linux-kernel - Re: [PATCH] perf/x86/intel: Fix unwind errors from PEBS entries (mk-II)

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Date:   Mon, 6 Aug 2018 20:04:23 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Fubo Chen <fubo.chen@...il.com>
Cc:     jpoimboe@...hat.com, Ingo Molnar <mingo@...nel.org>,
        bhole_prashant_q7@....ntt.co.jp,
        Linux Kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] perf/x86/intel: Fix unwind errors from PEBS entries
 (mk-II)

On Mon, Aug 06, 2018 at 09:54:23AM -0700, Fubo Chen wrote:
> On Mon, Aug 6, 2018 at 8:42 AM Peter Zijlstra <peterz@...radead.org> wrote:
> >
> > On Mon, Aug 06, 2018 at 08:35:07AM -0700, Fubo Chen wrote:
> > > On Thu, Jul 19, 2018 at 2:21 PM Peter Zijlstra <peterz@...radead.org> wrote:
> > > > --- a/include/uapi/linux/perf_event.h
> > > > +++ b/include/uapi/linux/perf_event.h
> > > > @@ -143,6 +143,8 @@ enum perf_event_sample_format {
> > > >         PERF_SAMPLE_PHYS_ADDR                   = 1U << 19,
> > > >
> > > >         PERF_SAMPLE_MAX = 1U << 20,             /* non-ABI */
> > > > +
> > > > +       __PERF_SAMPLE_CALLCHAIN_EARLY           = 1UL << 63,
> > > >  };
> > >
> > > The above change makes sparse unhappy :-( Sparse reports the following
> > > complaint about __PERF_SAMPLE_CALLCHAIN_EARLY:
> >
> > I thought I changed that to 1ULL before commit.
> 
> The sparse complaint was reported for code with the "1ULL << 63".

Ah ok.. and I think I see what you mean. The C standard says that enums
shall be 'int'. However C++ standard says any integer type that fits the
largest value.

I suppose GCC uses the C++ definition and I suspect many other compilers
will too.