Index: head/share/mk/bsd.dtb.mk
===================================================================
--- head/share/mk/bsd.dtb.mk
+++ head/share/mk/bsd.dtb.mk
@@ -1,22 +1,6 @@
 # $FreeBSD$
 
-# Search for kernel source tree in standard places.
-.if empty(KERNBUILDDIR)
-.if !defined(SYSDIR)
-.for _dir in ${SRCTOP:D${SRCTOP}/sys} \
-    ${.CURDIR}/../.. ${.CURDIR}/../../.. ${.CURDIR}/../../../.. \
-    ${.CURDIR}/../../../../.. /sys /usr/src/sys
-.if !defined(SYSDIR) && exists(${_dir}/kern/) && exists(${_dir}/conf/kmod.mk)
-SYSDIR=	${_dir}
-.endif
-.endfor
-.endif
-.if !defined(SYSDIR) || !exists(${SYSDIR}/kern/) || \
-    !exists(${SYSDIR}/conf/kmod.mk)
-.error Unable to locate the kernel source tree. Set SYSDIR to override.
-.endif
-.endif
-
+.include <bsd.sysdir.mk>
 .include "${SYSDIR}/conf/dtb.mk"
 
 .include <bsd.sys.mk>
Index: head/share/mk/bsd.kmod.mk
===================================================================
--- head/share/mk/bsd.kmod.mk
+++ head/share/mk/bsd.kmod.mk
@@ -1,20 +1,4 @@
 # $FreeBSD$
 
-# Search for kernel source tree in standard places.
-.if empty(KERNBUILDDIR)
-.if !defined(SYSDIR)
-.for _dir in ${SRCTOP:D${SRCTOP}/sys} \
-    ${.CURDIR}/../.. ${.CURDIR}/../../.. ${.CURDIR}/../../../.. \
-    ${.CURDIR}/../../../../.. /sys /usr/src/sys
-.if !defined(SYSDIR) && exists(${_dir}/kern/) && exists(${_dir}/conf/kmod.mk)
-SYSDIR=	${_dir:tA}
-.endif
-.endfor
-.endif
-.if !defined(SYSDIR) || !exists(${SYSDIR}/kern/) || \
-    !exists(${SYSDIR}/conf/kmod.mk)
-.error Unable to locate the kernel source tree. Set SYSDIR to override.
-.endif
-.endif
-
+.include <bsd.sysdir.mk>
 .include "${SYSDIR}/conf/kmod.mk"
Index: head/share/mk/bsd.sysdir.mk
===================================================================
--- head/share/mk/bsd.sysdir.mk
+++ head/share/mk/bsd.sysdir.mk
@@ -0,0 +1,16 @@
+# $FreeBSD$
+
+# Search for kernel source tree in standard places.
+.if !defined(SYSDIR)
+.for _dir in ${SRCTOP:D${SRCTOP}/sys} \
+    ${.CURDIR}/../.. ${.CURDIR}/../../.. ${.CURDIR}/../../../.. \
+    ${.CURDIR}/../../../../.. /sys /usr/src/sys
+.if !defined(SYSDIR) && exists(${_dir}/kern/) && exists(${_dir}/conf/kmod.mk)
+SYSDIR=	${_dir:tA}
+.endif
+.endfor
+.endif
+.if !defined(SYSDIR) || !exists(${SYSDIR}/kern/) || \
+    !exists(${SYSDIR}/conf/kmod.mk)
+.error Unable to locate the kernel source tree. Set SYSDIR to override.
+.endif
Index: head/sys/conf/dtb.build.mk
===================================================================
--- head/sys/conf/dtb.build.mk
+++ head/sys/conf/dtb.build.mk
@@ -11,12 +11,7 @@
 .if defined(S)
 SYSDIR=	${S}
 .else
-# Search for kernel source tree in standard places.
-.for _dir in ${.CURDIR}/../.. ${.CURDIR}/../../.. /sys /usr/src/sys
-.if exists(${_dir}/kern/)
-SYSDIR=	${_dir:tA}
-.endif
-.endfor
+.include <bsd.sysdir.mk>
 .endif	# defined(S)
 .endif	# defined(SYSDIR)
 
Index: head/sys/conf/kmod.mk
===================================================================
--- head/sys/conf/kmod.mk
+++ head/sys/conf/kmod.mk
@@ -79,21 +79,7 @@
 .include "kern.opts.mk"
 .include <bsd.compiler.mk>
 .include "config.mk"
-
-# Search for kernel source tree in standard places.
-.if empty(KERNBUILDDIR)
-.if !defined(SYSDIR)
-.for _dir in ${SRCTOP:D${SRCTOP}/sys} \
-    ${.CURDIR}/../.. ${.CURDIR}/../../.. /sys /usr/src/sys
-.if !defined(SYSDIR) && exists(${_dir}/kern/)
-SYSDIR=	${_dir:tA}
-.endif
-.endfor
-.endif
-.if !defined(SYSDIR) || !exists(${SYSDIR}/kern/)
-.error "can't find kernel source tree"
-.endif
-.endif
+.include <bsd.sysdir.mk>
 
 .SUFFIXES: .out .o .c .cc .cxx .C .y .l .s .S .m