lfs-book-zh_CN/chapter05/gcc-pass2.xml

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<sect1 id="ch-tools-gcc-pass2" role="wrap">
<title>GCC-&gcc-version; - Pass 2</title>
<?dbhtml filename="gcc-pass2.html"?>

<indexterm zone="ch-tools-gcc-pass2">
<primary sortas="a-GCC">GCC</primary>
<secondary>tools, pass 2</secondary></indexterm>

<sect2 role="package"><title/>

<segmentedlist>
<segtitle>&buildtime;</segtitle>
<segtitle>&diskspace;</segtitle>
<seglistitem><seg>11.0 SBU</seg><seg>274 MB</seg></seglistitem>
</segmentedlist>

<xi:include xmlns:xi="http://www.w3.org/2003/XInclude" href="../chapter06/gcc.xml" xpointer="xpointer(/sect1/sect2[1]/segmentedlist[2])"/>

</sect2>

<sect2 role="installation">
<title>Re-installation of GCC</title>

<para>This package is known to have issues when its default
optimization flags (including the <parameter>-march</parameter> and
<parameter>-mcpu</parameter> options) are changed. If any environment
variables that override default optimizations have been defined, such
as <envar>CFLAGS</envar> and <envar>CXXFLAGS</envar>,
unset them when building GCC.</para>

<para>The tools required to test GCC and Binutils&mdash;Tcl, Expect
and DejaGNU&mdash;are installed now. GCC and Binutils can now be
rebuilt, linking them against the new Glibc and testing them properly
(if running the test suites in this chapter). Please note that these
test suites are highly dependent on properly functioning PTYs which
are provided by the host. PTYs are most commonly implemented via the
<systemitem class="filesystem">devpts</systemitem> file system. Check
to see if the host system is set up correctly in this regard by
performing a quick test:</para>

<screen><userinput>expect -c "spawn ls"</userinput></screen>

<para>The response might be:</para>

<screen><computeroutput>The system has no more ptys.  
Ask your system administrator to create more.</computeroutput></screen>

<para>If the above message is received, the host does not have its
PTYs set up properly. In this case, there is no point in running the
test suites for GCC and Binutils until this issue is resolved. Please
consult the LFS Wiki at <ulink url="&wiki-root;"/> for more
information on how to get PTYs working.</para>

<para>Because the C and the C++ compilers will be built, unpack both
the core and the g++ tarballs (as well as test suite, if you want to
run the tests). By unpacking them in the working directory, they will
all unfold into a single <filename
class="directory">gcc-&gcc-version;/</filename> subdirectory.</para>

<para>First correct a known problem and make an essential adjustment:</para>

<screen><userinput>patch -Np1 -i ../&gcc-no_fixincludes-patch;
patch -Np1 -i ../&gcc-specs-patch;</userinput></screen>

<para>The first patch disables the GCC <command>fixincludes</command>
script. This was briefly mentioned earlier, but a more in-depth
explanation of the fixincludes process is warranted here. Under normal
circumstances, the GCC <command>fixincludes</command> script scans the
system for header files that need to be fixed. It might find that some
Glibc header files on the host system need to be fixed, and will fix
them and put them in the GCC private include directory. In <xref
linkend="chapter-building-system"/>, after the newer Glibc has been
installed, this private include directory will be searched before the
system include directory.  This may result in GCC finding the fixed
headers from the host system, which most likely will not match the
Glibc version used for the LFS system.</para>

<para>The second patch changes GCC's default location of the dynamic
linker (typically <filename class="libraryfile">ld-linux.so.2</filename>). It also removes
<filename class="directory">/usr/include</filename> from GCC's include
search path. Patching now rather than adjusting the specs file after
installation ensures that the new dynamic linker is used during the
actual build of GCC. That is, all of the final (and temporary)
binaries created during the build will link against the new
Glibc.</para>

<important><para>The above patches are critical in ensuring a
successful overall build. Do not forget to apply
them.</para></important>

<para>Create a separate build directory again:</para>

<screen><userinput>mkdir ../gcc-build
cd ../gcc-build</userinput></screen>

<para>Before starting to build GCC, remember to unset any environment
variables that override the default optimization flags.</para>

<para>Now prepare GCC for compilation:</para>

<screen><userinput>../gcc-&gcc-version;/configure --prefix=/tools \
    --libexecdir=/tools/lib --with-local-prefix=/tools \
    --enable-clocale=gnu --enable-shared \
    --enable-threads=posix --enable-__cxa_atexit \
    --enable-languages=c,c++ --disable-libstdcxx-pch</userinput></screen>

<para>The meaning of the new configure options:</para>

<variablelist>
<varlistentry>
<term><parameter>--enable-clocale=gnu</parameter></term>
<listitem><para>This option ensures the correct locale model is
selected for the C++ libraries under all circumstances. If the
configure script finds the <emphasis>de_DE</emphasis> locale installed, it will select the
correct gnu locale model. However, if the <emphasis>de_DE</emphasis> locale is not
installed, there is the risk of building Application Binary Interface
(ABI)-incompatible C++ libraries because the incorrect generic locale
model may be selected.</para></listitem>
</varlistentry>

<varlistentry>
<term><parameter>--enable-threads=posix</parameter></term>
<listitem><para>This enables C++ exception handling for multi-threaded
code.</para></listitem>
</varlistentry>

<varlistentry>
<term><parameter>--enable-__cxa_atexit</parameter></term>
<listitem><para>This option allows use of
<emphasis>__cxa_atexit</emphasis>, rather than
<emphasis>atexit</emphasis>, to register C++ destructors for local
statics and global objects.  This option is essential for fully
standards-compliant handling of destructors. It also effects the C++
ABI, and therefore results in C++ shared libraries and C++ programs
that are interoperable with other Linux
distributions.</para></listitem>
</varlistentry>

<varlistentry>
<term><parameter>--enable-languages=c,c++</parameter></term>
<listitem><para>This option
ensures that both the C and C++ compilers are built.</para></listitem>
</varlistentry>

<varlistentry>
<term><parameter>--disable-libstdcxx-pch</parameter></term>
<listitem><para>Do not build the pre-compiled header (PCH) for
<filename class="libraryfile">libstdc++</filename>. It takes up a lot of space,
and we have no use for it.</para></listitem>
</varlistentry>
</variablelist>

<para>Compile the package:</para>

<screen><userinput>make</userinput></screen>

<para>There is no need to use the <parameter>bootstrap</parameter>
target now because the compiler being used to compile this GCC was
built from the exact same version of the GCC sources used
earlier.</para>

<para>Compilation is now complete. As previously mentioned, running
the test suites for the temporary tools compiled in this chapter is
not mandatory. To run the GCC test suite anyway, use the following
command:</para>

<screen><userinput>make -k check</userinput></screen>

<para>The <parameter>-k</parameter> flag is used to make the test suite run
through to completion and not stop at the first failure. The GCC test
suite is very comprehensive and is almost guaranteed to generate a few
failures. To receive a summary of the test suite results, run:</para>
 
<screen><userinput>../gcc-&gcc-version;/contrib/test_summary</userinput></screen>

<para>For only the summaries, pipe the output through
<userinput>grep -A7 Summ</userinput>.</para>

<para>Results can be compared to those posted to the gcc-testresults
mailing list to see similar configurations to the one being built. For
an example of how current GCC-&gcc-version; should look on
i686-pc-linux-gnu, see <ulink
url="http://gcc.gnu.org/ml/gcc-testresults/2004-07/msg00179.html"/>.</para>

<para>A few unexpected failures cannot always be avoided. The
GCC developers are usually aware of these issues, but have not
resolved them yet. Unless the test results are vastly different from
those at the above URL, it is safe to continue.</para>

<para>Install the package:</para>

<screen><userinput>make install</userinput></screen>

<note><para>At this point it is strongly recommended to repeat the
sanity check we performed earlier in this chapter. Refer back to <xref
linkend="ch-tools-adjusting" role=","/> and repeat the test compilation.  If
the result is wrong, the most likely reason is that the GCC Specs
patch was not properly applied.</para></note>

</sect2>

<sect2 role="content"><title/>
<para>Details on this package are located in <xref
linkend="contents-gcc" role="."/></para>
</sect2>

</sect1>