linux-kernel - Re: [PATCH] arm64/debug: Fix registers on sleeping tasks

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Date:   Fri, 2 Mar 2018 10:43:24 -0800
From:   Doug Anderson <dianders@...omium.org>
To:     Will Deacon <will.deacon@....com>
Cc:     Catalin Marinas <catalin.marinas@....com>,
        Brian Norris <briannorris@...omium.org>, evgreen@...omium.org,
        LKML <linux-kernel@...r.kernel.org>,
        Ingo Molnar <mingo@...nel.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH] arm64/debug: Fix registers on sleeping tasks

Hi,

On Fri, Mar 2, 2018 at 10:01 AM, Will Deacon <will.deacon@....com> wrote:
> On Thu, Mar 01, 2018 at 11:38:03AM -0800, Douglas Anderson wrote:
>> This is the equivalent of commit 001bf455d206 ("ARM: 8428/1: kgdb: Fix
>> registers on sleeping tasks") but for arm64.  Nuff said.
>
> It's a pity that 001bf455d206 doesn't explain *why* past_pt_regs doesn't
> work.

Ah, sorry.  I can add that to the description but Mark Rutland also
explained it.  task_pt_regs are the userspace registers.  That's not
what kgdb needs.

> Anyway, does this mean you're actually using kgdb on arm64? Does the rest of
> it appear to work?

Yeah, I've been using it for years.  I had this patch on my list to
upstream but it conflicted with commit 0d15ef677839 ("arm64: kgdb:
Match pstate size with gdbserver protocol") and I never had time to
figure out if that mattered, so it's been sitting at
http://crosreview.com/371942 forever.

NOTE: in general I haven't been using single step and breakpoints
since those have always been a bit iffy on serial kgdb and especially
since we have read-only text on our system, but maybe I'll try that
now that I'm running with a newer kernel.

-Doug