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SamplingProfiler: stop the stack walk at a null entry frame instead of dereferencing vmEntryRecord(nullptr) #395

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SamplingProfiler: stop the stack walk at a null entry frame instead of dereferencing vmEntryRecord(nullptr) #395

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8ec8fb6
CallFrame::unsafeCallerFrame: treat a null entry frame as the end of …
robobun Aug 8, 2026
62128f5
TestWebKitAPI: add a deterministic test for unsafeCallerFrame with a …
robobun Aug 8, 2026
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9 changes: 9 additions & 0 deletions Source/JavaScriptCore/interpreter/CallFrame.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -178,6 +178,15 @@ CallFrame* CallFrame::callerFrame(EntryFrame*& currEntryFrame) const
SUPPRESS_ASAN CallFrame* CallFrame::unsafeCallerFrame(EntryFrame*& currEntryFrame) const
{
if (unsafeCallerFrameOrEntryFrame() == currEntryFrame) {
// The sampling profiler walks the sampled thread's unsafe state: it can
// start from a stale vm.topCallFrame, or from a machine frame inside
// vmEntryToJavaScript's prologue/epilogue, while its vm.topEntryFrame
// snapshot is null. A walked frame whose caller slot reads null then
// matches the null entry frame here, and vmEntryRecord(nullptr) faults
// reading near address zero. Treat a null entry frame as the end of the
// walk instead.
if (!currEntryFrame)
return nullptr;
VMEntryRecord* currVMEntryRecord = vmEntryRecord(currEntryFrame);
currEntryFrame = currVMEntryRecord->unsafePrevTopEntryFrame();
return currVMEntryRecord->unsafePrevTopCallFrame();
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