Minix Man Pages

Man Page or Keyword Search:
Man Architecture
Apropos Keyword Search (all sections) Output format
home | help 
__BUILTIN_OBJECT_SIZE(3) BSD Library Functions Manual __BUILTIN_OBJECT_SIZE(3)

NAME
     __builtin_object_size -- return the size of the given object

SYNOPSIS
     size_t
     __builtin_object_size(void *ptr, int type);

DESCRIPTION
     The __builtin_object_size() function is a gcc(1) built-in function that
     returns the size of the ptr object if known at compile time and the
     object does not have any side effects.

RETURN VALUES
     If the size of the object is not known or it has side effects the
     __builtin_object_size() function returns:

           (size_t)-1  for type 0 and 1.

           (size_t)0   for type 2 and 3.

     If the size of the object is known, then the __builtin_object_size()
     function returns the maximum size of all the objects that the compiler
     knows that they can be pointed to by ptr when type & 2 == 0, and the
     minimum size when type & 2 != 0.

SEE ALSO
     gcc(1), __builtin_return_address(3), attribute(3), ssp(3)

HISTORY
     The __builtin_object_size() appeared in GCC 4.1.

CAVEATS
     This is a non-standard, compiler-specific extension.

     Note that currently the object size calculation pass is only done at -O1
     or above, meaning that this function always returns -1 when the optimizer
     is off.

     There are some discussions about always doing the object size pass, but
     the issue is that without the optimization pass data sizes are not going
     to be correct.

     For that reason currently code fortification (size-checked replacement
     functions) is disabled when optimization is off.

BSD                              July 18, 2012                             BSD
NAME | SYNOPSIS | DESCRIPTION | RETURN VALUES | SEE ALSO | HISTORY | CAVEATS