Re: [PATCH] xen: Use __auto_type

[Frediano Ziglio <frediano.ziglio@xxxxxxxxx>]

On Mon, May 12, 2025 at 1:09 PM Andrew Cooper <andrew.cooper3@xxxxxxxxxx> wrote:
>
> On 12/05/2025 12:59 pm, Jan Beulich wrote:
> > On 05.05.2025 21:44, Stefano Stabellini wrote:
> >> On Mon, 5 May 2025, Andrew Cooper wrote:
> >>> In macros it is common to declare local variables using typeof(param) in 
> >>> order
> >>> to ensure that side effects are only evaluated once.  A consequence of 
> >>> this is
> >>> double textural expansion of the parameter, which can get out of hand very
> >>> quickly with nested macros.
> >>>
> >>> A GCC extension, __auto_type, is now avaialble in the new toolchain 
> >>> baseline
> >>> and avoids the double textural expansion.
> >> I think this is a good change
> > +1
>
> That looks like agreement.
>
> Now for the (new) controversial part.  Since sending this, Linux has
> decided to just #define auto __auto_type for C < 23, in order to start
> writing C23 compatible code from now.  It's more succinct, and has
> better longevity.
>
> We might want to consider the same, although it will introduce a new
> example of defining a keyword, which we'd have to call out in the
> MISRA/Eclair config.
>
> If we're going to do this, we should do it from the outset.
>
> Thoughts?
>
> ~Andrew
>

I vote for avoiding extensions when the same feature is implemented by
standard, so yes for using "auto".

Frediano