linux-kernel - Re: [PATCH] infiniband: avoid overflow warning

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Date:   Mon, 31 Jul 2017 15:32:00 +0000
From:   Bart Van Assche <Bart.VanAssche@....com>
To:     "monis@...lanox.com" <monis@...lanox.com>,
        "arnd@...db.de" <arnd@...db.de>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "keescook@...omium.org" <keescook@...omium.org>,
        "linux-rdma@...r.kernel.org" <linux-rdma@...r.kernel.org>,
        "parav@...lanox.com" <parav@...lanox.com>,
        "Michal.Kalderon@...ium.com" <Michal.Kalderon@...ium.com>,
        Bart Van Assche <Bart.VanAssche@....com>,
        "sean.hefty@...el.com" <sean.hefty@...el.com>,
        "danielmicay@...il.com" <danielmicay@...il.com>,
        "Ariel.Elior@...ium.com" <Ariel.Elior@...ium.com>,
        "hal.rosenstock@...il.com" <hal.rosenstock@...il.com>,
        "davem@...emloft.net" <davem@...emloft.net>,
        "dledford@...hat.com" <dledford@...hat.com>,
        "noaos@...lanox.com" <noaos@...lanox.com>
Subject: Re: [PATCH] infiniband: avoid overflow warning

On Mon, 2017-07-31 at 09:30 +0200, Arnd Bergmann wrote:
> On Mon, Jul 31, 2017 at 9:08 AM, Moni Shoua <monis@...lanox.com> wrote:
> > On Mon, Jul 31, 2017 at 9:50 AM, Arnd Bergmann <arnd@...db.de> wrote:
> > > --- a/include/rdma/ib_addr.h
> > > +++ b/include/rdma/ib_addr.h
> > > @@ -172,7 +172,8 @@ static inline int rdma_ip2gid(struct sockaddr *addr, union ib_gid *gid)
> > >                                        (struct in6_addr *)gid);
> > >                 break;
> > >         case AF_INET6:
> > > -               memcpy(gid->raw, &((struct sockaddr_in6 *)addr)->sin6_addr, 16);
> > > +               *(struct in6_addr *)&gid->raw =
> > > +                       ((struct sockaddr_in6 *)addr)->sin6_addr;
> > >                 break;
> > >         default:
> > >                 return -EINVAL;
> > 
> > what happens if you replace 16 with sizeof(struct in6_addr)?
> 
> Same thing: the problem is that gcc already knows the size of the structure we
> pass in here, and it is in fact shorter.
> 
> I also tried changing the struct sockaddr pointer to a sockaddr_storage pointer,
> without success. Other approaches that do work are:
> 
> - mark addr_event() as "noinline" to prevent gcc from seeing the true
> size of the
>   inetaddr_event stack object in rdma_ip2gid(). I considered this a little ugly.
> 
> - change inetaddr_event to put a larger structure on the stack, using
>   sockaddr_storage or sockaddr_in6. This would be less efficient.
> 
> - define a union of sockaddr_in and sockaddr_in6, and use that as the argument
>   to rdma_ip2gid/rdma_gid2ip, and change all callers to use that union type.
>   This is probably the cleanest approach as it gets rid of a lot of questionable
>   type casts, but it's a relatively large patch and also slightly less
> efficient as we have
>   to zero more stack storage in some cases.

Hello Arnd,

So inetaddr_event() assigns AF_INET so .sin_family and gcc warns about code
that is only executed if .sin_family == AF_INET6? Since this warning is the
result of incorrect interprocedural analysis by gcc, shouldn't this be
reported as a bug to the gcc authors?

Thanks,

Bart.