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Subject: Re: [RFC PATCH 3/4] powerpc: Optimize register usage for dear
 register
To:     sxwjean@me.com, linuxppc-dev@lists.ozlabs.org
Cc:     oleg@redhat.com, mpe@ellerman.id.au, benh@kernel.crashing.org,
        paulus@samba.org, ravi.bangoria@linux.ibm.com, npiggin@gmail.com,
        aneesh.kumar@linux.ibm.com, sandipan@linux.ibm.com,
        efremov@linux.com, peterx@redhat.com, akpm@linux-foundation.org,
        linux-kernel@vger.kernel.org, Xiongwei Song <sxwjean@gmail.com>
References: <20210726143053.532839-1-sxwjean@me.com>
 <20210726143053.532839-3-sxwjean@me.com>
From:   Christophe Leroy <christophe.leroy@csgroup.eu>
Message-ID: <56d9e3ce-f303-fd41-bd16-5655d9dc5e52@csgroup.eu>
Date:   Thu, 5 Aug 2021 12:09:19 +0200
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Le 26/07/2021 à 16:30, sxwjean@me.com a écrit :
> From: Xiongwei Song <sxwjean@gmail.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.

Same comment here as for patch 1.


> 
> Signed-off-by: Xiongwei Song <sxwjean@gmail.com>
> ---
>   arch/powerpc/include/asm/ptrace.h      | 5 ++++-
>   arch/powerpc/include/uapi/asm/ptrace.h | 5 ++++-
>   arch/powerpc/kernel/process.c          | 2 +-
>   arch/powerpc/kernel/ptrace/ptrace.c    | 2 ++
>   arch/powerpc/kernel/traps.c            | 5 ++++-
>   arch/powerpc/mm/fault.c                | 2 +-
>   6 files changed, 16 insertions(+), 5 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/include/uapi/asm/ptrace.h b/arch/powerpc/include/uapi/asm/ptrace.h
> index e357288b5f34..9ae150fb4c4b 100644
> --- a/arch/powerpc/include/uapi/asm/ptrace.h
> +++ b/arch/powerpc/include/uapi/asm/ptrace.h
> @@ -52,7 +52,10 @@ struct pt_regs
>   	unsigned long trap;		/* Reason for being here */
>   	/* N.B. for critical exceptions on 4xx, the dar and dsisr
>   	   fields are overloaded to hold srr0 and srr1. */
> -	unsigned long dar;		/* Fault registers */
> +	union {
> +		unsigned long dar;		/* Fault registers */
> +		unsigned long dear;
> +	};
>   	union {
>   		unsigned long dsisr;		/* on Book-S used for DSISR */
>   		unsigned long esr;		/* on 4xx/Book-E used for 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 00789ad2c4a3..969dca8b0718 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, dear));
>   	BUILD_BUG_ON(offsetof(struct pt_regs, dsisr) !=
>   		     offsetof(struct user_pt_regs, dsisr));
>   	BUILD_BUG_ON(offsetof(struct pt_regs, esr) !=
> diff --git a/arch/powerpc/kernel/traps.c b/arch/powerpc/kernel/traps.c
> index 2164f5705a0b..0796630d3d23 100644
> --- a/arch/powerpc/kernel/traps.c
> +++ b/arch/powerpc/kernel/traps.c
> @@ -1609,7 +1609,10 @@ DEFINE_INTERRUPT_HANDLER(alignment_exception)
>   	}
>   bad:
>   	if (user_mode(regs))
> -		_exception(sig, regs, code, regs->dar);
> +		if (IS_ENABLED(CONFIG_4xx) || IS_ENABLED(CONFIG_BOOKE))
> +			_exception(sig, regs, code, regs->dear);
> +		else
> +			_exception(sig, regs, code, regs->dar);
>   	else
>   		bad_page_fault(regs, sig);
>   }
> diff --git a/arch/powerpc/mm/fault.c b/arch/powerpc/mm/fault.c
> index 62953d4e7c93..3db6b39a1178 100644
> --- a/arch/powerpc/mm/fault.c
> +++ b/arch/powerpc/mm/fault.c
> @@ -542,7 +542,7 @@ static __always_inline void __do_page_fault(struct pt_regs *regs)
>   	long err;
>   
>   	if (IS_ENABLED(CONFIG_4xx) || IS_ENABLED(CONFIG_BOOKE))
> -		err = ___do_page_fault(regs, regs->dar, regs->esr);
> +		err = ___do_page_fault(regs, regs->dear, regs->esr);
>   	else
>   		err = ___do_page_fault(regs, regs->dar, regs->dsisr);
>   
>