Re: Compiler bug or violation of strict aliasing rule?

[Rin Okuyama <rokuyama.rk%gmail.com@localhost>]

On 2021/11/05 3:48, Christos Zoulas wrote:
> In article <b189f531-0837-be29-9053-1f33f01ac8ca%gmail.com@localhost>,
> Rin Okuyama  <rokuyama.rk%gmail.com@localhost> 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