Index: head/sys/conf/NOTES
===================================================================
--- head/sys/conf/NOTES
+++ head/sys/conf/NOTES
@@ -1078,6 +1078,14 @@
 
 # Make space in the kernel for a root filesystem on a md device.
 # Define to the number of kilobytes to reserve for the filesystem.
+# This is now optional.
+# If not defined, the root filesystem passed in as the MFS_IMAGE makeoption
+# will be automatically embedded in the kernel during linking. Its exact size
+# will be consumed within the kernel.
+# If defined, the old way of embedding the filesystem in the kernel will be
+# used. That is to say MD_ROOT_SIZE KB will be allocated in the kernel and
+# later, the filesystem image passed in as the MFS_IMAGE makeoption will be
+# dd'd into the reserved space if it fits.
 options 	MD_ROOT_SIZE=10
 
 # Make the md device a potential root device, either with preloaded
Index: head/sys/conf/kern.post.mk
===================================================================
--- head/sys/conf/kern.post.mk
+++ head/sys/conf/kern.post.mk
@@ -130,6 +130,9 @@
 	@rm -f ${.TARGET}
 	@echo linking ${.TARGET}
 	${SYSTEM_LD}
+.if !empty(MD_ROOT_SIZE_CONFIGURED) && defined(MFS_IMAGE)
+	@sh ${S}/tools/embed_mfs.sh ${.TARGET} ${MFS_IMAGE}
+.endif
 .if ${MK_CTF} != "no"
 	@echo ${CTFMERGE} ${CTFFLAGS} -o ${.TARGET} ...
 	@${CTFMERGE} ${CTFFLAGS} -o ${.TARGET} ${SYSTEM_OBJS} vers.o
@@ -353,6 +356,7 @@
 	${AWK} -f $S/tools/vnode_if.awk $S/kern/vnode_if.src -q
 
 .if ${MFS_IMAGE:Uno} != "no"
+.if empty(MD_ROOT_SIZE_CONFIGURED)
 # Generate an object file from the file system image to embed in the kernel
 # via linking. Make sure the contents are in the mfs section and rename the
 # start/end/size variables to __start_mfs, __stop_mfs, and mfs_size,
@@ -372,6 +376,7 @@
 		_binary_${MFS_IMAGE:C,[^[:alnum:]],_,g}_end=mfs_root_end \
 	    ${.TARGET}
 .endif
+.endif
 
 # XXX strictly, everything depends on Makefile because changes to ${PROF}
 # only appear there, but we don't handle that.
Index: head/sys/conf/kern.pre.mk
===================================================================
--- head/sys/conf/kern.pre.mk
+++ head/sys/conf/kern.pre.mk
@@ -195,9 +195,13 @@
 SYSTEM_OBJS= locore.o ${MDOBJS} ${OBJS}
 SYSTEM_OBJS+= ${SYSTEM_CFILES:.c=.o}
 SYSTEM_OBJS+= hack.So
+
+MD_ROOT_SIZE_CONFIGURED!=	grep MD_ROOT_SIZE opt_md.h || true ; echo
 .if ${MFS_IMAGE:Uno} != "no"
+.if empty(MD_ROOT_SIZE_CONFIGURED)
 SYSTEM_OBJS+= embedfs_${MFS_IMAGE:T:R}.o
 .endif
+.endif
 SYSTEM_LD= @${LD} -Bdynamic -T ${LDSCRIPT} ${_LDFLAGS} --no-warn-mismatch \
 	--warn-common --export-dynamic --dynamic-linker /red/herring \
 	-o ${.TARGET} -X ${SYSTEM_OBJS} vers.o
@@ -230,8 +234,9 @@
 
 # Architecture and output format arguments for objdump to convert image to
 # object file
-.if ${MFS_IMAGE:Uno} != "no"
 
+.if ${MFS_IMAGE:Uno} != "no"
+.if empty(MD_ROOT_SIZE_CONFIGURED)
 .if !defined(EMBEDFS_FORMAT.${MACHINE_ARCH})
 EMBEDFS_FORMAT.${MACHINE_ARCH}!= awk -F'"' '/OUTPUT_FORMAT/ {print $$2}' ${LDSCRIPT}
 .if empty(EMBEDFS_FORMAT.${MACHINE_ARCH})
@@ -254,6 +259,7 @@
 EMBEDFS_FORMAT.mips64el?=	elf64-tradlittlemips
 EMBEDFS_FORMAT.riscv?=		elf64-littleriscv
 .endif
+.endif
 
 # Detect kernel config options that force stack frames to be turned on.
 DDB_ENABLED!=	grep DDB opt_ddb.h || true ; echo
Index: head/sys/dev/md/md.c
===================================================================
--- head/sys/dev/md/md.c
+++ head/sys/dev/md/md.c
@@ -130,18 +130,12 @@
  */
 #if defined(MD_ROOT_SIZE)
 /*
+ * We put the mfs_root symbol into the oldmfs section of the kernel object file.
  * Applications that patch the object with the image can determine
- * the size looking at the start and end markers (strings),
- * so we want them contiguous.
+ * the size looking at the oldmfs section size within the kernel.
  */
-static struct {
-	u_char start[MD_ROOT_SIZE*1024];
-	u_char end[128];
-} mfs_root = {
-	.start = "MFS Filesystem goes here",
-	.end = "MFS Filesystem had better STOP here",
-};
-const int mfs_root_size = sizeof(mfs_root.start);
+u_char mfs_root[MD_ROOT_SIZE*1024] __attribute__ ((section ("oldmfs")));
+const int mfs_root_size = sizeof(mfs_root);
 #else
 extern volatile u_char __weak_symbol mfs_root;
 extern volatile u_char __weak_symbol mfs_root_end;
Index: head/sys/tools/embed_mfs.sh
===================================================================
--- head/sys/tools/embed_mfs.sh
+++ head/sys/tools/embed_mfs.sh
@@ -32,8 +32,20 @@
 # $2: MFS image filename
 #
 
-obs=`strings -at d $1 | grep "MFS Filesystem goes here" | awk '{print $1}'`
-dd if=$2 ibs=8192 of=$1 obs=${obs} oseek=1 conv=notrunc 2> /dev/null
+mfs_size=`stat -f '%z' $2 2> /dev/null`
+# If we can't determine MFS image size - bail.
+[ -z ${mfs_size} ] && echo "Can't determine MFS image size" && exit 1
 
-strings $1 | grep 'MFS Filesystem had better STOP here' > /dev/null || \
-	(rm $1 && echo "MFS image too large" && false)
+sec_info=`objdump -h $1 2> /dev/null | grep " oldmfs "`
+# If we can't find the mfs section within the given kernel - bail.
+[ -z "${sec_info}" ] && echo "Can't locate mfs section within kernel" && exit 1
+
+sec_size=`echo ${sec_info} | awk '{printf("%d", "0x" $3)}' 2> /dev/null`
+sec_start=`echo ${sec_info} | awk '{printf("%d", "0x" $6)}' 2> /dev/null`
+
+# If the mfs section size is smaller than the mfs image - bail.
+[ ${sec_size} -lt ${mfs_size} ] && echo "MFS image too large" && exit 1
+
+# Dump the mfs image into the mfs section
+dd if=$2 ibs=8192 of=$1 obs=${sec_start} oseek=1 conv=notrunc 2> /dev/null && \
+    echo "MFS image embedded into kernel" && exit 0