net: avoid an indirect call in ____sys_recvmsg()

CONFIG_RETPOLINE=y made indirect calls expensive.

gcc seems to add an indirect call in ____sys_recvmsg().

Rewriting the code slightly makes sure to avoid this indirection.

Alternative would be to not call sock_recvmsg() and instead
use security_socket_recvmsg() and sock_recvmsg_nosec(),
but this is less readable IMO.

Signed-off-by: Eric Dumazet <[email protected]>
Cc: Paolo Abeni <[email protected]>
Cc: David Laight <[email protected]>
Acked-by: Paolo Abeni <[email protected]>
Signed-off-by: David S. Miller <[email protected]>

Author: edumazet

net/socket.c

@@ -2559,7 +2559,12 @@ static int ____sys_recvmsg(struct socket *sock, struct msghdr *msg_sys,
 
 	if (sock->file->f_flags & O_NONBLOCK)
 		flags |= MSG_DONTWAIT;
-	err = (nosec ? sock_recvmsg_nosec : sock_recvmsg)(sock, msg_sys, flags);
+
+	if (unlikely(nosec))
+		err = sock_recvmsg_nosec(sock, msg_sys, flags);
+	else
+		err = sock_recvmsg(sock, msg_sys, flags);
+
 	if (err < 0)
 		goto out;
 	len = err;