linux-kernel - Re: [PATCH] perf: enum overflow in uapi/linux/perf

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Date:   Fri, 7 Sep 2018 16:15:33 +0200
From:   Christophe LEROY <christophe.leroy@....fr>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...hat.com>,
        Namhyung Kim <namhyung@...nel.org>,
        linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
        linux-sparse@...r.kernel.org
Subject: Re: [PATCH] perf: enum overflow in uapi/linux/perf_event.h



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@...6082vm linux-powerpc]# sparse --version
>> 0.5.2
>>
>> [root@...6082vm 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