Re: Compiler bug or violation of strict aliasing rule?

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,

christos