linux-kernel - Re: [PATCH] perf/x86/amd: Explicitly define PERF_COUNT_HW_REF_CPU

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Date:	Wed, 27 Apr 2016 10:03:45 +0200
From:	Ingo Molnar <mingo@...nel.org>
To:	Adam Borowski <kilobyte@...band.pl>
Cc:	linux-kernel@...r.kernel.org,
	Stephane Eranian <eranian@...gle.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
	Borislav Petkov <bp@...e.de>
Subject: Re: [PATCH] perf/x86/amd: Explicitly define
 PERF_COUNT_HW_REF_CPU_CYCLES as undefined.


* Adam Borowski <kilobyte@...band.pl> wrote:

> filter_events() relies on the value of 0 to remove events that are not
> applicable, like this one.
> 
> UBSAN: Undefined behaviour in arch/x86/events/amd/core.c:132:30
> index 9 is out of range for type 'u64 [9]'
> UBSAN: Undefined behaviour in arch/x86/events/amd/core.c:132:9
> load of address ffffffff81c021c8 with insufficient space
> for an object of type 'const u64'
> 
> Signed-off-by: Adam Borowski <kilobyte@...band.pl>
> ---
>  arch/x86/events/amd/core.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/arch/x86/events/amd/core.c b/arch/x86/events/amd/core.c
> index 86a9bec..5fa1b8e 100644
> --- a/arch/x86/events/amd/core.c
> +++ b/arch/x86/events/amd/core.c
> @@ -125,6 +125,7 @@ static const u64 amd_perfmon_event_map[] =
>    [PERF_COUNT_HW_BRANCH_MISSES]			= 0x00c3,
>    [PERF_COUNT_HW_STALLED_CYCLES_FRONTEND]	= 0x00d0, /* "Decoder empty" event */
>    [PERF_COUNT_HW_STALLED_CYCLES_BACKEND]	= 0x00d1, /* "Dispatch stalls" event */
> +  [PERF_COUNT_HW_REF_CPU_CYCLES]		=      0,
>  };

Hm, I think it would be cleaner and more robust to change this (and all other 
similar, if any) arrays to [PERF_COUNT_HW_MAX] instead.

Thanks,

	Ingo