Re: [XEN PATCH v2 1/2] automation/eclair: update configuration of Rule 20.7

[Stefano Stabellini <sstabellini@xxxxxxxxxx>]

On Tue, 10 Sep 2024, Federico Serafini wrote:
> MISRA C:2012 Rule 20.7 states that "Expressions resulting from the
> expansion of macro parameters shall be enclosed in parentheses".
> The rational of the rule is that if a macro argument expands to an
> expression, there may be problems related to operator precedence, e.g.,
> 
> define M(A, B) A * B
> 
> M(1+1, 2+2) will expand to: 1+1 * 2+2
> 
> Update ECLAIR configuration to tag as 'safe' the expansions of macro
> arguments surrounded tokens '{', '}' and ';', since in their presence
> problems related to operator precedence can not occur.
> 
> Signed-off-by: Federico Serafini <federico.serafini@xxxxxxxxxxx>

Acked-by: Stefano Stabellini <sstabellini@xxxxxxxxxx>


> ---
> Changes from v1:
> - more details to justify the deviation;
> - split modifications in two patches.
> ---
>  automation/eclair_analysis/ECLAIR/deviations.ecl | 4 ++++
>  docs/misra/deviations.rst                        | 5 +++++
>  2 files changed, 9 insertions(+)
> 
> diff --git a/automation/eclair_analysis/ECLAIR/deviations.ecl 
> b/automation/eclair_analysis/ECLAIR/deviations.ecl
> index 9051f41602..e0d9426b7a 100644
> --- a/automation/eclair_analysis/ECLAIR/deviations.ecl
> +++ b/automation/eclair_analysis/ECLAIR/deviations.ecl
> @@ -581,6 +581,10 @@ of this macro do not lead to developer confusion, and 
> can thus be deviated."
>  -config=MC3R1.R20.7,reports+={safe, 
> "any_area(any_loc(any_exp(macro(^count_args_$))))"}
>  -doc_end
>  
> +-doc_begin="Problems related to operator precedence can not occur if the 
> expansion of the macro argument is surrounded by tokens '{', '}' and ';'."
> +-config=MC3R1.R20.7,expansion_context+={safe, 
> "left_right(^[\\{;]$,^[;\\}]$)"}
> +-doc_end
> +
>  -doc_begin="Uses of variadic macros that have one of their arguments defined 
> as
>  a macro and used within the body for both ordinary parameter expansion and 
> as an
>  operand to the # or ## operators have a behavior that is well-understood and
> diff --git a/docs/misra/deviations.rst b/docs/misra/deviations.rst
> index b66c271c4e..69f93a6a91 100644
> --- a/docs/misra/deviations.rst
> +++ b/docs/misra/deviations.rst
> @@ -534,6 +534,11 @@ Deviations related to MISRA C:2012 Rules:
>         refactoring it to add parentheses breaks its functionality.
>       - Tagged as `safe` for ECLAIR.
>  
> +   * - R20.7
> +     - Problems related to operator precedence can not occur if the expansion
> +       of the macro argument is surrounded by tokens '{', '}' and ';'.
> +     - Tagged as `safe` for ECLAIR.
> +
>     * - R20.12
>       - Variadic macros that use token pasting often employ the gcc extension
>         `ext_paste_comma`, as detailed in `C-language-toolchain.rst`, which is
> -- 
> 2.34.1
>