Xen devel - Jun 2010 - debugging pv domU kernel lockups, kdb & hvc0 or gdbsx ?

With hvm domains we''ve always used kdb over serial, the standard
http://oss.sgi.com/projects/kdb version was all we needed. Just like
the good old bare metal days.

Does this not work with pv domains?

The pv-ops 2.6.32.x branch kernel with the most recent 2.6.32 kdb
patches appears not to work. Or, at least kdb doesn''t recognize the
domU''s hvc0 console.

The <ESC>KDB hotkey combination doesn''t work, and when I drop
into kdb:

Entering kdb (current=0xffff88009722ad80, pid 6958) on processor 0 Oops:
<NULL>
due to oops @ 0xffffffff812d6c70
     r15 = 0x00000000000000f8      r14 = 0x0000000000000000
     r13 = 0x00000000000000f0      r12 = 0x0000000000000087
      bp = 0xffff8800a41f9e28       bx = 0xffff8800a41f9e5c
     r11 = 0x0000000000000000      r10 = 0xffffea000210e200
      r9 = 0xffff8800a42f4000       r8 = 0x00000000000207b0
      ax = 0x0000000000000200       cx = 0x0000000000000001
      dx = 0x0000000000000007       si = 0x00000000000000f8
      di = 0x0000000000000000  orig_ax = 0xffffffffffffffff
      ip = 0xffffffff812d6c70       cs = 0x000000010000e030
   flags = 0x0000000000010012       sp = 0xffff8800a41f9de8
      ss = 0x000000000000e02b &regs = 0xffff8800a41f9d38

...there is no kdb prompt and the console is unresponsive.

Is this a problem with kdb expecting a serial console and the  the
hvc0 console on the pv domU?

The hvm domU shows:
# tty
/dev/ttyS0

whereas the pv domU shows:
# tty
/dev/hvc0

Do I just need to get kdb to use hvc0? If so, how?

Or, do we need to switch to gdbsx for pv domU debugging?
ala http://xenbits.xensource.com/ext/debuggers.hg ?
Or, is this the definitive domU debugging text
http://www.kernel.org/doc/ols/2006/ols2006v2-pages-9-24.pdf ?

Thanks.

-Bruce

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