Subject: Re: [PATCH 1/2] powerpc/perf: Expose instruction and data address registers as part of extended regs

From: Michael Ellerman <[email-masked]>
Date: Wed, 08 Sep 2021 15:17:15 +1000

Athira Rajeev <[email-masked]> writes:
> Patch adds support to include Sampled Instruction Address Register
> (SIAR) and Sampled Data Address Register (SDAR) SPRs as part of extended
> registers. Update the definition of PERF_REG_PMU_MASK_300/31 and
> PERF_REG_EXTENDED_MAX to include these SPR's.
>
> Signed-off-by: Athira Rajeev <[email-masked]>
> ---
>  arch/powerpc/include/uapi/asm/perf_regs.h | 12 +++++++-----
>  arch/powerpc/perf/perf_regs.c             |  4 ++++
>  2 files changed, 11 insertions(+), 5 deletions(-)
>
...
> diff --git a/arch/powerpc/perf/perf_regs.c b/arch/powerpc/perf/perf_regs.c
> index b931eed..51d31b6 100644
> --- a/arch/powerpc/perf/perf_regs.c
> +++ b/arch/powerpc/perf/perf_regs.c
> @@ -90,7 +90,11 @@ static u64 get_ext_regs_value(int idx)
>  		return mfspr(SPRN_SIER2);
>  	case PERF_REG_POWERPC_SIER3:
>  		return mfspr(SPRN_SIER3);
> +	case PERF_REG_POWERPC_SDAR:
> +		return mfspr(SPRN_SDAR);
>  #endif
> +	case PERF_REG_POWERPC_SIAR:
> +		return mfspr(SPRN_SIAR);
>  	default: return 0;
>  	}

This file is built for all powerpc configs that have PERF_EVENTS. Which
includes CPUs that don't have SDAR or SIAR.

Don't we need checks in perf_reg_value() like we do for SIER?

I guess we already got this wrong when we added the Power10 registers,
SIER2/3 etc.

cheers