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From bugzi...@apache.org
Subject DO NOT REPLY [Bug 18482] New: - JustIce Pass3bVerifier Verifies Exception Handlers too often
Date Fri, 28 Mar 2003 21:47:20 GMT
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http://nagoya.apache.org/bugzilla/show_bug.cgi?id=18482

JustIce Pass3bVerifier Verifies Exception Handlers too often

           Summary: JustIce Pass3bVerifier Verifies Exception Handlers too
                    often
           Product: BCEL
           Version: 5.0RC1
          Platform: All
               URL: http://www.markcrocker.com/~mcrocker/Computer/Purifier/j
                    ustIceExceptionHandlingIssue.shtml
        OS/Version: All
            Status: NEW
          Severity: Minor
          Priority: Other
         Component: Main
        AssignedTo: bcel-dev@jakarta.apache.org
        ReportedBy: mcrocker@markcrocker.com
                CC: ehaase@inf.fu-berlin.de


While using the JustIce Verifier that is built into BCEL to investigate some
issues with the Purifier project (a pure Java preverifier.  See
http://www.markcrocker.com/~mcrocker/Computer/Purifier/), I noticed that the
internal state of JustIce occasionally disagreed with the StackMaps produced by
Sun's preverifier.

The problem seems to be that JustIce considers Exception handlers to be possible
successors for EVERY instruction in a try block that result in merge changes
when the outgoing frame is merged with the incoming frame of the first
instruction in the Exception handler.

I believe that this is an overly broad interpretation of the specification. 
Only instructions that can actually throw the type (or subtype) of Exception
that a handler is designed to catch should be considered to have possible a
successor of the handler.

An excruciatingly detailed report with source code, bytecode and Data Flow
Analysis can be found at:
http://www.markcrocker.com/~mcrocker/Computer/Purifier/justIceExceptionHandlingIssue.shtml

The solution would be to check if an instruction can throw the type of Exception
that the handler can catch BEFORE checking to see if a merge causes a change. 
This would probably be a fairly involved task.

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