Description of problem:
 
Run dump-guest-memory failed when I am tryting to dump the core from qemu.

Version-Release number of selected component (if applicable):
HOST:
kernel-3.10.0-561.el7.x86_64
kernel-debuginfo-3.10.0-514.el7.x86_64
kernel-debuginfo-common-x86_64-3.10.0-514.el7.x86_64

qemu-kvm-rhev-2.8.0-5.el7.x86_64
qemu-kvm-rhev-debuginfo-2.8.0-5.el7.x86_64

GUEST:
kernel-3.10.0-514.el7.x86_64


How reproducible: 6/6


Steps to Reproduce:
1. Set 'ulimit -c unlimited' and 'echo "/var/core.%p-%u-%g-%s-%t-%h-%e" >
/proc/sys/kernel/core_pattern' in the host terminal

2.1.Boot up a guest with dump-guest-core=on.
e.g:
/usr/libexec/qemu-kvm \
    -name 'avocado-vt-vm1'  \
    -sandbox off  \
    -machine pc,dump-guest-core=on \
    -nodefaults  \
    -vga cirrus  \
    -device nec-usb-xhci,id=usbtest,bus=pci.0,addr=03 \
    -drive id=drive_image1,if=none,snapshot=off,aio=native,cache=none,format=qcow2,file=/home/kvm_autotest_root/images/rhel73-64-virtio.qcow2 \
    -device virtio-blk-pci,id=image1,drive=drive_image1,bootindex=0,bus=pci.0,addr=04 \
    -device virtio-net-pci,mac=9a:4d:4e:4f:50:51,id=id3DveCw,vectors=4,netdev=idgW5YRp,bus=pci.0,addr=05  \
    -netdev tap,id=idgW5YRp \
    -m 5457  \
    -smp 4,maxcpus=4,cores=2,threads=1,sockets=2  \
    -cpu 'SandyBridge',+kvm_pv_unhalt \
    -device usb-tablet,id=usb-tablet1,bus=usbtest.0,port=1  \
    -vnc :0  \
    -rtc base=utc,clock=host,driftfix=slew  \
    -boot order=cdn,once=c,menu=off,strict=off \
    -enable-kvm \
    -monitor stdio \

3.Kill the qemu-kvm process with SIGSEGV, as root:
# pkill -SEGV -x qemu-kvm
(qemu) Segmentation fault (core dumped)

4.Open the "coredump" file with gdb, and load the extension.
gdb /var/core.21378-0-0-11-1488273759-intel-e31225-16-3.englab.nay.redhat.com-qemu-kvm
(gdb) source /usr/share/qemu-kvm/dump-guest-memory.py

5.extract the guest vmcore with the new extension
(gdb) set height 0
(gdb) dump-guest-memory /tmp/vmcore X86_64


Actual results:

guest RAM blocks:
target_start     target_end       host_addr        message count
---------------- ---------------- ---------------- ------- -----
Python Exception <class 'gdb.error'> Attempt to extract a component of a value that is not a (null).: 
Error occurred in Python command: Attempt to extract a component of a value that is not a (null).

Expected results:

guest RAM blocks:
target_start     target_end       host_addr        message count
---------------- ---------------- ---------------- ------- -----
0000000000000000 00000000000a0000 00007f4d3b600000 added       1
00000000000a0000 00000000000b0000 00007f4d3a000000 added       2
00000000000c0000 00000000000ca000 00007f4d3b6c0000 added       3
00000000000ca000 00000000000cd000 00007f4d3b6ca000 joined      3
00000000000cd000 00000000000ec000 00007f4d3b6cd000 joined      3
00000000000ec000 00000000000f0000 00007f4d3b6ec000 joined      3
00000000000f0000 0000000000100000 00007f4d3b6f0000 joined      3
0000000000100000 00000000c0000000 00007f4d3b700000 joined      3
00000000fc000000 00000000fd000000 00007f4d3a000000 added       4
00000000fffc0000 0000000100000000 00007f4d3b400000 added       5
0000000100000000 0000000195100000 00007f4dfb600000 added       6
dumping range at 00007f4d3b600000 for length 00000000000a0000
dumping range at 00007f4d3a000000 for length 0000000000010000
dumping range at 00007f4d3b6c0000 for length 00000000bff40000
dumping range at 00007f4d3a000000 for length 0000000001000000
dumping range at 00007f4d3b400000 for length 0000000000040000
dumping range at 00007f4dfb600000 for length 0000000095100000


Additional info:
Test on HOST:
kernel-3.10.0-561.el7.x86_64
kernel-debuginfo-3.10.0-514.el7.x86_64
kernel-debuginfo-common-x86_64-3.10.0-514.el7.x86_64

qemu-kvm-rhev-debuginfo-2.6.0-27.el7.x86_64
qemu-kvm-rhev-2.6.0-27.el7.x86_64

GUEST:
kernel-3.10.0-514.el7.x86_64

It does not have this issue.