Xendbg: A Full-Featured Debugger for the Xen Hypervisor

However, in the course of my research, I quickly realized that there is little public tooling available that supports proper VM introspection of Xen guests — not even a reliable debugger! Searching outside the Xen codebase is similarly fruitless: most VMI API functions do not appear in any code available on the public Internet, and the miniscule number of extant Xen VMI tools thatdouse some of them typically just copy those usage patterns verbatim from Xen’s own example code, with no additional explanation. All these are available for both PV and HVM guests, except watchpoints, which are only supported on HVM due to limitations of the Xen VMI API.

Source: www.nccgroup.trust