The x-kernel uses a trace package to generate debugging information. To enable the tracing facility, edit the Makefile to set HOWTOCOMPILE to DEBUG; tracing can be disabled by setting HOWTOCOMPILE to OPTIMIZE. Then type make. See also section 8.
If you are interested in accurate performance timings, you should set HOWTOCOMPILE to OPTIMIZE in the Makefile. This causes all trace of tracing code to be eliminated from the kernel.