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

[Nicholas Piggin]

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.dovgal...@ispras.ru>
Signed-off-by: Nicholas Piggin <npig...@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);
+
+    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;
-- 
2.42.0