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

[Alexander Bulekov]

On 210114 1538, Miroslav Rezanina wrote:
> On Thu, Jan 14, 2021 at 09:19:20AM -0500, Alexander Bulekov wrote:
> > 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
> >
> 
> Yes, it is caused by the issue triggering the warning. Do you know
> whether the patch mentioned in bug was already sent?
> 
> Mirek

I don't think so..
-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>
> > > 
> > > 
> > 
>