Xkdebug (current release 951016) is a modification to David Hinds’s kdebug-1.2 allowing breakpoints and single-stepping in a Linux source-level kernel-debugger.
My version is incredibly old (for linux-1.3.30), but old source code (tar.gz, 28KB) is available. See the README file for more information. I’m not currently doing Linux kernel programming and so I’m not maintaining xkdebug.
A new version (tar.gz, 12KB) for linux-2.1.55 was sent to me from Keith Owens <kaos@ocs.com.au>. I haven’t been able to test it, but you might try it if you have a non-ancient Linux setup.
As of 25-Mar-98, Keith Owens has rolled xkdebug into his ikd package (Integrated Kernel Debugging) available from ftp://ftp.ocs.com.au/pub (as of March, version 2.1.84 is his most recent).