linux-kernel - Re: [PATCH V13 - RESEND 02/10] arm64/perf: Add BRBE registers and fields

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Message-ID: <20230728162011.GA22050@willie-the-truck>
Date:   Fri, 28 Jul 2023 17:20:13 +0100
From:   Will Deacon <will@...nel.org>
To:     Anshuman Khandual <anshuman.khandual@....com>
Cc:     linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        catalin.marinas@....com, mark.rutland@....com,
        Mark Brown <broonie@...nel.org>,
        James Clark <james.clark@....com>,
        Rob Herring <robh@...nel.org>, Marc Zyngier <maz@...nel.org>,
        Suzuki Poulose <suzuki.poulose@....com>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        linux-perf-users@...r.kernel.org
Subject: Re: [PATCH V13 - RESEND 02/10] arm64/perf: Add BRBE registers and
 fields

On Tue, Jul 11, 2023 at 01:54:47PM +0530, Anshuman Khandual wrote:
> This adds BRBE related register definitions and various other related field
> macros there in. These will be used subsequently in a BRBE driver which is
> being added later on.
> 
> Cc: Catalin Marinas <catalin.marinas@....com>
> Cc: Will Deacon <will@...nel.org>
> Cc: Marc Zyngier <maz@...nel.org>
> Cc: Mark Rutland <mark.rutland@....com>
> Cc: linux-arm-kernel@...ts.infradead.org
> Cc: linux-kernel@...r.kernel.org
> Tested-by: James Clark <james.clark@....com>
> Reviewed-by: Mark Brown <broonie@...nel.org>
> Signed-off-by: Anshuman Khandual <anshuman.khandual@....com>
> ---
>  arch/arm64/include/asm/sysreg.h | 103 +++++++++++++++++++++
>  arch/arm64/tools/sysreg         | 158 ++++++++++++++++++++++++++++++++
>  2 files changed, 261 insertions(+)
> 
> diff --git a/arch/arm64/include/asm/sysreg.h b/arch/arm64/include/asm/sysreg.h
> index b481935e9314..f95e30c13c8b 100644
> --- a/arch/arm64/include/asm/sysreg.h
> +++ b/arch/arm64/include/asm/sysreg.h
> @@ -163,6 +163,109 @@
>  #define SYS_DBGDTRTX_EL0		sys_reg(2, 3, 0, 5, 0)
>  #define SYS_DBGVCR32_EL2		sys_reg(2, 4, 0, 7, 0)
>  
> +#define __SYS_BRBINFO(n)		sys_reg(2, 1, 8, ((n) & 0xf), ((((n) & 0x10)) >> 2 + 0))
> +#define __SYS_BRBSRC(n)			sys_reg(2, 1, 8, ((n) & 0xf), ((((n) & 0x10)) >> 2 + 1))
> +#define __SYS_BRBTGT(n)			sys_reg(2, 1, 8, ((n) & 0xf), ((((n) & 0x10)) >> 2 + 2))

It's that time on a Friday but... aren't these macros busted? I think you
need brackets before adding the offset, otherwise wouldn't, for example,
target registers 0-15 all access info register 0 and __SYS_BRBTGT(16) would
then start accessing source register 0?

I'm surprised that the compiler doesn't warn about this, but even more
surprised that you managed to test this.

Please tell me I'm wrong!

Will