90 lines
4.3 KiB
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90 lines
4.3 KiB
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<title>Align - Using as</title>
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<meta name="description" content="Using as">
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<link title="Top" rel="start" href="index.html#Top">
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<link rel="up" href="Pseudo-Ops.html#Pseudo-Ops" title="Pseudo Ops">
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<link rel="prev" href="ABORT-_0028COFF_0029.html#ABORT-_0028COFF_0029" title="ABORT (COFF)">
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<link rel="next" href="Altmacro.html#Altmacro" title="Altmacro">
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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 Assembler "as".
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Copyright (C) 1991, 92, 93, 94, 95, 96, 97, 98, 99, 2000, 2001, 2002,
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2006, 2007 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 1.1
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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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<body>
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<div class="node">
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<p>
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<a name="Align"></a>Next: <a rel="next" accesskey="n" href="Altmacro.html#Altmacro">Altmacro</a>,
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Previous: <a rel="previous" accesskey="p" href="ABORT-_0028COFF_0029.html#ABORT-_0028COFF_0029">ABORT (COFF)</a>,
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Up: <a rel="up" accesskey="u" href="Pseudo-Ops.html#Pseudo-Ops">Pseudo Ops</a>
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<hr><br>
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</div>
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<h3 class="section">7.3 <code>.align </code><var>abs-expr</var><code>, </code><var>abs-expr</var><code>, </code><var>abs-expr</var></h3>
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<p><a name="index-padding-the-location-counter-275"></a><a name="index-_0040code_007balign_007d-directive-276"></a>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>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 some 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>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>The way the required alignment is specified varies from system to system.
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For the arc, hppa, i386 using ELF, i860, iq2000, m68k, or32,
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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 <span class="samp">.align 8</span> 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>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 <span class="samp">.align 3</span> 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>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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</body></html>
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