* Re: [PATCH v2 1/1] arm: perf: Fix ARCH=arm build with GCC
2023-12-15 17:56 ` [PATCH v2 1/1] " James Clark
@ 2023-12-15 18:20 ` Uwe Kleine-König
2023-12-16 12:44 ` Mark Rutland
1 sibling, 0 replies; 5+ messages in thread
From: Uwe Kleine-König @ 2023-12-15 18:20 UTC (permalink / raw)
To: James Clark
Cc: linux-arm-kernel, linux-perf-users, linux-next, will,
mark.rutland, Nathan Chancellor, Nick Desaulniers, Bill Wendling,
Justin Stitt, Anshuman Khandual, Suzuki K Poulose, linux-kernel,
llvm
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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@pengutronix.de>
> Closes: https://lore.kernel.org/linux-arm-kernel/20231215120817.h2f3akgv72zhrtqo@pengutronix.de/
> Signed-off-by: James Clark <james.clark@arm.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@pengutronix.de>
Thanks
Uwe
--
Pengutronix e.K. | Uwe Kleine-König |
Industrial Linux Solutions | https://www.pengutronix.de/ |
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^ permalink raw reply [flat|nested] 5+ messages in thread* Re: [PATCH v2 1/1] arm: perf: Fix ARCH=arm build with GCC
2023-12-15 17:56 ` [PATCH v2 1/1] " James Clark
2023-12-15 18:20 ` Uwe Kleine-König
@ 2023-12-16 12:44 ` Mark Rutland
1 sibling, 0 replies; 5+ messages in thread
From: Mark Rutland @ 2023-12-16 12:44 UTC (permalink / raw)
To: James Clark, will, catalin.marinas
Cc: linux-arm-kernel, linux-perf-users, linux-next, u.kleine-koenig,
Nathan Chancellor, Nick Desaulniers, Bill Wendling, Justin Stitt,
Anshuman Khandual, Suzuki K Poulose, linux-kernel, llvm
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).
It would be nice if this could explain the overflow problem, i.e.
| The GENMASK() macro creates masks of type unsigned long, and we use this to
| geenrate the ARMV8_PMU_EVTYPE_TH and ARMV8_PMU_EVTYPE_TC constants. These
| include bits above bit 31, and generating these requires shifting more than the
| size of unsigned long on 32-bit ARM.
|
| Consequently when building for 32-bit arm, GCC warns about their use:
|
| 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) & \
|
| ... though LLVM does not warn as the actual usage is not reachable on 32-bit
| ARM due to `if (IS_ENABLED(...)` checks.
|
| Avoid the warning by using GENMACK_ULL(), which doesn't overflow on 32-bit arm.
> Fixes: 3115ee021bfb ("arm64: perf: Include threshold control fields in PMEVTYPER mask")
> Reported-by: Uwe Kleine-K"onig <u.kleine-koenig@pengutronix.de>
> Closes: https://lore.kernel.org/linux-arm-kernel/20231215120817.h2f3akgv72zhrtqo@pengutronix.de/
> Signed-off-by: James Clark <james.clark@arm.com>
Thanks for this!
Acked-by: Mark Rutland <mark.rutland@arm.com>
Will, Catalin, the broken commit is queued in the arm64 for-next/perf branch
(and merged into for-next/core); is this something we can easily fold in?
Mark.
> ---
> 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 */
>
> /*
> * Event filters for PMUv3
> --
> 2.34.1
>
^ permalink raw reply [flat|nested] 5+ messages in thread