colin wrote: > As to adding watchpoint to kernel, there will be another problem. > ASID in kernel is variable. Therefore, we cannot indicate which thread we > want to watch by ASID. > What we can do is setting G (global) bit to WatchHi Register and then all > threads accessing that address will cause the exception. > In the exception, it will filter the threads by PID to find out the thread > we are watching. > > They're variable, but not very variable: the PID->ASID mapping will only change when the ASIDs roll over and the ASID gets reallocated to a different process, which will only happen after another 256 processes have been created. But in that case your watched process will have to be allocated a new ASID before it can run again. So you could, perhaps, modify the TLB management code to clear the Watch registers whenever an ASID belong to a process with watchpoints is recycled, and then reprogram the Watch registers when such a process is allocated a new ASID. Alternatively you could maintain pre-process copies of the Watch registers, and context switch them along with other per-process register state -- though that is adding context switch overhead to processes which don't use watchpoints, and might not be popular with the maintainer. Nigel
