Yeah, that would work, but now that I think about it it would give the same effect as just using uintptr here for both fields. Is the C 'int' in this struct always 4 bytes on i386 and 8 bytes on amd64? (I thought C has a lot of leeway with the size of int.) It could import "C" and use `C.int`, but that seems a little much.

As for the underscores, I don't care that much for all-caps C names. I would've used a prefix like "sys_" or "c_", but just "_" is ok IMO.