diff --git a/sys/src/9/bcm/mkfile b/sys/src/9/bcm/mkfile
index 495dd659f..e19afe540 100644
--- a/sys/src/9/bcm/mkfile
+++ b/sys/src/9/bcm/mkfile
@@ -74,14 +74,13 @@ LIB=\
 
 9:V: $p$CONF s$p$CONF
 
-$p$CONF:DQ:	$CONF.c $OBJ $LIB mkfile
-	$CC $CFLAGS '-DKERNDATE='`{date -n} $CONF.c
+$p$CONF:DQ:	$OBJ $CONF.$O $LIB
 	echo '# linking raw kernel'	# H6: no headers, data segment aligned
-	$LD -l -o $target -H6 -R4096 -T$loadaddr $OBJ $CONF.$O $LIB
+	$LD -l -o $target -H6 -R4096 -T$loadaddr $prereq
 
-s$p$CONF:DQ:	$CONF.$O $OBJ $LIB
+s$p$CONF:DQ:	$OBJ $CONF.$O $LIB
 	echo '# linking kernel with symbols'
-	$LD -l -o $target -R4096 -T$loadaddr $OBJ $CONF.$O $LIB
+	$LD -l -o $target -R4096 -T$loadaddr $prereq
 	size $target
 
 $p$CONF.gz:D:	$p$CONF
diff --git a/sys/src/9/bcm64/mkfile b/sys/src/9/bcm64/mkfile
index 6177f4b70..4ba978899 100644
--- a/sys/src/9/bcm64/mkfile
+++ b/sys/src/9/bcm64/mkfile
@@ -69,14 +69,13 @@ LIB=\
 
 9:V: $p$CONF s$p$CONF
 
-$p$CONF:DQ:	$CONF.c $OBJ $LIB mkfile
-	$CC $CFLAGS '-DKERNDATE='`{date -n} $CONF.c
+$p$CONF:DQ:	$OBJ $CONF.$O $LIB
 	echo '# linking raw kernel'	# H6: no headers, data segment aligned
-	$LD -s -l -o $target -H6 -R0x10000 -T$loadaddr $OBJ $CONF.$O $LIB
+	$LD -s -l -o $target -H6 -R0x10000 -T$loadaddr $prereq
 
-s$p$CONF:DQ:	$CONF.$O $OBJ $LIB
+s$p$CONF:DQ:	$OBJ $CONF.$O $LIB
 	echo '# linking kernel with symbols'
-	$LD -l -o $target -R0x10000 -T$loadaddr $OBJ $CONF.$O $LIB
+	$LD -l -o $target -R0x10000 -T$loadaddr $prereq
 	size $target
 
 $p$CONF.gz:D:	$p$CONF
diff --git a/sys/src/9/cycv/mkfile b/sys/src/9/cycv/mkfile
index e9e489f3d..e0a7d913d 100644
--- a/sys/src/9/cycv/mkfile
+++ b/sys/src/9/cycv/mkfile
@@ -64,12 +64,11 @@ LIB=\
 	/$objtype/lib/libmp.a\
 	/$objtype/lib/libc.a\
 
-$p$CONF.u:D: $p$CONF
+$p$CONF.u:D:	$p$CONF
 	aux/aout2uimage $p$CONF
 
-$p$CONF:D: $CONF.c $OBJ $LIB mkfile
-	$CC $CFLAGS '-DKERNDATE='`{date -n} $CONF.c
-	$LD -o $target -T$KTZERO -l $OBJ $CONF.$O $LIB
+$p$CONF:D:	$OBJ $CONF.$O $LIB
+	$LD -o $target -T$KTZERO -l $prereq
 
 <../boot/bootmkfile
 <../port/portmkfile
diff --git a/sys/src/9/kw/mkfile b/sys/src/9/kw/mkfile
index cf3564e38..8a9b16053 100644
--- a/sys/src/9/kw/mkfile
+++ b/sys/src/9/kw/mkfile
@@ -74,16 +74,13 @@ LIB=\
 
 9:V: $p$CONF s$p$CONF
 
-$p$CONF:DQ:	$CONF.c $OBJ $LIB mkfile
-	$CC $CFLAGS '-DKERNDATE='`{date -n} $CONF.c
+$p$CONF:DQ:	$OBJ $CONF.$O $LIB
 	echo '# linking raw kernel'
-#	sleep 1				# avoid relinking later
-	$LD -o $target -H0 -R4096 -T$loadaddr -l $OBJ $CONF.$O $LIB
+	$LD -o $target -H0 -R4096 -T$loadaddr -l $prereq
 
-s$p$CONF:DQ:	$CONF.$O $OBJ $LIB
+s$p$CONF:DQ:	$OBJ $CONF.$O $LIB
 	echo '# linking kernel with symbols'
-#	sleep 1				# avoid relinking later
-	$LD -o $target -R4096 -T$loadaddr -l $OBJ $CONF.$O $LIB
+	$LD -o $target -R4096 -T$loadaddr -l $prereq
 	size $target
 
 $p$CONF.gz:D:	$p$CONF
diff --git a/sys/src/9/mtx/mkfile b/sys/src/9/mtx/mkfile
index 797e96091..6dd9ba614 100644
--- a/sys/src/9/mtx/mkfile
+++ b/sys/src/9/mtx/mkfile
@@ -66,9 +66,8 @@ SDEV=`{echo devsd.c sd*.c | sed 's/\.c/.'$O'/g'}
 
 loadaddr = 0x80004020
 
-$p$CONF:	$CONF.c $OBJ $LIB
-	$CC $CFLAGS '-DKERNDATE='`{date -n} $CONF.c
-	$LD -R4 -o $target -T$loadaddr -l $OBJ $CONF.$O $LIB
+$p$CONF:	$OBJ $CONF.$O $LIB
+	$LD -R4 -o $target -T$loadaddr -l $prereq
 	ls -l $target
 
 install:V: $p$CONF
diff --git a/sys/src/9/omap/mkfile b/sys/src/9/omap/mkfile
index b3a359f2b..618e80e19 100644
--- a/sys/src/9/omap/mkfile
+++ b/sys/src/9/omap/mkfile
@@ -70,15 +70,13 @@ LIB=\
 
 9:V: $p$CONF s$p$CONF
 
-$p$CONF:DQ:	$CONF.c $OBJ $LIB mkfile
-	$CC $CFLAGS '-DKERNDATE='`{date -n} $CONF.c
+$p$CONF:DQ:	$OBJ $CONF.$O $LIB
 	echo '# linking raw kernel'
-	$LD -o $target -H0 -R4096 -T$loadaddr -l $OBJ $CONF.$O $LIB
+	$LD -o $target -H0 -R4096 -T$loadaddr -l $prereq
 
-s$p$CONF:DQ:	$CONF.$O $OBJ $LIB
+s$p$CONF:DQ:	$OBJ $CONF.$O $LIB
 	echo '# linking kernel with symbols'
-#	$LD -o $target -R4096 -T$loadaddr -l -a $OBJ $CONF.$O $LIB >$target.list
-	$LD -o $target -R4096 -T$loadaddr -l $OBJ $CONF.$O $LIB
+	$LD -o $target -R4096 -T$loadaddr -l $prereq
 	size $target
 
 $p$CONF.gz:D:	$p$CONF
diff --git a/sys/src/9/pc/mkfile b/sys/src/9/pc/mkfile
index 90670cb30..ea3fd9513 100644
--- a/sys/src/9/pc/mkfile
+++ b/sys/src/9/pc/mkfile
@@ -76,9 +76,8 @@ AUDIO=`{echo devaudio.c audio*.c | sed 's/\.c/.'$O'/g'}
 VGA=`{echo devvga.c screen.c vga*.c | sed 's/\.c/.'$O'/g'}
 SDEV=`{echo devsd.c sd*.c | sed 's/\.c/.'$O'/g'}
 
-$p$CONF:	$CONF.c $OBJ $LIB
-	$CC $CFLAGS '-DKERNDATE='`{date -n} $CONF.c
-	$LD -o $target -T$KTZERO -l $OBJ $CONF.$O $LIB
+$p$CONF:	$OBJ $CONF.$O $LIB
+	$LD -o $target -T$KTZERO -l $prereq
 	size $target
 
 # don't strip the gzipped kernels -- too frustrating when that's all you have!
diff --git a/sys/src/9/pc64/mkfile b/sys/src/9/pc64/mkfile
index 034ae6717..fad11b825 100644
--- a/sys/src/9/pc64/mkfile
+++ b/sys/src/9/pc64/mkfile
@@ -74,9 +74,8 @@ AUDIO=`{cd ../pc; echo devaudio.c audio*.c | sed 's/\.c/.'$O'/g'}
 VGA=`{cd ../pc; echo devvga.c screen.c vga*.c | sed 's/\.c/.'$O'/g'}
 SDEV=`{cd ../pc; echo devsd.c sd*.c | sed 's/\.c/.'$O'/g'}
 
-$p$CONF:	$CONF.c $OBJ $LIB
-	$CC $CFLAGS '-DKERNDATE='`{date -n} $CONF.c
-	$LD -o $target -T$KTZERO -R4096 -l $OBJ $CONF.$O $LIB
+$p$CONF:	$OBJ $CONF.$O $LIB
+	$LD -o $target -T$KTZERO -R4096 -l $prereq
 	size $target
 
 install:V:	$p$CONF
diff --git a/sys/src/9/port/portmkfile b/sys/src/9/port/portmkfile
index d9beaf144..5e88150c7 100644
--- a/sys/src/9/port/portmkfile
+++ b/sys/src/9/port/portmkfile
@@ -42,13 +42,13 @@ nuke:V:	clean
 
 %.$O:	/$objtype/include/u.h ../port/lib.h mem.h dat.h fns.h io.h ../port/error.h ../port/portdat.h ../port/portfns.h
 
-../port/systab.h:	/sys/src/libc/9syscall/sys.h ../port/mksystab
+../port/systab.h:D:	/sys/src/libc/9syscall/sys.h ../port/mksystab
 	rc ../port/mksystab > ../port/systab.h
 
-$CONF.$O:	$CONF.c
+$CONF.$O:	$CONF.c $OBJ $LIB
 	$CC $CFLAGS '-DKERNDATE='`{date -n} $CONF.c
 
-$CONF.c:	../port/mkdevc $CONF
+$CONF.c:D:	../port/mkdevc $CONF
 	rc ../port/mkdevc $CONF > $CONF.c
 	{echo 'uchar configfile[]={'
 	 xd -1x $CONF |
@@ -59,13 +59,13 @@ $CONF.c:	../port/mkdevc $CONF
 errstr.h:D:	../port/mkerrstr ../port/error.h
 	rc ../port/mkerrstr > errstr.h
 
-%.i:	%.out
+%.i:D:	%.out
 	{echo 'uchar '^$stem^'[]={'
 	 xd -1x <$stem.out |
 		sed -e 's/^[0-9a-f]+ //' -e 's/ ([0-9a-f][0-9a-f])/0x\1,/g'
 	 echo '};'} > $target
 
-%.db:		main.$O
+%.db:D:	main.c
 	$CC -s$stem main.c | dbfmt > $stem.db
 
 alloc.$O ucalloc.$O devswap.$O devproc.$O:	/sys/include/pool.h
diff --git a/sys/src/9/ppc/mkfile b/sys/src/9/ppc/mkfile
index 8891f94e5..424380e57 100644
--- a/sys/src/9/ppc/mkfile
+++ b/sys/src/9/ppc/mkfile
@@ -72,14 +72,12 @@ AFLAGS=$AFLAGS -D$CONF'conf='$CONF
 
 it:V: $p$CONF
 
-9blast:	$CONF.c $OBJ $LIB
-	$CC $CFLAGS '-DKERNDATE='`{date -n} $CONF.c
-	$LD -o $target -T$loadaddr -R4096 -l $OBJ $CONF.$O $LIB
-	size $p$CONF
+9blast:	$OBJ $CONF.$O $LIB
+	$LD -o $target -T$loadaddr -R4096 -l $prereq
+	size $target
 
-9ucu:	$CONF.c $OBJ $LIB
-	$CC $CFLAGS '-DKERNDATE='`{date -n} $CONF.c
-	$LD -R0x1000 -H5 -o $target -T$loadaddr -l $OBJ $CONF.$O $LIB
+9ucu:	$OBJ $CONF.$O $LIB
+	$LD -R0x1000 -H5 -o $target -T$loadaddr -l $prereq
 
 install:V: $p$CONF
 	cp $p$CONF /$objtype/$p$CONF
diff --git a/sys/src/9/sgi/mkfile b/sys/src/9/sgi/mkfile
index ff0ea189f..f7cdcbfc7 100644
--- a/sys/src/9/sgi/mkfile
+++ b/sys/src/9/sgi/mkfile
@@ -68,9 +68,8 @@ LIB=\
 	/$objtype/lib/libip.a\
 	/$objtype/lib/libc.a\
 
-$p$CONF:	$OBJ $CONF.c $LIB
-	$CC $CFLAGS '-DKERNDATE='`{date -n} $CONF.c
-	$LD -o $target -l -R8 -H3 -T$KTZERO $OBJ $CONF.$O $LIB
+$p$CONF:	$OBJ $CONF.$O $LIB
+	$LD -o $target -l -R8 -H3 -T$KTZERO $prereq
 	size $target
 
 install:V:	$p$CONF
diff --git a/sys/src/9/teg2/mkfile b/sys/src/9/teg2/mkfile
index 6ea2c9894..aaa484e56 100644
--- a/sys/src/9/teg2/mkfile
+++ b/sys/src/9/teg2/mkfile
@@ -83,15 +83,13 @@ LIB=\
 
 9:V: $p$CONF s$p$CONF
 
-$p$CONF:DQ:	$CONF.c $OBJ $LIB mkfile
-	$CC $CFLAGS '-DKERNDATE='`{date -n} $CONF.c
+$p$CONF:DQ:	$OBJ $CONF.$O $LIB
 	echo '# linking raw kernel'	# H6: no headers, data segment aligned
-	$LD -o $target -H6 -R4096 -T$loadaddr -l $OBJ $CONF.$O $LIB
+	$LD -o $target -H6 -R4096 -T$loadaddr -l $prereq
 
-s$p$CONF:DQ:	$CONF.$O $OBJ $LIB
+s$p$CONF:DQ:	$OBJ $CONF.$O $LIB
 	echo '# linking 9 kernel with symbols'
-#	$LD -o $target -R4096 -T$loadaddr -l -a $OBJ $CONF.$O $LIB >$target.list
-	$LD -o $target -R4096 -T$loadaddr -l $OBJ $CONF.$O $LIB
+	$LD -o $target -R4096 -T$loadaddr -l $prereq
 	size $target
 
 $p$CONF.gz:D:	$p$CONF
diff --git a/sys/src/9/xen/mkfile b/sys/src/9/xen/mkfile
index 9fc3131a7..21e4b2dd1 100644
--- a/sys/src/9/xen/mkfile
+++ b/sys/src/9/xen/mkfile
@@ -93,19 +93,13 @@ SDEV=`{echo devsd.c sd*.c | sed 's/\.c/.'$O'/g'}
 PAE=`{echo $PAE | sed 's/yes/yes[extended-cr3]/'}
 XENELF='LOADER=generic,XEN_VER=xen-3.0,ELF_PADDR_OFFSET=0,VIRT_BASE='$KZERO',VIRT_ENTRY='$KTZERO',PAE='$PAE
 
-#$p$CONF:	$CONF.c $OBJ $LIB xenbin.$cputype
-#	$CC $CFLAGS '-DKERNDATE='`{date -n} $CONF.c
-#	$LD -o $target.tmp -T$KTZERO -l $OBJ $CONF.$O $LIB
-#	./xenbin.$cputype <$target.tmp >$target
-#	rm $target.tmp
-#	size $target
-
-$p$CONF:	$CONF.c $OBJ $LIB xenelf.$cputype
-	$CC $CFLAGS '-DKERNDATE='`{date -n} $CONF.c
-	$LD -o $target.elf -H5 -T$KTZERO -P$KPZERO -l $OBJ $CONF.$O $LIB
-	./xenelf.$cputype $target.elf $target __xen_guest ''$XENELF''
+$p$CONF:D:	$p$CONF.elf xenelf.$cputype
+	./xenelf.$cputype $prereq(1) $target __xen_guest ''$XENELF''
 	size $target
 
+$p$CONF.elf:D:	$OBJ $CONF.$O $LIB
+	$LD -o $target -H5 -T$KTZERO -P$KPZERO -l $prereq
+
 $p$CONF.gz: $p$CONF
 	#strip -o /fd/1 $p$CONF | gzip -9 > $p$CONF.gz
 	gzip -9 $p$CONF > $p$CONF.gz
diff --git a/sys/src/9/zynq/mkfile b/sys/src/9/zynq/mkfile
index 999d0ea2b..e71ccb6a0 100644
--- a/sys/src/9/zynq/mkfile
+++ b/sys/src/9/zynq/mkfile
@@ -64,9 +64,8 @@ LIB=\
 	/$objtype/lib/libmp.a\
 	/$objtype/lib/libc.a\
 
-$p$CONF:D: $CONF.c $OBJ $LIB mkfile
-	$CC $CFLAGS '-DKERNDATE='`{date -n} $CONF.c
-	$LD -o $target -T$KTZERO -l $OBJ $CONF.$O $LIB
+$p$CONF:D:	$OBJ $CONF.$O $LIB
+	$LD -o $target -T$KTZERO -l $prereq
 
 <../boot/bootmkfile
 <../port/portmkfile