Re: [Qemu-devel] [PULL 5/8] target-sparc: Use global registers for the register window

[Paolo Bonzini]

On 24/06/2016 10:12, Peter Maydell wrote:
> On 24 June 2016 at 07:36, Paolo Bonzini <address@hidden> wrote:
>> Mark, perhaps you can try to use migration to reduce the amount of
>> logging?  (Start QEMU with -snapshot, try to stop the vm before it
>> fails.  If you succeed, do a "migrate exec:cat>foo.sav" followed by
>> "commit"; if you fail, try again).
> 
> Why drag migration into it? I usually use 'savevm' and then
> the -loadvm command line argument for this. (You need a
> qcow2 disk image.)

Well, migration and savevm are the same. :)  In this case IIUC the
failure happens from a CDROM so migration lets you avoid the qcow2
image.  In general I find it easier to manage migration files on disk
than saved snapshots.

Paolo

>> It would be nice to have a mechanism to stop the VM after executing N
>> basic blocks.  Binary search on this value then can help with coming up
>> with a more easily debuggable snapshot, possibly to a point where the
>> difference between pre-patch and post-patch becomes deterministic.
> 
> You can use the monitor and an expect script to say "take a
> snapshot 0.7 seconds into boot", which I've found to be
> a good enough approximation:
> 
> https://translatedcode.wordpress.com/2015/07/06/tricks-for-debugging-qemu-savevm-snapshots/
> 
> thanks
> -- PMM
>