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103 lines
6.2 KiB
HTML
103 lines
6.2 KiB
HTML
4 years ago
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<html lang="en">
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<head>
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<title>PowerPC ELF32 - Untitled</title>
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<meta http-equiv="Content-Type" content="text/html">
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<meta name="description" content="Untitled">
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<meta name="generator" content="makeinfo 4.13">
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<link title="Top" rel="start" href="index.html#Top">
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<link rel="up" href="Machine-Dependent.html#Machine-Dependent" title="Machine Dependent">
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<link rel="prev" href="Nios-II.html#Nios-II" title="Nios II">
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<link rel="next" href="PowerPC64-ELF64.html#PowerPC64-ELF64" title="PowerPC64 ELF64">
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<link href="http://www.gnu.org/software/texinfo/" rel="generator-home" title="Texinfo Homepage">
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<!--
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This file documents the GNU linker LD
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(GNU Binutils)
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version 2.26.
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Copyright (C) 1991-2015 Free Software Foundation, Inc.
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Permission is granted to copy, distribute and/or modify this document
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under the terms of the GNU Free Documentation License, Version 1.3
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or any later version published by the Free Software Foundation;
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with no Invariant Sections, with no Front-Cover Texts, and with no
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Back-Cover Texts. A copy of the license is included in the
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section entitled ``GNU Free Documentation License''.-->
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<style type="text/css"><!--
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--></style>
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</head>
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<body>
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<div class="node">
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<a name="PowerPC-ELF32"></a>
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<p>
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Next: <a rel="next" accesskey="n" href="PowerPC64-ELF64.html#PowerPC64-ELF64">PowerPC64 ELF64</a>,
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Previous: <a rel="previous" accesskey="p" href="Nios-II.html#Nios-II">Nios II</a>,
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Up: <a rel="up" accesskey="u" href="Machine-Dependent.html#Machine-Dependent">Machine Dependent</a>
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<hr>
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</div>
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<h3 class="section">4.12 <samp><span class="command">ld</span></samp> and PowerPC 32-bit ELF Support</h3>
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<p><a name="index-PowerPC-long-branches-663"></a><a name="index-g_t_002d_002drelax-on-PowerPC-664"></a>Branches on PowerPC processors are limited to a signed 26-bit
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displacement, which may result in <samp><span class="command">ld</span></samp> giving
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‘<samp><span class="samp">relocation truncated to fit</span></samp>’ errors with very large programs.
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‘<samp><span class="samp">--relax</span></samp>’ enables the generation of trampolines that can access
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the entire 32-bit address space. These trampolines are inserted at
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section boundaries, so may not themselves be reachable if an input
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section exceeds 33M in size. You may combine ‘<samp><span class="samp">-r</span></samp>’ and
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‘<samp><span class="samp">--relax</span></samp>’ to add trampolines in a partial link. In that case
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both branches to undefined symbols and inter-section branches are also
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considered potentially out of range, and trampolines inserted.
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<p><a name="index-PowerPC-ELF32-options-665"></a>
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<a name="index-PowerPC-PLT-666"></a>
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<a name="index-g_t_002d_002dbss_002dplt-667"></a>
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<dl><dt><samp><span class="option">--bss-plt</span></samp><dd>Current PowerPC GCC accepts a ‘<samp><span class="samp">-msecure-plt</span></samp>’ option that
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generates code capable of using a newer PLT and GOT layout that has
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the security advantage of no executable section ever needing to be
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writable and no writable section ever being executable. PowerPC
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<samp><span class="command">ld</span></samp> will generate this layout, including stubs to access the
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PLT, if all input files (including startup and static libraries) were
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compiled with ‘<samp><span class="samp">-msecure-plt</span></samp>’. ‘<samp><span class="samp">--bss-plt</span></samp>’ forces the old
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BSS PLT (and GOT layout) which can give slightly better performance.
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<p><a name="index-g_t_002d_002dsecure_002dplt-668"></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
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‘<samp><span class="samp">-fpic</span></samp>’ or ‘<samp><span class="samp">-fPIC</span></samp>’ code, but does not do so automatically
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when linking non-PIC code. This option requests the new PLT and GOT
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layout. A warning will be given if some object file requires the old
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style BSS PLT.
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<p><a name="index-PowerPC-GOT-669"></a><a name="index-g_t_002d_002dsdata_002dgot-670"></a><br><dt><samp><span class="option">--sdata-got</span></samp><dd>The new secure PLT and GOT are placed differently relative to other
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sections compared to older BSS PLT and GOT placement. The location of
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<code>.plt</code> must change because the new secure PLT is an initialized
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section while the old PLT is uninitialized. The reason for the
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<code>.got</code> change is more subtle: The new placement allows
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<code>.got</code> to be read-only in applications linked with
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‘<samp><span class="samp">-z relro -z now</span></samp>’. However, this placement means that
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<code>.sdata</code> cannot always be used in shared libraries, because the
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PowerPC ABI accesses <code>.sdata</code> in shared libraries from the GOT
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pointer. ‘<samp><span class="samp">--sdata-got</span></samp>’ forces the old GOT placement. PowerPC
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GCC doesn't use <code>.sdata</code> in shared libraries, so this option is
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really only useful for other compilers that may do so.
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<p><a name="index-PowerPC-stub-symbols-671"></a><a name="index-g_t_002d_002demit_002dstub_002dsyms-672"></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
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symbol that encodes the stub type and destination.
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<p><a name="index-PowerPC-TLS-optimization-673"></a><a name="index-g_t_002d_002dno_002dtls_002doptimize-674"></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
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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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</dl>
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</body></html>
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