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210 lines
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HTML
210 lines
10 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>Alignment Output (GNU Compiler Collection (GCC) Internals)</title>
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<meta name="description" content="Alignment Output (GNU Compiler Collection (GCC) Internals)">
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<meta name="keywords" content="Alignment Output (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="Assembler-Format.html#Assembler-Format" rel="up" title="Assembler Format">
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<link href="Debugging-Info.html#Debugging-Info" rel="next" title="Debugging Info">
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<link href="Exception-Region-Output.html#Exception-Region-Output" rel="prev" title="Exception Region Output">
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<style type="text/css">
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</style>
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</head>
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<body lang="en">
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<a name="Alignment-Output"></a>
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<div class="header">
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<p>
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Previous: <a href="Exception-Region-Output.html#Exception-Region-Output" accesskey="p" rel="prev">Exception Region Output</a>, Up: <a href="Assembler-Format.html#Assembler-Format" accesskey="u" rel="up">Assembler Format</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="Assembler-Commands-for-Alignment"></a>
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<h4 class="subsection">18.20.10 Assembler Commands for Alignment</h4>
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<p>This describes commands for alignment.
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</p>
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<dl>
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<dt><a name="index-JUMP_005fALIGN"></a>Macro: <strong>JUMP_ALIGN</strong> <em>(<var>label</var>)</em></dt>
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<dd><p>The alignment (log base 2) to put in front of <var>label</var>, which is
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a common destination of jumps and has no fallthru incoming edge.
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</p>
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<p>This macro need not be defined if you don’t want any special alignment
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to be done at such a time. Most machine descriptions do not currently
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define the macro.
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</p>
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<p>Unless it’s necessary to inspect the <var>label</var> parameter, it is better
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to set the variable <var>align_jumps</var> in the target’s
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<code>TARGET_OPTION_OVERRIDE</code>. Otherwise, you should try to honor the user’s
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selection in <var>align_jumps</var> in a <code>JUMP_ALIGN</code> implementation.
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</p></dd></dl>
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<dl>
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<dt><a name="index-TARGET_005fASM_005fJUMP_005fALIGN_005fMAX_005fSKIP"></a>Target Hook: <em>int</em> <strong>TARGET_ASM_JUMP_ALIGN_MAX_SKIP</strong> <em>(rtx_insn *<var>label</var>)</em></dt>
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<dd><p>The maximum number of bytes to skip before <var>label</var> when applying
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<code>JUMP_ALIGN</code>. This works only if
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<code>ASM_OUTPUT_MAX_SKIP_ALIGN</code> is defined.
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</p></dd></dl>
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<dl>
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<dt><a name="index-LABEL_005fALIGN_005fAFTER_005fBARRIER"></a>Macro: <strong>LABEL_ALIGN_AFTER_BARRIER</strong> <em>(<var>label</var>)</em></dt>
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<dd><p>The alignment (log base 2) to put in front of <var>label</var>, which follows
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a <code>BARRIER</code>.
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</p>
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<p>This macro need not be defined if you don’t want any special alignment
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to be done at such a time. Most machine descriptions do not currently
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define the macro.
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</p></dd></dl>
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<dl>
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<dt><a name="index-TARGET_005fASM_005fLABEL_005fALIGN_005fAFTER_005fBARRIER_005fMAX_005fSKIP"></a>Target Hook: <em>int</em> <strong>TARGET_ASM_LABEL_ALIGN_AFTER_BARRIER_MAX_SKIP</strong> <em>(rtx_insn *<var>label</var>)</em></dt>
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<dd><p>The maximum number of bytes to skip before <var>label</var> when applying
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<code>LABEL_ALIGN_AFTER_BARRIER</code>. This works only if
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<code>ASM_OUTPUT_MAX_SKIP_ALIGN</code> is defined.
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</p></dd></dl>
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<dl>
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<dt><a name="index-LOOP_005fALIGN"></a>Macro: <strong>LOOP_ALIGN</strong> <em>(<var>label</var>)</em></dt>
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<dd><p>The alignment (log base 2) to put in front of <var>label</var> that heads
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a frequently executed basic block (usually the header of a loop).
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</p>
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<p>This macro need not be defined if you don’t want any special alignment
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to be done at such a time. Most machine descriptions do not currently
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define the macro.
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</p>
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<p>Unless it’s necessary to inspect the <var>label</var> parameter, it is better
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to set the variable <code>align_loops</code> in the target’s
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<code>TARGET_OPTION_OVERRIDE</code>. Otherwise, you should try to honor the user’s
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selection in <code>align_loops</code> in a <code>LOOP_ALIGN</code> implementation.
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</p></dd></dl>
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<dl>
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<dt><a name="index-TARGET_005fASM_005fLOOP_005fALIGN_005fMAX_005fSKIP"></a>Target Hook: <em>int</em> <strong>TARGET_ASM_LOOP_ALIGN_MAX_SKIP</strong> <em>(rtx_insn *<var>label</var>)</em></dt>
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<dd><p>The maximum number of bytes to skip when applying <code>LOOP_ALIGN</code> to
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<var>label</var>. This works only if <code>ASM_OUTPUT_MAX_SKIP_ALIGN</code> is
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defined.
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</p></dd></dl>
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<dl>
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<dt><a name="index-LABEL_005fALIGN"></a>Macro: <strong>LABEL_ALIGN</strong> <em>(<var>label</var>)</em></dt>
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<dd><p>The alignment (log base 2) to put in front of <var>label</var>.
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If <code>LABEL_ALIGN_AFTER_BARRIER</code> / <code>LOOP_ALIGN</code> specify a different alignment,
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the maximum of the specified values is used.
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</p>
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<p>Unless it’s necessary to inspect the <var>label</var> parameter, it is better
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to set the variable <code>align_labels</code> in the target’s
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<code>TARGET_OPTION_OVERRIDE</code>. Otherwise, you should try to honor the user’s
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selection in <code>align_labels</code> in a <code>LABEL_ALIGN</code> implementation.
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</p></dd></dl>
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<dl>
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<dt><a name="index-TARGET_005fASM_005fLABEL_005fALIGN_005fMAX_005fSKIP"></a>Target Hook: <em>int</em> <strong>TARGET_ASM_LABEL_ALIGN_MAX_SKIP</strong> <em>(rtx_insn *<var>label</var>)</em></dt>
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<dd><p>The maximum number of bytes to skip when applying <code>LABEL_ALIGN</code>
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to <var>label</var>. This works only if <code>ASM_OUTPUT_MAX_SKIP_ALIGN</code>
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is defined.
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</p></dd></dl>
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<dl>
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<dt><a name="index-ASM_005fOUTPUT_005fSKIP"></a>Macro: <strong>ASM_OUTPUT_SKIP</strong> <em>(<var>stream</var>, <var>nbytes</var>)</em></dt>
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<dd><p>A C statement to output to the stdio stream <var>stream</var> an assembler
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instruction to advance the location counter by <var>nbytes</var> bytes.
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Those bytes should be zero when loaded. <var>nbytes</var> will be a C
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expression of type <code>unsigned HOST_WIDE_INT</code>.
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</p></dd></dl>
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<dl>
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<dt><a name="index-ASM_005fNO_005fSKIP_005fIN_005fTEXT"></a>Macro: <strong>ASM_NO_SKIP_IN_TEXT</strong></dt>
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<dd><p>Define this macro if <code>ASM_OUTPUT_SKIP</code> should not be used in the
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text section because it fails to put zeros in the bytes that are skipped.
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This is true on many Unix systems, where the pseudo–op to skip bytes
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produces no-op instructions rather than zeros when used in the text
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section.
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</p></dd></dl>
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<dl>
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<dt><a name="index-ASM_005fOUTPUT_005fALIGN"></a>Macro: <strong>ASM_OUTPUT_ALIGN</strong> <em>(<var>stream</var>, <var>power</var>)</em></dt>
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<dd><p>A C statement to output to the stdio stream <var>stream</var> an assembler
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command to advance the location counter to a multiple of 2 to the
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<var>power</var> bytes. <var>power</var> will be a C expression of type <code>int</code>.
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</p></dd></dl>
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<dl>
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<dt><a name="index-ASM_005fOUTPUT_005fALIGN_005fWITH_005fNOP"></a>Macro: <strong>ASM_OUTPUT_ALIGN_WITH_NOP</strong> <em>(<var>stream</var>, <var>power</var>)</em></dt>
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<dd><p>Like <code>ASM_OUTPUT_ALIGN</code>, except that the “nop” instruction is used
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for padding, if necessary.
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</p></dd></dl>
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<dl>
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<dt><a name="index-ASM_005fOUTPUT_005fMAX_005fSKIP_005fALIGN"></a>Macro: <strong>ASM_OUTPUT_MAX_SKIP_ALIGN</strong> <em>(<var>stream</var>, <var>power</var>, <var>max_skip</var>)</em></dt>
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<dd><p>A C statement to output to the stdio stream <var>stream</var> an assembler
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command to advance the location counter to a multiple of 2 to the
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<var>power</var> bytes, but only if <var>max_skip</var> or fewer bytes are needed to
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satisfy the alignment request. <var>power</var> and <var>max_skip</var> will be
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a C expression of type <code>int</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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Previous: <a href="Exception-Region-Output.html#Exception-Region-Output" accesskey="p" rel="prev">Exception Region Output</a>, Up: <a href="Assembler-Format.html#Assembler-Format" accesskey="u" rel="up">Assembler Format</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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