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
