This is a small multiboot application that you can upload to your GBA using an xboo cable and xboo communicator and have the GamePak's ROM dumped to a file on a machine running xboo communicator. It works with both Linux and Windows, and should work with any platform that the xboo communicator software gets ported to. yay!
Note that I haven't implemented the GamePak size detection code yet, and by default it will dump 32mbits. If you need to dump more edit the source code and edit the value returned by detect_size. 32mbits should be enough to dump the start of a flashcart for reverse engineering however,.. the reason I coded this.
The filename used is extracted from the header in the ROM,.. you should see this in the output from xboo communicator.
A tarball with the sourcecode and compiled application can be downloaded here, please note that although there is currently no license information in the tarball, it's GPL.