This is Info file gcc.info, produced by Makeinfo version 1.68 from the
input file
/tantor/build/intel-xscale/xscale-010413/i686-pc-linux-gnulibc2.1/src/gcc/gcc.texi.

START-INFO-DIR-ENTRY
* Gcc: (gcc).                           Using and Porting the GNU C compiler.
END-INFO-DIR-ENTRY

INFO-DIR-SECTION Programming
START-INFO-DIR-ENTRY
* gcc: (gcc).                  The GNU Compiler Collection.
END-INFO-DIR-ENTRY
   This file documents the use and the internals of the GNU compiler.

   Published by the Free Software Foundation 59 Temple Place - Suite 330
Boston, MA 02111-1307 USA

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

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

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

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


File: gcc.info,  Node: Installation,  Next: C Extensions,  Prev: Invoking GCC,  Up: Top

Installing GNU CC
*****************

* Menu:

* Configuration Files::  Files created by running `configure'.
* 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 GNU or Unix system.
See *Note VMS Install::, for VMS systems.  In this section we assume you
compile in the same directory that contains the source files; see *Note
Other Dir::, 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. 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'.

  4. 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.

  5. Specify the host, build and target machine configurations.  You do
     this when you run the `configure' script.

     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 `--host' option; the host and target will default to be
     the same as the host machine.  (If you are building a
     cross-compiler, see *Note Cross-Compiler::.)

     Here is an example:

          ./configure --host=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.

     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 *Note Configurations::, 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.

  6. When running `configure', you may also need to specify certain
     additional options that 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.

    `--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.

    `--enable-haifa'
    `--disable-haifa'
          Use `--enable-haifa' to enable use of an experimental
          instruction scheduler (from IBM Haifa).  This may or may not
          produce better code.  Some targets on which it is known to be
          a win enable it by default; use `--disable-haifa' to disable
          it in these cases.  `configure' will print out whether the
          Haifa scheduler is enabled when it is run.

    `--enable-threads=TYPE'
          Certain systems, notably Linux-based GNU systems, can't be
          relied on to supply a threads facility for the Objective C
          runtime and so will default to single-threaded runtime.  They
          may, however, have a library threads implementation
          available, in which case threads can be enabled with this
          option by supplying a suitable TYPE, probably `posix'.  The
          possibilities for TYPE are `single', `posix', `win32',
          `solaris', `irix' and `mach'.

    `--enable-checking'
          When you specify this option, the compiler is built to
          perform checking of tree node types when referencing fields
          of that node.  This does not change the generated code, but
          adds error checking within the compiler.  This will slow down
          the compiler and may only work properly if you are building
          the compiler with GNU C.

          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 (*note Config::.).  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'.

    `--enable-nls'
    `--disable-nls'
          The `--enable-nls' option enables Native Language Support
          (NLS), which lets GCC output diagnostics in languages other
          than American English.  No translations are available yet, so
          the main users of this option now are those translating GCC's
          diagnostics who want to test their work.  Once translations
          become available, Native Language Support will become enabled
          by default.  The `--disable-nls' option disables NLS.

    `--with-included-gettext'
          If NLS is enabled, the GCC build procedure normally attempts
          to use the host's `gettext' libraries, and falls back on
          GCC's copy of the GNU `gettext' library only if the host
          libraries do not suffice.  The `--with-included-gettext'
          option causes the build procedure to prefer its copy of GNU
          `gettext'.

    `--with-catgets'
          If NLS is enabled, and if the host lacks `gettext' but has the
          inferior `catgets' interface, the GCC build procedure normally
          ignores `catgets' and instead uses GCC's copy of the GNU
          `gettext' library.  The `--with-catgets' option causes the
          build procedure to use the host's `catgets' in this situation.

    `--enable-win32-registry'
    `--enable-win32-registry=KEY'
    `--disable-win32-registry'
          The `--enable-win32-registry' option enables Windows-hosted
          GCC to look up installations paths in the registry using the
          following key:

               `HKEY_LOCAL_MACHINE\SOFTWARE\Free Software Foundation\<KEY>'

          <KEY> defaults to GCC version number, and can be overridden
          by the `--enable-win32-registry=KEY' option. Vendors and
          distributors who use custom installers are encouraged to
          provide a different key, perhaps one comprised of vendor name
          and GCC version number, to avoid conflict with existing
          installations. This feature is enabled by default, and can be
          disabled by `--disable-win32-registry' option.  This option
          has no effect on the other hosts.

  7. In certain cases, you should specify certain other options when
     you run `configure'.

        * 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 `--with-local-prefix' option below.  The directory you
          specify need not exist, but its parent directory must exist.

        * Specify `--with-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 `--with-local-prefix' *only* if your site
          has a different convention (not `/usr/local') for where to put
          site-specific files.

          The default value for `--with-local-prefix' is `/usr/local'
          regardless of the value of `--prefix'.  Specifying `--prefix'
          has no effect on which directory GNU CC searches for local
          header files.  This may seem counterintuitive, but actually
          it is logical.

          The purpose of `--prefix' is to specify where to *install GNU
          CC*.  The local header files in `/usr/local/include'--if you
          put any in that directory--are not part of GNU CC.  They are
          part of other programs--perhaps many others.  (GNU CC
          installs its own header files in another directory which is
          based on the `--prefix' value.)

          *Do not* specify `/usr' as the `--with-local-prefix'!  The
          directory you use for `--with-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.

          Indications are that people who use this option use it based
          on mistaken ideas of what it is for.  People use it as if it
          specified where to install part of GNU CC.  Perhaps they make
          this assumption because installing GNU CC creates the
          directory.

  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', a warning about a comparison always being zero in
     `enquire.o', and warnings about shift counts exceeding type widths
     in `cexp.y'.  Any other compilation errors may represent bugs in
     the port to your machine or operating system, and should be
     investigated and reported (*note Bugs::.).

     Some 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.  *Note
     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. 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 (*note 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
     canonicalized form of 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 executables for compilers for other
     languages (e.g., `cc1plus' for C++) to the same directory.

     This also copies the driver program `xgcc' into
     `/usr/local/bin/gcc', so that it appears in typical execution
     search paths.  It also copies `gcc.1' into `/usr/local/man/man1'
     and info pages into `/usr/local/info'.

     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++, you need to install the C++ runtime
     library.  This includes all I/O functionality, special class
     libraries, etc.

     The standard C++ runtime library for GNU CC is called `libstdc++'.
     An obsolescent library `libg++' may also be available, but it's
     necessary only for older software that hasn't been converted yet;
     if you don't know whether you need `libg++' then you probably don't
     need it.

     Here's one way to build and install `libstdc++' for GNU CC:

        * Build and install GNU CC, so that invoking `gcc' obtains the
          GNU CC that was just built.

        * Obtain a copy of a compatible `libstdc++' distribution.  For
          example, the `libstdc++-2.8.0.tar.gz' distribution should be
          compatible with GCC 2.8.0.  GCC distributors normally
          distribute `libstdc++' as well.

        * Set the `CXX' environment variable to `gcc' while running the
          `libstdc++' distribution's `configure' command.  Use the same
          `configure' options that you used when you invoked GCC's
          `configure' command.

        * Invoke `make' to build the C++ runtime.

        * Invoke `make install' to install the C++ runtime.

     To summarize, after building and installing GNU CC, invoke the
     following shell commands in the topmost directory of the C++
     library distribution.  For CONFIGURE-OPTIONS, use the same options
     that you used to configure GNU CC.

          $ CXX=gcc ./configure CONFIGURE-OPTIONS
          $ make
          $ make install

 17. GNU CC includes a runtime library for Objective-C because it is an
     integral part of the language.  You can find the files associated
     with the library in the subdirectory `objc'.  The GNU Objective-C
     Runtime Library requires header files for the target's C library in
     order to be compiled,and also requires the header files for the
     target's thread library if you want thread support.  *Note
     Cross-Compilers and Header Files: Cross Headers, for discussion
     about header files issues for cross-compilation.

     When you run `configure', it picks the appropriate Objective-C
     thread implementation file for the target platform.  In some
     situations, you may wish to choose a different back-end as some
     platforms support multiple thread implementations or you may wish
     to disable thread support completely.  You do this by specifying a
     value for the OBJC_THREAD_FILE makefile variable on the command
     line when you run make, for example:

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

     Below is a list of the currently available back-ends.

        * thr-single Disable thread support, should work for all
          platforms.

        * thr-decosf1 DEC OSF/1 thread support.

        * thr-irix SGI IRIX thread support.

        * thr-mach Generic MACH thread support, known to work on
          NEXTSTEP.

        * thr-os2 IBM OS/2 thread support.

        * thr-posix Generix POSIX thread support.

        * thr-pthreads PCThreads on Linux-based GNU systems.

        * thr-solaris SUN Solaris thread support.

        * thr-win32 Microsoft Win32 API thread support.


File: gcc.info,  Node: Configuration Files,  Next: Configurations,  Up: Installation

Files Created by `configure'
============================

   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 (*note Config::.).  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.

