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117 lines
5.1 KiB
HTML
117 lines
5.1 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>Literal Position Directive (Using as)</title>
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<meta name="description" content="Literal Position Directive (Using as)">
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<meta name="keywords" content="Literal Position Directive (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="Xtensa-Directives.html#Xtensa-Directives" rel="up" title="Xtensa Directives">
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<link href="Literal-Prefix-Directive.html#Literal-Prefix-Directive" rel="next" title="Literal Prefix Directive">
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<link href="Literal-Directive.html#Literal-Directive" rel="prev" title="Literal 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.indentedblock {margin-right: 0em}
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blockquote.smallindentedblock {margin-right: 0em; font-size: smaller}
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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.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.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.nolinebreak {white-space: nowrap}
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span.roman {font-family: initial; 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">
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<a name="Literal-Position-Directive"></a>
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<div class="header">
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<p>
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Next: <a href="Literal-Prefix-Directive.html#Literal-Prefix-Directive" accesskey="n" rel="next">Literal Prefix Directive</a>, Previous: <a href="Literal-Directive.html#Literal-Directive" accesskey="p" rel="prev">Literal 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_005fposition"></a>
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<h4 class="subsubsection">9.54.5.5 literal_position</h4>
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<a name="index-literal_005fposition-directive"></a>
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<p>When using ‘<samp>--text-section-literals</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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</p>
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<div class="smallexample">
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<pre class="smallexample"> .literal_position
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</pre></div>
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<p>The <code>.literal_position</code> directive is ignored when the
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‘<samp>--text-section-literals</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>
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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>
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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>M</samp>’ will automatically be aligned correctly and is placed after
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the unconditional jump.
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</p>
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<div class="smallexample">
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<pre class="smallexample"> .global M
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code_start:
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</pre><pre class="smallexample"> j continue
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.literal_position
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.align 4
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</pre><pre class="smallexample">continue:
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movi a4, M
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</pre></div>
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</body>
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</html>
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