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  1. <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">

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  15. A GNU Manual

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  25. <title>PIC (GNU Compiler Collection (GCC) Internals)</title>

  26. 

  27. <meta name="description" content="PIC (GNU Compiler Collection (GCC) Internals)">

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  33. <link href="Option-Index.html#Option-Index" rel="index" title="Option Index">

  34. <link href="index.html#SEC_Contents" rel="contents" title="Table of Contents">

  35. <link href="Target-Macros.html#Target-Macros" rel="up" title="Target Macros">

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  69. <body lang="en">

  70. <a name="PIC"></a>

  71. <div class="header">

  72. <p>

  73. Next: <a href="Assembler-Format.html#Assembler-Format" accesskey="n" rel="next">Assembler Format</a>, Previous: <a href="Sections.html#Sections" accesskey="p" rel="prev">Sections</a>, Up: <a href="Target-Macros.html#Target-Macros" accesskey="u" rel="up">Target Macros</a> &nbsp; [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Option-Index.html#Option-Index" title="Index" rel="index">Index</a>]</p>

  74. </div>

  75. <hr>

  76. <a name="Position-Independent-Code"></a>

  77. <h3 class="section">18.19 Position Independent Code</h3>

  78. <a name="index-position-independent-code"></a>

  79. <a name="index-PIC"></a>

  80. 

  81. <p>This section describes macros that help implement generation of position

  82. independent code.  Simply defining these macros is not enough to

  83. generate valid PIC; you must also add support to the hook

  84. <code>TARGET_LEGITIMATE_ADDRESS_P</code> and to the macro

  85. <code>PRINT_OPERAND_ADDRESS</code>, as well as <code>LEGITIMIZE_ADDRESS</code>.  You

  86. must modify the definition of &lsquo;<samp>movsi</samp>&rsquo; to do something appropriate

  87. when the source operand contains a symbolic address.  You may also

  88. need to alter the handling of switch statements so that they use

  89. relative addresses.

  90. </p>

  91. <dl>

  92. <dt><a name="index-PIC_005fOFFSET_005fTABLE_005fREGNUM"></a>Macro: <strong>PIC_OFFSET_TABLE_REGNUM</strong></dt>

  93. <dd><p>The register number of the register used to address a table of static

  94. data addresses in memory.  In some cases this register is defined by a

  95. processor&rsquo;s &ldquo;application binary interface&rdquo; (ABI).  When this macro

  96. is defined, RTL is generated for this register once, as with the stack

  97. pointer and frame pointer registers.  If this macro is not defined, it

  98. is up to the machine-dependent files to allocate such a register (if

  99. necessary).  Note that this register must be fixed when in use (e.g.

  100. when <code>flag_pic</code> is true).

  101. </p></dd></dl>

  102. 

  103. <dl>

  104. <dt><a name="index-PIC_005fOFFSET_005fTABLE_005fREG_005fCALL_005fCLOBBERED"></a>Macro: <strong>PIC_OFFSET_TABLE_REG_CALL_CLOBBERED</strong></dt>

  105. <dd><p>A C expression that is nonzero if the register defined by

  106. <code>PIC_OFFSET_TABLE_REGNUM</code> is clobbered by calls.  If not defined,

  107. the default is zero.  Do not define

  108. this macro if <code>PIC_OFFSET_TABLE_REGNUM</code> is not defined.

  109. </p></dd></dl>

  110. 

  111. <dl>

  112. <dt><a name="index-LEGITIMATE_005fPIC_005fOPERAND_005fP"></a>Macro: <strong>LEGITIMATE_PIC_OPERAND_P</strong> <em>(<var>x</var>)</em></dt>

  113. <dd><p>A C expression that is nonzero if <var>x</var> is a legitimate immediate

  114. operand on the target machine when generating position independent code.

  115. You can assume that <var>x</var> satisfies <code>CONSTANT_P</code>, so you need not

  116. check this.  You can also assume <var>flag_pic</var> is true, so you need not

  117. check it either.  You need not define this macro if all constants

  118. (including <code>SYMBOL_REF</code>) can be immediate operands when generating

  119. position independent code.

  120. </p></dd></dl>

  121. 

  122. <hr>

  123. <div class="header">

  124. <p>

  125. Next: <a href="Assembler-Format.html#Assembler-Format" accesskey="n" rel="next">Assembler Format</a>, Previous: <a href="Sections.html#Sections" accesskey="p" rel="prev">Sections</a>, Up: <a href="Target-Macros.html#Target-Macros" accesskey="u" rel="up">Target Macros</a> &nbsp; [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Option-Index.html#Option-Index" title="Index" rel="index">Index</a>]</p>

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