Re: [ANNOUNCE] Merkey's Kernel Debugger

[Vivek Goyal <vgoyal@redhat.com>]

On Thu, Aug 07, 2008 at 01:34:22PM -0600, jmerkey@wolfmountaingroup.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