# Prerequisites for GCC

GCC requires that various tools and packages be available for use in the build procedure. Modifying GCC sources requires additional tools described below.

### Tools/packages necessary for building GCC

ISO C++11 compiler
  Necessary to bootstrap GCC.

  Versions of GCC prior to 11 also allow bootstrapping with an ISO C++98 compiler, versions of GCC prior to 4.8 also allow bootstrapping with a ISO C89 compiler, and versions of GCC prior to 3.4 also allow bootstrapping with a traditional (K&R) C compiler.

  To build all languages in a cross-compiler or other configuration where 3-stage bootstrap is not performed, you need to start with an existing GCC binary (version 4.8 or later) because source code for language frontends other than C might use GCC extensions.

C standard library and headers
  In order to build GCC, the C standard library and headers must be present for all target variants for which target libraries will be built (and not only the variant of the host C++ compiler).

  This affects the popular ``x86_64-pc-linux-gnu`' platform (among other multilib targets), for which 64-bit (``x86_64`') and 32-bit (``i386`') libc headers are usually packaged separately. If you do a build of a native compiler on ``x86_64-pc-linux-gnu`', make sure you either have the 32-bit libc developer package properly installed (the exact name of the package depends on your distro) or you must build GCC as a 64-bit only compiler by configuring with the option `--disable-multilib`. Otherwise, you may encounter an error such as ``fatal error: gnu/stubs-32.h: No such file`'

GNAT
  In order to build GNAT, the Ada compiler, you need a working GNAT compiler (GCC version 5.1 or later).

  This includes GNAT tools such as `gnatmake` and `gnatlink`, since the Ada front end is written in Ada and uses some GNAT-specific extensions.

  In order to build a cross compiler, it is strongly recommended to install the new compiler as native first, and then use it to build the cross compiler. Other native compiler versions may work but this is not guaranteed and will typically fail with hard to understand compilation errors during the build.

  Similarly, it is strongly recommended to use an older version of GNAT to build GNAT. More recent versions of GNAT than the version built are not guaranteed to work and will often fail during the build with compilation errors.

  Note that `configure` does not test whether the GNAT installation works and has a sufficiently recent version; if too old a GNAT version is installed and `--enable-languages=ada` is used, the build will fail.

  `ADA_INCLUDE_PATH` and `ADA_OBJECT_PATH` environment variables must not be set when building the Ada compiler, the Ada tools, or the Ada runtime libraries. You can check that your build environment is clean by verifying that ``gnatls -v`' lists only one explicit path in each section.

GDC
  In order to build GDC, the D compiler, you need a working GDC compiler (GCC version 9.1 or later) and D runtime library, ``libphobos`', as the D front end is written in D.

  Versions of GDC prior to 12 can be built with an ISO C++11 compiler, which can then be installed and used to bootstrap newer versions of the D front end.

  It is strongly recommended to use an older version of GDC to build GDC. More recent versions of GDC than the version built are not guaranteed to work and will often fail during the build with compilation errors relating to deprecations or removed features.

  Note that `configure` does not test whether the GDC installation works and has a sufficiently recent version. Though the implementation of the D front end does not make use of any GDC-specific extensions, or novel features of the D language, if too old a GDC version is installed and `--enable-languages=d` is used, the build will fail.

  On some targets, ``libphobos`' isn't enabled by default, but compiles and works if `--enable-libphobos` is used. Specifics are documented for affected targets.

A “working” POSIX compatible shell, or GNU bash
  Necessary when running `configure` because some `/bin/sh` shells have bugs and may crash when configuring the target libraries. In other cases, `/bin/sh` or `ksh` have disastrous corner-case performance problems. This can cause target `configure` runs to literally take days to complete in some cases.

  So on some platforms `/bin/ksh` is sufficient, on others it isn't. See the host/target specific instructions for your platform, or use `bash` to be sure. Then set `CONFIG_SHELL` in your environment to your “good” shell prior to running `configure`/`make`.

  `zsh` is not a fully compliant POSIX shell and will not work when configuring GCC.

A POSIX or SVR4 awk
  Necessary for creating some of the generated source files for GCC. If in doubt, use a recent GNU awk version, as some of the older ones are broken. GNU awk version 3.1.5 is known to work.
GNU binutils
  Necessary in some circumstances, optional in others. See the host/target specific instructions for your platform for the exact requirements.

  Note binutils 2.35 or newer is required for LTO to work correctly with GNU libtool that includes doing a bootstrap with LTO enabled.

gzip version 1.2.4 (or later) or
bzip2 version 1.0.2 (or later)
  Necessary to uncompress GCC `tar` files when source code is obtained via HTTPS mirror sites.
GNU make version 3.80 (or later)
  You must have GNU make installed to build GCC.
GNU tar version 1.14 (or later)
  Necessary (only on some platforms) to untar the source code. Many systems' `tar` programs will also work, only try GNU `tar` if you have problems.
Perl version between 5.6.1 and 5.6.24
  Necessary when targeting Darwin, building ``libstdc++`', and not using `--disable-symvers`. Necessary when targeting Solaris 2 with Solaris `ld` and not using `--disable-symvers`.

  Necessary when regenerating `Makefile` dependencies in libiberty. Necessary when regenerating `libiberty/functions.texi`. Necessary when generating manpages from Texinfo manuals. Used by various scripts to generate some files included in the source repository (mainly Unicode-related and rarely changing) from source tables.

  Used by `automake`.

Several support libraries are necessary to build GCC, some are required, others optional. While any sufficiently new version of required tools usually work, library requirements are generally stricter. Newer versions may work in some cases, but it's safer to use the exact versions documented. We appreciate bug reports about problems with newer versions, though. If your OS vendor provides packages for the support libraries then using those packages may be the simplest way to install the libraries.

GNU Multiple Precision Library (GMP) version 4.3.2 (or later)
  Necessary to build GCC. If a GMP source distribution is found in a subdirectory of your GCC sources named `gmp`, it will be built together with GCC. Alternatively, if GMP is already installed but it is not in your library search path, you will have to configure with the `--with-gmp` configure option. See also `--with-gmp-lib` and `--with-gmp-include`. The in-tree build is only supported with the GMP version that download_prerequisites installs.
MPFR Library version 3.1.0 (or later)
  Necessary to build GCC. It can be downloaded from https://www.mpfr.org. If an MPFR source distribution is found in a subdirectory of your GCC sources named `mpfr`, it will be built together with GCC. Alternatively, if MPFR is already installed but it is not in your default library search path, the `--with-mpfr` configure option should be used. See also `--with-mpfr-lib` and `--with-mpfr-include`. The in-tree build is only supported with the MPFR version that download_prerequisites installs.
MPC Library version 1.0.1 (or later)
  Necessary to build GCC. It can be downloaded from https://www.multiprecision.org/mpc/. If an MPC source distribution is found in a subdirectory of your GCC sources named `mpc`, it will be built together with GCC. Alternatively, if MPC is already installed but it is not in your default library search path, the `--with-mpc` configure option should be used. See also `--with-mpc-lib` and `--with-mpc-include`. The in-tree build is only supported with the MPC version that download_prerequisites installs.
isl Library version 0.15 or later.
  Necessary to build GCC with the Graphite loop optimizations. It can be downloaded from https://gcc.gnu.org/pub/gcc/infrastructure/. If an isl source distribution is found in a subdirectory of your GCC sources named `isl`, it will be built together with GCC. Alternatively, the `--with-isl` configure option should be used if isl is not installed in your default library search path.
zstd Library.
  Necessary to build GCC with zstd compression used for LTO bytecode. The library is searched in your default library patch search. Alternatively, the `--with-zstd` configure option should be used.

### Tools/packages necessary for modifying GCC

autoconf version 2.69
GNU m4 version 1.4.6 (or later)
  Necessary when modifying `configure.ac`, `aclocal.m4`, etc. to regenerate `configure` and `config.in` files.
automake version 1.15.1
  Necessary when modifying a `Makefile.am` file to regenerate its associated `Makefile.in`.

  Much of GCC does not use automake, so directly edit the `Makefile.in` file. Specifically this applies to the `gcc`, `intl`, `libcpp`, `libiberty`, `libobjc` directories as well as any of their subdirectories.

  For directories that use automake, GCC requires the latest release in the 1.15 series, which is currently 1.15.1. When regenerating a directory to a newer version, please update all the directories using an older 1.15 to the latest released version.

gettext version 0.14.5 (or later)
  Needed to regenerate `gcc.pot`.
gperf version 2.7.2 (or later)
  Necessary when modifying `gperf` input files, e.g. `gcc/cp/cfns.gperf` to regenerate its associated header file, e.g. `gcc/cp/cfns.h`.
DejaGnu version 1.5.3 (or later)
Expect
Tcl

  Necessary to run the GCC testsuite; see the section on testing for details.

autogen version 5.5.4 (or later) and
guile version 1.4.1 (or later)
  Necessary to regenerate `fixinc/fixincl.x` from `fixinc/inclhack.def` and `fixinc/*.tpl`.

  Necessary to run ``make check`' for `fixinc`.

  Necessary to regenerate the top level `Makefile.in` file from `Makefile.tpl` and `Makefile.def`.

Flex version 2.5.4 (or later)
  Necessary when modifying `*.l` files.

  Necessary to build GCC during development because the generated output files are not included in the version-controlled source repository. They are included in releases.

Texinfo version 4.7 (or later)
  Necessary for running `makeinfo` when modifying `*.texi` files to test your changes.

  Necessary for running `make dvi` or `make pdf` to create printable documentation in DVI or PDF format. Texinfo version 4.8 or later is required for `make pdf`.

  Necessary to build GCC documentation during development because the generated output files are not included in the repository. They are included in releases.

TeX (any working version)
  Necessary for running `texi2dvi` and `texi2pdf`, which are used when running `make dvi` or `make pdf` to create DVI or PDF files, respectively.
Sphinx version 1.0 (or later)
  Necessary to regenerate `jit/docs/_build/texinfo` from the `.rst` files in the directories below `jit/docs`.
git (any version)
SSH (any version)
  Necessary to access the source repository. Public releases and weekly snapshots of the development sources are also available via HTTPS.
GNU diffutils version 2.7 (or later)
  Useful when submitting patches for the GCC source code.
patch version 2.5.4 (or later)
  Necessary when applying patches, created with `diff`, to one's own sources.

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