source: chapter06/readjusting.xml@ 0c78fca

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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 the same 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>Start by adjusting the linker. The source and build directories from the
second pass of Binutils were retained for this purpose. Install the adjusted
linker by running the following command 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 the earlier warning to retain the Binutils source and
build directories from the second pass in <xref
linkend="chapter-temporary-tools"/> was missed, or if they were
accidentally deleted or are inaccessible, 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, testing has shown that the resulting
Binutils program binaries should be identical.</para></note>

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

<para>Remove the Binutils source and build directories now.</para>

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

<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>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>

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

</sect1>