[jira] [Created] (BCEL-283) Support for StackMap should be different from StackMapTable

["Mark Roberts (JIRA)" <ji...@apache.org>]

Mark Roberts created BCEL-283:
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             Summary: Support for StackMap should be different from StackMapTable
                 Key: BCEL-283
                 URL: https://issues.apache.org/jira/browse/BCEL-283
             Project: Commons BCEL
          Issue Type: Bug
            Reporter: Mark Roberts


It turns out we made a mistake with the StackMap renaming changes.  I ran into a problem decoding some old .class files and went back to the Java Specification Requests (JSRs) to try and understand the history of the StackMap attribute.  While I was not able to get the complete story, I have a pretty good guess at what happened and it does explain the problem I have seen.

The official introduction of StackMaps appears to be JSR 202 from (approx.) Sept. 2006 and it is part of JDK6 (see attached spec) .   However, StackMaps were originally proposed much earlier (approx.) March 2002 - see the attached verifier spec.  It appears there were some implementations of this earlier specification - the ASM tool was one and there may be others.  

The key differences are: 
Typechecker Spec:	StackMap attribute with fixed format and no frame type byte
JDK 6 Spec:		StackMapTable attribute with variable format including a frame type byte.

The JVM and the javap tool support BOTH formats.  BCEL recognizes both attribute names, but treats them the same, as JDK6 version.

I don't think the changes will be too difficult.  I will create a proposed fix within the next few days.




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