Re: [PATCH v1] misra: add deviation of Rule 10.1 for unary minus

[Julien Grall <julien@xxxxxxx>]

Hi Victor,

On 23/04/2025 18:54, victorm.lira@xxxxxxx wrote:
> From: Nicola Vetrini <nicola.vetrini@xxxxxxxxxxx>
>
> MISRA C Rule 10.1 states:
> "Operands shall not be of an inappropriate essential type"
>
> The unary minus operator applied to an unsigned quantity has
> a semantics (wrap around) that is well-known to all Xen developers.
> Thus, this operation is deemed safe.
>
> No functional change.
>
> Signed-off-by: Nicola Vetrini <nicola.vetrini@xxxxxxxxxxx>
> Signed-off-by: Federico Serafini <federico.serafini@xxxxxxxxxxx>
> Signed-off-by: Victor Lira <victorm.lira@xxxxxxx>
> ---
> Changes v1:
> - add rule title to commit message
> ---
> Cc: 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: Nicola Vetrini <nicola.vetrini@xxxxxxxxxxx>
> Cc: Federico Serafini <federico.serafini@xxxxxxxxxxx>
> Cc: Bertrand Marquis <bertrand.marquis@xxxxxxx>
> ---
>   automation/eclair_analysis/ECLAIR/deviations.ecl | 6 ++++++
>   docs/misra/deviations.rst                        | 6 ++++++
>   2 files changed, 12 insertions(+)
>
> diff --git a/automation/eclair_analysis/ECLAIR/deviations.ecl 
> b/automation/eclair_analysis/ECLAIR/deviations.ecl
> index 303b06203a..2cfce850bd 100644
> --- a/automation/eclair_analysis/ECLAIR/deviations.ecl
> +++ b/automation/eclair_analysis/ECLAIR/deviations.ecl
> @@ -347,6 +347,12 @@ constant expressions are required.\""
>     "any()"}
>   -doc_end
>
> +-doc_begin="Unary minus operations on non-negative integers have a semantics (wrap 
> around) that is well-known to all Xen developers."
> +-config=MC3A2.R10.1,etypes+={safe,
> +  "stmt(node(unary_operator)&&operator(minus))",
> +  "src_expr(definitely_in(0..))"}
> +-doc_end
> +
>   #
>   # Series 11
>   #
> diff --git a/docs/misra/deviations.rst b/docs/misra/deviations.rst
> index cfdd1a9838..c5897e31c5 100644
> --- a/docs/misra/deviations.rst
> +++ b/docs/misra/deviations.rst
> @@ -321,6 +321,12 @@ Deviations related to MISRA C:2012 Rules:
>          If no bits are set, 0 is returned.
>        - Tagged as `safe` for ECLAIR.
>
> +   * - R10.1
> +     - Applying the unary minus operator to an unsigned quantity has a
> +       semantics (wrap around) that is well-known to all Xen developers.
> +       For this reason, the operation is safe.
I have realized we use similar wording in the rest of the deviations, 
but this is rather fragile argument. "well-known" is very subjective and 
could change over time.
How many violations do we have? Could we deviate them one by one?

Cheers,

--
Julien Grall