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120 lines
4.4 KiB
HTML
120 lines
4.4 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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<!-- 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>RX-Modifiers (Using as)</title>
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<meta name="description" content="RX-Modifiers (Using as)">
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<meta name="keywords" content="RX-Modifiers (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="RX_002dDependent.html#RX_002dDependent" rel="up" title="RX-Dependent">
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<link href="RX_002dDirectives.html#RX_002dDirectives" rel="next" title="RX-Directives">
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<link href="RX_002dOpts.html#RX_002dOpts" rel="prev" title="RX-Opts">
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<style type="text/css">
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a.summary-letter {text-decoration: none}
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ul.no-bullet {list-style: none}
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-->
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</style>
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</head>
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<body lang="en">
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<a name="RX_002dModifiers"></a>
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<div class="header">
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<p>
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Next: <a href="RX_002dDirectives.html#RX_002dDirectives" accesskey="n" rel="next">RX-Directives</a>, Previous: <a href="RX_002dOpts.html#RX_002dOpts" accesskey="p" rel="prev">RX-Opts</a>, Up: <a href="RX_002dDependent.html#RX_002dDependent" accesskey="u" rel="up">RX-Dependent</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="Symbolic-Operand-Modifiers-3"></a>
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<h4 class="subsection">9.39.2 Symbolic Operand Modifiers</h4>
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<a name="index-RX-modifiers"></a>
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<a name="index-syntax_002c-RX"></a>
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<a name="index-_0025gp"></a>
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<p>The assembler supports one modifier when using symbol addresses
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in RX instruction operands. The general syntax is the following:
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</p>
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<div class="smallexample">
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<pre class="smallexample">%gp(symbol)
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</pre></div>
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<p>The modifier returns the offset from the <var>__gp</var> symbol to the
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specified symbol as a 16-bit value. The intent is that this offset
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should be used in a register+offset move instruction when generating
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references to small data. Ie, like this:
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</p>
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<div class="smallexample">
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<pre class="smallexample"> mov.W %gp(_foo)[%gpreg], r1
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</pre></div>
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<p>The assembler also supports two meta register names which can be used
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to refer to registers whose values may not be known to the
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programmer. These meta register names are:
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</p>
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<dl compact="compact">
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<dd>
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<a name="index-_0025gpreg"></a>
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</dd>
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<dt><code>%gpreg</code></dt>
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<dd><p>The small data address register.
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</p>
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<a name="index-_0025pidreg"></a>
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</dd>
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<dt><code>%pidreg</code></dt>
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<dd><p>The PID base address register.
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</p>
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</dd>
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</dl>
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<p>Both registers normally have the value r13, but this can change if
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some registers have been reserved for use by interrupt handlers or if
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both the small data limit and position independent data features are
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being used at the same time.
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</p>
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</body>
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</html>
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