Re: [PATCH] infiniband: avoid overflow warning

Arnd Bergmann
2017-07-31T19:19:22Z

On Mon, Jul 31, 2017 at 6:17 PM, Bart Van Assche <Bart.VanAssche-Sjgp3cTcYWE@public.gmane.org> wrote:
> On Mon, 2017-07-31 at 18:04 +0200, Arnd Bergmann wrote:
>> On Mon, Jul 31, 2017 at 5:32 PM, Bart Van Assche <Bart.VanAssche-Sjgp3cTcYWE@public.gmane.org> wrote:
>> > 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?
>>
>> I think the interprocedural analysis here is just a little worse than it could
>> be, but it's not actually correct. It's not gcc that prints the warning (if
>> it did, then I'd agree it would be a gcc bug) but the warning is triggered
>> intentionally by the fortified version of memcpy in include/linux/string.h.
>>
>> The problem as I understand it is that gcc cannot guarantee that it
>> tracks the value of addr->sa_family at least as far as the size of the
>> stack object, and it has no strict reason to do so, so the inlined
>> rdma_ip2gid() will still contain both cases.
>
> Hello Arnd,
>
> Had you already considered to uninline the rdma_ip2gid() function?

Not really, that would prevent the normal optimization from happening,
so that would be worse than uninlining addr_event() as I tried.

It would of course get rid of the warning, so if you think that's a better
solution, I won't complain.

Arnd