Hi Alex,
Thanks for getting back to me. It is definitely the latter case (i.e. it is
possible to change it while the target is stopped at a breakpoint before
resuming any VCPUs).
vm_state_notify() does look like it's intended for this type of notifications,
but unfortunately, it doesn't make a distinction between stepping and running
normally.
Below is the relevant code from gdbstub.c:
>static int gdb_continue_partial(char *newstates)
>{
> int flag = 0;
>
> /* Various corner cases omitted for brevity */
> if (vm_prepare_start()) {
> return 0;
> }
> CPU_FOREACH(cpu) {
> switch (newstates[cpu->cpu_index]) {
> case 's':
> trace_gdbstub_op_stepping(cpu->cpu_index);
> cpu_single_step(cpu, gdbserver_state.sstep_flags);
> cpu_resume(cpu);
> flag = 1;
> break;
> case 'c':
> trace_gdbstub_op_continue_cpu(cpu->cpu_index);
> cpu_resume(cpu);
> flag = 1;
> break;
> default:
> res = -1;
> break;
> }
> }
>}
Also:
>int vm_prepare_start(void)
>{
> runstate_set(RUN_STATE_RUNNING);
> vm_state_notify(1, RUN_STATE_RUNNING);
> return 0;
>}
and:
>void vm_state_notify(bool running, RunState state);
So, currently, vm_prepare_start() has no way of distinguishing between
single-stepping and normal running unless gdb_continue_partial() scans the
'newstates' array before calling it, and passes some extra argument to
vm_prepare_start(), indicating whether a step request was present anywhere in
the array.
I couldn't find any existing run state that would match single-stepping, and
adding another run state looks like a very non-trivial change that can easily
backfire. Adding another argument to vm_state_notify() could be easier, but I
am still afraid it could break some other part of QEMU, so I thought adding a
new member to AccelOpsClass would be a safer bet. But again, if you think
another way to do it is better, I am very open to it.
Best regards,
Ivan
-----Original Message-----
From: Alex Bennée <alex.ben...@linaro.org>
Sent: Monday, February 28, 2022 2:28 AM
To: Ivan Shcherbakov <i...@sysprogs.com>
Cc: 'Peter Maydell' <peter.mayd...@linaro.org>; 'Paolo Bonzini'
<pbonz...@redhat.com>; qemu-devel@nongnu.org; arm...@redhat.com; m...@redhat.com
Subject: Re: [PATCH 3/3] whpx: Added support for breakpoints and stepping
Is the limitation that whpx_set_exception_exit_bitmap needs to be set before
any vCPU can be run or that it cannot be set if any vCPUs are currently running?
If it is the later wouldn't adding a hook into the vm_change_state_head
callbacks be enough?
