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

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Message-ID: <CAEVVKH972N2hT-WP=5p6GrYEdEV1DO=D0PJo24WZ9gMVgqzaWA@mail.gmail.com>
Date:   Tue, 10 Aug 2021 16:33:44 +0800
From:   Xiongwei Song <sxwjean@...il.com>
To:     Christophe Leroy <christophe.leroy@...roup.eu>
Cc:     Xiongwei Song <sxwjean@...com>,
        PowerPC <linuxppc-dev@...ts.ozlabs.org>, oleg@...hat.com,
        Michael Ellerman <mpe@...erman.id.au>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>, npiggin@...il.com,
        ravi.bangoria@...ux.ibm.com, aneesh.kumar@...ux.ibm.com,
        efremov@...ux.com,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 3/4] powerpc: Optimize register usage for dear register

On Sat, Aug 7, 2021 at 2:58 PM Christophe Leroy
<christophe.leroy@...roup.eu> wrote:
>
>
>
> 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.

Same reply as the patch 1.

Regards,
Xiongwei

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