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Subject: Re: [PATCH] perf: enum overflow in uapi/linux/perf_event.h
To:     Peter Zijlstra <peterz@infradead.org>
Cc:     Ingo Molnar <mingo@redhat.com>,
        Arnaldo Carvalho de Melo <acme@kernel.org>,
        Alexander Shishkin <alexander.shishkin@linux.intel.com>,
        Jiri Olsa <jolsa@redhat.com>,
        Namhyung Kim <namhyung@kernel.org>,
        linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org,
        linux-sparse@vger.kernel.org
References: <a70172863fa7d3c138f788b18d36524bd45b0a73.1536326078.git.christophe.leroy@c-s.fr>
 <20180907134246.GC24106@hirez.programming.kicks-ass.net>
 <ae32181d-37b2-1a13-3c72-66775e05ff88@c-s.fr>
 <20180907135817.GF24106@hirez.programming.kicks-ass.net>
From:   Christophe LEROY <christophe.leroy@c-s.fr>
Message-ID: <7a086a56-a896-9513-7315-9d0d21b61a44@c-s.fr>
Date:   Fri, 7 Sep 2018 16:15:33 +0200
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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.
> 

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