1 | <?xml version="1.0" encoding="UTF-8"?>
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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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4 | <!ENTITY % general-entities SYSTEM "../general.ent">
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5 | %general-entities;
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6 | ]>
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7 |
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8 | <sect1 id="ch-system-stripping">
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9 | <?dbhtml filename="stripping.html"?>
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10 |
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11 | <title>Stripping</title>
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12 |
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13 | <para>This section is optional. If the intended user is not a
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14 | programmer and does not plan to do
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15 | any debugging of the system software, the system's size can be decreased
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16 | by some 2 GB by removing the debugging symbols, and some unnecessary symbol table
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17 | entries, from binaries and libraries. This causes no real inconvenience for
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18 | a typical Linux user.</para>
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19 |
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20 | <para>Most people who use the commands mentioned below do not
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21 | experience any difficulties. However, it is easy to make a mistake and
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22 | render the new system unusable. So before running the
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23 | <command>strip</command> commands, it is a good idea to make a
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24 | backup of the LFS system in its current state.</para>
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25 |
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26 | <para>A <command>strip</command> command with the
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27 | <parameter>--strip-unneeded</parameter> option removes all debug symbols
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28 | from a binary or library. It also removes all symbol table entries not
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29 | needed by the linker (for static libraries) or dynamic linker (for
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30 | dynamically linked binaries and shared libraries).</para>
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31 |
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32 | <!-- TODO: Zstd is better than Zlib for both speed and size.
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33 | Unfortunately Valgrind does not support Zstd-compressed debug
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34 | info yet: https://bugs.kde.org/show_bug.cgi?id=469782 -->
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35 | <para>The debugging symbols from selected libraries are compressed with
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36 | <application>Zlib</application> and preserved in separate files. That
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37 | debugging information is needed to run regression tests with <ulink
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38 | url='&blfs-book;/general/valgrind.html'>valgrind</ulink> or <ulink
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39 | url='&blfs-book;/general/gdb.html'>gdb</ulink> later, in BLFS.
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40 | </para>
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41 |
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42 | <para>Note that <command>strip</command> will overwrite the binary or library
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43 | file it is processing. This can crash the processes using code or data from
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44 | the file. If the process running <command>strip</command> is
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45 | affected, the binary or library being stripped can be destroyed; this can
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46 | make the system completely unusable. To avoid this problem we copy some libraries
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47 | and binaries into <filename class="directory">/tmp</filename>, strip them
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48 | there, then reinstall them with the <command>install</command> command.
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49 | (The related entry in <xref linkend="pkgmgmt-upgrade-issues"/> gives the
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50 | rationale for using the <command>install</command> command here.)</para>
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51 |
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52 | <note><para>The ELF loader's name is ld-linux-aarch64.so.1 on
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53 | little-endian systems and ld-linux-aarch64_be.so.1 on big-endian systems.
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54 | The construct below selects the
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55 | correct name for the current architecture, excluding anything ending
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56 | with <quote>g</quote>, in case the commands below have already been
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57 | run.</para></note>
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58 |
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59 | <important>
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60 | <para>
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61 | If there is any package whose version is different from the version
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62 | specified by the book (either following a security advisory or
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63 | satisfying personal preference), it may be necessary to update the
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64 | library file name in <envar>save_usrlib</envar> or
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65 | <envar>online_usrlib</envar>.
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66 | <emphasis role='bold'>Failing to do so may render the system
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67 | completely unusable.</emphasis>
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68 | </para>
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69 | </important>
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70 |
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71 | <!-- also of interest are libgfortan, libgo, libgomp, and libobjc from GCC -->
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72 |
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73 | <!--<screen><userinput>save_lib="ld-2.25.so libc-2.25.so libpthread-2.25.so libthread_db-1.0.so"-->
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74 | <screen><userinput>save_usrlib="$(cd /usr/lib; ls ld-linux*[^g])
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75 | libc.so.6
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76 | libthread_db.so.1
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77 | libquadmath.so.&libquadmath-version;
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78 | libstdc++.so.&libstdcpp-version;
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79 | libitm.so.&libitm-version;
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80 | libatomic.so.&libatomic-version;"
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81 |
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82 | cd /usr/lib
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83 |
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84 | for LIB in $save_usrlib; do
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85 | objcopy --only-keep-debug --compress-debug-sections=zlib $LIB $LIB.dbg
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86 | cp $LIB /tmp/$LIB
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87 | strip --strip-unneeded /tmp/$LIB
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88 | objcopy --add-gnu-debuglink=$LIB.dbg /tmp/$LIB
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89 | install -vm755 /tmp/$LIB /usr/lib
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90 | rm /tmp/$LIB
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91 | done
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92 |
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93 | online_usrbin="bash find strip"
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94 | online_usrlib="libbfd-&binutils-version;.so
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95 | libsframe.so.&libsframe-version;
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96 | libhistory.so.&readline-soversion;
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97 | libncursesw.so.&ncurses-version;
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98 | libm.so.6
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99 | libreadline.so.&readline-soversion;
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100 | libz.so.&zlib-version;
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101 | libzstd.so.&zstd-version;
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102 | $(cd /usr/lib; find libnss*.so* -type f)"
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103 |
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104 | for BIN in $online_usrbin; do
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105 | cp /usr/bin/$BIN /tmp/$BIN
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106 | strip --strip-unneeded /tmp/$BIN
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107 | install -vm755 /tmp/$BIN /usr/bin
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108 | rm /tmp/$BIN
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109 | done
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110 |
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111 | for LIB in $online_usrlib; do
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112 | cp /usr/lib/$LIB /tmp/$LIB
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113 | strip --strip-unneeded /tmp/$LIB
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114 | install -vm755 /tmp/$LIB /usr/lib
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115 | rm /tmp/$LIB
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116 | done
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117 |
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118 | for i in $(find /usr/lib -type f -name \*.so* ! -name \*dbg) \
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119 | $(find /usr/lib -type f -name \*.a) \
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120 | $(find /usr/{bin,sbin,libexec} -type f); do
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121 | case "$online_usrbin $online_usrlib $save_usrlib" in
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122 | *$(basename $i)* )
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123 | ;;
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124 | * ) strip --strip-unneeded $i
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125 | ;;
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126 | esac
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127 | done
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128 |
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129 | unset BIN LIB save_usrlib online_usrbin online_usrlib
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130 | </userinput></screen>
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131 |
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132 | <para>A large number of files will be flagged as errors because their file
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133 | format is not recognized. These warnings can be safely ignored. They
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134 | indicate that those files are scripts, not binaries.</para>
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135 |
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136 | </sect1>
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