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# Installing GNU CC

- Configurations: Configurations Supported by GNU CC.
- Other Dir: Compiling in a separate directory (not where the source is).
- Cross-Compiler: Building and installing a cross-compiler.
- Sun Install: See below for installation on the Sun.
- VMS Install: See below for installation on VMS.
- Collect2: How `collect2` works; how it finds `ld`.
- Header Dirs: Understanding the standard header file directories.

Here is the procedure for installing GNU CC on a Unix system. See section Installing GNU CC on VMS, for VMS systems. In this section we assume you compile in the same directory that contains the source files; see section Compilation in a Separate Directory, to find out how to compile in a separate directory on Unix systems.

You cannot install GNU C by itself on MSDOS; it will not compile under any MSDOS compiler except itself. You need to get the complete compilation package DJGPP, which includes binaries as well as sources, and includes all the necessary compilation tools and libraries.

1. If you have built GNU CC previously in the same directory for a different target machine, do ``make distclean'` to delete all files that might be invalid. One of the files this deletes is ``Makefile'`; if ``make distclean'` complains that ``Makefile'` does not exist, it probably means that the directory is already suitably clean.
2. 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.
3. Specify the host, build and target machine configurations. You do this by running the file ``configure'`. The build machine is the system which you are using, the host machine is the system where you want to run the resulting compiler (normally the build machine), and the target machine is the system for which you want the compiler to generate code. If you are building a compiler to produce code for the machine it runs on (a native compiler), you normally do not need to specify any operands to ``configure'`; it will try to guess the type of machine you are on and use that as the build, host and target machines. So you don't need to specify a configuration when building a native compiler unless ``configure'` cannot figure out what your configuration is or guesses wrong. In those cases, specify the build machine's configuration name with the ``--build'` option; the host and target will default to be the same as the build machine. (If you are building a cross-compiler, see section Building and Installing a Cross-Compiler.) Here is an example:

       ./configure --build=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. See section Configurations Supported by GNU CC, for a list of supported configuration names and notes on many of the configurations. You should check the notes in that section before proceeding any further with the installation of GNU CC. There are four additional options you can specify independently to describe variant hardware and software configurations. These are ``--with-gnu-as'`, ``--with-gnu-ld'`, ``--with-stabs'` and ``--nfp'`.
   ``--with-gnu-as'`
     If you will use GNU CC with the GNU assembler (GAS), you should declare this by using the ``--with-gnu-as'` option when you run ``configure'`. Using this option does not install GAS. It only modifies the output of GNU CC to work with GAS. Building and installing GAS is up to you. Conversely, if you do not wish to use GAS and do not specify ``--with-gnu-as'` when building GNU CC, it is up to you to make sure that GAS is not installed. GNU CC searches for a program named `as` in various directories; if the program it finds is GAS, then it runs GAS. If you are not sure where GNU CC finds the assembler it is using, try specifying ``-v'` when you run it. The systems where it makes a difference whether you use GAS are
     ``hppa1.0-any-any'`, ``hppa1.1-any-any'`, ``i386-any-sysv'`, ``i386-any-isc'`,
     ``i860-any-bsd'`, ``m68k-bull-sysv'`, ``m68k-hp-hpux'`, ``m68k-sony-bsd'`,
     ``m68k-altos-sysv'`, ``m68000-hp-hpux'`, ``m68000-att-sysv'`, ``any-lynx-lynxos'`, and ``mips-any'`). On any other system, ``--with-gnu-as'` has no effect. On the systems listed above (except for the HP-PA, for ISC on the 386, and for ``mips-sgi-irix5.*'`), if you use GAS, you should also use the GNU linker (and specify ``--with-gnu-ld'`).
   ``--with-gnu-ld'`
     Specify the option ``--with-gnu-ld'` if you plan to use the GNU linker with GNU CC. This option does not cause the GNU linker to be installed; it just modifies the behavior of GNU CC to work with the GNU linker. Specifically, it inhibits the installation of `collect2`, a program which otherwise serves as a front-end for the system's linker on most configurations.
   ``--with-stabs'`
     On MIPS based systems and on Alphas, you must specify whether you want GNU CC to create the normal ECOFF debugging format, or to use BSD-style stabs passed through the ECOFF symbol table. The normal ECOFF debug format cannot fully handle languages other than C. BSD stabs format can handle other languages, but it only works with the GNU debugger GDB. Normally, GNU CC uses the ECOFF debugging format by default; if you prefer BSD stabs, specify ``--with-stabs'` when you configure GNU CC. No matter which default you choose when you configure GNU CC, the user can use the ``-gcoff'` and ``-gstabs+'` options to specify explicitly the debug format for a particular compilation. ``--with-stabs'` is meaningful on the ISC system on the 386, also, if ``--with-gas'` is used. It selects use of stabs debugging information embedded in COFF output. This kind of debugging information supports C++ well; ordinary COFF debugging information does not. ``--with-stabs'` is also meaningful on 386 systems running SVR4. It selects use of stabs debugging information embedded in ELF output. The C++ compiler currently (2.6.0) does not support the DWARF debugging information normally used on 386 SVR4 platforms; stabs provide a workable alternative. This requires gas and gdb, as the normal SVR4 tools can not generate or interpret stabs.
   ``--nfp'`
     On certain systems, you must specify whether the machine has a floating point unit. These systems include ``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.
   The ``configure'` script searches subdirectories of the source directory for other compilers that are to be integrated into GNU CC. The GNU compiler for C++, called G++ is in a subdirectory named ``cp'`. ``configure'` inserts rules into ``Makefile'` to build all of those compilers. Here we spell out what files will be set up by `configure`. Normally you need not be concerned with these files.
   - A file named ``config.h'` is created that contains a ``#include'` of 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 file named ``tconfig.h'` is created which includes the top-level config file for your target machine. This is used for compiling certain programs to run on that machine.
   - A file named ``tm.h'` is created which includes the machine-description macro file for your target machine. It should be in the subdirectory ``config'` and its name is often ``machine.h'`.
   - The command file ``configure'` also constructs the file ``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 ``x-host'`. If these files do not exist, it means nothing needs to be added for a given target or host.
4. The standard directory for installing GNU CC is ``/usr/local/lib'`. If you want to install its files somewhere else, specify ``--prefix=dir'` when you run ``configure'`. Here dir is a directory name to use instead of ``/usr/local'` for all purposes with one exception: the directory ``/usr/local/include'` is searched for header files no matter where you install the compiler. To override this name, use the `--local-prefix` option below.
5. Specify ``--local-prefix=dir'` if you want the compiler to search directory ``dir/include'` for locally installed header files instead of ``/usr/local/include'`. You should specify ``--local-prefix'` only if your site has a different convention (not ``/usr/local'`) for where to put site-specific files. Do not specify ``/usr'` as the ``--local-prefix'`! The directory you use for ``--local-prefix'` must not contain any of the system's standard header files. If it did contain them, certain programs would be miscompiled (including GNU Emacs, on certain targets), because this would override and nullify the header file corrections made by the `fixincludes` script.
6. 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'`.
7. If you have chosen a configuration for GNU CC which requires other GNU tools (such as GAS or the GNU linker) instead of the standard system tools, install the required tools in the build directory under the names ``as'`, ``ld'` or whatever is appropriate. This will enable the compiler to find the proper tools for compilation of the program ``enquire'`. Alternatively, you can do subsequent compilation using a value of the `PATH` environment variable such that the necessary GNU tools come before the standard system tools.
8. 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'`. If you have any additional GNU compilers as subdirectories of the GNU CC source directory, you may also specify their names in this list. Ignore any warnings you may see about "statement not reached" in ``insn-emit.c'`; they are normal. Also, warnings about "unknown escape sequence" are normal in ``genopinit.c'` and perhaps some other files. Likewise, you should ignore warnings about "constant is so large that it is unsigned" in ``insn-emit.c'` and ``insn-recog.c'` and a warning about a comparison always being zero in ``enquire.o'`. 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.
9. If you are building a cross-compiler, stop here. See section Building and Installing a Cross-Compiler.
10. 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`.
11. If you have chosen a configuration for GNU CC which requires other GNU tools (such as GAS or the GNU linker) instead of the standard system tools, install the required tools in the ``stage1'` subdirectory under the names ``as'`, ``ld'` or whatever is appropriate. This will enable the stage 1 compiler to find the proper tools in the following stage. Alternatively, you can do subsequent compilation using a value of the `PATH` environment variable such that the necessary GNU tools come before the standard system tools.
12. Recompile the compiler with itself, with this command:

        make CC="stage1/xgcc -Bstage1/" CFLAGS="-g -O2"

    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++'`, ``objective-c'`, and ``proto'`. Separate the words with spaces. ``proto'` stands for the programs `protoize` and `unprotoize`; they are not a separate language, but you use `LANGUAGES` to enable or disable their installation. If you are going to build the stage 3 compiler, then you might want to build only the C language in stage 2. Once you have built the stage 2 compiler, if you are short of disk space, you can delete the subdirectory ``stage1'`. 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/xgcc -Bstage1/" CFLAGS="-g -O2 -msoft-float"

13. If you wish to test the compiler by compiling it with itself one more time, install any other necessary GNU tools (such as GAS or the GNU linker) in the ``stage2'` subdirectory as you did in the ``stage1'` subdirectory, then do this:

        make stage2
        make CC="stage2/xgcc -Bstage2/" CFLAGS="-g -O2"

    This is called making the stage 3 compiler. Aside from the ``-B'` option, the compiler options should be the same as when you made the stage 2 compiler. But the `LANGUAGES` option need not be the same. 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"'`, as described above. If you do not have to install any additional GNU tools, you may use the command

        make bootstrap LANGUAGES=language-list BOOT_CFLAGS=option-list

    instead of making ``stage1'`, ``stage2'`, and performing the two compiler builds.
14. Then compare the latest object files with the stage 2 object files--they ought to be identical, aside from time stamps (if any). On some systems, meaningful comparison of object files is impossible; they always appear "different." This is currently true on Solaris and some systems that use ELF object file format. On some versions of Irix on SGI machines and DEC Unix (OSF/1) on Alpha systems, you will not be able to compare the files without specifying ``-save-temps'`; see the description of individual systems above to see if you get comparison failures. You may have similar problems on other systems. Use this command to compare the files:

        make compare

    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). If your system does not put time stamps in the object files, then this is a faster way to compare them (using the Bourne shell):

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

    If you have built the compiler with the ``-mno-mips-tfile'` option on MIPS machines, you will not be able to compare the files.
15. Install the compiler driver, the compiler's passes and run-time support with ``make install'`. Use the same value for `CC`, `CFLAGS` and `LANGUAGES` that you used when compiling the files that are being installed. One reason this is necessary is that some versions of Make have bugs and recompile files gratuitously when you do this step. If you use the same variable values, those files will be recompiled properly. For example, if you have built the stage 2 compiler, you can use the following command:

        make install CC="stage2/xgcc -Bstage2/" CFLAGS="-g -O" LANGUAGES="list"

    This copies the files ``cc1'`, ``cpp'` and ``libgcc.a'` to files ``cc1'`, ``cpp'` and ``libgcc.a'` in the directory ``/usr/local/lib/gcc-lib/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. This also copies the driver program ``xgcc'` into ``/usr/local/bin/gcc'`, so that it appears in typical execution search paths. On some systems, this command causes recompilation of some files. This is usually due to bugs in `make`. You should either ignore this problem, or use GNU Make. Warning: there is a bug in `alloca` in the Sun library. To avoid this bug, be sure to install the executables of GNU CC that were compiled by GNU CC. (That is, the executables from stage 2 or 3, not stage 1.) They use `alloca` as a built-in function and never the one in the library. (It is usually better to install GNU CC executables from stage 2 or 3, since they usually run faster than the ones compiled with some other compiler.)
16. If you're going to use C++, it's likely that you need to also install the libg++ distribution. It should be available from the same place where you got the GNU C distribution. Just as GNU C does not distribute a C runtime library, it also does not include a C++ run-time library. All I/O functionality, special class libraries, etc., are available in the libg++ distribution.

## Configurations Supported by GNU CC

Here are the possible CPU types:

> 1750a, a29k, alpha, arm, cn, clipper, dsp16xx, elxsi, h8300, hppa1.0, hppa1.1, i370, i386, i486, i586, i860, i960, m68000, m68k, m88k, mips, mipsel, mips64, mips64el, ns32k, powerpc, powerpcle, pyramid, romp, rs6000, sh, sparc, sparclite, sparc64, vax, we32k.

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

> acorn, alliant, altos, apollo, att, bull, cbm, convergent, convex, crds, dec, dg, dolphin, elxsi, encore, harris, hitachi, hp, ibm, intergraph, isi, mips, motorola, ncr, next, ns, omron, plexus, sequent, sgi, sony, sun, tti, unicom, wrs.

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:

> 386bsd, aix, acis, amigados, aos, aout, bosx, bsd, clix, coff, ctix, cxux, dgux, dynix, ebmon, ecoff, elf, esix, freebsd, hms, genix, gnu, gnu/linux, hiux, hpux, iris, irix, isc, luna, lynxos, mach, minix, msdos, mvs, netbsd, newsos, nindy, ns, osf, osfrose, ptx, riscix, riscos, rtu, sco, sim, solaris, sunos, sym, sysv, udi, ultrix, unicos, uniplus, unos, vms, vsta, vxworks, winnt, xenix.

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

You can add a version number to the system type; this may or may not make a difference. For example, you can write ``bsd4.3'` or ``bsd4.4'` to distinguish versions of BSD. In practice, the version number is most needed for ``sysv3'` and ``sysv4'`, which are often treated differently.

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. GNU CC does not support all possible alternatives.

Often a particular model of machine has a name. Many machine names are recognized as aliases for CPU/company combinations. Thus, the machine name ``sun3'`, mentioned above, is an alias 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, 3bn, 7300, altos3068, altos, apollo68, att-7300, balance, convex-cn, crds, decstation-3100, decstation, delta, encore, fx2800, gmicro, hp7nn, hp8nn, hp9k2nn, hp9k3nn, hp9k7nn, hp9k8nn, iris4d, iris, isi68, m3230, magnum, merlin, miniframe, mmax, news-3600, news800, news, next, pbd, pc532, pmax, powerpc, powerpcle, ps2, risc-news, rtpc, sun2, sun386i, sun386, sun3, sun4, symmetry, tower-32, tower.

Remember that a machine name specifies both the cpu type and the company name. 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 configuration name without the cpu prefix is used to form the configuration file names.

Thus, if you specify ``m68k-local'`, configuration uses files ``m68k.md'`, ``local.h'`, ``m68k.c'`, ``xm-local.h'`, ``t-local'`, and ``x-local'`, all in the directory ``config/m68k'`.

Here is a list of configurations that have special treatment or special things you must know:

``1750a-*-*'`
  MIL-STD-1750A processors. Starting with GCC 2.6.1, the MIL-STD-1750A cross configuration no longer supports the Tektronix Assembler, but instead produces output for `as1750`, an assembler/linker available under the GNU Public License for the 1750A. Contact kellogg@space.otn.dasa.de for more details on obtaining ``as1750'`. A similarly licensed simulator for the 1750A is available from same address. You should ignore a fatal error during the building of libgcc (libgcc is not yet implemented for the 1750A.) The `as1750` assembler requires the file ``ms1750.inc'`, which is found in the directory ``config/1750a'`. GNU CC produced the same sections as the Fairchild F9450 C Compiler, namely:
  `Normal`
    The program code section.
  `Static`
    The read/write (RAM) data section.
  `Konst`
    The read-only (ROM) constants section.
  `Init`
    Initialization section (code to copy KREL to SREL).
  The smallest addressable unit is 16 bits (BITS_PER_UNIT is 16). This means that type `char' is represented with a 16-bit word per character. The 1750A's "Load/Store Upper/Lower Byte" instructions are not used by GNU CC.
``alpha-*-osf1'`
  Systems using processors that implement the DEC Alpha architecture and are running the DEC Unix (OSF/1) operating system, for example the DEC Alpha AXP systems. (VMS on the Alpha is not currently supported by GNU CC.) GNU CC writes a ``.verstamp'` directive to the assembler output file unless it is built as a cross-compiler. It gets the version to use from the system header file ``/usr/include/stamp.h'`. If you install a new version of DEC Unix, you should rebuild GCC to pick up the new version stamp. Note that since the Alpha is a 64-bit architecture, cross-compilers from 32-bit machines will not generate code as efficient as that generated when the compiler is running on a 64-bit machine because many optimizations that depend on being able to represent a word on the target in an integral value on the host cannot be performed. Building cross-compilers on the Alpha for 32-bit machines has only been tested in a few cases and may not work properly. `make compare` may fail on old versions of DEC Unix unless you add ``-save-temps'` to `CFLAGS`. On these systems, the name of the assembler input file is stored in the object file, and that makes comparison fail if it differs between the `stage1` and `stage2` compilations. The option ``-save-temps'` forces a fixed name to be used for the assembler input file, instead of a randomly chosen name in ``/tmp'`. Do not add ``-save-temps'` unless the comparisons fail without that option. If you add ``-save-temps'`, you will have to manually delete the ``.i'` and ``.s'` files after each series of compilations. GNU CC now supports both the native (ECOFF) debugging format used by DBX and GDB and an encapsulated STABS format for use only with GDB. See the discussion of the ``--with-stabs'` option of ``configure'` above for more information on these formats and how to select them. There is a bug in DEC's assembler that produces incorrect line numbers for ECOFF format when the ``.align'` directive is used. To work around this problem, GNU CC will not emit such alignment directives while writing ECOFF format debugging information even if optimization is being performed. Unfortunately, this has the very undesirable side-effect that code addresses when ``-O'` is specified are different depending on whether or not ``-g'` is also specified. To avoid this behavior, specify ``-gstabs+'` and use GDB instead of DBX. DEC is now aware of this problem with the assembler and hopes to provide a fix shortly.
``arm'`
  Advanced RISC Machines ARM-family processors. These are often used in embedded applications. There are no standard Unix configurations. This configuration corresponds to the basic instruction sequences and will produce a.out format object modules. You may need to make a variant of the file ``arm.h'` for your particular configuration.
``arm-*-riscix'`
  The ARM2 or ARM3 processor running RISC iX, Acorn's port of BSD Unix. If you are running a version of RISC iX prior to 1.2 then you must specify the version number during configuration. Note that the assembler shipped with RISC iX does not support stabs debugging information; a new version of the assembler, with stabs support included, is now available from Acorn.
``a29k'`
  AMD Am29k-family processors. These are normally used in embedded applications. There are no standard Unix configurations. This configuration corresponds to AMD's standard calling sequence and binary interface and is compatible with other 29k tools. You may need to make a variant of the file ``a29k.h'` for your particular configuration.
``a29k-*-bsd'`
  AMD Am29050 used in a system running a variant of BSD Unix.
``decstation-*'`
  DECstations can support three different personalities: Ultrix, DEC OSF/1, and OSF/rose. To configure GCC for these platforms use the following configurations:
  ``decstation-ultrix'`
    Ultrix configuration.
  ``decstation-osf1'`
    Dec's version of OSF/1.
  ``decstation-osfrose'`
    Open Software Foundation reference port of OSF/1 which uses the OSF/rose object file format instead of ECOFF. Normally, you would not select this configuration.
  The MIPS C compiler needs to be told to increase its table size for switch statements with the ``-Wf,-XNg1500'` option in order to compile ``cp/parse.c'`. If you use the ``-O2'` optimization option, you also need to use ``-Olimit 3000'`. Both of these options are automatically generated in the ``Makefile'` that the shell script ``configure'` builds. If you override the `CC` make variable and use the MIPS compilers, you may need to add ``-Wf,-XNg1500 -Olimit 3000'`.
``elxsi-elxsi-bsd'`
  The Elxsi's C compiler has known limitations that prevent it from compiling GNU C. Please contact `mrs@cygnus.com` for more details.
``dsp16xx'`
  A port to the AT&T DSP1610 family of processors.
``h8300-*-*'`
  The calling convention and structure layout has changed in release 2.6. All code must be recompiled. The calling convention now passes the first three arguments in function calls in registers. Structures are no longer a multiple of 2 bytes.
``hppa*-*-*'`
  There are two variants of this CPU, called 1.0 and 1.1, which have different machine descriptions. You must use the right one for your machine. All 7nn machines and 8n7 machines use 1.1, while all other 8nn machines use 1.0. The easiest way to handle this problem is to use ``configure hpnnn'` or ``configure hpnnn-hpux'`, where nnn is the model number of the machine. Then ``configure'` will figure out if the machine is a 1.0 or 1.1. Use ``uname -a'` to find out the model number of your machine. ``-g'` does not work on HP-UX, since that system uses a peculiar debugging format which GNU CC does not know about. However, ``-g'` will work if you also use GAS and GDB in conjunction with GCC. We highly recommend using GAS for all HP-PA configurations. You should be using GAS-2.3 (or later) along with GDB-4.12 (or later). These can be retrieved from all the traditional GNU ftp archive sites. Build GAS and install the resulting binary as:

      /usr/local/lib/gcc-lib/configuration/gccversion/as

  where configuration is the configuration name (perhaps ``hpnnn-hpux'`) and gccversion is the GNU CC version number. Do this before starting the build process, otherwise you will get errors from the HPUX assembler while building ``libgcc2.a'`. The command

      make install-dir

  will create the necessary directory hierarchy so you can install GAS before building GCC. To enable debugging, configure GNU CC with the ``--with-gnu-as'` option before building. It has been reported that GNU CC produces invalid assembly code for 1.1 machines running HP-UX 8.02 when using the HP assembler. Typically the errors look like this:

      as: bug.s @line#15 [err#1060]
        Argument 0 or 2 in FARG upper
               - lookahead = ARGW1=FR,RTNVAL=GR
      as: foo.s @line#28 [err#1060]
        Argument 0 or 2 in FARG upper
               - lookahead = ARGW1=FR

  You can check the version of HP-UX you are running by executing the command ``uname -r'`. If you are indeed running HP-UX 8.02 on a PA and using the HP assembler then configure GCC with "hpnnn-hpux8.02".
``i370-*-*'`
  This port is very preliminary and has many known bugs. We hope to have a higher-quality port for this machine soon.
``i386-*-linuxoldld'`
  Use this configuration to generate a.out binaries on Linux if you do not have gas/binutils version 2.5.2 or later installed. This is an obsolete configuration.
``i386-*-linuxaout'`
  Use this configuration to generate a.out binaries on Linux. This configuration is being superseded. You must use gas/binutils version 2.5.2 or later.
``i386-*-linux'`
  Use this configuration to generate ELF binaries on Linux. You must use gas/binutils version 2.5.2 or later.
``i386-*-sco'`
  Compilation with RCC is recommended. Also, it may be a good idea to link with GNU malloc instead of the malloc that comes with the system.
``i386-*-sco3.2v4'`
  Use this configuration for SCO release 3.2 version 4.
``i386-*-isc'`
  It may be a good idea to link with GNU malloc instead of the malloc that comes with the system. In ISC version 4.1, ``sed'` core dumps when building ``deduced.h'`. Use the version of ``sed'` from version 4.0.
``i386-*-esix'`
  It may be good idea to link with GNU malloc instead of the malloc that comes with the system.
``i386-ibm-aix'`
  You need to use GAS version 2.1 or later, and and LD from GNU binutils version 2.2 or later.
``i386-sequent-bsd'`
  Go to the Berkeley universe before compiling. In addition, you probably need to create a file named ``string.h'` containing just one line: ``#include <strings.h>'`.
``i386-sequent-ptx1*'`
  Sequent DYNIX/ptx 1.x.
``i386-sequent-ptx2*'`
  Sequent DYNIX/ptx 2.x.
``i386-sun-sunos4'`
  You may find that you need another version of GNU CC to begin bootstrapping with, since the current version when built with the system's own compiler seems to get an infinite loop compiling part of ``libgcc2.c'`. GNU CC version 2 compiled with GNU CC (any version) seems not to have this problem. See section Installing GNU CC on the Sun, for information on installing GNU CC on Sun systems.
``i[345]86-*-winnt3.5'`
  This version requires a GAS that has not let been released. Until it is, you can get a prebuilt binary version via anonymous ftp from ``cs.washington.edu:pub/gnat'` or ``cs.nyu.edu:pub/gnat'`. You must also use the Microsoft header files from the Windows NT 3.5 SDK. Find these on the CDROM in the ``/mstools/h'` directory dated 9/4/94. You must use a fixed version of Microsoft linker made especially for NT 3.5, which is also is available on the NT 3.5 SDK CDROM. If you do not have this linker, can you also use the linker from Visual C/C++ 1.0 or 2.0. Installing GNU CC for NT builds a wrapper linker, called ``ld.exe'`, which mimics the behaviour of Unix ``ld'` in the specification of libraries (``-L'` and ``-l'`). ``ld.exe'` looks for both Unix and Microsoft named libraries. For example, if you specify ``-lfoo'`, ``ld.exe'` will look first for ``libfoo.a'` and then for ``foo.lib'`. You may install GNU CC for Windows NT in one of two ways, depending on whether or not you have a Unix-like shell and various Unix-like utilities.
  1. If you do not have a Unix-like shell and few Unix-like utilities, you will use a DOS style batch script called ``configure.bat'`. Invoke it as `configure winnt` from an MSDOS console window or from the program manager dialog box. ``configure.bat'` assumes you have already installed and have in your path a Unix-like ``sed'` program which is used to create a working ``Makefile'` from ``Makefile.in'`. ``Makefile'` uses the Microsoft Nmake program maintenance utility and the Visual C/C++ V8.00 compiler to build GNU CC. You need only have the utilities ``sed'` and ``touch'` to use this installation method, which only automatically builds the compiler itself. You must then examine what ``fixinc.winnt'` does, edit the header files by hand and build ``libgcc.a'` manually.
  2. The second type of installation assumes you are running a Unix-like shell, have a complete suite of Unix-like utilities in your path, and have a previous version of GNU CC already installed, either through building it via the above installation method or acquiring a pre-built binary. In this case, use the ``configure'` script in the normal fashion.
``i860-intel-osf1'`
  This is the Paragon. If you have version 1.0 of the operating system, see section Installation Problems, for special things you need to do to compensate for peculiarities in the system.
``*-lynx-lynxos'`
  LynxOS 2.2 and earlier comes with GNU CC 1.x already installed as ``/bin/gcc'`. You should compile with this instead of ``/bin/cc'`. You can tell GNU CC to use the GNU assembler and linker, by specifying ``--with-gnu-as --with-gnu-ld'` when configuring. These will produce COFF format object files and executables; otherwise GNU CC will use the installed tools, which produce a.out format executables.
``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@cs.utah.edu` to get binaries of GNU CC for bootstrapping.
``m68k-altos'`
  Altos 3068. You must use the GNU assembler, linker and debugger. Also, you must fix a kernel bug. Details in the file ``README.ALTOS'`.
``m68k-att-sysv'`
  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. You can bootstrap it more easily with previous versions of GNU CC if you have them. 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.
``m68k-bull-sysv'`
  Bull DPX/2 series 200 and 300 with BOS-2.00.45 up to BOS-2.01. GNU CC works either with native assembler or GNU assembler. You can use GNU assembler with native coff generation by providing ``--with-gnu-as'` to the configure script or use GNU assembler with dbx-in-coff encapsulation by providing ``--with-gnu-as --stabs'`. For any problem with native assembler or for availability of the DPX/2 port of GAS, contact `F.Pierresteguy@frcl.bull.fr`.
``m68k-crds-unox'`
  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. (Perhaps simply defining `ALLOCA` in ``x-crds'` as described in the comments there will make the above paragraph superfluous. Please inform us of whether this works.) 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.
``m68k-hp-hpux'`
  HP 9000 series 300 or 400 running HP-UX. HP-UX version 8.0 has a bug in the assembler that prevents compilation of GNU CC. To fix it, get patch PHCO_4484 from HP. In addition, if you wish to use gas ``--with-gnu-as'` you must use gas version 2.1 or later, and you must use the GNU linker version 2.1 or later. Earlier versions of gas relied upon a program which converted the gas output into the native HP/UX format, but that program has not been kept up to date. gdb does not understand that native HP/UX format, so you must use gas if you wish to use gdb.
``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. See section Installing GNU CC on the Sun, for information on installing GNU CC on Sun systems.
``m88k-*-svr3'`
  Motorola m88k running the AT&T/Unisoft/Motorola V.3 reference port. These systems tend to use the Green Hills C, revision 1.8.5, as the standard C compiler. There are apparently bugs in this compiler that result in object files differences between stage 2 and stage 3. If this happens, make the stage 4 compiler and compare it to the stage 3 compiler. If the stage 3 and stage 4 object files are identical, this suggests you encountered a problem with the standard C compiler; the stage 3 and 4 compilers may be usable. It is best, however, to use an older version of GNU CC for bootstrapping if you have one.
``m88k-*-dgux'`
  Motorola m88k running DG/UX. To build 88open BCS native or cross compilers on DG/UX, specify the configuration name as ``m88k-*-dguxbcs'` and build in the 88open BCS software development environment. To build ELF native or cross compilers on DG/UX, specify ``m88k-*-dgux'` and build in the DG/UX ELF development environment. You set the software development environment by issuing ``sde-target'` command and specifying either ``m88kbcs'` or ``m88kdguxelf'` as the operand. If you do not specify a configuration name, ``configure'` guesses the configuration based on the current software development environment.
``m88k-tektronix-sysv3'`
  Tektronix XD88 running UTekV 3.2e. Do not turn on optimization while building stage1 if you bootstrap with the buggy Green Hills compiler. Also, The bundled LAI System V NFS is buggy so if you build in an NFS mounted directory, start from a fresh reboot, or avoid NFS all together. Otherwise you may have trouble getting clean comparisons between stages.
``mips-mips-bsd'`
  MIPS machines running the MIPS operating system in BSD mode. It's possible that some old versions of the system lack the functions `memcpy`, `memcmp`, and `memset`. If your system lacks these, you must remove or undo the definition of `TARGET_MEM_FUNCTIONS` in ``mips-bsd.h'`. The MIPS C compiler needs to be told to increase its table size for switch statements with the ``-Wf,-XNg1500'` option in order to compile ``cp/parse.c'`. If you use the ``-O2'` optimization option, you also need to use ``-Olimit 3000'`. Both of these options are automatically generated in the ``Makefile'` that the shell script ``configure'` builds. If you override the `CC` make variable and use the MIPS compilers, you may need to add ``-Wf,-XNg1500 -Olimit 3000'`.
``mips-mips-riscos*'`
  The MIPS C compiler needs to be told to increase its table size for switch statements with the ``-Wf,-XNg1500'` option in order to compile ``cp/parse.c'`. If you use the ``-O2'` optimization option, you also need to use ``-Olimit 3000'`. Both of these options are automatically generated in the ``Makefile'` that the shell script ``configure'` builds. If you override the `CC` make variable and use the MIPS compilers, you may need to add ``-Wf,-XNg1500 -Olimit 3000'`. MIPS computers running RISC-OS can support four different personalities: default, BSD 4.3, System V.3, and System V.4 (older versions of RISC-OS don't support V.4). To configure GCC for these platforms use the following configurations:
  ``mips-mips-riscos`rev`'`
    Default configuration for RISC-OS, revision `rev`.
  ``mips-mips-riscos`rev`bsd'`
    BSD 4.3 configuration for RISC-OS, revision `rev`.
  ``mips-mips-riscos`rev`sysv4'`
    System V.4 configuration for RISC-OS, revision `rev`.
  ``mips-mips-riscos`rev`sysv'`
    System V.3 configuration for RISC-OS, revision `rev`.
  The revision `rev` mentioned above is the revision of RISC-OS to use. You must reconfigure GCC when going from a RISC-OS revision 4 to RISC-OS revision 5. This has the effect of avoiding a linker bug (see section Installation Problems, for more details).
``mips-sgi-*'`
  In order to compile GCC on an SGI running IRIX 4, the "c.hdr.lib" option must be installed from the CD-ROM supplied from Silicon Graphics. This is found on the 2nd CD in release 4.0.1. In order to compile GCC on an SGI running IRIX 5, the "compiler_dev.hdr" subsystem must be installed from the IDO CD-ROM supplied by Silicon Graphics. `make compare` may fail on version 5 of IRIX unless you add ``-save-temps'` to `CFLAGS`. On these systems, the name of the assembler input file is stored in the object file, and that makes comparison fail if it differs between the `stage1` and `stage2` compilations. The option ``-save-temps'` forces a fixed name to be used for the assembler input file, instead of a randomly chosen name in ``/tmp'`. Do not add ``-save-temps'` unless the comparisons fail without that option. If you do you ``-save-temps'`, you will have to manually delete the ``.i'` and ``.s'` files after each series of compilations. The MIPS C compiler needs to be told to increase its table size for switch statements with the ``-Wf,-XNg1500'` option in order to compile ``cp/parse.c'`. If you use the ``-O2'` optimization option, you also need to use ``-Olimit 3000'`. Both of these options are automatically generated in the ``Makefile'` that the shell script ``configure'` builds. If you override the `CC` make variable and use the MIPS compilers, you may need to add ``-Wf,-XNg1500 -Olimit 3000'`. On Irix version 4.0.5F, and perhaps on some other versions as well, there is an assembler bug that reorders instructions incorrectly. To work around it, specify the target configuration ``mips-sgi-irix4loser'`. This configuration inhibits assembler optimization. In a compiler configured with target ``mips-sgi-irix4'`, you can turn off assembler optimization by using the ``-noasmopt'` option. This compiler option passes the option ``-O0'` to the assembler, to inhibit reordering. The ``-noasmopt'` option can be useful for testing whether a problem is due to erroneous assembler reordering. Even if a problem does not go away with ``-noasmopt'`, it may still be due to assembler reordering--perhaps GNU CC itself was miscompiled as a result. To enable debugging under Irix 5, you must use GNU as 2.5 or later, and use the ``--with-gnu-as'` configure option when configuring gcc. GNU as is distributed as part of the binutils package.
``mips-sony-sysv'`
  Sony MIPS NEWS. This works in NEWSOS 5.0.1, but not in 5.0.2 (which uses ELF instead of COFF). Support for 5.0.2 will probably be provided soon by volunteers. In particular, the linker does not like the code generated by GCC when shared libraries are linked in.
``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-sequent'`
  Go to the Berkeley universe before compiling. In addition, you probably need to create a file named ``string.h'` containing just one line: ``#include <strings.h>'`.
``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.
``romp-*-aos'`
``romp-*-mach'`
  The only operating systems supported for the IBM RT PC are AOS and MACH. GNU CC does not support AIX running on the RT. We recommend you compile GNU CC with an earlier version of itself; if you compile GNU CC with `hc`, the Metaware compiler, it will work, but you will get mismatches between the stage 2 and stage 3 compilers in various files. These errors are minor differences in some floating-point constants and can be safely ignored; the stage 3 compiler is correct.
``rs6000-*-aix'`
``powerpc-*-aix'`
  Various early versions of each release of the IBM XLC compiler will not bootstrap GNU CC. Symptoms include differences between the stage2 and stage3 object files, and errors when compiling ``libgcc.a'` or ``enquire'`. Known problematic releases include: xlc-1.2.1.8, xlc-1.3.0.0 (distributed with AIX 3.2.5), and xlc-1.3.0.19. Both xlc-1.2.1.28 and xlc-1.3.0.24 (PTF 432238) are known to produce working versions of GNU CC, but most other recent releases correctly bootstrap GNU CC. Also, releases of AIX prior to AIX 3.2.4 include a version of the IBM assembler which does not accept debugging directives: assembler updates are available as PTFs. Also, if you are using AIX 3.2.5 or greater and the GNU assembler, you must have a version modified after October 16th, 1995 in order for the GNU C compiler to build. See the file ``README.RS6000'` for more details on of these problems. GNU CC does not yet support the 64-bit PowerPC instructions. Objective C does not work on this architecture because it makes assumptions that are incompatible with the calling conventions. AIX on the RS/6000 provides support (NLS) for environments outside of the United States. Compilers and assemblers use NLS to support locale-specific representations of various objects including floating-point numbers ("." vs "," for separating decimal fractions). There have been problems reported where the library linked with GNU CC does not produce the same floating-point formats that the assembler accepts. If you have this problem, set the LANG environment variable to "C" or "En_US". Due to changes in the way that GNU CC invokes the binder (linker) for AIX 4.1, you may now receive warnings of duplicate symbols from the link step that were not reported before. The assembly files generated by GNU CC for AIX have always included multiple symbol definitions for certain global variable and function declarations in the original program. The warnings should not prevent the linker from producing a correct library or runnable executable.
``powerpc-*-elf'`
``powerpc-*-sysv4'`
  PowerPC system in big endian mode, running System V.4. This configuration is currently under development.
``powerpc-*-eabiaix'`
  Embedded PowerPC system in big endian mode with -mcall-aix selected as the default. This system is currently under development.
``powerpc-*-eabisim'`
  Embedded PowerPC system in big endian mode for use in running under the PSIM simulator. This system is currently under development.
``powerpc-*-eabi'`
  Embedded PowerPC system in big endian mode. This configuration is currently under development.
``powerpcle-*-elf'`
``powerpcle-*-sysv4'`
  PowerPC system in little endian mode, running System V.4. This configuration is currently under development.
``powerpcle-*-sysv4'`
  Embedded PowerPC system in little endian mode. This system is currently under development.
``powerpcle-*-eabisim'`
  Embedded PowerPC system in little endian mode for use in running under the PSIM simulator. This system is currently under development.
``powerpcle-*-eabi'`
  Embedded PowerPC system in little endian mode. This configuration is currently under development.
``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.
``sparc-sun-*'`
  See section Installing GNU CC on the Sun, for information on installing GNU CC on Sun systems.
``vax-dec-vms'`
  See section Installing GNU CC on VMS, for details on how to install GNU CC on VMS.
``we32k-*-*'`
  These computers are also known as the 3b2, 3b5, 3b20 and other similar names. (However, the 3b1 is actually a 68000; see section Configurations Supported by GNU CC.) Don't use ``-g'` when compiling with the system's compiler. The system's linker seems to be unable to handle such a large program with debugging information. The system's compiler runs out of capacity when compiling ``stmt.c'` in GNU CC. You can work around this by building ``cpp'` in GNU CC first, then use that instead of the system's preprocessor with the system's C compiler to compile ``stmt.c'`. Here is how:

      mv /lib/cpp /lib/cpp.att
      cp cpp /lib/cpp.gnu
      echo '/lib/cpp.gnu -traditional ${1+"$@"}' > /lib/cpp
      chmod +x /lib/cpp

  The system's compiler produces bad code for some of the GNU CC optimization files. So you must build the stage 2 compiler without optimization. Then build a stage 3 compiler with optimization. That executable should work. Here are the necessary commands:

      make LANGUAGES=c CC=stage1/xgcc CFLAGS="-Bstage1/ -g"
      make stage2
      make CC=stage2/xgcc CFLAGS="-Bstage2/ -g -O"

  You may need to raise the ULIMIT setting to build a C++ compiler, as the file ``cc1plus'` is larger than one megabyte.

## 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. If you have ever run ``configure'` in the source directory, you must undo the configuration. Do this by running:

       make distclean

3. Go to the directory in which you want to build the compiler 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.
4. Specify where to find ``configure'` when you run it:

       ../gcc/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/configure --srcdir=../gcc other options

   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.

## Building and Installing a Cross-Compiler

GNU CC can function as a cross-compiler for many machines, but not all.

- Cross-compilers for the Mips as target using the Mips assembler currently do not work, because the auxiliary programs ``mips-tdump.c'` and ``mips-tfile.c'` can't be compiled on anything but a Mips. It does work to cross compile for a Mips if you use the GNU assembler and linker.
- Cross-compilers between machines with different floating point formats have not all been made to work. GNU CC now has a floating point emulator with which these can work, but each target machine description needs to be updated to take advantage of it.
- Cross-compilation between machines of different word sizes is somewhat problematic and sometimes does not work.

Since GNU CC generates assembler code, you probably need a cross-assembler that GNU CC can run, in order to produce object files. If you want to link on other than the target machine, you need a cross-linker as well. You also need header files and libraries suitable for the target machine that you can install on the host machine.

- Steps of Cross: Using a cross-compiler involves several steps that may be carried out on different machines.
- Configure Cross: Configuring a cross-compiler.
- Tools and Libraries: Where to put the linker and assembler, and the C library.
- Cross Headers: Finding and installing header files for a cross-compiler.
- Cross Runtime: Supplying arithmetic runtime routines (``libgcc1.a'`).
- Build Cross: Actually compiling the cross-compiler.

### Steps of Cross-Compilation

To compile and run a program using a cross-compiler involves several steps:

- Run the cross-compiler on the host machine to produce assembler files for the target machine. This requires header files for the target machine.
- Assemble the files produced by the cross-compiler. You can do this either with an assembler on the target machine, or with a cross-assembler on the host machine.
- Link those files to make an executable. You can do this either with a linker on the target machine, or with a cross-linker on the host machine. Whichever machine you use, you need libraries and certain startup files (typically ``crt....o'`) for the target machine.

It is most convenient to do all of these steps on the same host machine, since then you can do it all with a single invocation of GNU CC. This requires a suitable cross-assembler and cross-linker. For some targets, the GNU assembler and linker are available.

### Configuring a Cross-Compiler

To build GNU CC as a cross-compiler, you start out by running ``configure'`. Use the ``--target=target'` to specify the target type. If ``configure'` was unable to correctly identify the system you are running on, also specify the ``--build=build'` option. For example, here is how to configure for a cross-compiler that produces code for an HP 68030 system running BSD on a system that ``configure'` can correctly identify:

    ./configure --target=m68k-hp-bsd4.3

### Tools and Libraries for a Cross-Compiler

If you have a cross-assembler and cross-linker available, you should install them now. Put them in the directory ``/usr/local/target/bin'`. Here is a table of the tools you should put in this directory:

``as'`
  This should be the cross-assembler.
``ld'`
  This should be the cross-linker.
``ar'`
  This should be the cross-archiver: a program which can manipulate archive files (linker libraries) in the target machine's format.
``ranlib'`
  This should be a program to construct a symbol table in an archive file.

The installation of GNU CC will find these programs in that directory, and copy or link them to the proper place to for the cross-compiler to find them when run later.

The easiest way to provide these files is to build the Binutils package and GAS. Configure them with the same ``--host'` and ``--target'` options that you use for configuring GNU CC, then build and install them. They install their executables automatically into the proper directory. Alas, they do not support all the targets that GNU CC supports.

If you want to install libraries to use with the cross-compiler, such as a standard C library, put them in the directory ``/usr/local/target/lib'`; installation of GNU CC copies all all the files in that subdirectory into the proper place for GNU CC to find them and link with them. Here's an example of copying some libraries from a target machine:

    ftp target-machine
    lcd /usr/local/target/lib
    cd /lib
    get libc.a
    cd /usr/lib
    get libg.a
    get libm.a
    quit

The precise set of libraries you'll need, and their locations on the target machine, vary depending on its operating system.

Many targets require "start files" such as ``crt0.o'` and ``crtn.o'` which are linked into each executable; these too should be placed in ``/usr/local/target/lib'`. There may be several alternatives for ``crt0.o'`, for use with profiling or other compilation options. Check your target's definition of `STARTFILE_SPEC` to find out what start files it uses. Here's an example of copying these files from a target machine:

    ftp target-machine
    lcd /usr/local/target/lib
    prompt
    cd /lib
    mget *crt*.o
    cd /usr/lib
    mget *crt*.o
    quit

### ``libgcc.a'` and Cross-Compilers

Code compiled by GNU CC uses certain runtime support functions implicitly. Some of these functions can be compiled successfully with GNU CC itself, but a few cannot be. These problem functions are in the source file ``libgcc1.c'`; the library made from them is called ``libgcc1.a'`.

When you build a native compiler, these functions are compiled with some other compiler--the one that you use for bootstrapping GNU CC. Presumably it knows how to open code these operations, or else knows how to call the run-time emulation facilities that the machine comes with. But this approach doesn't work for building a cross-compiler. The compiler that you use for building knows about the host system, not the target system.

So, when you build a cross-compiler you have to supply a suitable library ``libgcc1.a'` that does the job it is expected to do.

To compile ``libgcc1.c'` with the cross-compiler itself does not work. The functions in this file are supposed to implement arithmetic operations that GNU CC does not know how to open code for your target machine. If these functions are compiled with GNU CC itself, they will compile into infinite recursion.

On any given target, most of these functions are not needed. If GNU CC can open code an arithmetic operation, it will not call these functions to perform the operation. It is possible that on your target machine, none of these functions is needed. If so, you can supply an empty library as ``libgcc1.a'`.

Many targets need library support only for multiplication and division. If you are linking with a library that contains functions for multiplication and division, you can tell GNU CC to call them directly by defining the macros `MULSI3_LIBCALL`, and the like. These macros need to be defined in the target description macro file. For some targets, they are defined already. This may be sufficient to avoid the need for libgcc1.a; if so, you can supply an empty library.

Some targets do not have floating point instructions; they need other functions in ``libgcc1.a'`, which do floating arithmetic. Recent versions of GNU CC have a file which emulates floating point. With a certain amount of work, you should be able to construct a floating point emulator that can be used as ``libgcc1.a'`. Perhaps future versions will contain code to do this automatically and conveniently. That depends on whether someone wants to implement it.

Some embedded targets come with all the necessary ``libgcc1.a'` routines written in C or assembler. These targets build ``libgcc1.a'` automatically and you do not need to do anything special for them. Other embedded targets do not need any ``libgcc1.a'` routines since all the necessary operations are supported by the hardware.

If your target system has another C compiler, you can configure GNU CC as a native compiler on that machine, build just ``libgcc1.a'` with ``make libgcc1.a'` on that machine, and use the resulting file with the cross-compiler. To do this, execute the following on the target machine:

    cd target-build-dir
    ./configure --host=sparc --target=sun3
    make libgcc1.a

And then this on the host machine:

    ftp target-machine
    binary
    cd target-build-dir
    get libgcc1.a
    quit

Another way to provide the functions you need in ``libgcc1.a'` is to define the appropriate `perform_...` macros for those functions. If these definitions do not use the C arithmetic operators that they are meant to implement, you should be able to compile them with the cross-compiler you are building. (If these definitions already exist for your target file, then you are all set.)

To build ``libgcc1.a'` using the perform macros, use ``LIBGCC1=libgcc1.a OLDCC=./xgcc'` when building the compiler. Otherwise, you should place your replacement library under the name ``libgcc1.a'` in the directory in which you will build the cross-compiler, before you run `make`.

### Cross-Compilers and Header Files

If you are cross-compiling a standalone program or a program for an embedded system, then you may not need any header files except the few that are part of GNU CC (and those of your program). However, if you intend to link your program with a standard C library such as ``libc.a'`, then you probably need to compile with the header files that go with the library you use.

The GNU C compiler does not come with these files, because (1) they are system-specific, and (2) they belong in a C library, not in a compiler.

If the GNU C library supports your target machine, then you can get the header files from there (assuming you actually use the GNU library when you link your program).

If your target machine comes with a C compiler, it probably comes with suitable header files also. If you make these files accessible from the host machine, the cross-compiler can use them also.

Otherwise, you're on your own in finding header files to use when cross-compiling.

When you have found suitable header files, put them in ``/usr/local/target/include'`, before building the cross compiler. Then installation will run fixincludes properly and install the corrected versions of the header files where the compiler will use them.

Provide the header files before you build the cross-compiler, because the build stage actually runs the cross-compiler to produce parts of ``libgcc.a'`. (These are the parts that can be compiled with GNU CC.) Some of them need suitable header files.

Here's an example showing how to copy the header files from a target machine. On the target machine, do this:

    (cd /usr/include; tar cf - .) > tarfile

Then, on the host machine, do this:

    ftp target-machine
    lcd /usr/local/target/include
    get tarfile
    quit
    tar xf tarfile

### Actually Building the Cross-Compiler

Now you can proceed just as for compiling a single-machine compiler through the step of building stage 1. If you have not provided some sort of ``libgcc1.a'`, then compilation will give up at the point where it needs that file, printing a suitable error message. If you do provide ``libgcc1.a'`, then building the compiler will automatically compile and link a test program called ``libgcc1-test'`; if you get errors in the linking, it means that not all of the necessary routines in ``libgcc1.a'` are available.

You must provide the header file ``float.h'`. One way to do this is to compile ``enquire'` and run it on your target machine. The job of ``enquire'` is to run on the target machine and figure out by experiment the nature of its floating point representation. ``enquire'` records its findings in the header file ``float.h'`. If you can't produce this file by running ``enquire'` on the target machine, then you will need to come up with a suitable ``float.h'` in some other way (or else, avoid using it in your programs).

Do not try to build stage 2 for a cross-compiler. It doesn't work to rebuild GNU CC as a cross-compiler using the cross-compiler, because that would produce a program that runs on the target machine, not on the host. For example, if you compile a 386-to-68030 cross-compiler with itself, the result will not be right either for the 386 (because it was compiled into 68030 code) or for the 68030 (because it was configured for a 386 as the host). If you want to compile GNU CC into 68030 code, whether you compile it on a 68030 or with a cross-compiler on a 386, you must specify a 68030 as the host when you configure it.

To install the cross-compiler, use ``make install'`, as usual.

## Installing GNU CC on the Sun

On Solaris (version 2.1), do not use the linker or other tools in ``/usr/ucb'` to build GNU CC. Use `/usr/ccs/bin`.

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"

## 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.exe'`, ``gcc-cc1.exe'`, etc.) and the C include files are kept respectively. This should be done with the commands:

       $ assign /system /translation=concealed -
         disk:[gcc.] gnu_cc
       $ assign /system /translation=concealed -
         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$common:[syslib]dcltables -
         /output=sys$common:[syslib]dcltables gnu_cc:[000000]gcc
       $ install replace sys$common:[syslib]dcltables

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

       $ library/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 /system /translation=concealed -
         disk:[gcc.gxx_include.] gnu_gxx_include

   with the appropriate disk and directory name. If you are going to be using libg++, this is where the libg++ install procedure will install the libg++ header files.
2. Obtain the file ``gcc-cc1plus.exe'`, and place this in the same directory that ``gcc-cc1.exe'` is kept. 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 than 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. Execute the command procedure ``vmsconfig.com'` to set up the files ``tm.h'`, ``config.h'`, ``aux-output.c'`, and ``md.'`, and to create files ``tconfig.h'` and ``hconfig.h'`. This procedure also creates several linker option files used by ``make-cc1.com'` and a data file used by ``make-l2.com'`.

       $ @vmsconfig.com

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 /system /translation=concealed -
         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$common:[syslib]dcltables -
         /output=sys$common:[syslib]dcltables -
         gnu_bison:[000000]bison
       $ install replace sys$common:[syslib]dcltables

4. Type ``@make-gcc'` to recompile everything (alternatively, 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.
5. In order to use GCC, you need a library of functions which GCC compiled code will call to perform certain tasks, and these functions are defined in the file ``libgcc2.c'`. To compile this you should use the command procedure ``make-l2.com'`, which will generate the library ``libgcc2.olb'`. ``libgcc2.olb'` should be built using the compiler built from the same distribution that ``libgcc2.c'` came from, and ``make-gcc.com'` will automatically do all of this for you. To install the library, use the following commands:

       $ library gnu_cc:[000000]gcclib/delete=(new,eprintf)
       $ library gnu_cc:[000000]gcclib/delete=L_*
       $ library libgcc2/extract=*/output=libgcc2.obj
       $ library gnu_cc:[000000]gcclib libgcc2.obj

   The first command simply removes old modules that will be replaced with modules from ``libgcc2'` under different module names. The modules `new` and `eprintf` may not actually be present in your ``gcclib.olb'`---if the VMS librarian complains about those modules not being present, simply ignore the message and continue on with the next command. The second command removes the modules that came from the previous version of the library ``libgcc2.c'`. Whenever you update the compiler on your system, you should also update the library with the above procedure.
6. You may wish to build GCC in such a way that no files are written to the directory where the source files reside. An example would be the when the source files are on a read-only disk. In these cases, execute the following DCL commands (substituting your actual path names):

       $ assign dua0:[gcc.build_dir.]/translation=concealed, -
                dua1:[gcc.source_dir.]/translation=concealed  gcc_build
       $ set default gcc_build:[000000]

   where the directory ``dua1:[gcc.source_dir]'` contains the source code, and the directory ``dua0:[gcc.build_dir]'` is meant to contain all of the generated object files and executables. Once you have done this, you can proceed building GCC as described above. (Keep in mind that ``gcc_build'` is a rooted logical name, and thus the device names in each element of the search list must be an actual physical device name rather than another rooted logical name).
7. 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.
8. If you want to build GNU CC with the VAX C compiler, you will need to make minor changes in ``make-cccp.com'` and ``make-cc1.com'` to choose alternate definitions of `CC`, `CFLAGS`, and `LIBS`. See comments in those files. However, you must also have a working version of the GNU assembler (GNU as, aka GAS) as it is used as the back-end for GNU CC to produce binary object modules and is not included in the GNU CC sources. GAS is also needed to compile ``libgcc2'` in order to build ``gcclib'` (see above); ``make-l2.com'` expects to be able to find it operational in ``gnu_cc:[000000]gnu-as.exe'`. To use GNU CC on VMS, you need the VMS driver programs ``gcc.exe'`, ``gcc.com'`, and ``gcc.cld'`. They are distributed with the VMS binaries (``gcc-vms'`) rather than the GNU CC sources. GAS is also included in ``gcc-vms'`, as is Bison. Once you have successfully built GNU CC with VAX C, you should use the resulting compiler to rebuild itself. Before doing this, be sure to restore the `CC`, `CFLAGS`, and `LIBS` definitions in ``make-cccp.com'` and ``make-cc1.com'`. The second generation compiler will be able to take advantage of many optimizations that must be suppressed when building with other compilers.

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

Even with this version, however, GNU CC itself should not be linked with the sharable ``VAXCRTL'`. The version of `qsort` in ``VAXCRTL'` has a bug (known to be present in VMS versions V4.6 through V5.5) which causes the compiler to fail.

The executables are generated by ``make-cc1.com'` and ``make-cccp.com'` use the object library version of ``VAXCRTL'` in order to make use of the `qsort` routine in ``gcclib.olb'`. If you wish to link the compiler executables with the shareable image version of ``VAXCRTL'`, you should edit the file ``tm.h'` (created by ``vmsconfig.com'`) to define the macro `QSORT_WORKAROUND`.

`QSORT_WORKAROUND` is always defined when GNU CC is compiled with VAX C, to avoid a problem in case ``gcclib.olb'` is not yet available.

## `collect2`

Many target systems do not have support in the assembler and linker for "constructors"---initialization functions to be called before the official "start" of `main`. On such systems, GNU CC uses a utility called `collect2` to arrange to call these functions at start time.

The program `collect2` works by linking the program once and looking through the linker output file for symbols with particular names indicating they are constructor functions. If it finds any, it creates a new temporary ``.c'` file containing a table of them, compiles it, and links the program a second time including that file.

The actual calls to the constructors are carried out by a subroutine called `__main`, which is called (automatically) at the beginning of the body of `main` (provided `main` was compiled with GNU CC). Calling `__main` is necessary, even when compiling C code, to allow linking C and C++ object code together. (If you use ``-nostdlib'`, you get an unresolved reference to `__main`, since it's defined in the standard GCC library. Include ``-lgcc'` at the end of your compiler command line to resolve this reference.)

The program `collect2` is installed as `ld` in the directory where the passes of the compiler are installed. When `collect2` needs to find the real `ld`, it tries the following file names:

- ``real-ld'` in the directories listed in the compiler's search directories.
- ``real-ld'` in the directories listed in the environment variable `PATH`.
- The file specified in the `REAL_LD_FILE_NAME` configuration macro, if specified.
- ``ld'` in the compiler's search directories, except that `collect2` will not execute itself recursively.
- ``ld'` in `PATH`.

"The compiler's search directories" means all the directories where `gcc` searches for passes of the compiler. This includes directories that you specify with ``-B'`.

Cross-compilers search a little differently:

- ``real-ld'` in the compiler's search directories.
- ``target-real-ld'` in `PATH`.
- The file specified in the `REAL_LD_FILE_NAME` configuration macro, if specified.
- ``ld'` in the compiler's search directories.
- ``target-ld'` in `PATH`.

`collect2` explicitly avoids running `ld` using the file name under which `collect2` itself was invoked. In fact, it remembers up a list of such names--in case one copy of `collect2` finds another copy (or version) of `collect2` installed as `ld` in a second place in the search path.

`collect2` searches for the utilities `nm` and `strip` using the same algorithm as above for `ld`.

## Standard Header File Directories

`GCC_INCLUDE_DIR` means the same thing for native and cross. It is where GNU CC stores its private include files, and also where GNU CC stores the fixed include files. A cross compiled GNU CC runs `fixincludes` on the header files in ``$(tooldir)/include'`. (If the cross compilation header files need to be fixed, they must be installed before GNU CC is built. If the cross compilation header files are already suitable for ANSI C and GNU CC, nothing special need be done).

`GPLUS_INCLUDE_DIR` means the same thing for native and cross. It is where `g++` looks first for header files. `libg++` installs only target independent header files in that directory.

`LOCAL_INCLUDE_DIR` is used only for a native compiler. It is normally ``/usr/local/include'`. GNU CC searches this directory so that users can install header files in ``/usr/local/include'`.

`CROSS_INCLUDE_DIR` is used only for a cross compiler. GNU CC doesn't install anything there.

`TOOL_INCLUDE_DIR` is used for both native and cross compilers. It is the place for other packages to install header files that GNU CC will use. For a cross-compiler, this is the equivalent of ``/usr/include'`. When you build a cross-compiler, `fixincludes` processes any header files in this directory.

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