Re: [Qemu-devel] [PATCH v12 00/25] Fixing record/replay and adding reverse debugging

[Pavel Dovgalyuk]

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Pavel Dovgalyuk


> -----Original Message-----
> From: Pavel Dovgalyuk [mailto:address@hidden
> Sent: Tuesday, February 05, 2019 11:20 AM
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> Subject: [PATCH v12 00/25] Fixing record/replay and adding reverse debugging
> 
> GDB remote protocol supports reverse debugging of the targets.
> It includes 'reverse step' and 'reverse continue' operations.
> The first one finds the previous step of the execution,
> and the second one is intended to stop at the last breakpoint that
> would happen when the program is executed normally.
> 
> Reverse debugging is possible in the replay mode, when at least
> one snapshot was created at the record or replay phase.
> QEMU can use these snapshots for travelling back in time with GDB.
> 
> Running the execution in replay mode allows using GDB reverse debugging
> commands:
>  - reverse-stepi (or rsi): Steps one instruction to the past.
>    QEMU loads on of the prior snapshots and proceeds to the desired
>    instruction forward. When that step is reaches, execution stops.
>  - reverse-continue (or rc): Runs execution "backwards".
>    QEMU tries to find breakpoint or watchpoint by loaded prior snapshot
>    and replaying the execution. Then QEMU loads snapshots again and
>    replays to the latest breakpoint. When there are no breakpoints in
>    the examined section of the execution, QEMU finds one more snapshot
>    and tries again. After the first snapshot is processed, execution
>    stops at this snapshot.
> 
> The set of patches include the following modifications:
>  - gdbstub update for reverse debugging support
>  - functions that automatically perform reverse step and reverse
>    continue operations
>  - hmp/qmp commands for manipulating the replay process
>  - improvement of the snapshotting for saving the execution step
>    in the snapshot parameters
>  - other record/replay fixes
> 
> The patches are available in the repository:
> https://github.com/ispras/qemu/tree/rr-190205
> 
> v12 changes:
>  - style fixes
> 
> v11 changes:
>  - added can_do_io resetting before jumping to the next block in the chain
>  - rebase to the latest master
> 
> v10 changes:
>  - added patch for correct deadline calculation with external timers
>  - updated icount-related documentation in json files
>    (suggested by Markus Armbruster)
>  - fixed replay shutdown
>  - renamed some functions and variables to make them consistent with
>    the documentation and displayed messages
>  - minor changes
> 
> v9 changes:
>  - moved rr qapi stuff to the separate file (suggested by Markus Armbruster)
>  - minor coding style fixes
> 
> v8 changes:
>  - rebased to the new master
>  - added missing fix for prior rr patch
>  - updated 'since' version number in json-related patches
> 
> v7 changes:
>  - rebased to the new master with upstreamed patches from the series
>  - several improvements in hmp/qmp commands handling (suggested by Markus 
> Armbruster)
>  - fixed record/replay with '-rtc base' option enabled
>  - added document with virtual hardware requirements
> 
> v6 changes:
>  - rebased to the new version of master
>  - fixed build of linux-user configurations
>  - added new clock for slirp and vnc timers
> 
> v5 changes:
>  - multiple fixes of record/replay bugs appeared after QEMU core update
>  - changed reverse debugging to 'since 3.1'
> 
> v4 changes:
>  - changed 'since 2.13' to 'since 3.0' in json (as suggested by Eric Blake)
> 
> v3 changes:
>  - Fixed PS/2 bug with save/load vm, which caused failures of the replay.
>  - Rebased to the new code base.
>  - Minor fixes.
> 
> v2 changes:
>  - documented reverse debugging
>  - fixed start vmstate loading in record mode
>  - documented qcow2 changes (as suggested by Eric Blake)
>  - made icount SnapshotInfo field optional (as suggested by Eric Blake)
>  - renamed qmp commands (as suggested by Eric Blake)
>  - minor changes
> 
> ---
> 
> Pavel Dovgalyuk (24):
>       block: implement bdrv_snapshot_goto for blkreplay
>       replay: disable default snapshot for record/replay
>       replay: update docs for record/replay with block devices
>       replay: don't drain/flush bdrv queue while RR is working
>       replay: finish record/replay before closing the disks
>       qcow2: introduce icount field for snapshots
>       migration: introduce icount field for snapshots
>       replay: provide an accessor for rr filename
>       qapi: introduce replay.json for record/replay-related stuff
>       replay: introduce info hmp/qmp command
>       replay: introduce breakpoint at the specified step
>       replay: implement replay-seek command
>       replay: refine replay-time module
>       replay: flush rr queue before loading the vmstate
>       gdbstub: add reverse step support in replay mode
>       gdbstub: add reverse continue support in replay mode
>       replay: describe reverse debugging in docs/replay.txt
>       replay: add BH oneshot event for block layer
>       replay: init rtc after enabling the replay
>       replay: document development rules
>       util/qemu-timer: refactor deadline calculation for external timers
>       replay: fix replay shutdown
>       replay: rename step-related variables and functions
>       icount: clean up cpu_can_io before jumping to the next block
> 
> address@hidden (1):
>       replay: add missing fix for internal function
> 
> 
>  MAINTAINERS               |    1
>  Makefile.objs             |    4 -
>  accel/tcg/tcg-runtime.c   |    2
>  accel/tcg/translator.c    |    1
>  block/blkreplay.c         |    8 +
>  block/block-backend.c     |    8 +
>  block/io.c                |   32 ++++
>  block/iscsi.c             |    5 -
>  block/nfs.c               |    5 -
>  block/null.c              |    4 -
>  block/nvme.c              |    6 +
>  block/qapi.c              |   18 ++
>  block/qcow2-snapshot.c    |    9 +
>  block/qcow2.h             |    2
>  block/rbd.c               |    5 -
>  block/vxhs.c              |    5 -
>  blockdev.c                |   10 +
>  cpus.c                    |   30 +++-
>  docs/devel/replay.txt     |   46 ++++++
>  docs/interop/qcow2.txt    |    4 +
>  docs/replay.txt           |   45 ++++++
>  exec.c                    |    8 +
>  gdbstub.c                 |   52 +++++++
>  hmp-commands-info.hx      |   14 ++
>  hmp-commands.hx           |   53 +++++++
>  hmp.h                     |    4 +
>  include/block/snapshot.h  |    1
>  include/qemu/timer.h      |    7 -
>  include/sysemu/replay.h   |   30 ++++
>  migration/savevm.c        |   11 ++
>  qapi/block-core.json      |    8 +
>  qapi/block.json           |    3
>  qapi/misc.json            |   18 --
>  qapi/qapi-schema.json     |    1
>  qapi/replay.json          |  121 +++++++++++++++++
>  qtest.c                   |    2
>  replay/Makefile.objs      |    3
>  replay/replay-debugging.c |  327 
> +++++++++++++++++++++++++++++++++++++++++++++
>  replay/replay-events.c    |   18 ++
>  replay/replay-internal.c  |   10 +
>  replay/replay-internal.h  |   17 +-
>  replay/replay-snapshot.c  |    6 -
>  replay/replay-time.c      |   36 ++---
>  replay/replay.c           |   56 ++++++--
>  stubs/Makefile.objs       |    1
>  stubs/replay-user.c       |    9 +
>  stubs/replay.c            |   10 +
>  tests/ptimer-test-stubs.c |    2
>  tests/ptimer-test.c       |    4 -
>  util/qemu-timer.c         |   41 +++++-
>  vl.c                      |   21 ++-
>  51 files changed, 1010 insertions(+), 134 deletions(-)
>  create mode 100644 docs/devel/replay.txt
>  create mode 100644 qapi/replay.json
>  create mode 100644 replay/replay-debugging.c
>  create mode 100644 stubs/replay-user.c
> 
> --
> Pavel Dovgalyuk