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From Asaf Yaffe <asaf_ya...@yahoo.com>
Subject Re: [drlvm][verifier] Using the Harmony verifier code for computing the StackMapTable attribute
Date Wed, 07 Nov 2007 14:31:07 GMT
Hi Pavel,

What you said about ClassFileLoadHook *may* be true for Java-based Agents (implementing the
java.lang.instrument.* interfaces), but is not true for native JVMTI agents. All JVMs supporting
the can_generate_all_class_load_hook_events capability (basically all major 1.5+ JVMs on the
market) sends the ClassFileLoadHook for *all* classes (even for java.lang.Object). This is
fully documented in the JVMTI spec (see http://java.sun.com/j2se/1.5.0/docs/guide/jvmti/jvmti.html#ClassFileLoadHook).

Regards,
Asaf

----- Original Message ----
From: Pavel Pervov <pmcfirst@gmail.com>
To: dev@harmony.apache.org
Sent: Wednesday, November 7, 2007 4:17:18 PM
Subject: Re: [drlvm][verifier] Using the Harmony verifier code for computing the StackMapTable
attribute

Hello Asaf,

On 11/5/07, Asaf Yaffe <asaf_yaffe@yahoo.com> wrote:
>
> 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.


AFAIU, agent receives first ClassFileLoadHook event when JNI is already
available. So, you can safely implement class loading related
 functionality
through JNI. Class loader is passed into a callback so it can be used
 to
load all classes which are neccessary for verification.

 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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> >
> >
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>
>
>
>
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-- 
Pavel Pervov,
Intel Enterprise Solutions Software Division





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