source: chapter06/adjustingtoolchain.xml@ 30550b6c

<sect1 id="ch06-adjustingtoolchain">
<title>Re-adjusting the toolchain</title>
<?dbhtml filename="adjustingtoolchain.html" dir="chapter06"?>

<para>Now that the new C libraries have been installed, it's time to re-adjust
our toolchain. We'll adjust it so that it will link any newly compiled program
against the new C libraries. Basically, this is the reverse of what we did
in the "Locking in" stage in the beginning of the previous chapter.</para>

<para>The first thing to do is to 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>

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

<note><para>If you somehow missed the earlier warning to retain the Binutils
source and build directories from the second pass in Chapter 5 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 Glibc libraries in
<filename class="directory">/tools</filename> rather than
<filename class="directory">/usr</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>/usr/lib</filename> and
<filename>/lib</filename>. The extra
<userinput>INSTALL=/tools/bin/install</userinput> is needed because the Makefile
created during the second pass still contains the reference to
<filename>/usr/bin/install</filename>, 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>

<para><screen><userinput>SPECFILE=/tools/lib/gcc-lib/*/*/specs
sed -e 's@/tools/lib/ld-linux.so.2@/lib/ld-linux.so.2@g' \
&nbsp;&nbsp;&nbsp;&nbsp;$SPECFILE > newspecfile
mv newspecfile $SPECFILE
unset SPECFILE</userinput></screen></para>

<para>Again, cutting and pasting the above is recommended. And just like
before, it is a good idea to check the specs file to ensure the intended
changes were 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="ch05-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>

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

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

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

<para>If you did not receive the output as shown above, then something is
seriously wrong. This includes the output of the above command being empty!
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. Note especially that <filename>/lib</filename> now appears as
the prefix of our dynamic linker. Of course, if you are working on a platform
where the name of the dynamic linker is something other than
<filename>ld-linux.so.2</filename>, then the output will be slightly
different.</para>

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

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

</sect1>