C.1 Configuring and compiling GNU Libc

GNU libc can be compiled in the source directory, but we strongly advise to build it in a separate build directory. For example, if you have unpacked the glibc sources in /src/gnu/glibc-2.2.0, 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 found at the top level of the source tree. In the scenario above, you'd type

     $ ../glibc-2.2.0/configure args...

Please note that even if 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 you can get away with knowing only two: `--prefix' and `--enable-add-ons'. The --prefix option tells configure where you want glibc installed. This defaults to /usr/local. The `--enable-add-ons' option tells configure to use all the add-on bundles it finds in the source directory. Since important functionality is provided in add-ons, you should always specify this option.

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. It 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]'

Enable add-on packages in your source tree. If this option is specified with no list, it enables all the add-on packages it finds. If you do not wish to use some add-on package that you have present in your source tree, give this option a list of the add-ons that you do want used, like this: `--enable-add-ons=linuxthreads'

`--enable-kernel=version'

This option is currently only useful on 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 could 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.

`--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 against 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.

`--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 really wrong.

The compilation process takes several hours even on fast hardware. Expect at least two hours for the default configuration on i586 for Linux. For Hurd times are much longer. Except for EGCS 1.1 and GCC 2.95 (and later versions of GCC), all supported versions of GCC have a problem which causes them to take several minutes to compile certain files in the iconvdata directory. Do not panic if the compiler appears to hang.

If you want to run a parallel make, you can't just give make the `-j' option, because it won't be passed down to the sub-makes. Instead, edit the generated Makefile and uncomment the line

     # PARALLELMFLAGS = -j 4

You can change the `4' to some other number as appropriate for your system. Instead of changing the Makefile, you could give this option directly to make and call it as, for example, make PARALLELMFLAGS=-j4. If you're building in the source directory, you must use the latter approach since in this case no new Makefile is generated for you to change.

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.

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 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.