Re: [Qemu-devel] [RFC PATCH 00/22] Reverse execution and deterministic replay

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

On 01/07/2014 15:11, Vasily Eefimov wrote:
>
>
> On 01.07.2014 16:40, Frederic Konrad wrote:
>> Hi Pavel,
>>
>> Thanks for sharing.
>> I'll take a look at your patch-set.
>> I suggest you try the icount mechanism and I think it might be
> There is a problem with icount. I know it operates in two ways: 
> counting VCPU instructions (with TB size accuracy) and "warp"ing with 
> respect to host clock. The last one is necessary for interrupts, 
> timers (and other asynchronous events) while VCPU is halted (and other 
> cases in which VCPU instructions is not being executed). So, this 
> referencing to host clock (which is non-deterministic) make icount a 
> source of non-determinism. Hence, it cannot be used as deterministic 
> timer (for synchronization of asynchronous non-deterministic events) 
> while playing.

True, this is right for virtual clock. That's why we built a new clock 
which didn't take this warping in account but becomes deterministically 
correct relative to the instruction counter.

Fred
>> interesting to
>> combine our work to have a complete solution and to avoid double copy
>> patches
>> (for example command lines, gdb stub and the snapshot mechanism).
>>
>> I'll provides the last updates today or tomorrow.
>>
>> Also do you have any git tree somewhere so it is easier for us to 
>> test it?
>> I recommand you to use git send-email to submit your patches so you 
>> can CC
>> people and the patch set won't be cutted by other patches in the mailing
>> list.
>>
>> Thanks,
>> Fred
>>
>> On 01/07/2014 13:17, Pavel Dovgaluk wrote:
>>> Hi,
>>>
>>> This set of patches is related to the reverse execution and 
>>> deterministic
>>> replay of qemu execution  Our implementation of 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.
>>>
>>> Usage of the record/replay:
>>>   * First, record the execution, by adding '-record fname=replay.bin'
>>> to the
>>>     command line.
>>>   * Then you can replay it for the multiple times by using another
>>> command
>>>     line option: '-replay fname=replay.bin'
>>>   * Virtual machine should have at least one virtual disk, which is
>>> used to
>>>     store checkpoints. If you want to enable automatic checkpointing,
>>> simply
>>>     add ',period=XX' to record options, where XX is the checkpointing
>>> period
>>>     in seconds.
>>>   * Using of the network adapters in record/replay mode is possible 
>>> with
>>>     the following command-line options:
>>>     - '-net user' (or another host adapter) in record mode
>>>     - '-net replay' in replay mode. Every host network adapter 
>>> should be
>>>       replaced by 'replay' when replaying the execution.
>>>   * Reverse debugging can be used through gdb remote interface.
>>>     reverse-stepi and reverse-continue commands are supported. Other
>>> reverse
>>>     commands should also work, because they reuse these ones.
>>>   * Monitor is extended by the following commands:
>>>     - replay_info - prints information about replay mode and current 
>>> step
>>>       (number of instructions executed)
>>>     - replay_break - sets "breakpoint" at the specified instructions
>>> count.
>>>     - replay_seek - rewinds (using the checkpoints, if possible) to the
>>>       specified step of replay log.
>>>     - replay_events - prints list of the external events like network
>>> packet
>>>       input, or keyboard and mouse input.
>>>
>>> Paper with short description of deterministic replay implementation:
>>> http://www.computer.org/csdl/proceedings/csmr/2012/4666/00/4666a553-abs.html 
>>>
>>>
> ...
>>> Pavel Dovgalyuk
>>>
>>
>>
>