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
7// Make sure return values aren't scanned until they
8// are initialized, when calling functions and methods
9// via reflect.
10
11package main
12
13import (
14	"reflect"
15	"runtime"
16	"unsafe"
17)
18
19var badPtr uintptr
20
21var sink []byte
22
23func init() {
24	// Allocate large enough to use largeAlloc.
25	b := make([]byte, 1<<16-1)
26	sink = b // force heap allocation
27	//  Any space between the object and the end of page is invalid to point to.
28	badPtr = uintptr(unsafe.Pointer(&b[len(b)-1])) + 1
29}
30
31func f(d func() *byte) *byte {
32	// Initialize callee args section with a bad pointer.
33	g(badPtr)
34
35	// Then call a function which returns a pointer.
36	// That return slot starts out holding a bad pointer.
37	return d()
38}
39
40//go:noinline
41func g(x uintptr) {
42}
43
44type T struct {
45}
46
47func (t *T) Foo() *byte {
48	runtime.GC()
49	return nil
50}
51
52func main() {
53	// Functions
54	d := reflect.MakeFunc(reflect.TypeOf(func() *byte { return nil }),
55		func(args []reflect.Value) []reflect.Value {
56			runtime.GC()
57			return []reflect.Value{reflect.ValueOf((*byte)(nil))}
58		}).Interface().(func() *byte)
59	f(d)
60
61	// Methods
62	e := reflect.ValueOf(&T{}).Method(0).Interface().(func() *byte)
63	f(e)
64}
65