Native kernel compilation on the Odroid-C2:

The Odroid-C2's processor is fast enough to compile the Linux kernel on it natively, and as such, taking this path should eliminate the complexity involved in cross-compilation.

Installing tools

Depending on the distro you are running, and the packages you have installed, you might need to add the compiler and other build-related tools. For example, a minimal base Debian image would not have gcc, since an embedded Linux appliance generally has no requirement to be used as a development tool. This item shows how to install what you need: Adding Native Compiler and Tools

Grabbing the source

You can easily build the kernel on your own.

You can get the latest kernel snapshot or get a source for a specific Hardkernel released build. This link shows how to get a specific release: Use git and commit tag . If a snapshot is acceptable, use the wget step as shown next.

browse to https://github.com/hardkernel/linux
choose your branch (as of today -2013-01-12- it's odroid-3.0.y)

wget --no-check-certificate https://github.com/hardkernel/linux/archive/odroid-3.0.y.zip

This example gets a snapshot of the odroidxu kernel: (note: the board name is odroidxu)

wget --no-check-certificate https://github.com/hardkernel/linux/archive/odroidxu-3.4.y.zip

Unpacking the source

If you picked up a differently named source tarball, of course, substitute the names below:

sudo mkdir -p /usr/src 2>/dev/null
sudo chmod 777 /usr/src
mv odroid-3.0.y.zip /usr/src/linux.zip
cd /usr/src
7z x -y linux.zip > /dev/null

Add a symlink to the source tree:

ln -s  linux-odroid-3.0.y linux

Configuring the kernel

Warning: Now is the time to consider whether you want to work as the root user or to logout and proceed as a normal user. Usually file permissions trip up users new to Linux. Working as root can make things easier, but there is a risk of wrecking your system. On the plus side, with odroid, we can just re-flash it and get back to work.

You might want to install the sudo package if you don't have it already. This next section is optional. You have to reboot after this step to see sudo work for the new user.

sudo apt-get install
adduser odroid adm
echo "%adm ALL=(ALL) ALL" >> /etc/sudoers
echo "127.0.0.1  $(hostname )" >> /etc/hosts

Move to the linux source tree and change ownership to the normal user named odroid. Substitute your own username, if you are not using the odroid user account.

cd /usr/src
chown -R odroid:odroid linux
cd linux

Make sure to select the correct config for your device in the next step. execute the following to get a list of odroid kernel configs:

ls arch/arm/configs/odroid*ubuntu*

You will see something like the following:

odroidq_ubuntu_defconfig        odroidx2_ubuntu_defconfig
odroidu2_ubuntu_defconfig       odroidx2_ubuntu_mali_defconfig
odroidu2_ubuntu_mali_defconfig  odroidx_ubuntu_defconfig
odroidu_ubuntu_defconfig        odroidx_ubuntu_mali_defconfig

now choose your config and copy it to /usr/src/linux/.config (I chose odroidu2_ubuntu_defconfig)

This step prepares for building and copies the configuration from arch/arm/configs to .config:

make odroidu2_ubuntu_defconfig

Now you can build the kernel according to the configuration you chose, or you and make configuration changes.

You can configure the kernel using either text mode(ncurses-driven configurator) or with the GUI(menuconfig-driven configurator). The results are the same. The search functions in the GUI are nice. If you only have the serial console, you will need to use text mode.

(a).Text mode

Install the required tools:

apt-get install build-essential git libncurses5-dev
make menuconfig

(b).Graphical mode

Install the required tools and prepare the configurator:

apt-get install build-essential git qt4-dev-tools
make xconfig

change everything to your needs (use / for searching)

Configuration Example: MALI Overclock

The odroid-u2 can work with a faster clock for the GPU, you may want to configure your kernel to overclock it. For example, edit your .config file and search for CONFIG_MALI_OVERCLOCK. Select the speed you want to try.

# CONFIG_MALI_OVERCLOCK_533 is not set
# CONFIG_MALI_OVERCLOCK_640 is not set
# CONFIG_MALI_OVERCLOCK_733 is not set
# CONFIG_MALI_OVERCLOCK_800 is not set

For example, to select 640MHz, change:

# CONFIG_MALI_OVERCLOCK_640 is not set

CONFIG_MALI_OVERCLOCK_640=y

Only select one though! Think about it...

Building the kernel

Run:

make -j8
# If you are building as root:
make modules_install
# If you are building as user:
sudo make modules_install
make zImage

Mounting the Boot Partition

The boot partition is the section on the media, either on the SD-Card or the eMMC, that holds the kernel image and the initial root filesystem. For the Hardkernel Ubuntu systems, the boot partition would be mounted at /media/boot. For other distributions, the boot partition may not be mounted automatically and by default it might like to be mounted to a different location. For example, on Debian Wheezy, this is not a default mount, and this and other tutorials mount it at /boot when necessary.

You can work the tutorial and substitute /boot/media for /boot if you like, although it will not cause a problem if you just use /boot. Create the /boot directory to use as a mount point if you need to.

This code snippet shows one way to mount the boot partition:

if [ ! -d /boot ]; then
    mkdir -p /boot || exit 1
fi
mountpoint /boot >/dev/null
if [ $? -ne 0 ]; then
    mount -o rw /dev/mmcblk0p1 /boot || exit 1
fi

Building the initial ram filesystem

This is not always needed -- unless you need changes in phase 1 of the Linux boot, it is best to leave this alone.

If you need a custom filesystem driver, or you want to directly mount your root file system on a thumb drive or NAS drive, this would be the area to work in. You would need to know that this is a busybox-based system completely separate from the eventual distro you intend to boot.

kernelversion=`cat ./include/config/kernel.release`
mkinitramfs -c gzip -o ./initramfs-$kernelversion $kernelversion
mkimage -A arm -O linux -T ramdisk -C none -a 0 -e 0 -n initramfs -d ./initramfs-$kernelversion ./uInitrd
cp uInitrd /boot

Copying the kernel and initramfs to the boot partition:

kernelversion=`cat ./include/config/kernel.release`
cp /boot/zImage /boot/zImage.prev
cp /boot/uInitrd /boot/uInitrd.prev
cp arch/arm/boot/zImage /boot
cp .config /boot/config-$kernelversion

optionally:

cp System.map /boot/System.map-$kernelversion

Halt:

sync
shutdown -h 0

Then power cycle after that.

The new kernel will show something like this:

uname -a
Linux odroidu2-1 3.0.57 #1 SMP Sun Jan 13 21:53:37 UTC 2013 armv7l GNU/Linux

The #1 came from the file: /usr/src/linux/.version. Each time you build, this number will be incremented.

Warnings:

Your new kernel build may have kernel modules that may not be compatible with other builds.

Please don't post a private kernel without giving a warning. If could break another system. If you make small changes, like select an additional module, the result will probably not segfault other systems. On the other hand, if you select some networking options (especially) you may find that structs don't quite line up and eventually someone will segfault.

uInitrd:

This is an EXAMPLE script that shows how to update kernel modules in an EXISTING initrd. It may NOT work if you're running low on the boot partition's available space.

The issue is that if you use the normal build script shown for a native initrd build on the host, you end up with binaries for your host instead of for the ARM architecture! This script addresses that and builds kernel modules for the appropriate architecture detected on run-time:

#!/bin/sh
# filename: composite-drivers
# run this script from the kernel source top level directory
# It processes the odroid uInitrd to new-uInitrd, putting ALL the new kernel modules in the updated initial ram disk 
# the problem is that uInitrd is too large to be properly loaded by existing images (32MiB)
# This is a work in progress

workdir=initramfs
mkdir $workdir >/dev/null 2>&1
mkdir $workdir/newmodules >/dev/null 2>&1
workdir=$(realpath $workdir)
previousmodules=$workdir/"previousmodules.txt"
newmodules=$workdir/newmodules

kernelversion=`cat ./include/config/kernel.release`
modpath="$newmodules/lib/modules/$kernelversion/"
# default the cross compiler prefix.  Used to strip binaries
CROSS_COMPILE=${CROSS_COMPILE:-arm-linux-gnueabihf-}


step1() {
	cp uInitrd $workdir
	pushd $workdir >/dev/null
	echo stripping u-boot header
	dd if=uInitrd of=initrd skip=64 bs=1
	gunzip < initrd | cpio -i --make-directories
	rm initrd uInitrd
	popd >/dev/null
}

# This step doesn't actually do anything useful at this point.  Saves a list of previously used modules. 
step2() {
	echo "finding previous kernel module file names"
	pushd $workdir >/dev/null
	if [ -f $previousmodules ]; then 
		rm $previousmodules >/dev/null 2>&1
	fi
	filelist=$(find lib/modules -name '*.ko' )
	for f in $filelist; do 
		echo ${f#*/modules/*/} >> $previousmodules
	done
	popd >/dev/null
}

if [ ! -f uInitrd ]; then
	echo "Error.  Cannot file uInitrd"
	exit -1
fi


step3() {
	pushd $workdir >/dev/null
	echo "Removing existing modules"
	sudo rm -rf lib/modules
	popd >/dev/null
}

step4() {
	make INSTALL_MOD_PATH="$workdir/newmodules" modules_install >/dev/null
	rm $modpath/source
	rm $modpath/build
}

step5() {
	echo "Stripping debug symbols from kernel modules"
	find $modpath -name '*.ko' | xargs "$CROSS_COMPILE"strip -S
}

step6() {
	pushd $workdir >/dev/null
	previouslist=$(cat $previousmodules)
	for f in $previouslist; do
		if [ -f $modpath/$f ]; then 
			destname=$workdir/lib/modules/$kernelversion/$f
			sudo mkdir -p $( dirname $destname )
			sudo cp -a $modpath/$f $destname
		fi
	done
	popd >/dev/null	
}

step7() {
	pushd $workdir >/dev/null
	sudo rm -rf $modpath
	cpioname="initramfs-$kernelversion.cpio"
	find . | cpio -H newc -o > ../$cpioname
	popd >/dev/null
	mkimage -A arm -O linux -T ramdisk -C none -a 0 -e 0 -n initramfs -d ./$cpioname ./uInitrd-$kernelversion
	rm ./$cpioname
}


step1
step2
step3
step4
step5
step6
step7

Sometimes, you may want to do a kernel build outside the /usr/local directories. The following steps detail such a process in the command-line for the Odroid C2:

git clone --depth 1 --single-branch -b odroidc2-3.14.y https://github.com/hardkernel/linux
  cd linux
  make odroidc2_defconfig
  make -j 4 Image dtbs modules
  sudo cp arch/arm64/boot/Image arch/arm64/boot/dts/meson64_odroidc2.dtb /media/boot
  sudo make modules_install
  sudo make firmware_install
  sudo make headers_install INSTALL_HDR_PATH=/usr
  kver=`make kernelrelease`
  sudo cp .config /boot/config-${kver}
  cd /boot
  sudo update-initramfs -c -k ${kver}
  sudo mkimage -A arm64 -O linux -T ramdisk -a 0x0 -e 0x0 -n initrd.img-${kver} -d initrd.img-${kver} uInitrd-${kver}
  sudo cp uInitrd-${kver} /media/boot/uInitrd

Have fun, and port all things to Linux!