Questions on jvm interpreter

[Saravanaraj Velusamy]

Dmitry et al,

Thanks a ton for your inputs.

I forgot to mention an important constraint. We will have access only to
the compiled class file and not the source. So we are of the opinion that
modifying jvm interpreter or the usage of low level bytecode manipulation
library are our only options to solve the problem.

Please correct, if our understanding is wrong.

Regards,
Saravanaraj


On Fri, Mar 30, 2012 at 1:44 AM, Dmitry Samersoff <
Dmitry.Samersoff at oracle.com> wrote:

> Saravanaraj,
>
> I would recommend method below:
>  1. Add a static method to your class.
>     Use value returned by this method to drive all conditions.
>  2. Use ASM library to change body of this static method as necessary
>     in runtime.
>
> -Dmitry
>
>
> On 2012-03-29 20:48, Remi Forax wrote:
> > Take a look to java.lang.instrument that allow you to alter the bytecode
> > using by example ASM at runtime.
> >
> > Cheers,
> > Rémi
> >
> > Sent from my Phone
> >
> > ----- Reply message -----
> > From: "Saravanaraj Velusamy" <svelusa at ncsu.edu>
> > To: <distro-pkg-dev at openjdk.java.net>,
> > <hotspot-compiler-dev at openjdk.java.net>
> > Subject: Questions on jvm interpreter
> > Date: Thu, Mar 29, 2012 10:20
> >
> >
> > Hi All,
> >
> > We are trying to alter the branch conditions taken by a java program at
> > run time.
> >
> > For example if a Java code has conditions like this
> >
> > if( var == value1)
> >     PATH1;
> > else
> >     PATH2;
> >
> > Lets say we want to it take PATH2 (even though var might be equal to
> > value1). We might not change all branch statements in the class file and
> > we can assume there is another source (say a text file) which contains
> > what conditions needs to be changed.
> >
> > We have two ideas to do the same.
> > 1) To change the bytecode at that point during execution (like changing
> > if_icmpeq to if_icmpne)
> > 2) Find the place which contains the result of the first comparison and
> > complement the result of the comparison.
> >
> > The example has a simple conditional statement. We would also want to
> > consider loops, switch cases later.
> >
> > We would like to know what is the best way to go about and pointers in
> > the code related to this. We are currently looking into
> > bytecodeInterpreter.cpp of Zero instead of hotspot to avoid generated
> > assembly for interpreter.
> > Is there any way to find out the class file belonging to the current
> > opcode ? Since we are not interested in the standard Java class files
> > like String, Integer etc and focus on the ones from the User written
> > classes and methods.
> >
> > We have looked into BCEL, ASM, JVMTI and found out that we cannot change
> > the behavior at run time.
> >
> > Thanks in advance.
> > - Saravanaraj
>
>
> --
> Dmitry Samersoff
> Java Hotspot development team, SPB04
> * There will come soft rains ...
>
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