Xen provides a number of build-time options which should be set as environment variables or passed on make's command-line.
verbose=y
Enable debugging messages when Xen detects an unexpected condition. Also enables console output from all domains.
debug=y
Enable debug assertions. Implies verbose=y. (Primarily useful for tracing bugs in Xen).
debugger=y
Enable the in-Xen debugger. This can be used to debug Xen, guest OSes, and applications.
perfc=y
Enable performance counters for significant events within Xen. The counts can be reset or displayed on Xen's console via console control keys.