Dan Willemsen | 38f2dba | 2016-07-08 14:54:35 -0700 | [diff] [blame] | 1 | // run |
| 2 | |
| 3 | // Copyright 2016 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 | // Liveness calculations were wrong for a result parameter pushed onto |
| 8 | // the heap in a function that used defer. Program would crash with |
| 9 | // runtime: bad pointer in frame main.A at 0xc4201e6838: 0x1 |
| 10 | |
| 11 | package main |
| 12 | |
| 13 | import "errors" |
| 14 | |
| 15 | var sink interface{} |
| 16 | |
| 17 | //go:noinline |
| 18 | func f(err *error) { |
| 19 | if err != nil { |
| 20 | sink = err |
| 21 | } |
| 22 | } |
| 23 | |
| 24 | //go:noinline |
| 25 | func A(n, m int64) (res int64, err error) { |
| 26 | defer f(&err) // output parameter's address escapes to a defer. |
| 27 | if n < 0 { |
| 28 | err = errors.New("No negative") |
| 29 | return |
| 30 | } |
| 31 | if n <= 1 { |
| 32 | res = n |
| 33 | return |
| 34 | } |
| 35 | res = B(m) // This call to B drizzles a little junk on the stack. |
| 36 | res, err = A(n-1, m) |
| 37 | res++ |
| 38 | return |
| 39 | } |
| 40 | |
| 41 | // B does a little bit of recursion dribbling not-zero onto the stack. |
| 42 | //go:noinline |
| 43 | func B(n int64) (res int64) { |
| 44 | if n <= 1 { // Prefer to leave a 1 on the stack. |
| 45 | return n |
| 46 | } |
| 47 | return 1 + B(n-1) |
| 48 | } |
| 49 | |
| 50 | func main() { |
| 51 | x, e := A(0, 0) |
| 52 | for j := 0; j < 4; j++ { // j controls amount of B's stack dribble |
| 53 | for i := 0; i < 1000; i++ { // try more and more recursion until stack growth occurs in newobject in prologue |
| 54 | x, e = A(int64(i), int64(j)) |
| 55 | } |
| 56 | } |
| 57 | _, _ = x, e |
| 58 | } |