Xen's ability to run unmodified guests with the virtualization available in hardware opens new doors of possibilities in the kernel debugging. Now it's possible to debug the Linux kernel or any other PC operating system similar to debugging a user process in Linux. Since hardware virtualization in-processor enables Xen to implement full virtualization of a guest OS, there is no need to change the kernel in any way to debug it.
This paper demonstrates the new evolutionary debug techniques using examples. It also explains how the new technique actually works.