Re: Instrumenting Java Library

[Ondrej Lhotak <olhotak@sable.mcgill.ca>]

On Sat, Jan 31, 2004 at 06:32:54PM -0500, KENNETH LELAND wrote:
> I am having trouble instrumenting the java io and net libraries.  When i
> instrument the library i get various problems ie: deadlocking,
> exceptions, etc. when i run the instrumented code.  I am only adding a
> call to a function that just returns. if anyone can post a smallest
> example that works for instrumenting java libraries i would be
> grateful.( the examples in the soot tutorials dont seem to work for the
> libraries)

In my experience, instrumenting the standard libraries by modifying the
bytecode is very messy. The two main problems I've encountered are:

1) The VM makes assumptions about the libraries which are no longer true
when you modify them. For example, adding a field to java.lang.Object
causes several VMs to seg fault.

2) It's often difficult to write the instrumentation code without using
the part of the library that you are instrumenting.

If you can be more specific about where exactly you are inserting the
instrumentation and the kinds of exceptions you get and their stack
traces, I might be able to make some guesses about what is going wrong.

In general, if I need to instrument the libraries, I much prefer to do
it without modifying bytecode. I am aware of two ways to do this:

1) Use JVMPI or the debugger interface. Bruno Dufour has a very nice
tool for capturing and processing the information provided through
JVMPI. It used to be called AdaptJ, but I think now he calls it StarJ.
This is typically the easiest method, but only works if JVMPI provides
the information that you need.

2) Instrument a VM. I've done this in the past with Kaffe and found it
to be reasonably easy. The downside to Kaffe is that it doesn't run all
benchmarks. SableVM would be another possibility. There's also JikesRVM,
but it's more complicated, and it's difficult to separate the VM itself
(which is written in Java and runs itself) from the code it's running on
behalf of your benchmark. If you're planning to instrument a VM, you
should still have a look at Bruno's tool. Last time I talked to him
about it, he had plans to make it interface to a VM directly, so it
could save you a lot of work.

I hope this is helpful.

Ondrej

> 
>  ken
> 
>