mirror of https://github.com/tLDP/LDP
97 lines
4.6 KiB
XML
97 lines
4.6 KiB
XML
<sect1 id="ch06-adjustingtoolchain">
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<title>Re-adjusting the toolchain</title>
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<?dbhtml filename="adjustingtoolchain.html" dir="chapter06"?>
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<para>Now that the new C libraries have been installed, it's time to re-adjust
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our toolchain. We'll adjust it so that it will link any newly compiled program
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against the new C libraries. Basically, this is the reverse of what we did
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in the "locking in" stage in the beginning of the previous chapter.</para>
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<para>The first thing to do is to adjust the linker. For this we retained the
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source and build directories from the second pass over Binutils. Install the
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adjusted linker by running the following from within the
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<filename class="directory">binutils-build</filename> directory:</para>
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<screen><userinput>make -C ld INSTALL=/tools/bin/install install</userinput></screen>
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<note><para>If you somehow missed the earlier warning to retain the Binutils
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source and build directories from the second pass in Chapter 5 or otherwise
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accidentally deleted them or just don't have access to them, don't worry, all is
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not lost. Just ignore the above command. The result will be that the next
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package, Binutils, will link against the Glibc libraries in
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<filename class="directory">/tools</filename> rather than
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<filename class="directory">/usr</filename>. This is not ideal, however, our
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testing has shown that the resulting Binutils program binaries should be
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identical.</para></note>
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<para>From now on every compiled program will link <emphasis>only</emphasis>
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against the libraries in <filename>/usr/lib</filename> and
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<filename>/lib</filename>. The extra
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<userinput>INSTALL=/tools/bin/install</userinput> is needed because the Makefile
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created during the second pass still contains the reference to
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<filename>/usr/bin/install</filename>, which we obviously haven't installed yet.
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Some host distributions contain a <filename class="symlink">ginstall</filename>
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symbolic link which takes precedence in the Makefile and thus can cause a
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problem here. The above command takes care of this also.</para>
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<para>You can now remove the Binutils source and build directories.</para>
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<para>The next thing to do is to amend our GCC specs file so that it points
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to the new dynamic linker. Just like earlier on, we use a sed to accomplish
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this:</para>
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<!-- Ampersands are needed to allow cut and paste -->
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<screen><userinput>SPECFILE=/tools/lib/gcc-lib/*/*/specs &&
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sed -e 's@ /tools/lib/ld-linux.so.2@ /lib/ld-linux.so.2@g' \
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$SPECFILE > newspecfile &&
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mv -f newspecfile $SPECFILE &&
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unset SPECFILE</userinput></screen>
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<para>Again, cutting and pasting the above is recommended. And just like
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before, it is a good idea to check the specs file to ensure the intended
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changes were actually made.</para>
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<important><para>If you are working on a platform where the name of the dynamic
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linker is something other than <filename>ld-linux.so.2</filename>, you
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<emphasis>must</emphasis> substitute <filename>ld-linux.so.2</filename> with the
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name of your platform's dynamic linker in the above commands. Refer back to
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<xref linkend="ch05-toolchaintechnotes"/> if necessary.</para></important>
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<!-- HACK - Force some whitespace to appease tidy -->
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<literallayout></literallayout>
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<caution><para>It is imperative at this point to stop and ensure that the
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basic functions (compiling and linking) of the adjusted toolchain are working
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as expected. For this we are going to perform a simple sanity check:</para>
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<screen><userinput>echo 'main(){}' > dummy.c
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gcc dummy.c
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readelf -l a.out | grep ': /lib'</userinput></screen>
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<para>If everything is working correctly, there should be no errors, and the
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output of the last command will be:</para>
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<blockquote><screen>[Requesting program interpreter: /lib/ld-linux.so.2]</screen></blockquote>
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<para>If you did not receive the output as shown above, or received no output at
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all, then something is seriously wrong. You will need to investigate and retrace
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your steps to find out where the problem is and correct it. There is no point in
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continuing until this is done. Most likely something went wrong with the specs
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file amendment above. Note especially that <filename>/lib</filename> now appears
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as the prefix of our dynamic linker. Of course, if you are working on a platform
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where the name of the dynamic linker is something other than
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<filename>ld-linux.so.2</filename>, then the output will be slightly
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different.</para>
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<para>Once you are satisfied that all is well, clean up the test files:</para>
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<screen><userinput>rm dummy.c a.out</userinput></screen>
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</caution>
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<!-- HACK - Force some whitespace to appease tidy -->
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<literallayout></literallayout>
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</sect1>
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