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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, 06 Nov 2007 07:05:10 GMT
Hi Asaf,

since I know the verifier code it would be natural for me to add the
requested functionality. Since you know TPTP BCI it would be natural
for you to implement the mappings.

So, I'm starting to implement my part. We need to discuss (with
Harmony community) where this extra functionality should be
integrated.

For the dead code: the problem is dead code might be a common part of
two try blocks, handlers of which could have inconsistent stackmaps.
Thus we won't be able to build any solution unless we reduce try
blocks to exclude the dead code.
Is it possible to modify try blocks with the TPTP BCI?

Thanks,
Mikhail

2007/11/5, Asaf Yaffe <asaf_yaffe@yahoo.com>:
> Hi Mikhail,
>
> All class_*, method_* and field_* functions from the class interface can be mapped to
an implementation within the TPTP BCI engine. The main issue is with the Class Loader functions
(cl_*): generally, these functions can be implemented using JNI. However, some classes are
being instrumented during the JVM bootstrapping, where JNI is not yet available. Therefore,
we cannot guarantee that class loading functionality will always be available, and we will
need to somehow work around this limitation. One option, for example, is not to do any byte-code
modifications until the JVM is initialized, and then use RedefineClasses to instrument bootstrap
classes.
>
> Please let me know if there are any other issues, and what do you think should be the
next steps.
>
> Best regards,
> Asaf
>
>
> ----- Original Message ----
> From: Mikhail Loenko <mloenko@gmail.com>
> To: dev@harmony.apache.org
> Sent: Thursday, November 1, 2007 7:38:21 AM
> Subject: Re: [drlvm][verifier] Using the Harmony verifier code for computing the StackMapTable
attribute
>
> Hi Asaf
>
> see some questions below
>
> 2007/10/31, Asaf Yaffe <asaf_yaffe@yahoo.com>:
> > 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).
>
> I need to think about that...
>
>
> > - 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.
>
>
> Currently verifier uses the following list of functions from the
> class_interface:
>
> cl_get_class
> cl_load_class
>
> cl_acquire_lock
> cl_release_lock
>
> cl_get_verify_data_ptr
> cl_set_verify_data_ptr
>
> class_get_class_loader
>
> class_get_cp_class_name_index
> class_get_cp_descriptor_index
> class_get_cp_name_index
> class_get_cp_ref_class_index
> class_get_cp_ref_name_and_type_index
> class_get_cp_size
> class_get_cp_tag
> class_get_cp_utf8_bytes
> class_get_method
> class_get_method_number
> class_get_name
> class_get_super_class
> class_get_version
> class_is_interface_
> class_is_same_package
> class_resolve_method
> class_resolve_nonstatic_field
>
> field_is_protected
>
> method_get_bytecode
> method_get_code_length
> method_get_descriptor
> method_get_exc_handler_info
> method_get_exc_handler_number
> method_get_max_local
> method_get_max_stack
> method_get_name
> method_get_stackmaptable
> method_is_protected
> method_is_static
>
> The description of what these functions do can be found here[1]
> Please let me know whether there is a necessary functionality to
>  implement
> thse interface functions and whether they can be invoked at the moment
> when recompute of stackmap attribute happens
>
> Thanks,
> Mikhail
>
> [1]
>  http://svn.apache.org/viewvc/harmony/enhanced/drlvm/trunk/vm/vmcore/include/class_interface.h?view=markup
>
>
> >
> > 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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