1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
|
// Copyright 2020 The gVisor Authors.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
package state
import (
"fmt"
"reflect"
"runtime"
"unsafe"
)
// reflectValueRWAddr is equivalent to obj.Addr(), except that the returned
// reflect.Value is usable in assignments even if obj was obtained by the use
// of unexported struct fields.
//
// Preconditions: obj.CanAddr().
func reflectValueRWAddr(obj reflect.Value) reflect.Value {
return reflect.NewAt(obj.Type(), unsafe.Pointer(obj.UnsafeAddr()))
}
// reflectValueRWSlice3 is equivalent to arr.Slice3(i, j, k), except that the
// returned reflect.Value is usable in assignments even if obj was obtained by
// the use of unexported struct fields.
//
// Preconditions:
// * arr.Kind() == reflect.Array.
// * i, j, k >= 0.
// * i <= j <= k <= arr.Len().
func reflectValueRWSlice3(arr reflect.Value, i, j, k int) reflect.Value {
if arr.Kind() != reflect.Array {
panic(fmt.Sprintf("arr has kind %v, wanted %v", arr.Kind(), reflect.Array))
}
if i < 0 || j < 0 || k < 0 {
panic(fmt.Sprintf("negative subscripts (%d, %d, %d)", i, j, k))
}
if i > j {
panic(fmt.Sprintf("subscript i (%d) > j (%d)", i, j))
}
if j > k {
panic(fmt.Sprintf("subscript j (%d) > k (%d)", j, k))
}
if k > arr.Len() {
panic(fmt.Sprintf("subscript k (%d) > array length (%d)", k, arr.Len()))
}
sliceTyp := reflect.SliceOf(arr.Type().Elem())
if i == arr.Len() {
// By precondition, i == j == k == arr.Len().
return reflect.MakeSlice(sliceTyp, 0, 0)
}
slh := reflect.SliceHeader{
// reflect.Value.CanAddr() == false for arrays, so we need to get the
// address from the first element of the array.
Data: arr.Index(i).UnsafeAddr(),
Len: j - i,
Cap: k - i,
}
slobj := reflect.NewAt(sliceTyp, unsafe.Pointer(&slh)).Elem()
// Before slobj is constructed, arr holds the only pointer-typed pointer to
// the array since reflect.SliceHeader.Data is a uintptr, so arr must be
// kept alive.
runtime.KeepAlive(arr)
return slobj
}
|
