// there's a preemption between this call and the next.
func gcTestMoveStackOnNextCall() {
	gp := getg()
	gp.stackguard0 = stackForceMove
}

// gcTestIsReachable performs a GC and returns a bit set where bit i
// is set if ptrs[i] is reachable.
func gcTestIsReachable(ptrs ...unsafe.Pointer) (mask uint64) {
	// This takes the pointers as unsafe.Pointers in order to keep
	// them live long enough for us to attach specials. After