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<h3 class="appendixsec">C.1 Configuring and compiling GNU Libc</h3>

<p><a name="index-configuring-3813"></a><a name="index-compiling-3814"></a>
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 <samp><span class="file">/src/gnu/glibc-2.4</span></samp>, create a directory
<samp><span class="file">/src/gnu/glibc-build</span></samp> 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.

   <p>From your object directory, run the shell script <samp><span class="file">configure</span></samp> located
at the top level of the source tree.  In the scenario above, you'd type

<pre class="smallexample">     $ ../glibc-2.4/configure <var>args<small class="dots">...</small></var>
</pre>
   <p>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.

<p class="noindent"><code>configure</code> takes many options, but the only one that is usually
mandatory is &lsquo;<samp><span class="samp">--prefix</span></samp>&rsquo;.  This option tells <code>configure</code>
where you want glibc installed.  This defaults to <samp><span class="file">/usr/local</span></samp>,
but the normal setting to install as the standard system library is
&lsquo;<samp><span class="samp">--prefix=/usr</span></samp>&rsquo; for GNU/Linux systems and &lsquo;<samp><span class="samp">--prefix=</span></samp>&rsquo; (an
empty prefix) for GNU/Hurd systems.

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

   <p>The following list describes all of the available options for
 <code>configure</code>:

     <dl>
<dt>&lsquo;<samp><span class="samp">--prefix=</span><var>directory</var></samp>&rsquo;<dd>Install machine-independent data files in subdirectories of
<samp><var>directory</var></samp>.  The default is to install in <samp><span class="file">/usr/local</span></samp>.

     <br><dt>&lsquo;<samp><span class="samp">--exec-prefix=</span><var>directory</var></samp>&rsquo;<dd>Install the library and other machine-dependent files in subdirectories
of <samp><var>directory</var></samp>.  The default is to the &lsquo;<samp><span class="samp">--prefix</span></samp>&rsquo;
directory if that option is specified, or <samp><span class="file">/usr/local</span></samp> otherwise.

     <br><dt>&lsquo;<samp><span class="samp">--with-headers=</span><var>directory</var></samp>&rsquo;<dd>Look for kernel header files in <var>directory</var>, not
<samp><span class="file">/usr/include</span></samp>.  Glibc needs information from the kernel's private
header files.  Glibc will normally look in <samp><span class="file">/usr/include</span></samp> for them,
but if you specify this option, it will look in <var>DIRECTORY</var> instead.

     <p>This option is primarily of use on a system where the headers in
<samp><span class="file">/usr/include</span></samp> 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
<samp><span class="file">/usr/include</span></samp>.

     <br><dt>&lsquo;<samp><span class="samp">--enable-add-ons[=</span><var>list</var><span class="samp">]</span></samp>&rsquo;<dd>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 <var>list</var>, separated by
spaces or commas (if you use spaces, remember to quote them from the
shell).  Each add-on in <var>list</var> 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, &lsquo;<samp><span class="samp">--enable-add-ons=nptl,../glibc-libidn-2.4</span></samp>&rsquo;.

     <br><dt>&lsquo;<samp><span class="samp">--enable-kernel=</span><var>version</var></samp>&rsquo;<dd>This option is currently only useful on GNU/Linux systems.  The
<var>version</var> 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 <var>version</var> number is, the less
compatibility code is added, and the faster the code gets.

     <br><dt>&lsquo;<samp><span class="samp">--with-binutils=</span><var>directory</var></samp>&rsquo;<dd>Use the binutils (assembler and linker) in <samp><var>directory</var></samp>, 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, <code>configure</code> will detect the
problem and suppress these constructs, so that the library will still be
usable, but functionality may be lost&mdash;for example, you can't build a
shared libc with old binutils.

     <br><dt>&lsquo;<samp><span class="samp">--without-fp</span></samp>&rsquo;<dd>Use this option if your computer lacks hardware floating-point support
and your operating system does not emulate an FPU.

     <!-- disable static doesn't work currently -->
     <!-- @item -disable-static -->
     <!-- Don't build static libraries.  Static libraries aren't that useful -->
     <p>these
<!-- days, but we recommend you build them in case you need them. -->

     <br><dt>&lsquo;<samp><span class="samp">--disable-shared</span></samp>&rsquo;<dd>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.

     <br><dt>&lsquo;<samp><span class="samp">--disable-profile</span></samp>&rsquo;<dd>Don't build libraries with profiling information.  You may want to use
this option if you don't plan to do profiling.

     <br><dt>&lsquo;<samp><span class="samp">--enable-omitfp</span></samp>&rsquo;<dd>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.

     <br><dt>&lsquo;<samp><span class="samp">--disable-versioning</span></samp>&rsquo;<dd>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.

     <br><dt>&lsquo;<samp><span class="samp">--enable-static-nss</span></samp>&rsquo;<dd>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.

     <br><dt>&lsquo;<samp><span class="samp">--without-tls</span></samp>&rsquo;<dd>By default the C library is built with support for thread-local storage
if the used tools support it.  By using &lsquo;<samp><span class="samp">--without-tls</span></samp>&rsquo; this can be
prevented though there generally is no reason since it creates
compatibility problems.

     <br><dt>&lsquo;<samp><span class="samp">--build=</span><var>build-system</var></samp>&rsquo;<dt>&lsquo;<samp><span class="samp">--host=</span><var>host-system</var></samp>&rsquo;<dd>These options are for cross-compiling.  If you specify both options and
<var>build-system</var> is different from <var>host-system</var>, <code>configure</code>
will prepare to cross-compile glibc from <var>build-system</var> to be used
on <var>host-system</var>.  You'll probably need the &lsquo;<samp><span class="samp">--with-headers</span></samp>&rsquo;
option too, and you may have to override <var>configure</var>'s selection of
the compiler and/or binutils.

     <p>If you only specify &lsquo;<samp><span class="samp">--host</span></samp>&rsquo;, <code>configure</code> 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 <code>configure</code> guesses your machine as <code>i586-pc-linux-gnu</code> but
you want to compile a library for 386es, give
&lsquo;<samp><span class="samp">--host=i386-pc-linux-gnu</span></samp>&rsquo; or just &lsquo;<samp><span class="samp">--host=i386-linux</span></samp>&rsquo; and add
the appropriate compiler flags (&lsquo;<samp><span class="samp">-mcpu=i386</span></samp>&rsquo; will do the trick) to
<var>CFLAGS</var>.

     <p>If you specify just &lsquo;<samp><span class="samp">--build</span></samp>&rsquo;, <code>configure</code> will get confused. 
</dl>

   <p>To build the library and related programs, type <code>make</code>.  This will
produce a lot of output, some of which may look like errors from
<code>make</code> but isn't.  Look for error messages from <code>make</code>
containing &lsquo;<samp><span class="samp">***</span></samp>&rsquo;.  Those indicate that something is seriously wrong.

   <p>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.

   <p>If you want to run a parallel make, simply pass the &lsquo;<samp><span class="samp">-j</span></samp>&rsquo; option
with an appropriate numeric parameter to <code>make</code>.  You need a recent
GNU <code>make</code> version, though.

   <p>To build and run test programs which exercise some of the library
facilities, type <code>make check</code>.  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 <a href="Reporting-Bugs.html#Reporting-Bugs">Reporting Bugs</a>,
for instructions on reporting bugs.  Note that some of the tests assume
they are not being run by <code>root</code>.  We recommend you compile and
test glibc as an unprivileged user.

   <p>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 <samp><span class="file">/etc/passwd</span></samp>, <samp><span class="file">/etc/nsswitch.conf</span></samp> and others. 
These files must all contain correct and sensible content.

   <p>To format the <cite>GNU C Library Reference Manual</cite> for printing, type
<code>make&nbsp;dvi</code><!-- /@w -->.  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 <code>make&nbsp;info</code><!-- /@w -->, but it shouldn't be necessary.

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

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

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