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Re: [PATCH] xen: Use __auto_type
- To: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Mon, 12 May 2025 15:00:18 +0200
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- Cc: Xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxxx>, Anthony PERARD <anthony.perard@xxxxxxxxxx>, Michal Orzel <michal.orzel@xxxxxxx>, Julien Grall <julien@xxxxxxx>, Roger Pau Monné <roger.pau@xxxxxxxxxx>, Roberto Bagnara <roberto.bagnara@xxxxxxxxxxx>, Nicola Vetrini <nicola.vetrini@xxxxxxxxxxx>, "consulting @ bugseng . com" <consulting@xxxxxxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>
- Delivery-date: Mon, 12 May 2025 13:00:35 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 12.05.2025 14:09, Andrew Cooper 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.
I'm not outright opposed, as I don't think we use "auto" with its
original semantics, but it feels somewhat odd.
Jan
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