On Wed, Aug 21, 2024 at 05:43:42PM +0200, Martin Uecker wrote: > Am Mittwoch, dem 21.08.2024 um 15:24 +0000 schrieb Qing Zhao: > > > > > > But if we changed it to return a void pointer, we could make this > > > a compile-time check: > > > > > > auto ret = __builtin_get_counted_by(__p->FAM); > > > > > > _Generic(ret, void*: (void)0, default: *ret = COUNT); > > > > Is there any benefit to return a void pointer than a SIZE_T pointer for > > the NULL pointer? > > Yes! You can test with _Generic (or __builtin_types_compatible_p) > at compile-time based on the type whether you can set *ret to COUNT > or not as in the example above. > > So it is not a weird run-time test which needs to be optimized > away.
I don't have a strong opinion here, but I would tend to agree that returning "void *" is a better signal that it is not valid. And I do really like the _Generic example there, which makes it even easier to do the "set if counted_by" action. -- Kees Cook
