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In-Reply-To: <1850220.JuIOMCfrUL@townsend>
From: Jordan Niethe <jniethe5@gmail.com>
Date: Thu, 14 May 2020 22:29:16 +1000
Message-ID: <CACzsE9qFrCoKFQte6AZHzp5LKvXX7O3zQ+woR=eOefmPc4-Y9Q@mail.gmail.com>
Subject: Re: [PATCH v8 23/30] powerpc: Add prefixed instructions to
 instruction data type
To: Alistair Popple <alistair@popple.id.au>
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Cc: Christophe Leroy <christophe.leroy@c-s.fr>,
 Nicholas Piggin <npiggin@gmail.com>, Balamuruhan S <bala24@linux.ibm.com>,
 naveen.n.rao@linux.vnet.ibm.com, linuxppc-dev@lists.ozlabs.org,
 Daniel Axtens <dja@axtens.net>
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 <linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org>

On Thu, May 14, 2020 at 10:06 PM Alistair Popple <alistair@popple.id.au> wrote:
>
> On Thursday, 14 May 2020 4:11:43 PM AEST Christophe Leroy wrote:
> > @@ -249,7 +249,7 @@ int arch_prepare_optimized_kprobe(struct
> > optimized_kprobe *op, struct kprobe *p)
> > > * Fixup the template with instructions to:
> > > * 1. load the address of the actual probepoint
> > > */
> > > -       patch_imm64_load_insns((unsigned long)op, buff + TMPL_OP_IDX);
> > > +       patch_imm64_load_insns((unsigned long)op, 3, buff + TMPL_OP_IDX);
> > >
> > > /*
> > > * 2. branch to optimized_callback() and emulate_step()
> > > @@ -282,7 +282,11 @@ int arch_prepare_optimized_kprobe(struct
> > > optimized_kprobe *op, struct kprobe *p) /*
> > > * 3. load instruction to be emulated into relevant register, and
> > > */
> > > -       patch_imm32_load_insns(*p->ainsn.insn, buff + TMPL_INSN_IDX);
> > > +       temp = ppc_inst_read((struct ppc_inst *)p->ainsn.insn);
> > > +       patch_imm64_load_insns(ppc_inst_val(temp) |
> > > +                              ((u64)ppc_inst_suffix(temp) << 32),
> > > +                              4,
> >
> > So now we are also using r4 ? Any explanation somewhere on the way it
> > works ? This change seems unrelated to this patch, nothing in the
> > description about it. Can we suddenly use a new register without problem ?
>
> Unless I missed something there is no change in register usage here that I
> could see. patch_imm32_load_insns() was/is hardcoded to use register r4.
Yes, that is right.
>
> - Alistair
>
>