Using and Porting GNU CC

Richard M. Stallman

last updated 15 February 1992

for version 2.0

(preliminary draft, which will change)

Copyright © 1988, 1989, 1992 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 section entitled “GNU General Public License” is 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 section entitled “GNU General Public License” and this permission notice may be included in translations approved by the Free Software Foundation instead of in the original English.

GNU GENERAL PUBLIC LICENSE

Version 2, June 1991

Copyright © 1989, 1991 Free Software Foundation, Inc.
675 Mass Ave, Cambridge, MA 02139, 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.

1. 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.

2. 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.

3. 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:
   1. You must cause the modified files to carry prominent notices stating that you changed the files and the date of any change.
   2. 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.
   3. 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.

4. 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:
   1. 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,
   2. 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,
   3. 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.

5. 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.
6. 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.
7. 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.
8. 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.

9. 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.
10. 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.

11. 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.
12. 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.
13. 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.

Appendix: 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) 19yy  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., 675 Mass Ave, Cambridge, MA 02139, 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) 19yy 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 GNU CC

In addition to Richard Stallman, several people have written parts of GNU CC.

• The idea of using RTL and some of the optimization ideas came from the U. of Arizona Portable Optimizer, written by Jack Davidson and Christopher Fraser. See “Register Allocation and Exhaustive Peephole Optimization”, Software Practice and Experience 14 (9), Sept. 1984, 857-866.
• Paul Rubin wrote most of the preprocessor.
• Leonard Tower wrote parts of the parser, RTL generator, and RTL definitions, and of the Vax machine description.
• Ted Lemon wrote parts of the RTL reader and printer.
• Jim Wilson implemented loop strength reduction and some other loop optimizations.
• Nobuyuki Hikichi of Software Research Associates, Tokyo, contributed the support for the Sony NEWS machine.
• Charles LaBrec contributed the support for the Integrated Solutions 68020 system.
• Michael Tiemann of Cygnus Support wrote the front end for C++, as well as the support for inline functions and instruction scheduling. Also the descriptions of the National Semiconductor 32000 series cpu, the SPARC cpu and part of the Motorola 88000 cpu.
• Jan Stein of the Chalmers Computer Society provided support for Genix, as well as part of the 32000 machine description.
• Randy Smith finished the Sun FPA support.
• Robert Brown implemented the support for Encore 32000 systems.
• David Kashtan of SRI adapted GNU CC to the Vomit-Making System (VMS).
• Alex Crain provided changes for the 3b1.
• Greg Satz and Chris Hanson assisted in making GNU CC work on HP-UX for the 9000 series 300.
• William Schelter did most of the work on the Intel 80386 support.
• Christopher Smith did the port for Convex machines.
• Paul Petersen wrote the machine description for the Alliant FX/8.
• Alain Lichnewsky ported GNU CC to the Mips cpu.
• Devon Bowen, Dale Wiles and Kevin Zachmann ported GNU CC to the Tahoe.
• Jonathan Stone wrote the machine description for the Pyramid computer.
• Richard Kenner of New York University wrote the machine descriptions for the AMD 29000, the IBM RT PC, and the IBM RS/6000 as well as the support for instruction attributes. He also made changes to better support RISC processors including changes to common subexpression elimination, strength reduction, function calling sequence handling, and condition code support, in addition to generalizing the code for frame pointer elimination.
• Richard Kenner and Michael Tiemann jointly developed reorg.c, the delay slot scheduler.
• Mike Meissner and Tom Wood of Data General finished the port to the Motorola 88000.
• Masanobu Yuhara of Fujitsu Laboratories implemented the machine description for the Tron architecture (specifically, the Gmicro).
• NeXT, Inc. donated the front end that supports the Objective C language.
• James van Artsdalen wrote the code that makes efficient use of the Intel 80387 register stack.
• Mike Meissner at the Open Software Foundation finished the port to the MIPS cpu, including adding ECOFF debug support.
• Ron Guilmette implemented the protoize and unprotoize tools, the support for Dwarf symbolic debugging information, and much of the support for System V Release 4. He has also worked heavily on the Intel 386 and 860 support.

1 Protect Your Freedom—Fight “Look And Feel”

This section is a political message from the League for Programming Freedom to the users of GNU CC. It is included here as an expression of support for the League on the part of the Free Software Foundation.

Apple, Lotus and Xerox are trying to create a new form of legal monopoly: a copyright on a class of user interfaces. These monopolies would cause serious problems for users and developers of computer software and systems.

Until a few years ago, the law seemed clear: no one could restrict others from using a user interface; programmers were free to implement any interface they chose. Imitating interfaces, sometimes with changes, was standard practice in the computer field. The interfaces we know evolved gradually in this way; for example, the Macintosh user interface drew ideas from the Xerox interface, which in turn drew on work done at Stanford and SRI. 1-2-3 imitated VisiCalc, and dBase imitated a database program from JPL.

Most computer companies, and nearly all computer users, were happy with this state of affairs. The companies that are suing say it does not offer “enough incentive” to develop their products, but they must have considered it “enough” when they made their decision to do so. It seems they are not satisfied with the opportunity to continue to compete in the marketplace—not even with a head start.

If Xerox, Lotus, and Apple are permitted to make law through the courts, the precedent will hobble the software industry:

• Gratuitous incompatibilities will burden users. Imagine if each car manufacturer had to arrange the pedals in a different order.
• Software will become and remain more expensive. Users will be “locked in” to proprietary interfaces, for which there is no real competition.
• Large companies have an unfair advantage wherever lawsuits become commonplace. Since they can easily afford to sue, they can intimidate small companies with threats even when they don’t really have a case.
• User interface improvements will come slower, since incremental evolution through creative imitation will no longer be permitted.
• Even Apple, etc., will find it harder to make improvements if they can no longer adapt the good ideas that others introduce, for fear of weakening their own legal positions. Some users suggest that this stagnation may already have started.
• If you use GNU software, you might find it of some concern that user interface copyright will make it hard for the Free Software Foundation to develop programs compatible with the interfaces that you already know.

To protect our freedom from lawsuits like these, a group of programmers and users have formed a new grass-roots political organization, the League for Programming Freedom.

The purpose of the League is to oppose new monopolistic practices such as user-interface copyright and software patents; it calls for a return to the legal policies of the recent past, in which these practices were not allowed. The League is not concerned with free software as an issue, and not affiliated with the Free Software Foundation.

The League’s membership rolls include John McCarthy, inventor of Lisp, Marvin Minsky, founder of the Artificial Intelligence lab, Guy L. Steele, Jr., author of well-known books on Lisp and C, as well as Richard Stallman, the developer of GNU CC. Please join and add your name to the list. Membership dues in the League are $42 per year for programmers, managers and professionals; $10.50 for students; $21 for others.

The League needs both activist members and members who only pay their dues.

To join, or for more information, phone (617) 492-0023 or write to:

League for Programming Freedom
1 Kendall Square #143
P.O. Box 9171
Cambridge, MA 02139

You can also send electronic mail to league@prep.ai.mit.edu.

Here are some suggestions from the League for things you can do to protect your freedom to write programs:

• Don’t buy from Xerox, Lotus or Apple. Buy from their competitors or from the defendants they are suing.
• Don’t develop software to work with the systems made by these companies.
• Port your existing software to competing systems, so that you encourage users to switch.
• Write letters to company presidents to let them know their conduct is unacceptable.
• Tell your friends and colleagues about this issue and how it threatens to ruin the computer industry.
• Above all, don’t work for the look-and-feel plaintiffs, and don’t accept contracts from them.
• Write to Congress to explain the importance of this issue.

  House Subcommittee on Intellectual Property
  2137 Rayburn Bldg
  Washington, DC 20515
  
  Senate Subcommittee on Patents, Trademarks and Copyrights
  United States Senate
  Washington, DC 20510
  

  (These committees have received lots of mail already; let’s give them even more.)

Express your opinion! You can make a difference.

2 Installing GNU CC

Here is the procedure for installing GNU CC on a Unix system.

1. If you have built GNU CC previously in the same directory for a different target machine, do ‘make cleanconfig’ to delete all files that might be invalid.
2. On a Sequent system, go to the Berkeley universe.
3. On a System V release 4 system, make sure ‘/usr/bin’ precedes ‘/usr/ucb’ in PATH. The cc command in ‘/usr/ucb’ uses libraries which have bugs.
4. Specify the host and target machine configurations. You do this by running the file ‘configure’ with appropriate arguments.

   If you are building a compiler to produce code for the machine it runs on, specify just one machine type. To build a cross-compiler, specify two configurations, one for the host machine (which the compiler runs on), and one for the target machine (which the compiler produces code for). The command looks like this:

   configure --host=sun3-sunos3 --target=sparc-sun-sunos4.1
   

   A configuration name may be canonical or it may be more or less abbreviated.

   A canonical configuration name has three parts, separated by dashes. It looks like this: ‘cpu-company-system’. (The three parts may themselves contain dashes; ‘configure’ can figure out which dashes serve which purpose.) For example, ‘m68k-sun-sunos4.1’ specifies a Sun 3.

   You can also replace parts of the configuration by nicknames or aliases. For example, ‘sun3’ stands for ‘m68k-sun’, so ‘sun3-sunos4.1’ is another way to specify a Sun 3. You can also use simply ‘sun3-sunos’, since the version of Sunos is assumed by default to be version 4. ‘sun3-bsd’ also works, since ‘configure’ knows that the only BSD variant on a Sun 3 is Sunos.

   You can specify a version number after any of the system types, and some of the CPU types. In most cases, the version is irrelevant, and will be ignored. So you might as well specify the version if you know it.

   Here are the possible CPU types:

   a29k, arm, cn, hppa, i386, i860, m68000, m68k, m88k, mips, ns32k, romp, rs6000, sparc, vax.

   Note that the type hppa currently works only with Berkeley systems, not with HP/UX.

   Here are the recognized company names. As you can see, customary abbreviations are used rather than the longer official names.

   alliant, altos, apollo, att, convergent, convex, crds, dec, dg, encore, harris, hp, ibm, mips, motorola, ncr, next, ns, omron, sequent, sgi, sony, sun, tti, unicom.

   The company name is meaningful only to disambiguate when the rest of the information supplied is insufficient. You can omit it, writing just ‘cpu-system’, if it is not needed. For example, ‘vax-ultrix4.2’ is equivalent to ‘vax-dec-ultrix4.2’.

   Here is a list of system types:

   bsd, sysv, mach, minix, genix, ultrix, vms, sco, esix, isc, aix, sunos, hpux, unos, luna, dgux, newsos, osfrose, osf, dynix, aos, ctix.

   You can omit the system type; then ‘configure’ guesses the operating system from the CPU and company.

   Often a particular model of machine has a name. Many of these names are recognized as an alias for a CPU/company combination. The alias ‘sun3’, mentioned above, is an example of this: it stands for ‘m68k-sun’. Sometimes we accept a company name as a machine name, when the name is popularly used for a particular machine. Here is a table of the known machine names:

   3300, 3b1, 7300, altos3068, altos, apollo68, att-7300, balance, convex-cn, crds, decstation-3100, decstation-dec, decstation, delta, encore, gmicro, hp7nn, hp8nn, hp9k2nn, hp9k3nn, hp9k7nn, hp9k8nn, iris4d, iris, isi68, m3230, magnum, merlin, miniframe, mmax, news-3600, news800, news, next, pbd, pc532, pmax, ps2, risc-news, rtpc, sun2, sun386i, sun386, sun3, sun4, symmetry, tower-32, tower.

   If you specify an impossible combination such as ‘i860-dg-vms’, then you may get an error message from ‘configure’, or it may ignore part of the information and do the best it can with the rest. ‘configure’ always prints the canonical name for the alternative that it used.

   On certain systems, you must specify whether you want GNU CC to work with the usual compilation tools or with the GNU compilation tools (including GAS). Use the ‘--gas’ argument when you run ‘configure’, if you want to use the GNU tools. The systems were this makes a difference are ‘i386-anything-sysv’, ‘i860-anything-bsd’, ‘m68k-hp-hpux’, ‘m68k-sony-bsd’, ‘m68k-altos-sysv’, ‘m68000-hp-hpux’, and ‘m68000-att-sysv’. On any other system, ‘--gas’ has no effect.

   On certain systems, you must specify whether the machine has a floating point unit. These systems are ‘m68k-sun-sunosn’ and ‘m68k-isi-bsd’. On any other system, ‘--nfp’ currently has no effect, though perhaps there are other systems where it could usefully make a difference.

   If you want to install your own homemade configuration files, you can use ‘local’ as the company name to access them. If you use configuration ‘cpu-local’, the entire configuration name is used to form the configuration file names.

   Thus, if you specify ‘m68k-local’, then the files used are ‘m68k-local.md’, ‘m68k-local.h’, ‘m68k-local.c’, ‘xm-m68k-local.h’, ‘t-m68k-local’, and ‘x-m68k-local’.

   Here is a list of configurations that have special treatment:

   ‘m68000-att’

   AT&T 3b1, a.k.a. 7300 PC. Special procedures are needed to compile GNU CC with this machine’s standard C compiler, due to bugs in that compiler. See section Installing GNU CC on the 3b1. You can bootstrap it more easily with previous versions of GNU CC if you have them.

   ‘m68000-hp-bsd’

   HP 9000 series 200 running BSD. Note that the C compiler that comes with this system cannot compile GNU CC; contact law@super.org to get binaries of GNU CC for bootstrapping.

   ‘m68k-altos’

   Altos 3068. You must use the GNU assembler, linker and debugger, with COFF-encapsulation. Also, you must fix a kernel bug. Details in the file ‘ALTOS-README’.

   ‘m68k-hp-hpux’

   HP 9000 series 200 or 300 running HPUX. GNU CC does not support the special symbol table used by HP’s debugger, but you can debug programs with GDB if you specify ‘--gas’ to use the GNU tools instead. In order to use the GNU tools, you must install a library conversion program called hpxt.

   ‘m68k-sun’

   Sun 3. We do not provide a configuration file to use the Sun FPA by default, because programs that establish signal handlers for floating point traps inherently cannot work with the FPA.

   ‘m88k-dgux’

   Motorola m88k running DG/UX. To build native or cross compilers on DG/UX, you must first change to the 88open BCS software development environment. This is done by issuing this command:

   eval `sde-target m88kbcs`
   

   ‘ns32k-encore’

   Encore ns32000 system. Encore systems are supported only under BSD.

   ‘ns32k-*-genix’

   National Semiconductor ns32000 system. Genix has bugs in alloca and malloc; you must get the compiled versions of these from GNU Emacs.

   ‘ns32k-utek’

   UTEK ns32000 system (“merlin”). The C compiler that comes with this system cannot compile GNU CC; contact ‘tektronix!reed!mason’ to get binaries of GNU CC for bootstrapping.

   ‘rs6000-ibm’

   IBM PowerStation/6000 machines. Due to the nonstandard debugging information required for this machine, ‘-g’ is not available in this configuration.

   ‘vax-dec-ultrix’

   Don’t try compiling with Vax C (vcc). It produces incorrect code in some cases (for example, when alloca is used).

   Meanwhile, compiling ‘cp-parse.c’ with pcc does not work because of an internal table size limitation in that compiler. To avoid this problem, compile just the GNU C compiler first, and use it to recompile building all the languages that you want to run.

   Here we spell out what files will be set up by configure. Normally you need not be concerned with these files.

   • A symbolic link named ‘config.h’ is made to the top-level config file for the machine you will run the compiler on (see section The Configuration File). This file is responsible for defining information about the host machine. It includes ‘tm.h’.

     The top-level config file is located in the subdirectory ‘config’. Its name is always ‘xm-something.h’; usually ‘xm-machine.h’, but there are some exceptions.

     If your system does not support symbolic links, you might want to set up ‘config.h’ to contain a ‘#include’ command which refers to the appropriate file.

   • A symbolic link named ‘tconfig.h’ is made to the top-level config file for your target machine. This is used for compiling certain programs to run on that machine.
   • A symbolic link named ‘tm.h’ is made to the machine-description macro file for your target machine. It should be in the subdirectory ‘config’ and its name is often ‘machine.h’.
   • A symbolic link named ‘md’ will be made to the machine description pattern file. It should be in the ‘config’ subdirectory and its name should be ‘machine.md’; but machine is often not the same as the name used in the ‘tm.h’ file because the ‘md’ files are more general.
   • A symbolic link named ‘aux-output.c’ will be made to the output subroutine file for your machine. It should be in the ‘config’ subdirectory and its name should be ‘machine.c’.
   • The command file ‘configure’ also constructs ‘Makefile’ by adding some text to the template file ‘Makefile.in’. The additional text comes from files in the ‘config’ directory, named ‘t-target’ and ‘h-host’. If these files do not exist, it means nothing needs to be added for a given target or host.
5. Make sure the Bison parser generator is installed. (This is unnecessary if the Bison output files ‘c-parse.c’ and ‘cexp.c’ are more recent than ‘c-parse.y’ and ‘cexp.y’ and you do not plan to change the ‘.y’ files.)

   Bison versions older than Sept 8, 1988 will produce incorrect output for ‘c-parse.c’.

6. Build the compiler. Just type ‘make LANGUAGES=c’ in the compiler directory.

   ‘LANGUAGES=c’ specifies that only the C compiler should be compiled. The makefile normally builds compilers for all the supported languages; currently, C, C++ and Objective C. However, C is the only language that is sure to work when you build with other non-GNU C compilers. In addition, building anything but C at this stage is a waste of time.

   In general, you can specify the languages to build by typing the argument ‘LANGUAGES="list"’, where list is one or more words from the list ‘c’, ‘c++’, and ‘objective-c’.

   Ignore any warnings you may see about “statement not reached” in ‘insn-emit.c’; they are normal. Any other compilation errors may represent bugs in the port to your machine or operating system, and should be investigated and reported (see section Reporting Bugs).

   Some commercial compilers fail to compile GNU CC because they have bugs or limitations. For example, the Microsoft compiler is said to run out of macro space. Some Ultrix compilers run out of expression space; then you need to break up the statement where the problem happens.

7. If you are using COFF-encapsulation, you must convert ‘libgcc.a’ to a GNU-format library at this point. See the file ‘README-ENCAP’ in the directory containing the GNU binary file utilities, for directions.
8. Move the first-stage object files and executables into a subdirectory with this command:

   make stage1
   

   The files are moved into a subdirectory named ‘stage1’. Once installation is complete, you may wish to delete these files with rm -r stage1.

9. Recompile the compiler with itself, with this command:

   make CC=stage1/gcc CFLAGS="-g -O -Bstage1/"
   

   This is called making the stage 2 compiler.

   The command shown above builds compilers for all the supported languages. If you don’t want them all, you can specify the languages to build by typing the argument ‘LANGUAGES="list"’. list should contain one or more words from the list ‘c’, ‘c++’, and ‘objective-c’, separated by spaces.

   On a 68000 or 68020 system lacking floating point hardware, unless you have selected a ‘tm.h’ file that expects by default that there is no such hardware, do this instead:

   make CC=stage1/gcc CFLAGS="-g -O -Bstage1/ -msoft-float"
   

10. If you wish to test the compiler by compiling it with itself one more time, do this:

    make stage2
    make CC=stage2/gcc CFLAGS="-g -O -Bstage2/" 
    

    This is called making the stage 3 compiler. Aside from the ‘-B’ option, the options should be the same as when you made the stage 2 compiler.

    Then compare the latest object files with the stage 2 object files—they ought to be identical, unless they contain time stamps. On systems where object files do not contain time stamps, you can do this (in Bourne shell):

    for file in *.o; do
    cmp $file stage2/$file
    done
    

    This will mention any object files that differ between stage 2 and stage 3. Any difference, no matter how innocuous, indicates that the stage 2 compiler has compiled GNU CC incorrectly, and is therefore a potentially serious bug which you should investigate and report (see section Reporting Bugs).

    On systems that use COFF object files, bytes 5 to 8 will always be different, since it is a timestamp. On these systems, you can do the comparison as follows (in Bourne shell):

    for file in *.o; do
    tail +10c $file > foo1
    tail +10c stage2/$file > foo2
    cmp foo1 foo2 || echo $file
    done
    

    On MIPS machines, you need to use the shell script ‘ecoff-cmp’ to compare two object files if you have built the compiler with the ‘-mno-mips-tfile’ option. Thus, do this:

    for file in *.o; do
    ecoff-cmp $file stage2/$file
    done
    

11. Install the compiler driver, the compiler’s passes and run-time support. You can use the following command:

    make CC=stage2/gcc install
    

    (Use the same value for CC that you used when compiling the files that are being installed.)

    This copies the files ‘cc1’, ‘cpp’ and ‘libgcc.a’ to files ‘cc1’, ‘cpp’ and ‘libgcc.a’ in directory ‘/usr/local/lib/gcc/target/version’, which is where the compiler driver program looks for them. Here target is the target machine type specified when you ran ‘configure’, and version is the version number of GNU CC. This naming scheme permits various versions and/or cross-compilers to coexist.

    It also copies the driver program ‘gcc’ into the directory ‘/usr/local/bin’, so that it appears in typical execution search paths.

    Warning: there is a bug in alloca in the Sun library. To avoid this bug, install the binaries of GNU CC that were compiled by GNU CC. They use alloca as a built-in function and never the one in the library.

12. If you will be using C++ or Objective C, and your operating system does not handle constructors, then you must build and install the program collect2. Do this with the following command:

    make CC="stage2/gcc -O" install-collect2
    

    The systems that do handle constructors on their own include system V release 4, and system V release 3 on the Intel 386.

    Berkeley systems that use the “a.out” object file format handle constructors without collect2 if you use the GNU linker. But if you don’t use the GNU linker, then you need collect2 on these systems.

13. Build and install protoize if you want it. Type

    make CC="stage2/gcc -O" install-proto
    

    There is as yet no documentation for protoize. Sorry.

14. Correct errors in the header files on your machine.

    Various system header files often contain constructs which are incompatible with ANSI C, and they will not work when you compile programs with GNU CC. This behavior consists of substituting for macro argument names when they appear inside of character constants. The most common offender is ‘ioctl.h’.

    You can overcome this problem when you compile by specifying the ‘-traditional’ option.

    Alternatively, on Sun systems and 4.3BSD at least, you can correct the include files by running the shell script ‘fixincludes’. This installs modified, corrected copies of the files ‘ioctl.h’, ‘ttychars.h’ and many others, in a special directory where only GNU CC will normally look for them. This script will work on various systems because it chooses the files by searching all the system headers for the problem cases that we know about.

    Use the following command to do this:

    make install-fixincludes
    

    If you selected a different directory for GNU CC installation when you installed it, by specifying the Make variable prefix or libdir, specify it the same way in this command.

    Note that some systems are starting to come with ANSI C system header files. On these systems, don’t run ‘fixincludes’; it may not work, and is certainly not necessary.

If you cannot install the compiler’s passes and run-time support in ‘/usr/local/lib’, you can alternatively use the ‘-B’ option to specify a prefix by which they may be found. The compiler concatenates the prefix with the names ‘cpp’, ‘cc1’ and ‘libgcc.a’. Thus, you can put the files in a directory ‘/usr/foo/gcc’ and specify ‘-B/usr/foo/gcc/’ when you run GNU CC.

Also, you can specify an alternative default directory for these files by setting the Make variable libdir when you make GNU CC.

2.1 Compilation in a Separate Directory

If you wish to build the object files and executables in a directory other than the one containing the source files, here is what you must do differently:

1. Make sure you have a version of Make that supports the VPATH feature. (GNU Make supports it, as do Make versions on most BSD systems.)
2. Go to that directory before running ‘configure’:

   mkdir gcc-sun3
   cd gcc-sun3
   

   On systems that do not support symbolic links, this directory must be on the same file system as the source code directory.

3. Specify where to find ‘configure’ when you run it:

   ../gcc-2.00/configure …
   

   This also tells configure where to find the compiler sources; configure takes the directory from the file name that was used to invoke it. But if you want to be sure, you can specify the source directory with the ‘--srcdir’ option, like this:

   ../gcc-2.00/configure --srcdir=../gcc-2.00 sun3
   

   The directory you specify with ‘--srcdir’ need not be the same as the one that configure is found in.

Now, you can run make in that directory. You need not repeat the configuration steps shown above, when ordinary source files change. You must, however, run configure again when the configuration files change, if your system does not support symbolic links.

2.2 Installing GNU CC on the Sun

Make sure the environment variable FLOAT_OPTION is not set when you compile ‘libgcc.a’. If this option were set to f68881 when ‘libgcc.a’ is compiled, the resulting code would demand to be linked with a special startup file and would not link properly without special pains.

There is a bug in alloca in certain versions of the Sun library. To avoid this bug, install the binaries of GNU CC that were compiled by GNU CC. They use alloca as a built-in function and never the one in the library.

Some versions of the Sun compiler crash when compiling GNU CC. The problem is a segmentation fault in cpp. This problem seems to be due to the bulk of data in the environment variables. You may be able to avoid it by using the following command to compile GNU CC with Sun CC:

make CC="TERMCAP=x OBJS=x LIBFUNCS=x STAGESTUFF=x cc"

2.3 Installing GNU CC on the 3b1

Installing GNU CC on the 3b1 is difficult if you do not already have GNU CC running, due to bugs in the installed C compiler. However, the following procedure might work. We are unable to test it.

1. Comment out the ‘#include "config.h"’ line on line 37 of ‘cccp.c’ and do ‘make cpp’. This makes a preliminary version of GNU cpp.
2. Save the old ‘/lib/cpp’ and copy the preliminary GNU cpp to that file name.
3. Undo your change in ‘cccp.c’, or reinstall the original version, and do ‘make cpp’ again.
4. Copy this final version of GNU cpp into ‘/lib/cpp’.
5. Replace every occurrence of obstack_free in the file ‘tree.c’ with _obstack_free.
6. Run make to get the first-stage GNU CC.
7. Reinstall the original version of ‘/lib/cpp’.
8. Now you can compile GNU CC with itself and install it in the normal fashion.

2.4 Installing GNU CC on SCO System V 3.2

The compiler that comes with this system does not work properly with ‘-O’. Therefore, you should redefine the Make variable CCLIBFLAGS not to use ‘-O’.

In addition, the compiler produces incorrect output when compiling parts of GNU CC; the resulting executable ‘cc1’ does not work properly when it is used with ‘-O’.

Therefore, what you must do after building the first stage is use GNU CC to compile itself without optimization. Here is how:

make -k cc1 CC="./gcc -B./"

You can think of this as “stage 1.1” of the installation process. However, using this command has the effect of discarding the faulty stage 1 executable for ‘cc1’ and replacing it with stage 1.1. You can then proceed with ‘make stage1’ and the rest of installation.

On Xenix, the same thing is necessary; in addition, you may have to remove ‘-g’ from the options used with cc, and you may have to simplify complicated statements in the sources of GNU CC to get them to compile.

2.5 Installing GNU CC on Unos

Use ‘configure unos’ for building on Unos.

The Unos assembler is named casm instead of as. For some strange reason linking ‘/bin/as’ to ‘/bin/casm’ changes the behavior, and does not work. So, when installing GNU CC, you should install the following script as ‘as’ in the subdirectory where the passes of GCC are installed:

#!/bin/sh
casm $*

The default Unos library is named ‘libunos.a’ instead of ‘libc.a’. To allow GNU CC to function, either change all references to ‘-lc’ in ‘gcc.c’ to ‘-lunos’ or link ‘/lib/libc.a’ to ‘/lib/libunos.a’.

When compiling GNU CC with the standard compiler, to overcome bugs in the support of alloca, do not use ‘-O’ when making stage 2. Then use the stage 2 compiler with ‘-O’ to make the stage 3 compiler. This compiler will have the same characteristics as the usual stage 2 compiler on other systems. Use it to make a stage 4 compiler and compare that with stage 3 to verify proper compilation.

Unos uses memory segmentation instead of demand paging, so you will need a lot of memory. 5 Mb is barely enough if no other tasks are running. If linking ‘cc1’ fails, try putting the object files into a library and linking from that library.

2.6 Installing GNU CC on VMS

The VMS version of GNU CC is distributed in a backup saveset containing both source code and precompiled binaries.

To install the ‘gcc’ command so you can use the compiler easily, in the same manner as you use the VMS C compiler, you must install the VMS CLD file for GNU CC as follows:

1. Define the VMS logical names ‘GNU_CC’ and ‘GNU_CC_INCLUDE’ to point to the directories where the GNU CC executables (‘gcc-cpp’, ‘gcc-cc1’, etc.) and the C include files are kept. This should be done with the commands:

   $ assign /super /system disk:[gcc.] gnu_cc
   $ assign /super /system disk:[gcc.include.] gnu_cc_include
   

   with the appropriate disk and directory names. These commands can be placed in your system startup file so they will be executed whenever the machine is rebooted. You may, if you choose, do this via the ‘GCC_INSTALL.COM’ script in the ‘[GCC]’ directory.

2. Install the ‘GCC’ command with the command line:

   $ set command /table=sys$library:dcltables gnu_cc:[000000]gcc
   

3. To install the help file, do the following:

   $ lib/help sys$library:helplib.hlb gcc.hlp
   

   Now you can invoke the compiler with a command like ‘gcc /verbose file.c’, which is equivalent to the command ‘gcc -v -c file.c’ in Unix.

If you wish to use GNU C++ you must first install GNU CC, and then perform the following steps:

1. Define the VMS logical name ‘GNU_GXX_INCLUDE’ to point to the directory where the preprocessor will search for the C++ header files. This can be done with the command:

   $ assign /super /system disk:[gcc.gxx_include.] gnu_gxx_include
   

   with the appropriate disk and directory name. If you are going to be using libg++, you should place the libg++ header files in the directory that this logical name points to.

2. Obtain the file ‘gcc-cc1plus.exe’, and place this in the same directory that ‘gcc-cc1.exe’ is kept.
3. You will need several library functions which are used to call the constructors and destructors for global objects. These functions are part of the libg++ distribution, and you will automatically get them if you install libg++.

   If you are not planning to install libg++, you will need to obtain the files ‘gxx-startup-1.mar’ and ‘gstart.cc’ from the libg++ distribution, compile them, and supply them to the linker whenever you link a C++ program.

   The GNU C++ compiler can be invoked with a command like ‘gcc /plus /verbose file.cc’, which is equivalent to the command ‘g++ -v -c file.cc’ in Unix.

We try to put corresponding binaries and sources on the VMS distribution tape. But sometimes the binaries will be from an older version that the sources, because we don’t always have time to update them. (Use the ‘/version’ option to determine the version number of the binaries and compare it with the source file ‘version.c’ to tell whether this is so.) In this case, you should use the binaries you get to recompile the sources. If you must recompile, here is how:

1. Copy the file ‘vms.h’ to ‘tm.h’, ‘xm-vms.h’ to ‘config.h’, ‘vax.md’ to ‘md.’ and ‘vax.c’ to ‘aux-output.c’. The files to be copied are found in the subdirectory named ‘config’; they should be copied to the main directory of GNU CC. If you wish, you may use the command file ‘config-gcc.com’ to perform these steps for you.
2. Setup the logical names and command tables as defined above. In addition, define the VMS logical name ‘GNU_BISON’ to point at the to the directories where the Bison executable is kept. This should be done with the command:

   $ assign /super /system disk:[bison.] gnu_bison
   

   You may, if you choose, use the ‘INSTALL_BISON.COM’ script in the ‘[BISON]’ directory.

3. Install the ‘BISON’ command with the command line:

   $ set command /table=sys$library:dcltables gnu_bison:[000000]bison
   

4. Type ‘@make-gcc’ to recompile everything (alternatively, you may submit the file ‘make-gcc.com’ to a batch queue). If you wish to build the GNU C++ compiler as well as the GNU CC compiler, you must first edit ‘make-gcc.com’ and follow the instructions that appear in the comments.

   If you are building GNU CC with a previous version of GNU CC, you also should check to see that you have the newest version of the assembler. In particular, GNU CC version 2 treats global constant variables slightly differently from GNU CC version 1, and GAS version 1.38.1 does not have the patches required to work with GCC version 2. If you use GAS 1.38.1, then extern const variables will not have the read-only bit set, and the linker will generate warning messages about mismatched psect attributes for these variables. These warning messages are merely a nuisance, and can safely be ignored.

   If you are compiling with a version of GNU CC older than 1.33, specify ‘/DEFINE=("inline=")’ as an option in all the compilations. This requires editing all the gcc commands in ‘make-cc1.com’. (The older versions had problems supporting inline.) Once you have a working 1.33 or newer GNU CC, you can change this file back.

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

Even with this version, however, GNU CC itself should not be linked to the sharable ‘VAXCRTL’. The qsort routine supplied with ‘VAXCRTL’ has a bug which can cause a compiler crash.

Similarly, the preprocessor should not be linked to the sharable ‘VAXCRTL’. The strncat routine supplied with ‘VAXCRTL’ has a bug which can cause the preprocessor to go into an infinite loop.

If you attempt to link to the sharable ‘VAXCRTL’, the VMS linker will strongly resist any effort to force it to use the qsort and strncat routines from ‘gcclib’. Until the bugs in ‘VAXCRTL’ have been fixed, linking any of the compiler components to the sharable VAXCRTL is not recommended. (These routines can be bypassed by placing duplicate copies of qsort and strncat in ‘gcclib’ under different names, and patching the compiler sources to use these routines). Both of the bugs in ‘VAXCRTL’ are still present in VMS version 5.4-1, which is the most recent version as of this writing.

The executables that are generated by ‘make-cc1.com’ and ‘make-cccp.com’ use the nonshared version of ‘VAXCRTL’ (and thus use the qsort and strncat routines from ‘gcclib.olb’).

3 Known Causes of Trouble with GNU CC

Here are some of the things that have caused trouble for people installing or using GNU CC.

• On certain systems, defining certain environment variables such as CC can interfere with the functioning of make.
• 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. @xref{Cross-compilation}.

• Users often think it is a bug when GNU CC reports an error for code like this:

  int foo (short);
  
  int foo (x)
       short x;
  {…}
  

  The error message is correct: this code really is erroneous, because the old-style non-prototype definition passes subword integers in their promoted types. In other words, the argument is really an int, not a short. The correct prototype is this:

  int foo (int);
  

• Users often think it is a bug when GNU CC 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 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 ANSI 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 ANSI C just to avoid an error for the example shown above.

• Certain local variables aren’t recognized by debuggers when you compile with optimization.

  This occurs because sometimes GNU CC 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 GNU CC 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.

• -2147483648 is positive.

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

• Sometimes on a Sun 4 you may observe a crash in the program genflags while building GCC. This is said to be due to a bug in sh. You can probably get around it by running genflags manually and then retrying the make.
• On some versions of Ultrix, the system supplied compiler cannot compile ‘cp-parse.c’ because it cannot handle so many cases in a switch statement. You can work around this problem by compiling with GNU CC.
• 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.
• 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 ANSI C.

For additional common problems, see Incompatibilities of GNU CC.

4 How To Get Help with GNU CC

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

• Send a message to a suitable network mailing list. First try bug-gcc@prep.ai.mit.edu, and if that brings no response, try help-gcc@prep.ai.mit.edu.
• Look in the service directory for someone who might help you for a fee. The service directory is found in the file named ‘SERVICE’ in the GNU CC distribution.

5 Incompatibilities of GNU CC

There are several noteworthy incompatibilities between GNU C and most existing (non-ANSI) versions of C. The ‘-traditional’ option eliminates most of these incompatibilities, but not all, by telling GNU C to behave like the other C compilers.

• GNU CC normally makes string constants read-only. If several identical-looking string constants are used, GNU CC 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 GNU CC to handle string constants the same way most C compilers do. ‘-traditional’ also has this effect, among others.

• GNU CC does not substitute macro arguments when they appear inside of string constants. For example, the following macro in GNU CC

  #define foo(a) "a"
  

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

  The ‘-traditional’ option directs GNU CC to handle such cases (among others) in the old-fashioned (non-ANSI) 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 GNU CC 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.

• 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 ANSI 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.
• PCC allows whitespace in the middle of compound assignment operators such as ‘+=’. GNU CC, following the ANSI standard, does not allow this. The difficulty described immediately above applies here too.
• GNU CC will flag unterminated character constants inside of preprocessor conditionals that fail. Some programs have English comments enclosed in conditionals that are guaranteed to fail; if these comments contain apostrophes, GNU CC 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.

• When compiling functions that return float, PCC converts it to a double. GNU CC 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, GNU CC output code normally uses a method different from that used on most versions of Unix. As a result, code compiled with GNU CC cannot call a structure-returning function compiled with PCC, and vice versa.

  The method used by GNU CC 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 GNU CC 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. GNU CC 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. GNU CC 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 GNU CC to use a compatible convention for all structure and union returning with the option ‘-fpcc-struct-return’.

There are also system-specific incompatibilities.

• On the Alliant, the system’s own convention for returning structures and unions is unusual, and is not compatible with GNU CC no matter what options are used.
• On the IBM RT PC, the MetaWare HighC compiler (hc) uses yet another convention for structure and union returning. Use ‘-mhc-struct-return’ to tell GNU CC 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.

  GNU CC 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
  

• DBX rejects some files produced by GNU CC, 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.

6 Reporting Bugs

Your bug reports play an essential role in making GNU CC reliable.

When you encounter a problem, the first thing to do is to see if it is already known. See section Known Causes of Trouble with GNU CC. Also look in Incompatibilities of GNU CC. 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 How To Get Help with GNU CC.) In any case, the principal function of a bug report is to help the entire community by making the next version of GNU CC work better. Bug reports are your contribution to the maintenance of GNU CC.

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

6.1 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 section Incompatibilities of GNU CC). 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 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 GNU CC 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; GNU CC 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.

  Note that the following is not valid input, and the error message for it is not a bug:

  int foo (char);
  
  int
  foo (x)
       char x;
  { … }
  

  The prototype says to pass a char, while the definition says to pass an int and treat the value as a char. This is what the ANSI standard says, and it makes sense.

• 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 C compilers, your suggestions for improvement of GNU CC are welcome in any case.

6.2 How to Report Bugs

Send bug reports for GNU C to one of these addresses:

bug-gcc@prep.ai.mit.edu
{ucbvax|mit-eddie|uunet}!prep.ai.mit.edu!bug-gcc

Do not send bug reports to ‘help-gcc’, or to the newsgroup ‘gnu.gcc.help’. Most users of GNU CC do not want to receive bug reports. Those that do, have asked to be on ‘bug-gcc’.

The mailing list ‘bug-gcc’ has a newsgroup which serves as a repeater. The mailing list and the newsgroup carry exactly the same messages. Often people think of posting bug reports to the newsgroup instead of mailing them. This appears to work, but it has one problem which can be crucial: a newsgroup posting does not contain a mail path back to the sender. Thus, if I need to ask for more information, I may be unable to reach you. For this reason, it is better to send bug reports to the mailing list.

As a last resort, send bug reports on paper to:

GNU Compiler Bugs
Free Software Foundation
675 Mass Ave
Cambridge, MA 02139

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 me 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?” Those bug reports are useless, and I urge everyone to refuse to respond to them except to chide the sender to report bugs properly.

To enable me to fix the bug, you should include all these things:

• The version of GNU CC. You can get this by running it with the ‘-v’ option.

  Without this, I won’t know whether there is any point in looking for the bug in the current version of GNU CC.

• A complete input file that will reproduce the bug. If the bug is in the C preprocessor, send me a source file and any header files that it requires. If the bug is in the compiler proper (‘cc1’), run your source file through the C preprocessor by doing ‘gcc -E sourcefile > outfile’, then include the contents of outfile in the bug report. (Any ‘-I’, ‘-D’ or ‘-U’ options that you used in actual compilation should also be used when doing this.)

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

  Without a real example I can compile, all I 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.

• The command arguments you gave GNU CC to compile that example and observe the bug. For example, did you use ‘-O’? To guarantee you won’t omit something important, list them all.

  If I were to try to guess the arguments, I would probably guess wrong and then I 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 description of what behavior you observe that you believe is incorrect. For example, “It gets a fatal signal,” or, “There is an incorrect assembler instruction in the output.”

  Of course, if the bug is that the compiler gets a fatal signal, then I will certainly notice it. But if the bug is incorrect output, I might not notice unless it is glaringly wrong. I won’t study all the assembler code from a 50-line C program just on the off chance that it might be wrong.

  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 mine would not. If you told me to expect a crash, then when mine fails to crash, I would know that the bug was not happening for me. If you had not told me to expect a crash, then I would not be able to draw any conclusion from my observations.

  Often the observed symptom is incorrect output when your program is run. Sad to say, this is not enough information for me unless the program is short and simple. If you send me a large program, I don’t have time 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 me 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 a bug in the program itself.

• If you send me examples of output from GNU CC, 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 suggest changes to the GNU CC source, send me context diffs. If you even discuss something in the GNU CC source, refer to it by context, not by line number.

  The line numbers in my development sources don’t match those in your sources. Your line numbers would convey no useful information to me.

• Additional information from a debugger might enable me to find a problem on a machine which I do not have available myself. 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 GNU CC 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.

  In addition, include a debugging dump from just before the pass in which the crash happens. Most bugs involve a series of insns, not just one.

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 I will find the bug is by running a single example under the debugger with breakpoints, not by pure deduction from a series of examples. I recommend that you 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 for me. Errors in the output will be easier to spot, running under the debugger will take less time, etc. Most GNU CC 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 me the entire test case you used.

• A patch for the bug.

  A patch for the bug does help me 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 I need. I might see problems with your patch and decide to fix the problem another way, or I might not understand it at all.

  Sometimes with a program as complicated as GNU CC 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 me the example, I won’t be able to construct one, so I won’t be able to verify that the bug is fixed.

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

• 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.

6.3 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 GNU CC 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 will eliminate the need 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.

• Making bitfields unsigned by default on particular machines where “the ABI standard” says to do so.

  The ANSI 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 dialect you want with the option ‘-fsigned-bitfields’ or ‘-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 functions in any other object file, 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 GNU CC does and will treat plain bitfields in the same fashion on all types of machines (by default).

  (Of course, users strongly concerned about portability should indicate explicitly in each bitfield whether it is signed or not.)

• Undefining __STDC__ when ‘-ansi’ is not used.

  Currently, GNU CC 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 ANSI C, such as function prototypes or ANSI token concatenation. Since plain ‘gcc’ supports all the features of ANSI 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 ANSI C program, because the ANSI 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 ANSI C library.

  Sometimes people say that defining __STDC__ in a compiler that does not completely conform to the ANSI C standard somehow violates the standard. This is illogical. The standard is a standard for compilers that are supposed to conform. It says nothing about what any other compilers should do. Whatever the ANSI C standard says is relevant to the design of plain ‘gcc’ without ‘-ansi’ only for pragmatic reasons, not as a requirement.

• 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 ANSI 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 ANSI 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.

7 Using GNU CC on VMS

7.1 Include Files and VMS

Due to the differences between the filesystems of Unix and VMS, GNU CC 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. GNU CC 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, ‘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 GNU CC. VAX-C treats this much like a standard #include <foobar.h> directive. That is incompatible with the ANSI C behavior implemented by GNU CC: 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’. GNU CC 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.

GNU CC for VMS is distributed with a set of include files that is sufficient to compile most general purpose programs. Even though the GNU CC 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 GNU CC 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.

7.2 Global Declarations and VMS

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

int GLOBALREF (ijk);
int GLOBALDEF (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];
intvector GLOBALREF (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:

int GLOBALVALUEREF(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 ANSI C feature allowing macros that expand to use the same name as the macro itself.

int GLOBALVALUEREF (ss$_normal);
int GLOBALVALUEDEF (xyzzy,123);
#ifdef __GNUC__
#define ss$_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__
int GLOBALDEF (color, 0);
int GLOBALVALUEDEF (RED, 0);
int GLOBALVALUEDEF (BLUE, 1);
int GLOBALVALUEDEF (GREEN, 3);
#else
enum globaldef color {RED, BLUE, GREEN = 3};
#endif

7.3 Other VMS Issues

GNU CC 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 GNU CC did not provide this default.

GNU CC 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 GNU CC, 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.

The VMS linker does not distinguish between upper and lower case letters in function and variable names. However, usual practice in C is to distinguish case. Normally GNU CC (by means of the assembler GAS) implements usual C behavior by augmenting each name that is not all lower-case. A name is augmented by truncating it to at most 23 characters and then adding more characters at the end which encode the case pattern the rest.

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.

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.

8 GNU CC and Portability

The main goal of GNU CC 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.

GNU CC 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.

GNU CC 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.

9 Interfacing to GNU CC Output

GNU CC 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 (@pxref{Machine 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 GNU CC, and vice versa. This does not cause trouble often because few Unix library routines return structures or unions.

GNU CC 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. (GNU CC 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 GNU CC 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 GNU CC, 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, GNU CC 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.

GNU CC 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 GNU CC 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 GNU CC.

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. ANSI C says that automatic variables that are not declared volatile have undefined values after a longjmp. And this is all GNU CC promises to do, because it is very difficult to restore register variables correctly, and one of GNU CC’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 GNU CC 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 GNU CC 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 GNU CC, because each arithmetic function would compile into a call to itself!

10 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 the function rest_of_compilation or 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 (@pxref{Inline}).

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 for parsing C are ‘c-parse.y’, ‘c-decl.c’, ‘c-typeck.c’, ‘c-convert.c’, ‘c-lang.c’, and ‘c-aux-info.c’ along with header files ‘c-lex.h’, and ‘c-tree.h’.

  The source files for parsing C++ are ‘cp-parse.y’, ‘cp-class.c’, ‘cp-cvt.c’,
  ‘cp-decl.c’, ‘cp-decl.c’, ‘cp-decl2.c’, ‘cp-dem.c’, ‘cp-except.c’,
  ‘cp-expr.c’, ‘cp-init.c’, ‘cp-lex.c’, ‘cp-method.c’, ‘cp-ptree.c’,
  ‘cp-search.c’, ‘cp-tree.c’, ‘cp-type2.c’, and ‘cp-typeck.c’, along with header files ‘cp-tree.def’, ‘cp-tree.h’, and ‘cp-decl.h’.

  The special source files for parsing Objective C are ‘objc-parse.y’, ‘objc-actions.c’, ‘objc-tree.def’, and ‘objc-actions.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’, ‘function.c’, ‘expr.c’, ‘calls.c’, ‘explow.c’, ‘expmed.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 GNU CC. 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.

• 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.

• Stupid register allocation is performed at this point in a nonoptimizing compilation. It does a little data flow analysis as well. When stupid register allocation is in use, the next pass executed is the reloading pass; the others in between are skipped. The source file is ‘stupid.c’.
• 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.

• 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-alloc.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.

• 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’.

11 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 GNU CC 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.

FAILURE_EXIT_CODE

A C expression for the status code to be returned when the compiler exits after serious errors.

SUCCESS_EXIT_CODE

A C expression for the status code to be returned when the compiler exits without serious errors.

HOST_WORDS_BIG_ENDIAN

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

HOST_FLOAT_FORMAT

A numeric code distinguishing the floating point format for the host machine. See TARGET_FLOAT_FORMAT in @ref{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.

EXECUTABLE_SUFFIX

Define this macro if the host system uses a naming convention for executable files that involves a common suffix (such as, in some systems, ‘.exe’) that must be mentioned explicitly when you run the program.

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 GNU CC 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.

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

Index

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