Remove ubuntu-boot and replace with a simpler mbr

Makefile

@@ -1,69 +1,4 @@
-NONSNAP_GRUB_MODULES = \
-btrfs \
-hfsplus \
-iso9660 \
-part_apple \
-part_msdos \
-password_pbkdf2 \
-zfs \
-zfscrypt \
-zfsinfo \
-lvm \
-mdraid09 \
-mdraid1x \
-raid5rec \
-raid6rec \
-
-# filtered list of modules included in the signed EFI grub image, excluding
-# ones that we don't think are useful in snappy.
-GRUB_MODULES = \
-	all_video \
-	biosdisk \
-	boot \
-	cat \
-	chain \
-	configfile \
-	echo \
-	ext2 \
-	fat \
-	font \
-	gettext \
-	gfxmenu \
-	gfxterm \
-	gfxterm_background \
-	gzio \
-	halt \
-	jpeg \
-	keystatus \
-	loadenv \
-	loopback \
-	linux \
-	memdisk \
-	minicmd \
-	normal \
-	part_gpt \
-	png \
-	reboot \
-	regexp \
-	search \
-	search_fs_uuid \
-	search_fs_file \
-	search_label \
-	sleep \
-	squash4 \
-	test \
-	true \
-	video
-
-all:
-	dd if=/usr/lib/grub/i386-pc/boot.img of=pc-boot.img bs=440 count=1
-	/bin/echo -n -e '\x90\x90' | dd of=pc-boot.img seek=102 bs=1 conv=notrunc
-	grub-mkimage -O i386-pc -o pc-core.img -p '(,gpt2)/EFI/ubuntu' $(GRUB_MODULES)
-	# The first sector of the core image requires an absolute pointer to the
-	# second sector of the image.  Since this is always hard-coded, it means our
-	# BIOS boot partition must be defined with an absolute offset.  The
-	# particular value here is 2049, or 0x01 0x08 0x00 0x00 in little-endian.
-	/bin/echo -n -e '\x01\x08\x00\x00' | dd of=pc-core.img seek=500 bs=1 conv=notrunc
+all: mbr.img
 	# We must pull in dualsigned shim & grub with UC20 signature
 	# Do it by hand, as snapcraft doesn't have support for PPA archives yet
 	# And yet people try to rebuild this gadget snap
@@ -74,8 +9,19 @@ all:
 	cp shim/usr/lib/shim/shimx64.efi.dualsigned shim.efi.signed
 	cp grub/usr/lib/grub/x86_64-efi-signed/grubx64.efi.signed grubx64.efi
 
+legacy-bios/mbr.o: legacy-bios/mbr.s
+	gcc -Wall -O0 -c -m16 $< -o $@
+
+legacy-bios/mbr.bin: legacy-bios/mbr.o legacy-bios/mbr.ld
+	ld -melf_i386 -T legacy-bios/mbr.ld legacy-bios/mbr.o -o $@
+
+mbr.img: legacy-bios/mbr.bin
+	dd if=legacy-bios/mbr.bin of=mbr.img bs=440 count=1
+
 install:
-	install -m 644 pc-boot.img pc-core.img shim.efi.signed grubx64.efi $(DESTDIR)/
+	install -m 644 mbr.img shim.efi.signed grubx64.efi $(DESTDIR)/
 	install -m 644 grub.conf $(DESTDIR)/
 	install -d $(DESTDIR)/meta
 	install -m 644 gadget.yaml $(DESTDIR)/meta/
+
+.PHONY: install all

gadget.yaml

@@ -1,5 +1,6 @@
 volumes:
   pc:
+    schema: gpt
     # bootloader configuration is shipped and managed by snapd
     bootloader: grub
     structure:
@@ -9,21 +10,12 @@ volumes:
         update:
           edition: 1
         content:
-          - image: pc-boot.img
-      - name: BIOS Boot
-        type: DA,21686148-6449-6E6F-744E-656564454649
-        size: 1M
-        offset: 1M
-        offset-write: mbr+92
-        update:
-          edition: 2
-        content:
-          - image: pc-core.img
+          - image: mbr.img
       - name: ubuntu-seed
         role: system-seed
         filesystem: vfat
         # UEFI will boot the ESP partition by default first
-        type: EF,C12A7328-F81F-11D2-BA4B-00A0C93EC93B
+        type: C12A7328-F81F-11D2-BA4B-00A0C93EC93B
         size: 1200M
         update:
           edition: 2
@@ -37,7 +29,7 @@ volumes:
       - name: ubuntu-boot
         role: system-boot
         filesystem: ext4
-        type: 83,0FC63DAF-8483-4772-8E79-3D69D8477DE4
+        type: 0FC63DAF-8483-4772-8E79-3D69D8477DE4
         # whats the appropriate size?
         size: 750M
         update:
@@ -50,10 +42,10 @@ volumes:
       - name: ubuntu-save
         role: system-save
         filesystem: ext4
-        type: 83,0FC63DAF-8483-4772-8E79-3D69D8477DE4
+        type: 0FC63DAF-8483-4772-8E79-3D69D8477DE4
         size: 32M
       - name: ubuntu-data
         role: system-data
         filesystem: ext4
-        type: 83,0FC63DAF-8483-4772-8E79-3D69D8477DE4
+        type: 0FC63DAF-8483-4772-8E79-3D69D8477DE4
         size: 1G

legacy-bios/mbr.ld

@@ -0,0 +1,15 @@
+OUTPUT_FORMAT("binary");
+ENTRY(start);
+SECTIONS
+{
+    . = 0x7c00;
+    .text : AT(0x7c00) {
+        *(.text);
+    }
+    .data : {
+        *(.data);
+    }
+    /DISCARD/ : {
+        *(*);
+    }
+}

legacy-bios/mbr.s

@@ -0,0 +1,32 @@
+        .code16
+        .section .text
+        .globl start
+
+start:
+        jmp $0, $.entry
+.entry:
+        cli
+        xorw %ax, %ax
+        movw %ax, %ss
+        movw %ax, %ds
+        movw $0x7c00, %sp
+        sti
+        cld
+        movw $.message, %si
+.print:
+        lodsb
+        cmp $0, %al
+        je .done
+        push %si
+        movb $0xe, %ah
+        movw $0x0007, %bx
+        int $0x10
+        pop %si
+        jmp .print
+.done:
+        cli
+        hlt
+
+        .section .data
+.message:
+	.string	"Please boot in EFI mode.\r\n\0"

snapcraft.yaml

@@ -14,8 +14,6 @@ parts:
     source: .
     build-packages:
       - ubuntu-dev-tools
-      - grub-pc-bin
-      - grub-common
     plugin: make
 
 hooks: