Re: [Qemu-devel] [RFC PATCH v5 00/31] Deterministic replay and reverse execution

[Pavel Dovgaluk]

That covermail was wrong. Here is the correct one:




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:
   '-record fname=replay.bin -icount 7 -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: '-replay fname=replay.bin -icount 7 -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

v5 changes:
 * Minor changes.
 * Used fixed-width integer types for read/write functions (as suggested by 
Alex Bennee)
 * Moved savevm-related code out of the core.
 * Added new traced clock for deterministic virtual clock warping (as suggested 
by Paolo Bonzini)
 * Fixed exception_index reset for user mode (as suggested by Paolo Bonzini)
 * Adopted Paolo's icount patches
 * Fixed hardware interrupts replaying

v4 changes:
 * Updated block drivers to support new bdrv_open interface.
 * Moved migration patches into separate series (as suggested by Paolo Bonzini)
 * Fixed a bug in replay_break operation.
 * Fixed rtl8139 migration for replay.
 * Fixed 'period' parameter processing for record mode.
 * Fixed bug in 'reverse-stepi' implementation.
 * Fixed replay without making any snapshots (even the starting one).
 * Moved core replay patches into the separate series.
 * Fixed reverse step and reverse continue support.
 * Fixed several bugs in icount subsystem.
 * Reusing native qemu icount for replay instructions counting.
 * Separated core patches into their own series.

v3 changes:
 * Fixed bug with replay of the aio write operations.
 * Added virtual clock based on replay icount.
 * Removed duplicated saving of interrupt_request CPU field.
 * Fixed some coding style issues.
 * Renamed QMP commands for controlling reverse execution (as suggested by Eric 
Blake)
 * Replay mode and submode implemented as QAPI enumerations (as suggested by 
Eric Blake)
 * Added description and example for replay-info command (as suggested by Eric 
Blake)
 * Added information about the current breakpoint to the output of replay-info 
(as suggested by Eric Blake)
 * Updated version id for HPET vmstate (as suggested by Paolo Bonzini)
 * Removed static fields from parallel vmstate (as suggested by Paolo Bonzini)
 * New vmstate fields for mc146818rtc, pckbd, kvmapic, serial, fdc, rtl8139 
moved to subsection (as suggested by Paolo Bonzini)
 * Disabled textmode cursor blinking, when virtual machine is stopped (as 
suggested by Paolo Bonzini)
 * Extracted saving of exception_index to separate patch (as suggested by Paolo 
Bonzini)

v2 changes:
 * Patches are split to be reviewable and bisectable (as suggested by Kirill 
Batuzov)
 * Added QMP versions of replay commands (as suggested by Eric Blake)
 * Removed some optional features of replay to make patches cleaner
 * Minor changes and code cleanup were made