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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - Regression(r197648): JSObject::setPrototypeWithCycleCheck() allows for cycles but the rest of the code base does not"
href="https://bugs.webkit.org/show_bug.cgi?id=161534">161534</a>
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<th>Summary</th>
<td>Regression(r197648): JSObject::setPrototypeWithCycleCheck() allows for cycles but the rest of the code base does not
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<th>Classification</th>
<td>Unclassified
</td>
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<th>Product</th>
<td>WebKit
</td>
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<th>Version</th>
<td>WebKit Nightly Build
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<th>Hardware</th>
<td>Unspecified
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<th>OS</th>
<td>Unspecified
</td>
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<th>Status</th>
<td>NEW
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<th>Severity</th>
<td>Normal
</td>
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<th>Priority</th>
<td>P2
</td>
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<th>Component</th>
<td>JavaScriptCore
</td>
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<th>Assignee</th>
<td>webkit-unassigned@lists.webkit.org
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<th>Reporter</th>
<td>cdumez@apple.com
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<th>CC</th>
<td>ggaren@apple.com, mark.lam@apple.com, sbarati@apple.com
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<th>Blocks</th>
<td>155002
</td>
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<pre>JSObject::setPrototypeWithCycleCheck() allows for cycles but the rest of the code base does not deal properly with cycles.
This is because of the following check that was added:
if (UNLIKELY(asObject(nextPrototype)->methodTable(vm)->getPrototype != defaultGetPrototype))
break;
This was added to match the EcmaScript spec:
- <a href="https://tc39.github.io/ecma262/#sec-ordinarysetprototypeof">https://tc39.github.io/ecma262/#sec-ordinarysetprototypeof</a> (step 8)
However, if you create a cycles, we end up with an infinite loop later on under:
Structure::anyObjectInChainMayInterceptIndexedAccesses()
This is likely not the only place we traverse the prototype chain and except there is no cycle.
I noticed this when running html/browsers/history/the-location-interface/allow_prototype_cycle_through_location.sub.html with the patch for <a class="bz_bug_link
bz_status_REOPENED "
title="REOPENED - Align proto getter / setter behavior with other browsers"
href="show_bug.cgi?id=161455">Bug 161455</a> applied.</pre>
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