Re: [PATCH v3 1/2] Fix net.c warning on GCC 11

[Alexander Bulekov <alxndr@bu.edu>]

On 210114 1415, Philippe Mathieu-Daudé wrote:
> +Jason +Dmitry
> 
> On 1/14/21 8:07 AM, Miroslav Rezanina wrote:
> > When building qemu with GCC 11, compiling eth.c file produce following warning:
> > 
> >    warning: array subscript 'struct ip6_ext_hdr_routing[0]' is partly outside array bounds of 'struct ip6_ext_hdr[1]' [-Warray-bounds]
> > 
> > This is caused by retyping from ip6_ext_hdr to ip6_ext_hdr_routing that has more
> > attributes.
> > 
> > As this usage is expected, suppress the warning temporarily through the function
> > using this retyping.
> 
> This is not expected, this is a bug...
> 

Seems related: https://bugs.launchpad.net/qemu/+bug/1879531
-Alex

> > 
> > Signed-off-by: Miroslav Rezanina <mrezanin@redhat.com>
> > ---
> >  net/eth.c | 3 +++
> >  1 file changed, 3 insertions(+)
> > 
> > diff --git a/net/eth.c b/net/eth.c
> > index 1e0821c5f8..b9bdd0435c 100644
> > --- a/net/eth.c
> > +++ b/net/eth.c
> > @@ -405,6 +405,8 @@ _eth_get_rss_ex_dst_addr(const struct iovec *pkt, int pkt_frags,
> >                          struct ip6_ext_hdr *ext_hdr,
> >                          struct in6_address *dst_addr)
> >  {
> > +#pragma GCC diagnostic push
> > +#pragma GCC diagnostic ignored "-Warray-bounds"
> >      struct ip6_ext_hdr_routing *rthdr = (struct ip6_ext_hdr_routing *) ext_hdr;
> 
> eth_parse_ipv6_hdr() called iov_to_buf() to fill the 2 bytes of ext_hdr.
> 
> >      if ((rthdr->rtype == 2) &&
> 
> Here we access after the 2 bytes filled... rthdr->rtype is somewhere on
> eth_parse_ipv6_hdr's stack, its content is unknown.
> 
> > @@ -426,6 +428,7 @@ _eth_get_rss_ex_dst_addr(const struct iovec *pkt, int pkt_frags,
> >      }
> >  
> >      return false;
> > +#pragma GCC diagnostic pop
> 
> Nacked-by: Philippe Mathieu-Daudé <philmd@redhat.com>
> 
>