Re: struct mctelem_cookie missing definition

[Nicola Vetrini <nicola.vetrini@xxxxxxxxxxx>]

On 2025-02-14 04:00, Stefano Stabellini wrote:
> On Thu, 13 Feb 2025, Stefano Stabellini wrote:
> > > > diff --git a/xen/arch/x86/cpu/mcheck/mctelem.h 
> > b/xen/arch/x86/cpu/mcheck/mctelem.h
> > > > index f4c5ff848d..2ccd490e5d 100644
> > > > --- a/xen/arch/x86/cpu/mcheck/mctelem.h
> > > > +++ b/xen/arch/x86/cpu/mcheck/mctelem.h
> > > > @@ -52,7 +52,7 @@
> > > >   * the element from the processing list.
> > > >   */
> > > >
> > > > -typedef struct mctelem_cookie *mctelem_cookie_t;
> > > > +typedef uint64_t *mctelem_cookie_t;
> > >
> > > Yet that makes it possible to de-reference the pointer. Which, as Andrew
> > > explained, is intended to be impossible. If this could be properly
> > > replaced (not exactly what Andrew indicated by "file it in /dev/null"),
> > > fine. Truly purging the code (i.e. as Andrew suggests) may still be an
> > > option, with appropriate justification. But simply adjusting the type
> > > and then moving on is too little, imo. Even if you used void * (to make
> > > de-referencing impossible) I'd view it as largely papering over an issue;
> > > then converting to other pointers (without explicit cast, and hence
> > > without making apparent the badness of doing so) would become possible.
> >
> > What about converting to uintptr_t (not a pointer)?
> >
> >
> > In general, there are quite a few MISRA rules that we could mark as
> > blocking (clean) in our GitLab scan with just a few code changes like
> > this one. My goal is to make these rules blocking as soon as possible.
> > If I can improve the code in the process, that is even better, but it 
> > is
> > not mandatory. And I would rather spend one more hour marking a second
> > rule as blocking instead.
> >
> > What I mean is that I believe it would be acceptable to make some
> > compromises and accept non-perfect changes to the code if it helps us
> > enforce more rules as blocking in GitLab CI.
> After briefly speaking with Andrew about this, and re-reading Jan's
> email above, I think it is best to resolve this as a deviation.
>
> Would this deviation work for you? Please suggest a better wording if
> you prefer.
>
> Nicola, in reality I think it would be better to use deviations.rst
> because the SAF comment below would need to be replicated at every call
> side, if I am not mistaken.
Would deviating macros "COOKIE2MCTE" and "MCTE2COOKIE" work?
In that case, that is a simple configuration tweak which then will be 
justified in deviations.rst.
Thanks,
 Nicola

> diff --git a/docs/misra/safe.json b/docs/misra/safe.json
> index b8a4f878ea..d9fbe959d1 100644
> --- a/docs/misra/safe.json
> +++ b/docs/misra/safe.json
> @@ -92,6 +92,14 @@
>          },
>          {
>              "id": "SAF-11-safe",
> +            "analyser": {
> +                "eclair": "MC3A2.R11.2"
> +            },
> +            "name": "Rule 11.2: purposely impossible to dereference",
> +            "text": "Certain pointers points to incomplete types 
> purposely so that they are impossible to dereference."
> +        },
> +        {
> +            "id": "SAF-12-safe",
>              "analyser": {},
>              "name": "Sentinel",
>              "text": "Next ID to be used"
> diff --git a/xen/arch/x86/cpu/mcheck/mctelem.h 
> b/xen/arch/x86/cpu/mcheck/mctelem.h
> index f4c5ff848d..e845360c7d 100644
> --- a/xen/arch/x86/cpu/mcheck/mctelem.h
> +++ b/xen/arch/x86/cpu/mcheck/mctelem.h
> @@ -52,6 +52,7 @@
>   * the element from the processing list.
>   */
>
> +/* SAF-11-safe: impossible to dereference */
>  typedef struct mctelem_cookie *mctelem_cookie_t;
>
>  typedef enum mctelem_class {
--
Nicola Vetrini, B.Sc.
Software Engineer
BUGSENG (https://bugseng.com)
LinkedIn: https://www.linkedin.com/in/nicola-vetrini-a42471253