Re: struct mctelem_cookie missing definition

[Nicola Vetrini <nicola.vetrini@xxxxxxxxxxx>]

On 2025-02-15 00:04, Stefano Stabellini wrote:
> On Fri, 14 Feb 2025, Jan Beulich wrote:
> > > Would deviating macros "COOKIE2MCTE" and "MCTE2COOKIE" work?
> >
> > If it did, COOKIE2ID and ID2COOKIE would likely need including as 
> > well.
> I wrote this patch. Nicola, can you please check the changes to
> deviations.ecl, this is the first time I try to write the deviation
> myself :-)
>
> ---
> misra: add 11.2 deviation for incomplete types
>
> struct mctelem_cookie* is used exactly because it is an incomplete type
> so the pointer cannot be dereferenced. This is deliberate. So add a
> deviation for it.
>
> In deviations.ecl, add the list of macros that do the conversions to 
> and
> from struct mctelem_cookie*.
>
> Signed-off-by: Stefano Stabellini <stefano.stabellini@xxxxxxx>
>
> diff --git a/automation/eclair_analysis/ECLAIR/deviations.ecl 
> b/automation/eclair_analysis/ECLAIR/deviations.ecl
> index a28eb0ae76..87bfd2160c 100644
> --- a/automation/eclair_analysis/ECLAIR/deviations.ecl
> +++ b/automation/eclair_analysis/ECLAIR/deviations.ecl
> @@ -366,6 +366,14 @@ constant expressions are required.\""
>  }
>  -doc_end
>
> +-doc_begin="Certain pointers point to incomplete types purposely so 
> that they are impossible to dereference."
> +-config=MC3A2.R11.2,reports+={deliberate, 
> "any_area(any_loc(any_exp(macro(^COOKIE2MCTE$))))"}
> +-config=MC3A2.R11.2,reports+={deliberate, 
> "any_area(any_loc(any_exp(macro(^MCTE2COOKIE$))))"}
> +-config=MC3A2.R11.2,reports+={deliberate, 
> "any_area(any_loc(any_exp(macro(^COOKIE2ID$))))"}
> +-config=MC3A2.R11.2,reports+={deliberate, 
> "any_area(any_loc(any_exp(macro(^ID2COOKIE$))))"}
> +}
-config=MC3A2.R11.2,reports+={deliberate, 
"any_area(any_loc(any_exp(macro(name(COOKIE2MCTE||MCTE2COOKIE||COOKIE2ID||ID2COOKIE)))))"}
Note however that there is also this deviation in place

-doc_begin="The conversion from a pointer to an incomplete type to 
unsigned long does not lose any information, provided that the target 
type has enough bits to store it."
-config=MC3A2.R11.2,casts+={safe,
  "from(type(any()))
   &&to(type(canonical(builtin(unsigned long))))
   &&relation(definitely_preserves_value)"
}
-doc_end

I was a bit confused by Jan's remark, which seemed correct, but I 
couldn't see any violations in the report, so I dug a bit deeper. 
ID2COOKIE and COOKIE2ID, which operate to/from unsigned long are already 
excluded due to being safe. If you envision those macros to be used with 
other types, then your deviation should mention them, otherwise they are 
already handled.
> +-doc_end
> +
>  -doc_begin="Conversions to object pointers that have a pointee type 
> with a smaller (i.e., less strict) alignment requirement are safe."
>  -config=MC3A2.R11.3,casts+={safe,
>    "!relation(more_aligned_pointee)"
> diff --git a/docs/misra/deviations.rst b/docs/misra/deviations.rst
> index fe0b1e10a2..f3004d6023 100644
> --- a/docs/misra/deviations.rst
> +++ b/docs/misra/deviations.rst
> @@ -324,6 +324,12 @@ Deviations related to MISRA C:2012 Rules:
>         semantics that do not lead to unexpected behaviour.
>       - Tagged as `safe` for ECLAIR.
>
> +   * - R11.2
> +     - Certain pointers point to incomplete types purposely so that 
> they
> +       are impossible to dereference.
> +     - Tagged as `deliberate` for ECLAIR. Such pointer is struct
> +       mctelem_cookie \*.
> +
I think here (or above in the deviation text) the concern raised by the 
rationale of the rule should be addressed; namely, the rule states: 
"Conversions shall not be performed between a pointer to an incomplete 
type and any other type" because the resulting pointer might be 
misaligned, therefore there should be an argument as to why such thing 
is not possible.
>     * - R11.2
>       - The conversion from a pointer to an incomplete type to unsigned 
> long
>         does not lose any information, provided that the target type 
> has enough
Thanks,
 Nicola

--
Nicola Vetrini, B.Sc.
Software Engineer
BUGSENG (https://bugseng.com)
LinkedIn: https://www.linkedin.com/in/nicola-vetrini-a42471253