If we find ourselves trying to add an event to the log where time has
gone backwards it is because a vCPU event has occurred and the
main-loop is not yet aware of time moving forward. This should not
happen and if it does its better to fail early than generate a log
that will have weird behaviour.

Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
---
 replay/replay-internal.c | 4 ++++
 replay/replay.c          | 4 ++++
 2 files changed, 8 insertions(+)

diff --git a/replay/replay-internal.c b/replay/replay-internal.c
index bea7b4aa6b..fca8514012 100644
--- a/replay/replay-internal.c
+++ b/replay/replay-internal.c
@@ -195,6 +195,10 @@ void replay_save_instructions(void)
     if (replay_file && replay_mode == REPLAY_MODE_RECORD) {
         replay_mutex_lock();
         int diff = (int)(replay_get_current_step() - replay_state.current_step);
+
+        /* Time can only go forward */
+        assert(diff >= 0);
+
         if (diff > 0) {
             replay_put_event(EVENT_INSTRUCTION);
             replay_put_dword(diff);
diff --git a/replay/replay.c b/replay/replay.c
index 9e0724e756..f810628cac 100644
--- a/replay/replay.c
+++ b/replay/replay.c
@@ -84,6 +84,10 @@ void replay_account_executed_instructions(void)
         if (replay_state.instructions_count > 0) {
             int count = (int)(replay_get_current_step()
                               - replay_state.current_step);
+
+            /* Time can only go forward */
+            assert(count >= 0);
+
             replay_state.instructions_count -= count;
             replay_state.current_step += count;
             if (replay_state.instructions_count == 0) {
-- 
2.11.0

> From: Alex Bennée [mailto:alex.bennee@linaro.org]
> 
> If we find ourselves trying to add an event to the log where time has
> gone backwards it is because a vCPU event has occurred and the
> main-loop is not yet aware of time moving forward. This should not
> happen and if it does its better to fail early than generate a log
> that will have weird behaviour.
> 
> Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
> ---
>  replay/replay-internal.c | 4 ++++
>  replay/replay.c          | 4 ++++
>  2 files changed, 8 insertions(+)
> 
> diff --git a/replay/replay-internal.c b/replay/replay-internal.c
> index bea7b4aa6b..fca8514012 100644
> --- a/replay/replay-internal.c
> +++ b/replay/replay-internal.c
> @@ -195,6 +195,10 @@ void replay_save_instructions(void)
>      if (replay_file && replay_mode == REPLAY_MODE_RECORD) {
>          replay_mutex_lock();
>          int diff = (int)(replay_get_current_step() - replay_state.current_step);
> +
> +        /* Time can only go forward */
> +        assert(diff >= 0);
> +
>          if (diff > 0) {

This "if" is useless then.

>              replay_put_event(EVENT_INSTRUCTION);
>              replay_put_dword(diff);
> diff --git a/replay/replay.c b/replay/replay.c
> index 9e0724e756..f810628cac 100644
> --- a/replay/replay.c
> +++ b/replay/replay.c
> @@ -84,6 +84,10 @@ void replay_account_executed_instructions(void)
>          if (replay_state.instructions_count > 0) {
>              int count = (int)(replay_get_current_step()
>                                - replay_state.current_step);
> +
> +            /* Time can only go forward */
> +            assert(count >= 0);
> +
>              replay_state.instructions_count -= count;
>              replay_state.current_step += count;
>              if (replay_state.instructions_count == 0) {
> --
> 2.11.0


Pavel Dovgalyuk

On 05/04/2017 15:33, Pavel Dovgalyuk wrote:
>> +
>> +        /* Time can only go forward */
>> +        assert(diff >= 0);
>> +
>>          if (diff > 0) {
> This "if" is useless then.
> 

It isn't, "diff == 0" can happen.

Paolo

Paolo Bonzini <pbonzini@redhat.com> writes:

> On 05/04/2017 15:33, Pavel Dovgalyuk wrote:
>>> +
>>> +        /* Time can only go forward */
>>> +        assert(diff >= 0);
>>> +
>>>          if (diff > 0) {
>> This "if" is useless then.
>>
>
> It isn't, "diff == 0" can happen.

In my previous patchset I actually output-ed a EVENT_INSTRUCTION with a
zero diff for the negative case although it does seem redundant to
output that if we can avoid it?

--
Alex Bennée