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132 lines
6.2 KiB
HTML
132 lines
6.2 KiB
HTML
4 years ago
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<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
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<html>
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<!-- Copyright (C) 1988-2018 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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<!-- Created by GNU Texinfo 6.4, http://www.gnu.org/software/texinfo/ -->
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<head>
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<title>PIC (GNU Compiler Collection (GCC) Internals)</title>
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<meta name="description" content="PIC (GNU Compiler Collection (GCC) Internals)">
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<meta name="keywords" content="PIC (GNU Compiler Collection (GCC) Internals)">
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<meta name="resource-type" content="document">
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<meta name="distribution" content="global">
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<meta name="Generator" content="makeinfo">
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<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
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<link href="index.html#Top" rel="start" title="Top">
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<link href="Option-Index.html#Option-Index" rel="index" title="Option Index">
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<link href="index.html#SEC_Contents" rel="contents" title="Table of Contents">
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<link href="Target-Macros.html#Target-Macros" rel="up" title="Target Macros">
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<link href="Assembler-Format.html#Assembler-Format" rel="next" title="Assembler Format">
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<link href="Sections.html#Sections" rel="prev" title="Sections">
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<style type="text/css">
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<!--
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a.summary-letter {text-decoration: none}
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blockquote.indentedblock {margin-right: 0em}
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blockquote.smallindentedblock {margin-right: 0em; font-size: smaller}
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blockquote.smallquotation {font-size: smaller}
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div.display {margin-left: 3.2em}
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div.example {margin-left: 3.2em}
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div.lisp {margin-left: 3.2em}
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div.smalldisplay {margin-left: 3.2em}
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div.smallexample {margin-left: 3.2em}
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div.smalllisp {margin-left: 3.2em}
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kbd {font-style: oblique}
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pre.display {font-family: inherit}
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pre.format {font-family: inherit}
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pre.menu-comment {font-family: serif}
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pre.menu-preformatted {font-family: serif}
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pre.smalldisplay {font-family: inherit; font-size: smaller}
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pre.smallexample {font-size: smaller}
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pre.smallformat {font-family: inherit; font-size: smaller}
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pre.smalllisp {font-size: smaller}
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span.nolinebreak {white-space: nowrap}
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span.roman {font-family: initial; font-weight: normal}
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span.sansserif {font-family: sans-serif; font-weight: normal}
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ul.no-bullet {list-style: none}
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-->
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</style>
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</head>
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<body lang="en">
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<a name="PIC"></a>
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<div class="header">
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<p>
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Next: <a href="Assembler-Format.html#Assembler-Format" accesskey="n" rel="next">Assembler Format</a>, Previous: <a href="Sections.html#Sections" accesskey="p" rel="prev">Sections</a>, Up: <a href="Target-Macros.html#Target-Macros" accesskey="u" rel="up">Target Macros</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Option-Index.html#Option-Index" title="Index" rel="index">Index</a>]</p>
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</div>
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<hr>
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<a name="Position-Independent-Code"></a>
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<h3 class="section">18.19 Position Independent Code</h3>
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<a name="index-position-independent-code"></a>
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<a name="index-PIC"></a>
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<p>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>movsi</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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</p>
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<dl>
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<dt><a name="index-PIC_005fOFFSET_005fTABLE_005fREGNUM"></a>Macro: <strong>PIC_OFFSET_TABLE_REGNUM</strong></dt>
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<dd><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></dd></dl>
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<dl>
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<dt><a name="index-PIC_005fOFFSET_005fTABLE_005fREG_005fCALL_005fCLOBBERED"></a>Macro: <strong>PIC_OFFSET_TABLE_REG_CALL_CLOBBERED</strong></dt>
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<dd><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></dd></dl>
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<dl>
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<dt><a name="index-LEGITIMATE_005fPIC_005fOPERAND_005fP"></a>Macro: <strong>LEGITIMATE_PIC_OPERAND_P</strong> <em>(<var>x</var>)</em></dt>
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<dd><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></dd></dl>
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<hr>
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<div class="header">
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<p>
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Next: <a href="Assembler-Format.html#Assembler-Format" accesskey="n" rel="next">Assembler Format</a>, Previous: <a href="Sections.html#Sections" accesskey="p" rel="prev">Sections</a>, Up: <a href="Target-Macros.html#Target-Macros" accesskey="u" rel="up">Target Macros</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Option-Index.html#Option-Index" title="Index" rel="index">Index</a>]</p>
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</div>
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</body>
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</html>
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