Re: [PATCH v6 00/14] Reverse debugging

[Pavel Dovgalyuk]

On 02.10.2020 18:39, Paolo Bonzini wrote:
> On 29/09/20 13:01, Pavel Dovgalyuk wrote:
> > 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
> >   - avocado-based acceptance tests for reverse debugging
> >
> > The patches are available in the repository:
> > https://github.com/ispras/qemu/tree/rr-200901
>
> Hi Pavel,
>
> I'm still seeing failures in "make check-block":
>
> https://gitlab.com/bonzini/qemu/-/jobs/769653852

Ok, now I can reproduce it with manually running 'check -qcow2 261'.
I'll send a patch soon.

> Paolo
>
> > v6 changes:
> >   - removed passing err variable without checking it's value after
> > v5 changes:
> >   - disabled reverse debugging tests for gitlab-based testing
> >     due to the unidentified timeout problem
> > v4 changes:
> >   - added VM snapshot creation on gdb connect (suggested by Alex Bennée)
> >   - removed useless calls to error_free
> >   - updated poll interrupt processing
> >   - minor changes
> > v3 changes:
> >   - rebased to support the new build system
> >   - bumped avocado framework version for using fixed remote gdb client
> > v2 changes:
> >   - rebased to the latest upstream version
> >   - fixed replaying of the POLL interrupts after the latest debug changes
> >
> > ---
> >
> > Pavel Dovgaluk (11):
> >        replay: provide an accessor for rr filename
> >        qcow2: introduce icount field for snapshots
> >        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: 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
> >        tests/acceptance: add reverse debugging test
> >
> > Pavel Dovgalyuk (3):
> >        replay: don't record interrupt poll
> >        migration: introduce icount field for snapshots
> >        replay: create temporary snapshot at debugger connection
> >
> >
> >   MAINTAINERS                           |    2
> >   accel/tcg/cpu-exec.c                  |   21 ++
> >   accel/tcg/translator.c                |    1
> >   block/qapi.c                          |   18 +-
> >   block/qcow2-snapshot.c                |    9 +
> >   block/qcow2.h                         |    3
> >   blockdev.c                            |   10 +
> >   docs/interop/qcow2.txt                |    5
> >   docs/replay.txt                       |   46 +++++
> >   exec.c                                |    8 +
> >   gdbstub.c                             |   64 ++++++
> >   hmp-commands-info.hx                  |   11 +
> >   hmp-commands.hx                       |   50 +++++
> >   include/block/snapshot.h              |    1
> >   include/monitor/hmp.h                 |    4
> >   include/sysemu/replay.h               |   26 +++
> >   migration/savevm.c                    |   17 +-
> >   qapi/block-core.json                  |   11 +
> >   qapi/meson.build                      |    1
> >   qapi/misc.json                        |   18 --
> >   qapi/qapi-schema.json                 |    1
> >   qapi/replay.json                      |  121 ++++++++++++
> >   replay/meson.build                    |    1
> >   replay/replay-debugging.c             |  332 +++++++++++++++++++++++++++++++++
> >   replay/replay-events.c                |    4
> >   replay/replay-internal.h              |    6 -
> >   replay/replay.c                       |   22 ++
> >   softmmu/cpus.c                        |   19 ++
> >   stubs/replay.c                        |   15 +
> >   tests/acceptance/reverse_debugging.py |  208 +++++++++++++++++++++
> >   tests/qemu-iotests/267.out            |   48 ++---
> >   31 files changed, 1039 insertions(+), 64 deletions(-)
> >   create mode 100644 qapi/replay.json
> >   create mode 100644 replay/replay-debugging.c
> >   create mode 100644 tests/acceptance/reverse_debugging.py
> >
> > --
> > Pavel Dovgalyuk