Trapping to the Mach kernel is done through one of the syscall0, syscall1, syscall2, syscall3, syscall4, or syscall miscops. The first argument to these miscops is the number of the Unix syscall that is to be invoked. Any other arguments the syscall requires are passed in order after the first one. Syscall0 accepts only the syscall number and no other arguments; syscall1 accepts the syscall number and a single argument to the syscall; etc. Syscall accepts the syscall number and five or more arguments to the Unix syscall. These syscalls generally return two values: the result twice if the syscall succeeded and a -1 and the Unix error code if the syscall failed.