linux-kernel - Re: [ANNOUNCE] Merkey's Kernel Debugger

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Date:	Thu, 7 Aug 2008 21:26:23 -0400
From:	Vivek Goyal <vgoyal@...hat.com>
To:	jmerkey@...fmountaingroup.com
Cc:	Jay Lan <jlan@....com>,
	Christoph Lameter <cl@...ux-foundation.org>,
	Stefan Richter <stefanr@...6.in-berlin.de>,
	Nick Piggin <nickpiggin@...oo.com.au>,
	Andi Kleen <andi@...stfloor.org>,
	Geert Uytterhoeven <geert@...ux-m68k.org>,
	Josh Boyer <jwboyer@...il.com>, linux-kernel@...r.kernel.org,
	Takenori Nagano <t-nagano@...jp.nec.com>,
	Bernhard Walle <bwalle@...e.de>, Keith Owens <kaos@....com.au>
Subject: Re: [ANNOUNCE] Merkey's Kernel Debugger

On Thu, Aug 07, 2008 at 01:34:22PM -0600, jmerkey@...fmountaingroup.com wrote:
> > Christoph Lameter wrote:
> >> Stefan Richter wrote:
> >>> Christoph Lameter wrote:
> >>>> The competing implementation is kdb not kgdb. kgdb is just a stub for
> >>>> remote
> >>>> debugging using gdb. kdb is an in-kernel debugger like the one
> >>>> proposed here.
> >>> Is there work underway to get kdb merged?  (I'm just asking because I
> >>> don't know; I personally don't need kdb nor mdb.)
> >>
> >> KDB still exists in patches but the merge effort was given up when Linus
> >> stated that he did not want a kernel debugger. No problem to start merge
> >> attempts again AFAICT. Jay?
> >
> > To merge KDB or any other RAS tools, you need to deal with kdump. Kdump
> > hijack panic() before the die calling chain. For KDB or a RAS tool to
> > work, an infrastructure such as the "add new notifier function" by
> > Takenori Nagano should be in place.
> >
> > His last attempt fell short, in my opinion, was partly due to his
> > "[PATCH 3/3] Move crash_kexec() into  panic_notifier" did not do what it
> > meant to do: to fit kexec/kdump into the new infrastructure. That is
> > not fatal; it can be fixed to make it right. If community is interested
> > in getting a kernel debugger to the kernel, we can continue Takenori's
> > work. Once the infrastructure is accepted, then merging KDB or any other
> > kernel debugger will make sense.
> >
> > Regards,
> >  - jay
> >
> >
> >>
> 
> As I look through entry_32.S and traps_32.c I do not see where kdump is
> hooking the notify_die handler which would intercept calls to a debugger.
> 
> Where does kdump hook this path?
> 

kdump uses crash_kexec() call for hooking. It hooks in panic(), die_nmi()
and die().

Thanks
Vivek
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