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6.7 KiB
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128 lines
6.7 KiB
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<html lang="en">
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<head>
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<title>Literal 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 4.7">
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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="Transform-Directive.html#Transform-Directive" title="Transform Directive">
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<link rel="next" href="Literal-Position-Directive.html#Literal-Position-Directive" title="Literal Position 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, 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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under the terms of the GNU Free Documentation License, Version 1.1
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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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man end-->
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<style type="text/css"><!--
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span.roman { font-family: serif; font-weight: normal; }
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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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<p>
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<a name="Literal-Directive"></a>Next: <a rel="next" accesskey="n" href="Literal-Position-Directive.html#Literal-Position-Directive">Literal Position Directive</a>,
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Previous: <a rel="previous" accesskey="p" href="Transform-Directive.html#Transform-Directive">Transform 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><br>
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</div>
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<h5 class="subsubsection">9.36.5.4 literal</h5>
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<p><a name="index-_0040code_007bliteral_007d-directive-1890"></a>
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The <code>.literal</code> directive is used to define literal pool data, i.e.,
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read-only 32-bit data accessed via <code>L32R</code> instructions.
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<pre class="smallexample"> .literal <var>label</var>, <var>value</var>[, <var>value</var>...]
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</pre>
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<p>This directive is similar to the standard <code>.word</code> directive, except
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that the actual location of the literal data is determined by the
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assembler and linker, not by the position of the <code>.literal</code>
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directive. Using this directive gives the assembler freedom to locate
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the literal data in the most appropriate place and possibly to combine
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identical literals. For example, the code:
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<pre class="smallexample"> entry sp, 40
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.literal .L1, sym
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l32r a4, .L1
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</pre>
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<p>can be used to load a pointer to the symbol <code>sym</code> into register
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<code>a4</code>. The value of <code>sym</code> will not be placed between the
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<code>ENTRY</code> and <code>L32R</code> instructions; instead, the assembler puts
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the data in a literal pool.
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<p>Literal pools are placed by default in separate literal sections;
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however, when using the <span class="samp">--text-section-literals</span>
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option (see <a href="Xtensa-Options.html#Xtensa-Options">Command Line Options</a>), the literal
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pools for PC-relative mode <code>L32R</code> instructions
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are placed in the current section.<a rel="footnote" href="#fn-1" name="fnd-1"><sup>1</sup></a>
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These text section literal
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pools are created automatically before <code>ENTRY</code> instructions and
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manually after <span class="samp">.literal_position</span> directives (see <a href="Literal-Position-Directive.html#Literal-Position-Directive">literal_position</a>). If there are no preceding
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<code>ENTRY</code> instructions, explicit <code>.literal_position</code> directives
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must be used to place the text section literal pools; otherwise,
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<span class="command">as</span> will report an error.
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<p>When literals are placed in separate sections, the literal section names
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are derived from the names of the sections where the literals are
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defined. The base literal section names are <code>.literal</code> for
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PC-relative mode <code>L32R</code> instructions and <code>.lit4</code> for absolute
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mode <code>L32R</code> instructions (see <a href="Absolute-Literals-Directive.html#Absolute-Literals-Directive">absolute-literals</a>). These base names are used for literals defined in
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the default <code>.text</code> section. For literals defined in other
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sections or within the scope of a <code>literal_prefix</code> directive
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(see <a href="Literal-Prefix-Directive.html#Literal-Prefix-Directive">literal_prefix</a>), the following rules
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determine the literal section name:
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<ol type=1 start=1>
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<li>If the current section is a member of a section group, the literal
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section name includes the group name as a suffix to the base
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<code>.literal</code> or <code>.lit4</code> name, with a period to separate the base
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name and group name. The literal section is also made a member of the
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group.
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<li>If the current section name (or <code>literal_prefix</code> value) begins with
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“<code>.gnu.linkonce.</code><var>kind</var><code>.</code>”, the literal section name is formed
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by replacing “<code>.</code><var>kind</var>” with the base <code>.literal</code> or
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<code>.lit4</code> name. For example, for literals defined in a section named
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<code>.gnu.linkonce.t.func</code>, the literal section will be
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<code>.gnu.linkonce.literal.func</code> or <code>.gnu.linkonce.lit4.func</code>.
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<li>If the current section name (or <code>literal_prefix</code> value) ends with
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<code>.text</code>, the literal section name is formed by replacing that
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suffix with the base <code>.literal</code> or <code>.lit4</code> name. For example,
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for literals defined in a section named <code>.iram0.text</code>, the literal
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section will be <code>.iram0.literal</code> or <code>.iram0.lit4</code>.
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<li>If none of the preceding conditions apply, the literal section name is
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formed by adding the base <code>.literal</code> or <code>.lit4</code> name as a
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suffix to the current section name (or <code>literal_prefix</code> value).
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</ol>
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<div class="footnote">
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<hr>
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<h4>Footnotes</h4><p class="footnote"><small>[<a name="fn-1" href="#fnd-1">1</a>]</small> Literals for the
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<code>.init</code> and <code>.fini</code> sections are always placed in separate
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sections, even when <span class="samp">--text-section-literals</span> is enabled.</p>
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<p><hr></div>
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</body></html>
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