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

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Message-ID: <d335905e-38bb-1994-57f6-533852b7a560@arm.com>
Date: Fri, 15 Dec 2023 17:42:50 +0000
From: James Clark <james.clark@....com>
To: Mark Rutland <mark.rutland@....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 15/12/2023 16:21, Mark Rutland wrote:
> 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.
> 

You're right that does work. For some reason I thought there was some
component of writing it to the mask that was the issue as well.

I'll send another version with that fix instead.

Thanks
James

>>
>> 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
>>