source: chapter05/adjusting.xml@ 6d3af72

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<sect1 id="ch-tools-adjusting">
<title>Adjusting the toolchain</title>
<?dbhtml filename="adjusting.html"?>

<para>Now that the temporary C libraries have been installed, all
the 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 adjsted.</para>

<para> Some people would say that there is <emphasis><quote>black magic juju
below this line</quote></emphasis>, but it is really very simple.</para>

<para>First, the linker, adjusted at the end of the first pass of Binutils, is
installed by running the following command from within
the <filename class="directory">binutils-build</filename> directory:</para>

<screen><userinput>make -C ld install</userinput></screen>

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

<note><para>If you missed the earlier warning to retain the Binutils
source and build directories from the first pass, dont worry - all is not lost.
Just ignore the above command. This results in a small chance of the subsequent
testing programs linking against libraries on the host. This is not ideal, but
it's not a major problem. The situation is corrected when the second pass of
Binutils is installed later on.</para></note>

<para>Now that the adjusted linker is installed, the Binutils build and source
directories should be <emphasis>removed</emphasis>.</para>

<para>The next task is to amend our GCC specs file so that it points
to the new dynamic linker. A simple sed script will accomplish this:</para>

<!-- Ampersands are needed to allow cut and paste -->

<screen><userinput>SPECFILE=`gcc --print-file specs` &amp;&amp;
sed 's@ /lib/ld-linux.so.2@ /tools/lib/ld-linux.so.2@g' \
    $SPECFILE &gt; tempspecfile &amp;&amp;
mv -f tempspecfile $SPECFILE &amp;&amp;
unset SPECFILE</userinput></screen>

<para>It is recommended that the above command be cut-and-pasted in order to
ensure correctness - Alternatively, the specs file can be edited by hand. This
is done simply 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 you are working on a platform where the name of the dynamic
linker is something other than <filename>ld-linux.so.2</filename>, you
<emphasis>must</emphasis> replace <filename>ld-linux.so.2</filename> with the
name of your platform's dynamic linker in the above commands. Refer back to
<xref linkend="ch-tools-toolchaintechnotes"/> if necessary.</para></important>

<para>Lastly, there is a possibility that some include files from the host
system have found their way into GCC's private include dir. This can happen
as a result of of GCC's <quote>fixincludes</quote> process which runs as part
of the GCC build.  We'll explain more about this further on in this chapter.
Run the following commands to eliminate this possibility:</para>

<screen><userinput>rm -f /tools/lib/gcc/*/*/include/{pthread.h,bits/sigthread.h}</userinput></screen>


<caution><para>It is imperative at this point to stop and ensure that the basic
functions (compiling and linking) of the new toolchain are working as expected.
To perform a simple 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>

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

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

<para>If the output is not
as shown above, or there was no output at all, then something is seriously
wrong. You will need to investigate and retrace your steps to find out where the
problem is and correct it. There is no point in continuing until this is done.
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"/> and install the symlink. Second, ensure your PATH
is correct. You can check this by running <userinput>echo $PATH</userinput> and
verifying that <filename class="directory">/tools/bin</filename> is at the head
of the list. If the PATH is wrong it could mean you're not logged in as user
<emphasis>lfs</emphasis> or something went wrong back in
<xref linkend="ch-tools-settingenviron"/>. Third, something may have gone wrong with
the specs file amendment above. In this case redo the specs file amendment
being careful to cut-and-paste the commands.</para>

<para>Once you are satisfied that all is well, clean up the test files:</para>

<screen><userinput>rm dummy.c a.out</userinput></screen>
</caution>


</sect1>