linux-kernel - Re: [PATCH 3/4] arm64: Allow hw watchpoint of length 3,5,6 and 7

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Message-ID: <CAJt8pk-7XntQkfojtnP7ZLk6=CWKLfdvK1+vMzJxoRBxgwiW+Q@mail.gmail.com>
Date:   Thu, 13 Oct 2016 15:29:17 +0100
From:   Pavel Labath <labath@...gle.com>
To:     Pratyush Anand <panand@...hat.com>, Yao Qi <qiyaoltc@...il.com>
Cc:     onestero@...hat.com, Will Deacon <will.deacon@....com>,
        Mark Rutland <mark.rutland@....com>,
        linux-kernel@...r.kernel.org,
        Jan Kratochvil <jan.kratochvil@...hat.com>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH 3/4] arm64: Allow hw watchpoint of length 3,5,6 and 7

On 13 October 2016 at 11:22, Pratyush Anand <panand@...hat.com> wrote:
>
>
> On Wednesday 12 October 2016 04:46 PM, Yao Qi wrote:
>>
>> On Wed, Oct 12, 2016 at 6:58 AM, Pratyush Anand <panand@...hat.com> wrote:
>>>
>>> Since, arm64 can support all offset within a double word limit.
>>> Therefore,
>>> now support other lengths within that range as well.
>>
>>
>> How does ptracer (like GDB) detect kernel has already supported all byte
>> address select values?  I suppose ptrace(NT_ARM_HW_WATCH, ) with
>> len is 3 or 5 fail on current kernel but is of success after your patches
>> applied.
>>
>
> Thanks for testing these patches.
>
> I do not know if we can know that other than the failure of
> ptrace(PTRACE_SETREGSET, .., NT_ARM_HW_WATCH, ..). I do not see any such
> option in `man ptrace`.
That's how I intend to implement support for this in LLDB.
if (setExactWatchpoint())
  return true; // watchpoint set, new kernel
if (setApproxWatchpoint())
  return true; // watchpoint set, old kernel
return false; // watchpoints not working

seems straight-forward enough to me.