118 lines
5.2 KiB
HTML
118 lines
5.2 KiB
HTML
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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 Position Directive</title>
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<meta name="description" content="Using as: Literal Position Directive">
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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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<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">9.52.5.5 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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