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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - GC stack scan should include ABI red zone"
href="https://bugs.webkit.org/show_bug.cgi?id=148976">148976</a>
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<th>Summary</th>
<td>GC stack scan should include ABI red zone
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<th>Classification</th>
<td>Unclassified
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<th>Product</th>
<td>WebKit
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<th>Version</th>
<td>WebKit Local Build
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<th>Hardware</th>
<td>Unspecified
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<th>OS</th>
<td>Unspecified
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<th>Status</th>
<td>NEW
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<th>Severity</th>
<td>Normal
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<th>Priority</th>
<td>P2
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<th>Component</th>
<td>JavaScriptCore
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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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<p>
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<pre>The x86_64 ABI section 3.2.2 (<a href="http://people.freebsd.org/~obrien/amd64-elf-abi.pdf">http://people.freebsd.org/~obrien/amd64-elf-abi.pdf</a>) and ARM64 ABI (<a href="https://developer.apple.com/library/ios/documentation/Xcode/Conceptual/iPhoneOSABIReference/Articles/ARM64FunctionCallingConventions.html#//apple_ref/doc/uid/TP40013702-SW7">https://developer.apple.com/library/ios/documentation/Xcode/Conceptual/iPhoneOSABIReference/Articles/ARM64FunctionCallingConventions.html#//apple_ref/doc/uid/TP40013702-SW7</a>) both states that there is a 128 byte red zone below the stack pointer (reserved by the OS), and that "functions may use this area for temporary data that is not needed across function calls".
Hence, it is possible for a thread to store JSCell pointers in the red zone area, and the conservative GC thread scanner needs to scan that area as well.</pre>
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