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| <title>GNU Compiler Collection (GCC) Internals: Libgcc</title> |
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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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| <table class="menu" border="0" cellspacing="0"> |
| <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"> |
| </td></tr> |
| <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"> |
| </td></tr> |
| <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"> |
| </td></tr> |
| <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"> |
| </td></tr> |
| <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"> |
| </td></tr> |
| <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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