Re: struct mctelem_cookie missing definition

[Stefano Stabellini <sstabellini@xxxxxxxxxx>]

On Tue, 18 Feb 2025, Jan Beulich wrote:
> On 18.02.2025 03:45, Stefano Stabellini wrote:
> > On Mon, 17 Feb 2025, Jan Beulich wrote:
> >> On 15.02.2025 09:59, Nicola Vetrini wrote:
> >>> 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.
> >>
> >> Yet then can't we leverage that deviation to also make the other two
> >> covered:
> >>
> >> #define    COOKIE2MCTE(c)          ((struct mctelem_ent *)(unsigned 
> >> long)(c))
> >> #define    MCTE2COOKIE(tep)        ((mctelem_cookie_t)(unsigned long)(tep))
> > 
> > Jan is asking why ID2COOKIE and COOKIE2ID are considered safe, while
> > COOKIE2MCTE and MCTE2COOKIE are not. I think the reason is that
> > ID2COOKIE and COOKIE2ID convert to/from unsigned long and that falls
> > under the other deviation we already have:
> > 
> > -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)"
> > 
> > On the other hand COOKIE2MCTE and MCTE2COOKIE convert to/from another
> > pointer type, so they don't fall under the same deviation.
> 
> And then the adjusted forms suggested above ought to also be covered,
> I would have thought.

I understand your point. I tried it, but it does not work. I do not know
why. Someone with more knowledge of ECLAIR internals than I have might
be able to explain.

https://saas.eclairit.com:3787/fs/var/local/eclair/xen-project.ecdf/xen-project/people/sstabellini/xen/ECLAIR_normal/my-eclair-11.2-4-1/X86_64/9176469474/PROJECT.ecd;/by_service/MC3A2.R11.2.html#{%22select%22:true,%22selection%22:{%22hiddenAreaKinds%22:[],%22hiddenSubareaKinds%22:[],%22show%22:false,%22selector%22:{%22enabled%22:true,%22negated%22:true,%22kind%22:0,%22domain%22:%22kind%22,%22inputs%22:[{%22enabled%22:true,%22text%22:%22violation%22}]}}}


I suggest we go with this patch instead.

---
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..d33b777e6a 100644
--- a/automation/eclair_analysis/ECLAIR/deviations.ecl
+++ b/automation/eclair_analysis/ECLAIR/deviations.ecl
@@ -366,6 +366,10 @@ 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(name(COOKIE2MCTE||MCTE2COOKIE||COOKIE2ID||ID2COOKIE)))))"}
+-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..04ffc62f44 100644
--- a/docs/misra/deviations.rst
+++ b/docs/misra/deviations.rst
@@ -324,6 +324,13 @@ 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, since they cannot be dereferenced,
+       pointers alignments considerations do not apply.
+     - Tagged as `deliberate` for ECLAIR. Such pointer is struct
+       mctelem_cookie \*.
+
    * - 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