Ubuntu Wiki

Here's how to cross-build the kernel from the git repository.

Initial setup

Having ccache installed is optional but helpful if you are often rebuilding the package from scratch with minor modifications.

sudo apt-get install gcc-arm-linux-gnueabihf ccache git kernel-wedge

Get the source

git clone git://kernel.ubuntu.com/jani/ubuntu-nexus7.git

Create an alias called fdr that points to fakeroot debian/rules. You can stick this in ~/.bash_aliases and then source the file to make it permanent.

alias fdr="fakeroot debian/rules"

Rebuild the package

Go to the source directory

cd ubuntu-nexus7

Remove leftover from previous builds or other cruft

git clean -xdf

You need to do the following in order to disable cross-building of the linux-tools binary package, as that requires multiarch setup and some armhf libs installed in the host system.

sed -i '/do_tools/ s/true/false/' debian.linaro/rules.d/armhf.mk

Calling fakeroot debian/rules (fdr) clean is necessary before each build.

fdr clean 

Next we create the package, and depending on your system speed, ccache and on the kernel configurations that are enabled it can take anywhere between 3 minutes and a couple of hours. The value for parallel works best when it equals the number of CPUs in your system + 1.

debuild -eDEB_BUILD_OPTIONS="parallel=3" -eCROSS_COMPILE="ccache arm-linux-gnueabihf-" -b -aarmhf -us -uc -nc

Change the configuration

The configuration file is in debian.linaro/config/config.common.ubuntu

Bring up menuconfig

fdr editconfigs

See what you have changed

git diff

Or edit that file manually and then updateconfigs so it checks your changes and fixes up any possible side-effects

fdr updateconfigs

Then run debuild again as above

Build zImage only

Sometimes you just want a zImage for a quick test such as inserting it in a boot.img and trying it out without a full deb installation.

This does an out of source tree build of a zImage (no modules) using the current Ubuntu configs. Faster than a full package build. Like the value for parallel mentioned above, the -j value works best when it is number of CPUs + 1.

cd ubuntu-nexus7
mkdir ../build
cp debian.linaro/config/config.common.ubuntu ../build/.config
CROSS_COMPILE="ccache arm-linux-gnueabihf-"  ARCH=arm make  O=../build -j3 zImage