Re: [RFC XEN PATCH] x86/mctelem: address violations of MISRA C: 2012 Rule 5.3

[Nicola Vetrini <nicola.vetrini@xxxxxxxxxxx>]

On 2024-06-24 11:00, Jan Beulich wrote:
> On 21.06.2024 11:50, Nicola Vetrini wrote:
> > From: Alessandro Zucchelli <alessandro.zucchelli@xxxxxxxxxxx>
> >
> > This addresses violations of MISRA C:2012 Rule 5.3 which states as
> > following: An identifier declared in an inner scope shall not hide an
> > identifier declared in an outer scope. In this case the shadowing is 
> > between
> > local variables "mctctl" and the file-scope static struct variable 
> > with the
> > same name.
> >
> > No functional change.
> >
> > Signed-off-by: Alessandro Zucchelli <alessandro.zucchelli@xxxxxxxxxxx>
> > Signed-off-by: Nicola Vetrini <nicola.vetrini@xxxxxxxxxxx>
> > ---
> > RFC because I'm not 100% sure the semantics of the code is preserved.
> > I think so, and it passes gitlab pipelines [1], but there may be some 
> > missing
> > information.
> Details as to your concerns would help. I see no issue, not even a 
> concern.
That's reassuring. My main concern was that somehow the global (trough 
perhaps some macro expansion) would be updated instead of the local (or 
viceversa).
> > --- a/xen/arch/x86/cpu/mcheck/mctelem.c
> > +++ b/xen/arch/x86/cpu/mcheck/mctelem.c
> > @@ -168,14 +168,14 @@ static void mctelem_xchg_head(struct mctelem_ent 
> > **headp,
> >  void mctelem_defer(mctelem_cookie_t cookie, bool lmce)
> >  {
> >         struct mctelem_ent *tep = COOKIE2MCTE(cookie);
> > -       struct mc_telem_cpu_ctl *mctctl = &this_cpu(mctctl);
> > +       struct mc_telem_cpu_ctl *mctctl_cpu = &this_cpu(mctctl);
> When possible (i.e. without loss of meaning) I'd generally prefer names 
> to
> be shortened. Wouldn't just "ctl" work here?
I can try. I do not expect shadowing with "ctl", but it may happen. I'll 
try and let you know.
> > -       ASSERT(mctctl->pending == NULL || mctctl->lmce_pending == NULL);
> > +	ASSERT(mctctl_cpu->pending == NULL || mctctl_cpu->lmce_pending == 
> > NULL);
> > -       if (mctctl->pending)
> > -               mctelem_xchg_head(&mctctl->pending, &tep->mcte_next, tep);
> > +       if (mctctl_cpu->pending)
> > +               mctelem_xchg_head(&mctctl_cpu->pending, &tep->mcte_next, tep);
> >         else if (lmce)
> > -               mctelem_xchg_head(&mctctl->lmce_pending, &tep->mcte_next, tep);
> > +               mctelem_xchg_head(&mctctl_cpu->lmce_pending, &tep->mcte_next, 
> > tep);
> >         else {
> >                 /*
> >                  * LMCE is supported on Skylake-server and later CPUs, on
> > @@ -186,10 +186,10 @@ void mctelem_defer(mctelem_cookie_t cookie, bool 
> > lmce)
> >                  * moment. As a result, the following two exchanges together
> >                  * can be treated as atomic.
> >                  */
> In the middle of this comment the variable is also mentioned, and hence
> also wants adjusting (twice).
Ok, will update.

> > -               if (mctctl->lmce_pending)
> > -                       mctelem_xchg_head(&mctctl->lmce_pending,
> > -                                         &mctctl->pending, NULL);
> > -               mctelem_xchg_head(&mctctl->pending, &tep->mcte_next, tep);
> > +               if (mctctl_cpu->lmce_pending)
> > +                       mctelem_xchg_head(&mctctl_cpu->lmce_pending,
> > +                                         &mctctl_cpu->pending, NULL);
> > +               mctelem_xchg_head(&mctctl_cpu->pending, &tep->mcte_next, tep);
> >         }
> >  }
> >
> > @@ -213,7 +213,7 @@ void mctelem_process_deferred(unsigned int cpu,
> >  {
> >         struct mctelem_ent *tep;
> >         struct mctelem_ent *head, *prev;
> > -       struct mc_telem_cpu_ctl *mctctl = &per_cpu(mctctl, cpu);
> > +       struct mc_telem_cpu_ctl *mctctl_cpu = &per_cpu(mctctl, cpu);
> >         int ret;
> >
> >         /*
> > @@ -232,7 +232,7 @@ void mctelem_process_deferred(unsigned int cpu,
> >          * Any MC# occurring after the following atomic exchange will be
> >          * handled by another round of MCE softirq.
> >          */
> > -       mctelem_xchg_head(lmce ? &mctctl->lmce_pending : &mctctl->pending,
> > +	mctelem_xchg_head(lmce ? &mctctl_cpu->lmce_pending : 
> > &mctctl_cpu->pending,
> >                           &this_cpu(mctctl.processing), NULL);
> By shortening the variable name here you'd also avoid going past line
> length limits.
Ok.

--
Nicola Vetrini, BSc
Software Engineer, BUGSENG srl (https://bugseng.com)