Re: [XEN PATCH] misra: deviate violations of Rule 21.6

[Stefano Stabellini <sstabellini@xxxxxxxxxx>]

On Tue, 1 Jul 2025, Dmytro Prokopchuk1 wrote:
> From: Federico Serafini <federico.serafini@xxxxxxxxxxx>
> 
> MISRA C Rule 21.6 states that "The Standard Library input/output
> functions shall not be used".
> 
> Xen does not use the functions provided by the Standard Library,
> uses -nostdlib to ensure this.
> Xen implements a set of functions that share the same names as their
> Standard Library equivalent. The implementation of these functions is
> available in source form: if some undefined or unspecified behavior
> does arise in the implementation, it falls under the jurisdiction of
> other MISRA guidelines.
> 
> Update ECLAIR configuration to deviate violations of the rule,
> tag it as clean and add it to the monitored set.
> 
> Updated docs/misra/deviations.rst accordingly.
> 
> Signed-off-by: Federico Serafini <federico.serafini@xxxxxxxxxxx>
> Signed-off-by: Dmytro Prokopchuk <dmytro_prokopchuk1@xxxxxxxx>

Reviewed-by: Stefano Stabellini <sstabellini@xxxxxxxxxx>


> ---
> 
> The latest Eclair analysis shows 20 violations (ARM64 and X86_64) of the rule 
> MC3A2.R21.6.
> In details:
> 14 violations - use of function `snprintf(char*, size_t, const char*, ...)' 
> (<stdio.h>)
> 6  violations - use of function `vsnprintf(char*, size_t, const char*, 
> va_list)' (<stdio.h>)
> As mentioned before Xen doen't use Standard Library input/output functions.
> It implements its own functions in the common/vsprintf.c.
> So this Rule can be deviated.
> 
>  automation/eclair_analysis/ECLAIR/deviations.ecl |  3 ++-
>  automation/eclair_analysis/ECLAIR/monitored.ecl  |  1 +
>  automation/eclair_analysis/ECLAIR/tagging.ecl    |  1 +
>  docs/misra/deviations.rst                        | 11 ++++++++++-
>  4 files changed, 14 insertions(+), 2 deletions(-)
> 
> diff --git a/automation/eclair_analysis/ECLAIR/deviations.ecl 
> b/automation/eclair_analysis/ECLAIR/deviations.ecl
> index 9c67358d46..3a4d9ee3c0 100644
> --- a/automation/eclair_analysis/ECLAIR/deviations.ecl
> +++ b/automation/eclair_analysis/ECLAIR/deviations.ecl
> @@ -650,7 +650,8 @@ implements a set of functions that share the same names 
> as their Standard Librar
>  The implementation of these functions is available in source form, so the 
> undefined, unspecified
>  or implementation-defined behaviors contemplated by the C Standard do not 
> apply.
>  If some undefined or unspecified behavior does arise in the implementation, 
> it
> -falls under the jurisdiction of other MISRA rules."
> +falls under the jurisdiction of other MISRA guidelines."
> +-config=MC3A2.R21.6,reports+={deliberate, "any()"}
>  -config=MC3A2.R21.9,reports+={deliberate, "any()"}
>  -config=MC3A2.R21.10,reports+={deliberate, "any()"}
>  -doc_end
> diff --git a/automation/eclair_analysis/ECLAIR/monitored.ecl 
> b/automation/eclair_analysis/ECLAIR/monitored.ecl
> index ca2f5e3c7f..e2ad224d79 100644
> --- a/automation/eclair_analysis/ECLAIR/monitored.ecl
> +++ b/automation/eclair_analysis/ECLAIR/monitored.ecl
> @@ -82,6 +82,7 @@
>  -enable=MC3A2.R20.14
>  -enable=MC3A2.R21.3
>  -enable=MC3A2.R21.4
> +-enable=MC3A2.R21.6
>  -enable=MC3A2.R21.5
>  -enable=MC3A2.R21.7
>  -enable=MC3A2.R21.8
> diff --git a/automation/eclair_analysis/ECLAIR/tagging.ecl 
> b/automation/eclair_analysis/ECLAIR/tagging.ecl
> index f9da5d5f4d..5bf214f480 100644
> --- a/automation/eclair_analysis/ECLAIR/tagging.ecl
> +++ b/automation/eclair_analysis/ECLAIR/tagging.ecl
> @@ -93,6 +93,7 @@ MC3A2.R20.14||
>  MC3A2.R21.3||
>  MC3A2.R21.4||
>  MC3A2.R21.5||
> +MC3A2.R21.6||
>  MC3A2.R21.7||
>  MC3A2.R21.8||
>  MC3A2.R21.9||
> diff --git a/docs/misra/deviations.rst b/docs/misra/deviations.rst
> index fe0b1e10a2..6cd8f48c91 100644
> --- a/docs/misra/deviations.rst
> +++ b/docs/misra/deviations.rst
> @@ -587,7 +587,16 @@ Deviations related to MISRA C:2012 Rules:
>         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.
> -     
> +
> +   * - R21.6
> +     - Xen does not use the input/output functions provided by the C
> +       Standard Library, but provides in source form its own implementation,
> +       therefore any unspecified or undefined behavior associated to the
> +       functions provided by the Standard Library does not apply. Any such
> +       behavior that may exist in such functions is therefore under the
> +       jurisdiction of other MISRA C guidelines.
> +     - Tagged as `deliberate` for ECLAIR.
> +
>     * - R21.9
>       - Xen does not use the `bsearch` and `qsort` functions provided by the C
>         Standard Library, but provides in source form its own implementation,
> -- 
> 2.43.0
>