tcp: remove indirect calls for icsk->icsk_af_ops->send_check

Mitigate RETPOLINE costs in __tcp_transmit_skb()
by using INDIRECT_CALL_INET() wrapper.

Signed-off-by: Eric Dumazet <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

include/net/ip6_checksum.h

···
 	th->check = ~tcp_v6_check(0, &ipv6h->saddr, &ipv6h->daddr, 0);
 }
 
-#if IS_ENABLED(CONFIG_IPV6)
-static inline void tcp_v6_send_check(struct sock *sk, struct sk_buff *skb)
-{
-	struct ipv6_pinfo *np = inet6_sk(sk);
-
-	__tcp_v6_send_check(skb, &np->saddr, &sk->sk_v6_daddr);
-}
-#endif
-
 static inline __sum16 udp_v6_check(int len,
 				   const struct in6_addr *saddr,
 				   const struct in6_addr *daddr,

include/net/tcp.h

···
 #endif
 	return 0;
 }
+
+INDIRECT_CALLABLE_DECLARE(void tcp_v6_send_check(struct sock *sk, struct sk_buff *skb));
+
 #endif
 
 static inline bool inet_exact_dif_match(struct net *net, struct sk_buff *skb)

net/ipv4/tcp_output.c

···
 
 INDIRECT_CALLABLE_DECLARE(int ip_queue_xmit(struct sock *sk, struct sk_buff *skb, struct flowi *fl));
 INDIRECT_CALLABLE_DECLARE(int inet6_csk_xmit(struct sock *sk, struct sk_buff *skb, struct flowi *fl));
+INDIRECT_CALLABLE_DECLARE(void tcp_v4_send_check(struct sock *sk, struct sk_buff *skb));
 
 /* This routine actually transmits TCP packets queued in by
  * tcp_do_sendmsg().  This is used by both the initial
···
 	}
 #endif
 
-	icsk->icsk_af_ops->send_check(sk, skb);
+	INDIRECT_CALL_INET(icsk->icsk_af_ops->send_check,
+			   tcp_v6_send_check, tcp_v4_send_check,
+			   sk, skb);
 
 	if (likely(tcb->tcp_flags & TCPHDR_ACK))
 		tcp_event_ack_sent(sk, tcp_skb_pcount(skb), rcv_nxt);

net/ipv6/tcp_ipv6.c

···
 	.twsk_destructor = tcp_twsk_destructor,
 };
 
+INDIRECT_CALLABLE_SCOPE void tcp_v6_send_check(struct sock *sk, struct sk_buff *skb)
+{
+	struct ipv6_pinfo *np = inet6_sk(sk);
+
+	__tcp_v6_send_check(skb, &np->saddr, &sk->sk_v6_daddr);
+}
+
 const struct inet_connection_sock_af_ops ipv6_specific = {
 	.queue_xmit	   = inet6_csk_xmit,
 	.send_check	   = tcp_v6_send_check,