linux-kernel - Re: [PATCH v2 1/1] arm: perf: Fix ARCH=arm build with GCC

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Date: Fri, 15 Dec 2023 19:20:32 +0100
From: Uwe Kleine-König <u.kleine-koenig@...gutronix.de>
To: James Clark <james.clark@....com>
Cc: linux-arm-kernel@...ts.infradead.org, linux-perf-users@...r.kernel.org,
	linux-next@...r.kernel.org, will@...nel.org, mark.rutland@....com,
	Nathan Chancellor <nathan@...nel.org>,
	Nick Desaulniers <ndesaulniers@...gle.com>,
	Bill Wendling <morbo@...gle.com>,
	Justin Stitt <justinstitt@...gle.com>,
	Anshuman Khandual <anshuman.khandual@....com>,
	Suzuki K Poulose <suzuki.poulose@....com>,
	linux-kernel@...r.kernel.org, llvm@...ts.linux.dev
Subject: Re: [PATCH v2 1/1] arm: perf: Fix ARCH=arm build with GCC

On Fri, Dec 15, 2023 at 05:56:48PM +0000, James Clark wrote:
> LLVM ignores everything inside the if statement and doesn't generate
> errors, but GCC doesn't ignore it, resulting in the following error:
> 
>   drivers/perf/arm_pmuv3.c: In function ‘armv8pmu_write_evtype’:
>   include/linux/bits.h:34:29: error: left shift count >= width of type [-Werror=shift-count-overflow]
>   34 |         (((~UL(0)) - (UL(1) << (l)) + 1) & \
> 
> Fix it by using GENMASK_ULL which doesn't overflow on arm32 (even though
> the value is never used there).
> 
> Fixes: 3115ee021bfb ("arm64: perf: Include threshold control fields in PMEVTYPER mask")
> Reported-by: Uwe Kleine-König <u.kleine-koenig@...gutronix.de>
> Closes: https://lore.kernel.org/linux-arm-kernel/20231215120817.h2f3akgv72zhrtqo@pengutronix.de/
> Signed-off-by: James Clark <james.clark@....com>
> ---
>  include/linux/perf/arm_pmuv3.h | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/include/linux/perf/arm_pmuv3.h b/include/linux/perf/arm_pmuv3.h
> index 0f4d62ef3a9a..46377e134d67 100644
> --- a/include/linux/perf/arm_pmuv3.h
> +++ b/include/linux/perf/arm_pmuv3.h
> @@ -234,8 +234,8 @@
>   * PMXEVTYPER: Event selection reg
>   */
>  #define ARMV8_PMU_EVTYPE_EVENT	GENMASK(15, 0)	/* Mask for EVENT bits */
> -#define ARMV8_PMU_EVTYPE_TH	GENMASK(43, 32)
> -#define ARMV8_PMU_EVTYPE_TC	GENMASK(63, 61)
> +#define ARMV8_PMU_EVTYPE_TH	GENMASK_ULL(43, 32) /* arm64 only */
> +#define ARMV8_PMU_EVTYPE_TC	GENMASK_ULL(63, 61) /* arm64 only */

As expected this fixes compilation on my end, too and it's nicer than
v1.

Reviewed-by: Uwe Kleine-König <u.kleine-koenig@...gutronix.de>

Thanks
Uwe

-- 
Pengutronix e.K.                           | Uwe Kleine-König            |
Industrial Linux Solutions                 | https://www.pengutronix.de/ |

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