Bug 64387

Summary: DFG JIT put_by_id transition caching does not inform the GC about the structure and prototype chain that it is referencing
Product: WebKit Reporter: Filip Pizlo <fpizlo>
Component: JavaScriptCoreAssignee: Nobody <webkit-unassigned>
Severity: Normal CC: webkit.review.bot
Priority: P2    
Version: 528+ (Nightly build)   
Hardware: All   
OS: All   
Description Flags
the patch none

Description Filip Pizlo 2011-07-12 13:46:27 PDT
The DFG JIT, like the old JIT, may perform put_by_id transition caching.  In a transition cache, code is emitted that changes the structure of an object, so long as the object has a specific previous structure, and it has a specific prototype chain.  The code contains immediates referencing the old structure, the new structure, and the prototype chain.  Hence, the code is only correct if the GC keeps all of these objects (structures and prototypes) alive.  To do so, the DFG JIT must inform the GC that it has pinned those objects.  Currently, the DFG JIT does not do this, which results in spurious crashes on websites like gmail.com.
Comment 1 Filip Pizlo 2011-07-12 14:02:16 PDT
Created attachment 100557 [details]
the patch
Comment 2 WebKit Review Bot 2011-07-12 14:52:05 PDT
Comment on attachment 100557 [details]
the patch

Clearing flags on attachment: 100557

Committed r90854: <http://trac.webkit.org/changeset/90854>
Comment 3 WebKit Review Bot 2011-07-12 14:52:09 PDT
All reviewed patches have been landed.  Closing bug.