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

[Pedro Alves]

On 05/27/2015 11:50 AM, Florian Weimer wrote:
> On 05/27/2015 11:19 AM, Pedro Alves wrote:
>> On 05/20/2015 05:27 PM, Steve Ellcey wrote:
>>
>>> diff --git a/resolv/res_hconf.c b/resolv/res_hconf.c
>>> index 73942e8..3b05287 100644
>>> --- a/resolv/res_hconf.c
>>> +++ b/resolv/res_hconf.c
>>> @@ -444,13 +444,13 @@ _res_hconf_reorder_addrs (struct hostent *hp)
>>>  
>>>  	      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;
>>> +		cur_ifr->ifr_addr_in.sin_addr.s_addr;
>>
>> Without adding a new union member, isn't the simplest to just take a
>> copy step?
> 
> I think it's still undefined behavior.

How so?  AFAIK, it's implementation defined, and GCC allows type-punning provided
the memory is accessed through the union type.

 https://gcc.gnu.org/onlinedocs/gcc-5.1.0/gcc/Optimize-Options.html#Type-punning

> 
>> etc.  Maybe the compiler even elides the copying.
> 
> If it does, we are back to square one, I fear.
> 


Thanks,
Pedro Alves