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Re: [Xen-devel] pdb missing files?

  • To: "Jonathan M. McCune" <jonmccune@xxxxxxx>
  • From: Kip Macy <kip.macy@xxxxxxxxx>
  • Date: Fri, 30 Sep 2005 13:49:03 -0700
  • Cc: NAHieu <nahieu@xxxxxxxxx>, Arvind Seshadri <arvinds@xxxxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxx, Bryan Parno <parno@xxxxxxx>
  • Delivery-date: Fri, 30 Sep 2005 20:46:41 +0000
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  • List-id: Xen developer discussion <xen-devel.lists.xensource.com>

The next obstacle is that gdbserver-xen is segfaulting upon connection
from gdb in dom0.  Again, this works great with an unmodified domU.  You
asked me to give the output from the two different runs of gdbserver-xen.

I actually meant when you gave it an invalid domain id, but that isn't a key issue ...


#0  0x40021fb4 in map_domain_va () from /usr/lib/libxenctrl.so.3.0
(gdb) bt
#0  0x40021fb4 in map_domain_va () from /usr/lib/libxenctrl.so.3.0
#1  0x4002268a in xc_ptrace () from /usr/lib/libxenctrl.so.3.0
#2  0x0804cb27 in linux_read_memory (memaddr=0, myaddr=0xbff5ab50 "", len=8)
    at ../../../gdb-6.2.1/gdb/gdbserver/linux-xen-low.c:394
#3  0x0804bd41 in read_inferior_memory (memaddr=The value of variable
'memaddr' is distributed across several
locations, and GDB cannot access its value.

That is a rather strange place for it to be blowing up. In the past there were cases where it would blow up in xc_ptrace when it tried to dereference an address that had not been successfully mapped to. In principle using alloca could bite you if len were so long that you ran off your stack, but you have a small stack and you're only reading 8 bytes. I'll see if I can determine any more by spelunking at the assembly level.

Just to confirm that I'm looking at the same code, is your line 394:

       buffer[i] = myptrace (xc_handle, PTRACE_PEEKTEXT, inferior_pid, (PTRACE_ARG3_TYPE) addr, 0);

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