77 lines
2.4 KiB
Go
77 lines
2.4 KiB
Go
// Copyright 2020 The gVisor Authors.
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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package state
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import (
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"fmt"
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"reflect"
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"runtime"
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"unsafe"
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)
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// reflectValueRWAddr is equivalent to obj.Addr(), except that the returned
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// reflect.Value is usable in assignments even if obj was obtained by the use
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// of unexported struct fields.
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//
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// Preconditions: obj.CanAddr().
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func reflectValueRWAddr(obj reflect.Value) reflect.Value {
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return reflect.NewAt(obj.Type(), unsafe.Pointer(obj.UnsafeAddr()))
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}
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// reflectValueRWSlice3 is equivalent to arr.Slice3(i, j, k), except that the
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// returned reflect.Value is usable in assignments even if obj was obtained by
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// the use of unexported struct fields.
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//
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// Preconditions:
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// * arr.Kind() == reflect.Array.
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// * i, j, k >= 0.
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// * i <= j <= k <= arr.Len().
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func reflectValueRWSlice3(arr reflect.Value, i, j, k int) reflect.Value {
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if arr.Kind() != reflect.Array {
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panic(fmt.Sprintf("arr has kind %v, wanted %v", arr.Kind(), reflect.Array))
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}
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if i < 0 || j < 0 || k < 0 {
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panic(fmt.Sprintf("negative subscripts (%d, %d, %d)", i, j, k))
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}
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if i > j {
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panic(fmt.Sprintf("subscript i (%d) > j (%d)", i, j))
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}
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if j > k {
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panic(fmt.Sprintf("subscript j (%d) > k (%d)", j, k))
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}
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if k > arr.Len() {
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panic(fmt.Sprintf("subscript k (%d) > array length (%d)", k, arr.Len()))
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}
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sliceTyp := reflect.SliceOf(arr.Type().Elem())
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if i == arr.Len() {
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// By precondition, i == j == k == arr.Len().
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return reflect.MakeSlice(sliceTyp, 0, 0)
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}
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slh := reflect.SliceHeader{
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// reflect.Value.CanAddr() == false for arrays, so we need to get the
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// address from the first element of the array.
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Data: arr.Index(i).UnsafeAddr(),
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Len: j - i,
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Cap: k - i,
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}
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slobj := reflect.NewAt(sliceTyp, unsafe.Pointer(&slh)).Elem()
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// Before slobj is constructed, arr holds the only pointer-typed pointer to
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// the array since reflect.SliceHeader.Data is a uintptr, so arr must be
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// kept alive.
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runtime.KeepAlive(arr)
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return slobj
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}
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