> From: Paolo Bonzini [mailto:paolo.bonz...@gmail.com] On Behalf Of Paolo > Bonzini > On 18/02/2015 12:55, Pavel Dovgalyuk wrote: > > This set of patches is related to the reverse execution and deterministic > > replay of qemu execution. This implementation of deterministic replay can > > be used for deterministic debugging of guest code through gdb remote > > interface. > > > > These patches include only core function of the replay, > > excluding the support for replaying serial, audio, network, and USB devices' > > operations. Reverse debugging and monitor commands were also excluded to > > be submitted later as separate patches. > > > > 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. > > > > Deterministic replay 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 and mouse > > input devices. > > * Supports auto-checkpointing for convenient reverse debugging. > > > > Usage of the record/replay: > > * First, record the execution, by adding the following string to the > > command line: > > '-icount shift=7,rr=record,rrfile=replay.bin -net none'. > > Block devices' images are not actually changed in the recording mode, > > because all of the changes are written to the temporary overlay file. > > * Then you can replay it for the multiple times by using another command > > line option: '-icount shift=7,rr=replay,rrfile=replay.bin -net none' > > * '-net none' option should also be specified if network replay patches > > are not applied. > > > > Paper with short description of deterministic replay implementation: > > http://www.computer.org/csdl/proceedings/csmr/2012/4666/00/4666a553-abs.html > > > > Modifications of qemu include: > > * wrappers for clock and time functions to save their return values in the > > log > > * saving different asynchronous events (e.g. system shutdown) into the log > > * synchronization of the bottom halves execution > > * synchronization of the threads from thread pool > > * recording/replaying user input (mouse and keyboard) > > * adding internal events for cpu and io synchronization > > > > v9 changes: > > * Replaced fwrite/fread with putc/getc (as suggested by Paolo Bonzini) > > * Stopping virtual machine in case of replay file end (as suggested by > > Paolo Bonzini) > > * Removed one of the replay mutexes (as suggested by Paolo Bonzini) > > * Fixed RCU queue for bottom halves (as suggested by Paolo Bonzini) > > * Updated command line options' names (as suggested by Paolo Bonzini) > > * Added design document for record/replay (as suggested by Paolo Bonzini) > > * Simplified checkpoints for the timers > > * Added cloning InputEvent objects for replay (as suggested by Paolo > > Bonzini) > > * Added replay blockers instead of checking the command line (as suggested > > by Paolo > Bonzini) > > * Some functions renaming and extracting. > > I haven't yet reviewed patch 23 completely, and I have to think (a lot > :)) more about block devices. In the meanwhile I understand the replay > code much better so I had some suggestions.
Do you have more comments? I'm ready to submit a new version. > > In general, the handling of replay_has_unread_data / replay_data_kind is > a bit messy. It would be nice if you could call > replay_fetch_data_kind() only when replay_has_unread_data == 0. Or, > even, remove replay_has_unread_data altogether: just call > replay_fetch_data_kind() when you'd set it to zero. That would simplify > a lot the code for readers. Fixed. Pavel Dovgalyuk