Re: [PATCH v3 4/9] replay: allow runstate shutdown->running when replaying trace

["Alex Bennée" <alex.bennee@linaro.org>]

Nicholas Piggin <npiggin@gmail.com> writes:

> When replaying a trace, it is possible to go from shutdown to running
> with a reverse-debugging step. This can be useful if the problem being
> debugged triggers a reset or shutdown.
>
> This can be tested by making a recording of a machine that shuts down,
> then using -action shutdown=pause when replaying it. Continuing to the
> end of the trace then reverse-stepping in gdb crashes due to invalid
> runstate transition.
>
> Just permitting the transition seems to be all that's necessary for
> reverse-debugging to work well in such a state.
>
> Reviewed-by: Pavel Dovgalyuk <Pavel.Dovgalyuk@ispras.ru>
> Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
> ---
>  include/sysemu/runstate.h |  1 +
>  replay/replay.c           |  2 ++
>  system/runstate.c         | 19 +++++++++++++++++++
>  3 files changed, 22 insertions(+)
>
> diff --git a/include/sysemu/runstate.h b/include/sysemu/runstate.h
> index 0117d243c4..fe25eed3c0 100644
> --- a/include/sysemu/runstate.h
> +++ b/include/sysemu/runstate.h
> @@ -9,6 +9,7 @@ void runstate_set(RunState new_state);
>  RunState runstate_get(void);
>  bool runstate_is_running(void);
>  bool runstate_needs_reset(void);
> +void runstate_replay_enable(void);
>  
>  typedef void VMChangeStateHandler(void *opaque, bool running, RunState state);
>  
> diff --git a/replay/replay.c b/replay/replay.c
> index 3fd241a4fc..2951eed3bd 100644
> --- a/replay/replay.c
> +++ b/replay/replay.c
> @@ -383,6 +383,8 @@ static void replay_enable(const char *fname, int mode)
>          /* go to the beginning */
>          fseek(replay_file, HEADER_SIZE, SEEK_SET);
>          replay_fetch_data_kind();
> +
> +        runstate_replay_enable();
>      }
>  
>      replay_init_events();
> diff --git a/system/runstate.c b/system/runstate.c
> index d6ab860eca..bd0fed8657 100644
> --- a/system/runstate.c
> +++ b/system/runstate.c
> @@ -182,6 +182,12 @@ static const RunStateTransition runstate_transitions_def[] = {
>      { RUN_STATE__MAX, RUN_STATE__MAX },
>  };
>  
> +static const RunStateTransition replay_runstate_transitions_def[] = {
> +    { RUN_STATE_SHUTDOWN, RUN_STATE_RUNNING},
> +
> +    { RUN_STATE__MAX, RUN_STATE__MAX },
> +};
> +
>  static bool runstate_valid_transitions[RUN_STATE__MAX][RUN_STATE__MAX];
>  
>  bool runstate_check(RunState state)
> @@ -189,6 +195,19 @@ bool runstate_check(RunState state)
>      return current_run_state == state;
>  }
>  
> +void runstate_replay_enable(void)
> +{
> +    const RunStateTransition *p;
> +
> +    assert(replay_mode == REPLAY_MODE_PLAY);
> +

As the bellow is common to runstate_init it could be
re-factored into a helper taking the runstate_transitions_def pointer.

> +    for (p = &replay_runstate_transitions_def[0]; p->from != RUN_STATE__MAX;
> +         p++) {
> +        runstate_valid_transitions[p->from][p->to] = true;
> +    }
> +
> +}
> +
>  static void runstate_init(void)
>  {
>      const RunStateTransition *p;

-- 
Alex Bennée
Virtualisation Tech Lead @ Linaro