PT_STEP
if (ptrace(PT_STEP, proc_getpid(phdl), (caddr_t)1, 0) < 0) {
error = kern_ptrace(td, PT_STEP, pid, (void *)1, sig);
case PT_STEP:
case PT_STEP:
case PT_STEP:
REQUIRE_EQ(ptrace(PT_STEP, fpid, (caddr_t)1, SIGUSR1), 0);
REQUIRE_EQ(ptrace(PT_STEP, fpid, (caddr_t)1, 0), 0);