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Re: [RFA/commit] arm-tdep.c: Do not single-step after hitting a watchpoint.
- From: Pedro Alves <palves at redhat dot com>
- To: Joel Brobecker <brobecker at adacore dot com>
- Cc: Marcus Shawcroft <marcus dot shawcroft at gmail dot com>, Terry Guo <terry dot guo at arm dot com>, Marcus Shawcroft <marcus dot shawcroft at arm dot com>, lgustavo at codesourcery dot com, Yao Qi <yao at codesourcery dot com>, "gdb-patches at sourceware dot org" <gdb-patches at sourceware dot org>, Will Deacon <will dot deacon at arm dot com>, peter dot maydell at arm dot com, "gareth at blacksphere dot co dot nz >> Gareth McMullin" <gareth at blacksphere dot co dot nz>
- Date: Mon, 29 Sep 2014 22:04:11 +0100
- Subject: Re: [RFA/commit] arm-tdep.c: Do not single-step after hitting a watchpoint.
- Authentication-results: sourceware.org; auth=none
- References: <1410786062-19274-1-git-send-email-brobecker at adacore dot com> <87bnqf2578 dot fsf at codesourcery dot com> <20140916115936 dot GM4871 at adacore dot com> <5418279A dot 1040604 at codesourcery dot com> <20140916124814 dot GO4871 at adacore dot com> <54183681 dot 3010504 at codesourcery dot com> <5418556E dot 7010502 at redhat dot com> <CAFqB+PxZM3Zb0J2HRoULU+e30jMP9OowRFsgJCjaWf7tNvagTA at mail dot gmail dot com> <541C6860 dot 9070907 at redhat dot com> <20140929175151 dot GC6927 at adacore dot com>
On 09/29/2014 06:51 PM, Joel Brobecker wrote:
> Hello all,
>> Hmm. So when the data abort triggers at fault+8, the instruction
>> that triggered the abort hasn't actually completed, right? No memory
>> has changed yet.
>> So if nothing does the adjustment, like Gareth found out happens with
>> the Black Magic Probe, then we'll resume execution from the
>> wrong address/instruction (with the effects of the skipped instructions
>> missing, including the memory write...). Did I understand that
>> right? (Gareth, is that what you see?)
> I have been trying to understand the various contributions, and
> I admit I am still not quite sure...
> Does it look like the patch I proposed is correct? It seems to be
> supported by Terry Guo's experiments as well...
Nope, Terry's experiments supported the current code.
The experiments (which were on Linux) showed that the watchpoint was
reported to GDB first with the PC pointing at the instruction that
accessed memory, and then GDB single-stepped once, and the PC ends up
pointing at one instruction after the instruction that changed memory.