164 lines
8.3 KiB
HTML
164 lines
8.3 KiB
HTML
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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) 1991-2016 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 5.2, http://www.gnu.org/software/texinfo/ -->
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<head>
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<title>Using as: Literal Directive</title>
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<meta name="description" content="Using as: Literal Directive">
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<meta name="keywords" content="Using as: Literal Directive">
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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="Xtensa-Directives.html#Xtensa-Directives" rel="up" title="Xtensa Directives">
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<link href="Literal-Position-Directive.html#Literal-Position-Directive" rel="next" title="Literal Position Directive">
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<link href="Transform-Directive.html#Transform-Directive" rel="prev" title="Transform Directive">
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<style type="text/css">
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<!--
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a.summary-letter {text-decoration: none}
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blockquote.smallquotation {font-size: smaller}
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div.display {margin-left: 3.2em}
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div.example {margin-left: 3.2em}
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div.indentedblock {margin-left: 3.2em}
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div.lisp {margin-left: 3.2em}
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div.smalldisplay {margin-left: 3.2em}
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div.smallexample {margin-left: 3.2em}
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div.smallindentedblock {margin-left: 3.2em; font-size: smaller}
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div.smalllisp {margin-left: 3.2em}
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kbd {font-style:oblique}
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pre.display {font-family: inherit}
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pre.format {font-family: inherit}
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pre.menu-comment {font-family: serif}
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pre.menu-preformatted {font-family: serif}
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pre.smalldisplay {font-family: inherit; font-size: smaller}
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pre.smallexample {font-size: smaller}
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pre.smallformat {font-family: inherit; font-size: smaller}
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pre.smalllisp {font-size: smaller}
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span.nocodebreak {white-space:nowrap}
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span.nolinebreak {white-space:nowrap}
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span.roman {font-family:serif; font-weight:normal}
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span.sansserif {font-family:sans-serif; font-weight:normal}
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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" bgcolor="#FFFFFF" text="#000000" link="#0000FF" vlink="#800080" alink="#FF0000">
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<a name="Literal-Directive"></a>
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<div class="header">
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<p>
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Next: <a href="Literal-Position-Directive.html#Literal-Position-Directive" accesskey="n" rel="next">Literal Position Directive</a>, Previous: <a href="Transform-Directive.html#Transform-Directive" accesskey="p" rel="prev">Transform Directive</a>, Up: <a href="Xtensa-Directives.html#Xtensa-Directives" accesskey="u" rel="up">Xtensa Directives</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="literal"></a>
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<h4 class="subsubsection">9.52.5.4 literal</h4>
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<a name="index-literal-directive"></a>
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<p>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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</p>
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<div class="smallexample">
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<pre class="smallexample"> .literal <var>label</var>, <var>value</var>[, <var>value</var>…]
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</pre></div>
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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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</p>
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<div class="smallexample">
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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></div>
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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>
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<p>Literal pools are placed by default in separate literal sections;
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however, when using the ‘<samp>--text-section-literals</samp>’
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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 name="DOCF3" href="#FOOT3"><sup>3</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 ‘<samp>.literal_position</samp>’ 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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<code>as</code> will report an error.
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</p>
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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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</p>
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<ol>
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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><li> If the current section name (or <code>literal_prefix</code> value) begins with
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“<code>.gnu.linkonce.<var>kind</var>.</code>”, the literal section name is formed
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by replacing “<code>.<var>kind</var></code>” 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><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><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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</li></ol>
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<div class="footnote">
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<hr>
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<h4 class="footnotes-heading">Footnotes</h4>
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<h3><a name="FOOT3" href="#DOCF3">(3)</a></h3>
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<p>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 ‘<samp>--text-section-literals</samp>’ is enabled.</p>
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</div>
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<hr>
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<div class="header">
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<p>
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Next: <a href="Literal-Position-Directive.html#Literal-Position-Directive" accesskey="n" rel="next">Literal Position Directive</a>, Previous: <a href="Transform-Directive.html#Transform-Directive" accesskey="p" rel="prev">Transform Directive</a>, Up: <a href="Xtensa-Directives.html#Xtensa-Directives" accesskey="u" rel="up">Xtensa Directives</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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</body>
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</html>
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