Re: Compiler bug or violation of strict aliasing rule?

On 2021/11/05 3:48, Christos Zoulas wrote:
> In article <[email protected]>,
> Rin Okuyama  <[email protected]> wrote:
>> For aarch64eb, GCC 9 and 10 compile this "if" block of
>> tests/net/net/t_tcp.c:
>>
>> https://nxr.netbsd.org/xref/src/tests/net/net/t_tcp.c#141
>>
>>     141          if (sfamily == AF_INET6 && cfamily == AF_INET) {
>>     142                  ss = bs;
>>     143                  sin6 = (void *)&ss;
>>     144                  sin = (void *)&bs;
>>     145                  addrlen = sizeof(*sin);
>>     146  #ifdef BSD4_4
>>     147                  sin->sin_len = sizeof(*sin);
>>     148  #endif
>>     149                  sin->sin_family = AF_INET;
>>     150                  sin->sin_port = sin6->sin6_port;
>>     151                  sin->sin_addr.s_addr = htonl(INADDR_LOOPBACK);
>>     152          }
>>
>> into a code, where fetch for "sin6->sin6_port" is preceding to
>> structure copy "ss = bs".
>>
>> This is apparently not what the author of this code intended.
>>
>> However, I'm not sure whether this is a compiler bug, or a kind of
>> violation of strict aliasing rule.
>>
>> Note that the emitted code is "fixed" if (1) -fno-strict-aliasing
>> option is added, or (2) the attached patch is applied.
>>
>> Thoughts?
> 
> I'd apply the patch.

Thanks for your comment! I will commit the patch soon.

rin