Re: [PATCH] xen: Use __auto_type

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 05/05/2025 1:57 pm, Nicola Vetrini wrote:
> On 2025-05-05 14:46, 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.
>>
>> Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
>> ---
>> CC: Anthony PERARD <anthony.perard@xxxxxxxxxx>
>> CC: Michal Orzel <michal.orzel@xxxxxxx>
>> CC: Jan Beulich <jbeulich@xxxxxxxx>
>> CC: Julien Grall <julien@xxxxxxx>
>> CC: Roger Pau Monné <roger.pau@xxxxxxxxxx>
>> CC: Stefano Stabellini <sstabellini@xxxxxxxxxx>
>> CC: Roberto Bagnara <roberto.bagnara@xxxxxxxxxxx>
>> CC: Nicola Vetrini <nicola.vetrini@xxxxxxxxxxx>
>> CC: consulting@xxxxxxxxxxx <consulting@xxxxxxxxxxx>
>>
>> The resulting build is identical.
>>
>> RFC.  This requires a MISRA change, as it currently manifests as a R1.1
>> violation.  Nevertheless, I think we want to start using in places
>> where we
>> currently use typeof(expression of <initilaiser>).
>>
>> Eclair run on this patch (expecting a failure):
>>  
>> https://gitlab.com/xen-project/hardware/xen-staging/-/pipelines/1800631949
>>
>
> Hi,
>
> to make the analysis pass you need a couple of hunks in
> eclair_analysis/ECLAIR/toolchain.ecl:
>
> -name_selector+={auto_type, "^__auto_type$"}
>
> and add auto_type to the STD.tokenext config below around line 25,
> then later
>
> -name_selector+={ext_auto_type, "^ext_auto_type$"}
>
> and add "ext_auto_type" to the -config lines below
>
> around line 125, along with a reference to the gcc docs above the
> configurations and in C-language-toolchain.rst
>
> This is an extension, so it's usable without further MISRA impact.

Excellent, thankyou.

I'll leave this email out for discussion, and if it goes in a positive
direction, I'll submit a v2 with (hopefully) all the MISRA/Eclair
changes required.

~Andrew