lfs-book/chapter05/gcc-pass1.xml

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<sect1 id="ch-tools-gcc-pass1" role="wrap">
  <?dbhtml filename="gcc-pass1.html"?>

  <title>GCC-&gcc-version; - Pass 1</title>

  <indexterm zone="ch-tools-gcc-pass1">
    <primary sortas="a-GCC">GCC</primary>
    <secondary>tools, pass 1</secondary>
  </indexterm>

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

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

    <segmentedlist>
      <segtitle>&buildtime;</segtitle>
      <segtitle>&diskspace;</segtitle>

      <seglistitem>
        <seg>&gcc-ch5p1-sbu;</seg>
        <seg>&gcc-ch5p1-du;</seg>
      </seglistitem>
    </segmentedlist>

  </sect2>

  <sect2 role="installation">
    <title>Installation of GCC</title>

    <para>The GCC documentation recommends building GCC outside of the
    source directory in a dedicated build directory:</para>

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

    <para>Test to see if the host is a multilib capable machine and set a variable 
    if it is. This ensures that only 64-bit binaries are built if using such a host.
    Also, the --with-arch flag is only necessary for x86 machines.</para>

<screen><userinput>case $(uname -m) in
  x86) WITHARCH="--with-arch=i486" ;;
  x86_64) M64="-m64" ;;
esac</userinput></screen>

    <para>Prepare GCC for compilation:</para>

<screen><userinput>CC="gcc -B/usr/bin/ $M64" ../gcc-&gcc-version;/configure --prefix=/tools \
    --with-local-prefix=/tools --disable-nls --disable-shared \
    --enable-languages=c --disable-multilib \
    $WITHARCH
unset M64 WITHARCH</userinput></screen>

    <variablelist>
      <title>The meaning of the configure options:</title>

      <varlistentry>
        <term><envar>CC="gcc -B/usr/bin/"</envar></term>
        <listitem>
          <para>This forces <command>gcc</command> to prefer the linker from
          the host in <filename class="directory">/usr/bin</filename>. This
          is necessary on some hosts where the new <command>ld</command>
          built in the previous section is not compatible with the host's
          <command>gcc</command>.</para>
        </listitem>
      </varlistentry>

      <varlistentry>
        <term><parameter>--with-local-prefix=/tools</parameter></term>
        <listitem>
          <para>The purpose of this switch is to remove <filename
          class="directory">/usr/local/include</filename> from
          <command>gcc</command>'s include search path. This is not
          absolutely essential, however, it helps to minimize the
          influence of the host system.</para>
        </listitem>
      </varlistentry>

      <varlistentry>
        <term><parameter>--disable-shared</parameter></term>
        <listitem>
          <para>This forces gcc to link its internal libraries statically. We do this
	  to avoid possible issues with the host system.</para>
        </listitem>
      </varlistentry>

      <varlistentry>
        <term><parameter>--enable-languages=c</parameter></term>
        <listitem>
          <para>This option ensures that only the C compiler is built.</para>
        </listitem>
      </varlistentry>

      <varlistentry>
        <term><parameter>--disable-multilib</parameter></term>
        <listitem>
          <para>We currently only want to build support for 64-bit libraries.</para>
        </listitem>
      </varlistentry>

      <varlistentry>
        <term><parameter>--with-arch=i486</parameter></term>
        <listitem>
    	  <para>On x86 machines Glibc needs to be built for a minimum architecture
	  of <quote>i486</quote>. Setting this for the GCC build ensures that the
	  entire system is built consistently.</para>
        </listitem>
      </varlistentry>

    </variablelist>

    <para>The following command will compile GCC not once, but several times. It
    uses the programs compiled in a first round to compile itself a second time,
    and then again a third time. It then compares these second and third compiles
    to make sure it can reproduce itself flawlessly. This is called
    <quote>bootstrapping</quote>. Building GCC in this way ensures that it was
    compiled correctly and is now the default configuration for the released
    package. Continue with compiling by running:</para>

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

    <para>Compilation is now complete. At this point, the test suite would
    normally be run, but, as mentioned before, the test suite framework is
    not in place yet. The benefits of running the tests at this point
    are minimal since the programs from this first pass will soon be
    replaced.</para>

    <para>Install the package:</para>

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

    <para>Using <command>--disable-shared</command> means that the file
    <filename class="libraryfile">libgcc_eh.a</filename>
    isn't created and installed. The next package, Glibc, depends on this 
    library as it uses <command>-lgcc_eh</command> within its build system.
    We can satisfy that dependency by creating a symlink to
    <filename class="libraryfile">libgcc.a</filename>, since that file will
    end up containing the objects normally contained in
    <filename class="libraryfile">libgcc_eh.a</filename>.</para>

<screen><userinput>ln -vs libgcc.a `gcc -print-libgcc-file-name | \
    sed 's/libgcc/&amp;_eh/'`</userinput></screen>

    <para>As a finishing touch, create a symlink. Many programs and scripts
    run <command>cc</command> instead of <command>gcc</command>, which is
    used to keep programs generic and therefore usable on all kinds of UNIX
    systems where the GNU C compiler is not always installed. Running
    <command>cc</command> leaves the system administrator free to decide
    which C compiler to install:</para>

<screen><userinput>ln -vs gcc /tools/bin/cc</userinput></screen>

  </sect2>

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

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

  </sect2>

</sect1>