Sure platform specific things can be useful. But that's exactly what `syscall()` is. As far as I'm aware, other platforms don't have any real equivalent. On other platforms syscalls must be made via libraries (as Go rather famously found out the hard way).
Doesn't most platforms have a reasonably stable interface for functions that are supposed to be reached from userspace? When does it actually matter if that border coincide with where execution privileges are raised?
