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From "Mikhail Loenko" <mloe...@gmail.com>
Subject Re: [drlvm][verifier] Using the Harmony verifier code for computing the StackMapTable attribute
Date Tue, 30 Oct 2007 15:51:23 GMT
Hi Asaf!

Welcome to Harmony dev forum :)

I beleive current implementation of Harmony verifier [1] already covers most
of what's necessary for you. It contains both old-style (Java5) verification
and new-style (StackMapTable attribute based) one. So, it seems like
a lightweigh extension to what Harmony already has would be enough.

So, I have some questions.
IsStackMapTableAttributeValid() - this seems to be the same as a full
(or partial) new-style verification of a method. The following three
ways are easiest to implement given current Harmony verifier design

1) check only structure of the attribute
2) the structure PLUS content except assignability of not-loaded
classes (i.e. make a full verification WITHOUT checking assignability
of not-loaded classes)
3) load missing classes and make a full verification

Will anything from above suit your needs?

Can the method byte-codes contain subroutines? Dead (unreachable) code?
as a result of stackmaptable calculation it might be necessary to extend
constant pool of the class. Is it acceptable in your environment?


[1] http://svn.apache.org/viewvc/harmony/enhanced/drlvm/trunk/vm/vmcore/src/verifier-3363/

2007/10/30, Asaf Yaffe <asaf_yaffe@yahoo.com>:
> Hi,
> My name is Asaf Yaffe and I am a committer on the Eclipse Test and Performance Tool Platform
(TPTP) Java Profiler project. We are currently working on updating our Binary Code Instrumentation
(BCI) engine to support the new Java 6 class file format (version 50.0) and the new StackMapTable
attribute. When the BCI engine modifies the byte-codes of a method, it must recompute the
StackMapTable attribute to successfully pass the Java 6 verifier. The current implementation
of Java 6 gracefully "falls-back" to the old verification scheme (which does not depend on
the StackMapTable attribute) in face of a missing/invalid StackMapTable attribute. This may
not be the case in future Java versions, and tool writers are encouraged to update their BCI-based
tools (see here for more information: https://jdk.dev.java.net/verifier.html).
> Instead of developing StackMapTable calculation for the BCI engine, we would like to
explore the option of reusing code from the Harmony byte-code verifier to recompute the StackMapTable
of a method from its byte-codes. Ideally, we would like to have a stand-alone library (provided
in source or binary form – exact distribution model should be discussed) which exports two
> -    IsStackMapTableAttributeValid(): given the method byte-codes and StackMapTable,
checks whether the StackMapTable is valid.
> -    RecomputeStackMapTableAttribute(): given the method byte-codes, produces a new valid
StackMapTable that can be used by the Java 6 verifier of any Java 6-compliant JVM.
> With best regards,
> Asaf Yaffe
> Eclipse TPTP Committer, JVMTI Profiler component.
> __________________________________________________
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