Re: [PATCH] arm64: arm64_ftr_reg->name may not be a human-readable string

From: Marc Zyngier <maz@kernel.org>
To: Reiji Watanabe <reijiw@google.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>,
	Will Deacon <will@kernel.org>,
	linux-arm-kernel@lists.infradead.org,
	Peter Shier <pshier@google.com>,
	Ricardo Koller <ricarkol@google.com>,
	Oliver Upton <oupton@google.com>,
	Jing Zhang <jingzhangos@google.com>,
	Raghavendra Rao Anata <rananta@google.com>
Subject: Re: [PATCH] arm64: arm64_ftr_reg->name may not be a human-readable string
Date: Mon, 01 Nov 2021 10:25:00 +0000	[thread overview]
Message-ID: <87a6io9nr7.wl-maz@kernel.org> (raw)
In-Reply-To: <20211101045421.2215822-1-reijiw@google.com>

On Mon, 01 Nov 2021 04:54:21 +0000,
Reiji Watanabe <reijiw@google.com> wrote:
> 
> The id argument of ARM64_FTR_REG_OVERRIDE() is used for two purposes:
> one as the system register encoding (used for the sys_id field of
> __ftr_reg_entry), and the other as the register name (stringified
> and used for the name field of arm64_ftr_reg), which is debug
> information. The id argument is supposed to be a macro that
> indicates an encoding of the register (eg. SYS_ID_AA64PFR0_EL1, etc).
> 
> ARM64_FTR_REG(), which also has the same id argument,
> uses ARM64_FTR_REG_OVERRIDE() and passes the id to the macro.
> Since the id argument is completely macro-expanded before it is
> substituted into a macro body of ARM64_FTR_REG_OVERRIDE(),
> the stringified id in the body of ARM64_FTR_REG_OVERRIDE is not
> a human-readable register name, but a string of numeric bitwise
> operations.
> 
> Fix this so that human-readable register names are available as
> debug information.
> 
> Fixes: 8f266a5d878a ("arm64: cpufeature: Add global feature override facility")
> Signed-off-by: Reiji Watanabe <reijiw@google.com>
> ---
>  arch/arm64/kernel/cpufeature.c | 10 +++++++---
>  1 file changed, 7 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
> index 6ec7036ef7e1..7553c98f379f 100644
> --- a/arch/arm64/kernel/cpufeature.c
> +++ b/arch/arm64/kernel/cpufeature.c
> @@ -573,15 +573,19 @@ static const struct arm64_ftr_bits ftr_raz[] = {
>  	ARM64_FTR_END,
>  };
>  
> -#define ARM64_FTR_REG_OVERRIDE(id, table, ovr) {		\
> +#define __ARM64_FTR_REG_OVERRIDE(id_str, id, table, ovr) {	\
>  		.sys_id = id,					\
>  		.reg = 	&(struct arm64_ftr_reg){		\
> -			.name = #id,				\
> +			.name = id_str,				\
>  			.override = (ovr),			\
>  			.ftr_bits = &((table)[0]),		\
>  	}}
>  
> -#define ARM64_FTR_REG(id, table) ARM64_FTR_REG_OVERRIDE(id, table, &no_override)
> +#define ARM64_FTR_REG_OVERRIDE(id, table, ovr)	\
> +	__ARM64_FTR_REG_OVERRIDE(#id, id, table, ovr)
> +
> +#define ARM64_FTR_REG(id, table)		\
> +	__ARM64_FTR_REG_OVERRIDE(#id, id, table, &no_override)
>  
>  struct arm64_ftr_override __ro_after_init id_aa64mmfr1_override;
>  struct arm64_ftr_override __ro_after_init id_aa64pfr1_override;

Seems reasonable to me.

Acked-by: Marc Zyngier <maz@kernel.org>

	M.

-- 
Without deviation from the norm, progress is not possible.

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