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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 Mon, 05 Nov 2007 11:17:38 GMT
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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>
>
>
>
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