lfs-book/chapter06/readjusting.xml

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<sect1 id="ch-system-readjusting">
<title>Re-adjusting the Toolchain</title>
<?dbhtml filename="readjusting.html"?>

<para>Now that the final C libraries have been installed, it is time to adjust
the toolchain again. The toolchain will be adjusted so that it will link any
newly compiled program against these new libraries. This is a similar process
used in the <quote>Adjusting</quote> phase in the beginning of <xref
linkend="chapter-temporary-tools"/>, but with the adjustments reversed. In <xref
linkend="chapter-temporary-tools"/>, the chain was guided from the host's
<filename class="directory">/{,usr/}lib</filename> directories to the new
<filename class="directory">/tools/lib</filename> directory. Now, the chain will
be guided from that same <filename class="directory">/tools/lib</filename>
directory to the LFS <filename class="directory">/{,usr/}lib</filename>
directories.</para>

<para>First, create a symlink to the adjusted linker we created in chapter 5.</para>

<screen><userinput>ln -sv /tools/bin/ld-new /usr/bin/ld</userinput></screen>

<para>Next, amend the GCC specs file so that it points to the new
dynamic linker. A <command>sed</command> command accomplishes this:</para>

<screen><userinput>SPECFILE=`dirname $(gcc -print-libgcc-file-name)`/specs &amp;&amp;
gcc -dumpspecs > $SPECFILE &amp;&amp;
sed -i -e '/^\*link:$/{n;s,$, -L/usr/lib,}' \
       -e 's@^/tools/lib/ld-linux.so.2@/lib/ld-linux.so.2@g' $SPECFILE &amp;&amp;
unset SPECFILE</userinput></screen>

<para>It is a good idea to visually inspect the specs file to verify the intended 
change was actually 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>, substitute
<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>Now create a temporary wrapper script for <filename>gcc</filename>.
This script will point to the real <filename>gcc</filename>
in <filename class="directory">/tools</filename> but with adjusted parameters
to ensure that GCC in the next section links to our newly installed Glibc.</para>

<screen><userinput>cat &gt; /usr/bin/gcc &lt;&lt; "EOF"
#!/bin/bash
/tools/bin/gcc -B/usr/lib/ -B/usr/bin/ $@
EOF
chmod 755 /usr/bin/gcc
ln -s gcc /usr/bin/cc</userinput></screen>

<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. To do this, perform a sanity
check:</para>

<screen><userinput>echo 'main(){}' &gt; dummy.c
cc dummy.c -Wl,--verbose &amp;&gt; dummy.log
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 that <filename class="directory">/lib</filename> is now
the prefix of our dynamic linker.</para>

<para>Now make sure that we're setup to use the correct start files:</para>

<screen><userinput>grep "/usr/lib/crt.* " dummy.log</userinput></screen>

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

<screen><computeroutput>attempt to open /usr/lib/crt1.o succeeded
attempt to open /usr/lib/crti.o succeeded
attempt to open /usr/lib/crtn.o succeeded</computeroutput></screen>

<para>Next make sure that we're using the correct libc:</para>

<screen><userinput>grep "/lib/libc.so.6 " dummy.log</userinput></screen>

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

<screen><computeroutput>attempt to open /lib/libc.so.6 succeeded</computeroutput></screen>

<para>Lastly, make sure GCC is using the correct dynamic linker:</para>

<screen><userinput>grep found dummy.log</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>found ld-linux.so.2 at /lib/ld-linux.so.2</computeroutput></screen>

<para>If the output does not appear as shown above or is not received
at all, then something is seriously wrong. Investigate and retrace the
steps to find out where the problem is and correct it. The most likely
reason is that something went wrong with the specs file amendment
above. Any issues will need to be resolved before continuing on with
the process.</para>

<para>Once everything is working correctly, clean up the test
files:</para>

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

</sect1>