Branch: refs/heads/main
Home: https://github.com/WebKit/WebKit
Commit: 3f22094cdc45a72a7a7e0b9e10149470628b1ac0
https://github.com/WebKit/WebKit/commit/3f22094cdc45a72a7a7e0b9e10149470628b1ac0
Author: Sosuke Suzuki <[email protected]>
Date: 2026-03-27 (Fri, 27 Mar 2026)
Changed paths:
A JSTests/stress/describe-null-butterfly.js
M Source/JavaScriptCore/runtime/JSCJSValue.cpp
Log Message:
-----------
[JSC] Fix null butterfly dereference in
JSValue::dumpInContextAssumingStructure
https://bugs.webkit.org/show_bug.cgi?id=310783
Reviewed by Yusuke Suzuki.
JSValue::dumpInContextAssumingStructure unconditionally calls
butterfly()->base(structure) without checking if butterfly() returns
null. Objects with only inline properties (no indexed storage, no
out-of-line properties) have a null butterfly pointer. When the DFG
graph dump or describe() prints such objects, this triggers undefined
behavior caught by UBSAN:
Butterfly.h:182:21: runtime error: member call on null pointer of
type 'JSC::Butterfly *'
The call chain does only pointer arithmetic so it does not crash in
practice, but the output "(base=0xfffffffffffffff8)" is meaningless
and the member call on a null pointer is still UB.
Fix by checking if butterfly is null before computing the base address.
* JSTests/stress/describe-null-butterfly.js: Added.
* Source/JavaScriptCore/runtime/JSCJSValue.cpp:
(JSC::JSValue::dumpInContextAssumingStructure const):
Canonical link: https://commits.webkit.org/310137@main
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