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83 lines
3.4 KiB
HTML
83 lines
3.4 KiB
HTML
4 years ago
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<html lang="en">
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<title>RX-Modifiers - 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="RX_002dDependent.html#RX_002dDependent" title="RX-Dependent">
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<link rel="prev" href="RX_002dOpts.html#RX_002dOpts" title="RX-Opts">
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<link rel="next" href="RX_002dDirectives.html#RX_002dDirectives" title="RX-Directives">
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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) 1991-2015 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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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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--></style>
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</head>
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<body>
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<div class="node">
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<a name="RX-Modifiers"></a>
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<a name="RX_002dModifiers"></a>
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<p>
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Next: <a rel="next" accesskey="n" href="RX_002dDirectives.html#RX_002dDirectives">RX-Directives</a>,
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Previous: <a rel="previous" accesskey="p" href="RX_002dOpts.html#RX_002dOpts">RX-Opts</a>,
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Up: <a rel="up" accesskey="u" href="RX_002dDependent.html#RX_002dDependent">RX-Dependent</a>
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<hr>
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</div>
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<h4 class="subsection">9.37.2 Symbolic Operand Modifiers</h4>
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<p><a name="index-RX-modifiers-1853"></a><a name="index-syntax_002c-RX-1854"></a><a name="index-g_t_0025gp-1855"></a>
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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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<pre class="smallexample"> %gp(symbol)
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</pre>
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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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<pre class="smallexample"> mov.W %gp(_foo)[%gpreg], r1
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</pre>
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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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<a name="index-g_t_0040samp_007b_0025gpreg_007d-1856"></a>
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<dl><dt><code>%gpreg</code><dd>The small data address register.
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<p><a name="index-g_t_0040samp_007b_0025pidreg_007d-1857"></a><br><dt><code>%pidreg</code><dd>The PID base address register.
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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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</body></html>
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