Bug 134906

Summary: Flattening dictionaries with oversize backing stores can cause crashes
Product: WebKit Reporter: Mark Hahnenberg <mhahnenberg>
Component: JavaScriptCoreAssignee: Mark Hahnenberg <mhahnenberg>
Status: RESOLVED FIXED    
Severity: Normal CC: commit-queue
Priority: P2    
Version: 528+ (Nightly build)   
Hardware: Unspecified   
OS: Unspecified   
Attachments:
Description Flags
Patch none

Description Mark Hahnenberg 2014-07-14 15:14:35 PDT 
The collector expects any pointers into CopiedSpace passed to copyLater are within 32 KB of the CopiedBlock header. This was always the case except for when flattening a dictionary caused the size of the Butterfly to decrease. This was equivalent to moving the base of the Butterfly to higher addresses. If the object was reduced sufficiently in size, the base would no longer be within the first 32 KB of the CopiedBlock and the next collection would choke on the Butterfly pointer.

The fix is to detect this situation during flattening and to memmove the Butterfly down to where the old base was.
Comment 1 Mark Hahnenberg 2014-07-14 15:14:56 PDT 
<rdar://problem/17556957>
Comment 2 Mark Hahnenberg 2014-07-14 15:20:09 PDT 
Created attachment 234884 [details]
Patch
Comment 3 WebKit Commit Bot 2014-07-14 16:59:39 PDT 
Comment on attachment 234884 [details]
Patch

Clearing flags on attachment: 234884

Committed r171092: <http://trac.webkit.org/changeset/171092>
Comment 4 WebKit Commit Bot 2014-07-14 16:59:41 PDT 
All reviewed patches have been landed.  Closing bug.