Re: [PATCH v6 00/14] Reverse debugging

[Pavel Dovgalyuk <pavel.dovgalyuk@ispras.ru>]

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

Please, find the new version.
The patches 3 and 4 were updated.

However, is there any reason that not all the tests are executed?
I ran 'check -qcow2' without list of the tests, and encountered some 
problems with test 286 (that are fixed now).
But this test was not executed in your gitlab repository and with 'make 
check' on my local machine.

> 
> 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
>>
>