syscall: Fix handling of Unix domain @ addresses.

From-SVN: r193783

libgo/go/syscall/socket.go

@@ -87,12 +87,16 @@ func (sa *SockaddrUnix) sockaddr() (*RawSockaddrAny, Socklen_t, error) {
 	for i := 0; i < n; i++ {
 		sa.raw.Path[i] = int8(name[i])
 	}
+	// length is family (uint16), name, NUL.
+	sl := 2 + Socklen_t(n) + 1
 	if sa.raw.Path[0] == '@' {
 		sa.raw.Path[0] = 0
+		// Don't count trailing NUL for abstract address.
+		sl--
 	}
 
 	// length is family (uint16), name, NUL.
-	return (*RawSockaddrAny)(unsafe.Pointer(&sa.raw)), 2 + Socklen_t(n) + 1, nil
+	return (*RawSockaddrAny)(unsafe.Pointer(&sa.raw)), sl, nil
 }
 
 func anyToSockaddr(rsa *RawSockaddrAny) (Sockaddr, error) {

libgo/go/syscall/socket_linux.go

@@ -103,7 +103,7 @@ func (sa *RawSockaddrUnix) getLen() (int, error) {
 	// to be uninterpreted fixed-size binary blobs--but
 	// everyone uses this convention.
 	n := 0
-	for n < len(sa.Path)-3 && sa.Path[n] != 0 {
+	for n < len(sa.Path) && sa.Path[n] != 0 {
 		n++
 	}