.

     GLOBALVALUEREF (int, ss$_normal);
     GLOBALVALUEDEF (int, xyzzy,123);
     #ifdef __GNUC__
     #define ss$_normal ((int) ss$_normal)
     #define xyzzy ((int) xyzzy)
     #endif

Don't use globaldef or globalref with a variable whose type is an enumeration type; this is not implemented.  Instead, make the variable an integer, and use a globalvaluedef for each of the enumeration values.  An example of this would be:

     #ifdef __GNUC__
     GLOBALDEF (int, color, 0);
     GLOBALVALUEDEF (int, RED, 0);
     GLOBALVALUEDEF (int, BLUE, 1);
     GLOBALVALUEDEF (int, GREEN, 3);
     #else
     enum globaldef color {RED, BLUE, GREEN = 3};
     #endif

Other VMS Issues
================

GCC automatically arranges for main to return 1 by default if you fail to specify an explicit return value.  This will be interpreted by VMS as a status code indicating a normal successful completion. Version 1 of GCC did not provide this default.

GCC on VMS works only with the GNU assembler, GAS.  You need version 1.37 or later of GAS in order to produce value debugging information for the VMS debugger.  Use the ordinary VMS linker with the object files produced by GAS.

Under previous versions of GCC, the generated code would occasionally give strange results when linked to the sharable VAXCRTL library. Now this should work.

A caveat for use of const global variables: the const modifier must be specified in every external declaration of the variable in all of the source files that use that variable.  Otherwise the linker will issue warnings about conflicting attributes for the variable.  Your program will still work despite the warnings, but the variable will be placed in writable storage.

Although the VMS linker does distinguish between upper and lower case letters in global symbols, most VMS compilers convert all such symbols into upper case and most run-time library routines also have upper case names.  To be able to reliably call such routines, GCC (by means of the assembler GAS) converts global symbols into upper case like other VMS compilers.  However, since the usual practice in C is to distinguish case, GCC (via GAS) tries to preserve usual C behavior by augmenting each name that is not all lower case.  This means truncating the name to at most 23 characters and then adding more characters at the end which encode the case pattern of those 23.   Names which contain at least one dollar sign are an exception; they are converted directly into upper case without augmentation.

Name augmentation yields bad results for programs that use precompiled libraries (such as Xlib) which were generated by another compiler.  You can use the compiler option /NOCASE_HACK to inhibit augmentation; it makes external C functions and variables case-independent as is usual on VMS.  Alternatively, you could write all references to the functions and variables in such libraries using lower case; this will work on VMS, but is not portable to other systems.  The compiler option /NAMES also provides control over global name handling.

Function and variable names are handled somewhat differently with GNU C++.  The GNU C++ compiler performs name mangling on function names, which means that it adds information to the function name to describe the data types of the arguments that the function takes.  One result of this is that the name of a function can become very long. Since the VMS linker only recognizes the first 31 characters in a name, special action is taken to ensure that each function and variable has a unique name that can be represented in 31 characters.

If the name (plus a name augmentation, if required) is less than 32 characters in length, then no special action is performed.  If the name is longer than 31 characters, the assembler (GAS) will generate a hash string based upon the function name, truncate the function name to 23 characters, and append the hash string to the truncated name.  If the /VERBOSE compiler option is used, the assembler will print both the full and truncated names of each symbol that is truncated.

The /NOCASE_HACK compiler option should not be used when you are compiling programs that use libg++.  libg++ has several instances of objects (i.e.  Filebuf and filebuf) which become indistinguishable in a case-insensitive environment.  This leads to cases where you need to inhibit augmentation selectively (if you were using libg++ and Xlib in the same program, for example).  There is no special feature for doing this, but you can get the result by defining a macro for each mixed case symbol for which you wish to inhibit augmentation.  The macro should expand into the lower case equivalent of itself.  For example:

     #define StuDlyCapS studlycaps

These macro definitions can be placed in a header file to minimize the number of changes to your source code.

Makefile Targets
****************

all
     This is the default target.  Depending on what your build/host/target configuration is, it coordinates all the things that need to be built.

doc
     Produce info-formatted documentation.  Also, make dvi is available for DVI-formatted documentation, and make generated-manpages to generate man pages.

mostlyclean
     Delete the files made while building the compiler.

clean
     That, and all the other files built by make all.

distclean
     That, and all the files created by configure.

extraclean
     That, and any temporary or intermediate files, like emacs backup files.

maintainer-clean
     Distclean plus any file that can be generated from other files.  Note that additional tools may be required beyond what is normally needed to build gcc.

install
     Installs gcc.

uninstall
     Deletes installed files.

check
     Run the testsuite.  This creates a testsuite subdirectory that has various .sum and .log files containing the results of the testing.  You can run subsets with, for example, make check-gcc. You can specify specific tests by setting RUNTESTFLAGS to be the name of the .exp file, optionally followed by (for some tests) an equals and a file wildcard, like:

          make check-gcc RUNTESTFLAGS="execute.exp=19980413-*"

     Note that running the testsuite may require additional tools be installed, such as TCL or dejagnu.

bootstrap
     Builds gcc three times - once with the native compiler, once with the native-built compiler it just built, and once with the compiler it built the second time.  In theory, the last two should produce the same results, which make compare can check.  Each step of this process is called a "stage", and the results of each stage N (N=1..3) are copied to a subdirectory stageN/.

bootstrap-lean
     Like bootstrap, except that the various stages are removed once they're no longer needed.  This saves disk space.

bubblestrap
     Once bootstrapped, this incrementally rebuilds each of the three stages, one at a time.  It does this by "bubbling" the stages up from their stubdirectories, rebuilding them, and copying them back to their subdirectories.  This will allow you to, for example, quickly rebuild a bootstrapped compiler after changing the sources, without having to do a full bootstrap.

quickstrap
     Rebuilds the most recently built stage.  Since each stage requires special invocation, using this target means you don't have to keep track of which stage you're on or what invocation that stage needs.

cleanstrap
     Removed everything (make clean) and rebuilds (make bootstrap).

stageN (N=1..4)
     For each stage, moves the appropriate files to the stageN subdirectory.

unstageN (N=1..4)
     Undoes the corresponding stageN.

restageN (N=1..4)
     Undoes the corresponding stageN and rebuilds it with the appropriate flags.

compare
     Compares the results of stages 2 and 3.  This ensures that the compiler is running properly, since it should produce the same object files regardless of how it itself was compiled.

GCC and Portability
*******************

The main goal of GCC was to make a good, fast compiler for machines in the class that the GNU system aims to run on: 32-bit machines that address 8-bit bytes and have several general registers.  Elegance, theoretical power and simplicity are only secondary.

GCC gets most of the information about the target machine from a machine description which gives an algebraic formula for each of the machine's instructions.  This is a very clean way to describe the target.  But when the compiler needs information that is difficult to express in this fashion, I have not hesitated to define an ad-hoc parameter to the machine description.  The purpose of portability is to reduce the total work needed on the compiler; it was not of interest for its own sake.

GCC does not contain machine dependent code, but it does contain code that depends on machine parameters such as endianness (whether the most significant byte has the highest or lowest address of the bytes in a word) and the availability of autoincrement addressing.  In the RTL-generation pass, it is often necessary to have multiple strategies for generating code for a particular kind of syntax tree, strategies that are usable for different combinations of parameters.  Often I have not tried to address all possible cases, but only the common ones or only the ones that I have encountered. As a result, a new target may require additional strategies.  You will know if this happens because the compiler will call abort.  Fortunately, the new strategies can be added in a machine-independent fashion, and will affect only the target machines that need them.

Interfacing to GCC Output
*************************

GCC is normally configured to use the same function calling convention normally in use on the target system.  This is done with the machine-description macros described (see Target Macros).

However, returning of structure and union values is done differently on some target machines.  As a result, functions compiled with PCC returning such types cannot be called from code compiled with GCC, and vice versa.  This does not cause trouble often because few Unix library routines return structures or unions.

GCC code returns structures and unions that are 1, 2, 4 or 8 bytes long in the same registers used for int or double return values.  (GCC typically allocates variables of such types in registers also.)  Structures and unions of other sizes are returned by storing them into an address passed by the caller (usually in a register).  The machine-description macros STRUCT_VALUE and STRUCT_INCOMING_VALUE tell GCC where to pass this address.

By contrast, PCC on most target machines returns structures and unions of any size by copying the data into an area of static storage, and then returning the address of that storage as if it were a pointer value. The caller must copy the data from that memory area to the place where the value is wanted.  This is slower than the method used by GCC, and fails to be reentrant.

On some target machines, such as RISC machines and the 80386, the standard system convention is to pass to the subroutine the address of where to return the value.  On these machines, GCC has been configured to be compatible with the standard compiler, when this method is used.  It may not be compatible for structures of 1, 2, 4 or 8 bytes.

GCC uses the system's standard convention for passing arguments.  On some machines, the first few arguments are passed in registers; in others, all are passed on the stack.  It would be possible to use registers for argument passing on any machine, and this would probably result in a significant speedup.  But the result would be complete incompatibility with code that follows the standard convention.  So this change is practical only if you are switching to GCC as the sole C compiler for the system.  We may implement register argument passing on certain machines once we have a complete GNU system so that we can compile the libraries with GCC.

On some machines (particularly the Sparc), certain types of arguments are passed ``by invisible reference''.  This means that the value is stored in memory, and the address of the memory location is passed to the subroutine.

If you use longjmp, beware of automatic variables.  ISO C says that automatic variables that are not declared volatile have undefined values after a longjmp.  And this is all GCC promises to do, because it is very difficult to restore register variables correctly, and one of GCC's features is that it can put variables in registers without your asking it to.

If you want a variable to be unaltered by longjmp, and you don't want to write volatile because old C compilers don't accept it, just take the address of the variable.  If a variable's address is ever taken, even if just to compute it and ignore it, then the variable cannot go in a register:

     {
       int careful;
       &careful;
       ...
     }

Code compiled with GCC may call certain library routines.  Most of them handle arithmetic for which there are no instructions.  This includes multiply and divide on some machines, and floating point operations on any machine for which floating point support is disabled with -msoft-float.  Some standard parts of the C library, such as bcopy or memcpy, are also called automatically.  The usual function call interface is used for calling the library routines.

These library routines should be defined in the library libgcc.a, which GCC automatically searches whenever it links a program.  On machines that have multiply and divide instructions, if hardware floating point is in use, normally libgcc.a is not needed, but it is searched just in case.

Each arithmetic function is defined in libgcc1.c to use the corresponding C arithmetic operator.  As long as the file is compiled with another C compiler, which supports all the C arithmetic operators, this file will work portably.  However, libgcc1.c does not work if compiled with GCC, because each arithmetic function would compile into a call to itself!

Passes and Files of the Compiler
********************************

The overall control structure of the compiler is in toplev.c.  This file is responsible for initialization, decoding arguments, opening and closing files, and sequencing the passes.

The parsing pass is invoked only once, to parse the entire input.  The RTL intermediate code for a function is generated as the function is parsed, a statement at a time.  Each statement is read in as a syntax tree and then converted to RTL; then the storage for the tree for the statement is reclaimed.  Storage for types (and the expressions for their sizes), declarations, and a representation of the binding contours and how they nest, remain until the function is finished being compiled; these are all needed to output the debugging information.

Each time the parsing pass reads a complete function definition or top-level declaration, it calls either the function rest_of_compilation, or the function rest_of_decl_compilation in toplev.c, which are responsible for all further processing necessary, ending with output of the assembler language.  All other compiler passes run, in sequence, within rest_of_compilation.  When that function returns from compiling a function definition, the storage used for that function definition's compilation is entirely freed, unless it is an inline function (see An Inline Function is As Fast As a Macro).

Here is a list of all the passes of the compiler and their source files. Also included is a description of where debugging dumps can be requested with -d options.

  * Parsing.  This pass reads the entire text of a function definition, constructing partial syntax trees.  This and RTL generation are no longer truly separate passes (formerly they were), but it is easier to think of them as separate.

     The tree representation does not entirely follow C syntax, because it is intended to support other languages as well.

     Language-specific data type analysis is also done in this pass, and every tree node that represents an expression has a data type attached. Variables are represented as declaration nodes.

     Constant folding and some arithmetic simplifications are also done during this pass.

     The language-independent source files for parsing are stor-layout.c, fold-const.c, and tree.c. There are also header files tree.h and tree.def which define the format of the tree representation.

     The source files to parse C are c-parse.in, c-decl.c, c-typeck.c, c-aux-info.c, c-convert.c, and c-lang.c along with header files c-lex.h, and c-tree.h.

     The source files for parsing C++ are in cp/. They are parse.y, class.c,

     cvt.c, decl.c, decl2.c, except.c,

     expr.c, init.c, lex.c, method.c, ptree.c,

     search.c, tree.c, typeck2.c, and typeck.c, along with header files cp-tree.def, cp-tree.h, and decl.h.

     The special source files for parsing Objective C are in objc/. They are objc-parse.y, objc-act.c, objc-tree.def, and objc-act.h.  Certain C-specific files are used for this as well.

     The file c-common.c is also used for all of the above languages.

  * RTL generation.  This is the conversion of syntax tree into RTL code. It is actually done statement-by-statement during parsing, but for most purposes it can be thought of as a separate pass.

     This is where the bulk of target-parameter-dependent code is found, since often it is necessary for strategies to apply only when certain standard kinds of instructions are available.  The purpose of named instruction patterns is to provide this information to the RTL generation pass.

     Optimization is done in this pass for if-conditions that are comparisons, boolean operations or conditional expressions.  Tail recursion is detected at this time also.  Decisions are made about how best to arrange loops and how to output switch statements.

     The source files for RTL generation include stmt.c, calls.c, expr.c, explow.c, expmed.c, function.c, optabs.c and emit-rtl.c. Also, the file insn-emit.c, generated from the machine description by the program genemit, is used in this pass.  The header file expr.h is used for communication within this pass.

     The header files insn-flags.h and insn-codes.h, generated from the machine description by the programs genflags and gencodes, tell this pass which standard names are available for use and which patterns correspond to them.

     Aside from debugging information output, none of the following passes refers to the tree structure representation of the function (only part of which is saved).

     The decision of whether the function can and should be expanded inline in its subsequent callers is made at the end of rtl generation.  The function must meet certain criteria, currently related to the size of the function and the types and number of parameters it has.  Note that this function may contain loops, recursive calls to itself (tail-recursive functions can be inlined!), gotos, in short, all constructs supported by GCC.  The file integrate.c contains the code to save a function's rtl for later inlining and to inline that rtl when the function is called.  The header file integrate.h is also used for this purpose.

     The option -dr causes a debugging dump of the RTL code after this pass.  This dump file's name is made by appending .rtl to the input file name.

  * Jump optimization.  This pass simplifies jumps to the following instruction, jumps across jumps, and jumps to jumps.  It deletes unreferenced labels and unreachable code, except that unreachable code that contains a loop is not recognized as unreachable in this pass. (Such loops are deleted later in the basic block analysis.)  It also converts some code originally written with jumps into sequences of instructions that directly set values from the results of comparisons, if the machine has such instructions.

     Jump optimization is performed two or three times.  The first time is immediately following RTL generation.  The second time is after CSE, but only if CSE says repeated jump optimization is needed.  The last time is right before the final pass.  That time, cross-jumping and deletion of no-op move instructions are done together with the optimizations described above.

     The source file of this pass is jump.c.

     The option -dj causes a debugging dump of the RTL code after this pass is run for the first time.  This dump file's name is made by appending .jump to the input file name.

  * Register scan.  This pass finds the first and last use of each register, as a guide for common subexpression elimination.  Its source is in regclass.c.

  * Jump threading.  This pass detects a condition jump that branches to an identical or inverse test.  Such jumps can be threaded through the second conditional test.  The source code for this pass is in jump.c.  This optimization is only performed if -fthread-jumps is enabled.

  * Common subexpression elimination.  This pass also does constant propagation.  Its source file is cse.c.  If constant propagation causes conditional jumps to become unconditional or to become no-ops, jump optimization is run again when CSE is finished.

     The option -ds causes a debugging dump of the RTL code after this pass.  This dump file's name is made by appending .cse to the input file name.

  * Global common subexpression elimination.  This pass performs GCSE using Morel-Renvoise Partial Redundancy Elimination, with the exception that it does not try to move invariants out of loops - that is left to the loop optimization pass.  This pass also performs global constant and copy propagation.

     The source file for this pass is gcse.c.

     The option -dG causes a debugging dump of the RTL code after this pass.  This dump file's name is made by appending .gcse to the input file name.

  * Loop optimization.  This pass moves constant expressions out of loops, and optionally does strength-reduction and loop unrolling as well. Its source files are loop.c and unroll.c, plus the header loop.h used for communication between them.  Loop unrolling uses some functions in integrate.c and the header integrate.h.

     The option -dL causes a debugging dump of the RTL code after this pass.  This dump file's name is made by appending .loop to the input file name.

  * If -frerun-cse-after-loop was enabled, a second common subexpression elimination pass is performed after the loop optimization pass.  Jump threading is also done again at this time if it was specified.

     The option -dt causes a debugging dump of the RTL code after this pass.  This dump file's name is made by appending .cse2 to the input file name.

  * Data flow analysis (flow.c).  This pass divides the program into basic blocks (and in the process deletes unreachable loops); then it computes which pseudo-registers are live at each point in the program, and makes the first instruction that uses a value point at the instruction that computed the value.

     This pass also deletes computations whose results are never used, and combines memory references with add or subtract instructions to make autoincrement or autodecrement addressing.

     The option -df causes a debugging dump of the RTL code after this pass.  This dump file's name is made by appending .flow to the input file name.  If stupid register allocation is in use, this dump file reflects the full results of such allocation.

  * Instruction combination (combine.c).  This pass attempts to combine groups of two or three instructions that are related by data flow into single instructions.  It combines the RTL expressions for the instructions by substitution, simplifies the result using algebra, and then attempts to match the result against the machine description.

     The option -dc causes a debugging dump of the RTL code after this pass.  This dump file's name is made by appending .combine to the input file name.

  * Register movement (regmove.c). This pass looks for cases where matching constraints would force an instruction to need a reload, and this reload would be a register to register move.  It then attempts to change the registers used by the instruction to avoid the move instruction.

     The option -dN causes a debugging dump of the RTL code after this pass.  This dump file's name is made by appending .regmove to the input file name.

  * Instruction scheduling (sched.c).  This pass looks for instructions whose output will not be available by the time that it is used in subsequent instructions.  (Memory loads and floating point instructions often have this behavior on RISC machines).  It re-orders instructions within a basic block to try to separate the definition and use of items that otherwise would cause pipeline stalls.

     Instruction scheduling is performed twice.  The first time is immediately after instruction combination and the second is immediately after reload.

     The option -dS causes a debugging dump of the RTL code after this pass is run for the first time.  The dump file's name is made by appending .sched to the input file name.

  * Register class preferencing.  The RTL code is scanned to find out which register class is best for each pseudo register.  The source file is regclass.c.

  * Local register allocation (local-alloc.c).  This pass allocates hard registers to pseudo registers that are used only within one basic block.  Because the basic block is linear, it can use fast and powerful techniques to do a very good job.

     The option -dl causes a debugging dump of the RTL code after this pass.  This dump file's name is made by appending .lreg to the input file name.

  * Global register allocation (global.c).  This pass allocates hard registers for the remaining pseudo registers (those whose life spans are not contained in one basic block).

  * Reloading.  This pass renumbers pseudo registers with the hardware registers numbers they were allocated.  Pseudo registers that did not get hard registers are replaced with stack slots.  Then it finds instructions that are invalid because a value has failed to end up in a register, or has ended up in a register of the wrong kind.  It fixes up these instructions by reloading the problematical values temporarily into registers.  Additional instructions are generated to do the copying.

     The reload pass also optionally eliminates the frame pointer and inserts instructions to save and restore call-clobbered registers around calls.

     Source files are reload.c and reload1.c, plus the header reload.h used for communication between them.

     The option -dg causes a debugging dump of the RTL code after this pass.  This dump file's name is made by appending .greg to the input file name.

  * Instruction scheduling is repeated here to try to avoid pipeline stalls due to memory loads generated for spilled pseudo registers.

     The option -dR causes a debugging dump of the RTL code after this pass.  This dump file's name is made by appending .sched2 to the input file name.

  * Jump optimization is repeated, this time including cross-jumping and deletion of no-op move instructions.

     The option -dJ causes a debugging dump of the RTL code after this pass.  This dump file's name is made by appending .jump2 to the input file name.

  * Delayed branch scheduling.  This optional pass attempts to find instructions that can go into the delay slots of other instructions, usually jumps and calls.  The source file name is reorg.c.

     The option -dd causes a debugging dump of the RTL code after this pass.  This dump file's name is made by appending .dbr to the input file name.

  * Branch shortening.  On many RISC machines, branch instructions have a limited range.  Thus, longer sequences of instructions must be used for long branches.  In this pass, the compiler figures out what how far each instruction will be from each other instruction, and therefore whether the usual instructions, or the longer sequences, must be used for each branch.

  * Conversion from usage of some hard registers to usage of a register stack may be done at this point.  Currently, this is supported only for the floating-point registers of the Intel 80387 coprocessor.   The source file name is reg-stack.c.

     The options -dk causes a debugging dump of the RTL code after this pass.  This dump file's name is made by appending .stack to the input file name.

  * Final.  This pass outputs the assembler code for the function.  It is also responsible for identifying spurious test and compare instructions.  Machine-specific peephole optimizations are performed at the same time.  The function entry and exit sequences are generated directly as assembler code in this pass; they never exist as RTL.

     The source files are final.c plus insn-output.c; the latter is generated automatically from the machine description by the tool genoutput.  The header file conditions.h is used for communication between these files.

  * Debugging information output.  This is run after final because it must output the stack slot offsets for pseudo registers that did not get hard registers.  Source files are dbxout.c for DBX symbol table format, sdbout.c for SDB symbol table format, and dwarfout.c for DWARF symbol table format.

Some additional files are used by all or many passes:

  * Every pass uses machmode.def and machmode.h which define the machine modes.

  * Several passes use real.h, which defines the default representation of floating point constants and how to operate on them.

  * All the passes that work with RTL use the header files rtl.h and rtl.def, and subroutines in file rtl.c.  The tools gen* also use these files to read and work with the machine description RTL.

  * Several passes refer to the header file insn-config.h which contains a few parameters (C macro definitions) generated automatically from the machine description RTL by the tool genconfig.

  * Several passes use the instruction recognizer, which consists of recog.c and recog.h, plus the files insn-recog.c and insn-extract.c that are generated automatically from the machine description by the tools genrecog and genextract.

  * Several passes use the header files regs.h which defines the information recorded about pseudo register usage, and basic-block.h which defines the information recorded about basic blocks.

  * hard-reg-set.h defines the type HARD_REG_SET, a bit-vector with a bit for each hard register, and some macros to manipulate it. This type is just int if the machine has few enough hard registers; otherwise it is an array of int and some of the macros expand into loops.

  * Several passes use instruction attributes.  A definition of the attributes defined for a particular machine is in file insn-attr.h, which is generated from the machine description by the program genattr.  The file insn-attrtab.c contains subroutines to obtain the attribute values for insns.  It is generated from the machine description by the program genattrtab.

     [file rtl.texi not included]
     [file md.texi not included]
     [file tm.texi not included]

The Configuration File
**********************

The configuration file xm-MACHINE.h contains macro definitions that describe the machine and system on which the compiler is running, unlike the definitions in MACHINE.h, which describe the machine for which the compiler is producing output.  Most of the values in xm-MACHINE.h are actually the same on all machines that GCC runs on, so large parts of all configuration files are identical.  But there are some macros that vary:

USG
     Define this macro if the host system is System V.

VMS
     Define this macro if the host system is VMS.

FATAL_EXIT_CODE
     A C expression for the status code to be returned when the compiler exits after serious errors.  The default is the system-provided macro EXIT_FAILURE, or 1 if the system doesn't define that macro.  Define this macro only if these defaults are incorrect.

SUCCESS_EXIT_CODE
     A C expression for the status code to be returned when the compiler exits without serious errors.  (Warnings are not serious errors.)  The default is the system-provided macro EXIT_SUCCESS, or 0 if the system doesn't define that macro.  Define this macro only if these defaults are incorrect.

HOST_WORDS_BIG_ENDIAN
     Defined if the host machine stores words of multi-word values in big-endian order.  (GCC does not depend on the host byte ordering within a word.)

HOST_FLOAT_WORDS_BIG_ENDIAN
     Define this macro to be 1 if the host machine stores DFmode, XFmode or TFmode floating point numbers in memory with the word containing the sign bit at the lowest address; otherwise, define it to be zero.

     This macro need not be defined if the ordering is the same as for multi-word integers.

HOST_FLOAT_FORMAT
     A numeric code distinguishing the floating point format for the host machine.  See TARGET_FLOAT_FORMAT in Storage Layout for the alternatives and default.

HOST_BITS_PER_CHAR
     A C expression for the number of bits in char on the host machine.

HOST_BITS_PER_SHORT
     A C expression for the number of bits in short on the host machine.

HOST_BITS_PER_INT
     A C expression for the number of bits in int on the host machine.

HOST_BITS_PER_LONG
     A C expression for the number of bits in long on the host machine.

ONLY_INT_FIELDS
     Define this macro to indicate that the host compiler only supports int bit fields, rather than other integral types, including enum, as do most C compilers.

OBSTACK_CHUNK_SIZE
     A C expression for the size of ordinary obstack chunks. If you don't define this, a usually-reasonable default is used.

OBSTACK_CHUNK_ALLOC
     The function used to allocate obstack chunks. If you don't define this, xmalloc is used.

OBSTACK_CHUNK_FREE
     The function used to free obstack chunks. If you don't define this, free is used.

USE_C_ALLOCA
     Define this macro to indicate that the compiler is running with the alloca implemented in C.  This version of alloca can be found in the file alloca.c; to use it, you must also alter the Makefile variable ALLOCA.  (This is done automatically for the systems on which we know it is needed.)

     If you do define this macro, you should probably do it as follows:

          #ifndef __GNUC__
          #define USE_C_ALLOCA
          #else
          #define alloca __builtin_alloca
          #endif

     so that when the compiler is compiled with GCC it uses the more efficient built-in alloca function.

FUNCTION_CONVERSION_BUG
     Define this macro to indicate that the host compiler does not properly handle converting a function value to a pointer-to-function when it is used in an expression.

MULTIBYTE_CHARS
     Define this macro to enable support for multibyte characters in the input to GCC.  This requires that the host system support the ISO C library functions for converting multibyte characters to wide characters.

POSIX
     Define this if your system is POSIX.1 compliant.

PATH_SEPARATOR
     Define this macro to be a C character constant representing the character used to separate components in paths.  The default value is the colon character

DIR_SEPARATOR
     If your system uses some character other than slash to separate directory names within a file specification, define this macro to be a C character constant specifying that character.  When GCC displays file names, the character you specify will be used.  GCC will test for both slash and the character you specify when parsing filenames.

OBJECT_SUFFIX
     Define this macro to be a C string representing the suffix for object files on your machine.  If you do not define this macro, GCC will use .o as the suffix for object files.

EXECUTABLE_SUFFIX
     Define this macro to be a C string representing the suffix for executable files on your machine.  If you do not define this macro, GCC will use the null string as the suffix for object files.

NO_AUTO_EXE_SUFFIX
     Define this macro if executable files on your machine have a suffix, but the compiler driver should not automatically append it to the output file name, if user hasn't specified one.

HOST_BIT_BUCKET
     The name of a file or file-like object on the host system which acts as a ``bit bucket''.  If you do not define this macro, GCC will use /dev/null as the bit bucket.  If the target does not support a bit bucket, this should be defined to the null string, or some other illegal filename.  If the bit bucket is not writable, GCC will use a temporary file instead.

COLLECT_EXPORT_LIST
     If defined, collect2 will scan the individual object files specified on its command line and create an export list for the linker. Define this macro for systems like AIX, where the linker discards object files that are not referenced from main and uses export lists.

COLLECT2_HOST_INITIALIZATION
     If defined, a C statement (sans semicolon) that performs host-dependent initialization when collect2 is being initialized.

GCC_DRIVER_HOST_INITIALIZATION
     If defined, a C statement (sans semicolon) that performs host-dependent initialization when a compilation driver is being initialized.

UPDATE_PATH_HOST_CANONICALIZE (PATH, KEY)
     If defined, a C statement (sans semicolon) that performs host-dependent canonicalization when a path used in a compilation driver or preprocessor is canonicalized. PATH is the path to be canonicalized, and KEY is a translation prefix when its value isn't NULL. If the C statement does canonicalize PATH, the new path should be returned.

In addition, configuration files for system V define bcopy, bzero and bcmp as aliases.  Some files define alloca as a macro when compiled with GCC, in order to take advantage of the benefit of GCC's built-in alloca.

Makefile Fragments
******************

When you configure GCC using the configure script (see Installation), it will construct the file Makefile from the template file Makefile.in.  When it does this, it will incorporate makefile fragment files from the config directory, named t-TARGET and x-HOST.  If these files do not exist, it means nothing needs to be added for a given target or host.

The Target Makefile Fragment
============================

The target makefile fragment, t-TARGET, defines special target dependent variables and targets used in the Makefile:

LIBGCC1
     The rule to use to build libgcc1.a. If your target does not need to use the functions in libgcc1.a, set this to empty. See Interface.

CROSS_LIBGCC1
     The rule to use to build libgcc1.a when building a cross compiler.  If your target does not need to use the functions in libgcc1.a, set this to empty.  See Cross Runtime.

LIBGCC2_CFLAGS
     Compiler flags to use when compiling libgcc2.c.

LIB2FUNCS_EXTRA
     A list of source file names to be compiled or assembled and inserted into libgcc.a.

Floating Point Emulation
     To have GCC include software floating point libraries in libgcc.a define FPBIT and DPBIT along with a few rules as follows:

          # We want fine grained libraries, so use the new code to build the
          # floating point emulation libraries.
          FPBIT = fp-bit.c
          DPBIT = dp-bit.c

          fp-bit.c: $(srcdir)/config/fp-bit.c
                  echo '#define FLOAT' > fp-bit.c
                  cat $(srcdir)/config/fp-bit.c >> fp-bit.c

          dp-bit.c: $(srcdir)/config/fp-bit.c
                  cat $(srcdir)/config/fp-bit.c > dp-bit.c

     You may need to provide additional #defines at the beginning of fp-bit.c and dp-bit.c to control target endianness and other options.

CRTSTUFF_T_CFLAGS
     Special flags used when compiling crtstuff.c. See Initialization.

CRTSTUFF_T_CFLAGS_S
     Special flags used when compiling crtstuff.c for shared linking.  Used if you use crtbeginS.o and crtendS.o in EXTRA-PARTS. See Initialization.

MULTILIB_OPTIONS
     For some targets, invoking GCC in different ways produces objects that can not be linked together.  For example, for some targets GCC produces both big and little endian code.  For these targets, you must arrange for multiple versions of libgcc.a to be compiled, one for each set of incompatible options.  When GCC invokes the linker, it arranges to link in the right version of libgcc.a, based on the command line options used.

     The MULTILIB_OPTIONS macro lists the set of options for which special versions of libgcc.a must be built.  Write options that are mutually incompatible side by side, separated by a slash.  Write options that may be used together separated by a space.  The build procedure will build all combinations of compatible options.

     For example, if you set MULTILIB_OPTIONS to m68000/m68020 msoft-float, Makefile will build special versions of libgcc.a using the following sets of options:  -m68000, -m68020, -msoft-float, -m68000 -msoft-float, and -m68020 -msoft-float.

MULTILIB_DIRNAMES
     If MULTILIB_OPTIONS is used, this variable specifies the directory names that should be used to hold the various libraries. Write one element in MULTILIB_DIRNAMES for each element in MULTILIB_OPTIONS.  If MULTILIB_DIRNAMES is not used, the default value will be MULTILIB_OPTIONS, with all slashes treated as spaces.

     For example, if MULTILIB_OPTIONS is set to m68000/m68020 msoft-float, then the default value of MULTILIB_DIRNAMES is m68000 m68020 msoft-float.  You may specify a different value if you desire a different set of directory names.

MULTILIB_MATCHES
     Sometimes the same option may be written in two different ways.  If an option is listed in MULTILIB_OPTIONS, GCC needs to know about any synonyms.  In that case, set MULTILIB_MATCHES to a list of items of the form option=option to describe all relevant synonyms.  For example, m68000=mc68000 m68020=mc68020.

MULTILIB_EXCEPTIONS
     Sometimes when there are multiple sets of MULTILIB_OPTIONS being specified, there are combinations that should not be built.  In that case, set MULTILIB_EXCEPTIONS to be all of the switch exceptions in shell case syntax that should not be built.

     For example, in the PowerPC embedded ABI support, it is not desirable to build libraries compiled with the -mcall-aix option and either of the -fleading-underscore or -mlittle options at the same time.  Therefore MULTILIB_EXCEPTIONS is set to *mcall-aix/*fleading-underscore* *mlittle/*mcall-aix*.

MULTILIB_EXTRA_OPTS
     Sometimes it is desirable that when building multiple versions of libgcc.a certain options should always be passed on to the compiler.  In that case, set MULTILIB_EXTRA_OPTS to be the list of options to be used for all builds.

The Host Makefile Fragment
==========================

The host makefile fragment, x-HOST, defines special host dependent variables and targets used in the Makefile:

CC
     The compiler to use when building the first stage.

CLIB
     Additional host libraries to link with.

OLDCC
     The compiler to use when building libgcc1.a for a native compilation.

OLDAR
     The version of ar to use when building libgcc1.a for a native compilation.

INSTALL
     The install program to use.

Funding Free Software
*********************

If you want to have more free software a few years from now, it makes sense for you to help encourage people to contribute funds for its development.  The most effective approach known is to encourage commercial redistributors to donate.

Users of free software systems can boost the pace of development by encouraging for-a-fee distributors to donate part of their selling price to free software developers---the Free Software Foundation, and others.

The way to convince distributors to do this is to demand it and expect it from them.  So when you compare distributors, judge them partly by how much they give to free software development.  Show distributors they must compete to be the one who gives the most.

To make this approach work, you must insist on numbers that you can compare, such as, ``We will donate ten dollars to the Frobnitz project for each disk sold.''  Don't be satisfied with a vague promise, such as ``A portion of the profits are donated,'' since it doesn't give a basis for comparison.

Even a precise fraction ``of the profits from this disk'' is not very meaningful, since creative accounting and unrelated business decisions can greatly alter what fraction of the sales price counts as profit. If the price you pay is $50, ten percent of the profit is probably less than a dollar; it might be a few cents, or nothing at all.

Some redistributors do development work themselves.  This is useful too; but to keep everyone honest, you need to inquire how much they do, and what kind.  Some kinds of development make much more long-term difference than others.  For example, maintaining a separate version of a program contributes very little; maintaining the standard version of a program for the whole community contributes much.  Easy new ports contribute little, since someone else would surely do them; difficult ports such as adding a new CPU to the GNU Compiler Collection contribute more; major new features or packages contribute the most.

By establishing the idea that supporting further development is ``the proper thing to do'' when distributing free software for a fee, we can assure a steady flow of resources into making more free software.

     Copyright (C) 1994 Free Software Foundation, Inc.
     Verbatim copying and redistribution of this section is permitted
     without royalty; alteration is not permitted.

Linux and the GNU Project
*************************

Many computer users run a modified version of the GNU system every day, without realizing it.  Through a peculiar turn of events, the version of GNU which is widely used today is more often known as ``Linux'', and many users are not aware of the extent of its connection with the GNU Project.

There really is a Linux; it is a kernel, and these people are using it.  But you can't use a kernel by itself; a kernel is useful only as part of a whole system.  The system in which Linux is typically used is a modified variant of the GNU system---in other words, a Linux-based GNU system.

Many users are not fully aware of the distinction between the kernel, which is Linux, and the whole system, which they also call ``Linux''. The ambiguous use of the name doesn't promote understanding.

Programmers generally know that Linux is a kernel.  But since they have generally heard the whole system called ``Linux'' as well, they often envisage a history which fits that name.  For example, many believe that once Linus Torvalds finished writing the kernel, his friends looked around for other free software, and for no particular reason most everything necessary to make a Unix-like system was already available.

What they found was no accident---it was the GNU system.  The available free software added up to a complete system because the GNU Project had been working since 1984 to make one.  The GNU Manifesto had set forth the goal of developing a free Unix-like system, called GNU.  By the time Linux was written, the system was almost finished.

Most free software projects have the goal of developing a particular program for a particular job.  For example, Linus Torvalds set out to write a Unix-like kernel (Linux); Donald Knuth set out to write a text formatter (TeX); Bob Scheifler set out to develop a window system (X Windows).  It's natural to measure the contribution of this kind of project by specific programs that came from the project.

If we tried to measure the GNU Project's contribution in this way, what would we conclude?  One CD-ROM vendor found that in their ``Linux distribution'', GNU software was the largest single contingent, around 28% of the total source code, and this included some of the essential major components without which there could be no system.  Linux itself was about 3%.  So if you were going to pick a name for the system based on who wrote the programs in the system, the most appropriate single choice would be ``GNU''.

But we don't think that is the right way to consider the question. The GNU Project was not, is not, a project to develop specific software packages.  It was not a project to develop a C compiler, although we did.  It was not a project to develop a text editor, although we developed one.  The GNU Project's aim was to develop a complete free Unix-like system.

Many people have made major contributions to the free software in the system, and they all deserve credit.  But the reason it is a system---and not just a collection of useful programs---is because the GNU Project set out to make it one.  We wrote the programs that were needed to make a complete free system.  We wrote essential but unexciting major components, such as the assembler and linker, because you can't have a system without them.  A complete system needs more than just programming tools, so we wrote other components as well, such as the Bourne Again SHell, the PostScript interpreter Ghostscript, and the GNU C library.

By the early 90s we had put together the whole system aside from the kernel (and we were also working on a kernel, the GNU Hurd, which runs on top of Mach).  Developing this kernel has been a lot harder than we expected, and we are still working on finishing it.

Fortunately, you don't have to wait for it, because Linux is working now.  When Linus Torvalds wrote Linux, he filled the last major gap. People could then put Linux together with the GNU system to make a complete free system: a Linux-based GNU system (or GNU/Linux system, for short).

Putting them together sounds simple, but it was not a trivial job. The GNU C library (called glibc for short) needed substantial changes. Integrating a complete system as a distribution that would work ``out of the box'' was a big job, too.  It required addressing the issue of how to install and boot the system---a problem we had not tackled, because we hadn't yet reached that point.  The people who developed the various system distributions made a substantial contribution.

The GNU Project supports GNU/Linux systems as well as the GNU system---even with funds.  We funded the rewriting of the Linux-related extensions to the GNU C library, so that now they are well integrated, and the newest GNU/Linux systems use the current library release with no changes.  We also funded an early stage of the development of Debian GNU/Linux.

We use Linux-based GNU systems today for most of our work, and we hope you use them too.  But please don't confuse the public by using the name ``Linux'' ambiguously.  Linux is the kernel, one of the essential major components of the system.  The system as a whole is more or less the GNU system.

GNU GENERAL PUBLIC LICENSE
**************************

Version 2, June 1991

     Copyright © 1989, 1991 Free Software Foundation, Inc.
     59 Temple Place - Suite 330, Boston, MA 02111-1307, USA

     Everyone is permitted to copy and distribute verbatim copies
     of this license document, but changing it is not allowed.

Preamble
========

The licenses for most software are designed to take away your freedom to share and change it.  By contrast, the GNU General Public License is intended to guarantee your freedom to share and change free software---to make sure the software is free for all its users.  This General Public License applies to most of the Free Software Foundation's software and to any other program whose authors commit to using it.  (Some other Free Software Foundation software is covered by the GNU Library General Public License instead.)  You can apply it to your programs, too.

When we speak of free software, we are referring to freedom, not price.  Our General Public Licenses are designed to make sure that you have the freedom to distribute copies of free software (and charge for this service if you wish), that you receive source code or can get it if you want it, that you can change the software or use pieces of it in new free programs; and that you know you can do these things.

To protect your rights, we need to make restrictions that forbid anyone to deny you these rights or to ask you to surrender the rights. These restrictions translate to certain responsibilities for you if you distribute copies of the software, or if you modify it.

For example, if you distribute copies of such a program, whether gratis or for a fee, you must give the recipients all the rights that you have.  You must make sure that they, too, receive or can get the source code.  And you must show them these terms so they know their rights.

We protect your rights with two steps: (1) copyright the software, and (2) offer you this license which gives you legal permission to copy, distribute and/or modify the software.

Also, for each author's protection and ours, we want to make certain that everyone understands that there is no warranty for this free software.  If the software is modified by someone else and passed on, we want its recipients to know that what they have is not the original, so that any problems introduced by others will not reflect on the original authors' reputations.

Finally, any free program is threatened constantly by software patents.  We wish to avoid the danger that redistributors of a free program will individually obtain patent licenses, in effect making the program proprietary.  To prevent this, we have made it clear that any patent must be licensed for everyone's free use or not licensed at all.

The precise terms and conditions for copying, distribution and modification follow.

TERMS AND CONDITIONS FOR COPYING, DISTRIBUTION AND MODIFICATION

 0. This License applies to any program or other work which contains a notice placed by the copyright holder saying it may be distributed under the terms of this General Public License.  The ``Program'', below, refers to any such program or work, and a ``work based on the Program'' means either the Program or any derivative work under copyright law: that is to say, a work containing the Program or a portion of it, either verbatim or with modifications and/or translated into another language.  (Hereinafter, translation is included without limitation in the term ``modification''.)  Each licensee is addressed as ``you''.

     Activities other than copying, distribution and modification are not covered by this License; they are outside its scope.  The act of running the Program is not restricted, and the output from the Program is covered only if its contents constitute a work based on the Program (independent of having been made by running the Program). Whether that is true depends on what the Program does.

 1. You may copy and distribute verbatim copies of the Program's source code as you receive it, in any medium, provided that you conspicuously and appropriately publish on each copy an appropriate copyright notice and disclaimer of warranty; keep intact all the notices that refer to this License and to the absence of any warranty; and give any other recipients of the Program a copy of this License along with the Program.

     You may charge a fee for the physical act of transferring a copy, and you may at your option offer warranty protection in exchange for a fee.

 2. You may modify your copy or copies of the Program or any portion of it, thus forming a work based on the Program, and copy and distribute such modifications or work under the terms of Section 1 above, provided that you also meet all of these conditions:

      a. You must cause the modified files to carry prominent notices stating that you changed the files and the date of any change.

      b. You must cause any work that you distribute or publish, that in whole or in part contains or is derived from the Program or any part thereof, to be licensed as a whole at no charge to all third parties under the terms of this License.

      c. If the modified program normally reads commands interactively when run, you must cause it, when started running for such interactive use in the most ordinary way, to print or display an announcement including an appropriate copyright notice and a notice that there is no warranty (or else, saying that you provide a warranty) and that users may redistribute the program under these conditions, and telling the user how to view a copy of this License.  (Exception: if the Program itself is interactive but does not normally print such an announcement, your work based on the Program is not required to print an announcement.)

     These requirements apply to the modified work as a whole.  If identifiable sections of that work are not derived from the Program, and can be reasonably considered independent and separate works in themselves, then this License, and its terms, do not apply to those sections when you distribute them as separate works.  But when you distribute the same sections as part of a whole which is a work based on the Program, the distribution of the whole must be on the terms of this License, whose permissions for other licensees extend to the entire whole, and thus to each and every part regardless of who wrote it.

     Thus, it is not the intent of this section to claim rights or contest your rights to work written entirely by you; rather, the intent is to exercise the right to control the distribution of derivative or collective works based on the Program.

     In addition, mere aggregation of another work not based on the Program with the Program (or with a work based on the Program) on a volume of a storage or distribution medium does not bring the other work under the scope of this License.

 3. You may copy and distribute the Program (or a work based on it, under Section 2) in object code or executable form under the terms of Sections 1 and 2 above provided that you also do one of the following:

      a. Accompany it with the complete corresponding machine-readable source code, which must be distributed under the terms of Sections 1 and 2 above on a medium customarily used for software interchange; or,

      b. Accompany it with a written offer, valid for at least three years, to give any third party, for a charge no more than your cost of physically performing source distribution, a complete machine-readable copy of the corresponding source code, to be distributed under the terms of Sections 1 and 2 above on a medium customarily used for software interchange; or,

      c. Accompany it with the information you received as to the offer to distribute corresponding source code.  (This alternative is allowed only for noncommercial distribution and only if you received the program in object code or executable form with such an offer, in accord with Subsection b above.)

     The source code for a work means the preferred form of the work for making modifications to it.  For an executable work, complete source code means all the source code for all modules it contains, plus any associated interface definition files, plus the scripts used to control compilation and installation of the executable.  However, as a special exception, the source code distributed need not include anything that is normally distributed (in either source or binary form) with the major components (compiler, kernel, and so on) of the operating system on which the executable runs, unless that component itself accompanies the executable.

     If distribution of executable or object code is made by offering access to copy from a designated place, then offering equivalent access to copy the source code from the same place counts as distribution of the source code, even though third parties are not compelled to copy the source along with the object code.

 4. You may not copy, modify, sublicense, or distribute the Program except as expressly provided under this License.  Any attempt otherwise to copy, modify, sublicense or distribute the Program is void, and will automatically terminate your rights under this License. However, parties who have received copies, or rights, from you under this License will not have their licenses terminated so long as such parties remain in full compliance.

 5. You are not required to accept this License, since you have not signed it.  However, nothing else grants you permission to modify or distribute the Program or its derivative works.  These actions are prohibited by law if you do not accept this License.  Therefore, by modifying or distributing the Program (or any work based on the Program), you indicate your acceptance of this License to do so, and all its terms and conditions for copying, distributing or modifying the Program or works based on it.

 6. Each time you redistribute the Program (or any work based on the Program), the recipient automatically receives a license from the original licensor to copy, distribute or modify the Program subject to these terms and conditions.  You may not impose any further restrictions on the recipients' exercise of the rights granted herein. You are not responsible for enforcing compliance by third parties to this License.

 7. If, as a consequence of a court judgment or allegation of patent infringement or for any other reason (not limited to patent issues), conditions are imposed on you (whether by court order, agreement or otherwise) that contradict the conditions of this License, they do not excuse you from the conditions of this License.  If you cannot distribute so as to satisfy simultaneously your obligations under this License and any other pertinent obligations, then as a consequence you may not distribute the Program at all.  For example, if a patent license would not permit royalty-free redistribution of the Program by all those who receive copies directly or indirectly through you, then the only way you could satisfy both it and this License would be to refrain entirely from distribution of the Program.

     If any portion of this section is held invalid or unenforceable under any particular circumstance, the balance of the section is intended to apply and the section as a whole is intended to apply in other circumstances.

     It is not the purpose of this section to induce you to infringe any patents or other property right claims or to contest validity of any such claims; this section has the sole purpose of protecting the integrity of the free software distribution system, which is implemented by public license practices.  Many people have made generous contributions to the wide range of software distributed through that system in reliance on consistent application of that system; it is up to the author/donor to decide if he or she is willing to distribute software through any other system and a licensee cannot impose that choice.

     This section is intended to make thoroughly clear what is believed to be a consequence of the rest of this License.

 8. If the distribution and/or use of the Program is restricted in certain countries either by patents or by copyrighted interfaces, the original copyright holder who places the Program under this License may add an explicit geographical distribution limitation excluding those countries, so that distribution is permitted only in or among countries not thus excluded.  In such case, this License incorporates the limitation as if written in the body of this License.

 9. The Free Software Foundation may publish revised and/or new versions of the General Public License from time to time.  Such new versions will be similar in spirit to the present version, but may differ in detail to address new problems or concerns.

     Each version is given a distinguishing version number.  If the Program specifies a version number of this License which applies to it and ``any later version'', you have the option of following the terms and conditions either of that version or of any later version published by the Free Software Foundation.  If the Program does not specify a version number of this License, you may choose any version ever published by the Free Software Foundation.

 10. If you wish to incorporate parts of the Program into other free programs whose distribution conditions are different, write to the author to ask for permission.  For software which is copyrighted by the Free Software Foundation, write to the Free Software Foundation; we sometimes make exceptions for this.  Our decision will be guided by the two goals of preserving the free status of all derivatives of our free software and of promoting the sharing and reuse of software generally.

     NO WARRANTY

 11. BECAUSE THE PROGRAM IS LICENSED FREE OF CHARGE, THERE IS NO WARRANTY FOR THE PROGRAM, TO THE EXTENT PERMITTED BY APPLICABLE LAW.  EXCEPT WHEN OTHERWISE STATED IN WRITING THE COPYRIGHT HOLDERS AND/OR OTHER PARTIES PROVIDE THE PROGRAM ``AS IS'' WITHOUT WARRANTY OF ANY KIND, EITHER EXPRESSED OR IMPLIED, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.  THE ENTIRE RISK AS TO THE QUALITY AND PERFORMANCE OF THE PROGRAM IS WITH YOU.  SHOULD THE PROGRAM PROVE DEFECTIVE, YOU ASSUME THE COST OF ALL NECESSARY SERVICING, REPAIR OR CORRECTION.

 12. IN NO EVENT UNLESS REQUIRED BY APPLICABLE LAW OR AGREED TO IN WRITING WILL ANY COPYRIGHT HOLDER, OR ANY OTHER PARTY WHO MAY MODIFY AND/OR REDISTRIBUTE THE PROGRAM AS PERMITTED ABOVE, BE LIABLE TO YOU FOR DAMAGES, INCLUDING ANY GENERAL, SPECIAL, INCIDENTAL OR CONSEQUENTIAL DAMAGES ARISING OUT OF THE USE OR INABILITY TO USE THE PROGRAM (INCLUDING BUT NOT LIMITED TO LOSS OF DATA OR DATA BEING RENDERED INACCURATE OR LOSSES SUSTAINED BY YOU OR THIRD PARTIES OR A FAILURE OF THE PROGRAM TO OPERATE WITH ANY OTHER PROGRAMS), EVEN IF SUCH HOLDER OR OTHER PARTY HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES.

END OF TERMS AND CONDITIONS

How to Apply These Terms to Your New Programs
=============================================

If you develop a new program, and you want it to be of the greatest possible use to the public, the best way to achieve this is to make it free software which everyone can redistribute and change under these terms.

To do so, attach the following notices to the program.  It is safest to attach them to the start of each source file to most effectively convey the exclusion of warranty; and each file should have at least the ``copyright'' line and a pointer to where the full notice is found.

     ONE LINE TO GIVE THE PROGRAM'S NAME AND A BRIEF IDEA OF WHAT IT DOES.
     Copyright (C) YYYY  NAME OF AUTHOR

     This program is free software; you can redistribute it and/or modify
     it under the terms of the GNU General Public License as published by
     the Free Software Foundation; either version 2 of the License, or
     (at your option) any later version.

     This program is distributed in the hope that it will be useful,
     but WITHOUT ANY WARRANTY; without even the implied warranty of
     MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
     GNU General Public License for more details.

     You should have received a copy of the GNU General Public License
     along with this program; if not, write to the Free Software
     Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.

Also add information on how to contact you by electronic and paper mail.

If the program is interactive, make it output a short notice like this when it starts in an interactive mode:

     Gnomovision version 69, Copyright (C) YYYY NAME OF AUTHOR
     Gnomovision comes with ABSOLUTELY NO WARRANTY; for details
     type `show w'.
     This is free software, and you are welcome to redistribute it
     under certain conditions; type `show c' for details.

The hypothetical commands show w and show c should show the appropriate parts of the General Public License.  Of course, the commands you use may be called something other than show w and show c; they could even be mouse-clicks or menu items---whatever suits your program.

You should also get your employer (if you work as a programmer) or your school, if any, to sign a ``copyright disclaimer'' for the program, if necessary.  Here is a sample; alter the names:

     Yoyodyne, Inc., hereby disclaims all copyright interest in the program
     `Gnomovision' (which makes passes at compilers) written by James Hacker.

     SIGNATURE OF TY COON, 1 April 1989
     Ty Coon, President of Vice

This General Public License does not permit incorporating your program into proprietary programs.  If your program is a subroutine library, you may consider it more useful to permit linking proprietary applications with the library.  If this is what you want to do, use the GNU Library General Public License instead of this License.

Contributors to GCC
*******************

     [file contrib.texi not included]