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From: Michael Walle <michael@walle.cc>
Date: Mon, 06 Oct 2014 00:07:25 +0200
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Subject: Re: [Qemu-devel] [PATCH] gdbstub: Allow target CPUs to specify
	watchpoint STOP_BEFORE_ACCESS flag
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To: Peter Maydell <peter.maydell@linaro.org>
Cc: Patch Tracking <patches@linaro.org>, QEMU Developers <qemu-devel@nongnu.org>, Max Filippov <jcmvbkbc@gmail.com>, "Edgar E. Iglesias" <edgar.iglesias@gmail.com>, Aurelien Jarno <aurelien@aurel32.net>, Richard Henderson <rth@twiddle.net>

Am Sonntag, 5. Oktober 2014, 22:48:05 schrieb Peter Maydell:
> On 5 October 2014 22:36, Peter Maydell <peter.maydell@linaro.org> wrote:
> > On 5 October 2014 22:00, Michael Walle <michael@walle.cc> wrote:
> >> I can confirm that your patch makes qemu stop one instruction earlier.
> >> Without your patch the program is stopped at (3). With your patch
> >> applied the program is stopped at (2). But I guess the correct point to
> >> stop is (1), right?> 
> > No, gdb wants execution to stop with the PC just after the
> > instruction which issued the memory access, with whatever
> > effects the instruction had having already taken place.
> > So (2) is correct. (I think nicer UI would indeed be to
> > stop at (1) but you can't get that effect on CPUs like
> > x86 which only stop after the wp insn has executed, and
> > they'd rather be consistent.)
> 
> ...and incidentally the way it achieves this for "stop before
> wp insn" CPU targets is that it unsets the watchpoint
> and automatically steps one instruction before returning
> control to the gdb user. (You can see this if you turn
> gdb's remote-protocol debug on.)

Ah, now it makes sense :)

Tested-by: Michael Walle <michael@walle.cc> (for lm32)

-- 
-michael