[libvirt-users] 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 use libvrt xml configure kgdb. <qemu:commandline> <qemu:arg value='-gdb'/> <qemu:arg value='tcp::1234'/> </qemu:commandline> But configure xml use kgdb is differnet on kernel boot. use qemu cmd, before I connect kernel use gdb , the kernel still not boot, When I use 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