mirror of
https://github.com/golang/go
synced 2024-09-05 07:54:46 +00:00
![Keith Randall](/assets/img/avatar_default.png)
Pointer arithemetic is done mod 2^32 on 386, so we can just drop the high bits of any large constant offsets. The bounds check will make sure wraparounds are never observed. Fixes #21655 Change-Id: I68ae5bbea9f02c73968ea2b21ca017e5ecb89223 Reviewed-on: https://go-review.googlesource.com/82675 Run-TryBot: Keith Randall <khr@golang.org> TryBot-Result: Gobot Gobot <gobot@golang.org> Reviewed-by: David Chase <drchase@google.com>
63 lines
1.5 KiB
Go
63 lines
1.5 KiB
Go
// compile
|
|
|
|
// Copyright 2017 The Go Authors. All rights reserved.
|
|
// Use of this source code is governed by a BSD-style
|
|
// license that can be found in the LICENSE file.
|
|
|
|
// Make sure assembly offsets don't get too large.
|
|
|
|
// To trigger issue21655, the index offset needs to be small
|
|
// enough to fit into an int32 (to get rewritten to an ADDQconst)
|
|
// but large enough to overflow an int32 after multiplying by the stride.
|
|
|
|
package main
|
|
|
|
func f1(a []int64, i int64) int64 {
|
|
return a[i+1<<30]
|
|
}
|
|
func f2(a []int32, i int64) int32 {
|
|
return a[i+1<<30]
|
|
}
|
|
func f3(a []int16, i int64) int16 {
|
|
return a[i+1<<30]
|
|
}
|
|
func f4(a []int8, i int64) int8 {
|
|
return a[i+1<<31]
|
|
}
|
|
func f5(a []float64, i int64) float64 {
|
|
return a[i+1<<30]
|
|
}
|
|
func f6(a []float32, i int64) float32 {
|
|
return a[i+1<<30]
|
|
}
|
|
|
|
// Note: Before the fix for issue 21655, f{1,2,5,6} made
|
|
// the compiler crash. f3 silently generated the wrong
|
|
// code, using an offset of -1<<31 instead of 1<<31.
|
|
// (This is due to the assembler accepting offsets
|
|
// like 0x80000000 and silently using them as
|
|
// signed 32 bit offsets.)
|
|
// f4 was ok, but testing it can't hurt.
|
|
|
|
func f7(ss []*string, i int) string {
|
|
const offset = 3 << 29 // 3<<29 * 4 = 3<<31 = 1<<31 mod 1<<32.
|
|
if i > offset {
|
|
return *ss[i-offset]
|
|
}
|
|
return ""
|
|
}
|
|
func f8(ss []*string, i int) string {
|
|
const offset = 3<<29 + 10
|
|
if i > offset {
|
|
return *ss[i-offset]
|
|
}
|
|
return ""
|
|
}
|
|
func f9(ss []*string, i int) string {
|
|
const offset = 3<<29 - 10
|
|
if i > offset {
|
|
return *ss[i-offset]
|
|
}
|
|
return ""
|
|
}
|