inet.af/netstack@v0.0.0-20220214151720-7585b01ddccf/atomicbitops/aligned_32bit_unsafe.go (about)

     1  // Copyright 2021 The gVisor Authors.
     2  //
     3  // Licensed under the Apache License, Version 2.0 (the "License");
     4  // you may not use this file except in compliance with the License.
     5  // You may obtain a copy of the License at
     6  //
     7  //     http://www.apache.org/licenses/LICENSE-2.0
     8  //
     9  // Unless required by applicable law or agreed to in writing, software
    10  // distributed under the License is distributed on an "AS IS" BASIS,
    11  // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    12  // See the License for the specific language governing permissions and
    13  // limitations under the License.
    14  
    15  //go:build arm || mips || mipsle || 386
    16  // +build arm mips mipsle 386
    17  
    18  package atomicbitops
    19  
    20  import (
    21  	"sync/atomic"
    22  	"unsafe"
    23  )
    24  
    25  // AlignedAtomicInt64 is an atomic int64 that is guaranteed to be 64-bit
    26  // aligned, even on 32-bit systems.
    27  //
    28  // Per https://golang.org/pkg/sync/atomic/#pkg-note-BUG:
    29  //
    30  // "On ARM, 386, and 32-bit MIPS, it is the caller's responsibility to arrange
    31  // for 64-bit alignment of 64-bit words accessed atomically. The first word in
    32  // a variable or in an allocated struct, array, or slice can be relied upon to
    33  // be 64-bit aligned."
    34  //
    35  // +stateify savable
    36  type AlignedAtomicInt64 struct {
    37  	value   int64
    38  	value32 int32
    39  }
    40  
    41  func (aa *AlignedAtomicInt64) ptr() *int64 {
    42  	// On 32-bit systems, aa.value is guaranteed to be 32-bit aligned. It means
    43  	// that in the 12-byte aa.value, there are guaranteed to be 8 contiguous bytes
    44  	// with 64-bit alignment.
    45  	return (*int64)(unsafe.Pointer((uintptr(unsafe.Pointer(&aa.value)) + 4) &^ 7))
    46  }
    47  
    48  // Load is analagous to atomic.LoadInt64.
    49  func (aa *AlignedAtomicInt64) Load() int64 {
    50  	return atomic.LoadInt64(aa.ptr())
    51  }
    52  
    53  // Store is analagous to atomic.StoreInt64.
    54  func (aa *AlignedAtomicInt64) Store(v int64) {
    55  	atomic.StoreInt64(aa.ptr(), v)
    56  }
    57  
    58  // Add is analagous to atomic.AddInt64.
    59  func (aa *AlignedAtomicInt64) Add(v int64) int64 {
    60  	return atomic.AddInt64(aa.ptr(), v)
    61  }
    62  
    63  // AlignedAtomicUint64 is an atomic uint64 that is guaranteed to be 64-bit
    64  // aligned, even on 32-bit systems.
    65  //
    66  // Per https://golang.org/pkg/sync/atomic/#pkg-note-BUG:
    67  //
    68  // "On ARM, 386, and 32-bit MIPS, it is the caller's responsibility to arrange
    69  // for 64-bit alignment of 64-bit words accessed atomically. The first word in
    70  // a variable or in an allocated struct, array, or slice can be relied upon to
    71  // be 64-bit aligned."
    72  //
    73  // +stateify savable
    74  type AlignedAtomicUint64 struct {
    75  	value   uint64
    76  	value32 uint32
    77  }
    78  
    79  func (aa *AlignedAtomicUint64) ptr() *uint64 {
    80  	// On 32-bit systems, aa.value is guaranteed to be 32-bit aligned. It means
    81  	// that in the 12-byte aa.value, there are guaranteed to be 8 contiguous bytes
    82  	// with 64-bit alignment.
    83  	return (*uint64)(unsafe.Pointer((uintptr(unsafe.Pointer(&aa.value)) + 4) &^ 7))
    84  }
    85  
    86  // Load is analagous to atomic.LoadUint64.
    87  func (aa *AlignedAtomicUint64) Load() uint64 {
    88  	return atomic.LoadUint64(aa.ptr())
    89  }
    90  
    91  // Store is analagous to atomic.StoreUint64.
    92  func (aa *AlignedAtomicUint64) Store(v uint64) {
    93  	atomic.StoreUint64(aa.ptr(), v)
    94  }
    95  
    96  // Add is analagous to atomic.AddUint64.
    97  func (aa *AlignedAtomicUint64) Add(v uint64) uint64 {
    98  	return atomic.AddUint64(aa.ptr(), v)
    99  }