[Lguest] Kprobes module makes lguest crash when inserted

[Rusty Russell]

On Mon, 2007-09-10 at 15:53 +0900, Alexandre Courbot wrote:
> Hello everyone,
> 
> I'm just playing around with lguest that I just discovered. I hope to
> use it for testing/debugging a kernel module of mine instead of
> crashing my workstation every time I break something. I considered UML
> at first, but my module uses kprobes, which has no support for UML.
> 
> Well, maybe there is something wrong about using kprobes within lguest
> too (although nothing would suggest that to me - but I'm not a kernel
> expert), but every time I insert my module (just plain insmod
> mymodule.ko) from the guest, it crashes very badly with a huge pile of
> messages. Here is the end (cannot log everything, the list of error
> messages is too long for my console buffer):

Hi Alexandre!

	Yes, I'm not surprised it fails.  We don't support debug register
manipulation in the guest.  Not for any particularly good reason, mind
you, I just never got around to it and you're the first person to want
it.

It's not that hard to do, but it requires some understanding of debug
registers.  Anyone with an Intel manual can implement it (a new
hypercall plus some sanity checking plus restoring debug registers
before entering the guest).

Sorry,
Rusty.