ddd and jni

Hi,

i want to debug a C-code shared library loaded via JNI from
a java application.
Opening the library with ddd i'm able to set breakpoints.
I think i don't attach ddd in the correct way to the jvm.
What i do is: 
1. Start the GUI of my java application (java ... at command line)
2. attach ddd to the process of the jvm
3. waiting for the jvm to stop at the jni-call to my breakpoint

Nothing happens. Does this only work if i use jdb to start my
java code? Does anyone know a tutorial "how to debug jni-c-code"?
Might it be a problem that i use cygwin with the mingw dll?

By the way: Loading the library in ddd i get the message:
Line 1 of "PM_ML.cc" is at address 0x10002960 <Java_mtbdd_PrismMTBDD_PM_1ML> but
contains no code
What's wrong here?

Thank you in advance, regards

Johann Schuster