From: tixy@linaro.org (Jon Medhurst (Tixy))
To: linux-arm-kernel@lists.infradead.org
Subject: [PATCH 2/5] arm64: alternative: Allow immediate branch as alternative instruction
Date: Fri, 27 Mar 2015 10:42:22 +0000 [thread overview]
Message-ID: <1427452942.2658.3.camel@linaro.org> (raw)
In-Reply-To: <20150326221955.4b8fe6f0@arm.com>
On Thu, 2015-03-26 at 22:19 +0000, Marc Zyngier wrote:
> On Thu, 26 Mar 2015 22:03:23 +0000
> Will Deacon <will.deacon@arm.com> wrote:
>
> > On Thu, Mar 19, 2015 at 01:59:33PM +0000, Marc Zyngier wrote:
> > > Since all immediate branches are PC-relative on Aarch64, these
> > > instructions cannot be used as an alternative with the simplistic
> > > approach we currently have (the immediate has been computed from
> > > the .altinstr_replacement section, and end-up being completely off
> > > if we insert it directly).
> > >
> > > This patch handles the b and bl instructions in a different way,
> > > using the insn framework to recompute the immediate, and generate
> > > the right displacement.
> > >
> > > Reviewed-by: Andre Przywara <andre.przywara@arm.com>
> > > Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
> > > ---
> > > arch/arm64/kernel/alternative.c | 55 +++++++++++++++++++++++++++++++++++++++--
> > > 1 file changed, 53 insertions(+), 2 deletions(-)
> >
> > [...]
> >
> > > static int __apply_alternatives(void *alt_region)
> > > {
> > > struct alt_instr *alt;
> > > @@ -40,16 +83,24 @@ static int __apply_alternatives(void *alt_region)
> > > u8 *origptr, *replptr;
> > >
> > > for (alt = region->begin; alt < region->end; alt++) {
> > > + u32 insn;
> > > + int i;
> > > +
> > > if (!cpus_have_cap(alt->cpufeature))
> > > continue;
> > >
> > > - BUG_ON(alt->alt_len > alt->orig_len);
> > > + BUG_ON(alt->alt_len != alt->orig_len);
> > >
> > > pr_info_once("patching kernel code\n");
> > >
> > > origptr = (u8 *)&alt->orig_offset + alt->orig_offset;
> > > replptr = (u8 *)&alt->alt_offset + alt->alt_offset;
> > > - memcpy(origptr, replptr, alt->alt_len);
> > > +
> > > + for (i = 0; i < alt->alt_len; i += sizeof(insn)) {
> > > + insn = get_alt_insn(origptr + i, replptr + i);
> > > + *(u32 *)(origptr + i) = insn;
> >
> > My brain's not firing on all cylinders right now, but do you need a
> > cpu_to_le32 here?
>
> I'm not 100% awake myself (probably some acute form of firmwaritis),
> but I suspect you're quite right (get_alt_insn calls aarch64_insn_read,
> which does a le32_to_cpu). Obviously, we need to revert the conversion
> when writing the instruction back.
Isn't aarch64_insn_write the inverse of aarch64_insn_read and more
correct than using cpu_to_le32?
--
Tixy
next prev parent reply other threads:[~2015-03-27 10:42 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-03-19 13:59 [PATCH 0/5] arm64: Patching branches for fun and profit Marc Zyngier
2015-03-19 13:59 ` [PATCH 1/5] arm64: insn: Add aarch64_insn_decode_immediate Marc Zyngier
2015-03-19 13:59 ` [PATCH 2/5] arm64: alternative: Allow immediate branch as alternative instruction Marc Zyngier
2015-03-26 22:03 ` Will Deacon
2015-03-26 22:19 ` Marc Zyngier
2015-03-26 22:31 ` Will Deacon
2015-03-27 10:42 ` Jon Medhurst (Tixy) [this message]
2015-03-27 11:08 ` Marc Zyngier
2015-03-19 13:59 ` [PATCH 3/5] arm64: Extract feature parsing code from cpu_errata.c Marc Zyngier
2015-03-19 13:59 ` [PATCH 4/5] arm64: alternative: Introduce feature for GICv3 CPU interface Marc Zyngier
2015-03-19 13:59 ` [PATCH 5/5] arm64: KVM: Switch vgic save/restore to alternative_insn Marc Zyngier
2015-03-26 22:04 ` [PATCH 0/5] arm64: Patching branches for fun and profit Will Deacon
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