Xen ARM DEBUG hypercalls
If you are trying to DEBUG early boot code in your guest kernel, either Dom0 or DomU, you might find the Xen on ARM DEBUG hypercalls useful. They are only available to DEBUG builds, i.e. builds with Debugging Options ---> Developer Checks enabled.
Simply add one of the following hvc instructions to your code, and Xen will print something on the console for you:
prints the program counter
prints first byte of register x0
prints all registers and stack of the guest
prints program counter and a register: e0 prints x0, e1 prints x1, etc.