adjusting.xml 5.0 KB

123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960616263646566676869707172737475767778798081828384858687888990919293949596979899100101102103104105106107108109110111112113114115116117
  1. <?xml version="1.0" encoding="ISO-8859-1"?>
  2. <!DOCTYPE sect1 PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
  3. "http://www.oasis-open.org/docbook/xml/4.5/docbookx.dtd" [
  4. <!ENTITY % general-entities SYSTEM "../general.ent">
  5. %general-entities;
  6. ]>
  7. <sect1 id="ch-system-adjusting">
  8. <?dbhtml filename="adjusting.html"?>
  9. <title>Adjusting the Toolchain</title>
  10. <para>Now that the final C libraries have been installed, it is time to adjust
  11. the toolchain so that it will link any
  12. newly compiled program against these new libraries.</para>
  13. <para>First, backup the <filename class="directory">/tools</filename> linker,
  14. and replace it with the adjusted linker we made in chapter 5. We'll also create
  15. a link to its counterpart in <filename class="directory">/tools/$(gcc
  16. -dumpmachine)/bin</filename>:</para>
  17. <screen><userinput>mv -v /tools/bin/{ld,ld-old}
  18. mv -v /tools/$(gcc -dumpmachine)/bin/{ld,ld-old}
  19. mv -v /tools/bin/{ld-new,ld}
  20. ln -sv /tools/bin/ld /tools/$(gcc -dumpmachine)/bin/ld</userinput></screen>
  21. <para>Next, amend the GCC specs file so that it points to the new
  22. dynamic linker. Simply deleting all instances of <quote>/tools</quote> should
  23. leave us with the correct path to the dynamic linker. Also adjust the specs file
  24. so that GCC knows where to find the correct headers and Glibc start files.
  25. A <command>sed</command> command accomplishes this:</para>
  26. <screen><userinput>gcc -dumpspecs | sed -e 's@/tools@@g' \
  27. -e '/\*startfile_prefix_spec:/{n;s@.*@/usr/lib/ @}' \
  28. -e '/\*cpp:/{n;s@$@ -isystem /usr/include@}' &gt; \
  29. `dirname $(gcc --print-libgcc-file-name)`/specs</userinput></screen>
  30. <para>It is a good idea to visually inspect the specs file to verify the
  31. intended change was actually made.</para>
  32. <para>It is imperative at this point to ensure that the basic
  33. functions (compiling and linking) of the adjusted toolchain are working
  34. as expected. To do this, perform the following sanity checks:</para>
  35. <screen os="a"><userinput>echo 'main(){}' &gt; dummy.c
  36. cc dummy.c -v -Wl,--verbose &amp;&gt; dummy.log
  37. readelf -l a.out | grep ': /lib'</userinput></screen>
  38. <para os="b">There should be no errors,
  39. and the output of the last command will be (allowing for
  40. platform-specific differences in dynamic linker name):</para>
  41. <screen os="c"><computeroutput>[Requesting program interpreter: /lib/ld-linux.so.2]</computeroutput></screen>
  42. <para>Note that <filename class="directory">/lib</filename> is now
  43. the prefix of our dynamic linker.</para>
  44. <para os="d">Now make sure that we're setup to use the correct startfiles:</para>
  45. <screen os="e"><userinput>grep -o '/usr/lib.*/crt[1in].*succeeded' dummy.log</userinput></screen>
  46. <para os="f">The output of the last command should be:</para>
  47. <screen><computeroutput>/usr/lib/crt1.o succeeded
  48. /usr/lib/crti.o succeeded
  49. /usr/lib/crtn.o succeeded</computeroutput></screen>
  50. <para os="g">Verify that the compiler is searching for the correct header
  51. files:</para>
  52. <screen><userinput>grep -B1 '^ /usr/include' dummy.log</userinput></screen>
  53. <para os="h">This command should return the following output:</para>
  54. <screen><computeroutput>#include &lt;...&gt; search starts here:
  55. /usr/include</computeroutput></screen>
  56. <para os="i">Next, verify that the new linker is being used with the correct search paths:</para>
  57. <screen os="j"><userinput>grep 'SEARCH.*/usr/lib' dummy.log |sed 's|; |\n|g'</userinput></screen>
  58. <para os="k">References to paths that have components with '-linux-gnu' should
  59. be ignored, but otherwise the output of the last command should be:</para>
  60. <screen><computeroutput>SEARCH_DIR("/usr/lib")
  61. SEARCH_DIR("/lib");</computeroutput></screen>
  62. <para os="l">Next make sure that we're using the correct libc:</para>
  63. <screen os="m"><userinput>grep "/lib.*/libc.so.6 " dummy.log</userinput></screen>
  64. <para os="n">The output of the last command (allowing for a lib64 directory
  65. on 64-bit hosts) should be:</para>
  66. <screen os="o"><computeroutput>attempt to open /lib/libc.so.6 succeeded</computeroutput></screen>
  67. <para os="p">Lastly, make sure GCC is using the correct dynamic linker:</para>
  68. <screen os="q"><userinput>grep found dummy.log</userinput></screen>
  69. <para os="r"> The output of the last command should be (allowing for
  70. platform-specific differences in dynamic linker name and a lib64 directory on
  71. 64-bit hosts):</para>
  72. <screen os="s"><computeroutput>found ld-linux.so.2 at /lib/ld-linux.so.2</computeroutput></screen>
  73. <para os="t">If the output does not appear as shown above or is not received
  74. at all, then something is seriously wrong. Investigate and retrace the
  75. steps to find out where the problem is and correct it. The most likely
  76. reason is that something went wrong with the specs file adjustment. Any
  77. issues will need to be resolved before continuing on with the process.</para>
  78. <para os="u">Once everything is working correctly, clean up the test files:</para>
  79. <screen os="v"><userinput>rm -v dummy.c a.out dummy.log</userinput></screen>
  80. </sect1>