Re: [PATCH] x86/xen: silence smatch warning in pmu_msr_chk_emulated()

[Boris Ostrovsky]

On 10/20/22 9:34 AM, Juergen Gross wrote:
> On 20.10.22 15:16, Jan Beulich wrote:
> > On 20.10.2022 13:37, Juergen Gross wrote:
> > > Commit 8714f7bcd3c2 ("xen/pv: add fault recovery control to pmu msr
> > > accesses") introduced code resulting in a warning issued by the smatch
> > > static checker, claiming to use an uninitialized variable.
> > >
> > > This is a false positive, but work around the warning nevertheless.
> >
> > The risk of introducing a problem might be quite low here, but in general
> > it exists: With the adjustment you remove any chance of the compiler
> > spotting a missing initialization before use. And I'm not convinced using
> > 0 in such a case would actually be ending up sufficiently benign.
>
> Hmm, an alternative would be to initialize it to -1 and add a test for the
> index to be >= 0 before using it.
>
> Or to live with the smash warning with the chance, that a compiler might be
> warning for the same reason in the future.


Is smatch complaining about both variables or just index? There are two cases in is_intel_pmu_msr() where it returns true but index is not set so perhaps that's what bothers smatch? It shold not complain if is_intel_pmu_msr() returns false.


-boris