From: Pavel Dovgalyuk <pavel.dovgalyuk@ispras.ru>
To: "Alex Bennée" <alex.bennee@linaro.org>,
gdb@gnu.org, "QEMU Developers" <qemu-devel@nongnu.org>,
"Luis Machado" <luis.machado@linaro.org>
Cc: "Daniel P. Berrangé" <berrange@redhat.com>
Subject: Re: Best approach for supporting snapshots for QEMU's gdbstub?
Date: Sat, 15 May 2021 09:12:08 +0300 [thread overview]
Message-ID: <4dd935c3-fe40-6ecc-f037-e6eaf7dc7821@ispras.ru> (raw)
In-Reply-To: <87y2chjmsf.fsf@linaro.org>
On 14.05.2021 19:06, Alex Bennée wrote:
> Hi,
>
> I've been playing around with QEMU's reverse debugging support which
> I have working with Pavel's latest patches for supporting virtio with
> record/replay. Once you get the right command line it works well enough
> although currently each step backwards requires replaying the entire
> execution history until you get to the right point.
>
> QEMU can quite easily snapshot the entire VM state so I was looking to
> see what the best way to integrate this would be. As far as I can tell
> there are two interfaces gdb supports: bookmarks and checkpoints.
>
> As far as I can tell bookmarks where added as part of GDB's reverse
> debugging support but attempting to use them from the gdbstub reports:
>
> (gdb) bookmark
> You can't do that when your target is `remote'
>
> so I guess that would need an extension to the stub protocol to support?
>
> The other option I found was checkpoints which seem to predate support
> for reverse debugging. However:
>
> (gdb) checkpoint
> checkpoint: can't find fork function in inferior.
>
> I couldn't tell what feature needs to be negotiated but I suspect it's
> something like fork-events if the checkpoint mechanism is designed for
> user space with a fork/freeze approach.
>
> We could of course just add a custom monitor command like the
> qemu.sstep= command which could be used manually. However that would be
> a QEMU gdbstub specific approach.
For now you can just use 'monitor savevm sn1' in gdb.
But something like 'bookmark' seems more convenient.
> The other thing would be to be more intelligent on QEMU's side and save
> snapshots each time we hit an event, for example each time we hit a
> given breakpoint. However I do worry that might lead to snapshots
> growing quite quickly.
>
> Any thoughts/suggestions?
>
next prev parent reply other threads:[~2021-05-15 6:12 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-05-14 16:06 Alex Bennée
2021-05-15 6:12 ` Pavel Dovgalyuk [this message]
2021-05-17 16:49 ` Luis Machado
2021-05-17 17:27 ` Alex Bennée
2021-05-17 17:54 ` Luis Machado
2021-05-17 19:01 ` Peter Maydell
2021-05-18 5:26 ` Pavel Dovgalyuk
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