Re: [Xen-devel] Re: follow-up to guest debug support patches

To:	jfv@xxxxxxxxxxxx
Subject:	Re: [Xen-devel] Re: follow-up to guest debug support patches
From:	Kip Macy <kip.macy@xxxxxxxxx>
Date:	Sat, 12 Mar 2005 11:05:30 -0800
Cc:	Ian Pratt <m+Ian.Pratt@xxxxxxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxxxx, Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>, Ian.Pratt@xxxxxxxxxxxx, Christian Limpach <Christian.Limpach@xxxxxxxxxxxx>, jfv@xxxxxxxxxx
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Reply-to:	Kip Macy <kip.macy@xxxxxxxxx>
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> I
> > > think
> > > this needs some kind of flag to enable/disable this behaviour.
> >
> > I thought about that, but is there an In-guest kernel debugger that
> > can set breakpoints? All I know of are stubs that require a serial
> > port. Does NetBSD's in-kernel debugger allow one to set breakpoints
> > and continue? If so I can just put the debugger option back in
> > Rules.mk.

I spoke / wrote too soon. DDB probably does this as well. Although
I've never used it. I'd be surprised if most people didn't find the
user-level gdbserver more useful and generic than in-kernel debuggers.

Rather than being a compile-time option it should be a boot-time option.

> I believe there is a kdb patch for i386 Linux, and I have intended
> to extend my x86_64 kdb patch to Xen soon.

Cool.

> 
> I had even had thoughts of an extended debugger in dom0, but have
> been too busy to think that through. Any thoughts from others on
> that?

Interesting. In the meantime, unless someone beats me to it (wishful
thinking), I'll be extending cdb into a normal stop and continue GDB
stub.

> I recall a particularly nasty AIX bug that I worked on once
> on an S390 machine, the debugger in the nucleus (on VM/ESA) allowed
> me to set a watchpoint outside the guest and made a memory corruption
> problem MUCH easier to track down :)

That sounds more like what I've implemented than an in-kernel solution.

               -Kip


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