Re: [discuss] semantics, "replay debugging" vs. "reverse debugging"

teawater
2008-10-22T03:26:07Z

I think your not clear my idea.

> I think maybe some instruction can do it.
> Such as add instruction. When it forward execute, it add some number
> to a value of register. When it reverse, it can sub this number from
> the value of register. It can reverse without record.

Maybe you can read this part again.

And what is the status of program? Most of time, it's just the values
of registers and memory. Do not think anything that complex.

On Tue, Oct 21, 2008 at 15:28, Jakob Engblom <jakob@virtutech.com> wrote:
>
>> > One could have reverse without record/replay if,
>> > for instance, one had a machine architecture where
>> > all instructions were reversable, ie. the machine
>> > itself could reverse-execute an instruction.
>>
>> I think maybe some instruction can do it.
>> Such as add instruction. When it forward execute, it add some number
>> to a value of register. When it reverse, it can sub this number from
>> the value of register. It can reverse without record.
>>
>> In P record, I make a interface to use it in record_t need_dasm. But I
>> still not use it. Maybe I can use it in the future.
>
> When thinking about overflow semantics, etc., it is clear that this can never
> work in general.
>
> The easiest way to create a reversible system is to
>
> 1. Impose determinisim
>
> 2. Make sure you can get back to a previous state
>
> And then you simply jump back and reexecute until some chosen point in time.
> Works like a charm, and is very general.
>
> /jakob
>
>