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89 lines
4.0 KiB
HTML
89 lines
4.0 KiB
HTML
4 years ago
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<title>Literal Position Directive - Using as</title>
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<meta http-equiv="Content-Type" content="text/html">
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<meta name="description" content="Using as">
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<meta name="generator" content="makeinfo 4.13">
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<link title="Top" rel="start" href="index.html#Top">
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<link rel="up" href="Xtensa-Directives.html#Xtensa-Directives" title="Xtensa Directives">
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<link rel="prev" href="Literal-Directive.html#Literal-Directive" title="Literal Directive">
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<link rel="next" href="Literal-Prefix-Directive.html#Literal-Prefix-Directive" title="Literal Prefix Directive">
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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="Literal-Position-Directive"></a>
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<p>
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Next: <a rel="next" accesskey="n" href="Literal-Prefix-Directive.html#Literal-Prefix-Directive">Literal Prefix Directive</a>,
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Previous: <a rel="previous" accesskey="p" href="Literal-Directive.html#Literal-Directive">Literal Directive</a>,
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Up: <a rel="up" accesskey="u" href="Xtensa-Directives.html#Xtensa-Directives">Xtensa Directives</a>
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<hr>
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</div>
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<h5 class="subsubsection">9.52.5.5 literal_position</h5>
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<p><a name="index-g_t_0040code_007bliteral_005fposition_007d-directive-2495"></a>
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When using ‘<samp><span class="samp">--text-section-literals</span></samp>’ to place literals inline
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in the section being assembled, the <code>.literal_position</code> directive
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can be used to mark a potential location for a literal pool.
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<pre class="smallexample"> .literal_position
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</pre>
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<p>The <code>.literal_position</code> directive is ignored when the
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‘<samp><span class="samp">--text-section-literals</span></samp>’ option is not used or when
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<code>L32R</code> instructions use the absolute addressing mode.
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<p>The assembler will automatically place text section literal pools
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before <code>ENTRY</code> instructions, so the <code>.literal_position</code>
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directive is only needed to specify some other location for a literal
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pool. You may need to add an explicit jump instruction to skip over an
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inline literal pool.
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<p>For example, an interrupt vector does not begin with an <code>ENTRY</code>
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instruction so the assembler will be unable to automatically find a good
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place to put a literal pool. Moreover, the code for the interrupt
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vector must be at a specific starting address, so the literal pool
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cannot come before the start of the code. The literal pool for the
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vector must be explicitly positioned in the middle of the vector (before
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any uses of the literals, due to the negative offsets used by
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PC-relative <code>L32R</code> instructions). The <code>.literal_position</code>
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directive can be used to do this. In the following code, the literal
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for ‘<samp><span class="samp">M</span></samp>’ will automatically be aligned correctly and is placed after
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the unconditional jump.
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<pre class="smallexample"> .global M
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code_start:
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j continue
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.literal_position
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.align 4
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continue:
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movi a4, M
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</pre>
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</body></html>
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