// queued for gp.
func wantAsyncPreempt(gp *g) bool {
	// Check both the G and the P.
	return (gp.preempt || gp.m.p != 0 && gp.m.p.ptr().preempt) && readgstatus(gp)&^_Gscan == _Grunning
}

// isAsyncSafePoint reports whether gp at instruction PC is an
// asynchronous safe point. This indicates that:
//
// 1. It's safe to suspend gp and conservatively scan its stack and

	unlock(&suspendLock)

	// Does it want a preemption and is it safe to preempt?
	gp := gFromSP(mp, c.sp())
	if gp != nil && wantAsyncPreempt(gp) {
		if ok, newpc := isAsyncSafePoint(gp, c.ip(), c.sp(), c.lr()); ok {
			// Inject call to asyncPreempt
			targetPC := abi.FuncPCABI0(asyncPreempt)
			switch GOARCH {
			default:
				throw("unsupported architecture")
			case "386", "amd64":

// doSigPreempt handles a preemption signal on gp.
func doSigPreempt(gp *g, ctxt *sigctxt) {
	// Check if this G wants to be preempted and is safe to
	// preempt.
	if wantAsyncPreempt(gp) {
		if ok, newpc := isAsyncSafePoint(gp, ctxt.sigpc(), ctxt.sigsp(), ctxt.siglr()); ok {
			// Adjust the PC and inject a call to asyncPreempt.
			ctxt.pushCall(abi.FuncPCABI0(asyncPreempt), newpc)
		}
	}

	// Acknowledge the preemption.

		// during the stack growth check. In that case, the function has
		// not yet had a chance to do any writes to SP and is safe to unwind.
		// isAsyncSafePoint does not allow assembly functions to be async preempted,
		// and preemptPark double-checks that SPWRITE functions are not async preempted.
		// So for GC stack traversal, we can safely ignore SPWRITE for the innermost frame,

		dumpgstatus(gp)
		throw("bad g status")
	}

	if gp.asyncSafePoint {
		// Double-check that async preemption does not
		// happen in SPWRITE assembly functions.
		// isAsyncSafePoint must exclude this case.
		f := findfunc(gp.sched.pc)
		if !f.valid() {
			throw("preempt at unknown pc")
		}
		if f.flag&abi.FuncFlagSPWrite != 0 {