lfs-book/chapter06/readjusting.xml

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<sect1 id="ch-system-readjusting">
  <?dbhtml filename="readjusting.html"?>

  <title>Re-adjusting the Toolchain</title>

  <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, backup the <filename class="directory">/tools</filename> linker,
  and replace it with the adjusted linker we made in chapter 5. We'll also create
  a link to its counterpart in <filename class="directory">/tools/$(gcc
  -dumpmachine)/bin</filename>:</para>

<screen><userinput>mv -v /tools/bin/{ld,ld-old}
mv -v /tools/$(gcc -dumpmachine)/bin/{ld,ld-old}
mv -v /tools/bin/{ld-new,ld}
ln -sv /tools/bin/ld /tools/$(gcc -dumpmachine)/bin/ld</userinput></screen>

  <para>Next, amend the GCC specs file so that it points to the new
  dynamic linker, and so that GCC knows where to find the correct headers
  and Glibc start files. A <command>sed</command> command accomplishes
  this:</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 following commands. Refer to <xref
    linkend="ch-tools-toolchaintechnotes" role=","/> if necessary.</para>
  </important>

<screen><userinput>gcc -dumpspecs | sed \
    -e 's@/tools/lib/ld-linux.so.2@/lib/ld-linux.so.2@g' \
    -e '/\*startfile_prefix_spec:/{n;s@.*@/usr/lib/ @}' \
    -e '/\*cpp:/{n;s@$@ -isystem /usr/include@}' &gt; \
    `dirname $(gcc --print-libgcc-file-name)`/specs</userinput></screen>

  <para>It is a good idea to visually inspect the specs file to verify the
  intended change was actually made.</para>

  <para>It is imperative at this point to ensure that the basic
  functions (compiling and linking) of the adjusted toolchain are working
  as expected. To do this, perform the following sanity checks:</para>

<screen os="a"><userinput>echo 'main(){}' &gt; dummy.c
cc dummy.c -v -Wl,--verbose &amp;&gt; dummy.log
readelf -l a.out | grep ': /lib'</userinput></screen>

  <para os="b">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 os="c"><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 os="d">Now make sure that we're setup to use the correct startfiles:</para>

<screen os="e"><userinput>grep -o '/usr/lib.*/crt[1in].*succeeded' dummy.log</userinput></screen>

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

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

  <para os="g">Verify that the compiler is searching for the correct header
  files:</para>

<screen><userinput>grep -B1 '^ /usr/include' dummy.log</userinput></screen>

  <para os="h">This command should return successfully with the following output:</para>

<screen><computeroutput>#include &lt;...&gt; search starts here:
 /usr/include</computeroutput></screen>

  <para os="i">Next, verify that the new linker is being used with the correct search paths:</para>

<screen os="j"><userinput>grep 'SEARCH.*/usr/lib' dummy.log |sed 's|; |\n|g'</userinput></screen>

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

<screen><computeroutput>SEARCH_DIR("/tools/i686-pc-linux-gnu/lib")
SEARCH_DIR("/usr/lib")
SEARCH_DIR("/lib");</computeroutput></screen>

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

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

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

<screen os="o"><computeroutput>attempt to open /lib/libc.so.6 succeeded</computeroutput></screen>

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

<screen os="q"><userinput>grep found dummy.log</userinput></screen>

  <para os="r">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 os="s"><computeroutput>found ld-linux.so.2 at /lib/ld-linux.so.2</computeroutput></screen>

  <para os="t">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 adjustment. Any
  issues will need to be resolved before continuing on with the process.</para>

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

<screen os="v"><userinput>rm -v dummy.c a.out dummy.log</userinput></screen>

</sect1>