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speculationFromCell: reject misaligned StringImpl* from concurrent zap residue #285

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speculationFromCell: reject misaligned StringImpl* from concurrent zap residue #285

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4 changes: 3 additions & 1 deletion Source/JavaScriptCore/bytecode/SpeculatedType.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -602,7 +602,9 @@ SpeculatedType speculationFromCell(JSCell* cell)
if (cell->isString()) {
JSString* string = uncheckedDowncast<JSString>(cell);
if (const StringImpl* impl = string->tryGetValueImpl()) {
if (!Integrity::isSanePointer(impl)) [[unlikely]] {
// Alignment check rejects HeapCell::zap residue in m_fiber seen on weak-memory-order
// CPUs when a freshly-allocated JSString is read before its m_fiber store is visible.
if (!Integrity::isSanePointer(impl) || (reinterpret_cast<uintptr_t>(impl) & (alignof(StringImpl) - 1))) [[unlikely]] {
ASSERT_NOT_REACHED();
return SpecNone;
}
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