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Posted to issues@commons.apache.org by "Benedikt Ritter (JIRA)" <ji...@apache.org> on 2017/08/30 19:23:00 UTC
[jira] [Updated] (BCEL-283) Support for StackMap should be
different from StackMapTable
[ https://issues.apache.org/jira/browse/BCEL-283?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]
Benedikt Ritter updated BCEL-283:
---------------------------------
Assignee: Benedikt Ritter
> 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
> Assignee: Benedikt Ritter
> Attachments: Appendix1-verifier.pdf, Attribute.diff, ClassFileCMP-SE6.0.pdf
>
>
> 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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