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.