# Installing GCC: Configuration

Like most GNU software, GCC must be configured before it can be built. This document describes the recommended configuration procedure for both native and cross targets.

We use srcdir to refer to the toplevel source directory for GCC; we use objdir to refer to the toplevel build/object directory.

If you obtained the sources via SVN, srcdir must refer to the top `gcc` directory, the one where the `MAINTAINERS` file can be found, and not its `gcc` subdirectory, otherwise the build will fail.

If either srcdir or objdir is located on an automounted NFS file system, the shell's built-in `pwd` command will return temporary pathnames. Using these can lead to various sorts of build problems. To avoid this issue, set the `PWDCMD` environment variable to an automounter-aware `pwd` command, e.g., `pawd` or ‘`amq -w`’, during the configuration and build phases.

First, we highly recommend that GCC be built into a separate directory from the sources which does not reside within the source tree. This is how we generally build GCC; building where srcdir == objdir should still work, but doesn't get extensive testing; building where objdir is a subdirectory of srcdir is unsupported.

If you have previously built GCC 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 or issues a message like “don't know how to make distclean” it probably means that the directory is already suitably clean. However, with the recommended method of building in a separate objdir, you should simply use a different objdir for each target.

Second, when configuring a native system, either `cc` or `gcc` must be in your path or you must set `CC` in your environment before running configure. Otherwise the configuration scripts may fail.

To configure GCC:

         % mkdir objdir
         % cd objdir
         % srcdir/configure [options] [target]

### Distributor options

If you will be distributing binary versions of GCC, with modifications to the source code, you should use the options described in this section to make clear that your version contains modifications.

`--with-pkgversion=`version
  Specify a string that identifies your package. You may wish to include a build number or build date. This version string will be included in the output of `gcc --version`. This suffix does not replace the default version string, only the ‘`GCC`’ part.

  The default value is ‘`GCC`’.

`--with-bugurl=`url
  Specify the URL that users should visit if they wish to report a bug. You are of course welcome to forward bugs reported to you to the FSF, if you determine that they are not bugs in your modifications.

  The default value refers to the FSF's GCC bug tracker.

### Target specification

- GCC has code to correctly determine the correct value for target for nearly all native systems. Therefore, we highly recommend you do not provide a configure target when configuring a native compiler.
- target must be specified as `--target=target` when configuring a cross compiler; examples of valid targets would be m68k-elf, sh-elf, etc.
- Specifying just target instead of `--target=target` implies that the host defaults to target.

### Options specification

Use options to override several configure time options for GCC. A list of supported options follows; ‘`configure --help`’ may list other options, but those not listed below may not work and should not normally be used.

Note that each `--enable` option has a corresponding `--disable` option and that each `--with` option has a corresponding `--without` option.

`--prefix=`dirname
  Specify the toplevel installation directory. This is the recommended way to install the tools into a directory other than the default. The toplevel installation directory defaults to `/usr/local`.

  We highly recommend against dirname being the same or a subdirectory of objdir or vice versa. If specifying a directory beneath a user's home directory tree, some shells will not expand dirname correctly if it contains the ‘`~`’ metacharacter; use `$HOME` instead.

  The following standard `autoconf` options are supported. Normally you should not need to use these options.

  `--exec-prefix=`dirname
    Specify the toplevel installation directory for architecture-dependent files. The default is `prefix`.
  `--bindir=`dirname
    Specify the installation directory for the executables called by users (such as `gcc` and `g++`). The default is `exec-prefix/bin`.
  `--libdir=`dirname
    Specify the installation directory for object code libraries and internal data files of GCC. The default is `exec-prefix/lib`.
  `--libexecdir=`dirname
    Specify the installation directory for internal executables of GCC. The default is `exec-prefix/libexec`.
  `--with-slibdir=`dirname
    Specify the installation directory for the shared libgcc library. The default is `libdir`.
  `--datarootdir=`dirname
    Specify the root of the directory tree for read-only architecture-independent data files referenced by GCC. The default is `prefix/share`.
  `--infodir=`dirname
    Specify the installation directory for documentation in info format. The default is `datarootdir/info`.
  `--datadir=`dirname
    Specify the installation directory for some architecture-independent data files referenced by GCC. The default is `datarootdir`.
  `--docdir=`dirname
    Specify the installation directory for documentation files (other than Info) for GCC. The default is `datarootdir/doc`.
  `--htmldir=`dirname
    Specify the installation directory for HTML documentation files. The default is `docdir`.
  `--pdfdir=`dirname
    Specify the installation directory for PDF documentation files. The default is `docdir`.
  `--mandir=`dirname
    Specify the installation directory for manual pages. The default is `datarootdir/man`. (Note that the manual pages are only extracts from the full GCC manuals, which are provided in Texinfo format. The manpages are derived by an automatic conversion process from parts of the full manual.)
  `--with-gxx-include-dir=`dirname
    Specify the installation directory for G++ header files. The default depends on other configuration options, and differs between cross and native configurations.
  `--with-specs=`specs
    Specify additional command line driver SPECS. This can be useful if you need to turn on a non-standard feature by default without modifying the compiler's source code, for instance `--with-specs=%{!fcommon:%{!fno-common:-fno-common}}`. See “Spec Files” in the main manual
`--program-prefix=`prefix
  GCC supports some transformations of the names of its programs when installing them. This option prepends prefix to the names of programs to install in bindir (see above). For example, specifying `--program-prefix=foo-` would result in ‘`gcc`’ being installed as `/usr/local/bin/foo-gcc`.
`--program-suffix=`suffix
  Appends suffix to the names of programs to install in bindir (see above). For example, specifying `--program-suffix=-3.1` would result in ‘`gcc`’ being installed as `/usr/local/bin/gcc-3.1`.
`--program-transform-name=`pattern
  Applies the ‘`sed`’ script pattern to be applied to the names of programs to install in bindir (see above). pattern has to consist of one or more basic ‘`sed`’ editing commands, separated by semicolons. For example, if you want the ‘`gcc`’ program name to be transformed to the installed program `/usr/local/bin/myowngcc` and the ‘`g++`’ program name to be transformed to `/usr/local/bin/gspecial++` without changing other program names, you could use the pattern `--program-transform-name='s/^gcc$/myowngcc/; s/^g++$/gspecial++/'` to achieve this effect.

  All three options can be combined and used together, resulting in more complex conversion patterns. As a basic rule, prefix (and suffix) are prepended (appended) before further transformations can happen with a special transformation script pattern.

  As currently implemented, this option only takes effect for native builds; cross compiler binaries' names are not transformed even when a transformation is explicitly asked for by one of these options.

  For native builds, some of the installed programs are also installed with the target alias in front of their name, as in ‘`i686-pc-linux-gnu-gcc`’. All of the above transformations happen before the target alias is prepended to the name—so, specifying `--program-prefix=foo-` and `program-suffix=-3.1`, the resulting binary would be installed as `/usr/local/bin/i686-pc-linux-gnu-foo-gcc-3.1`.

  As a last shortcoming, none of the installed Ada programs are transformed yet, which will be fixed in some time.

`--with-local-prefix=`dirname
  Specify the installation directory for local include files. The default is `/usr/local`. Specify this option if you want the compiler to search directory `dirname/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 GCC searches for local header files. This may seem counterintuitive, but actually it is logical.

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

  Both the local-prefix include directory and the GCC-prefix include directory are part of GCC's “system include” directories. Although these two directories are not fixed, they need to be searched in the proper order for the correct processing of the include_next directive. The local-prefix include directory is searched before the GCC-prefix include directory. Another characteristic of system include directories is that pedantic warnings are turned off for headers in these directories.

  Some autoconf macros add `-I directory` options to the compiler command line, to ensure that directories containing installed packages' headers are searched. When directory is one of GCC's system include directories, GCC will ignore the option so that system directories continue to be processed in the correct order. This may result in a search order different from what was specified but the directory will still be searched.

  GCC automatically searches for ordinary libraries using `GCC_EXEC_PREFIX`. Thus, when the same installation prefix is used for both GCC and packages, GCC will automatically search for both headers and libraries. This provides a configuration that is easy to use. GCC behaves in a manner similar to that when it is installed as a system compiler in `/usr`.

  Sites that need to install multiple versions of GCC may not want to use the above simple configuration. It is possible to use the `--program-prefix`, `--program-suffix` and `--program-transform-name` options to install multiple versions into a single directory, but it may be simpler to use different prefixes and the `--with-local-prefix` option to specify the location of the site-specific files for each version. It will then be necessary for users to specify explicitly the location of local site libraries (e.g., with `LIBRARY_PATH`).

  The same value can be used for both `--with-local-prefix` and `--prefix` provided it is not `/usr`. This can be used to avoid the default search of `/usr/local/include`.

  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 GCC. Perhaps they make this assumption because installing GCC creates the directory.

`--with-native-system-header-dir=`dirname
  Specifies that dirname is the directory that contains native system header files, rather than `/usr/include`. This option is most useful if you are creating a compiler that should be isolated from the system as much as possible. It is most commonly used with the `--with-sysroot` option and will cause GCC to search dirname inside the system root specified by that option.
`--enable-shared[=`package`[,...]]`
  Build shared versions of libraries, if shared libraries are supported on the target platform. Unlike GCC 2.95.x and earlier, shared libraries are enabled by default on all platforms that support shared libraries.

  If a list of packages is given as an argument, build shared libraries only for the listed packages. For other packages, only static libraries will be built. Package names currently recognized in the GCC tree are ‘`libgcc`’ (also known as ‘`gcc`’), ‘`libstdc++`’ (not ‘`libstdc++-v3`’), ‘`libffi`’, ‘`zlib`’, ‘`boehm-gc`’, ‘`ada`’, ‘`libada`’, ‘`libjava`’, ‘`libgo`’, and ‘`libobjc`’. Note ‘`libiberty`’ does not support shared libraries at all.

  Use `--disable-shared` to build only static libraries. Note that `--disable-shared` does not accept a list of package names as argument, only `--enable-shared` does.

`--with-gnu-as`
  Specify that the compiler should assume that the assembler it finds is the GNU assembler. However, this does not modify the rules to find an assembler and will result in confusion if the assembler found is not actually the GNU assembler. (Confusion may also result if the compiler finds the GNU assembler but has not been configured with `--with-gnu-as`.) If you have more than one assembler installed on your system, you may want to use this option in connection with `--with-as=pathname` or `--with-build-time-tools=pathname`.

  The following systems are the only ones where it makes a difference whether you use the GNU assembler. On any other system, `--with-gnu-as` has no effect.

  - ‘`hppa1.0-any-any`’
  - ‘`hppa1.1-any-any`’
  - ‘`sparc-sun-solaris2.any`’
  - ‘`sparc64-any-solaris2.any`’
`--with-as=`pathname
  Specify that the compiler should use the assembler pointed to by pathname, rather than the one found by the standard rules to find an assembler, which are:
  - Unless GCC is being built with a cross compiler, check the `libexec/gcc/target/version` directory. libexec defaults to `exec-prefix/libexec`; exec-prefix defaults to prefix, which defaults to `/usr/local` unless overridden by the `--prefix=pathname` switch described above. target is the target system triple, such as ‘`sparc-sun-solaris2.7`’, and version denotes the GCC version, such as 3.0.
  - If the target system is the same that you are building on, check operating system specific directories (e.g. `/usr/ccs/bin` on Sun Solaris 2).
  - Check in the `PATH` for a tool whose name is prefixed by the target system triple.
  - Check in the `PATH` for a tool whose name is not prefixed by the target system triple, if the host and target system triple are the same (in other words, we use a host tool if it can be used for the target as well).

  You may want to use `--with-as` if no assembler is installed in the directories listed above, or if you have multiple assemblers installed and want to choose one that is not found by the above rules.

`--with-gnu-ld`
  Same as `--with-gnu-as` but for the linker.
`--with-ld=`pathname
  Same as `--with-as` but for the linker.
`--with-stabs`
  Specify that stabs debugging information should be used instead of whatever format the host normally uses. Normally GCC uses the same debug format as the host system.

  On MIPS based systems and on Alphas, you must specify whether you want GCC 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, GCC uses the ECOFF debugging format by default; if you prefer BSD stabs, specify `--with-stabs` when you configure GCC.

  No matter which default you choose when you configure GCC, 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.

`--with-tls=`dialect
  Specify the default TLS dialect, for systems were there is a choice. For ARM targets, possible values for dialect are `gnu` or `gnu2`, which select between the original GNU dialect and the GNU TLS descriptor-based dialect.
`--enable-multiarch`
  Specify whether to enable or disable multiarch support. The default is to check for glibc start files in a multiarch location, and enable it if the files are found. The auto detection is enabled for native builds, and for cross builds configured with `--with-sysroot`, and without `--with-native-system-header-dir`. More documentation about multiarch can be found at http://wiki.debian.org/Multiarch.
`--disable-multilib`
  Specify that multiple target libraries to support different target variants, calling conventions, etc. should not be built. The default is to build a predefined set of them.

  Some targets provide finer-grained control over which multilibs are built (e.g., `--disable-softfloat`):

  `arm-*-*`
    fpu, 26bit, underscore, interwork, biendian, nofmult.
  `m68*-*-*`
    softfloat, m68881, m68000, m68020.
  `mips*-*-*`
    single-float, biendian, softfloat.
  `powerpc*-*-*, rs6000*-*-*`
    aix64, pthread, softfloat, powercpu, powerpccpu, powerpcos, biendian, sysv, aix.
`--with-multilib-list=`list
`--without-multilib-list`
  Specify what multilibs to build. Currently only implemented for sh*-*-* and x86-64-*-linux*.
  `sh*-*-*`
    list is a comma separated list of CPU names. These must be of the form `sh*` or `m*` (in which case they match the compiler option for that processor). The list should not contain any endian options - these are handled by `--with-endian`.

    If list is empty, then there will be no multilibs for extra processors. The multilib for the secondary endian remains enabled.

    As a special case, if an entry in the list starts with a `!` (exclamation point), then it is added to the list of excluded multilibs. Entries of this sort should be compatible with ‘`MULTILIB_EXCLUDES`’ (once the leading `!` has been stripped).

    If `--with-multilib-list` is not given, then a default set of multilibs is selected based on the value of `--target`. This is usually the complete set of libraries, but some targets imply a more specialized subset.

    Example 1: to configure a compiler for SH4A only, but supporting both endians, with little endian being the default:

                       --with-cpu=sh4a --with-endian=little,big --with-multilib-list=

    Example 2: to configure a compiler for both SH4A and SH4AL-DSP, but with only little endian SH4AL:

                       --with-cpu=sh4a --with-endian=little,big \
                       --with-multilib-list=sh4al,!mb/m4al

  `x86-64-*-linux*`
    list is a comma separated list of `m32`, `m64` and `mx32` to enable 32-bit, 64-bit and x32 run-time libraries, respectively. If list is empty, then there will be no multilibs and only the default run-time library will be enabled.

    If `--with-multilib-list` is not given, then only 32-bit and 64-bit run-time libraries will be enabled.

`--with-endian=`endians
  Specify what endians to use. Currently only implemented for sh*-*-*.

  endians may be one of the following:

  `big`
    Use big endian exclusively.
  `little`
    Use little endian exclusively.
  `big,little`
    Use big endian by default. Provide a multilib for little endian.
  `little,big`
    Use little endian by default. Provide a multilib for big endian.
`--enable-threads`
  Specify that the target supports threads. This affects the Objective-C compiler and runtime library, and exception handling for other languages like C++ and Java. On some systems, this is the default.

  In general, the best (and, in many cases, the only known) threading model available will be configured for use. Beware that on some systems, GCC has not been taught what threading models are generally available for the system. In this case, `--enable-threads` is an alias for `--enable-threads=single`.

`--disable-threads`
  Specify that threading support should be disabled for the system. This is an alias for `--enable-threads=single`.
`--enable-threads=`lib
  Specify that lib is the thread support library. This affects the Objective-C compiler and runtime library, and exception handling for other languages like C++ and Java. The possibilities for lib are:
  `aix`
    AIX thread support.
  `dce`
    DCE thread support.
  `lynx`
    LynxOS thread support.
  `mipssde`
    MIPS SDE thread support.
  `no`
    This is an alias for ‘`single`’.
  `posix`
    Generic POSIX/Unix98 thread support.
  `rtems`
    RTEMS thread support.
  `single`
    Disable thread support, should work for all platforms.
  `tpf`
    TPF thread support.
  `vxworks`
    VxWorks thread support.
  `win32`
    Microsoft Win32 API thread support.
`--enable-tls`
  Specify that the target supports TLS (Thread Local Storage). Usually configure can correctly determine if TLS is supported. In cases where it guesses incorrectly, TLS can be explicitly enabled or disabled with `--enable-tls` or `--disable-tls`. This can happen if the assembler supports TLS but the C library does not, or if the assumptions made by the configure test are incorrect.
`--disable-tls`
  Specify that the target does not support TLS. This is an alias for `--enable-tls=no`.
`--with-cpu=`cpu
`--with-cpu-32=`cpu
`--with-cpu-64=`cpu
  Specify which cpu variant the compiler should generate code for by default. cpu will be used as the default value of the `-mcpu=` switch. This option is only supported on some targets, including ARM, i386, M68k, PowerPC, and SPARC. The `--with-cpu-32` and `--with-cpu-64` options specify separate default CPUs for 32-bit and 64-bit modes; these options are only supported for i386, x86-64 and PowerPC.
`--with-schedule=`cpu
`--with-arch=`cpu
`--with-arch-32=`cpu
`--with-arch-64=`cpu
`--with-tune=`cpu
`--with-tune-32=`cpu
`--with-tune-64=`cpu
`--with-abi=`abi
`--with-fpu=`type
`--with-float=`type
  These configure options provide default values for the `-mschedule=`, `-march=`, `-mtune=`, `-mabi=`, and `-mfpu=` options and for `-mhard-float` or `-msoft-float`. As with `--with-cpu`, which switches will be accepted and acceptable values of the arguments depend on the target.
`--with-mode=`mode
  Specify if the compiler should default to `-marm` or `-mthumb`. This option is only supported on ARM targets.
`--with-stack-offset=`num
  This option sets the default for the -mstack-offset=num option, and will thus generally also control the setting of this option for libraries. This option is only supported on Epiphany targets.
`--with-fpmath=`isa
  This options sets `-mfpmath=sse` by default and specifies the default ISA for floating-point arithmetics. You can select either ‘`sse`’ which enables `-msse2` or ‘`avx`’ which enables `-mavx` by default. This option is only supported on i386 and x86-64 targets.
`--with-divide=`type
  Specify how the compiler should generate code for checking for division by zero. This option is only supported on the MIPS target. The possibilities for type are:
  `traps`
    Division by zero checks use conditional traps (this is the default on systems that support conditional traps).
  `breaks`
    Division by zero checks use the break instruction.
`--with-llsc`
  On MIPS targets, make `-mllsc` the default when no `-mno-llsc` option is passed. This is the default for Linux-based targets, as the kernel will emulate them if the ISA does not provide them.
`--without-llsc`
  On MIPS targets, make `-mno-llsc` the default when no `-mllsc` option is passed.
`--with-synci`
  On MIPS targets, make `-msynci` the default when no `-mno-synci` option is passed.
`--without-synci`
  On MIPS targets, make `-mno-synci` the default when no `-msynci` option is passed. This is the default.
`--with-mips-plt`
  On MIPS targets, make use of copy relocations and PLTs. These features are extensions to the traditional SVR4-based MIPS ABIs and require support from GNU binutils and the runtime C library.
`--enable-__cxa_atexit`
  Define if you want to use __cxa_atexit, rather than atexit, to register C++ destructors for local statics and global objects. This is essential for fully standards-compliant handling of destructors, but requires __cxa_atexit in libc. This option is currently only available on systems with GNU libc. When enabled, this will cause `-fuse-cxa-atexit` to be passed by default.
`--enable-gnu-indirect-function`
  Define if you want to enable the `ifunc` attribute. This option is currently only available on systems with GNU libc on certain targets.
`--enable-target-optspace`
  Specify that target libraries should be optimized for code space instead of code speed. This is the default for the m32r platform.
`--with-cpp-install-dir=`dirname
  Specify that the user visible `cpp` program should be installed in `prefix/dirname/cpp`, in addition to bindir.
`--enable-comdat`
  Enable COMDAT group support. This is primarily used to override the automatically detected value.
`--enable-initfini-array`
  Force the use of sections `.init_array` and `.fini_array` (instead of `.init` and `.fini`) for constructors and destructors. Option `--disable-initfini-array` has the opposite effect. If neither option is specified, the configure script will try to guess whether the `.init_array` and `.fini_array` sections are supported and, if they are, use them.
`--enable-maintainer-mode`
  The build rules that regenerate the Autoconf and Automake output files as well as the GCC master message catalog `gcc.pot` are normally disabled. This is because it can only be rebuilt if the complete source tree is present. If you have changed the sources and want to rebuild the catalog, configuring with `--enable-maintainer-mode` will enable this. Note that you need a recent version of the `gettext` tools to do so.
`--disable-bootstrap`
  For a native build, the default configuration is to perform a 3-stage bootstrap of the compiler when ‘`make`’ is invoked, testing that GCC can compile itself correctly. If you want to disable this process, you can configure with `--disable-bootstrap`.
`--enable-bootstrap`
  In special cases, you may want to perform a 3-stage build even if the target and host triplets are different. This is possible when the host can run code compiled for the target (e.g. host is i686-linux, target is i486-linux). Starting from GCC 4.2, to do this you have to configure explicitly with `--enable-bootstrap`.
`--enable-generated-files-in-srcdir`
  Neither the .c and .h files that are generated from Bison and flex nor the info manuals and man pages that are built from the .texi files are present in the SVN development tree. When building GCC from that development tree, or from one of our snapshots, those generated files are placed in your build directory, which allows for the source to be in a readonly directory.

  If you configure with `--enable-generated-files-in-srcdir` then those generated files will go into the source directory. This is mainly intended for generating release or prerelease tarballs of the GCC sources, since it is not a requirement that the users of source releases to have flex, Bison, or makeinfo.

`--enable-version-specific-runtime-libs`
  Specify that runtime libraries should be installed in the compiler specific subdirectory (`libdir/gcc`) rather than the usual places. In addition, ‘`libstdc++`’'s include files will be installed into `libdir` unless you overruled it by using `--with-gxx-include-dir=dirname`. Using this option is particularly useful if you intend to use several versions of GCC in parallel. This is currently supported by ‘`libgfortran`’, ‘`libjava`’, ‘`libmudflap`’, ‘`libstdc++`’, and ‘`libobjc`’.
`--enable-languages=`lang1`,`lang2`,...`
  Specify that only a particular subset of compilers and their runtime libraries should be built. For a list of valid values for langN you can issue the following command in the `gcc` directory of your GCC source tree:

                grep language= */config-lang.in

  Currently, you can use any of the following: `all`, `ada`, `c`, `c++`, `fortran`, `go`, `java`, `objc`, `obj-c++`. Building the Ada compiler has special requirements, see below. If you do not pass this flag, or specify the option `all`, then all default languages available in the `gcc` sub-tree will be configured. Ada, Go and Objective-C++ are not default languages; the rest are.

`--enable-stage1-languages=`lang1`,`lang2`,...`
  Specify that a particular subset of compilers and their runtime libraries should be built with the system C compiler during stage 1 of the bootstrap process, rather than only in later stages with the bootstrapped C compiler. The list of valid values is the same as for `--enable-languages`, and the option `all` will select all of the languages enabled by `--enable-languages`. This option is primarily useful for GCC development; for instance, when a development version of the compiler cannot bootstrap due to compiler bugs, or when one is debugging front ends other than the C front end. When this option is used, one can then build the target libraries for the specified languages with the stage-1 compiler by using `make stage1-bubble all-target`, or run the testsuite on the stage-1 compiler for the specified languages using `make stage1-start check-gcc`.
`--disable-libada`
  Specify that the run-time libraries and tools used by GNAT should not be built. This can be useful for debugging, or for compatibility with previous Ada build procedures, when it was required to explicitly do a ‘`make -C gcc gnatlib_and_tools`’.
`--disable-libssp`
  Specify that the run-time libraries for stack smashing protection should not be built.
`--disable-libquadmath`
  Specify that the GCC quad-precision math library should not be built. On some systems, the library is required to be linkable when building the Fortran front end, unless `--disable-libquadmath-support` is used.
`--disable-libquadmath-support`
  Specify that the Fortran front end and `libgfortran` do not add support for `libquadmath` on systems supporting it.
`--disable-libgomp`
  Specify that the run-time libraries used by GOMP should not be built.
`--with-dwarf2`
  Specify that the compiler should use DWARF 2 debugging information as the default.
`--enable-targets=all`
`--enable-targets=`target_list
  Some GCC targets, e.g. powerpc64-linux, build bi-arch compilers. These are compilers that are able to generate either 64-bit or 32-bit code. Typically, the corresponding 32-bit target, e.g. powerpc-linux for powerpc64-linux, only generates 32-bit code. This option enables the 32-bit target to be a bi-arch compiler, which is useful when you want a bi-arch compiler that defaults to 32-bit, and you are building a bi-arch or multi-arch binutils in a combined tree. On mips-linux, this will build a tri-arch compiler (ABI o32/n32/64), defaulted to o32. Currently, this option only affects sparc-linux, powerpc-linux, x86-linux, mips-linux and s390-linux.
`--enable-secureplt`
  This option enables `-msecure-plt` by default for powerpc-linux. See “RS/6000 and PowerPC Options” in the main manual
`--enable-cld`
  This option enables `-mcld` by default for 32-bit x86 targets. See “i386 and x86-64 Options” in the main manual
`--enable-win32-registry`
`--enable-win32-registry=`key
`--disable-win32-registry`
  The `--enable-win32-registry` option enables Microsoft 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.

`--nfp`
  Specify that the machine does not have a floating point unit. This option only applies to ‘`m68k-sun-sunosn`’. On any other system, `--nfp` has no effect.
`--enable-werror`
`--disable-werror`
`--enable-werror=yes`
`--enable-werror=no`
  When you specify this option, it controls whether certain files in the compiler are built with `-Werror` in bootstrap stage2 and later. If you don't specify it, `-Werror` is turned on for the main development trunk. However it defaults to off for release branches and final releases. The specific files which get `-Werror` are controlled by the Makefiles.
`--enable-checking`
`--enable-checking=`list
  When you specify this option, the compiler is built to perform internal consistency checks of the requested complexity. 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 GCC. This is ‘`yes`’ by default when building from SVN or snapshots, but ‘`release`’ for releases. The default for building the stage1 compiler is ‘`yes`’. More control over the checks may be had by specifying list. The categories of checks available are ‘`yes`’ (most common checks ‘`assert,misc,tree,gc,rtlflag,runtime`’), ‘`no`’ (no checks at all), ‘`all`’ (all but ‘`valgrind`’), ‘`release`’ (cheapest checks ‘`assert,runtime`’) or ‘`none`’ (same as ‘`no`’). Individual checks can be enabled with these flags ‘`assert`’, ‘`df`’, ‘`fold`’, ‘`gc`’, ‘`gcac`’ ‘`misc`’, ‘`rtl`’, ‘`rtlflag`’, ‘`runtime`’, ‘`tree`’, and ‘`valgrind`’.

  The ‘`valgrind`’ check requires the external `valgrind` simulator, available from http://valgrind.org/. The ‘`df`’, ‘`rtl`’, ‘`gcac`’ and ‘`valgrind`’ checks are very expensive. To disable all checking, ‘`--disable-checking`’ or ‘`--enable-checking=none`’ must be explicitly requested. Disabling assertions will make the compiler and runtime slightly faster but increase the risk of undetected internal errors causing wrong code to be generated.

`--disable-stage1-checking`
`--enable-stage1-checking`
`--enable-stage1-checking=`list
  If no `--enable-checking` option is specified the stage1 compiler will be built with ‘`yes`’ checking enabled, otherwise the stage1 checking flags are the same as specified by `--enable-checking`. To build the stage1 compiler with different checking options use `--enable-stage1-checking`. The list of checking options is the same as for `--enable-checking`. If your system is too slow or too small to bootstrap a released compiler with checking for stage1 enabled, you can use ‘`--disable-stage1-checking`’ to disable checking for the stage1 compiler.
`--enable-coverage`
`--enable-coverage=`level
  With this option, the compiler is built to collect self coverage information, every time it is run. This is for internal development purposes, and only works when the compiler is being built with gcc. The level argument controls whether the compiler is built optimized or not, values are ‘`opt`’ and ‘`noopt`’. For coverage analysis you want to disable optimization, for performance analysis you want to enable optimization. When coverage is enabled, the default level is without optimization.
`--enable-gather-detailed-mem-stats`
  When this option is specified more detailed information on memory allocation is gathered. This information is printed when using `-fmem-report`.
`--enable-nls`
`--disable-nls`
  The `--enable-nls` option enables Native Language Support (NLS), which lets GCC output diagnostics in languages other than American English. Native Language Support is enabled by default if not doing a canadian cross build. The `--disable-nls` option disables NLS.
`--with-included-gettext`
  If NLS is enabled, 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.
`--with-libiconv-prefix=`dir
  Search for libiconv header files in `dir/include` and libiconv library files in `dir/lib`.
`--enable-obsolete`
  Enable configuration for an obsoleted system. If you attempt to configure GCC for a system (build, host, or target) which has been obsoleted, and you do not specify this flag, configure will halt with an error message.

  All support for systems which have been obsoleted in one release of GCC is removed entirely in the next major release, unless someone steps forward to maintain the port.

`--enable-decimal-float`
`--enable-decimal-float=yes`
`--enable-decimal-float=no`
`--enable-decimal-float=bid`
`--enable-decimal-float=dpd`
`--disable-decimal-float`
  Enable (or disable) support for the C decimal floating point extension that is in the IEEE 754-2008 standard. This is enabled by default only on PowerPC, i386, and x86_64 GNU/Linux systems. Other systems may also support it, but require the user to specifically enable it. You can optionally control which decimal floating point format is used (either ‘`bid`’ or ‘`dpd`’). The ‘`bid`’ (binary integer decimal) format is default on i386 and x86_64 systems, and the ‘`dpd`’ (densely packed decimal) format is default on PowerPC systems.
`--enable-fixed-point`
`--disable-fixed-point`
  Enable (or disable) support for C fixed-point arithmetic. This option is enabled by default for some targets (such as MIPS) which have hardware-support for fixed-point operations. On other targets, you may enable this option manually.
`--with-long-double-128`
  Specify if `long double` type should be 128-bit by default on selected GNU/Linux architectures. If using `--without-long-double-128`, `long double` will be by default 64-bit, the same as `double` type. When neither of these configure options are used, the default will be 128-bit `long double` when built against GNU C Library 2.4 and later, 64-bit `long double` otherwise.
`--with-gmp=`pathname
`--with-gmp-include=`pathname
`--with-gmp-lib=`pathname
`--with-mpfr=`pathname
`--with-mpfr-include=`pathname
`--with-mpfr-lib=`pathname
`--with-mpc=`pathname
`--with-mpc-include=`pathname
`--with-mpc-lib=`pathname
  If you want to build GCC but do not have the GMP library, the MPFR library and/or the MPC library installed in a standard location and do not have their sources present in the GCC source tree then you can explicitly specify the directory where they are installed (‘`--with-gmp=gmpinstalldir`’, ‘`--with-mpfr=mpfrinstalldir`’, ‘`--with-mpc=mpcinstalldir`’). The `--with-gmp=gmpinstalldir` option is shorthand for `--with-gmp-lib=gmpinstalldir/lib` and `--with-gmp-include=gmpinstalldir/include`. Likewise the `--with-mpfr=mpfrinstalldir` option is shorthand for `--with-mpfr-lib=mpfrinstalldir/lib` and `--with-mpfr-include=mpfrinstalldir/include`, also the `--with-mpc=mpcinstalldir` option is shorthand for `--with-mpc-lib=mpcinstalldir/lib` and `--with-mpc-include=mpcinstalldir/include`. If these shorthand assumptions are not correct, you can use the explicit include and lib options directly. You might also need to ensure the shared libraries can be found by the dynamic linker when building and using GCC, for example by setting the runtime shared library path variable (`LD_LIBRARY_PATH` on GNU/Linux and Solaris systems).

  These flags are applicable to the host platform only. When building a cross compiler, they will not be used to configure target libraries.

`--with-isl=`pathname
`--with-isl-include=`pathname
`--with-isl-lib=`pathname
`--with-cloog=`pathname
`--with-cloog-include=`pathname
`--with-cloog-lib=`pathname
  If you do not have ISL and the CLooG libraries installed in a standard location and you want to build GCC, you can explicitly specify the directory where they are installed (‘`--with-isl=islinstalldir`’, ‘`--with-cloog=clooginstalldir`’). The `--with-isl=islinstalldir` option is shorthand for `--with-isl-lib=islinstalldir/lib` and `--with-isl-include=islinstalldir/include`. Likewise the `--with-cloog=clooginstalldir` option is shorthand for `--with-cloog-lib=clooginstalldir/lib` and `--with-cloog-include=clooginstalldir/include`. If these shorthand assumptions are not correct, you can use the explicit include and lib options directly.

  These flags are applicable to the host platform only. When building a cross compiler, they will not be used to configure target libraries.

`--with-host-libstdcxx=`linker-args
  If you are linking with a static copy of PPL, you can use this option to specify how the linker should find the standard C++ library used internally by PPL. Typical values of linker-args might be ‘`-lstdc++`’ or ‘`-Wl,-Bstatic,-lstdc++,-Bdynamic -lm`’. If you are linking with a shared copy of PPL, you probably do not need this option; shared library dependencies will cause the linker to search for the standard C++ library automatically.
`--with-stage1-ldflags=`flags
  This option may be used to set linker flags to be used when linking stage 1 of GCC. These are also used when linking GCC if configured with `--disable-bootstrap`. By default no special flags are used.
`--with-stage1-libs=`libs
  This option may be used to set libraries to be used when linking stage 1 of GCC. These are also used when linking GCC if configured with `--disable-bootstrap`. The default is the argument to `--with-host-libstdcxx`, if specified.
`--with-boot-ldflags=`flags
  This option may be used to set linker flags to be used when linking stage 2 and later when bootstrapping GCC. If neither –with-boot-libs nor –with-host-libstdcxx is set to a value, then the default is ‘`-static-libstdc++ -static-libgcc`’.
`--with-boot-libs=`libs
  This option may be used to set libraries to be used when linking stage 2 and later when bootstrapping GCC. The default is the argument to `--with-host-libstdcxx`, if specified.
`--with-debug-prefix-map=`map
  Convert source directory names using `-fdebug-prefix-map` when building runtime libraries. ‘`map`’ is a space-separated list of maps of the form ‘`old=new`’.
`--enable-linker-build-id`
  Tells GCC to pass `--build-id` option to the linker for all final links (links performed without the `-r` or `--relocatable` option), if the linker supports it. If you specify `--enable-linker-build-id`, but your linker does not support `--build-id` option, a warning is issued and the `--enable-linker-build-id` option is ignored. The default is off.
`--with-linker-hash-style=`choice
  Tells GCC to pass `--hash-style=choice` option to the linker for all final links. choice can be one of ‘`sysv`’, ‘`gnu`’, and ‘`both`’ where ‘`sysv`’ is the default.
`--enable-gnu-unique-object`
`--disable-gnu-unique-object`
  Tells GCC to use the gnu_unique_object relocation for C++ template static data members and inline function local statics. Enabled by default for a native toolchain with an assembler that accepts it and GLIBC 2.11 or above, otherwise disabled.
`--enable-lto`
`--disable-lto`
  Enable support for link-time optimization (LTO). This is enabled by default, and may be disabled using `--disable-lto`.
`--with-plugin-ld=`pathname
  Enable an alternate linker to be used at link-time optimization (LTO) link time when `-fuse-linker-plugin` is enabled. This linker should have plugin support such as gold starting with version 2.20 or GNU ld starting with version 2.21. See `-fuse-linker-plugin` for details.
`--enable-canonical-system-headers`
`--disable-canonical-system-headers`
  Enable system header path canonicalization for `libcpp`. This can produce shorter header file paths in diagnostics and dependency output files, but these changed header paths may conflict with some compilation environments. Enabled by default, and may be disabled using `--disable-canonical-system-headers`.

#### Cross-Compiler-Specific Options

The following options only apply to building cross compilers.

`--with-sysroot`
`--with-sysroot=`dir
  Tells GCC to consider dir as the root of a tree that contains (a subset of) the root filesystem of the target operating system. Target system headers, libraries and run-time object files will be searched for in there. More specifically, this acts as if `--sysroot=dir` was added to the default options of the built compiler. The specified directory is not copied into the install tree, unlike the options `--with-headers` and `--with-libs` that this option obsoletes. The default value, in case `--with-sysroot` is not given an argument, is `${gcc_tooldir}/sys-root`. If the specified directory is a subdirectory of `${exec_prefix}`, then it will be found relative to the GCC binaries if the installation tree is moved.

  This option affects the system root for the compiler used to build target libraries (which runs on the build system) and the compiler newly installed with `make install`; it does not affect the compiler which is used to build GCC itself.

  If you specify the `--with-native-system-header-dir=dirname` option then the compiler will search that directory within dirname for native system headers rather than the default `/usr/include`.

`--with-build-sysroot`
`--with-build-sysroot=`dir
  Tells GCC to consider dir as the system root (see `--with-sysroot`) while building target libraries, instead of the directory specified with `--with-sysroot`. This option is only useful when you are already using `--with-sysroot`. You can use `--with-build-sysroot` when you are configuring with `--prefix` set to a directory that is different from the one in which you are installing GCC and your target libraries.

  This option affects the system root for the compiler used to build target libraries (which runs on the build system); it does not affect the compiler which is used to build GCC itself.

  If you specify the `--with-native-system-header-dir=dirname` option then the compiler will search that directory within dirname for native system headers rather than the default `/usr/include`.

`--with-headers`
`--with-headers=`dir
  Deprecated in favor of `--with-sysroot`. Specifies that target headers are available when building a cross compiler. The dir argument specifies a directory which has the target include files. These include files will be copied into the `gcc` install directory. This option with the dir argument is required when building a cross compiler, if `prefix/target/sys-include` doesn't pre-exist. If `prefix/target/sys-include` does pre-exist, the dir argument may be omitted. `fixincludes` will be run on these files to make them compatible with GCC.
`--without-headers`
  Tells GCC not use any target headers from a libc when building a cross compiler. When crossing to GNU/Linux, you need the headers so GCC can build the exception handling for libgcc.
`--with-libs`
`--with-libs="`dir1 dir2`...` dirN`"`
  Deprecated in favor of `--with-sysroot`. Specifies a list of directories which contain the target runtime libraries. These libraries will be copied into the `gcc` install directory. If the directory list is omitted, this option has no effect.
`--with-newlib`
  Specifies that ‘`newlib`’ is being used as the target C library. This causes `__eprintf` to be omitted from `libgcc.a` on the assumption that it will be provided by ‘`newlib`’.
`--with-avrlibc`
  Specifies that ‘`AVR-Libc`’ is being used as the target C library. This causes float support functions like `__addsf3` to be omitted from `libgcc.a` on the assumption that it will be provided by `libm.a`. For more technical details, cf. PR54461. This option is only supported for the AVR target. It is not supported for RTEMS configurations, which currently use newlib. The option is supported since version 4.7.2 and is the default in 4.8.0 and newer.
`--with-build-time-tools=`dir
  Specifies where to find the set of target tools (assembler, linker, etc.) that will be used while building GCC itself. This option can be useful if the directory layouts are different between the system you are building GCC on, and the system where you will deploy it.

  For example, on an ‘`ia64-hp-hpux`’ system, you may have the GNU assembler and linker in `/usr/bin`, and the native tools in a different path, and build a toolchain that expects to find the native tools in `/usr/bin`.

  When you use this option, you should ensure that dir includes `ar`, `as`, `ld`, `nm`, `ranlib` and `strip` if necessary, and possibly `objdump`. Otherwise, GCC may use an inconsistent set of tools.

#### Java-Specific Options

The following option applies to the build of the Java front end.

`--disable-libgcj`
  Specify that the run-time libraries used by GCJ should not be built. This is useful in case you intend to use GCJ with some other run-time, or you're going to install it separately, or it just happens not to build on your particular machine. In general, if the Java front end is enabled, the GCJ libraries will be enabled too, unless they're known to not work on the target platform. If GCJ is enabled but ‘`libgcj`’ isn't built, you may need to port it; in this case, before modifying the top-level `configure.in` so that ‘`libgcj`’ is enabled by default on this platform, you may use `--enable-libgcj` to override the default.

The following options apply to building ‘`libgcj`’.

##### General Options

`--enable-java-maintainer-mode`
  By default the ‘`libjava`’ build will not attempt to compile the `.java` source files to `.class`. Instead, it will use the `.class` files from the source tree. If you use this option you must have executables named `ecj1` and `gjavah` in your path for use by the build. You must use this option if you intend to modify any `.java` files in `libjava`.
`--with-java-home=`dirname
  This ‘`libjava`’ option overrides the default value of the ‘`java.home`’ system property. It is also used to set ‘`sun.boot.class.path`’ to `dirname/lib/rt.jar`. By default ‘`java.home`’ is set to `prefix` and ‘`sun.boot.class.path`’ to `datadir/java/libgcj-version.jar`.
`--with-ecj-jar=`filename
  This option can be used to specify the location of an external jar file containing the Eclipse Java compiler. A specially modified version of this compiler is used by `gcj` to parse `.java` source files. If this option is given, the ‘`libjava`’ build will create and install an `ecj1` executable which uses this jar file at runtime.

  If this option is not given, but an `ecj.jar` file is found in the topmost source tree at configure time, then the ‘`libgcj`’ build will create and install `ecj1`, and will also install the discovered `ecj.jar` into a suitable place in the install tree.

  If `ecj1` is not installed, then the user will have to supply one on his path in order for `gcj` to properly parse `.java` source files. A suitable jar is available from ftp://sourceware.org/pub/java/.

`--disable-getenv-properties`
  Don't set system properties from `GCJ_PROPERTIES`.
`--enable-hash-synchronization`
  Use a global hash table for monitor locks. Ordinarily, ‘`libgcj`’'s ‘`configure`’ script automatically makes the correct choice for this option for your platform. Only use this if you know you need the library to be configured differently.
`--enable-interpreter`
  Enable the Java interpreter. The interpreter is automatically enabled by default on all platforms that support it. This option is really only useful if you want to disable the interpreter (using `--disable-interpreter`).
`--disable-java-net`
  Disable java.net. This disables the native part of java.net only, using non-functional stubs for native method implementations.
`--disable-jvmpi`
  Disable JVMPI support.
`--disable-libgcj-bc`
  Disable BC ABI compilation of certain parts of libgcj. By default, some portions of libgcj are compiled with `-findirect-dispatch` and `-fno-indirect-classes`, allowing them to be overridden at run-time.

  If `--disable-libgcj-bc` is specified, libgcj is built without these options. This allows the compile-time linker to resolve dependencies when statically linking to libgcj. However it makes it impossible to override the affected portions of libgcj at run-time.

`--enable-reduced-reflection`
  Build most of libgcj with `-freduced-reflection`. This reduces the size of libgcj at the expense of not being able to do accurate reflection on the classes it contains. This option is safe if you know that code using libgcj will never use reflection on the standard runtime classes in libgcj (including using serialization, RMI or CORBA).
`--with-ecos`
  Enable runtime eCos target support.
`--without-libffi`
  Don't use ‘`libffi`’. This will disable the interpreter and JNI support as well, as these require ‘`libffi`’ to work.
`--enable-libgcj-debug`
  Enable runtime debugging code.
`--enable-libgcj-multifile`
  If specified, causes all `.java` source files to be compiled into `.class` files in one invocation of ‘`gcj`’. This can speed up build time, but is more resource-intensive. If this option is unspecified or disabled, ‘`gcj`’ is invoked once for each `.java` file to compile into a `.class` file.
`--with-libiconv-prefix=DIR`
  Search for libiconv in `DIR/include` and `DIR/lib`.
`--enable-sjlj-exceptions`
  Force use of the `setjmp`/`longjmp`-based scheme for exceptions. ‘`configure`’ ordinarily picks the correct value based on the platform. Only use this option if you are sure you need a different setting.
`--with-system-zlib`
  Use installed ‘`zlib`’ rather than that included with GCC.
`--with-win32-nlsapi=ansi, unicows or unicode`
  Indicates how MinGW ‘`libgcj`’ translates between UNICODE characters and the Win32 API.
`--enable-java-home`
  If enabled, this creates a JPackage compatible SDK environment during install. Note that if –enable-java-home is used, –with-arch-directory=ARCH must also be specified.
`--with-arch-directory=ARCH`
  Specifies the name to use for the `jre/lib/ARCH` directory in the SDK environment created when –enable-java-home is passed. Typical names for this directory include i386, amd64, ia64, etc.
`--with-os-directory=DIR`
  Specifies the OS directory for the SDK include directory. This is set to auto detect, and is typically 'linux'.
`--with-origin-name=NAME`
  Specifies the JPackage origin name. This defaults to the 'gcj' in java-1.5.0-gcj.
`--with-arch-suffix=SUFFIX`
  Specifies the suffix for the sdk directory. Defaults to the empty string. Examples include '.x86_64' in 'java-1.5.0-gcj-1.5.0.0.x86_64'.
`--with-jvm-root-dir=DIR`
  Specifies where to install the SDK. Default is $(prefix)/lib/jvm.
`--with-jvm-jar-dir=DIR`
  Specifies where to install jars. Default is $(prefix)/lib/jvm-exports.
`--with-python-dir=DIR`
  Specifies where to install the Python modules used for aot-compile. DIR should not include the prefix used in installation. For example, if the Python modules are to be installed in /usr/lib/python2.5/site-packages, then –with-python-dir=/lib/python2.5/site-packages should be passed. If this is not specified, then the Python modules are installed in $(prefix)/share/python.
`--enable-aot-compile-rpm`
  Adds aot-compile-rpm to the list of installed scripts.
`--enable-browser-plugin`
  Build the gcjwebplugin web browser plugin.
`--enable-static-libjava`
  Build static libraries in libjava. The default is to only build shared libraries.
  `ansi`
    Use the single-byte `char` and the Win32 A functions natively, translating to and from UNICODE when using these functions. If unspecified, this is the default.
  `unicows`
    Use the `WCHAR` and Win32 W functions natively. Adds `-lunicows` to `libgcj.spec` to link with ‘`libunicows`’. `unicows.dll` needs to be deployed on Microsoft Windows 9X machines running built executables. `libunicows.a`, an open-source import library around Microsoft's `unicows.dll`, is obtained from http://libunicows.sourceforge.net/, which also gives details on getting `unicows.dll` from Microsoft.
  `unicode`
    Use the `WCHAR` and Win32 W functions natively. Does not add `-lunicows` to `libgcj.spec`. The built executables will only run on Microsoft Windows NT and above.

##### AWT-Specific Options

`--with-x`
  Use the X Window System.
`--enable-java-awt=PEER(S)`
  Specifies the AWT peer library or libraries to build alongside ‘`libgcj`’. If this option is unspecified or disabled, AWT will be non-functional. Current valid values are `gtk` and `xlib`. Multiple libraries should be separated by a comma (i.e. `--enable-java-awt=gtk,xlib`).
`--enable-gtk-cairo`
  Build the cairo Graphics2D implementation on GTK.
`--enable-java-gc=TYPE`
  Choose garbage collector. Defaults to `boehm` if unspecified.
`--disable-gtktest`
  Do not try to compile and run a test GTK+ program.
`--disable-glibtest`
  Do not try to compile and run a test GLIB program.
`--with-libart-prefix=PFX`
  Prefix where libart is installed (optional).
`--with-libart-exec-prefix=PFX`
  Exec prefix where libart is installed (optional).
`--disable-libarttest`
  Do not try to compile and run a test libart program.

##### Overriding `configure` test results

Sometimes, it might be necessary to override the result of some `configure` test, for example in order to ease porting to a new system or work around a bug in a test. The toplevel `configure` script provides three variables for this:

`build_configargs`
  The contents of this variable is passed to all build `configure` scripts.
`host_configargs`
  The contents of this variable is passed to all host `configure` scripts.
`target_configargs`
  The contents of this variable is passed to all target `configure` scripts.

In order to avoid shell and `make` quoting issues for complex overrides, you can pass a setting for `CONFIG_SITE` and set variables in the site file.

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