grub: add host support

This part is intended as a hint to people trying to use buildroot for embedded x86 targets in the hope it helps. Included here is a reference shell script that doesn't require root privileges, which you can use as a template for your own projects :

This change makes it possible to use a grub executable built for the host to install the boot loader inside an image. It's also a hack to make it possible to work around x86_64 issues, as long as the user has 32-bits libraries available to his native toolchain.

-- Informative part --

This change alone doesn't mean you'll have grub magically installed in your rootfs. First, legacy grub apparently requires a partition table to mount file systems. You must work around this limitation yourself. Then, it requires crafting the file system so that grub stuff is provided at the proper location (e.g. in boot/grub inside your rootfs). On x86_64 systems, the target grub simply doesn't build, so you'll need to build host-grub manually and, for example, make your post-build script do anything necessary so that the host grub is able to setup the boot loader on your disk image.

This part is intended as a hint to people trying to use buildroot for embedded x86 targets in the hope it helps. Included here is a reference shell script that doesn't require root privileges, which you can use as a template for your own projects :

set -e

CF_SIZE=1024966656 # 1024 MB
CF_BOOT_SIZE=8388608 # 8 MiB
CF_HPC=16 # Heads per cylinder
CF_SPT=63 # Sectors per track

IMAGES_DIR="output/images"
KERNEL_IMG="$IMAGES_DIR/bzImage"
CF_IMG="$IMAGES_DIR/cf.img"
BOOT_DIR="output/target_boot"
BOOT_IMG="$IMAGES_DIR/bootfs.ext2"
ROOTFS_IMG="$IMAGES_DIR/rootfs.squashfs"

HOST_DIR="output/host"
SFDISK="$HOST_DIR/usr/sbin/sfdisk"
GENEXT2FS="$HOST_DIR/usr/bin/genext2fs"
E2FSCK="$HOST_DIR/usr/sbin/e2fsck"
GRUB="$HOST_DIR/usr/sbin/grub"

rm -f $CF_IMG $BOOT_IMG

make host-util-linux host-genext2fs host-e2fsprogs host-grub

echo

cf_boot_start=64 cf_boot_size=$(($CF_BOOT_SIZE / 512)) cf_rootfs_start=$(($cf_boot_start + $cf_boot_size)) cf_sectors=$(($CF_SIZE / 512)) cf_rootfs_size=$(($cf_sectors - $cf_rootfs_start))

cat << EOF
CF layout :
boot: $cf_boot_start ($cf_boot_size)
rootfs: $cf_rootfs_start ($cf_rootfs_size)

EOF

cf_cylinders=$(($cf_sectors / ($CF_SPT * $CF_HPC))) cf_heads=$((($cf_sectors / $CF_SPT) % $CF_HPC)) cf_sectors=$((($cf_sectors % $CF_SPT) + 1))

cat << EOF
CHS emulation:
cylinders: $cf_cylinders
heads: $cf_heads
sectors: $cf_sectors

EOF

dd if=/dev/zero of=$CF_IMG bs=1 count=0 seek=$CF_SIZE
$SFDISK -q -L -uS -C $cf_cylinders -H $cf_heads -S $cf_sectors --no-reread $CF_IMG << EOF $cf_boot_start $cf_boot_size L *
$cf_rootfs_start $cf_rootfs_size
EOF

$GENEXT2FS -m 0 -b $(($cf_boot_size / 2)) -d $BOOT_DIR -N 64 -U $BOOT_IMG $E2FSCK -fyDC0 $BOOT_IMG || true
dd if=$BOOT_IMG of=$CF_IMG conv=notrunc seek=$cf_boot_start bs=512

dd if=$ROOTFS_IMG of=$CF_IMG conv=notrunc seek=$cf_rootfs_start bs=512

$GRUB --device-map=/dev/null --batch << EOF
device (hd0) $CF_IMG
root (hd0,0)
setup (hd0)
EOF

echo

Signed-off-by Richard Braun <[email protected]>

---
 boot/grub/grub.mk |   19 +++++++++++++++++++
 1 files changed, 19 insertions(+), 0 deletions(-)

boot/grub/grub.mk +19 -0

index e8d66f1..c4f52cc 100644
@@ -82,4 +82,23 @@ define GRUB_UNINSTALL_TARGET_CMDS
 	rm -rf $(TARGET_DIR)/boot/grub
 endef
 
+HOST_GRUB_POST_PATCH_HOOKS += GRUB_DEBIAN_PATCHES
+
+HOST_GRUB_CONF_ENV = \
+	CFLAGS="$(GRUB_CFLAGS) -fno-stack-protector" \
+	grub_cv_prog_objcopy_absolute=yes
+
+HOST_GRUB_CONF_OPT = \
+	--disable-auto-linux-mem-opt \
+	--disable-graphics
+
+define HOST_GRUB_INSTALL_CMDS
+	install -m 0755 -D $(@D)/grub/grub $(HOST_DIR)/usr/sbin/grub
+	mkdir -p $(HOST_DIR)/boot/grub
+	cp $(@D)/stage1/stage1 $(HOST_DIR)/boot/grub
+	cp $(@D)/stage2/*1_5   $(HOST_DIR)/boot/grub
+	cp $(@D)/stage2/stage2 $(HOST_DIR)/boot/grub
+endef
+
 $(eval $(autotools-package))
+$(eval $(host-autotools-package))

Since you had a look some time ago at Grub (and the problem of building it on x86-64), could you have a look at the below proposal from Richard?

Richard proposes to add a host variant of Grub. At some point, I think we discussed changing the target variant so that it gets built with the host compiler (since Grub is always built for x86/x86-64 systems).

With Richard's proposal below, I'm a bit worried about the fact that the user needs to do "make host-grub" manually. Of course, we can add the host-grub package for the "Host utilities" menu. But anyway, I want your opinion on this.