Kerninst is a framework for dynamically splicing code into a running kernel, almost anywhere, anytime. Code can be removed and changed at will. Kerninst works on standard (unmodified) Solaris and Linux kernels, no kernel re-compilation is necessary. The framework includes an instrumentation daemon (kerninstd) and a kernel module (/dev/kerninst) both running on the host whose kernel is to be instrumented.
For details, see http://www.paradyn.org/projects/legacy/kerninst/.