1// run
2
3// Copyright 2018 The Go Authors. All rights reserved.
4// Use of this source code is governed by a BSD-style
5// license that can be found in the LICENSE file.
6
7package main
8
9import (
10	"runtime"
11)
12
13var nilp *int
14var forceHeap interface{}
15
16func main() {
17	// x is a pointer on the stack to heap-allocated memory.
18	x := new([32]*int)
19	forceHeap = x
20	forceHeap = nil
21
22	// Push a defer to be run when we panic below.
23	defer func() {
24		// Ignore the panic.
25		recover()
26		// Force a stack walk. Go 1.11 will fail because x is now
27		// considered live again.
28		runtime.GC()
29	}()
30	// Make x live at the defer's PC.
31	runtime.KeepAlive(x)
32
33	// x is no longer live. Garbage collect the [32]*int on the
34	// heap.
35	runtime.GC()
36	// At this point x's dead stack slot points to dead memory.
37
38	// Trigger a sigpanic. Since this is an implicit panic, we
39	// don't have an explicit liveness map here.
40	// Traceback used to use the liveness map of the most recent defer,
41	// but in that liveness map, x will be live again even though
42	// it points to dead memory. The fix is to use the liveness
43	// map of a deferreturn call instead.
44	*nilp = 0
45}
46