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
0and1. (size_t)0- for type
2and3.
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
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.