Cross Compiling Linux kernel for ARM

Get latest stable kernel source code

 git clone https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git 

To get kernel-next branch clone

 git clone https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git 

Get toolchain, e.g you can download linaro toolchain from Linaro toolchain for arm

set your path variable /path/to/linaro/binary/linaro/aarch64-unknown-linux-gnu_4.9-2014.05-01/bin

 export PATH=$PATH:/path/to/linaro/binary/linaro/aarch64-unknown-linux-gnu_4.9-2014.05-01/bin 

Setup defconfig file

 make ARCH=arm64 CROSS_COMPILE=aarch64-unknown-linux-gnu- O=output defconfig 

Make kernel image

 make ARCH=arm64 CROSS_COMPILE=aarch64-unknown-linux-gnu- O=output -j8 

To modify kernel configuration use

 make ARCH=arm64 CROSS_COMPILE=aarch64-unknown-linux-gnu- O=output menuconfig 

To save your modified defconfig file

 make ARCH=arm64 CROSS_COMPILE=aarch64-unknown-linux-gnu- O=output savedefconfig 

This will create defconfig file in output directory. Copy this file to your arch/arm64/configs directory