code review 7406050: syscall: fix FD passing on FreeBSD, NetBSD and OpenBSD

src/pkg/syscall/sockcmsg_unix.go

 // Copyright 2011 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.
 
 // +build darwin freebsd linux netbsd openbsd
 
 // Socket control messages
 
 package syscall
 
@@ skipping 19 matching lines @@
         return cmsgAlignOf(SizeofCmsghdr) + datalen
 }
 
 // CmsgSpace returns the number of bytes an ancillary element with
 // payload of the passed data length occupies.
 func CmsgSpace(datalen int) int {
         return cmsgAlignOf(SizeofCmsghdr) + cmsgAlignOf(datalen)
 }
 
 func cmsgData(h *Cmsghdr) unsafe.Pointer {
-        return unsafe.Pointer(uintptr(unsafe.Pointer(h)) + SizeofCmsghdr)
+        return unsafe.Pointer(uintptr(unsafe.Pointer(h)) + uintptr(cmsgAlignOf(SizeofCmsghdr)))
 }
 
 // SocketControlMessage represents a socket control message.
 type SocketControlMessage struct {
         Header Cmsghdr
         Data   []byte
 }
 
 // ParseSocketControlMessage parses b as an array of socket control
 // messages.
@@ skipping 45 matching lines @@
         if m.Header.Type != SCM_RIGHTS {
                 return nil, EINVAL
         }
         fds := make([]int, len(m.Data)>>2)
         for i, j := 0, 0; i < len(m.Data); i += 4 {
                 fds[j] = int(*(*int32)(unsafe.Pointer(&m.Data[i])))
                 j++
         }
         return fds, nil
 }