mirror of
https://github.com/golang/go
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4efa216c9d
Allow the user to construct slices that are larger than the Go heap as long as they don't overflow the address space. Updates #48798. Change-Id: I659c8334d04676e1f253b9c3cd499eab9b9f989a Reviewed-on: https://go-review.googlesource.com/c/go/+/355489 Trust: Matthew Dempsky <mdempsky@google.com> Run-TryBot: Matthew Dempsky <mdempsky@google.com> Reviewed-by: Ian Lance Taylor <iant@golang.org>
70 lines
1.5 KiB
Go
70 lines
1.5 KiB
Go
// run
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// Copyright 2021 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 (
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"math"
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"unsafe"
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)
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const maxUintptr = 1 << (8 * unsafe.Sizeof(uintptr(0)))
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func main() {
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var p [10]byte
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// unsafe.Add
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{
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p1 := unsafe.Pointer(&p[1])
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assert(unsafe.Add(p1, 1) == unsafe.Pointer(&p[2]))
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assert(unsafe.Add(p1, -1) == unsafe.Pointer(&p[0]))
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}
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// unsafe.Slice
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{
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s := unsafe.Slice(&p[0], len(p))
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assert(&s[0] == &p[0])
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assert(len(s) == len(p))
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assert(cap(s) == len(p))
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// nil pointer with zero length returns nil
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assert(unsafe.Slice((*int)(nil), 0) == nil)
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// nil pointer with positive length panics
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mustPanic(func() { _ = unsafe.Slice((*int)(nil), 1) })
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// negative length
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var neg int = -1
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mustPanic(func() { _ = unsafe.Slice(new(byte), neg) })
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// length too large
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var tooBig uint64 = math.MaxUint64
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mustPanic(func() { _ = unsafe.Slice(new(byte), tooBig) })
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// size overflows address space
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mustPanic(func() { _ = unsafe.Slice(new(uint64), maxUintptr/8) })
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mustPanic(func() { _ = unsafe.Slice(new(uint64), maxUintptr/8+1) })
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// sliced memory overflows address space
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last := (*byte)(unsafe.Pointer(^uintptr(0)))
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_ = unsafe.Slice(last, 1)
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mustPanic(func() { _ = unsafe.Slice(last, 2) })
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}
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}
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func assert(ok bool) {
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if !ok {
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panic("FAIL")
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}
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}
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func mustPanic(f func()) {
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defer func() {
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assert(recover() != nil)
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}()
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f()
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}
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