unix: use correct cmsg alignment for openbsd/arm

The OpenBSD armv7 port requires 64-bit alignment for cmsgs.

Rework the cmsg alignment code to facilitate this.

Change-Id: Ie3eae1d367e2f3ac200fa8b78e97a2eb2eccae6a
Reviewed-on: https://go-review.googlesource.com/c/153619
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

unix/sockcmsg_unix.go

diff --git a/unix/sockcmsg_unix.go b/unix/sockcmsg_unix.go
index 9dd2f32..52b6e22 100644
--- a/unix/sockcmsg_unix.go
+++ b/unix/sockcmsg_unix.go
@@ -8,18 +8,33 @@
 
 package unix
 
-import "unsafe"
+import (
+	"runtime"
+	"unsafe"
+)
+
+var cmsgAlign = SizeofPtr
+
+func init() {
+	switch runtime.GOOS {
+	case "darwin", "dragonfly", "solaris":
+		// NOTE: It seems like 64-bit Darwin, DragonFly BSD and
+		// Solaris kernels still require 32-bit aligned access to
+		// network subsystem.
+		if SizeofPtr == 8 {
+			cmsgAlign = 4
+		}
+	case "openbsd":
+		// OpenBSD armv7 requires 64-bit alignment.
+		if runtime.GOARCH == "arm" {
+			cmsgAlign = 8
+		}
+	}
+}
 
 // Round the length of a raw sockaddr up to align it properly.
 func cmsgAlignOf(salen int) int {
-	salign := SizeofPtr
-	// NOTE: It seems like 64-bit Darwin, DragonFly BSD and
-	// Solaris kernels still require 32-bit aligned access to
-	// network subsystem.
-	if darwin64Bit || dragonfly64Bit || solaris64Bit {
-		salign = 4
-	}
-	return (salen + salign - 1) & ^(salign - 1)
+	return (salen + cmsgAlign - 1) & ^(cmsgAlign - 1)
 }
 
 // CmsgLen returns the value to store in the Len field of the Cmsghdr

unix/syscall_unix.go

diff --git a/unix/syscall_unix.go b/unix/syscall_unix.go
index 64fcda4..a21486f 100644
--- a/unix/syscall_unix.go
+++ b/unix/syscall_unix.go
@@ -8,7 +8,6 @@
 
 import (
 	"bytes"
-	"runtime"
 	"sort"
 	"sync"
 	"syscall"
@@ -21,13 +20,6 @@
 	Stderr = 2
 )
 
-const (
-	darwin64Bit    = runtime.GOOS == "darwin" && SizeofPtr == 8
-	dragonfly64Bit = runtime.GOOS == "dragonfly" && SizeofPtr == 8
-	netbsd32Bit    = runtime.GOOS == "netbsd" && SizeofPtr == 4
-	solaris64Bit   = runtime.GOOS == "solaris" && SizeofPtr == 8
-)
-
 // Do the interface allocations only once for common
 // Errno values.
 var (