__builtin_object_size(3) - NetBSD Manual Pages

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__BUILTIN_OBJECT_SIZ... NetBSD Library Functions Manual__BUILTIN_OBJECT_SIZ...


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 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.

NetBSD 10.1                      July 18, 2012                     NetBSD 10.1