Fix crash from turning on DevTools in the middle of catch prediction

Fix crash from turning on DevTools in the middle of catch prediction

If DevTools is turned on in the middle of doing some things with async
functions, then more items may be popped from the Promise stack than were
pushed to it. In this sort of case, it's OK to have a catch misprediction,
but a crash is unacceptable. This patch defensively handles this edge
case where the Promise stack is unexpectedly empty for that reason.

BUG=v8:5167
Committed: https://crrev.com/cd049c2c761739590e42dd3e4213a88959163b8d
Cr-Commit-Position: refs/heads/master@{#39705}

[Dan Ehrenberg, 2016-09-24 00:55:33]

The CQ bit was checked by littledan@chromium.org to run a CQ dry run

[commit-bot: I haz the power, 2016-09-24 00:55:41]

Dry run: CQ is trying da patch. Follow status at
 
https://chromium-cq-status.appspot.com/v2/patch-status/codereview.chromium.or...

[Dan Ehrenberg, 2016-09-24 00:55:43]

littledan@chromium.org changed reviewers:
+ gsathya@chromium.org, jgruber@chromium.org

[gsathya, 2016-09-24 01:14:09]

https://codereview.chromium.org/2361333003/diff/20001/src/isolate.cc
File src/isolate.cc (right):

https://codereview.chromium.org/2361333003/diff/20001/src/isolate.cc#newcode1763
src/isolate.cc:1763: if (promise_on_stack) retval = promise_on_stack->promise();
Can you not return early if you hit an undefined?

https://codereview.chromium.org/2361333003/diff/20001/src/isolate.cc#newcode1768
src/isolate.cc:1768: continue;
Do you need this continue?

[commit-bot: I haz the power, 2016-09-24 01:31:21]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2016-09-24 01:31:22]

Dry run: This issue passed the CQ dry run.

[Dan Ehrenberg, 2016-09-24 02:37:49]

The CQ bit was checked by littledan@chromium.org to run a CQ dry run

[commit-bot: I haz the power, 2016-09-24 02:37:57]

Dry run: CQ is trying da patch. Follow status at
 
https://chromium-cq-status.appspot.com/v2/patch-status/codereview.chromium.or...

[commit-bot: I haz the power, 2016-09-24 03:07:38]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2016-09-24 03:07:39]

Dry run: This issue passed the CQ dry run.

[Dan Ehrenberg, 2016-09-24 03:08:20]

https://codereview.chromium.org/2361333003/diff/20001/src/isolate.cc
File src/isolate.cc (right):

https://codereview.chromium.org/2361333003/diff/20001/src/isolate.cc#newcode1763
src/isolate.cc:1763: if (promise_on_stack) retval = promise_on_stack->promise();
On 2016/09/24 at 01:14:09, gsathya wrote:
> Can you not return early if you hit an undefined?

You're right, that's a cleaner way to do it. Fixed.

https://codereview.chromium.org/2361333003/diff/20001/src/isolate.cc#newcode1768
src/isolate.cc:1768: continue;
On 2016/09/24 at 01:14:09, gsathya wrote:
> Do you need this continue?

In this switch statement, each case ends with either return or continue. I think
the pattern makes the code easier to read because it means that the reader
doesn't have to look to the end of the loop to figure out what's going to
happen.

[gsathya, 2016-09-24 03:28:00]

lgtm

[Dan Ehrenberg, 2016-09-24 03:28:29]

The CQ bit was checked by littledan@chromium.org

[commit-bot: I haz the power, 2016-09-24 03:28:39]

CQ is trying da patch. Follow status at
 
https://chromium-cq-status.appspot.com/v2/patch-status/codereview.chromium.or...

[commit-bot: I haz the power, 2016-09-24 03:30:59]

Committed patchset #3 (id:40001)

[commit-bot: I haz the power, 2016-09-24 03:31:24]

Description was changed from

==========
Fix crash from turning on DevTools in the middle of catch prediction

If DevTools is turned on in the middle of doing some things with async
functions, then more items may be popped from the Promise stack than were
pushed to it. In this sort of case, it's OK to have a catch misprediction,
but a crash is unacceptable. This patch defensively handles this edge
case where the Promise stack is unexpectedly empty for that reason.

BUG=v8:5167
==========

to

==========
Fix crash from turning on DevTools in the middle of catch prediction

If DevTools is turned on in the middle of doing some things with async
functions, then more items may be popped from the Promise stack than were
pushed to it. In this sort of case, it's OK to have a catch misprediction,
but a crash is unacceptable. This patch defensively handles this edge
case where the Promise stack is unexpectedly empty for that reason.

BUG=v8:5167

Committed: https://crrev.com/cd049c2c761739590e42dd3e4213a88959163b8d
Cr-Commit-Position: refs/heads/master@{#39705}
==========

[commit-bot: I haz the power, 2016-09-24 03:31:25]

Patchset 3 (id:??) landed as
https://crrev.com/cd049c2c761739590e42dd3e4213a88959163b8d
Cr-Commit-Position: refs/heads/master@{#39705}