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<title>GNU Compiler Collection (GCC) Internals: Libgcc</title>
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<a name="Libgcc"></a>
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<p>
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Next: <a href="Languages.html#Languages" accesskey="n" rel="next">Languages</a>, Previous: <a href="Interface.html#Interface" accesskey="p" rel="prev">Interface</a>, Up: <a href="index.html#Top" accesskey="u" rel="up">Top</a> [<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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<hr>
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<a name="The-GCC-low_002dlevel-runtime-library"></a>
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<h2 class="chapter">4 The GCC low-level runtime library</h2>
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<p>GCC provides a low-level runtime library, <samp>libgcc.a</samp> or
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<samp>libgcc_s.so.1</samp> on some platforms. GCC generates calls to
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routines in this library automatically, whenever it needs to perform
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some operation that is too complicated to emit inline code for.
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</p>
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<p>Most of the routines in <code>libgcc</code> handle arithmetic operations
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that the target processor cannot perform directly. This includes
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integer multiply and divide on some machines, and all floating-point
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and fixed-point operations on other machines. <code>libgcc</code> also includes
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routines for exception handling, and a handful of miscellaneous operations.
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</p>
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<p>Some of these routines can be defined in mostly machine-independent C.
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Others must be hand-written in assembly language for each processor
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that needs them.
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</p>
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<p>GCC will also generate calls to C library routines, such as
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<code>memcpy</code> and <code>memset</code>, in some cases. The set of routines
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that GCC may possibly use is documented in <a href="http://gcc.gnu.org/onlinedocs/gcc/Other-Builtins.html#Other-Builtins">Other
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Builtins</a> in <cite>Using the GNU Compiler Collection (GCC)</cite>.
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</p>
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<p>These routines take arguments and return values of a specific machine
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mode, not a specific C type. See <a href="Machine-Modes.html#Machine-Modes">Machine Modes</a>, for an explanation
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of this concept. For illustrative purposes, in this chapter the
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floating point type <code>float</code> is assumed to correspond to <code>SFmode</code>;
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<code>double</code> to <code>DFmode</code>; and <code>long double<!-- /@w --></code> to both
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<code>TFmode</code> and <code>XFmode</code>. Similarly, the integer types <code>int</code>
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</p>
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<table class="menu" border="0" cellspacing="0">
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<tr><td align="left" valign="top">• <a href="Integer-library-routines.html#Integer-library-routines" accesskey="1">Integer library routines</a>:</td><td> </td><td align="left" valign="top">
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</td></tr>
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<tr><td align="left" valign="top">• <a href="Soft-float-library-routines.html#Soft-float-library-routines" accesskey="2">Soft float library routines</a>:</td><td> </td><td align="left" valign="top">
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</td></tr>
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<tr><td align="left" valign="top">• <a href="Decimal-float-library-routines.html#Decimal-float-library-routines" accesskey="3">Decimal float library routines</a>:</td><td> </td><td align="left" valign="top">
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</td></tr>
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<tr><td align="left" valign="top">• <a href="Fixed_002dpoint-fractional-library-routines.html#Fixed_002dpoint-fractional-library-routines" accesskey="4">Fixed-point fractional library routines</a>:</td><td> </td><td align="left" valign="top">
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</td></tr>
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<tr><td align="left" valign="top">• <a href="Exception-handling-routines.html#Exception-handling-routines" accesskey="5">Exception handling routines</a>:</td><td> </td><td align="left" valign="top">
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</td></tr>
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<tr><td align="left" valign="top">• <a href="Miscellaneous-routines.html#Miscellaneous-routines" accesskey="6">Miscellaneous routines</a>:</td><td> </td><td align="left" valign="top">
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</td></tr>
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</table>
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<p>
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Next: <a href="Languages.html#Languages" accesskey="n" rel="next">Languages</a>, Previous: <a href="Interface.html#Interface" accesskey="p" rel="prev">Interface</a>, Up: <a href="index.html#Top" accesskey="u" rel="up">Top</a> [<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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