Re: [PATCH] perf: enum overflow in uapi/linux/perf_event.h

[Christophe LEROY]

Le 07/09/2018 Ã 15:58, Peter Zijlstra a ÃcritÂ:
> On Fri, Sep 07, 2018 at 01:50:18PM +0000, Christophe Leroy wrote:
> > On 09/07/2018 01:42 PM, Peter Zijlstra wrote:
> > > On Fri, Sep 07, 2018 at 01:27:19PM +0000, Christophe Leroy wrote:
> > > > On PPC32, enums are 32 bits, so __PERF_SAMPLE_CALLCHAIN_EARLY is
> > > > out of scope. The following sparse warning is encountered:
> > > >
> > > >     CHECK   arch/powerpc/kernel/process.c
> > > > ./include/uapi/linux/perf_event.h:147:56: warning: cast truncates bits from constant value (8000000000000000 becomes 0)
> > >
> > > Urgh... what compiler is that? I've not seen anything like that from the
> > > build bots.
> >
> > [root@pc16082vm linux-powerpc]# sparse --version
> > 0.5.2
> >
> > [root@pc16082vm linux-powerpc]# ppc-linux-gcc --version
> > ppc-linux-gcc (GCC) 5.4.0
>
> Ah, that's a sparse warning. But does your GCC agree? The thing is,
> sparse uses the C enum spec, but I suspect GCC uses the C++ enum spec
> and it all works fine.

Ah yes, it seems that GCC is happy. So sparse should be fixed instead ?

Anyway, is it really correct to put this constant inside that enum, 
after PERF_SAMPLE_MAX  ?

Christophe