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References: <20210807010239.416055-1-sxwjean@me.com> <20210807010239.416055-2-sxwjean@me.com>
 <127de0c7-5e30-6797-1e72-6414d4a60119@csgroup.eu>
In-Reply-To: <127de0c7-5e30-6797-1e72-6414d4a60119@csgroup.eu>
From:   Xiongwei Song <sxwjean@gmail.com>
Date:   Tue, 10 Aug 2021 16:33:08 +0800
Message-ID: <CAEVVKH_G1GjofNU4M0mtuaOAtLyTZ+Fcjjr3ywqeXJrJVwpgrA@mail.gmail.com>
Subject: Re: [PATCH v2 1/4] powerpc: Optimize register usage for esr register
To:     Christophe Leroy <christophe.leroy@csgroup.eu>
Cc:     Xiongwei Song <sxwjean@me.com>,
        PowerPC <linuxppc-dev@lists.ozlabs.org>, oleg@redhat.com,
        Michael Ellerman <mpe@ellerman.id.au>,
        Benjamin Herrenschmidt <benh@kernel.crashing.org>,
        Paul Mackerras <paulus@samba.org>, npiggin@gmail.com,
        ravi.bangoria@linux.ibm.com, aneesh.kumar@linux.ibm.com,
        efremov@linux.com,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
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On Sat, Aug 7, 2021 at 2:57 PM Christophe Leroy
<christophe.leroy@csgroup.eu> wrote:
>
>
>
> Le 07/08/2021 =C3=A0 03:02, sxwjean@me.com a =C3=A9crit :
> > From: Xiongwei Song <sxwjean@gmail.com>
> >
> > Create an anonymous union for dsisr and esr regsiters, we can reference
> > esr to get the exception detail when CONFIG_4xx=3Dy or CONFIG_BOOKE=3Dy=
.
> > Otherwise, reference dsisr. This makes code more clear.
> >
> > Signed-off-by: Xiongwei Song <sxwjean@gmail.com>
> > ---
> >   arch/powerpc/include/asm/ptrace.h          | 5 ++++-
> >   arch/powerpc/kernel/process.c              | 2 +-
> >   arch/powerpc/kernel/ptrace/ptrace.c        | 2 ++
> >   arch/powerpc/kernel/traps.c                | 2 +-
> >   arch/powerpc/platforms/44x/machine_check.c | 4 ++--
> >   arch/powerpc/platforms/4xx/machine_check.c | 2 +-
> >   6 files changed, 11 insertions(+), 6 deletions(-)
> >
> > diff --git a/arch/powerpc/include/asm/ptrace.h b/arch/powerpc/include/a=
sm/ptrace.h
> > index 3e5d470a6155..c252d04b1206 100644
> > --- a/arch/powerpc/include/asm/ptrace.h
> > +++ b/arch/powerpc/include/asm/ptrace.h
> > @@ -44,7 +44,10 @@ struct pt_regs
> >   #endif
> >                       unsigned long trap;
> >                       unsigned long dar;
> > -                     unsigned long dsisr;
> > +                     union {
> > +                             unsigned long dsisr;
> > +                             unsigned long esr;
> > +                     };
> >                       unsigned long result;
> >               };
> >       };
> > diff --git a/arch/powerpc/kernel/process.c b/arch/powerpc/kernel/proces=
s.c
> > index 185beb290580..f74af8f9133c 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 =3D=3D INTERRUPT_DATA_STORAGE ||
> >           trap =3D=3D INTERRUPT_ALIGNMENT) {
> >               if (IS_ENABLED(CONFIG_4xx) || IS_ENABLED(CONFIG_BOOKE))
> > -                     pr_cont("DEAR: "REG" ESR: "REG" ", regs->dar, reg=
s->dsisr);
> > +                     pr_cont("DEAR: "REG" ESR: "REG" ", regs->dar, reg=
s->esr);
> >               else
> >                       pr_cont("DAR: "REG" DSISR: %08lx ", regs->dar, re=
gs->dsisr);
> >       }
> > diff --git a/arch/powerpc/kernel/ptrace/ptrace.c b/arch/powerpc/kernel/=
ptrace/ptrace.c
> > index 0a0a33eb0d28..a222fd4d6334 100644
> > --- a/arch/powerpc/kernel/ptrace/ptrace.c
> > +++ b/arch/powerpc/kernel/ptrace/ptrace.c
> > @@ -375,6 +375,8 @@ void __init pt_regs_check(void)
> >                    offsetof(struct user_pt_regs, dar));
> >       BUILD_BUG_ON(offsetof(struct pt_regs, dsisr) !=3D
> >                    offsetof(struct user_pt_regs, dsisr));
> > +     BUILD_BUG_ON(offsetof(struct pt_regs, esr) !=3D
> > +                  offsetof(struct user_pt_regs, dsisr));
>
> esr and dsisr are the same, so checking the same thing a second time is p=
ointless.

Hmm...it's better to check if the changes on pt_regs structure is
expected I think.

Regards,
Xiongwei

>
> >       BUILD_BUG_ON(offsetof(struct pt_regs, result) !=3D
> >                    offsetof(struct user_pt_regs, result));
> >
> > diff --git a/arch/powerpc/kernel/traps.c b/arch/powerpc/kernel/traps.c
> > index dfbce527c98e..2164f5705a0b 100644
> > --- a/arch/powerpc/kernel/traps.c
> > +++ b/arch/powerpc/kernel/traps.c
> > @@ -562,7 +562,7 @@ static inline int check_io_access(struct pt_regs *r=
egs)
> >   #ifdef CONFIG_PPC_ADV_DEBUG_REGS
> >   /* On 4xx, the reason for the machine check or program exception
> >      is in the ESR. */
> > -#define get_reason(regs)     ((regs)->dsisr)
> > +#define get_reason(regs)     ((regs)->esr)
> >   #define REASON_FP           ESR_FP
> >   #define REASON_ILLEGAL              (ESR_PIL | ESR_PUO)
> >   #define REASON_PRIVILEGED   ESR_PPR
> > diff --git a/arch/powerpc/platforms/44x/machine_check.c b/arch/powerpc/=
platforms/44x/machine_check.c
> > index a5c898bb9bab..5d19daacd78a 100644
> > --- a/arch/powerpc/platforms/44x/machine_check.c
> > +++ b/arch/powerpc/platforms/44x/machine_check.c
> > @@ -11,7 +11,7 @@
> >
> >   int machine_check_440A(struct pt_regs *regs)
> >   {
> > -     unsigned long reason =3D regs->dsisr;
> > +     unsigned long reason =3D regs->esr;
> >
> >       printk("Machine check in kernel mode.\n");
> >       if (reason & ESR_IMCP){
> > @@ -48,7 +48,7 @@ int machine_check_440A(struct pt_regs *regs)
> >   #ifdef CONFIG_PPC_47x
> >   int machine_check_47x(struct pt_regs *regs)
> >   {
> > -     unsigned long reason =3D regs->dsisr;
> > +     unsigned long reason =3D regs->esr;
> >       u32 mcsr;
> >
> >       printk(KERN_ERR "Machine check in kernel mode.\n");
> > diff --git a/arch/powerpc/platforms/4xx/machine_check.c b/arch/powerpc/=
platforms/4xx/machine_check.c
> > index a71c29892a91..a905da1d6f41 100644
> > --- a/arch/powerpc/platforms/4xx/machine_check.c
> > +++ b/arch/powerpc/platforms/4xx/machine_check.c
> > @@ -10,7 +10,7 @@
> >
> >   int machine_check_4xx(struct pt_regs *regs)
> >   {
> > -     unsigned long reason =3D regs->dsisr;
> > +     unsigned long reason =3D regs->esr;
> >
> >       if (reason & ESR_IMCP) {
> >               printk("Instruction");
> >