[673b0d8] | 1 | <?xml version="1.0" encoding="ISO-8859-1"?>
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[b06ca36] | 2 | <!DOCTYPE sect1 PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
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| 3 | "http://www.oasis-open.org/docbook/xml/4.5/docbookx.dtd" [
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[673b0d8] | 4 | <!ENTITY % general-entities SYSTEM "../general.ent">
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| 5 | %general-entities;
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| 6 | ]>
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[3f3931b0] | 7 |
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[d38ac3a] | 8 | <sect1 id="ch-system-adjusting">
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| 9 | <?dbhtml filename="adjusting.html"?>
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[3f3931b0] | 10 |
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[d38ac3a] | 11 | <title>Adjusting the Toolchain</title>
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[3f3931b0] | 12 |
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| 13 | <para>Now that the final C libraries have been installed, it is time to adjust
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[d38ac3a] | 14 | the toolchain so that it will link any
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| 15 | newly compiled program against these new libraries.</para>
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[3f3931b0] | 16 |
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| 17 | <para>First, backup the <filename class="directory">/tools</filename> linker,
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| 18 | and replace it with the adjusted linker we made in chapter 5. We'll also create
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[8035f937] | 19 | a link to its counterpart in
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| 20 | <filename class="directory">/tools/$(uname -m)-pc-linux-gnu/bin</filename>:</para>
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[2914987b] | 21 |
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[1ba726f] | 22 | <screen><userinput>mv -v /tools/bin/{ld,ld-old}
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[8035f937] | 23 | mv -v /tools/$(uname -m)-pc-linux-gnu/bin/{ld,ld-old}
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[1ba726f] | 24 | mv -v /tools/bin/{ld-new,ld}
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[8035f937] | 25 | ln -sv /tools/bin/ld /tools/$(uname -m)-pc-linux-gnu/bin/ld</userinput></screen>
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[2914987b] | 26 |
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[04a77025] | 27 | <para>Next, amend the GCC specs file so that it points to the new
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[4e82d47] | 28 | dynamic linker. Simply deleting all instances of <quote>/tools</quote> should
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| 29 | leave us with the correct path to the dynamic linker. Also adjust the specs file
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| 30 | so that GCC knows where to find the correct headers and Glibc start files.
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| 31 | A <command>sed</command> command accomplishes this:</para>
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[54592a1] | 32 |
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[6458e31] | 33 | <screen><userinput>gcc -dumpspecs | sed -e 's@/tools@@g' \
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[e9a652b] | 34 | -e '/\*startfile_prefix_spec:/{n;s@.*@/usr/lib/ @}' \
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[395cf94f] | 35 | -e '/\*cpp:/{n;s@$@ -isystem /usr/include@}' > \
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[3f3931b0] | 36 | `dirname $(gcc --print-libgcc-file-name)`/specs</userinput></screen>
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| 37 |
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| 38 | <para>It is a good idea to visually inspect the specs file to verify the
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| 39 | intended change was actually made.</para>
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| 40 |
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[09f1daf] | 41 | <para>It is imperative at this point to ensure that the basic
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| 42 | functions (compiling and linking) of the adjusted toolchain are working
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| 43 | as expected. To do this, perform the following sanity checks:</para>
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[673b0d8] | 44 |
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[3d56263] | 45 | <screen os="a"><userinput>echo 'int main(){}' > dummy.c
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[e9a652b] | 46 | cc dummy.c -v -Wl,--verbose &> dummy.log
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[673b0d8] | 47 | readelf -l a.out | grep ': /lib'</userinput></screen>
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| 48 |
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[75128f91] | 49 | <para os="b">There should be no errors,
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[09f1daf] | 50 | and the output of the last command will be (allowing for
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| 51 | platform-specific differences in dynamic linker name):</para>
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[673b0d8] | 52 |
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[09f1daf] | 53 | <screen os="c"><computeroutput>[Requesting program interpreter: /lib/ld-linux.so.2]</computeroutput></screen>
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[673b0d8] | 54 |
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[09f1daf] | 55 | <para>Note that <filename class="directory">/lib</filename> is now
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| 56 | the prefix of our dynamic linker.</para>
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[673b0d8] | 57 |
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[d730742] | 58 | <note><para>On 64-bit systems the interpreter should be
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| 59 | /lib64/ld-linux-x86-64.so.2.</para></note>
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| 60 |
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[edbeeb5] | 61 | <para os="d">Now make sure that we're setup to use the correct start files:</para>
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[2914987b] | 62 |
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[570f6bb] | 63 | <screen os="e"><userinput>grep -o '/usr/lib.*/crt[1in].*succeeded' dummy.log</userinput></screen>
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[2914987b] | 64 |
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[75128f91] | 65 | <para os="f">The output of the last command should be:</para>
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[2914987b] | 66 |
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[09f1daf] | 67 | <screen><computeroutput>/usr/lib/crt1.o succeeded
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| 68 | /usr/lib/crti.o succeeded
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| 69 | /usr/lib/crtn.o succeeded</computeroutput></screen>
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[2914987b] | 70 |
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[d730742] | 71 | <note><para>On 64-bit systems, the path above will be
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| 72 | /usr/lib/gcc/x86_64-unknown-linux-gnu/5.3.0/../../../../lib64/. This
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| 73 | reduces to /usr/lib64 and /usr/lib64 is a symlink that points to
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| 74 | /usr/lib.</para></note>
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| 75 |
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[e9a652b] | 76 | <para os="g">Verify that the compiler is searching for the correct header
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| 77 | files:</para>
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[2914987b] | 78 |
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[006ed03] | 79 | <screen><userinput>grep -B1 '^ /usr/include' dummy.log</userinput></screen>
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[2914987b] | 80 |
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[75128f91] | 81 | <para os="h">This command should return the following output:</para>
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[e9a652b] | 82 |
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| 83 | <screen><computeroutput>#include <...> search starts here:
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| 84 | /usr/include</computeroutput></screen>
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| 85 |
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| 86 | <para os="i">Next, verify that the new linker is being used with the correct search paths:</para>
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| 87 |
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[006ed03] | 88 | <screen os="j"><userinput>grep 'SEARCH.*/usr/lib' dummy.log |sed 's|; |\n|g'</userinput></screen>
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[e9a652b] | 89 |
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[6a0d235] | 90 | <para os="k">References to paths that have components with '-linux-gnu' should
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| 91 | be ignored, but otherwise the output of the last command should be:</para>
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[09f1daf] | 92 |
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[a1b60e2] | 93 | <screen><computeroutput>SEARCH_DIR("/usr/lib")
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[09f1daf] | 94 | SEARCH_DIR("/lib");</computeroutput></screen>
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| 95 |
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[e9a652b] | 96 | <para os="l">Next make sure that we're using the correct libc:</para>
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[09f1daf] | 97 |
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[6e88633] | 98 | <screen os="m"><userinput>grep "/lib.*/libc.so.6 " dummy.log</userinput></screen>
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[09f1daf] | 99 |
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[75128f91] | 100 | <para os="n">The output of the last command (allowing for a lib64 directory
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| 101 | on 64-bit hosts) should be:</para>
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[2914987b] | 102 |
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[e9a652b] | 103 | <screen os="o"><computeroutput>attempt to open /lib/libc.so.6 succeeded</computeroutput></screen>
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[2914987b] | 104 |
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[e9a652b] | 105 | <para os="p">Lastly, make sure GCC is using the correct dynamic linker:</para>
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[2914987b] | 106 |
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[006ed03] | 107 | <screen os="q"><userinput>grep found dummy.log</userinput></screen>
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[2914987b] | 108 |
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[75128f91] | 109 | <para os="r"> The output of the last command should be (allowing for
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| 110 | platform-specific differences in dynamic linker name and a lib64 directory on
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| 111 | 64-bit hosts):</para>
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[2914987b] | 112 |
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[e9a652b] | 113 | <screen os="s"><computeroutput>found ld-linux.so.2 at /lib/ld-linux.so.2</computeroutput></screen>
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[2914987b] | 114 |
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[e9a652b] | 115 | <para os="t">If the output does not appear as shown above or is not received
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[09f1daf] | 116 | at all, then something is seriously wrong. Investigate and retrace the
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| 117 | steps to find out where the problem is and correct it. The most likely
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| 118 | reason is that something went wrong with the specs file adjustment. Any
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| 119 | issues will need to be resolved before continuing on with the process.</para>
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[673b0d8] | 120 |
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[e9a652b] | 121 | <para os="u">Once everything is working correctly, clean up the test files:</para>
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[81fd230] | 122 |
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[006ed03] | 123 | <screen os="v"><userinput>rm -v dummy.c a.out dummy.log</userinput></screen>
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[673b0d8] | 124 |
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| 125 | </sect1>
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