[Webkit-unassigned] [Bug 186765] New: [Armv7] Linkbuffer: executableOffsetFor() fails for location 2

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=186765

            Bug ID: 186765
           Summary: [Armv7] Linkbuffer: executableOffsetFor() fails for
                    location 2
           Product: WebKit
           Version: WebKit Nightly Build
          Hardware: Other
                OS: Linux
            Status: NEW
          Severity: Normal
          Priority: P2
         Component: JavaScriptCore
          Assignee: webkit-unassigned at lists.webkit.org
          Reporter: guijemont at igalia.com

On THUMB2, instructions can be 2 bytes long, and therefore are not guaranteed to be 4-aligned. This is the case for jump origins and targets, which means that the parameter of executableOffsetFor() can be the value 2, in which case executableOffsetFor() returns a value taken from before the start of the buffer. Since r231961, we see in unit tests cases where executableOffsetFor() is passed 2 as a parameter, which leads to the wrong offset being used and eventually a segfault as we generate a jump to an unpredictable address.

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