=====================================================================
Addition of the kernel option KDTRACE_HOOKS which is required in order to be able to load the 'dtrace' kernel module.
---------------------------------------------------------------------
--- /u/freebsd/head/src/sys/conf/NOTES	2008-05-23 09:04:19.000000000 +1000
+++ /u/p4/dtrace/src/sys/conf/NOTES	2008-05-23 09:02:02.000000000 +1000
@@ -358,6 +358,12 @@
 options 	GDB
 
 #
+# Enable the kernel DTrace hooks which are required to load the DTrace
+# kernel modules.
+#
+options 	KDTRACE_HOOKS
+
+#
 # SYSCTL_DEBUG enables a 'sysctl' debug tree that can be used to dump the
 # contents of the registered sysctl nodes on the console.  It is disabled by
 # default because it generates excessively verbose console output that can
=====================================================================
Add kern_dtrace.c which contains the struct proc and struct thread memory allocation and deallocation if the KDTRACE_HOOKS kernel option is defined.
---------------------------------------------------------------------
--- /u/freebsd/head/src/sys/conf/files	2008-05-21 07:25:51.000000000 +1000
+++ /u/p4/dtrace/src/sys/conf/files	2008-05-21 07:27:18.000000000 +1000
@@ -1632,6 +1632,7 @@
 kern/kern_linker.c		standard
 kern/kern_lock.c		standard
 kern/kern_lockf.c		standard
+kern/kern_lockstat.c		optional kdtrace_hooks
 kern/kern_malloc.c		standard
 kern/kern_mbuf.c		standard
 kern/kern_mib.c			standard