Re: [Qemu-devel] [PATCH 04/12] slirp: add in6_multicast() and use it instead of IN6_IS_ADDR_MULTICAST()

[Thomas Huth]

On 09.01.2018 17:33, Richard Henderson wrote:
> On 01/08/2018 09:28 AM, Philippe Mathieu-Daudé wrote:
>> Host: Mac OS 10.12.5
>> Compiler: Apple LLVM version 8.1.0 (clang-802.0.42)
>>
>>   slirp/ip6_icmp.c:79:32: warning: taking address of packed member 'ip_src' 
>> of class or
>>         structure 'ip6' may result in an unaligned pointer value
>>         [-Waddress-of-packed-member]
>>       if (IN6_IS_ADDR_MULTICAST(&ip->ip_src) ||
>>                                  ^~~~~~~~~~
>>   /usr/include/netinet6/in6.h:299:36: note: expanded from macro 
>> 'IN6_IS_ADDR_MULTICAST'
>>   #define IN6_IS_ADDR_MULTICAST(a)        ((a)->s6_addr[0] == 0xff)
> 
> The fact that you replace a macro with a function of exactly the same code in
> order to avoid a diagnostic sure looks like a compiler bug to me.

I think this might also be a bug in the macro definitions. On Linux, it
is defined like this:

#define IN6_IS_ADDR_MULTICAST(a) (((const uint8_t *) (a))[0] == 0xff)

 Thomas