mirror of https://github.com/tLDP/LDP
118 lines
5.0 KiB
XML
118 lines
5.0 KiB
XML
<?xml version="1.0" encoding="ISO-8859-1"?>
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<!DOCTYPE sect1 PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
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"http://www.oasis-open.org/docbook/xml/4.5/docbookx.dtd" [
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<!ENTITY % general-entities SYSTEM "../general.ent">
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%general-entities;
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]>
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<sect1 id="ch-system-adjusting">
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<?dbhtml filename="adjusting.html"?>
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<title>Adjusting the Toolchain</title>
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<para>Now that the final C libraries have been installed, it is time to adjust
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the toolchain so that it will link any
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newly compiled program against these new libraries.</para>
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<para>First, backup the <filename class="directory">/tools</filename> linker,
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and replace it with the adjusted linker we made in chapter 5. We'll also create
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a link to its counterpart in <filename class="directory">/tools/$(gcc
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-dumpmachine)/bin</filename>:</para>
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<screen><userinput>mv -v /tools/bin/{ld,ld-old}
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mv -v /tools/$(gcc -dumpmachine)/bin/{ld,ld-old}
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mv -v /tools/bin/{ld-new,ld}
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ln -sv /tools/bin/ld /tools/$(gcc -dumpmachine)/bin/ld</userinput></screen>
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<para>Next, amend the GCC specs file so that it points to the new
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dynamic linker. Simply deleting all instances of <quote>/tools</quote> should
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leave us with the correct path to the dynamic linker. Also adjust the specs file
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so that GCC knows where to find the correct headers and Glibc start files.
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A <command>sed</command> command accomplishes this:</para>
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<screen><userinput>gcc -dumpspecs | sed -e 's@/tools@@g' \
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-e '/\*startfile_prefix_spec:/{n;s@.*@/usr/lib/ @}' \
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-e '/\*cpp:/{n;s@$@ -isystem /usr/include@}' > \
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`dirname $(gcc --print-libgcc-file-name)`/specs</userinput></screen>
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<para>It is a good idea to visually inspect the specs file to verify the
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intended change was actually made.</para>
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<para>It is imperative at this point to ensure that the basic
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functions (compiling and linking) of the adjusted toolchain are working
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as expected. To do this, perform the following sanity checks:</para>
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<screen os="a"><userinput>echo 'int main(){}' > dummy.c
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cc dummy.c -v -Wl,--verbose &> dummy.log
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readelf -l a.out | grep ': /lib'</userinput></screen>
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<para os="b">There should be no errors,
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and the output of the last command will be (allowing for
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platform-specific differences in dynamic linker name):</para>
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<screen os="c"><computeroutput>[Requesting program interpreter: /lib/ld-linux.so.2]</computeroutput></screen>
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<para>Note that <filename class="directory">/lib</filename> is now
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the prefix of our dynamic linker.</para>
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<para os="d">Now make sure that we're setup to use the correct start files:</para>
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<screen os="e"><userinput>grep -o '/usr/lib.*/crt[1in].*succeeded' dummy.log</userinput></screen>
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<para os="f">The output of the last command should be:</para>
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<screen><computeroutput>/usr/lib/crt1.o succeeded
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/usr/lib/crti.o succeeded
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/usr/lib/crtn.o succeeded</computeroutput></screen>
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<para os="g">Verify that the compiler is searching for the correct header
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files:</para>
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<screen><userinput>grep -B1 '^ /usr/include' dummy.log</userinput></screen>
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<para os="h">This command should return the following output:</para>
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<screen><computeroutput>#include <...> search starts here:
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/usr/include</computeroutput></screen>
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<para os="i">Next, verify that the new linker is being used with the correct search paths:</para>
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<screen os="j"><userinput>grep 'SEARCH.*/usr/lib' dummy.log |sed 's|; |\n|g'</userinput></screen>
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<para os="k">References to paths that have components with '-linux-gnu' should
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be ignored, but otherwise the output of the last command should be:</para>
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<screen><computeroutput>SEARCH_DIR("/usr/lib")
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SEARCH_DIR("/lib");</computeroutput></screen>
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<para os="l">Next make sure that we're using the correct libc:</para>
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<screen os="m"><userinput>grep "/lib.*/libc.so.6 " dummy.log</userinput></screen>
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<para os="n">The output of the last command (allowing for a lib64 directory
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on 64-bit hosts) should be:</para>
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<screen os="o"><computeroutput>attempt to open /lib/libc.so.6 succeeded</computeroutput></screen>
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<para os="p">Lastly, make sure GCC is using the correct dynamic linker:</para>
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<screen os="q"><userinput>grep found dummy.log</userinput></screen>
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<para os="r"> The output of the last command should be (allowing for
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platform-specific differences in dynamic linker name and a lib64 directory on
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64-bit hosts):</para>
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<screen os="s"><computeroutput>found ld-linux.so.2 at /lib/ld-linux.so.2</computeroutput></screen>
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<para os="t">If the output does not appear as shown above or is not received
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at all, then something is seriously wrong. Investigate and retrace the
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steps to find out where the problem is and correct it. The most likely
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reason is that something went wrong with the specs file adjustment. Any
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issues will need to be resolved before continuing on with the process.</para>
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<para os="u">Once everything is working correctly, clean up the test files:</para>
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<screen os="v"><userinput>rm -v dummy.c a.out dummy.log</userinput></screen>
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</sect1>
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