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

On Fri, Sep 07, 2018 at 08:43:59PM +0200, Luc Van Oostenryck wrote:

On Fri, Sep 07, 2018 at 04:15:33PM +0200, Christophe LEROY wrote:

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Le 07/09/2018 à 15:58, Peter Zijlstra a écrit :

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On Fri, Sep 07, 2018 at 01:50:18PM +0000, Christophe Leroy wrote:

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On 09/07/2018 01:42 PM, Peter Zijlstra wrote:

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On Fri, Sep 07, 2018 at 01:27:19PM +0000, Christophe Leroy wrote:

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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.

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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).

It's definitively a bug in sparse. A relatively nasty one and which
open a can of worms. Fortunately, I had already looked at these
problems in May, I just didn't had the time to push the patches.

-- Luc