gcc/doc/gccint/the-gcc-low-level-runtime-library.rst

   1 ..
   2   Copyright 1988-2022 Free Software Foundation, Inc.
   3   This is part of the GCC manual.
   4   For copying conditions, see the copyright.rst file.
   5
   6   Contributed by Aldy Hernandez <aldy@quesejoda.com>
   7
   8 .. _libgcc:
   9
  10 The GCC low-level runtime library
  11 ---------------------------------
  12
  13 GCC provides a low-level runtime library, :samp:`libgcc.a` or
  14 :samp:`libgcc_s.so.1` on some platforms.  GCC generates calls to
  15 routines in this library automatically, whenever it needs to perform
  16 some operation that is too complicated to emit inline code for.
  17
  18 Most of the routines in ``libgcc`` handle arithmetic operations
  19 that the target processor cannot perform directly.  This includes
  20 integer multiply and divide on some machines, and all floating-point
  21 and fixed-point operations on other machines.  ``libgcc`` also includes
  22 routines for exception handling, and a handful of miscellaneous operations.
  23
  24 Some of these routines can be defined in mostly machine-independent C.
  25 Others must be hand-written in assembly language for each processor
  26 that needs them.
  27
  28 GCC will also generate calls to C library routines, such as
  29 ``memcpy`` and ``memset``, in some cases.  The set of routines
  30 that GCC may possibly use is documented in :ref:`gcc:other-builtins`.
  31
  32 These routines take arguments and return values of a specific machine
  33 mode, not a specific C type.  See :ref:`machine-modes`, for an explanation
  34 of this concept.  For illustrative purposes, in this chapter the
  35 floating point type ``float`` is assumed to correspond to ``SFmode`` ;
  36 ``double`` to ``DFmode`` ; and ``long double`` to both
  37 ``TFmode`` and ``XFmode``.  Similarly, the integer types ``int``
  38 and ``unsigned int`` correspond to ``SImode`` ; ``long`` and
  39 ``unsigned long`` to ``DImode`` ; and ``long long`` and
  40 ``unsigned long long`` to ``TImode``.
  41
  42 .. toctree::
  43   :maxdepth: 2
  44
  45   the-gcc-low-level-runtime-library/routines-for-integer-arithmetic
  46   the-gcc-low-level-runtime-library/routines-for-floating-point-emulation
  47   the-gcc-low-level-runtime-library/routines-for-decimal-floating-point-emulation
  48   the-gcc-low-level-runtime-library/routines-for-fixed-point-fractional-emulation
  49   the-gcc-low-level-runtime-library/language-independent-routines-for-exception-handling
  50   the-gcc-low-level-runtime-library/miscellaneous-runtime-library-routines