RE: J2ME bytecode modification

[Jose Andrés Pérez <jo...@m-centric.com>]

Hello everybody,

> I am wondering if I can use BCEL to modify J2ME MIDlets since any bytecode
> modification in J2ME would require running a J2ME verifier on the modified
> bytecodes. My understanding is that J2ME preverification involves
> computing
> StackMap attributes. Does BCEL automatically take care of recomputing and
> updating StackMap attribute in the case of J2ME MIDlets ?

I´m working on that way, modifing J2ME MIDlets bytecode. I could modify
MIDlets bytecode but when I tried to run it on any emulator or on a mobile
device errors appeared. The problem is that the class files need a StackMap
for the KVM classfile verification. This new attribute (StackMap) is defined
by "KVM Specification" but not by "The Java Virtual Machine Specification".

BCEL includes a class for managing StackMaps
"org.apache.bcel.classfile.StackMap", then the only thing to do is update
that attribute to its new value. I´m working around this but, so far, I´m
not success.

> If not, is anyone aware of J2ME MIDlet verifier similar to JustIce for
J2SE?

BCEL has also a verifier. I tried it but it only checks your bytecode and
notices to you if it passes the checking.


Thanks,
Jose


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RE: J2ME bytecode modification

[Jim Redman <jr...@ergotech.com>]

I have a project that removes all the floating point code from J2ME code
and replaces it with soft floating point.  I don't remember having any
particular problem with J2ME code.  I take the code before verification,
modify it, then verify it.

Since most J2ME implementations (eg J9) now come with floating point
support, I haven't spent much time on the project recently so maybe I
mis-remember.

Jim

> Hello everybody,
>
>> I am wondering if I can use BCEL to modify J2ME MIDlets since any
>> bytecode modification in J2ME would require running a J2ME verifier on
>> the modified bytecodes. My understanding is that J2ME preverification
>> involves computing
>> StackMap attributes. Does BCEL automatically take care of recomputing
>> and updating StackMap attribute in the case of J2ME MIDlets ?
>
> I´m working on that way, modifing J2ME MIDlets bytecode. I could modify
> MIDlets bytecode but when I tried to run it on any emulator or on a
> mobile device errors appeared. The problem is that the class files need
> a StackMap for the KVM classfile verification. This new attribute
> (StackMap) is defined by "KVM Specification" but not by "The Java
> Virtual Machine Specification".
>
> BCEL includes a class for managing StackMaps
> "org.apache.bcel.classfile.StackMap", then the only thing to do is
> update that attribute to its new value. I´m working around this but, so
> far, I´m not success.
>
>> If not, is anyone aware of J2ME MIDlet verifier similar to JustIce for
> J2SE?
>
> BCEL has also a verifier. I tried it but it only checks your bytecode
> and notices to you if it passes the checking.
>
>
> Thanks,
> Jose
>
>
> --
> To unsubscribe, e-mail:
> <ma...@jakarta.apache.org> For additional
> commands, e-mail: <ma...@jakarta.apache.org>


-- 
Jim Redman
ErgoTech Systems, Inc.
+1 505 662 5156



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