linux-kernel - Re: [PATCH 1/2] arm: perf: Fix ARCH=arm build with GCC in armv8pmu_write

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Date: Fri, 15 Dec 2023 16:21:45 +0000
From: Mark Rutland <mark.rutland@....com>
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,
	u.kleine-koenig@...gutronix.de,
	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 1/2] arm: perf: Fix ARCH=arm build with GCC in
 armv8pmu_write_evtype()

On Fri, Dec 15, 2023 at 03:00:38PM +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 changing the if to #if.

I reckon it'd be cleaner to use GENMASK_ULL for the TH and TC fields, in
include/linux/perf/arm_pmu.h have:

| /*
|  * PMXEVTYPER: Event selection reg
|  */
| #define ARMV8_PMU_EVTYPE_EVENT GENMASK(15, 0)          /* Mask for EVENT bits */
| #define ARMV8_PMU_EVTYPE_TH    GENMASK_ULL(43, 32)     /* arm64 only */
| #define ARMV8_PMU_EVTYPE_TC    GENMASK_ULL(63, 61)     /* arm64 only */

IIUC that should silence this warning, and it'd remove the need for the
ifdeffery and other changes in patch 2.

Does that work, or am I missing something?

Thanks,
Mark.

> 
> Fixes: 3115ee021bfb ("arm64: perf: Include threshold control fields in PMEVTYPER mask")
> Reported-by: Uwe Kleine-K"onig <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>
> ---
>  drivers/perf/arm_pmuv3.c | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/perf/arm_pmuv3.c b/drivers/perf/arm_pmuv3.c
> index 23fa6c5da82c..3ed2086cefc3 100644
> --- a/drivers/perf/arm_pmuv3.c
> +++ b/drivers/perf/arm_pmuv3.c
> @@ -631,8 +631,9 @@ static void armv8pmu_write_evtype(int idx, unsigned long val)
>  			     ARMV8_PMU_EXCLUDE_EL0 |
>  			     ARMV8_PMU_EXCLUDE_EL1;
>  
> -	if (IS_ENABLED(CONFIG_ARM64))
> -		mask |= ARMV8_PMU_EVTYPE_TC | ARMV8_PMU_EVTYPE_TH;
> +#if IS_ENABLED(CONFIG_ARM64)
> +	mask |= ARMV8_PMU_EVTYPE_TC | ARMV8_PMU_EVTYPE_TH;
> +#endif
>  
>  	val &= mask;
>  	write_pmevtypern(counter, val);
> -- 
> 2.34.1
>