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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - ShadowChicken::visitChildren() should not visit tailMarkers and throwMarkers."
href="https://bugs.webkit.org/show_bug.cgi?id=156532">156532</a>
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<th>Summary</th>
<td>ShadowChicken::visitChildren() should not visit tailMarkers and throwMarkers.
</td>
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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 Local Build
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<th>Hardware</th>
<td>Unspecified
</td>
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<th>OS</th>
<td>Unspecified
</td>
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<th>Status</th>
<td>NEW
</td>
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<th>Severity</th>
<td>Normal
</td>
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<th>Priority</th>
<td>P2
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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>mark.lam@apple.com
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<pre>ShadowChicken can store tailMarkers and throwMarkers in its log, specifically in the callee field of a log packet. However, ShadowChicken::visitChildren() unconditionally visits the callee field of each packet as if they are real objects. If visitChildren() encounters one of these markers in the log, we get a crash.
This crash was observed in the v8-v6/v8-regexp.js stress test running with shadow chicken when r199393 landed. r199393 introduced tail calls to a RegExp split fast path, and the v8-regexp.js test exercised this fast path a lot. Throw in some timely GCs, and we get a crash party.
The fix is to have ShadowChicken::visitChildren() filter out the tailMarker and throwMarker.
Alternatively, if perf is an issue, we can allocate 2 dedicated objects for these markers so that ShadowChicken can continue to visit them. For now, I'm going with the filter.</pre>
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