[PATCH v2 0/1] arm: perf: Fix ARCH=arm build with GCC

[PATCH v2 0/1] arm: perf: Fix ARCH=arm build with GCC

[James Clark]

Changes since V1:

  * Instead of wrapping everything in #if, just use GENMASK_ULL instead
    which fixes both issues in one commit.

A fix for the broken build with GCC currently in linux-next
(next-20231214)


James Clark (1):
  arm: perf: Fix ARCH=arm build with GCC

 include/linux/perf/arm_pmuv3.h | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

-- 
2.34.1


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[PATCH v2 1/1] arm: perf: Fix ARCH=arm build with GCC

[James Clark]

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 */
 
 /*
  * Event filters for PMUv3
-- 
2.34.1


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

[Uwe Kleine-König]

[-- Attachment #1.1: Type: text/plain, Size: 1881 bytes --]

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

[Mark Rutland]

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
> 

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Re: [PATCH v2 0/1] arm: perf: Fix ARCH=arm build with GCC

[Will Deacon]

On Fri, 15 Dec 2023 17:56:47 +0000, James Clark wrote:
> Changes since V1:
> 
>   * Instead of wrapping everything in #if, just use GENMASK_ULL instead
>     which fixes both issues in one commit.
> 
> A fix for the broken build with GCC currently in linux-next
> (next-20231214)
> 
> [...]

Applied to will (for-next/perf), thanks!

[1/1] arm: perf: Fix ARCH=arm build with GCC
      https://git.kernel.org/will/c/bb339db4d363

Cheers,
-- 
Will

https://fixes.arm64.dev
https://next.arm64.dev
https://will.arm64.dev

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