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Re: [Qemu-devel] [RFC PATCH 00/17] reverse debugging
From: |
Ciro Santilli |
Subject: |
Re: [Qemu-devel] [RFC PATCH 00/17] reverse debugging |
Date: |
Thu, 26 Apr 2018 13:21:15 +0100 |
On Wed, Apr 25, 2018 at 1:45 PM, Pavel Dovgalyuk
<address@hidden> 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.
>
Hi Pavel,
1)
Can you provide more details on how to run the reverse debugging? In
particular how to take the checkpoint?
My test setup is described in detail at:
https://github.com/cirosantilli/qemu-test/tree/8127452e5685ed233dc7357a1fe34b7a2d173480
command "x86_64/reverse-debug".
Here are the actual commands:
#!/usr/bin/env bash
set -eu
dir="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)/.."
cmd="\
time \
./x86_64-softmmu/qemu-system-x86_64 \
-M pc \
-append 'root=/dev/sda console=ttyS0 nokaslr printk.time=y -
lkmc_eval=\"/rand_check.out;/sbin/ifup -a;wget -S
google.com;/poweroff.out;\"' \
-kernel '${dir}/out/x86_64/buildroot/images/bzImage' \
-nographic \
-serial mon:stdio \
-monitor telnet::45454,server,nowait \
\
-drive
file='${dir}/out/x86_64/buildroot/images/rootfs.ext2.qcow2,if=none,id=img-direct,format=qcow2,snapshot'
\
-drive driver=blkreplay,if=none,image=img-direct,id=img-blkreplay \
-device ide-hd,drive=img-blkreplay \
\
-netdev user,id=net1 \
-device rtl8139,netdev=net1 \
-object filter-replay,id=replay,netdev=net1 \
"
cmd="${cmd} $@"
echo "$cmd"
eval "$cmd -icount 'shift=7,rr=record,rrfile=replay.bin'"
eval "$cmd -icount 'shift=7,rr=replay,rrfile=replay.bin' -S -s"
Then I take a snapshot right at the beginning of the execution:
telnet 45454
savevm a
And on another shell:
/data/git/linux-kernel-module-cheat/out/x86_64/buildroot/host/usr/bin/x86_64-linux-gdb
\
-q \
-ex 'file vmlinux' \
-ex 'target remote localhost:1234' \
-ex 'break start_kernel' \
-ex 'continue' \
But now if I try on GDB:
next
next
next
reverse-continue
hoping to go back to start_kernel, but nothing happens.
Same behavior if I take the snapshot after reaching start_kernel instead.
2)
I wonder if it would be possible to expose checkpoint taking through
GDB example via:
https://sourceware.org/gdb/onlinedocs/gdb/Checkpoint_002fRestart.html
Or some other more convenient checkpoint generation method, e.g.
automatically take checkpoints every N instructions.
> 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-180207
>
> ---
>
> Pavel Dovgalyuk (17):
> 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
> migration: introduce icount field for snapshots
> qcow2: introduce icount field for snapshots
> replay: introduce info hmp/qmp command
> replay: introduce breakpoint at the specified step
> replay: implement replay_seek command to proceed to the desired step
> replay: flush events when exitting
> timer: remove replay clock probe in deadline calculation
> replay: refine replay-time module
> translator: fix breakpoint processing
> replay: flush rr queue before loading the vmstate
> gdbstub: add reverse step support in replay mode
> gdbstub: add reverse continue support in replay mode
>
>
> accel/tcg/translator.c | 8 +
> block/blkreplay.c | 8 +
> block/io.c | 22 +++
> block/qapi.c | 11 +-
> block/qcow2-snapshot.c | 9 +
> block/qcow2.h | 2
> blockdev.c | 3
> cpus.c | 19 ++-
> docs/replay.txt | 12 +-
> exec.c | 6 +
> gdbstub.c | 50 +++++++-
> hmp-commands-info.hx | 14 ++
> hmp-commands.hx | 30 +++++
> hmp.h | 3
> include/block/snapshot.h | 1
> include/sysemu/replay.h | 18 +++
> migration/savevm.c | 11 +-
> qapi/block-core.json | 5 +
> qapi/block.json | 3
> qapi/misc.json | 69 +++++++++++
> replay/Makefile.objs | 3
> replay/replay-debugging.c | 286
> +++++++++++++++++++++++++++++++++++++++++++++
> replay/replay-events.c | 14 --
> replay/replay-internal.h | 10 +-
> replay/replay-time.c | 27 ++--
> replay/replay.c | 22 +++
> stubs/replay.c | 10 ++
> util/qemu-timer.c | 11 --
> vl.c | 11 +-
> 29 files changed, 625 insertions(+), 73 deletions(-)
> create mode 100644 replay/replay-debugging.c
>
> --
> Pavel Dovgalyuk
- [Qemu-devel] [RFC PATCH 10/17] replay: implement replay_seek command to proceed to the desired step, (continued)
- [Qemu-devel] [RFC PATCH 10/17] replay: implement replay_seek command to proceed to the desired step, Pavel Dovgalyuk, 2018/04/25
- [Qemu-devel] [RFC PATCH 11/17] replay: flush events when exitting, Pavel Dovgalyuk, 2018/04/25
- [Qemu-devel] [RFC PATCH 12/17] timer: remove replay clock probe in deadline calculation, Pavel Dovgalyuk, 2018/04/25
- [Qemu-devel] [RFC PATCH 13/17] replay: refine replay-time module, Pavel Dovgalyuk, 2018/04/25
- [Qemu-devel] [RFC PATCH 15/17] replay: flush rr queue before loading the vmstate, Pavel Dovgalyuk, 2018/04/25
- [Qemu-devel] [RFC PATCH 14/17] translator: fix breakpoint processing, Pavel Dovgalyuk, 2018/04/25
- [Qemu-devel] [RFC PATCH 17/17] gdbstub: add reverse continue support in replay mode, Pavel Dovgalyuk, 2018/04/25
- [Qemu-devel] [RFC PATCH 16/17] gdbstub: add reverse step support in replay mode, Pavel Dovgalyuk, 2018/04/25
- Re: [Qemu-devel] [RFC PATCH 00/17] reverse debugging, Pavel Dovgalyuk, 2018/04/25
- Re: [Qemu-devel] [RFC PATCH 00/17] reverse debugging,
Ciro Santilli <=
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