1// run
2
3// Copyright 2017 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
7// Issue 19078: liveness & zero-initialization of results
8// when there is a defer.
9package main
10
11import "unsafe"
12
13func main() {
14	// Construct an invalid pointer.  We do this by
15	// making a pointer which points to the unused space
16	// between the last 48-byte object in a span and the
17	// end of the span (there are 32 unused bytes there).
18	p := new([48]byte)              // make a 48-byte object
19	sink = &p                       // escape it, so it allocates for real
20	u := uintptr(unsafe.Pointer(p)) // get its address
21	u = u >> 13 << 13               // round down to page size
22	u += 1<<13 - 1                  // add almost a page
23
24	for i := 0; i < 1000000; i++ {
25		_ = identity(u)         // installs u at return slot
26		_ = liveReturnSlot(nil) // incorrectly marks return slot as live
27	}
28}
29
30//go:noinline
31func liveReturnSlot(x *int) *int {
32	defer func() {}() // causes return slot to be marked live
33	sink = &x         // causes x to be moved to the heap, triggering allocation
34	return x
35}
36
37//go:noinline
38func identity(x uintptr) uintptr {
39	return x
40}
41
42var sink interface{}
43