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<?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 of the system software, the system's size can be decreased
by some 2 GB by removing the debugging symbols, and some unnecessary symbol table
entries, from binaries and libraries. This causes no real inconvenience for
a typical Linux user.</para>
<para>Most people who use the commands mentioned below do not
experience any difficulties. However, it is easy to make a mistake 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 the
<parameter>--strip-unneeded</parameter> option removes all debug symbols
from a binary or library. It also removes all symbol table entries not
needed by the linker (for static libraries) or dynamic linker (for
dynamically linked binaries and shared libraries).</para>
<!-- TODO: Zstd is better than Zlib for both speed and size.
Unfortunately Valgrind does not support Zstd-compressed debug
info yet: https://bugs.kde.org/show_bug.cgi?id=469782 -->
<para>The debugging symbols from selected libraries are compressed with
<application>Zlib</application> and preserved in separate files. That
debugging information is needed to run regression tests with <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> is
affected, the binary or library being stripped can be destroyed; this can
make the system completely unusable. To avoid this problem we copy some libraries
and binaries into <filename class="directory">/tmp</filename>, strip them
there, then reinstall them with the <command>install</command> command.
(The related entry in <xref linkend="pkgmgmt-upgrade-issues"/> gives the
rationale for using 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>
<important>
<para>
If there is any package whose version is different from the version
specified by the book (either following a security advisory or
satisfying personal preference), it may be necessary to update the
library file name in <envar>save_usrlib</envar> or
<envar>online_usrlib</envar>.
<emphasis role='bold'>Failing to do so may render the system
completely unusable.</emphasis>
</para>
</important>
<!-- 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 --compress-debug-sections=zlib $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
online_usrbin="bash find strip"
online_usrlib="libbfd-&binutils-version;.so
libsframe.so.&libsframe-version;
libhistory.so.&readline-soversion;
libncursesw.so.&ncurses-version;
libm.so.6
libreadline.so.&readline-soversion;
libz.so.&zlib-version;
libzstd.so.&zstd-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
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
unset BIN LIB save_usrlib online_usrbin online_usrlib
</userinput></screen>
<para>A large number of files will be flagged as errors because their file
format is not recognized. These warnings can be safely ignored. They
indicate that those files are scripts, not binaries.</para>
</sect1>
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