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122 lines
5.8 KiB
HTML
122 lines
5.8 KiB
HTML
<!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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<!-- This file documents the GNU Assembler "as".
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Copyright (C) 1991-2019 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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-->
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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>Align (Using as)</title>
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<meta name="description" content="Align (Using as)">
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<meta name="keywords" content="Align (Using as)">
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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="AS-Index.html#AS-Index" rel="index" title="AS Index">
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<link href="index.html#SEC_Contents" rel="contents" title="Table of Contents">
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<link href="Pseudo-Ops.html#Pseudo-Ops" rel="up" title="Pseudo Ops">
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<link href="Altmacro.html#Altmacro" rel="next" title="Altmacro">
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<link href="ABORT-_0028COFF_0029.html#ABORT-_0028COFF_0029" rel="prev" title="ABORT (COFF)">
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<style type="text/css">
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a.summary-letter {text-decoration: none}
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kbd {font-style: oblique}
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ul.no-bullet {list-style: none}
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</style>
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</head>
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<body lang="en">
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<a name="Align"></a>
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<div class="header">
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<p>
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Next: <a href="Altmacro.html#Altmacro" accesskey="n" rel="next">Altmacro</a>, Previous: <a href="ABORT-_0028COFF_0029.html#ABORT-_0028COFF_0029" accesskey="p" rel="prev">ABORT (COFF)</a>, Up: <a href="Pseudo-Ops.html#Pseudo-Ops" accesskey="u" rel="up">Pseudo Ops</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="AS-Index.html#AS-Index" title="Index" rel="index">Index</a>]</p>
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</div>
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<hr>
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<a name="g_t_002ealign-abs_002dexpr_002c-abs_002dexpr_002c-abs_002dexpr"></a>
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<h3 class="section">7.3 <code>.align <var>abs-expr</var>, <var>abs-expr</var>, <var>abs-expr</var></code></h3>
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<a name="index-padding-the-location-counter"></a>
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<a name="index-align-directive"></a>
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<p>Pad the location counter (in the current subsection) to a particular storage
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boundary. The first expression (which must be absolute) is the alignment
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required, as described below.
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</p>
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<p>The second expression (also absolute) gives the fill value to be stored in the
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padding bytes. It (and the comma) may be omitted. If it is omitted, the
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padding bytes are normally zero. However, on most systems, if the section is
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marked as containing code and the fill value is omitted, the space is filled
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with no-op instructions.
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</p>
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<p>The third expression is also absolute, and is also optional. If it is present,
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it is the maximum number of bytes that should be skipped by this alignment
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directive. If doing the alignment would require skipping more bytes than the
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specified maximum, then the alignment is not done at all. You can omit the
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fill value (the second argument) entirely by simply using two commas after the
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required alignment; this can be useful if you want the alignment to be filled
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with no-op instructions when appropriate.
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</p>
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<p>The way the required alignment is specified varies from system to system.
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For the arc, hppa, i386 using ELF, iq2000, m68k, or1k,
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s390, sparc, tic4x, tic80 and xtensa, the first expression is the
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alignment request in bytes. For example ‘<samp>.align 8</samp>’ advances
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the location counter until it is a multiple of 8. If the location counter
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is already a multiple of 8, no change is needed. For the tic54x, the
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first expression is the alignment request in words.
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</p>
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<p>For other systems, including ppc, i386 using a.out format, arm and
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strongarm, it is the
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number of low-order zero bits the location counter must have after
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advancement. For example ‘<samp>.align 3</samp>’ advances the location
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counter until it a multiple of 8. If the location counter is already a
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multiple of 8, no change is needed.
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</p>
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<p>This inconsistency is due to the different behaviors of the various
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native assemblers for these systems which GAS must emulate.
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GAS also provides <code>.balign</code> and <code>.p2align</code> directives,
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described later, which have a consistent behavior across all
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architectures (but are specific to GAS).
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</p>
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<hr>
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<div class="header">
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<p>
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Next: <a href="Altmacro.html#Altmacro" accesskey="n" rel="next">Altmacro</a>, Previous: <a href="ABORT-_0028COFF_0029.html#ABORT-_0028COFF_0029" accesskey="p" rel="prev">ABORT (COFF)</a>, Up: <a href="Pseudo-Ops.html#Pseudo-Ops" accesskey="u" rel="up">Pseudo Ops</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="AS-Index.html#AS-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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