Re: [PATCH] Fix strict-aliasing warning in resolv/res_hconf.c

[Steve Ellcey <sellcey at imgtec dot com>]

On Tue, 2015-05-19 at 15:12 -0700, Paul Eggert wrote:
> On 05/19/2015 02:09 PM, Steve Ellcey wrote:
> > It uses the same casts as before but splits up the assignment into
> > two parts and that seems to be sufficient to get rid of the GCC
> > warning.
> 
> It's warning about a portability problem that seems to be genuine. Can't 
> we fix the problem using a union as before?  That should be better than 
> trying to fool GCC into not warning about the problem.

OK, how is this version with no casts.

Steve Ellcey
sellcey@imgtec.com



2015-05-19  Steve Ellcey  <sellcey@imgtec.com>

	* resolv/res_hconf.c (_res_hconf_reorder_addrs): Split up assignment
	and use union to avoid GCC strict aliasing warning.


diff --git a/resolv/res_hconf.c b/resolv/res_hconf.c
index 73942e8..0dbee2e 100644
--- a/resolv/res_hconf.c
+++ b/resolv/res_hconf.c
@@ -407,6 +407,11 @@ _res_hconf_reorder_addrs (struct hostent *hp)
   if (num_ifs <= 0)
     {
       struct ifreq *ifr, *cur_ifr;
+      union
+	{
+	struct sockaddr *sa;
+	struct sockaddr_in *sin;
+	} ss;
       int sd, num, i;
       /* Save errno.  */
       int save = errno;
@@ -443,14 +448,14 @@ _res_hconf_reorder_addrs (struct hostent *hp)
 		continue;
 
 	      ifaddrs[new_num_ifs].addrtype = AF_INET;
-	      ifaddrs[new_num_ifs].u.ipv4.addr =
-		((struct sockaddr_in *) &cur_ifr->ifr_addr)->sin_addr.s_addr;
+	      ss.sa = &cur_ifr->ifr_addr;
+	      ifaddrs[new_num_ifs].u.ipv4.addr = ss.sin->sin_addr.s_addr;
 
 	      if (__ioctl (sd, SIOCGIFNETMASK, cur_ifr) < 0)
 		continue;
 
-	      ifaddrs[new_num_ifs].u.ipv4.mask =
-		((struct sockaddr_in *) &cur_ifr->ifr_netmask)->sin_addr.s_addr;
+	      ss.sa = &cur_ifr->ifr_netmask;
+	      ifaddrs[new_num_ifs].u.ipv4.mask = ss.sin->sin_addr.s_addr;
 
 	      /* Now we're committed to this entry.  */
 	      ++new_num_ifs;