Re: [PATCH v2 08/12] powerpc: Don't use 'struct ppc_inst' to reference instruction location

From: Jordan Niethe <jniethe5@gmail.com>
To: Michael Ellerman <mpe@ellerman.id.au>
Cc: Christophe Leroy <christophe.leroy@csgroup.eu>,
	Benjamin Herrenschmidt <benh@kernel.crashing.org>,
	Paul Mackerras <paulus@samba.org>,
	"Naveen N. Rao" <naveen.n.rao@linux.vnet.ibm.com>,
	linux-kernel@vger.kernel.org,
	linuxppc-dev <linuxppc-dev@lists.ozlabs.org>
Subject: Re: [PATCH v2 08/12] powerpc: Don't use 'struct ppc_inst' to reference instruction location
Date: Tue, 15 Jun 2021 13:47:41 +1000	[thread overview]
Message-ID: <CACzsE9pajbu70rm4AAk8=S1zDj6LCfSwemEd+dhRyPw2F4WF+A@mail.gmail.com> (raw)
In-Reply-To: <871r93vqcb.fsf@mpe.ellerman.id.au>

On Tue, Jun 15, 2021 at 12:01 PM Michael Ellerman <mpe@ellerman.id.au> wrote:
>
> Christophe Leroy <christophe.leroy@csgroup.eu> writes:
> > diff --git a/arch/powerpc/include/asm/inst.h b/arch/powerpc/include/asm/inst.h
> > index 5a0740ebf132..32d318c3b180 100644
> > --- a/arch/powerpc/include/asm/inst.h
> > +++ b/arch/powerpc/include/asm/inst.h
> > @@ -139,7 +139,7 @@ static inline int ppc_inst_len(struct ppc_inst x)
> >   * Return the address of the next instruction, if the instruction @value was
> >   * located at @location.
> >   */
> > -static inline struct ppc_inst *ppc_inst_next(void *location, struct ppc_inst *value)
> > +static inline unsigned int *ppc_inst_next(unsigned int *location, unsigned int *value)
> >  {
> >       struct ppc_inst tmp;
> >
>
> It's not visible in the diff, but the rest of the function is:
>
>         tmp = ppc_inst_read(value);
>
>         return location + ppc_inst_len(tmp);
> }
>
> And so changing the type of location from void * to int * changes the
> result of that addition, ie. previously it was in units of bytes, now
> it's units of 4 bytes.
>
> To fix it I've kept location as unsigned int *, and added a cast where
> we do the addition. That way users of the function just see unsigned int *,
> the cast to void * is an implementation detail.
>
> We only have a handful of uses of ppc_inst_len(), so maybe that should
> change name and return a result in units of int *. But that can be a
> separate change.
>
> > diff --git a/arch/powerpc/platforms/86xx/mpc86xx_smp.c b/arch/powerpc/platforms/86xx/mpc86xx_smp.c
> > index 87f524e4b09c..302f2a1e0361 100644
> > --- a/arch/powerpc/platforms/86xx/mpc86xx_smp.c
> > +++ b/arch/powerpc/platforms/86xx/mpc86xx_smp.c
> > @@ -83,7 +83,7 @@ smp_86xx_kick_cpu(int nr)
> >               mdelay(1);
> >
> >       /* Restore the exception vector */
> > -     patch_instruction((struct ppc_inst *)vector, ppc_inst(save_vector));
> > +     patch_instruction(vector, ppc_inst(save_vector));
> >
> >       local_irq_restore(flags);
> >
>
> There was another usage in here:
>
>         /* Setup fake reset vector to call __secondary_start_mpc86xx. */
>         target = (unsigned long) __secondary_start_mpc86xx;
> -       patch_branch((struct ppc_inst *)vector, target, BRANCH_SET_LINK);
> +       patch_branch(vector, target, BRANCH_SET_LINK);
>
>         /* Kick that CPU */
>         smp_86xx_release_core(nr);
>
> I fixed it up.
>
> cheers
fwiw
Reviewed by: Jordan Niethe <jniethe5@gmail.com>