Subject: Re: [BRIDGE] Unaligned access on IA64 when comparing ethernet addresses

From: Stephen Hemminger <[email-masked]>
Date: Tue, 17 Apr 2007 13:37:23 -0700

The previous patch relied on the bridge id being aligned by
the compiler (which happens as a side effect). So please use
this instead.

compare_ether_addr() implicitly requires that the addresses
passed are 2-bytes aligned in memory.

This is not true for br_stp_change_bridge_id() and
br_stp_recalculate_bridge_id() in which one of the addresses
is unsigned char *, and thus may not be 2-bytes aligned.

Signed-off-by: Evgeny Kravtsunov <[email-masked]>
Signed-off-by: Kirill Korotaev <[email-masked]>
Signed-off-by: Pavel Emelianov <[email-masked]>
Signed-off-by: Stephen Hemminger <[email-masked]>

---

--- linux-2.6.orig/net/bridge/br_stp_if.c	2007-04-16
20:03:04.000000000 -0700 +++ linux-2.6/net/bridge/br_stp_if.c
2007-04-17 13:25:52.000000000 -0700 @@ -126,23 +126,22 @@
 /* called under bridge lock */
 void br_stp_change_bridge_id(struct net_bridge *br, const unsigned
char *addr) {
-	unsigned char oldaddr[6];
+	bridge_id old_id;
 	struct net_bridge_port *p;
 	int wasroot;
 
 	wasroot = br_is_root_bridge(br);
 
-	memcpy(oldaddr, br->bridge_id.addr, ETH_ALEN);
+	old_id = br->bridge_id;
 	memcpy(br->bridge_id.addr, addr, ETH_ALEN);
 	memcpy(br->dev->dev_addr, addr, ETH_ALEN);
 
 	list_for_each_entry(p, &br->port_list, list) {
-		if (!compare_ether_addr(p->designated_bridge.addr,
oldaddr))
+		if (!compare_ether_addr(p->designated_bridge.addr,
old_id.addr)) memcpy(p->designated_bridge.addr, addr, ETH_ALEN);
 
-		if (!compare_ether_addr(p->designated_root.addr,
oldaddr))
+		if (!compare_ether_addr(p->designated_root.addr,
old_id.addr)) memcpy(p->designated_root.addr, addr, ETH_ALEN);
-
 	}
 
 	br_configuration_update(br);
@@ -151,19 +150,17 @@
 		br_become_root_bridge(br);
 }
 
-static const unsigned char br_mac_zero[6];
-
 /* called under bridge lock */
 void br_stp_recalculate_bridge_id(struct net_bridge *br)
 {
-	const unsigned char *addr = br_mac_zero;
+	static const bridge_id id_zero;
+	const unsigned char *addr = id_zero.addr;
 	struct net_bridge_port *p;
 
 	list_for_each_entry(p, &br->port_list, list) {
-		if (addr == br_mac_zero ||
+		if (addr == id_zero.addr ||
 		    memcmp(p->dev->dev_addr, addr, ETH_ALEN) < 0)
 			addr = p->dev->dev_addr;
-
 	}
 
 	if (compare_ether_addr(br->bridge_id.addr, addr))
--- linux-2.6.orig/net/bridge/br_private.h	2007-04-17
13:26:48.000000000 -0700 +++ linux-2.6/net/bridge/br_private.h
2007-04-17 13:30:29.000000000 -0700 @@ -36,7 +36,7 @@
 {
 	unsigned char	prio[2];
 	unsigned char	addr[6];
-};
+} __attribute__((aligned(8)));
 
 struct mac_addr
 {