Re: [PATCH v2 16/19] gendwarfksyms: Add support for reserved structure fields

[Sami Tolvanen]

Hi Benno,

On Thu, Sep 12, 2024 at 11:08 AM Benno Lossin <benno.lossin@xxxxxxxxx> wrote:
>
> On 12.09.24 18:06, Sami Tolvanen wrote:
> >
> > I thought about this a bit and I wonder if we need a separate
> > mechanism for that, or is it sufficient to just #define any additional
> > hidden values you want to add instead of including them in the enum?
> >
> >   enum e {
> >       A,
> >       B,
> >   #define C (B + 1)
> >   #define D (C + 1)
> >   };
> >
> >
> > Do you see any issues with this approach? I think Clang would complain
> > about this with -Wassign-enum, but I'm not sure if we even enable that
> > in the kernel, and as long as you don't overflow the underlying type,
> > which is a requirement for not breaking the ABI anyway, it should be
> > fine.
>
> Rust has problems with `#define`-style enums, because bindgen (the tool
> that generates definitions for Rust to be able to call C code) isn't
> able to convert them to Rust enums.
>
> So if you can come up with an approach that allows you to continue to
> use C enums instead of `#define`, we would appreciate that, since it
> would make our lives a lot easier.

That's an interesting point. Is the problem that you cannot assign
arbitrary values to the Rust enum that bindgen generates, or is using
a #define the problem? We could probably just make the hidden enum
values visible to bindgen only if needed.

Sami