Re: [PATCH] mm/vmstat: Fix -Wenum-enum-conversion warning in vmstat.h

[Nathan Chancellor]

On Fri, Oct 11, 2024 at 02:05:00PM +0000, Arnd Bergmann wrote:
> I'm fairly sure I saw users mix up 'dma_data_direction' with
> 'dma_transfer_direction' and unrelated enum-enum mixups in
> amdgpu. There were probably more.

Yes, those have definitely happened but those are -Wenum-conversion, not
-Wenum-enum-conversion.

> I think what happened is that in clang-18 and earlier, the
> warning option caught mistakes of passing the wrong enum 
> to a function and a few others, but it did not catch arithmetic
> operations between enums, so clang-19 now produces a lot more
> output than older versions, and I don't think we can
> control those independently.

A contrived example: https://godbolt.org/z/Ydx6rxsvb

We should be able to disable -Wenum-enum-conversion without impacting
the ability to catch the cases that you mentioned above. It also helps
that GCC supports -Wenum-conversion, but it does not seem like they have
an equivalent for -Wenum-enum-conversion.

Cheers,
Nathan