From: Masami Hiramatsu <mhiramat@kernel.org>
To: Jean-Philippe Brucker <jean-philippe@linaro.org>
Cc: catalin.marinas@arm.com, Will Deacon <will@kernel.org>,
dianders@chromium.org, linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH] arm64: Fix early single-stepping
Date: Wed, 28 Oct 2020 21:21:45 +0900 [thread overview]
Message-ID: <20201028212145.e8fc44671c3193da076351e5@kernel.org> (raw)
In-Reply-To: <20201028094827.GC2328726@myrica>
On Wed, 28 Oct 2020 10:48:27 +0100
Jean-Philippe Brucker <jean-philippe@linaro.org> wrote:
> On Wed, Oct 28, 2020 at 06:07:31PM +0900, Masami Hiramatsu wrote:
> > > > Yes, I think so. Same order problem as the OS lock, they need to be reset
> > > > before enable_debug_monitors(). On CPU0 that would be before
> > > > early_initcall and for secondaries the hotplug notifier needs to be
> > > > installed earlier as well. I'll send a v2.
> > >
> > > Cheers. An alternative (which I think would be better in the long run
> > > anyway) would be to avoid using hardware step in kprobes and instead rely
> > > on a BRK instruction to trap after running the trampoline.
> >
> > But how we trap the instruction which can change pc? (like br?)
> > Are all those instruction emulated now?
>
> According to aarch64_insn_is_steppable() anything that changes the PC is
> emulated.
OK, that sounds good. Then we can put the BRK right after the copied instruction.
> I'm also checking whether there is a change of behavior with
> synchronous exceptions taken while single-stepping (page faults).
Thanks! From the kprobe_fault_handler(), it seems the page faults handled
before the single-stepping exception and the fault handler disables single
steping explicitly. So if we use BRK, that code will not be needed.
Thank you,
--
Masami Hiramatsu <mhiramat@kernel.org>
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next prev parent reply other threads:[~2020-10-28 12:22 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-10-26 17:29 [PATCH] arm64: Fix early single-stepping Jean-Philippe Brucker
2020-10-26 17:38 ` Will Deacon
2020-10-27 0:48 ` Masami Hiramatsu
2020-10-27 10:13 ` Masami Hiramatsu
2020-10-27 10:42 ` Masami Hiramatsu
2020-10-27 11:59 ` Jean-Philippe Brucker
2020-10-27 12:33 ` Will Deacon
2020-10-27 13:49 ` Masami Hiramatsu
2020-10-28 8:28 ` Jean-Philippe Brucker
2020-10-28 8:36 ` Will Deacon
2020-10-28 9:07 ` Masami Hiramatsu
2020-10-28 9:48 ` Jean-Philippe Brucker
2020-10-28 12:21 ` Masami Hiramatsu [this message]
2020-11-25 16:09 ` Masami Hiramatsu
2020-11-25 16:11 ` Will Deacon
2020-11-25 16:18 ` Masami Hiramatsu
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