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   1 ..
   2   Copyright 1988-2022 Free Software Foundation, Inc.
   3   This is part of the GCC manual.
   4   For copying conditions, see the copyright.rst file.
   5
   6 .. _configuration:
   7
   8 Configuration in the gcc Directory
   9 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  10
  11 The :samp:`gcc` directory is configured with an Autoconf-generated
  12 script :samp:`configure`.  The :samp:`configure` script is generated
  13 from :samp:`configure.ac` and :samp:`aclocal.m4`.  From the files
  14 :samp:`configure.ac` and :samp:`acconfig.h`, Autoheader generates the
  15 file :samp:`config.in`.  The file :samp:`cstamp-h.in` is used as a
  16 timestamp.
  17
  18 .. toctree::
  19   :maxdepth: 2
  20
  21
  22 .. _config-fragments:
  23
  24 Scripts Used by configure
  25 ~~~~~~~~~~~~~~~~~~~~~~~~~
  26
  27 :samp:`configure` uses some other scripts to help in its work:
  28
  29 * The standard GNU :samp:`config.sub` and :samp:`config.guess`
  30   files, kept in the top level directory, are used.
  31
  32 * The file :samp:`config.gcc` is used to handle configuration
  33   specific to the particular target machine.  The file
  34   :samp:`config.build` is used to handle configuration specific to the
  35   particular build machine.  The file :samp:`config.host` is used to handle
  36   configuration specific to the particular host machine.  (In general,
  37   these should only be used for features that cannot reasonably be tested in
  38   Autoconf feature tests.)
  39   See :ref:`system-config`, for details of the contents of these files.
  40
  41 * Each language subdirectory has a file
  42   :samp:`{language}/config-lang.in` that is used for
  43   front-end-specific configuration.  See :ref:`front-end-config`, for details of this file.
  44
  45 * A helper script :samp:`configure.frag` is used as part of
  46   creating the output of :samp:`configure`.
  47
  48 .. _system-config:
  49
  50 The config.build; config.host; and config.gcc Files
  51 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  52
  53 The :samp:`config.build` file contains specific rules for particular systems
  54 which GCC is built on.  This should be used as rarely as possible, as the
  55 behavior of the build system can always be detected by autoconf.
  56
  57 The :samp:`config.host` file contains specific rules for particular systems
  58 which GCC will run on.  This is rarely needed.
  59
  60 The :samp:`config.gcc` file contains specific rules for particular systems
  61 which GCC will generate code for.  This is usually needed.
  62
  63 Each file has a list of the shell variables it sets, with descriptions, at the
  64 top of the file.
  65
  66 .. todo:: document the contents of these files, and what variables should
  67   be set to control build, host and target configuration.
  68
  69 .. _configuration-files:
  70
  71 Files Created by configure
  72 ~~~~~~~~~~~~~~~~~~~~~~~~~~
  73
  74 Here we spell out what files will be set up by :samp:`configure` in the
  75 :samp:`gcc` directory.  Some other files are created as temporary files
  76 in the configuration process, and are not used in the subsequent
  77 build; these are not documented.
  78
  79 * :samp:`Makefile` is constructed from :samp:`Makefile.in`, together with
  80   the host and target fragments (see :ref:`fragments`) :samp:`t-{target}` and :samp:`x-{host}` from
  81   :samp:`config`, if any, and language Makefile fragments
  82   :samp:`{language}/Make-lang.in`.
  83
  84 * :samp:`auto-host.h` contains information about the host machine
  85   determined by :samp:`configure`.  If the host machine is different from
  86   the build machine, then :samp:`auto-build.h` is also created,
  87   containing such information about the build machine.
  88
  89 * :samp:`config.status` is a script that may be run to recreate the
  90   current configuration.
  91
  92 * :samp:`configargs.h` is a header containing details of the arguments
  93   passed to :samp:`configure` to configure GCC, and of the thread model
  94   used.
  95
  96 * :samp:`cstamp-h` is used as a timestamp.
  97
  98 * If a language :samp:`config-lang.in` file (see :ref:`front-end-config`) sets ``outputs``, then
  99   the files listed in ``outputs`` there are also generated.
 100
 101 The following configuration headers are created from the Makefile,
 102 using :samp:`mkconfig.sh`, rather than directly by :samp:`configure`.
 103 :samp:`config.h`, :samp:`bconfig.h` and :samp:`tconfig.h` all contain the
 104 :samp:`xm-{machine}.h` header, if any, appropriate to the host,
 105 build and target machines respectively, the configuration headers for
 106 the target, and some definitions; for the host and build machines,
 107 these include the autoconfigured headers generated by
 108 :samp:`configure`.  The other configuration headers are determined by
 109 :samp:`config.gcc`.  They also contain the typedefs for ``rtx``,
 110 ``rtvec`` and ``tree``.
 111
 112 * :samp:`config.h`, for use in programs that run on the host machine.
 113
 114 * :samp:`bconfig.h`, for use in programs that run on the build machine.
 115
 116 * :samp:`tconfig.h`, for use in programs and libraries for the target
 117   machine.
 118
 119 * :samp:`tm_p.h`, which includes the header :samp:`{machine}-protos.h`
 120   that contains prototypes for functions in the target
 121   :samp:`{machine}.c` file.  The
 122   :samp:`{machine}-protos.h` header is included after the :samp:`rtl.h`
 123   and/or :samp:`tree.h` would have been included.
 124   The :samp:`tm_p.h` also
 125   includes the header :samp:`tm-preds.h` which is generated by
 126   :samp:`genpreds` program during the build to define the declarations
 127   and inline functions for the predicate functions.