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From "Pavel Pervov" <pmcfi...@gmail.com>
Subject Re: [drlvm][verifier] Using the Harmony verifier code for computing the StackMapTable attribute
Date Wed, 07 Nov 2007 14:29:28 GMT
Hello, Asaf

On 10/31/07, Asaf Yaffe <asaf_yaffe@yahoo.com> wrote:
>
> Hi Mikhail,
>
> Thank you for the prompt reply. This information is encouraging!
>
> Here are the answers to your questions:
>
> IsStackMapTableAttributeValid(): the original idea behind this function is
> to optimize the process and do not compute the StackMapTable if not
> necessary. However, after considering your options, it seems that only
> option 3 makes sense and hence we will not gain any performance benefit
> (because we effectively run full verification). I also think that the TPTP
> instrumentation engine has enough knowledge to know if a computation is
> really needed. Therefore, lets consider option 3 (for completeness) but I
> think this function is not required for TPTP.
>
> RecomputeStackMapTableAttribute():
> - subroutines: we can assume there are no subroutines (jsr/ret
> instructions). Java 6 classes should not have them in the first place. Our
> instrumentation engine may use these instructions (e.g., some probe
> injections in Probekit use jsr/ret), but we can update the engine.
> - dead-code: while our instrumentation engine does not add "dead-code", I
> assume that the code we instrument may contain dead code. We should further
> discuss what are the best ways of handling this case (dead-code removal,
> "nop-ing" the dead code, etc).
> - extending the constant pool: no problem. We have the necessary
> functionality to arbitrarily modify the constant pool. Exposing this
> functionality to the verifier seems like a simple thing to do.


 Extending constant pool may become impossible if a class' constant pool is
already at its boundary (only 64K entries are allowed in constant pool). I'm
afraid you'll have to skip instrumentation of such classes.

Best regards,
> Asaf
>
>
> ----- Original Message ----
> From: Mikhail Loenko <mloenko@gmail.com>
> To: dev@harmony.apache.org
> Sent: Tuesday, October 30, 2007 5:51:23 PM
> Subject: Re: [drlvm][verifier] Using the Harmony verifier code for
> computing the StackMapTable attribute
>
>
> 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?
>
> RecomputeStackMapTableAttribute()
> 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?
>
> Thanks,
> Mikhail
>
> [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 APIs:
> > -    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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>
>
>
>
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-- 
Pavel Pervov,
Intel Enterprise Solutions Software Division

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