__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 min‐
imum size when type & 2 != 0.
SEE ALSOgcc(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
