mirror of
https://github.com/golang/go
synced 2024-11-18 10:54:40 -07:00
613383c765
Before, a slice with cap=0 or a string with len=0 might have its base pointer pointing beyond the actual slice/string data into the next block. The collector had to ignore slices and strings with cap=0 in order to avoid misinterpreting the base pointer. Now, a slice with cap=0 or a string with len=0 still has a base pointer pointing into the actual slice/string data, no matter what. The collector can now always scan the pointer, which means strings and slices are no longer special. Fixes #8404. LGTM=khr, josharian R=josharian, khr, dvyukov CC=golang-codereviews https://golang.org/cl/112570044
91 lines
1.9 KiB
Go
91 lines
1.9 KiB
Go
// run
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// Copyright 2014 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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package main
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import "unsafe"
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var (
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hello = "hello"
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bytes = []byte{1, 2, 3, 4, 5}
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ints = []int32{1, 2, 3, 4, 5}
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five = 5
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ok = true
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)
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func notOK() {
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if ok {
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println("BUG:")
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ok = false
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}
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}
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func checkString(desc, s string) {
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p1 := *(*uintptr)(unsafe.Pointer(&s))
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p2 := *(*uintptr)(unsafe.Pointer(&hello))
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if p1-p2 >= 5 {
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notOK()
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println("string", desc, "has invalid base")
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}
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}
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func checkBytes(desc string, s []byte) {
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p1 := *(*uintptr)(unsafe.Pointer(&s))
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p2 := *(*uintptr)(unsafe.Pointer(&bytes))
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if p1-p2 >= 5 {
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println("byte slice", desc, "has invalid base")
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}
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}
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func checkInts(desc string, s []int32) {
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p1 := *(*uintptr)(unsafe.Pointer(&s))
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p2 := *(*uintptr)(unsafe.Pointer(&ints))
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if p1-p2 >= 5*4 {
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println("int slice", desc, "has invalid base")
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}
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}
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func main() {
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{
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x := hello
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checkString("x", x)
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checkString("x[5:]", x[5:])
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checkString("x[five:]", x[five:])
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checkString("x[5:five]", x[5:five])
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checkString("x[five:5]", x[five:5])
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checkString("x[five:five]", x[five:five])
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checkString("x[1:][2:][2:]", x[1:][2:][2:])
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y := x[4:]
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checkString("y[1:]", y[1:])
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}
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{
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x := bytes
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checkBytes("x", x)
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checkBytes("x[5:]", x[5:])
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checkBytes("x[five:]", x[five:])
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checkBytes("x[5:five]", x[5:five])
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checkBytes("x[five:5]", x[five:5])
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checkBytes("x[five:five]", x[five:five])
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checkBytes("x[1:][2:][2:]", x[1:][2:][2:])
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y := x[4:]
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checkBytes("y[1:]", y[1:])
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}
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{
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x := ints
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checkInts("x", x)
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checkInts("x[5:]", x[5:])
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checkInts("x[five:]", x[five:])
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checkInts("x[5:five]", x[5:five])
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checkInts("x[five:5]", x[five:5])
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checkInts("x[five:five]", x[five:five])
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checkInts("x[1:][2:][2:]", x[1:][2:][2:])
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y := x[4:]
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checkInts("y[1:]", y[1:])
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}
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}
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