[GSoC Weekly Status #4] bhyve debug server enhancements

Hello,

My activities during this last week were mostly related to testing and
fixing the hardware
watchpoint feature for bhyve's debug server that was implemented during the
previous week.

The main goal was to make sure that the hardware watchpoints set by the gdb
stub do not interfere
with the guest's execution. The gdb stub dynamically tracks which debug
register are in use by
the guest and relocates its watchpoints accordingly. To test this behavior,
I've been debugging a
process inside the guest using watchpoints while at least one of the gdb
stub's watchpoints was
active.

There were a lot of subtle details and vendor-specific differences in some
parts of the virtualization
extensions that got in the way, but I've managed to get this feature fully
working on AMD hosts
and almost fully working on Intel hosts. During the next week I plan to
resolve a minor issue on
Intel hosts, polish the code and prepare it for a differential, and
thoroughly document both this
and the single-stepping feature.

Bojan