Re: Making operand stack copy

Hi Andrew,
  Thanks a lot for the information and links. I will chk out those and
will post a message on list if I can find the way out.

Thanks again
Shrinivas Joshi.


			-Shrinivas Balkrishna Joshi ([email protected])

On Fri, 18 Feb 2005, Andrew Huntwork wrote:

> yes you can.  but how hard it's going to be depends on your exact problem.
>
> If you want to save function arguments, it's easy, because you already
> know the types of the arguments and you can generate the appropriate
> load instructions using getArgumentTypes and
> InstructionFactory.createStore.
>
> If on the other hand you want to save the whole stack, you have problems:
>
> f(a,b?c(d) : e,g,h,i)
>
> if you want to save the stack before calling c, it has at least one
> object a on it that's not an argument to your function, so it's
> difficult to know what instructions to generate to correctly save the
> entire stack.
>
> But it's not impossible.  BCEL implements a bytecode verifier that
> definitely knows for every instruction everything that's on the stack.
> You can probably use
> org.apache.bcel.verifier.structurals.ControlFlowGraph and some
> modification of ExecutionVisitor.
>
> Alternatively, SandMark, which uses BCEL, has a StackSimulator* object
> that's specifically for finding out this type of information.  sandmark
> does this save and restore operation in many places.  ask on
> [email protected] for help with sandmark.
>
> [*]
> http://cgi.cs.arizona.edu/~sandmark/SandMark3.1.1/API/sandmark/util/stacksimulator/StackSimulator.html
>
> (no, sandmark does not still use old (de.fub.bytecode) bcel, these are
> just old javadocs)
>
> Shrinivas Balkrishna Joshi wrote:
> > Hi All,
> >   I want to know if one can use BCEL to make a copy of JVM operand stack.
> > Actually I want to save parameters being passed to a particular function
> > before the function is called. If there are less than 3 parameters I can
> > use DUP instruction to create copy of stack values and save the arguments.
> > However, this method wont help in function calls involving more than 3
> > parameters. So I was just wondering whether one can make a copy of whole
> > stack at a particular instance of program execution and manipulate it
> > using BCELA API.
> > Thanking you in anticipation
> > -Shrinivas Joshi ([email protected])
> >
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