Question

Using OpenJDK 7 from the command line on OS X Lion, how can I use jdb to debug an application that requires execution under a 32-bit JVM, due to JNI native code?

I know I can invoke java as java -d32 and it will use a 32-bit JVM. I can also pass that -d32 flag to jdb without an error, but it does not seem to have any effect: I still get the same error messages when the application tries to link its native code. Passing -J-d32 exhibits the same behaviour.

Answer 1

It is possible to achieve the above by starting java and jdb as separate processes from two different Terminal windows. So execute these commands, each in its own window:

java -d32 -Xdebug -Xrunjdwp:transport=dt_socket,server=y,suspend=y,address=127.0.0.1:5463 -classpath . MainClass
jdb -attach 127.0.0.1:5463

The first will start the JVM for the application, but suspend it immediately after creation. The second will start the debugger and attach it to the JVm just created. Then you can type run in that second window to launch the application. As an added bonus, output from the application and the debugger are not intermixed, as each has its own window.

References: The jdb help lists possible command line arguments, and JPDA has a section on transports.

Although the above does work for me, I’d welcome other answers providing easier solutions, preferrably as a single command and/or without any need to choose port numbers in an arbitrary fashion. The shared memory connector does not seem to work for my JVM.