[Webkit-unassigned] [Bug 176558] New: DFG OSR exit value recovery may recover values beyond the bounds of the stack pointer.

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=176558

            Bug ID: 176558
           Summary: DFG OSR exit value recovery may recover values beyond
                    the bounds of the stack pointer.
           Product: WebKit
           Version: WebKit Nightly 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

This means that the recovered values may be trashed by interrupts.  I discovered this when working on https://bugs.webkit.org/show_bug.cgi?id=175144, using the validation patch (https://bugs.webkit.org/attachment.cgi?id=319676) that compares the recovered stack and registers using the jit based OSR exits vs the probe based OSR exits.  The recovered values beyond the sp manifested as differences in my test (which is what drew my attention to them).  This feels like either:
1. the sp was not set correctly, or
2. we have no need to recovering those values.

However, I modified the test code to write 0xbadbeef0 into the recovered stack values that reside beyond sp, and found that this did not result in any crash or test failure (on Octane's pdfjs).  That suggests that those values are not needed.

Regardless, we should investigate why this is happening.

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