golang unsafe_test 代码
文件路径：/src/cmd/compile/internal/test/testdata/unsafe_test.go
/ Copyright 2015 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.
package main
import (
"runtime"
"testing"
"unsafe"
)
/ global pointer slot
var a *[8]uint
/ unfoldable true
var always = true
/ Test to make sure that a pointer value which is alive
/ across a call is retained, even when there are matching
/ conversions to/from uintptr around the call.
/ We arrange things very carefully to have to/from
/ conversions on either side of the call which cannot be
/ combined with any other conversions.
func f_ssa() *[8]uint {
/ Make x a uintptr pointing to where a points.
var x uintptr
if always {
x = uintptr(unsafe.Pointer(a))
} else {
x = 0
}
/ Clobber the global pointer. The only live ref
/ to the allocated object is now x.
a = nil
/ Convert to pointer so it should hold
/ the object live across GC call.
p := unsafe.Pointer(x)
/ Call gc.
runtime.GC()
/ Convert back to uintptr.
y := uintptr(p)
/ Mess with y so that the subsequent cast
/ to unsafe.Pointer can't be combined with the
/ uintptr cast above.
var z uintptr
if always {
z = y
} else {
z = 0
}
return (*[8]uint)(unsafe.Pointer(z))
}
/ g_ssa is the same as f_ssa, but with a bit of pointer
/ arithmetic for added insanity.
func g_ssa() *[7]uint {
/ Make x a uintptr pointing to where a points.
var x uintptr
if always {
x = uintptr(unsafe.Pointer(a))
} else {
x = 0
}
/ Clobber the global pointer. The only live ref
/ to the allocated object is now x.
a = nil
/ Offset x by one int.
x += unsafe.Sizeof(int(0))
/ Convert to pointer so it should hold
/ the object live across GC call.
p := unsafe.Pointer(x)
/ Call gc.
runtime.GC()
/ Convert back to uintptr.
y := uintptr(p)
/ Mess with y so that the subsequent cast
/ to unsafe.Pointer can't be combined with the
/ uintptr cast above.
var z uintptr
if always {
z = y
} else {
z = 0
}
return (*[7]uint)(unsafe.Pointer(z))
}
func testf(t *testing.T) {
a = new([8]uint)
for i := 0; i < 8; i++ {
a[i] = 0xabcd
}
c := f_ssa()
for i := 0; i < 8; i++ {
if c[i] != 0xabcd {
t.Fatalf("%d:%x\n", i, c[i])
}
}
}
func testg(t *testing.T) {
a = new([8]uint)
for i := 0; i < 8; i++ {
a[i] = 0xabcd
}
c := g_ssa()
for i := 0; i < 7; i++ {
if c[i] != 0xabcd {
t.Fatalf("%d:%x\n", i, c[i])
}
}
}
func alias_ssa(ui64 *uint64, ui32 *uint32) uint32 {
*ui32 = 0xffffffff
*ui64 = 0 / store
ret := *ui32 / load from same address, should be zero
*ui64 = 0xffffffffffffffff / store
return ret
}
func testdse(t *testing.T) {
x := int64(-1)
/ construct two pointers that alias one another
ui64 := (*uint64)(unsafe.Pointer(&x))
ui32 := (*uint32)(unsafe.Pointer(&x))
if want, got := uint32(0), alias_ssa(ui64, ui32); got != want {
t.Fatalf("alias_ssa: wanted %d, got %d\n", want, got)
}
}
func TestUnsafe(t *testing.T) {
testf(t)
testg(t)
testdse(t)
}