__BUILTIN_OBJECT_SIZE(3)                      FreeBSD Library Functions Manual

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 clang(1) and gcc(1) built-in
     function that returns the size of the object referenced by ptr if known
     at compile time.  If the ptr expression has any side effects, then they
     will not be evaluated.

RETURN VALUES

     If the size of the object is not known or the ptr expression 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 can be pointed to by ptr when type & 2 == 0, and the minimum size
     when type & 2 != 0.

SEE ALSO

     clang(1), 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 code fortification (size-checked replacement functions)
     is currently disabled when optimization is off.

FreeBSD 15.1-STABLE-HBSD        April 27, 2024        __BUILTIN_OBJECT_SIZE(3)