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<a name="The-GCC-low_002dlevel-runtime-library"></a>
<h2 class="chapter">4 The GCC low-level runtime library</h2>

<p>GCC provides a low-level runtime library, <samp>libgcc.a</samp> or
<samp>libgcc_s.so.1</samp> on some platforms.  GCC generates calls to
routines in this library automatically, whenever it needs to perform
some operation that is too complicated to emit inline code for.
</p>
<p>Most of the routines in <code>libgcc</code> handle arithmetic operations
that the target processor cannot perform directly.  This includes
integer multiply and divide on some machines, and all floating-point
and fixed-point operations on other machines.  <code>libgcc</code> also includes
routines for exception handling, and a handful of miscellaneous operations.
</p>
<p>Some of these routines can be defined in mostly machine-independent C.
Others must be hand-written in assembly language for each processor
that needs them.
</p>
<p>GCC will also generate calls to C library routines, such as
<code>memcpy</code> and <code>memset</code>, in some cases.  The set of routines
that GCC may possibly use is documented in <a href="http://gcc.gnu.org/onlinedocs/gcc/Other-Builtins.html#Other-Builtins">Other
Builtins</a> in <cite>Using the GNU Compiler Collection (GCC)</cite>.
</p>
<p>These routines take arguments and return values of a specific machine
mode, not a specific C type.  See <a href="Machine-Modes.html#Machine-Modes">Machine Modes</a>, for an explanation
of this concept.  For illustrative purposes, in this chapter the
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<tr><td align="left" valign="top">&bull; <a href="Integer-library-routines.html#Integer-library-routines" accesskey="1">Integer library routines</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">
</td></tr>
<tr><td align="left" valign="top">&bull; <a href="Soft-float-library-routines.html#Soft-float-library-routines" accesskey="2">Soft float library routines</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">
</td></tr>
<tr><td align="left" valign="top">&bull; <a href="Decimal-float-library-routines.html#Decimal-float-library-routines" accesskey="3">Decimal float library routines</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">
</td></tr>
<tr><td align="left" valign="top">&bull; <a href="Fixed_002dpoint-fractional-library-routines.html#Fixed_002dpoint-fractional-library-routines" accesskey="4">Fixed-point fractional library routines</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">
</td></tr>
<tr><td align="left" valign="top">&bull; <a href="Exception-handling-routines.html#Exception-handling-routines" accesskey="5">Exception handling routines</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">
</td></tr>
<tr><td align="left" valign="top">&bull; <a href="Miscellaneous-routines.html#Miscellaneous-routines" accesskey="6">Miscellaneous routines</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">
</td></tr>
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