Re: [PATCH v3] automation/eclair: deviate R2.6 for the x86 emulator

[Nicola Vetrini <nicola.vetrini@xxxxxxxxxxx>]

On 2026-11-10 14:49, Shuaidong Chen wrote:
> MISRA C:2012 Rule 2.6 (advisory) states that "a function should not
> contain unused label declarations".
>
> Depending on which parts of the x86 emulator are compiled in, some of
> its labels end up with no goto targeting them.  For example, with
> CONFIG_HVM=n private.h defines X86EMUL_NO_FPU, X86EMUL_NO_MMX and
> X86EMUL_NO_SIMD: the CASE_SIMD_* macros then expand to plain labels
> instead of case labels, and the gotos to several hand-written simd_*
> labels are preprocessed out, leaving 91 unused labels in
> x86_emulate.c.  The build already acknowledges this by passing
> -Wno-unused-label for that object.
>
> Annotating these labels would only add churn to the emulator.  As done
> for Rule 16.2, deviate the rule for the emulator as a whole.
>
> Signed-off-by: Shuaidong Chen <shuaidong.chen@xxxxxxx>
Acked-by: Nicola Vetrini <nicola.vetrini@xxxxxxxxxxx> # eclair

See below for a small nit

> ---
> v3:
> - Drop the CONFIG_HVM=n specifics from the deviation text, as the
>   deviation itself isn't limited to that configuration.
>
> v2:
> - Drop the __maybe_unused annotations (v1 patch 1) and the CASE_SIMD_*
>   specific deviation (v1 patch 2) in favour of an emulator-wide
>   deviation, following the existing one for Rule 16.2.
> - Trim the Cc list.
>
>  automation/eclair_analysis/ECLAIR/deviations.ecl | 5 +++++
>  docs/misra/deviations.rst                        | 8 ++++++++
>  2 files changed, 13 insertions(+)
>
> diff --git a/automation/eclair_analysis/ECLAIR/deviations.ecl 
> b/automation/eclair_analysis/ECLAIR/deviations.ecl
> index 296340bb4c..12afc758dd 100644
> --- a/automation/eclair_analysis/ECLAIR/deviations.ecl
> +++ b/automation/eclair_analysis/ECLAIR/deviations.ecl
> @@ -55,6 +55,11 @@ removed by the compiler, the resulting slowdown is 
> negligible."
>  -config=MC3A2.R2.6,reports+={deliberate, 
> "any_area(text(^.*__maybe_unused.*$))"}
>  -doc_end
>
> +-doc_begin="Depending on which parts of the x86 emulator are compiled 
> in, some of its labels, many of them generated by the CASE_SIMD_* 
> macros, may end up with no goto targeting them.
> +Annotating them would only add churn to the emulator, therefore it is 
> deemed better to leave such files as is."
> +-config=MC3A2.R2.6,reports+={deliberate, 
> "any_area(any_loc(file(^xen/arch/x86/x86_emulate/.*$)))"}
> +-doc_end
> +
There is already a definition of that directory pattern for Rule 16.2 
[1]:
-file_tag+={x86_emulate,"^xen/arch/x86/x86_emulate/.*$"}

so you could just reuse that by moving this file_tag definition earlier. 
For instance:
-file_tag+={x86_emulate,"^xen/arch/x86/x86_emulate/.*$"}
[..]
-config=MC3A2.R2.6,reports+={deliberate, 
"any_area(any_loc(file(x86_emulate)))"}
[..]
-config=MC3A2.R16.2,reports+={deliberate, 
"any_area(any_loc(file(x86_emulate||x86_svm_emulate)))"}
[1] 
https://gitlab.com/xen-project/hardware/xen/-/blob/staging/automation/eclair_analysis/ECLAIR/deviations.ecl#L534
>  #
>  # Series 3.
>  #
> diff --git a/docs/misra/deviations.rst b/docs/misra/deviations.rst
> index bee4686675..7b983db264 100644
> --- a/docs/misra/deviations.rst
> +++ b/docs/misra/deviations.rst
> @@ -116,6 +116,14 @@ Deviations related to MISRA C:2012 Rules:
>         such labels poses no risks.
>       - Tagged as `deliberate` for ECLAIR.
>
> +   * - R2.6
> +     - Depending on which parts of the x86 emulator are compiled in, 
> some of
> +       its labels, many of them generated by the CASE_SIMD_* macros, 
> may end
> +       up with no goto targeting them. Annotating them would only add 
> churn
> +       to the emulator, therefore it is deemed better to leave such 
> files as
> +       is.
> +     - Tagged as `deliberate` for ECLAIR.
> +
>     * - R3.1
>       - Comments starting with '/\*' and containing URLs are safe as 
> they are
>         not instances of commented-out code.
--
Nicola Vetrini, B.Sc.
Software Engineer
BUGSENG (https://bugseng.com)
LinkedIn: https://www.linkedin.com/in/nicola-vetrini-a42471253