batman-adv: Annotate bitwise integer pointer casts

The sparse commit 6002ded74587 ("add a flag to warn on casts to/from
bitwise pointers") introduced a check for non-direct casts from/to
restricted datatypes (when -Wbitwise-pointer is enabled).

This triggered various warnings in batman-adv when some (already big
endian) buffer content was casted to/from the corresponding big endian
integer data types. But these were correct and can therefore be marked with
__force to signalize sparse an intended cast from/to a bitwise type.

Signed-off-by: Sven Eckelmann <sven@narfation.org>
Signed-off-by: Simon Wunderlich <sw@simonwunderlich.de>

net/batman-adv/bridge_loop_avoidance.c

@@ -844,7 +844,7 @@ static bool batadv_handle_announce(struct batadv_priv *bat_priv, u8 *an_addr,
 
 	/* handle as ANNOUNCE frame */
 	backbone_gw->lasttime = jiffies;
-	crc = ntohs(*((__be16 *)(&an_addr[4])));
+	crc = ntohs(*((__force __be16 *)(&an_addr[4])));
 
 	batadv_dbg(BATADV_DBG_BLA, bat_priv,
 		   "%s(): ANNOUNCE vid %d (sent by %pM)... CRC = %#.4x\n",

net/batman-adv/distributed-arp-table.c

@@ -246,7 +246,7 @@ static u8 *batadv_arp_hw_src(struct sk_buff *skb, int hdr_size)
  */
 static __be32 batadv_arp_ip_src(struct sk_buff *skb, int hdr_size)
 {
-	return *(__be32 *)(batadv_arp_hw_src(skb, hdr_size) + ETH_ALEN);
+	return *(__force __be32 *)(batadv_arp_hw_src(skb, hdr_size) + ETH_ALEN);
 }
 
 /**
@@ -270,7 +270,9 @@ static u8 *batadv_arp_hw_dst(struct sk_buff *skb, int hdr_size)
  */
 static __be32 batadv_arp_ip_dst(struct sk_buff *skb, int hdr_size)
 {
-	return *(__be32 *)(batadv_arp_hw_src(skb, hdr_size) + ETH_ALEN * 2 + 4);
+	u8 *dst = batadv_arp_hw_src(skb, hdr_size) + ETH_ALEN * 2 + 4;
+
+	return *(__force __be32 *)dst;
 }
 
 /**
@@ -287,7 +289,7 @@ static u32 batadv_hash_dat(const void *data, u32 size)
 	const unsigned char *key;
 	u32 i;
 
-	key = (const unsigned char *)&dat->ip;
+	key = (__force const unsigned char *)&dat->ip;
 	for (i = 0; i < sizeof(dat->ip); i++) {
 		hash += key[i];
 		hash += (hash << 10);