+ -- when the return type is integral and word-sized or smaller, it
+ -- must be assigned as type ffi_arg (#3516). To see what type
+ -- libffi is expecting here, take a look in its own testsuite, e.g.
+ -- libffi/testsuite/libffi.call/cls_align_ulonglong.c
+ ffi_cResType
+ | is_ffi_arg_type = text "ffi_arg"
+ | otherwise = cResType
+ where
+ res_ty_key = getUnique (getName (typeTyCon res_hty))
+ is_ffi_arg_type = res_ty_key `notElem`
+ [floatTyConKey, doubleTyConKey,
+ int64TyConKey, word64TyConKey]
+