[Webkit-unassigned] [Bug 258757] New: Undefined behavior in FunctionExecutable::lastLine()

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=258757

            Bug ID: 258757
           Summary: Undefined behavior in FunctionExecutable::lastLine()
           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: cdumez at apple.com
                CC: mark.lam at apple.com

Undefined behavior in FunctionExecutable::lastLine() when running media/modern-media-controls/pip-support/pip-support-click.html  with UBSan:
```
SUMMARY: UndefinedBehaviorSanitizer: undefined-behavior /Volumes/Work/WebKit/OpenSource/WebKitBuild/Release/DerivedSources/JavaScriptCore/BytecodeStructs.h:16853:71 in 
runtime/FunctionExecutable.h:208:28: runtime error: signed integer overflow: 1 + 2147483647 cannot be represented in type 'int'
```

Code looks like:
```
int lastLine() const
{
   return firstLine() + lineCount();
}
```

Looks to me that lineCount() returns either an uninitialized value or -1 that was casted to an unsigned type.

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