4 The GCC low-level runtime library
GCC provides a low-level runtime library, libgcc.a or libgcc_s.so.1 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.
Most of the routines in
libgcc 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.
libgcc also includes
routines for exception handling, and a handful of miscellaneous operations.
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.
GCC will also generate calls to C library routines, such as
memset, in some cases. The set of routines
that GCC may possibly use is documented in Other Builtins (Using the GNU Compiler Collection (GCC)).
These routines take arguments and return values of a specific machine
mode, not a specific C type. See Machine Modes, for an explanation
of this concept. For illustrative purposes, in this chapter the
floating point type
float is assumed to correspond to
long double to both
XFmode. Similarly, the integer types
unsigned int correspond to
unsigned long to
long long and
unsigned long long to