linux-kernel - Re: [PATCH v2 3/4] powerpc: Optimize register usage for dear register

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Message-ID: <dfd24c4a-c43f-912c-5876-f1cac704f336@csgroup.eu>
Date:   Sat, 7 Aug 2021 08:57:24 +0200
From:   Christophe Leroy <christophe.leroy@...roup.eu>
To:     sxwjean@...com, linuxppc-dev@...ts.ozlabs.org
Cc:     oleg@...hat.com, mpe@...erman.id.au, benh@...nel.crashing.org,
        paulus@...ba.org, npiggin@...il.com, ravi.bangoria@...ux.ibm.com,
        aneesh.kumar@...ux.ibm.com, efremov@...ux.com,
        linux-kernel@...r.kernel.org, Xiongwei Song <sxwjean@...il.com>
Subject: Re: [PATCH v2 3/4] powerpc: Optimize register usage for dear register



Le 07/08/2021 à 03:02, sxwjean@...com a écrit :
> From: Xiongwei Song <sxwjean@...il.com>
> 
> Create an anonymous union for dar and dear regsiters, we can reference
> dear to get the effective address when CONFIG_4xx=y or CONFIG_BOOKE=y.
> Otherwise, reference dar. This makes code more clear.
> 
> Signed-off-by: Xiongwei Song <sxwjean@...il.com>
> ---
>   arch/powerpc/include/asm/ptrace.h   | 5 ++++-
>   arch/powerpc/kernel/process.c       | 2 +-
>   arch/powerpc/kernel/ptrace/ptrace.c | 2 ++
>   3 files changed, 7 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/powerpc/include/asm/ptrace.h b/arch/powerpc/include/asm/ptrace.h
> index c252d04b1206..fa725e3238c2 100644
> --- a/arch/powerpc/include/asm/ptrace.h
> +++ b/arch/powerpc/include/asm/ptrace.h
> @@ -43,7 +43,10 @@ struct pt_regs
>   			unsigned long mq;
>   #endif
>   			unsigned long trap;
> -			unsigned long dar;
> +			union {
> +				unsigned long dar;
> +				unsigned long dear;
> +			};
>   			union {
>   				unsigned long dsisr;
>   				unsigned long esr;
> diff --git a/arch/powerpc/kernel/process.c b/arch/powerpc/kernel/process.c
> index f74af8f9133c..50436b52c213 100644
> --- a/arch/powerpc/kernel/process.c
> +++ b/arch/powerpc/kernel/process.c
> @@ -1499,7 +1499,7 @@ static void __show_regs(struct pt_regs *regs)
>   	    trap == INTERRUPT_DATA_STORAGE ||
>   	    trap == INTERRUPT_ALIGNMENT) {
>   		if (IS_ENABLED(CONFIG_4xx) || IS_ENABLED(CONFIG_BOOKE))
> -			pr_cont("DEAR: "REG" ESR: "REG" ", regs->dar, regs->esr);
> +			pr_cont("DEAR: "REG" ESR: "REG" ", regs->dear, regs->esr);
>   		else
>   			pr_cont("DAR: "REG" DSISR: %08lx ", regs->dar, regs->dsisr);
>   	}
> diff --git a/arch/powerpc/kernel/ptrace/ptrace.c b/arch/powerpc/kernel/ptrace/ptrace.c
> index a222fd4d6334..7c7093c17c45 100644
> --- a/arch/powerpc/kernel/ptrace/ptrace.c
> +++ b/arch/powerpc/kernel/ptrace/ptrace.c
> @@ -373,6 +373,8 @@ void __init pt_regs_check(void)
>   		     offsetof(struct user_pt_regs, trap));
>   	BUILD_BUG_ON(offsetof(struct pt_regs, dar) !=
>   		     offsetof(struct user_pt_regs, dar));
> +	BUILD_BUG_ON(offsetof(struct pt_regs, dear) !=
> +		     offsetof(struct user_pt_regs, dar));

dar and dear are the same, so checking the same thing a second time is pointless.

>   	BUILD_BUG_ON(offsetof(struct pt_regs, dsisr) !=
>   		     offsetof(struct user_pt_regs, dsisr));
>   	BUILD_BUG_ON(offsetof(struct pt_regs, esr) !=
>