source: chapter08/stripping.xml@ fd4792b

<?xml version="1.0" encoding="ISO-8859-1"?>
<!DOCTYPE sect1 PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
  "http://www.oasis-open.org/docbook/xml/4.5/docbookx.dtd" [
  <!ENTITY % general-entities SYSTEM "../general.ent">
  %general-entities;
]>

<sect1 id="ch-system-stripping">
  <?dbhtml filename="stripping.html"?>

  <title>Stripping</title>

  <para>This section is optional.  If the intended user is not a
  programmer and does not plan to do
  any debugging on the system software, the system size can be decreased
  by about 2 GB by removing the debugging symbols and unneeded symbol table
  entries from binaries and libraries. This causes no inconvenience other
  than not being able to debug the software fully anymore.</para>

  <para>Most people who use the commands mentioned below do not
  experience any difficulties. However, it is easy to make a typo and
  render the new system unusable, so before running the
  <command>strip</command> commands, it is a good idea to make a
  backup of the LFS system in its current state.</para>

  <para>A <command>strip</command> command with
  <parameter>--strip-unneeded</parameter> option removes all debug symbols
  from a binary or library.  And, it removes all symbol table entries not
  needed by the linker (for static libraries) or dynamic linker (for
  dynamic-linked binaries and shared libraries).</para>

  <para>The debugging symbols for selected libraries are placed
  in separate files.  This debugging information is needed if running
  regression tests that use <ulink
  url='&blfs-book;/general/valgrind.html'>valgrind</ulink> or <ulink
  url='&blfs-book;/general/gdb.html'>gdb</ulink> later in BLFS.
  </para>

  <para>Note that <command>strip</command> will overwrite the binary or library
  file it is processing.  This can crash the processes using code or data from
  the file.  If the process running <command>strip</command> itself is
  affected, the binary or library being stripped can be destroyed and can
  make the system completely unusable.  To avoid it, we'll copy some libraries
  and binaries into <filename class="directory">/tmp</filename>, strip them
  there, and install them back with the <command>install</command> command.
  Read the related entry in <xref linkend="pkgmgmt-upgrade-issues"/> for the
  rationale to use the <command>install</command> command here.</para>

  <note><para>The ELF loader's name is ld-linux-x86-64.so.2 on 64-bit systems
  and ld-linux.so.2 on 32-bit systems.  The construct below selects the
  correct name for the current architecture, excluding anything ending
  with <quote>g</quote>, in case the commands below have already been
  run.</para></note>

<!-- also of interest are libgfortan, libgo, libgomp, and libobjc from GCC -->

<!--<screen><userinput>save_lib="ld-2.25.so libc-2.25.so libpthread-2.25.so libthread_db-1.0.so"-->
<screen><userinput>save_usrlib="$(cd /usr/lib; ls ld-linux*[^g])
             libc.so.6
             libthread_db.so.1
             libquadmath.so.&libquadmath-version;
             libstdc++.so.&libstdcpp-version;
             libitm.so.&libitm-version;
             libatomic.so.&libatomic-version;"

cd /usr/lib
for LIB in $save_usrlib; do
    objcopy --only-keep-debug $LIB $LIB.dbg
    cp $LIB /tmp/$LIB
    strip --strip-unneeded /tmp/$LIB
    objcopy --add-gnu-debuglink=$LIB.dbg /tmp/$LIB
    install -vm755 /tmp/$LIB /usr/lib
    rm /tmp/$LIB
done</userinput>
<userinput arch="ml_32,ml_all">
cd /usr/lib32
for LIB in $save_usrlib; do
    objcopy --only-keep-debug $LIB $LIB.dbg
    cp $LIB /tmp/$LIB
    strip --strip-unneeded /tmp/$LIB
    objcopy --add-gnu-debuglink=$LIB.dbg /tmp/$LIB
    install -vm755 /tmp/$LIB /usr/lib32
    rm /tmp/$LIB
done</userinput>
<userinput arch="ml_x32,ml_all">
cd /usr/libx32
for LIB in $save_usrlib; do
    objcopy --only-keep-debug $LIB $LIB.dbg
    cp $LIB /tmp/$LIB
    strip --strip-unneeded /tmp/$LIB
    objcopy --add-gnu-debuglink=$LIB.dbg /tmp/$LIB
    install -vm755 /tmp/$LIB /usr/libx32
    rm /tmp/$LIB
done</userinput><userinput>

online_usrbin="bash find strip"
online_usrlib="libbfd-&binutils-version;.so
               libhistory.so.&readline-soversion;
               libncursesw.so.&ncurses-version;
               libm.so.6
               libreadline.so.&readline-soversion;
               libz.so.&zlib-version;
               $(cd /usr/lib; find libnss*.so* -type f)"

for BIN in $online_usrbin; do
    cp /usr/bin/$BIN /tmp/$BIN
    strip --strip-unneeded /tmp/$BIN
    install -vm755 /tmp/$BIN /usr/bin
    rm /tmp/$BIN
done

for LIB in $online_usrlib; do
    cp /usr/lib/$LIB /tmp/$LIB
    strip --strip-unneeded /tmp/$LIB
    install -vm755 /tmp/$LIB /usr/lib
    rm /tmp/$LIB
done</userinput><userinput arch="ml_32,ml_all">
for LIB in $online_usrlib; do
    cp /usr/lib32/$LIB /tmp/$LIB
    strip --strip-unneeded /tmp/$LIB
    install -vm755 /tmp/$LIB /usr/lib32
    rm /tmp/$LIB
done</userinput><userinput arch="ml_x32,ml_all">
for LIB in $online_usrlib; do
    cp /usr/libx32/$LIB /tmp/$LIB
    strip --strip-unneeded /tmp/$LIB
    install -vm755 /tmp/$LIB /usr/libx32
    rm /tmp/$LIB
done</userinput><userinput>

for i in $(find /usr/lib -type f -name \*.so* ! -name \*dbg) \
         $(find /usr/lib -type f -name \*.a)                 \
         $(find /usr/{bin,sbin,libexec} -type f); do
    case "$online_usrbin $online_usrlib $save_usrlib" in
        *$(basename $i)* )
            ;;
        * ) strip --strip-unneeded $i
            ;;
    esac
done</userinput><userinput arch="ml_32,ml_all">
for i in $(find /usr/lib32 -type f -name \*.so* ! -name \*dbg) \
         $(find /usr/lib32 -type f -name \*.a); do
    case "$online_usrbin $online_usrlib $save_usrlib" in
        *$(basename $i)* )
            ;;
        * ) strip --strip-unneeded $i
            ;;
    esac
done</userinput><userinput arch="ml_x32,ml_all">
for i in $(find /usr/libx32 -type f -name \*.so* ! -name \*dbg) \
         $(find /usr/libx32 -type f -name \*.a); do
    case "$online_usrbin $online_usrlib $save_usrlib" in
        *$(basename $i)* )
            ;;
        * ) strip --strip-unneeded $i
            ;;
    esac
done</userinput><userinput>

unset BIN LIB save_usrlib online_usrbin online_usrlib
</userinput></screen>

  <para>A large number of files will be reported as having their file
  format not recognized. These warnings can be safely ignored. They
  indicate that those files are scripts instead of binaries.</para>

</sect1>