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125 lines
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This file documents the GNU linker LD
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(GNU Binutils)
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version 2.19.
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Copyright (C) 1991, 92, 93, 94, 95, 96, 97, 98, 99, 2000,
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2001, 2002, 2003, 2004, 2005, 2006, 2007 Free Software Foundation, Inc.
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<a name="PowerPC64-ELF64"></a>Next: <a rel="next" accesskey="n" href="SPU-ELF.html#SPU-ELF">SPU ELF</a>,
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<h3 class="section">4.10 <span class="command">ld</span> and PowerPC64 64-bit ELF Support</h3>
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<p><a name="index-PowerPC64-ELF64-options-579"></a>
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<a name="index-PowerPC64-stub-grouping-580"></a>
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<a name="index-_002d_002dstub_002dgroup_002dsize-581"></a>
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<dl><dt><span class="option">--stub-group-size</span><dd>Long branch stubs, PLT call stubs and TOC adjusting stubs are placed
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by <span class="command">ld</span> in stub sections located between groups of input sections.
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<span class="samp">--stub-group-size</span> specifies the maximum size of a group of input
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sections handled by one stub section. Since branch offsets are signed,
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a stub section may serve two groups of input sections, one group before
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the stub section, and one group after it. However, when using
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conditional branches that require stubs, it may be better (for branch
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prediction) that stub sections only serve one group of input sections.
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A negative value for <span class="samp">N</span> chooses this scheme, ensuring that
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branches to stubs always use a negative offset. Two special values of
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<span class="samp">N</span> are recognized, <span class="samp">1</span> and <span class="samp">-1</span>. These both instruct
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<span class="command">ld</span> to automatically size input section groups for the branch types
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detected, with the same behaviour regarding stub placement as other
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positive or negative values of <span class="samp">N</span> respectively.
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<p>Note that <span class="samp">--stub-group-size</span> does not split input sections. A
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single input section larger than the group size specified will of course
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create a larger group (of one section). If input sections are too
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large, it may not be possible for a branch to reach its stub.
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<p><a name="index-PowerPC64-stub-symbols-582"></a><a name="index-_002d_002demit_002dstub_002dsyms-583"></a><br><dt><span class="option">--emit-stub-syms</span><dd>This option causes <span class="command">ld</span> to label linker stubs with a local
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symbol that encodes the stub type and destination.
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<p><a name="index-PowerPC64-dot-symbols-584"></a><a name="index-_002d_002ddotsyms-585"></a><a name="index-_002d_002dno_002ddotsyms-586"></a><br><dt><span class="option">--dotsyms, --no-dotsyms</span><dd>These two options control how <span class="command">ld</span> interprets version patterns
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in a version script. Older PowerPC64 compilers emitted both a
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function descriptor symbol with the same name as the function, and a
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code entry symbol with the name prefixed by a dot (<span class="samp">.</span>). To
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properly version a function <span class="samp">foo</span>, the version script thus needs
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to control both <span class="samp">foo</span> and <span class="samp">.foo</span>. The option
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<span class="samp">--dotsyms</span>, on by default, automatically adds the required
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dot-prefixed patterns. Use <span class="samp">--no-dotsyms</span> to disable this
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feature.
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<p><a name="index-PowerPC64-TLS-optimization-587"></a><a name="index-_002d_002dno_002dtls_002doptimize-588"></a><br><dt><span class="option">--no-tls-optimize</span><dd>PowerPC64 <span class="command">ld</span> normally performs some optimization of code
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sequences used to access Thread-Local Storage. Use this option to
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disable the optimization.
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<p><a name="index-PowerPC64-OPD-optimization-589"></a><a name="index-_002d_002dno_002dopd_002doptimize-590"></a><br><dt><span class="option">--no-opd-optimize</span><dd>PowerPC64 <span class="command">ld</span> normally removes <code>.opd</code> section entries
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corresponding to deleted link-once functions, or functions removed by
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the action of <span class="samp">--gc-sections</span> or linker script <code>/DISCARD/</code>.
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Use this option to disable <code>.opd</code> optimization.
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<p><a name="index-PowerPC64-OPD-spacing-591"></a><a name="index-_002d_002dnon_002doverlapping_002dopd-592"></a><br><dt><span class="option">--non-overlapping-opd</span><dd>Some PowerPC64 compilers have an option to generate compressed
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<code>.opd</code> entries spaced 16 bytes apart, overlapping the third word,
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the static chain pointer (unused in C) with the first word of the next
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entry. This option expands such entries to the full 24 bytes.
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<p><a name="index-PowerPC64-TOC-optimization-593"></a><a name="index-_002d_002dno_002dtoc_002doptimize-594"></a><br><dt><span class="option">--no-toc-optimize</span><dd>PowerPC64 <span class="command">ld</span> normally removes unused <code>.toc</code> section
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entries. Such entries are detected by examining relocations that
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reference the TOC in code sections. A reloc in a deleted code section
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marks a TOC word as unneeded, while a reloc in a kept code section
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marks a TOC word as needed. Since the TOC may reference itself, TOC
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relocs are also examined. TOC words marked as both needed and
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unneeded will of course be kept. TOC words without any referencing
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reloc are assumed to be part of a multi-word entry, and are kept or
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discarded as per the nearest marked preceding word. This works
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reliably for compiler generated code, but may be incorrect if assembly
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code is used to insert TOC entries. Use this option to disable the
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optimization.
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<p><a name="index-PowerPC64-multi_002dTOC-595"></a><a name="index-_002d_002dno_002dmulti_002dtoc-596"></a><br><dt><span class="option">--no-multi-toc</span><dd>By default, PowerPC64 GCC generates code for a TOC model where TOC
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entries are accessed with a 16-bit offset from r2. This limits the
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total TOC size to 64K. PowerPC64 <span class="command">ld</span> extends this limit by
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grouping code sections such that each group uses less than 64K for its
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TOC entries, then inserts r2 adjusting stubs between inter-group
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calls. <span class="command">ld</span> does not split apart input sections, so cannot
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help if a single input file has a <code>.toc</code> section that exceeds
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64K, most likely from linking multiple files with <span class="command">ld -r</span>.
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Use this option to turn off this feature.
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</dl>
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</body></html>
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