Re: [PATCH v3 09/15] replay: implement replay-seek command

[Pavel Dovgalyuk]

On 07.09.2020 19:25, Alex Bennée wrote:
> Pavel Dovgalyuk <pavel.dovgalyuk@ispras.ru> writes:
>
> > On 07.09.2020 17:59, Alex Bennée wrote:
> > > Pavel Dovgalyuk <pavel.dovgalyuk@ispras.ru> writes:
> > >
> > > > On 07.09.2020 15:58, Alex Bennée wrote:
> > > > > Pavel Dovgalyuk <pavel.dovgalyuk@ispras.ru> writes:
> > > > >
> > > > > > From: Pavel Dovgalyuk <Pavel.Dovgaluk@ispras.ru>
> > > > > >
> > > > > > This patch adds hmp/qmp commands replay_seek/replay-seek that proceed
> > > > > > the execution to the specified instruction count.
> > > > > > The command automatically loads nearest snapshot and replays the execution
> > > > > > to find the desired instruction count.
> > > > >
> > > > > Should there be an initial snapshot created at instruction 0? Using a
> > > > > separate monitor channel:
> > > >
> > > > Right, you can't go to the prior state, when there is no preceding
> > > > snapshot available.
> > >
> > > It seems creating an initial snapshot automatically would be more user
> >
> > Please take a look at 'Snapshotting' section of docs/replay.txt.
> > Reverse debugging is considered to be run with disk image (overlay)
> > and rrsnapshot option of icount, which allows creating an initial
> > VM snapshot.
>
> Given that I'm using the block device purely for VM snapshots I think it
> would be useful to document the minimal "no disk" approach - i.e. where
> the disk is only used for record/replay.
>
> However I'm still having trouble. I can record the trace with:
>
>    ./qemu-system-aarch64 -cpu cortex-a53 -display none -serial stdio \
>      -machine virt -kernel zephyr.elf -net none \
>      -icount 
> shift=6,align=off,sleep=off,rr=record,rrfile=record.out,rrsnapshot=rrstart  \
>      -drive file=record.qcow2,if=none,id=rr \
>      -monitor telnet:127.0.0.1:4444 -S

Can you provide your zephyr.elf image?

> which shows:
>
>    (qemu) info snapshots
>    info snapshots
>    List of snapshots present on all disks:
>    ID        TAG               VM SIZE                DATE     VM CLOCK     
> ICOUNT
>    --        rrstart           653 KiB 2020-09-07 17:12:42 00:00:00.000         
>  0
>
> but do I need a whole separate overlay in the replay case? I thought
> supplying snapshot to the drive would prevent the replay case
> overwriting what has been recorded but with:
>
>      -icount shift=6,align=off,sleep=off,rr=replay,rrfile=record.out \
>      -drive file=record.qcow2,if=none,id=rr,snapshot

When you provide qcow2 (overlay or not) for snapshotting, you don't need 
any 'snapshot' option on drive.

> but I get:
>
>    (qemu) info snapshots
>    info snapshots
>    There is no snapshot available.
>
> so if I drop the ,snapshot from the line I can at least see the snapshot
> but continue doesn't seem to work:
>
>    (qemu) info snapshots
>    info snapshots
>    List of snapshots present on all disks:
>    ID        TAG               VM SIZE                DATE     VM CLOCK     
> ICOUNT
>    --        rrstart           653 KiB 2020-09-07 17:12:42 00:00:00.000         
>  0
>    (qemu) replay_break 190505
>    replay_break 190505
>    (qemu) c
>    c
>    (qemu) info replay
>    info replay
>    Replaying execution 'record.out': instruction count = 0

It seems, that replay hangs. Can you try removing '-S' in record command 
line?

>    (qemu)
>
> If I manually loadvm then we get somewhere but replay_seek breaks:
>
>    (qemu) loadvm rrstart
>    loadvm rrstart
>    (qemu) info replay
>    info replay
>    Replaying execution 'record.out': instruction count = 190505
>    (qemu) replay_seek 190000
>    replay_seek 190000
>    snapshotting is disabled
>
> with a crash:
>
>    ./qemu-system-aarch64 -cpu cortex-a53 -display none -serial stdio -machine 
> virt -kernel zephyr.elf -net none -icount 
> shift=6,align=off,sleep=off,rr=replay,rrfile=record.out
>   -drive file=record.qcow2,if=none,id=rr -monitor telnet:127.0.0.1:4444 -S
> *** Booting Zephyr OS build zephyr-v2.3.0-1183-ge5628ad0faf3  ***
> Hello World! qemu_cortex_a53
> free(): invalid pointer
> fish: “./qemu-system-aarch64 -cpu cort…” terminated by signal SIGABRT (Abort)
>
>
> > > friendly? What can you do to trigger a snapshot, say for example on a
> > > gdb connect?
> >
> > This makes sense when executing with temporary overlay, thanks.
> >
> > > > >

Pavel Dovgalyuk