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building-notes: mention -Wl,-z,pack-relative-relocs

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Xi Ruoyao 2023-07-22 12:26:23 +08:00
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1 changed files with 28 additions and 14 deletions
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introduction/important/building-notes.xml
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@ -1067,10 +1067,20 @@ chmod 744 /usr/sbin/strip-all.sh</userinput></screen>
</para>
<para>
For <envar>LDFLAGS</envar>, there are two options can be used
for optimization. With <option>-Wl,-O1</option>, the linker will
optimize the hash table to speed up the dynamic linking. And with
<option>-Wl,--as-needed</option>, the linker will disregard
For <envar>LDFLAGS</envar>, there are three options can be used
for optimization. They are quite safe to use and the building
system of some packages use some of these options as the default.
</para>
<para>
With <option>-Wl,-O1</option>, the linker will
optimize the hash table to speed up the dynamic linking.
Note that <option>-Wl,-O1</option> is completely unrelated to the
compiler optimization flag <option>-O1</option>.
</para>
<para>
With <option>-Wl,--as-needed</option>, the linker will disregard
unnecessary <option>-l<replaceable>foo</replaceable></option> options
from the command line, i. e. the shared library <systemitem
class='library'>lib<replaceable>foo</replaceable></systemitem>
@ -1078,22 +1088,26 @@ chmod 744 /usr/sbin/strip-all.sh</userinput></screen>
class='library'>lib<replaceable>foo</replaceable></systemitem> is
really referred from the executable or shared library being linked.
This can sometimes mitigate the <quote>excessive dependencies to
shared librarues</quote> issues caused by
<application>libtool</application>. Note that the
<option>-Wl,</option> prefix is necessary because despite the
shared libraries</quote> issues caused by
<application>libtool</application>.
</para>
<para>
With <option>-Wl,-z,pack-relative-relocs</option>, the linker
generates a more compacted form of the relative relocation entries
for PIEs and shared libraries. It reduces the size of the linked
PIE or shared library, and speeds up the loading of the PIE or
shared library.
</para>
<para>
The <option>-Wl,</option> prefix is necessary because despite the
variable is named <envar>LDFLAGS</envar>, its content is actually
passed to <command>gcc</command> (or <command>g++</command>,
<command>clang</command>, etc.) during the link stage, not directly
passed to <command>ld</command>.
</para>
<para>
Note that <option>-Wl,-O1</option> is completely unrelated to the
compiler optimization flag <option>-O1</option>. Some packages are
using <option>-Wl,-O1</option> and <option>-Wl,--as-needed</option>
as the default in their building systems.
</para>
</sect2>
<sect2 id="hardening">