in Java: programmatically determining addresses of C/C++ variables given a COFF/ELF/DWARF executable

Question

This is a situation I run into now and then:

For an embedded system which does not use virtual addressing, I have an executable file that was compiled from C or C++ code with debugging information included. It's usually in COFF or ELF/DWARF (I get those two mixed up) format.

At runtime, on a PC, I would like to determine the address of a variable given its name. (e.g. "foo.bar[7].baz") This allows me to read/write the variable's value on the embedded system (given a debugging protocol that is beyond the scope of this question). Obviously, any variables that are stack-based or heap-based are out since they don't have static addresses.

I've done this before myself in C++ to parse COFF files from TI's compiler for their 2800 series DSPs, and it was kind of a pain. I was wondering if there was a Java library out there that does this sort of thing already, since I'm facing the same thing with one or two other processors' executable files.

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Update: (11/18/2009) A promising clue!

Has anyone out there used the Eclipse CDT ELF parser?

(See http://help.eclipse.org/help33/index.jsp?topic=/org.eclipse.cdt.doc.isv/reference/api/org/eclipse/cdt/core/model/IBinary.html for one of the javadoc pgs)

TI's Code Composer 4 (based on Eclipse) seems to use this, so it seems like if I can figure out where the documentation is maybe I can use that to solve my problem.

Answer 1

Does gdb support your target CPU?

If yes, your program that implements the debugging protocol and talks to the target could also implement the GDB Remote Serial Protocol and provide a TCP socket for gdb to communicate with.

The arrangement would be something like this

gdb <--gdb protocol--> java-prog <--your debug protocol--> target

To run the whole thing, assuming your target is already running your program

1. Run java-prog

2. Run gdb your-executable and connect to java-prog

   (gdb) target remote 127.0.0.1:port

3. Ask gdb to read a value

   (gdb) p foo.bar[7].baz

This is translated to gdb packets which are sent to java-prog over TCP. java-prog should do the translation between the gdb protocol and your custom debug protocol.

Answer 2

You could build a JNI interface to GNU binutils compiled for your platform. However, if the GPL conflicts with your software's license, then this will not be a viable solution.