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78 lines
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<title>ARM-Instruction-Set - Using as</title>
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<link rel="up" href="ARM-Syntax.html#ARM-Syntax" title="ARM Syntax">
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<link rel="next" href="ARM_002dChars.html#ARM_002dChars" title="ARM-Chars">
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<!--
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This file documents the GNU Assembler "as".
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Copyright (C) 1991-2015 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
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or any later version published by the Free Software Foundation;
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<div class="node">
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<a name="ARM-Instruction-Set"></a>
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<a name="ARM_002dInstruction_002dSet"></a>
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<p>
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Next: <a rel="next" accesskey="n" href="ARM_002dChars.html#ARM_002dChars">ARM-Chars</a>,
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Up: <a rel="up" accesskey="u" href="ARM-Syntax.html#ARM-Syntax">ARM Syntax</a>
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<hr>
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</div>
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<h5 class="subsubsection">9.4.2.1 Instruction Set Syntax</h5>
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<p>Two slightly different syntaxes are support for ARM and THUMB
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instructions. The default, <code>divided</code>, uses the old style where
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ARM and THUMB instructions had their own, separate syntaxes. The new,
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<code>unified</code> syntax, which can be selected via the <code>.syntax</code>
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directive, and has the following main features:
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<ul>
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<li>Immediate operands do not require a <code>#</code> prefix.
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<li>The <code>IT</code> instruction may appear, and if it does it is validated
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against subsequent conditional affixes. In ARM mode it does not
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generate machine code, in THUMB mode it does.
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<li>For ARM instructions the conditional affixes always appear at the end
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of the instruction. For THUMB instructions conditional affixes can be
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used, but only inside the scope of an <code>IT</code> instruction.
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<li>All of the instructions new to the V6T2 architecture (and later) are
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available. (Only a few such instructions can be written in the
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<code>divided</code> syntax).
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<li>The <code>.N</code> and <code>.W</code> suffixes are recognized and honored.
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<li>All instructions set the flags if and only if they have an <code>s</code>
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affix.
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</ul>
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</body></html>
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