Re: [XEN PATCH v2] automation/eclair_analysis: deviate certain macros for Rule 20.12

[Stefano Stabellini <sstabellini@xxxxxxxxxx>]

On Thu, 15 Feb 2024, Nicola Vetrini wrote:
> Certain macros are allowed to violate the Rule, since their meaning and
> intended use is well-known to all Xen developers.
> 
> Variadic macros that rely on the GCC extension for removing a trailing
> comma when token pasting the variable argument are similarly
> well-understood and therefore allowed.
> 
> No functional change.
> 
> Signed-off-by: Nicola Vetrini <nicola.vetrini@xxxxxxxxxxx>

Reviewed-by: Stefano Stabellini <sstabellini@xxxxxxxxxx>



> ---
> Changes in v2:
> - Restrict deviation for GENERATE_CASE to vcpreg.c.
> - Improve deviation justifications.
> ---
>  .../eclair_analysis/ECLAIR/deviations.ecl     | 20 +++++++++++++++++
>  docs/misra/deviations.rst                     | 22 +++++++++++++++++++
>  2 files changed, 42 insertions(+)
> 
> diff --git a/automation/eclair_analysis/ECLAIR/deviations.ecl 
> b/automation/eclair_analysis/ECLAIR/deviations.ecl
> index fd32ff8a9cae..04cb41e16a50 100644
> --- a/automation/eclair_analysis/ECLAIR/deviations.ecl
> +++ b/automation/eclair_analysis/ECLAIR/deviations.ecl
> @@ -387,6 +387,26 @@ in assignments."
>  {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
> +deliberate."
> +-config=MC3R1.R20.12,macros+={deliberate, "variadic()"}
> +-doc_end
> +
> +-doc_begin="Uses of a macro parameter for ordinary expansion and as an 
> operand
> +to the # or ## operators within the following macros are deliberate, to 
> provide
> +useful diagnostic messages to the user."
> +-config=MC3R1.R20.12,macros+={deliberate, 
> "name(ASSERT||BUILD_BUG_ON||BUILD_BUG_ON_ZERO)"}
> +-doc_end
> +
> +-doc_begin="The helper macro GENERATE_CASE may use a macro parameter for 
> ordinary
> +expansion and token pasting to improve readability. Only instances where this
> +leads to a violation of the Rule are deviated."
> +-file_tag+={deliberate_generate_case, "^xen/arch/arm/vcpreg\\.c$"}
> +-config=MC3R1.R20.12,macros+={deliberate, 
> "name(GENERATE_CASE)&&loc(file(deliberate_generate_case))"}
> +-doc_end
> +
>  #
>  # General
>  #
> diff --git a/docs/misra/deviations.rst b/docs/misra/deviations.rst
> index 123c78e20a01..84da637ef888 100644
> --- a/docs/misra/deviations.rst
> +++ b/docs/misra/deviations.rst
> @@ -330,6 +330,28 @@ Deviations related to MISRA C:2012 Rules:
>         (4) as lhs in assignments.
>       - 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
> +       not easily replaceable; macros that in addition perform regular 
> argument
> +       expansion on the same argument subject to the # or ## operators 
> violate
> +       the Rule if the argument is a macro. 
> +     - Tagged as `deliberate` for ECLAIR.
> +
> +   * - R20.12
> +     - Macros that are used for runtime or build-time assertions contain
> +       deliberate uses of an argument as both a regular argument and a
> +       stringification token, to provide useful diagnostic messages.
> +     - Tagged as `deliberate` for ECLAIR.
> +
> +   * - R20.12
> +     - GENERATE_CASE is a local helper macro that allows some selected switch
> +       statements to be more compact and readable. As such, the risk of
> +       developer confusion in using such macro is deemed negligible. This
> +       construct is deviated only in Translation Units that present a 
> violation
> +       of the Rule due to uses of this macro.
> +     - Tagged as `deliberate` for ECLAIR.
> +
>  Other deviations:
>  -----------------
>  
> -- 
> 2.34.1
>