linux-kernel - Re: [PATCH v3 0/2] arm64: Fix pending single-step debugging issues

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Date:   Fri, 8 Jul 2022 17:31:35 +0100
From:   Will Deacon <will@...nel.org>
To:     Doug Anderson <dianders@...omium.org>
Cc:     Sumit Garg <sumit.garg@...aro.org>,
        Daniel Thompson <daniel.thompson@...aro.org>,
        Wei Li <liwei391@...wei.com>,
        Catalin Marinas <catalin.marinas@....com>,
        Mark Rutland <mark.rutland@....com>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Jason Wessel <jason.wessel@...driver.com>,
        Marc Zyngier <maz@...nel.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3 0/2] arm64: Fix pending single-step debugging issues

On Fri, Jul 01, 2022 at 03:14:16PM -0700, Doug Anderson wrote:
> Hi,
> 
> On Tue, May 10, 2022 at 11:05 PM Sumit Garg <sumit.garg@...aro.org> wrote:
> >
> > This patch-set reworks pending fixes from Wei's series [1] to make
> > single-step debugging via kgdb/kdb on arm64 work as expected. There was
> > a prior discussion on ML [2] regarding if we should keep the interrupts
> > enabled during single-stepping. So patch #1 follows suggestion from Will
> > [3] to not disable interrupts during single stepping but rather skip
> > single stepping within interrupt handler.
> >
> > [1] https://lore.kernel.org/all/20200509214159.19680-1-liwei391@huawei.com/
> > [2] https://lore.kernel.org/all/CAD=FV=Voyfq3Qz0T3RY+aYWYJ0utdH=P_AweB=13rcV8GDBeyQ@mail.gmail.com/
> > [3] https://lore.kernel.org/all/20200626095551.GA9312@willie-the-truck/
> >
> > Changes in v3:
> > - Reword commit descriptions as per Daniel's suggestions.
> >
> > Changes in v2:
> > - Replace patch #1 to rather follow Will's suggestion.
> >
> > Sumit Garg (2):
> >   arm64: entry: Skip single stepping into interrupt handlers
> >   arm64: kgdb: Set PSTATE.SS to 1 to re-enable single-step
> >
> >  arch/arm64/include/asm/debug-monitors.h |  1 +
> >  arch/arm64/kernel/debug-monitors.c      |  5 +++++
> >  arch/arm64/kernel/entry-common.c        | 18 +++++++++++++++++-
> >  arch/arm64/kernel/kgdb.c                |  2 ++
> >  4 files changed, 25 insertions(+), 1 deletion(-)
> 
> Sorry it took so long for me to respond. I kept dreaming that I'd find
> the time to really dig deep into this to understand it fully and I'm
> finally giving up on it. I'm going to hope that Will and/or Catalin
> knows this area of the code well and can give it a good review. If not
> then I'll strive harder to make the time...

So the good news is that I spent a couple of days on this last week.

The bad news is that I'm nowhere done and about to disappear on holiday
for a week!

But anyway, I might be able to give this a review when I'm back. Failing
that, I wonder if enough of us have a little bit of time each that we
could hack on an agreed design together which covers the debug exception
behaviour beyond kgdb?

Will