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

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Message-ID: <1bc0dce6-eb26-dbf5-dd0c-d36055f5f1fe@redhat.com>
Date:   Thu, 13 Oct 2016 15:52:17 +0530
From:   Pratyush Anand <panand@...hat.com>
To:     Yao Qi <qiyaoltc@...il.com>, onestero@...hat.com
Cc:     will.deacon@....com, Mark Rutland <mark.rutland@....com>,
        labath@...gle.com, linux-kernel@...r.kernel.org,
        Jan Kratochvil <jan.kratochvil@...hat.com>,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH 3/4] arm64: Allow hw watchpoint of length 3,5,6 and 7



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`.


> GDB is aware of the byte address select limitation in kernel, so it always
> sets 1,2,4,8 in len in ctrl.  GDB needs to know whether the limitation is still
> there or not.
>

Not sure if other than "kernel version" anything will help here.

~Pratyush