Re: [PATCH v2 02/16] thunderbolt: Don't pass a bitfield to FIELD_GET

Yury Norov
2025-12-13T02:28:33Z

On Fri, Dec 12, 2025 at 07:37:07PM +0000, david.laight.linux@gmail.com wrote:
> From: David Laight <david.laight.linux@gmail.com>
>
> None of sizeof(), typeof() or __auto_type can be used with bitfields
> which makes it difficult to assign a #define parameter to a local
> without promoting char and short to int.
>
> Change:
> u32 thunderbolt_version:8;
> to the equivalent:
> u8 thunderbolt_version;
> (and the other three bytes of 'DWORD 4' to match).
>
> This is necessary so that FIELD_GET can use sizeof() to verify 'reg'.
>
> Signed-off-by: David Laight <david.laight.linux@gmail.com>
> ---
>
> Changes for v2:
> - Change structure definition instead of call to FIELD_GET().
>
> FIELD_GET currently uses _Generic() which behaves differently for
> gcc and clang (I suspect both are wrong!).
> gcc treats 'u32 foo:8' as 'u8', but will take the 'default' for other
> widths (which will generate an error in FIED_GET().
> clang treats 'u32 foo:n' as 'u32'.

FIELD_GET() works just well with bitfields, and whatever you do breaks
it. I pointed that in v1, but instead of fixing it, you do really well
hiding the problem.

I see no reasons to hack a random victim because of your rework. So
NAK for this.

In v3, please add an explicit test to make sure that bitfields are not
broken with new implementation.

Thanks,
Yury