[Webkit-unassigned] [Bug 148976] New: GC stack scan should include ABI red zone

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=148976

            Bug ID: 148976
           Summary: GC stack scan should include ABI red zone
    Classification: Unclassified
           Product: WebKit
           Version: WebKit Local Build
          Hardware: Unspecified
                OS: Unspecified
            Status: NEW
          Severity: Normal
          Priority: P2
         Component: JavaScriptCore
          Assignee: webkit-unassigned at lists.webkit.org
          Reporter: mark.lam at apple.com

The x86_64 ABI section 3.2.2 (http://people.freebsd.org/~obrien/amd64-elf-abi.pdf) and ARM64 ABI (https://developer.apple.com/library/ios/documentation/Xcode/Conceptual/iPhoneOSABIReference/Articles/ARM64FunctionCallingConventions.html#//apple_ref/doc/uid/TP40013702-SW7) 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.

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