Re: [RFA/commit] arm-tdep.c: Do not single-step after hitting a watchpoint

Pedro Alves
2014-09-30T10:38:14Z

On 09/30/2014 11:17 AM, Peter Maydell wrote:
> On 30 September 2014 11:07, Pedro Alves <palves@redhat.com> wrote:
>> WFAR - Watchpoint Fault Address Register
>>
>> The WFAR is updated to indicate the address of the instruction that
>> accessed the watchpointed address:
>>
>> - the address of the instruction + 8 in ARM state
>> - the address of the instruction + 4 in ThumbÂ® state
>>
>> What wasn't clear to me was whether this meant that the
>> instruction at the address of the instruction, and
>> at the the address of the instruction +4/+2 (ARM/Thumb) had
>> executed completely or not. It's my understanding now that,
>> yes, both the instruction that caused the watchpoint and the
>> instruction after that one have already been executed.
>
> No, you are misinterpreting this. The WFAR records
> the address of the offending instruction + an offset
> which you have to correct for. The offset does *not*
> have any relation to how many further instructions
> the CPU has executed after the offending instruction,
> which could be none, one, two or ten. Asynchronous
> watchpoints are *asynchronous*, which means there
> is no timing guarantee about how soon the CPU will
> notice that one has fired and stop executing insns.
> The only guarantee you get in v7 is that you'll get
> the watchpoint before any exception that might be
> caused by a following instruction.

OK. It's clear now.

Thanks you!

Pedro Alves