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// Copyright 2021 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.
//go:build (darwin && !ios) || linux
package unix
import "unsafe"
// SysvShmAttach attaches the Sysv shared memory segment associated with the
// shared memory identifier id.
func SysvShmAttach(id int, addr uintptr, flag int) ([]byte, error) {
addr, errno := shmat(id, addr, flag)
if errno != nil {
return nil, errno
// Retrieve the size of the shared memory to enable slice creation
var info SysvShmDesc
_, err := SysvShmCtl(id, IPC_STAT, &info)
if err != nil {
// release the shared memory if we can't find the size
// ignoring error from shmdt as there's nothing sensible to return here
return nil, err
// Use unsafe to convert addr into a []byte.
b := unsafe.Slice((*byte)(unsafe.Pointer(addr)), int(info.Segsz))
return b, nil
// SysvShmDetach unmaps the shared memory slice returned from SysvShmAttach.
// It is not safe to use the slice after calling this function.
func SysvShmDetach(data []byte) error {
if len(data) == 0 {
return EINVAL
return shmdt(uintptr(unsafe.Pointer(&data[0])))
// SysvShmGet returns the Sysv shared memory identifier associated with key.
// If the IPC_CREAT flag is specified a new segment is created.
func SysvShmGet(key, size, flag int) (id int, err error) {
return shmget(key, size, flag)