Re: [Qemu-devel] Reverse execution and deterministic replay

[Frederic Konrad <fred.konrad@greensocs.com>]

On 27/06/2014 08:11, Peter Crosthwaite wrote:
> Hi Pavel,
>
> On Fri, Jun 27, 2014 at 3:18 PM, Pavel Dovgaluk
> <Pavel.Dovgaluk@ispras.ru> wrote:
>> Hello!
>>
>> We want to publish set of patches related to the reverse execution and deterministic replay of qemu.
>> Our implementation of deterministic replay can be used for deterministic and reverse debugging of
>> guest code through gdb remote interface.
>>
>> Execution recording writes non-deterministic events log, which can be later used for replaying the
>> execution anywhere and for unlimited number of times. It also supports checkpointing for faster
>> rewinding during reverse debugging. Execution replaying reads the log and replays all
>> non-deterministic events including external input, hardware clocks, and interrupts.
>>
>> Reverse execution has the following features:
>>   * Deterministically replays whole system execution and all contents of the memory,
>>     state of the hadrware devices, clocks, and screen of the VM.
>>   * Writes execution log into the file for latter replaying for multiple times
>>     on different machines.
>>   * Supports i386, x86_64, and ARM hardware platforms.
>>   * Performs deterministic replay of all operations with keyboard, mouse, network adapters,
>>     audio devices, serial interfaces, and physical USB devices connected to the emulator.
>>   * Provides support for gdb reverse debugging commands like reverse-step and reverse-continue.
>>   * Supports auto-checkpointing for convenient reverse debugging.
>>   * Allows "going to the live execution" from the replay mode.
>>
>> Our implementation is completely tested for qemu 1.5 and is in beta state for 2.0.50.
>>
>> Some details about our implementation of reverse execution can be found in paper:
>> http://www.computer.org/csdl/proceedings/csmr/2012/4666/00/4666a553-abs.html
>>
> Add relevant implementation details to the git commit messages.
>
>> Can anyone review our patches?
>>
> Fred Konrad is doing a series on reverse exe at the moment. CC. Is the
> an independent implementation of the same thing or are you building on
> it?

Hi,

Yes seems we are doing the same thing only we use icount as an instruction
counter and you created a new instruction counter?

This has advantage of having it working everywhere icount works but the
disavantages of having to use icount for reverse execution.

I think we can use both way so the reverse execution will works on other
architecture the time an instruction counter is added to them.

I'm sure your patches will add to our solution and I can review your patches
when you'll send them.

It would help if you rebase them on the patch set that is currently on 
the list:
"[RFC PATCH v5 00/13] Reverse execution." I sent two days ago.

Thanks,
Fred
>
> I suggest posting a full RFC, this looks to me just like a cover
> letter but without a series.
>
> Note that we are going into hard freeze imminently so there will be
> some delay for merge.
>
> Regards,
> Peter
>
>> Pavel Dovgaluk
>>
>>
>>