93 lines
4.4 KiB
HTML
93 lines
4.4 KiB
HTML
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<title>Xtensa Directives - Using as</title>
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<link rel="up" href="Xtensa_002dDependent.html#Xtensa_002dDependent" title="Xtensa-Dependent">
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<link rel="prev" href="Xtensa-Relaxation.html#Xtensa-Relaxation" title="Xtensa Relaxation">
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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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or any later version published by the Free Software Foundation;
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</head>
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<body>
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<div class="node">
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<p>
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<a name="Xtensa-Directives"></a>Previous: <a rel="previous" accesskey="p" href="Xtensa-Relaxation.html#Xtensa-Relaxation">Xtensa Relaxation</a>,
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Up: <a rel="up" accesskey="u" href="Xtensa_002dDependent.html#Xtensa_002dDependent">Xtensa-Dependent</a>
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<hr><br>
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</div>
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<h4 class="subsection">9.36.5 Directives</h4>
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<p><a name="index-Xtensa-directives-1882"></a><a name="index-directives_002c-Xtensa-1883"></a>
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The Xtensa assembler supports a region-based directive syntax:
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<pre class="smallexample"> .begin <var>directive</var> [<var>options</var>]
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...
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.end <var>directive</var>
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</pre>
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<p>All the Xtensa-specific directives that apply to a region of code use
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this syntax.
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<p>The directive applies to code between the <code>.begin</code> and the
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<code>.end</code>. The state of the option after the <code>.end</code> reverts to
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what it was before the <code>.begin</code>.
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A nested <code>.begin</code>/<code>.end</code> region can further
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change the state of the directive without having to be aware of its
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outer state. For example, consider:
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<pre class="smallexample"> .begin no-transform
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L: add a0, a1, a2
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.begin transform
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M: add a0, a1, a2
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.end transform
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N: add a0, a1, a2
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.end no-transform
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</pre>
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<p>The <code>ADD</code> opcodes at <code>L</code> and <code>N</code> in the outer
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<code>no-transform</code> region both result in <code>ADD</code> machine instructions,
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but the assembler selects an <code>ADD.N</code> instruction for the
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<code>ADD</code> at <code>M</code> in the inner <code>transform</code> region.
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<p>The advantage of this style is that it works well inside macros which can
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preserve the context of their callers.
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<p>The following directives are available:
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<ul class="menu">
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<li><a accesskey="1" href="Schedule-Directive.html#Schedule-Directive">Schedule Directive</a>: Enable instruction scheduling.
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<li><a accesskey="2" href="Longcalls-Directive.html#Longcalls-Directive">Longcalls Directive</a>: Use Indirect Calls for Greater Range.
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<li><a accesskey="3" href="Transform-Directive.html#Transform-Directive">Transform Directive</a>: Disable All Assembler Transformations.
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<li><a accesskey="4" href="Literal-Directive.html#Literal-Directive">Literal Directive</a>: Intermix Literals with Instructions.
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<li><a accesskey="5" href="Literal-Position-Directive.html#Literal-Position-Directive">Literal Position Directive</a>: Specify Inline Literal Pool Locations.
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<li><a accesskey="6" href="Literal-Prefix-Directive.html#Literal-Prefix-Directive">Literal Prefix Directive</a>: Specify Literal Section Name Prefix.
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<li><a accesskey="7" href="Absolute-Literals-Directive.html#Absolute-Literals-Directive">Absolute Literals Directive</a>: Control PC-Relative vs. Absolute Literals.
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</ul>
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</body></html>
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