lfs-book/chapter05/adjusting.xml

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<sect1 id="ch-tools-adjusting">
  <?dbhtml filename="adjusting.html"?>

  <title>Adjusting the Toolchain</title>

  <para>Now that the temporary C libraries have been installed, all
  tools compiled in the rest of this chapter should be linked against
  these libraries. In order to accomplish this, the linker and the
  compiler's specs file need to be adjusted.</para>

  <para>The linker, adjusted at the end of the first pass of Binutils, needs
  to be renamed so that it can be properly found and used. First, backup the
  original linker, then replace it with the adjusted linker. We'll also
  create a link to its counterpart in <filename class="directory">
  /tools/$(gcc -dumpmachine)/bin</filename></para>

<screen><userinput>mv -v /tools/bin/{ld,ld-old}
mv -v /tools/$(gcc -dumpmachine)/bin/{ld,ld-old}
mv -v /tools/bin/{ld-new,ld}
ln -sv /tools/bin/ld /tools/$(gcc -dumpmachine)/bin/ld</userinput></screen>

  <para>From this point onwards, everything will link only against the
  libraries in <filename class="directory">/tools/lib</filename>.</para>

  <para>The next task is to point GCC to the new dynamic linker. This is done by
  dumping GCC's <quote>specs</quote> file to a location where GCC will look for it
  by default. A simple <command>sed</command> substitution then alters the
  dynamic linker that GCC will use:</para>

<!-- Ampersands are needed to allow copy and paste -->
<screen><userinput>SPECFILE=`dirname $(gcc -print-libgcc-file-name)`/specs &amp;&amp;
gcc -dumpspecs > $SPECFILE &amp;&amp;
sed 's@^/lib/ld-linux.so.2@/tools&amp;@g' $SPECFILE &gt; tempspecfile &amp;&amp;
mv -vf tempspecfile $SPECFILE &amp;&amp;
unset SPECFILE</userinput></screen>

  <para>It is recommended that the above command be copy-and-pasted in order to
  ensure accuracy. Alternatively, the specs file can be edited by hand. This is
  done by replacing every occurrence of <quote>/lib/ld-linux.so.2</quote> with
  <quote>/tools/lib/ld-linux.so.2</quote></para>

  <para>Be sure to visually inspect the specs file in order to verify the
  intended changes have been made.</para>

  <important>
    <para>If working on a platform where the name of the dynamic linker is
    something other than <filename class="libraryfile">ld-linux.so.2</filename>,
    replace <quote>ld-linux.so.2</quote> with the name of the platform's
    dynamic linker in the above commands. Refer back to <xref
    linkend="ch-tools-toolchaintechnotes" role=","/> if necessary.</para>
  </important>

  <para>During the build process, GCC runs a script
  (<command>fixincludes</command>) that scans the system for header files
  that may need to be fixed (they might contain syntax errors, for example),
  and installs the fixed versions in a private include directory. There is a
  possibility that, as a result of this process, some header files from the
  host system have found their way into GCC's private include directory. As
  the rest of this chapter only requires the headers from GCC and Glibc,
  which have both been installed at this point, any <quote>fixed</quote>
  headers can safely be removed. This helps to avoid any host headers
  polluting the build environment. Run the following commands to remove the
  header files in GCC's private include directory (you may find it easier to
  copy and paste these commands, rather than typing them by hand, due to
  their length):</para>

<!-- && used to ease copy and pasting -->
<screen><userinput>GCC_INCLUDEDIR=`dirname $(gcc -print-libgcc-file-name)`/include &amp;&amp;
find ${GCC_INCLUDEDIR}/* -maxdepth 0 -xtype d -exec rm -rvf '{}' \; &amp;&amp;
rm -vf `grep -l "DO NOT EDIT THIS FILE" ${GCC_INCLUDEDIR}/*` &amp;&amp;
unset GCC_INCLUDEDIR</userinput></screen>

  <caution>
    <para>At this point, it is imperative to stop and ensure that the basic
    functions (compiling and linking) of the new toolchain are working as
    expected. To perform a sanity check, run the following commands:</para>

<screen><userinput>echo 'main(){}' &gt; dummy.c
cc dummy.c
readelf -l a.out | grep ': /tools'</userinput></screen>

    <para>If everything is working correctly, there should be no errors,
    and the output of the last command will be of the form:</para>

<screen><computeroutput>[Requesting program interpreter:
    /tools/lib/ld-linux.so.2]</computeroutput></screen>

    <para>Note that <filename class="directory">/tools/lib</filename>
    appears as the prefix of the dynamic linker.</para>

    <para>If the output is not shown as above or there was no output at all,
    then something is wrong. Investigate and retrace the steps to find out
    where the problem is and correct it. This issue must be resolved before
    continuing on. First, perform the sanity check again, using
    <command>gcc</command> instead of <command>cc</command>. If this works,
    then the <filename class="symlink">/tools/bin/cc</filename> symlink is
    missing. Revisit <xref linkend="ch-tools-gcc-pass1" role=","/> and install
    the symlink. Next, ensure that the <envar>PATH</envar> is correct. This
    can be checked by running <command>echo $PATH</command> and verifying that
    <filename class="directory">/tools/bin</filename> is at the head of the
    list. If the <envar>PATH</envar> is wrong it could mean that you are not
    logged in as user <systemitem class="username">lfs</systemitem> or that
    something went wrong back in <xref linkend="ch-tools-settingenviron"
    role="."/> Another option is that something may have gone wrong with the
    specs file amendment above. In this case, redo the specs file amendment,
    being careful to copy-and-paste the commands.</para>

    <para>Once all is well, clean up the test files:</para>

<screen><userinput>rm -v dummy.c a.out</userinput></screen>

    <para>Building TCL in the next section will serve as an additional check that
    the toolchain has been built properly.  If TCL fails to build, it is an
    indication that something has gone wrong with the Binutils, GCC, or Glibc
    installation, but not with TCL itself.</para>
  </caution>

</sect1>