runtime: zero saved frame pointer when reusing goroutine stack on arm64

When a goroutine stack is reused on arm64, the spot on the stack where
the "caller's" frame pointer goes for the topmost frame should be
explicitly zeroed. Otherwise, the frame pointer check in adjustframe
with debugCheckBP enabled will fail on the topmost frame of a call stack
the first time a reused stack is grown.

Updates #39524, #58432

Change-Id: Ic1210dc005e3ecdbf9cd5d7b98846566e56df8f5
Reviewed-on: https://go-review.googlesource.com/c/go/+/481636
Reviewed-by: Felix Geisendörfer <[email protected]>
Reviewed-by: Dmitri Shuralyov <[email protected]>
Reviewed-by: Cherry Mui <[email protected]>
TryBot-Result: Gopher Robot <[email protected]>
Auto-Submit: Dmitri Shuralyov <[email protected]>

Author: nsrip-dd

src/runtime/proc.go

@@ -4540,12 +4540,14 @@ func newproc1(fn *funcval, callergp *g, callerpc uintptr) *g {
 	totalSize := uintptr(4*goarch.PtrSize + sys.MinFrameSize) // extra space in case of reads slightly beyond frame
 	totalSize = alignUp(totalSize, sys.StackAlign)
 	sp := newg.stack.hi - totalSize
-	spArg := sp
 	if usesLR {
 		// caller's LR
 		*(*uintptr)(unsafe.Pointer(sp)) = 0
 		prepGoExitFrame(sp)
-		spArg += sys.MinFrameSize
+	}
+	if GOARCH == "arm64" {
+		// caller's FP
+		*(*uintptr)(unsafe.Pointer(sp - goarch.PtrSize)) = 0
 	}
 
 	memclrNoHeapPointers(unsafe.Pointer(&newg.sched), unsafe.Sizeof(newg.sched))