libvirt users - Jan 2018 - debug kernel

libvirt 3.4.0
centos 7.4



Hi:

    I want usr libvrit create vm to debug linux kernel. Previous , I usr qemu
cmd(-gdb tcp::1234) directly. When I search on Internet, I found I can usr
libvrt xml configure kgdb.
<qemu:commandline>
        <qemu:arg value='-gdb'/>
        <qemu:arg value='tcp::1234'/>
  </qemu:commandline>
But configure xml usr kgdb is differnet on kernel boot. usr qemu cmd, before I
connect kernel usr gdb , the kernel still not boot, When I usr gdb connect the
vm and put continue cmd on gdb, the kernel will start boot. But I usr libvirt
xml configure kgdb, the kernel not stop, I want known that have some way I can
use libvirt xml configure kgdb let kernel stop boot before I put continue on
gdb?

Thanks