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103 lines
5.0 KiB
HTML
103 lines
5.0 KiB
HTML
4 years ago
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<html lang="en">
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<head>
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<title>PIC - GNU Compiler Collection (GCC) Internals</title>
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<meta http-equiv="Content-Type" content="text/html">
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<meta name="description" content="GNU Compiler Collection (GCC) Internals">
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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="Target-Macros.html#Target-Macros" title="Target Macros">
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<link rel="prev" href="Sections.html#Sections" title="Sections">
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<link rel="next" href="Assembler-Format.html#Assembler-Format" title="Assembler Format">
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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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Copyright (C) 1988-2015 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 or
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any later version published by the Free Software Foundation; with the
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Invariant Sections being ``Funding Free Software'', the Front-Cover
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Texts being (a) (see below), and with the Back-Cover Texts being (b)
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(see below). A copy of the license is included in the section entitled
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``GNU Free Documentation License''.
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(a) The FSF's Front-Cover Text is:
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A GNU Manual
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(b) The FSF's Back-Cover Text is:
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You have freedom to copy and modify this GNU Manual, like GNU
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software. Copies published by the Free Software Foundation raise
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funds for GNU development.-->
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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="PIC"></a>
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<p>
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Next: <a rel="next" accesskey="n" href="Assembler-Format.html#Assembler-Format">Assembler Format</a>,
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Previous: <a rel="previous" accesskey="p" href="Sections.html#Sections">Sections</a>,
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Up: <a rel="up" accesskey="u" href="Target-Macros.html#Target-Macros">Target Macros</a>
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<hr>
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</div>
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<h3 class="section">17.19 Position Independent Code</h3>
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<p><a name="index-position-independent-code-4550"></a><a name="index-PIC-4551"></a>
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This section describes macros that help implement generation of position
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independent code. Simply defining these macros is not enough to
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generate valid PIC; you must also add support to the hook
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<code>TARGET_LEGITIMATE_ADDRESS_P</code> and to the macro
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<code>PRINT_OPERAND_ADDRESS</code>, as well as <code>LEGITIMIZE_ADDRESS</code>. You
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must modify the definition of ‘<samp><span class="samp">movsi</span></samp>’ to do something appropriate
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when the source operand contains a symbolic address. You may also
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need to alter the handling of switch statements so that they use
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relative addresses.
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<!-- i rearranged the order of the macros above to try to force one of -->
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<!-- them to the next line, to eliminate an overfull hbox. -mew 10feb93 -->
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<div class="defun">
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— Macro: <b>PIC_OFFSET_TABLE_REGNUM</b><var><a name="index-PIC_005fOFFSET_005fTABLE_005fREGNUM-4552"></a></var><br>
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<blockquote><p>The register number of the register used to address a table of static
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data addresses in memory. In some cases this register is defined by a
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processor's “application binary interface” (ABI). When this macro
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is defined, RTL is generated for this register once, as with the stack
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pointer and frame pointer registers. If this macro is not defined, it
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is up to the machine-dependent files to allocate such a register (if
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necessary). Note that this register must be fixed when in use (e.g.
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when <code>flag_pic</code> is true).
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</p></blockquote></div>
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<div class="defun">
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— Macro: <b>PIC_OFFSET_TABLE_REG_CALL_CLOBBERED</b><var><a name="index-PIC_005fOFFSET_005fTABLE_005fREG_005fCALL_005fCLOBBERED-4553"></a></var><br>
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<blockquote><p>A C expression that is nonzero if the register defined by
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<code>PIC_OFFSET_TABLE_REGNUM</code> is clobbered by calls. If not defined,
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the default is zero. Do not define
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this macro if <code>PIC_OFFSET_TABLE_REGNUM</code> is not defined.
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</p></blockquote></div>
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<div class="defun">
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— Macro: <b>LEGITIMATE_PIC_OPERAND_P</b> (<var>x</var>)<var><a name="index-LEGITIMATE_005fPIC_005fOPERAND_005fP-4554"></a></var><br>
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<blockquote><p>A C expression that is nonzero if <var>x</var> is a legitimate immediate
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operand on the target machine when generating position independent code.
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You can assume that <var>x</var> satisfies <code>CONSTANT_P</code>, so you need not
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check this. You can also assume <var>flag_pic</var> is true, so you need not
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check it either. You need not define this macro if all constants
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(including <code>SYMBOL_REF</code>) can be immediate operands when generating
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position independent code.
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</p></blockquote></div>
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</body></html>
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