KernelBuild
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
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. Note: Most people working with the kernel package add an alias of the fakeroot debian/rules command to fdr.
fakeroot debian/rules 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