Index: sys/boot/efi/boot1/Makefile
===================================================================
--- sys/boot/efi/boot1/Makefile
+++ sys/boot/efi/boot1/Makefile
@@ -139,7 +139,7 @@
 	uudecode ${.CURDIR}/fat-${MACHINE}.tmpl.bz2.uu
 	mv fat-${MACHINE}.tmpl.bz2 ${.TARGET}.bz2
 	bzip2 -f -d ${.TARGET}.bz2
-	${DD} if=${.ALLSRC} of=${.TARGET} seek=${BOOT1_OFFSET} conv=notrunc
+	${DD} if=${.ALLSRC} of=${.TARGET} seek=${BOOT1_${MACHINE}_OFFSET} conv=notrunc
 
 CLEANFILES= boot1.efi boot1.efifat
 
Index: sys/boot/efi/boot1/Makefile.fat
===================================================================
--- sys/boot/efi/boot1/Makefile.fat
+++ sys/boot/efi/boot1/Makefile.fat
@@ -1,4 +1,7 @@
 # This file autogenerated by generate-fat.sh - DO NOT EDIT
 # $FreeBSD$
-BOOT1_OFFSET=0x2d
 BOOT1_MAXSIZE=131072
+BOOT1_amd64_OFFSET=0x2d
+BOOT1_arm64_OFFSET=0x2d
+BOOT1_arm_OFFSET=0x2d
+BOOT1_i386_OFFSET=0x2d
Index: sys/boot/efi/boot1/generate-fat.sh
===================================================================
--- sys/boot/efi/boot1/generate-fat.sh
+++ sys/boot/efi/boot1/generate-fat.sh
@@ -15,48 +15,11 @@
 
 BOOT1_SIZE=128k
 
-#
-# Known filenames
-# amd64:   BOOTx64.efi
-# arm64:   BOOTaa64.efi
-# arm:     BOOTarm.efi
-# i386:    BOOTia32.efi
-#
-if [ -z "$2" ]; then
-	echo "Usage: $0 arch boot-filename"
+if [ $(id -u) != 0 ]; then
+	echo "${0##*/}: must run as root" >&2
 	exit 1
 fi
 
-ARCH=$1
-FILENAME=$2
-
-# Generate 800K FAT image
-OUTPUT_FILE=fat-${ARCH}.tmpl
-
-dd if=/dev/zero of=$OUTPUT_FILE bs=512 count=$FAT_SIZE
-DEVICE=`mdconfig -a -f $OUTPUT_FILE`
-newfs_msdos -F 12 -L EFI $DEVICE
-mkdir stub
-mount -t msdosfs /dev/$DEVICE stub
-
-# Create and bless a directory for the boot loader
-mkdir -p stub/efi/boot
-
-# Make a dummy file for boot1
-echo 'Boot1 START' | dd of=stub/efi/boot/$FILENAME cbs=$BOOT1_SIZE count=1 conv=block
-# Provide a fallback startup.nsh
-echo $FILENAME > stub/efi/boot/startup.nsh
-
-umount stub
-mdconfig -d -u $DEVICE
-rmdir stub
-
-# Locate the offset of the fake file
-BOOT1_OFFSET=$(hd $OUTPUT_FILE | grep 'Boot1 START' | cut -f 1 -d ' ')
-
-# Convert to number of blocks
-BOOT1_OFFSET=$(echo 0x$BOOT1_OFFSET | awk '{printf("%x\n",$1/512);}')
-
 # Record maximum boot1 size in bytes
 case $BOOT1_SIZE in
 *k)
@@ -69,14 +32,47 @@
 
 echo '# This file autogenerated by generate-fat.sh - DO NOT EDIT' > Makefile.fat
 echo "# \$FreeBSD\$" >> Makefile.fat
-echo "BOOT1_OFFSET=0x$BOOT1_OFFSET" >> Makefile.fat
 echo "BOOT1_MAXSIZE=$BOOT1_MAXSIZE" >> Makefile.fat
 
-bzip2 $OUTPUT_FILE
-echo 'FAT template boot filesystem created by generate-fat.sh' > $OUTPUT_FILE.bz2.uu
-echo 'DO NOT EDIT' >> $OUTPUT_FILE.bz2.uu
-echo "\$FreeBSD\$" >> $OUTPUT_FILE.bz2.uu
-
-uuencode $OUTPUT_FILE.bz2 $OUTPUT_FILE.bz2 >> $OUTPUT_FILE.bz2.uu
-rm $OUTPUT_FILE.bz2
-
+while read ARCH FILENAME; do
+	# Generate 800K FAT image
+	OUTPUT_FILE=fat-${ARCH}.tmpl
+
+	dd if=/dev/zero of=$OUTPUT_FILE bs=512 count=$FAT_SIZE
+	DEVICE=`mdconfig -a -f $OUTPUT_FILE`
+	newfs_msdos -F 12 -L EFI $DEVICE
+	mkdir stub
+	mount -t msdosfs /dev/$DEVICE stub
+
+	# Create and bless a directory for the boot loader
+	mkdir -p stub/efi/boot
+
+	# Make a dummy file for boot1
+	echo 'Boot1 START' | dd of=stub/efi/boot/$FILENAME cbs=$BOOT1_SIZE count=1 conv=block
+	# Provide a fallback startup.nsh
+	echo $FILENAME > stub/efi/boot/startup.nsh
+
+	umount stub
+	mdconfig -d -u $DEVICE
+	rmdir stub
+
+	# Locate the offset of the fake file
+	BOOT1_OFFSET=$(hd $OUTPUT_FILE | grep 'Boot1 START' | cut -f 1 -d ' ')
+
+	# Convert to number of blocks
+	BOOT1_OFFSET=$(echo 0x$BOOT1_OFFSET | awk '{printf("%x\n",$1/512);}')
+	echo "BOOT1_${ARCH}_OFFSET=0x$BOOT1_OFFSET" >> Makefile.fat
+
+	bzip2 $OUTPUT_FILE
+	echo 'FAT template boot filesystem created by generate-fat.sh' > $OUTPUT_FILE.bz2.uu
+	echo 'DO NOT EDIT' >> $OUTPUT_FILE.bz2.uu
+	echo "\$FreeBSD\$" >> $OUTPUT_FILE.bz2.uu
+
+	uuencode $OUTPUT_FILE.bz2 $OUTPUT_FILE.bz2 >> $OUTPUT_FILE.bz2.uu
+	rm $OUTPUT_FILE.bz2
+done <<EOF
+	amd64	BOOTx64.efi
+	arm64	BOOTaa64.efi
+	arm	BOOTarm.efi
+	i386	BOOTia32.efi
+EOF