[gentoo-embedded] Gentoo/arm64 quickstart

[Mike Frysinger]

for people wanting to get their hands dirty

first you'll want to build stuff

- make sure you sync first; a lot of work is recent
	emerge --sync
- make sure you have latest crossdev
	emerge '>=crossdev-20140118'
- create your cross-compiler
	crossdev arm64
- update the profile
	ln -sfT /usr/portage/profiles/default/linux/arm64/13.0 \
		/usr/aarch64-unknown-linux-gnu/etc/portage/make.profile
- adjust your USE flags in /usr/aarch64-unknown-linux-gnu/etc/portage/make.conf
	suggest adding USE='-fortran -openmp -go -mudflap'
- cross-compile a bunch of packages
	aarch64-unknown-linux-gnu-emerge @system
	aarch64-unknown-linux-gnu-emerge <more stuff!>
- if you want python, use 2.7 for now as 3.3 does not cross-compile
- perl & pam do not cross-compile today, so don't bother
- binutils & gcc work fine, so you can easily create a self hosting system

tweak a few things in /usr/aarch64-unknown-linux-gnu/etc to get it booting

- hack /etc/inittab to enable an automatic root shell
	sed -i -e '/^c[1-6]/s:^:#:' etc/inittab
	echo 's0:12345:respawn:/bin/bash' >> etc/inittab
- disable some useless init scripts
	cd etc/runlevels
	rm */consolefont */hostname */hwclock */keymaps */modules  \
		*/swap */termencoding */mtab
- enable net.eth0/swclock
	ln -s /etc/init.d/swclock sysinit/
	ln -s /etc/init.d/net.eth0 boot/
- simplify mtab
	cd etc/
	ln -s /proc/mounts mtab

now you'll want to build a disk image using that sysroot

- create a sparse disk image
	# It won't take up 20G, but may grow to fill that.
	truncate -s 20G gentoo.img
- partition the disk image
	# This will create two partitions automatically.
	# A small vfat /boot and a large ext4 /.
	printf '%s\n' n p 1 '' +50MB n p 2 '' '' t 1 b w | fdisk gentoo.img
- format the disk image
	losetup -P /dev/loop5 gentoo.img
	mkfs.vfat /dev/loop5p1
	mkfs.ext4 /dev/loop5p2
- mount the disks
	mkdir -p root
	mount /dev/loop5p2 root
- copy the sysroot to the root partition
	rsync -a /usr/aarch64-unknown-linux-gnu/ root/
- unmount the disks
	umount root
	losetup -d /dev/loop5
- repeat the mount/rsync/umount steps if you want to install more packages

now we'll need something to boot

- get linux-3.12.6 from kernel.org
	tar xf linux-3.12.6.tar.xz
	# Create a linux symlink to it.
	ln -s linux-3.12 linux
- build the kernel (worry about customizing after you have a working system)
	make ARCH=arm64 CROSS_COMPILE=aarch64-unknown-linux-gnu- defconfig
	# Enable CONFIG_DEVTMPFS_MOUNT to fix booting.
	make ARCH=arm64 CROSS_COMPILE=aarch64-unknown-linux-gnu- menuconfig
	make ARCH=arm64 CROSS_COMPILE=aarch64-unknown-linux-gnu- -j4
- build a boot image for the emulator
	git clone git://git.kernel.org/pub/scm/linux/kernel/git/cmarinas/boot-
wrapper-aarch64.git
	cd boot-wrapper-aarch64
	for f in ../linux/arch/arm64/boot/dts/*.dts* ; do ln -s $f ; done
	ln -s ../linux/arch/arm64/boot/Image
	make \
		CROSS_COMPILE=aarch64-unknown-linux-gnu- \
		BOOTARGS='"root=/dev/vda2 consolelog=9 rw console=ttyAMA0"' \
		FDT_SRC=foundation-v8.dts \
		IMAGE=gentoo.axf

finally let's boot the fsckin thing

- install the armv8 foundation model
	emerge armv8-fast-model
- run it (should be done in a GUI as it'll run an xterm of the console)
	Foundation_v8 \
		--image gentoo.axf \
		--block-device gentoo.img \
		--network=nat
- wait a little while because it's slow
- profit!

this default mode gives you a network connection where the emulator can 
connect out, but you can't easily connect to it.  the good news is that dhcpcd 
"Just works" and you can get going.

if you do want to connect to the system, that's what --network=bridged mode is 
for.  the downside is you have to run it as root.  then on your dev system:
	ifconfig ARM0 10.1.1.1
and in the emulator:
	ifconfig eth0 10.1.1.2
now you can ping/ssh to each other.
-mike