Fix alignment issue with 64-bit atomics on 32 bit machines

1 files changed, 80 insertions, 0 deletions

diff --git a/pkg/tcpip/aligned_unsafe.go b/pkg/tcpip/aligned_unsafe.go
new file mode 100644
index 000000000..35e869453
--- /dev/null
+++ b/pkg/tcpip/aligned_unsafe.go
@@ -0,0 +1,80 @@
+// Copyright 2021 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.
+
+// +build arm 386
+
+package tcpip
+
+import (
+	"sync/atomic"
+	"unsafe"
+)
+
+// AlignedAtomicInt64 is an atomic int64 that is guaranteed to be 64-bit
+// aligned, even on 32-bit systems.
+//
+// Per https://golang.org/pkg/sync/atomic/#pkg-note-BUG:
+//
+// "On ARM, 386, and 32-bit MIPS, it is the caller's responsibility to arrange
+// for 64-bit alignment of 64-bit words accessed atomically. The first word in
+// a variable or in an allocated struct, array, or slice can be relied upon to
+// be 64-bit aligned."
+type AlignedAtomicInt64 struct {
+	value [15]byte
+}
+
+func (aa *AlignedAtomicInt64) ptr() *int64 {
+	return (*int64)(unsafe.Pointer((uintptr(unsafe.Pointer(&aa.value)) + 7) &^ 7))
+}
+
+func (aa *AlignedAtomicInt64) Load() int64 {
+	return atomic.LoadInt64(aa.ptr())
+}
+
+func (aa *AlignedAtomicInt64) Store(v int64) {
+	atomic.StoreInt64(aa.ptr(), v)
+}
+
+func (aa *AlignedAtomicInt64) Add(v int64) int64 {
+	return atomic.AddInt64(aa.ptr(), v)
+}
+
+// AlignedAtomicUint64 is an atomic uint64 that is guaranteed to be 64-bit
+// aligned, even on 32-bit systems.
+//
+// Per https://golang.org/pkg/sync/atomic/#pkg-note-BUG:
+//
+// "On ARM, 386, and 32-bit MIPS, it is the caller's responsibility to arrange
+// for 64-bit alignment of 64-bit words accessed atomically. The first word in
+// a variable or in an allocated struct, array, or slice can be relied upon to
+// be 64-bit aligned."
+type AlignedAtomicUint64 struct {
+	value [15]byte
+}
+
+func (aa *AlignedAtomicUint64) ptr() *uint64 {
+	return (*uint64)(unsafe.Pointer((uintptr(unsafe.Pointer(&aa.value)) + 7) &^ 7))
+}
+
+func (aa *AlignedAtomicUint64) Load() uint64 {
+	return atomic.LoadUint64(aa.ptr())
+}
+
+func (aa *AlignedAtomicUint64) Store(v uint64) {
+	atomic.StoreUint64(aa.ptr(), v)
+}
+
+func (aa *AlignedAtomicUint64) Add(v uint64) uint64 {
+	return atomic.AddUint64(aa.ptr(), v)
+}