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<h3 class="section">4.11 <samp><span class="command">ld</span></samp> and PowerPC 32-bit ELF Support</h3>

<p><a name="index-PowerPC-long-branches-702"></a><a name="index-g_t_002d_002drelax-on-PowerPC-703"></a>Branches on PowerPC processors are limited to a signed 26-bit
displacement, which may result in <samp><span class="command">ld</span></samp> giving
&lsquo;<samp><span class="samp">relocation truncated to fit</span></samp>&rsquo; errors with very large programs. 
&lsquo;<samp><span class="samp">--relax</span></samp>&rsquo; enables the generation of trampolines that can access
the entire 32-bit address space.  These trampolines are inserted at
section boundaries, so may not themselves be reachable if an input
section exceeds 33M in size.  You may combine &lsquo;<samp><span class="samp">-r</span></samp>&rsquo; and
&lsquo;<samp><span class="samp">--relax</span></samp>&rsquo; to add trampolines in a partial link.  In that case
both branches to undefined symbols and inter-section branches are also
considered potentially out of range, and trampolines inserted.

   <p><a name="index-PowerPC-ELF32-options-704"></a>
     
<a name="index-PowerPC-PLT-705"></a>
<a name="index-g_t_002d_002dbss_002dplt-706"></a>
<dl><dt><samp><span class="option">--bss-plt</span></samp><dd>Current PowerPC GCC accepts a &lsquo;<samp><span class="samp">-msecure-plt</span></samp>&rsquo; option that
generates code capable of using a newer PLT and GOT layout that has
the security advantage of no executable section ever needing to be
writable and no writable section ever being executable.  PowerPC
<samp><span class="command">ld</span></samp> will generate this layout, including stubs to access the
PLT, if all input files (including startup and static libraries) were
compiled with &lsquo;<samp><span class="samp">-msecure-plt</span></samp>&rsquo;.  &lsquo;<samp><span class="samp">--bss-plt</span></samp>&rsquo; forces the old
BSS PLT (and GOT layout) which can give slightly better performance.

     <p><a name="index-g_t_002d_002dsecure_002dplt-707"></a><br><dt><samp><span class="option">--secure-plt</span></samp><dd><samp><span class="command">ld</span></samp> will use the new PLT and GOT layout if it is linking new
&lsquo;<samp><span class="samp">-fpic</span></samp>&rsquo; or &lsquo;<samp><span class="samp">-fPIC</span></samp>&rsquo; code, but does not do so automatically
when linking non-PIC code.  This option requests the new PLT and GOT
layout.  A warning will be given if some object file requires the old
style BSS PLT.

     <p><a name="index-PowerPC-GOT-708"></a><a name="index-g_t_002d_002dsdata_002dgot-709"></a><br><dt><samp><span class="option">--sdata-got</span></samp><dd>The new secure PLT and GOT are placed differently relative to other
sections compared to older BSS PLT and GOT placement.  The location of
<code>.plt</code> must change because the new secure PLT is an initialized
section while the old PLT is uninitialized.  The reason for the
<code>.got</code> change is more subtle:  The new placement allows
<code>.got</code> to be read-only in applications linked with
&lsquo;<samp><span class="samp">-z relro -z now</span></samp>&rsquo;.  However, this placement means that
<code>.sdata</code> cannot always be used in shared libraries, because the
PowerPC ABI accesses <code>.sdata</code> in shared libraries from the GOT
pointer.  &lsquo;<samp><span class="samp">--sdata-got</span></samp>&rsquo; forces the old GOT placement.  PowerPC
GCC doesn't use <code>.sdata</code> in shared libraries, so this option is
really only useful for other compilers that may do so.

     <p><a name="index-PowerPC-stub-symbols-710"></a><a name="index-g_t_002d_002demit_002dstub_002dsyms-711"></a><br><dt><samp><span class="option">--emit-stub-syms</span></samp><dd>This option causes <samp><span class="command">ld</span></samp> to label linker stubs with a local
symbol that encodes the stub type and destination.

     <p><a name="index-PowerPC-TLS-optimization-712"></a><a name="index-g_t_002d_002dno_002dtls_002doptimize-713"></a><br><dt><samp><span class="option">--no-tls-optimize</span></samp><dd>PowerPC <samp><span class="command">ld</span></samp> normally performs some optimization of code
sequences used to access Thread-Local Storage.  Use this option to
disable the optimization. 
</dl>

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