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

[Luc Van Oostenryck <luc.vanoostenryck@gmail.com>]

On Fri, Sep 07, 2018 at 04:15:33PM +0200, Christophe LEROY wrote:
> Le 07/09/2018 à 15:58, Peter Zijlstra a écrit :
> > 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.

Sparse is a bit weird about the exact underlying type used for enums.

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

I'll investigate (I suppose the same is given on x86-32).

-- Luc