There are times when the registers are in "the registers", on the kernel stack, or
in memory. If you are in a remote heart you cannot access the other heart's
registers. If you are a kernel thread, it is still extraordinarily hard to properly
access a threads registers while they are on the kernel stack with any degree
of reliability. So, in general it is best to wait until any kernel activities have been
cleaned up and the thread registers are in a known place in memory--AND--that
the thread is locked against being Activated into execution. This is the state a
debugger accesses a threads registers and memory.