Last Comment Bug 653026 - GC hazard with NoSuchMethod
: GC hazard with NoSuchMethod
: regression
Product: Core
Classification: Components
Component: JavaScript Engine (show other bugs)
: unspecified
: All All
: -- normal (vote)
: ---
Assigned To: [PTO to Dec5] Bill McCloskey (:billm)
: Jason Orendorff [:jorendorff]
Depends on:
Blocks: 584917
  Show dependency treegraph
Reported: 2011-04-26 18:10 PDT by [PTO to Dec5] Bill McCloskey (:billm)
Modified: 2011-08-12 09:09 PDT (History)
7 users (show)
See Also:
Crash Signature:
QA Whiteboard:
Iteration: ---
Points: ---
Has Regression Range: ---
Has STR: ---

testcase (148 bytes, text/plain)
2011-04-26 18:10 PDT, [PTO to Dec5] Bill McCloskey (:billm)
no flags Details
patch (3.23 KB, patch)
2011-04-27 10:31 PDT, [PTO to Dec5] Bill McCloskey (:billm)
jwalden+bmo: review+
dmandelin: approval‑mozilla‑beta+
Details | Diff | Splinter Review

Description [PTO to Dec5] Bill McCloskey (:billm) 2011-04-26 18:10:04 PDT
Created attachment 528500 [details]

This script crashes in a shell with no jit options.
Comment 1 [PTO to Dec5] Bill McCloskey (:billm) 2011-04-27 10:31:34 PDT
Created attachment 528630 [details] [diff] [review]

The basic problem is that the new object being allocated in js_OnUnknownMethod is the only thing that roots the method. This object is not scanned during a GC because it has a NULL shape, so it's treated as a newborn object. This was apparently sort of intentional, to ensure that these objects don't escape into user code. However, I think it's more important that we scan them.

I set the shape so that the object looks non-native, and then I added a trace hook to the class. I thought about making it a native object, but I think then we'd need a proto for it, and I didn't want to deal with that. Please correct me if I'm wrong, Jeff.
Comment 2 Jeff Walden [:Waldo] (remove +bmo to email) 2011-04-27 15:34:49 PDT
Comment on attachment 528630 [details] [diff] [review]

Sounds reasonable.
Comment 3 Johnny Stenback (:jst, 2011-05-19 14:03:24 PDT
Can this land now that it's reviewed n' all? Would this patch be safe for beta?
Comment 4 [PTO to Dec5] Bill McCloskey (:billm) 2011-05-19 14:05:38 PDT
Sorry for the delay. I meant to land it yesterday but I forgot. I'll make sure it gets into the beta.
Comment 5 [PTO to Dec5] Bill McCloskey (:billm) 2011-05-20 12:23:48 PDT

I pushed without the test. That needs to go in later.
Comment 6 Chris Leary [:cdleary] (not checking bugmail) 2011-05-23 14:17:02 PDT
cdleary-bot mozilla-central merge info:
Comment 7 David Mandelin [:dmandelin] 2011-05-24 18:04:41 PDT
Comment 8 David Mandelin [:dmandelin] 2011-05-25 10:41:57 PDT
This made it to mozilla-aurora as
Comment 9 Daniel Veditz [:dveditz] 2011-06-08 10:51:59 PDT
On the 1.9.2 branch I get "TypeError: obj.x(a()) is not a function" rather than a crash. Does that mean that branch is not affected by this bug? Do we know what regressed it?
Comment 10 [PTO to Dec5] Bill McCloskey (:billm) 2011-06-09 17:04:44 PDT
It looks like the testcase in the bug regressed in bug 584917, so 3.6 should be safe. Before that patch, we rooted the function to call via the NoSuchMethod object's parent (or proto, I forget the argument order).

I'm still a bit worried about whether the other thing stored in the NoSuchMethod object in rooted. It can only be a jsid, but it seems like e4x might somehow allow an object to be stashed there. I don't really understand the code too well though. It would be good if someone who understands e4x better could take a look. I'm guessing this means Brendan or Igor?
Comment 11 Daniel Veditz [:dveditz] 2011-06-09 18:12:53 PDT
Thanks, for now we'll not track this on the old branch.
Comment 12 Virgil Dicu [:virgil] [QA] 2011-08-12 09:09:38 PDT
Mozilla/5.0 (X11; Linux x86_64; rv:6.0) Gecko/20100101 Firefox/6.0

Could you please provide some clear STR in order to verify this issue?

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