}

// CheckPtrAlignmentNilPtr tests that checkptrAlignment doesn't crash
// on nil pointers (#47430).
func CheckPtrAlignmentNilPtr() {
	var do func(int)
	do = func(n int) {
		// Inflate the stack so runtime.shrinkstack gets called during GC
		if n > 0 {
			do(n - 1)
		}

		var p unsafe.Pointer
		_ = (*int)(p)
	}

	go func() {
		for {
			runtime.GC()
		}
	}()

	go func() {
		for i := 0; ; i++ {

}

// Maybe shrink the stack being used by gp.
//
// gp must be stopped and we must own its stack. It may be in
// _Grunning, but only if this is our own user G.
func shrinkstack(gp *g) {
	if gp.stack.lo == 0 {
		throw("missing stack in shrinkstack")
	}
	if s := readgstatus(gp); s&_Gscan == 0 {
		// We don't own the stack via _Gscan. We could still
		// own it if this is our own user G and we're on the

func ShrinkStackAndVerifyFramePointers() {
	before := stackPoisonCopy
	defer func() { stackPoisonCopy = before }()
	stackPoisonCopy = 1

	gp := getg()
	systemstack(func() {
		shrinkstack(gp)
	})
	// If our new stack contains frame pointers into the old stack, this will
	// crash because the old stack has been poisoned.
	FPCallers(make([]uintptr, 1024))
}

// releaseSudog to allocate and free them.
type sudog struct {
	// The following fields are protected by the hchan.lock of the
	// channel this sudog is blocking on. shrinkstack depends on
	// this for sudogs involved in channel ops.

	g *g

	next *sudog
	prev *sudog
	elem unsafe.Pointer // data element (may point to stack)

	p := getg().m.p.ptr()
	p.scannedStackSize += uint64(scannedSize)
	p.scannedStacks++

	if isShrinkStackSafe(gp) {
		// Shrink the stack if not much of it is being used.
		shrinkstack(gp)
	} else {
		// Otherwise, shrink the stack at the next sync safe point.
		gp.preemptShrink = true
	}

	var state stackScanState
	state.stack = gp.stack

	if stackTraceDebug {