Some uCR targets have GDB support included. To use gdb to do source-line debugging of code on your target, you will need to compile and install a cross-debugger.
The GNU debugger does not by default come with support for uCR targets, so patches are included with the uCR distribution to add the necessary target-specific details. Detailed instructions, and the mentioned patches, can be found in $UCR/source/util/gdb. The README file explains how to patch and configure your gdb source.