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Absolute-Literals-Directive.html 4.6KB

3 лет назад
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  59. Previous: <a href="Literal-Prefix-Directive.html#Literal-Prefix-Directive" accesskey="p" rel="prev">Literal Prefix Directive</a>, Up: <a href="Xtensa-Directives.html#Xtensa-Directives" accesskey="u" rel="up">Xtensa Directives</a> &nbsp; [<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>
  60. </div>
  61. <hr>
  62. <a name="absolute_002dliterals"></a>
  63. <h4 class="subsubsection">9.55.5.7 absolute-literals</h4>
  64. <a name="index-absolute_002dliterals-directive"></a>
  65. <a name="index-no_002dabsolute_002dliterals-directive"></a>
  66. <p>The <code>absolute-literals</code> and <code>no-absolute-literals</code>
  67. directives control the absolute vs. PC-relative mode for <code>L32R</code>
  68. instructions. These are relevant only for Xtensa configurations that
  69. include the absolute addressing option for <code>L32R</code> instructions.
  70. </p>
  71. <div class="smallexample">
  72. <pre class="smallexample"> .begin [no-]absolute-literals
  73. .end [no-]absolute-literals
  74. </pre></div>
  75. <p>These directives do not change the <code>L32R</code> mode&mdash;they only cause
  76. the assembler to emit the appropriate kind of relocation for <code>L32R</code>
  77. instructions and to place the literal values in the appropriate section.
  78. To change the <code>L32R</code> mode, the program must write the
  79. <code>LITBASE</code> special register. It is the programmer&rsquo;s responsibility
  80. to keep track of the mode and indicate to the assembler which mode is
  81. used in each region of code.
  82. </p>
  83. <p>If the Xtensa configuration includes the absolute <code>L32R</code> addressing
  84. option, the default is to assume absolute <code>L32R</code> addressing unless
  85. the &lsquo;<samp>--no-absolute-literals</samp>&rsquo; command-line option is specified.
  86. Otherwise, the default is to assume PC-relative <code>L32R</code> addressing.
  87. The <code>absolute-literals</code> directive can then be used to override
  88. the default determined by the command-line options.
  89. </p>
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