Configuring and compiling - The GNU C Library

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### C.1 Configuring and compiling GNU Libc

GNU libc cannot be compiled in the source directory. You must build it in a separate build directory. For example, if you have unpacked the glibc sources in `/src/gnu/glibc-2.4`, create a directory `/src/gnu/glibc-build` to put the object files in. This allows removing the whole build directory in case an error occurs, which is the safest way to get a fresh start and should always be done.

From your object directory, run the shell script `configure` located at the top level of the source tree. In the scenario above, you'd type

         $ ../glibc-2.4/configure args...

Please note that even though you're building in a separate build directory, the compilation needs to modify a few files in the source directory, especially some files in the manual subdirectory.

`configure` takes many options, but the only one that is usually mandatory is ‘`--prefix`’. This option tells `configure` where you want glibc installed. This defaults to `/usr/local`, but the normal setting to install as the standard system library is ‘`--prefix=/usr`’ for GNU/Linux systems and ‘`--prefix=`’ (an empty prefix) for GNU/Hurd systems.

It may also be useful to set the CC and CFLAGS variables in the environment when running `configure`. CC selects the C compiler that will be used, and CFLAGS sets optimization options for the compiler.

The following list describes all of the available options for `configure`:

‘`--prefix=directory`’
  Install machine-independent data files in subdirectories of `directory`. The default is to install in `/usr/local`.
‘`--exec-prefix=directory`’
  Install the library and other machine-dependent files in subdirectories of `directory`. The default is to the ‘`--prefix`’ directory if that option is specified, or `/usr/local` otherwise.
‘`--with-headers=directory`’
  Look for kernel header files in directory, not `/usr/include`. Glibc needs information from the kernel's private header files. Glibc will normally look in `/usr/include` for them, but if you specify this option, it will look in DIRECTORY instead.

  This option is primarily of use on a system where the headers in `/usr/include` come from an older version of glibc. Conflicts can occasionally happen in this case. Note that Linux libc5 qualifies as an older version of glibc. You can also use this option if you want to compile glibc with a newer set of kernel headers than the ones found in `/usr/include`.

‘`--enable-add-ons[=list]`’
  Specify add-on packages to include in the build. If this option is specified with no list, it enables all the add-on packages it finds in the main source directory; this is the default behavior. You may specify an explicit list of add-ons to use in list, separated by spaces or commas (if you use spaces, remember to quote them from the shell). Each add-on in list can be an absolute directory name or can be a directory name relative to the main source directory, or relative to the build directory (that is, the current working directory). For example, ‘`--enable-add-ons=nptl,../glibc-libidn-2.4`’.
‘`--enable-kernel=version`’
  This option is currently only useful on GNU/Linux systems. The version parameter should have the form X.Y.Z and describes the smallest version of the Linux kernel the generated library is expected to support. The higher the version number is, the less compatibility code is added, and the faster the code gets.
‘`--with-binutils=directory`’
  Use the binutils (assembler and linker) in `directory`, not the ones the C compiler would default to. You can use this option if the default binutils on your system cannot deal with all the constructs in the GNU C library. In that case, `configure` will detect the problem and suppress these constructs, so that the library will still be usable, but functionality may be lost—for example, you can't build a shared libc with old binutils.
‘`--without-fp`’
  Use this option if your computer lacks hardware floating-point support and your operating system does not emulate an FPU.

  these

‘`--disable-shared`’
  Don't build shared libraries even if it is possible. Not all systems support shared libraries; you need ELF support and (currently) the GNU linker.
‘`--disable-profile`’
  Don't build libraries with profiling information. You may want to use this option if you don't plan to do profiling.
‘`--enable-omitfp`’
  Use maximum optimization for the normal (static and shared) libraries, and compile separate static libraries with debugging information and no optimization. We recommend not doing this. The extra optimization doesn't gain you much, it may provoke compiler bugs, and you won't be able to trace bugs through the C library.
‘`--disable-versioning`’
  Don't compile the shared libraries with symbol version information. Doing this will make the resulting library incompatible with old binaries, so it's not recommended.
‘`--enable-static-nss`’
  Compile static versions of the NSS (Name Service Switch) libraries. This is not recommended because it defeats the purpose of NSS; a program linked statically with the NSS libraries cannot be dynamically reconfigured to use a different name database.
‘`--without-tls`’
  By default the C library is built with support for thread-local storage if the used tools support it. By using ‘`--without-tls`’ this can be prevented though there generally is no reason since it creates compatibility problems.
‘`--build=build-system`’
‘`--host=host-system`’
  These options are for cross-compiling. If you specify both options and build-system is different from host-system, `configure` will prepare to cross-compile glibc from build-system to be used on host-system. You'll probably need the ‘`--with-headers`’ option too, and you may have to override configure's selection of the compiler and/or binutils.

  If you only specify ‘`--host`’, `configure` will prepare for a native compile but use what you specify instead of guessing what your system is. This is most useful to change the CPU submodel. For example, if `configure` guesses your machine as `i586-pc-linux-gnu` but you want to compile a library for 386es, give ‘`--host=i386-pc-linux-gnu`’ or just ‘`--host=i386-linux`’ and add the appropriate compiler flags (‘`-mcpu=i386`’ will do the trick) to CFLAGS.

  If you specify just ‘`--build`’, `configure` will get confused.

To build the library and related programs, type `make`. This will produce a lot of output, some of which may look like errors from `make` but isn't. Look for error messages from `make` containing ‘`***`’. Those indicate that something is seriously wrong.

The compilation process can take a long time, depending on the configuration and the speed of your machine. Some complex modules may take a very long time to compile, as much as several minutes on slower machines. Do not panic if the compiler appears to hang.

If you want to run a parallel make, simply pass the ‘`-j`’ option with an appropriate numeric parameter to `make`. You need a recent GNU `make` version, though.

To build and run test programs which exercise some of the library facilities, type `make check`. If it does not complete successfully, do not use the built library, and report a bug after verifying that the problem is not already known. See Reporting Bugs, for instructions on reporting bugs. Note that some of the tests assume they are not being run by `root`. We recommend you compile and test glibc as an unprivileged user.

Before reporting bugs make sure there is no problem with your system. The tests (and later installation) use some pre-existing files of the system such as `/etc/passwd`, `/etc/nsswitch.conf` and others. These files must all contain correct and sensible content.

To format the GNU C Library Reference Manual for printing, type `make dvi`. You need a working TeX installation to do this. The distribution already includes the on-line formatted version of the manual, as Info files. You can regenerate those with `make info`, but it shouldn't be necessary.

The library has a number of special-purpose configuration parameters which you can find in `Makeconfig`. These can be overwritten with the file `configparms`. To change them, create a `configparms` in your build directory and add values as appropriate for your system. The file is included and parsed by `make` and has to follow the conventions for makefiles.

It is easy to configure the GNU C library for cross-compilation by setting a few variables in `configparms`. Set `CC` to the cross-compiler for the target you configured the library for; it is important to use this same `CC` value when running `configure`, like this: ‘`CC=target-gcc configure target`’. Set `BUILD_CC` to the compiler to use for programs run on the build system as part of compiling the library. You may need to set `AR` and `RANLIB` to cross-compiling versions of `ar` and `ranlib` if the native tools are not configured to work with object files for the target you configured for.