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

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<a name="Position-Independent-Code"></a>
<h3 class="section">17.20 Position Independent Code</h3>
<a name="index-position-independent-code"></a>
<a name="index-PIC"></a>

<p>This section describes macros that help implement generation of position
independent code.  Simply defining these macros is not enough to
generate valid PIC; you must also add support to the hook
<code>TARGET_LEGITIMATE_ADDRESS_P</code> and to the macro
<code>PRINT_OPERAND_ADDRESS</code>, as well as <code>LEGITIMIZE_ADDRESS</code>.  You
must modify the definition of &lsquo;<samp>movsi</samp>&rsquo; to do something appropriate
when the source operand contains a symbolic address.  You may also
need to alter the handling of switch statements so that they use
relative addresses.
</p>
<dl>
<dt><a name="index-PIC_005fOFFSET_005fTABLE_005fREGNUM"></a>Macro: <strong>PIC_OFFSET_TABLE_REGNUM</strong></dt>
<dd><p>The register number of the register used to address a table of static
data addresses in memory.  In some cases this register is defined by a
processor&rsquo;s &ldquo;application binary interface&rdquo; (ABI).  When this macro
is defined, RTL is generated for this register once, as with the stack
pointer and frame pointer registers.  If this macro is not defined, it
is up to the machine-dependent files to allocate such a register (if
necessary).  Note that this register must be fixed when in use (e.g.
when <code>flag_pic</code> is true).
</p></dd></dl>

<dl>
<dt><a name="index-PIC_005fOFFSET_005fTABLE_005fREG_005fCALL_005fCLOBBERED"></a>Macro: <strong>PIC_OFFSET_TABLE_REG_CALL_CLOBBERED</strong></dt>
<dd><p>A C expression that is nonzero if the register defined by
<code>PIC_OFFSET_TABLE_REGNUM</code> is clobbered by calls.  If not defined,
the default is zero.  Do not define
this macro if <code>PIC_OFFSET_TABLE_REGNUM</code> is not defined.
</p></dd></dl>

<dl>
<dt><a name="index-LEGITIMATE_005fPIC_005fOPERAND_005fP"></a>Macro: <strong>LEGITIMATE_PIC_OPERAND_P</strong> <em>(<var>x</var>)</em></dt>
<dd><p>A C expression that is nonzero if <var>x</var> is a legitimate immediate
operand on the target machine when generating position independent code.
You can assume that <var>x</var> satisfies <code>CONSTANT_P</code>, so you need not
check this.  You can also assume <var>flag_pic</var> is true, so you need not
check it either.  You need not define this macro if all constants
(including <code>SYMBOL_REF</code>) can be immediate operands when generating
position independent code.
</p></dd></dl>

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