Last Comment Bug 704510 - js::MaybeGC(JSContext*) (jsgc.cpp:2167): Conditional jump or move depends on uninitialised value(s)
: js::MaybeGC(JSContext*) (jsgc.cpp:2167): Conditional jump or move depends on ...
: regression
Product: Core
Classification: Components
Component: JavaScript Engine (show other bugs)
: Trunk
: All All
: -- normal (vote)
: mozilla11
Assigned To: Terrence Cole [:terrence]
: Jason Orendorff [:jorendorff]
Depends on:
Blocks: 700357
  Show dependency treegraph
Reported: 2011-11-22 09:18 PST by Josh Aas
Modified: 2012-02-22 11:44 PST (History)
9 users (show)
See Also:
Crash Signature:
QA Whiteboard:
Iteration: ---
Points: ---
Has Regression Range: ---
Has STR: ---

v1: trivial (886 bytes, patch)
2011-11-22 10:57 PST, Terrence Cole [:terrence]
wmccloskey: review+
christian: approval‑mozilla‑aurora+
Details | Diff | Splinter Review

Description Josh Aas 2011-11-22 09:18:43 PST
Seen running Firefox trunk x86_64 build on Mac OS X 10.6 under valgrind:

==97971== Conditional jump or move depends on uninitialised value(s)
==97971==    at 0x108C9551F: js::MaybeGC(JSContext*) (jsgc.cpp:2167)
==97971==    by 0x108BFD3A3: JS_MaybeGC (jsapi.cpp:2767)
==97971==    by 0x107C21546: nsJSContext::ScriptEvaluated(bool) (nsJSEnvironment.cpp:3127)
==97971==    by 0x107C20667: nsJSContext::EvaluateStringWithValue(nsAString_internal const&, JSObject*, nsIPrincipal*, char const*, unsigned int, unsigned int, JS::Value*, bool*) (nsJSEnvironment.cpp:1336)
==97971==    by 0x107BC0639: nsXBLProtoImplField::InstallField(nsIScriptContext*, JSObject*, nsIPrincipal*, nsIURI*, bool*) const (nsXBLProtoImplField.cpp:151)
==97971==    by 0x107BA1139: XBLResolve(JSContext*, JSObject*, jsid, unsigned int, JSObject**) (nsXBLBinding.cpp:199)
==97971==    by 0x106FCEF02: CallResolveOp(JSContext*, JSObject*, JSObject*, jsid, unsigned int, JSObject**, JSProperty**, bool*) (jsobj.cpp:5402)
==97971==    by 0x106FCF3B4: js::LookupPropertyWithFlags(JSContext*, JSObject*, jsid, unsigned int, JSObject**, JSProperty**) (jsobj.cpp:5455)
==97971==    by 0x106FDDB4D: js_SetPropertyHelper(JSContext*, JSObject*, jsid, unsigned int, JS::Value*, int) (jsobj.cpp:6105)
==97971==    by 0x106F8F235: js::Interpret(JSContext*, js::StackFrame*, js::InterpMode) (jsinterp.cpp:3743)
==97971==    by 0x106FBA3C6: js::RunScript(JSContext*, JSScript*, js::StackFrame*) (jsinterp.cpp:584)
==97971==    by 0x106FBB6F8: js::InvokeKernel(JSContext*, js::CallArgs, js::MaybeConstruct) (jsinterp.cpp:647)

Will mark as security sensitive to be safe, hopefully it isn't necessary.
Comment 1 [PTO to Dec5] Bill McCloskey (:billm) 2011-11-22 09:27:45 PST
Could you take a look at this, Terrence? It looks like gcNumFreeArenas isn't initialized. It should be done in the JSRuntime constructor, which is in jsapi.cpp.
Comment 2 Gregor Wagner [:gwagner] 2011-11-22 09:37:38 PST
At worst we perform a GC the first time we enter MaybeGC so it's not sec-sensitive.
Comment 3 Josh Aas 2011-11-22 10:51:56 PST
The pages I loaded under valgrind when this came up: the Mozilla nightly home page,, and
Comment 4 Terrence Cole [:terrence] 2011-11-22 10:57:53 PST
Created attachment 576209 [details] [diff] [review]
v1: trivial
Comment 5 [PTO to Dec5] Bill McCloskey (:billm) 2011-11-22 11:31:17 PST
Comment on attachment 576209 [details] [diff] [review]
v1: trivial

Comment 6 Terrence Cole [:terrence] 2011-11-22 14:23:25 PST
Comment 7 Curtis Koenig [:curtisk-use]] 2011-11-23 06:27:15 PST
If your sure this is not sec-sensative then please unhide.

This appears to be resolved, so I am marking it (resolved->fixed), per request from Ed Morely who monitors mozilla-inbound > mozilla-central merges.
Comment 8 Ian Melven :imelven 2011-11-23 09:12:21 PST
adding the changeset that landed this in m-c :

and setting target milestone to FF 11
Comment 9 Daniel Veditz [:dveditz] 2011-11-23 10:36:52 PST
This is a "regression" from bug 700357 which added this property. Unfortunately that landed the day before the merge and made it into Fx 10, so we need to land this fix on Aurora as well.
Comment 10 Daniel Veditz [:dveditz] 2011-11-23 10:47:45 PST
Looking at the code I agree w/Gregor in comment 2: the only decision based on this possibly bogus value is whether to GC now or wait a bit and that's not a security problem.
Comment 11 Terrence Cole [:terrence] 2011-11-23 11:55:26 PST
Daniel, thanks for unhiding this: I don't have permission bits to do that.

If we want to go ahead and push this to FF10, there is zero risk in doing so.
Comment 12 Terrence Cole [:terrence] 2011-11-23 11:57:12 PST
*sigh* Bugzilla, why do you do these things to me?  I can't even see the fields I just unset.

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