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On Tue, Jun 28, 2022 at 10:36:51AM -0300, Jason Gunthorpe wrote:
> On Tue, Jun 28, 2022 at 04:21:29AM +0200, Gustavo A. R. Silva wrote:
>
> > > > Though maybe we could just switch off
> > > > -Wgnu-variable-sized-type-not-at-end during configuration ?
>
> > We need to think in a different strategy.
>
> I think we will need to switch off the warning in userspace - this is
> doable for rdma-core.
>
> On the other hand, if the goal is to enable the array size check
> compiler warning I would suggest focusing only on those structs that
> actually hit that warning in the kernel. IIRC infiniband doesn't
> trigger it because it just pointer casts the flex array to some other
> struct.
Yep; this is actually why I reverted those changes in rdma (before
sending out the patch) when 0-day reported the same problems you pointed
out[1].
Also, that's the strategy I'm following right now with the one-element
array into flex-array member transformations. I'm addressing those cases
in which the trailing array is actually being iterated over, first.
I just added the patch to my -next tree, so it can be build-tested by
other people, and let's see what else is reported this week. :)
--
Gustavo
[1] https://lore.kernel.org/lkml/620ca2a5.NkAEIDEfiYoxE9%2Fu%25lkp@xxxxxxxxx/
>
> It isn't actually an array it is a placeholder for a trailing
> structure, so it is never indexed.
>
> This is also why we hit the warning because the convient way for
> userspace to compose the message is to squash the header and trailer
> structs together in a super struct on the stack, then invoke the
> ioctl.
>
> Jason
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