Getting userspace stack traces with userspace probes ?

["Daniel P. Berrange" <berrange at redhat dot com>]

I'm doing some troubleshooting of the libvirt daemon
using userspace probes. My stap script looks like

  probe process("/usr/lib64/libvirt.so").function("virDomainObjUnref") {
      printf("Unref %p %d\n", $dom, $dom->refs);
  }

  probe process("/usr/lib64/libvirt.so").function("virDomainObjRef") {
      printf("Ref %p %d\n", $dom, $dom->refs);
  }

  probe process("/usr/lib64/libvirt.so").function("virDomainObjNew").return {
      printf("New %p %d\n", $return, $return->refs);
  }

This is printing what I expect. I now want to get associated
userspace stack traces, so I tried adding

      print_ustack(ubacktrace())

And / or

      print_ubacktrace()

To all the probe points, all it ever prints for a stack trace is

 0x3992a52e10 : virDomainObjUnref+0x0/0x100 [libvirt.so.0.8.4]
 0x45900f [libvirtd+0x5900f/0xe8000]

Which is far too small compared to what GDB says the stack
trace is, eg I'm expecting at least 6-8 levels deep

  (gdb) bt
  #0  virDomainObjUnref (dom=0x1b49390) at conf/domain_conf.c:828
  #1  0x0000000000470f33 in qemuMonitorFree (mon=0x1cb6640) at qemu/qemu_monitor.c:202
  #2  qemuMonitorUnref (mon=0x1cb6640) at qemu/qemu_monitor.c:221
  #3  0x0000000000416ebf in virEventCleanupHandles () at event.c:548
  #4  0x0000000000417c8e in virEventRunOnce () at event.c:612
  #5  0x0000000000418593 in qemudOneLoop () at libvirtd.c:2226
  #6  0x00000000004188b9 in qemudRunLoop (opaque=0x1b42850) at libvirtd.c:2335
  #7  0x0000003980e07761 in start_thread (arg=0x7f6e63423700) at pthread_create.c:301
  #8  0x00000039806e098d in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:115

Am I using the wrong functions for getting stack traces,
or is it just not possible to get reliable stacks from
userspace probes ?

FYI, I'm using systemtap-1.3-3.fc13.x86_64 and
kernel 2.6.34.7-66.fc13.x86_64

Regards,
Daniel