source: chapter06/readjusting.xml@ 29723b9

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<!DOCTYPE section [
  <!ENTITY % general-entities SYSTEM "../general.ent">
  %general-entities;
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<section xmlns="http://docbook.org/docbook-ng"
         xml:id="ch-system-readjusting">
<title>Re-adjusting the toolchain</title>
<?dbhtml filename="readjusting.html"?>

<para>Now that the new and final C libraries have been installed, it's time to
adjust our toolchain again. We'll adjust it so that it will link any newly
compiled program against these new libraries. This is in fact the same thing we
did in the <quote>Adjusting</quote> phase in the beginning of the previous
chapter, even though it looks like the reverse: then we guided the chain from
the host's <filename class="directory">/{,usr/}lib</filename> to the new
<filename class="directory">/tools/lib</filename>, now we guide it from that
same <filename class="directory">/tools/lib</filename> to the LFS's <filename
class="directory">/{,usr/}lib</filename>.</para>

<para>First we adjust the linker. For this we retained the
source and build directories from the second pass over Binutils. Install the
adjusted linker by running the following from within the
<filename class="directory">binutils-build</filename> directory:</para>

<screen><userinput>make -C ld INSTALL=/tools/bin/install install</userinput></screen>

<note><para>If you somehow missed the earlier warning to retain the Binutils
source and build directories from the second pass in
<xref linkend="chapter-temporary-tools"/>, or otherwise accidentally deleted them or just
don't have access to them, don't worry, all is not lost. Just ignore the above
command. The result will be that the next package, Binutils, will link against
the C libraries in <filename class="directory">/tools</filename> rather
than in <filename class="directory">/{,usr/}lib</filename>. This is not ideal,
however, our testing has shown that the resulting Binutils program binaries
should be identical.</para></note>

<para>From now on every compiled program will link <emphasis>only</emphasis>
against the libraries in <filename class="directory">/usr/lib</filename> and
<filename class="directory">/lib</filename>. The extra
<parameter>INSTALL=/tools/bin/install</parameter> is needed because the Makefile
created during the second pass still contains the reference to
<command>/usr/bin/install</command>, which we obviously haven't installed yet.
Some host distributions contain a <filename class="symlink">ginstall</filename>
symbolic link which takes precedence in the Makefile and thus can cause a
problem here. The above command takes care of this also.</para>

<para>You can now remove the Binutils source and build directories.</para>

<para>The next thing to do is to amend our GCC specs file so that it points
to the new dynamic linker. Just like earlier on, we use a sed to accomplish
this:</para>

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

<screen><userinput>perl -pi -e 's@ /tools/lib/ld-linux.so.2@ /lib/ld-linux.so.2@g;' \
    -e 's@\*startfile_prefix_spec:\n@$_/usr/lib/@g;' \
    `gcc --print-file specs`</userinput></screen>

<para>Again, cutting and pasting the above is recommended. And just like
before, it is a good idea to visually inspect the specs file to verify the
intended change was actually 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> substitute <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>


<caution><para>It is imperative at this point to stop and ensure that the
basic functions (compiling and linking) of the adjusted toolchain are working
as expected. For this we are going to perform a simple sanity check:</para>

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

<para>If everything is working correctly, there should be no errors, and the
output of the last command will be (allowing for platform specific differences
in dynamic linker name):</para>

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

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

<para> If you did not receive the output
as shown above, or received 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.
Most likely something went wrong with the specs file amendment above.</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>


</section>