How to customize the Linux Kernel

From menuconfig

The most frequent way of customization of the Linux Kernel is to change the .config file that contains the Kernel options. Setup the environment and run:

  Host    select

~/architech_sdk/architech/pengwyn/yocto/build$ bitbake linux-pengwyn -c cleanall
...
~/architech_sdk/architech/pengwyn/yocto/build$ bitbake linux-pengwyn -c menuconfig
...

a new window, like the following one, will pop-up

follow the instructions, save and exit, than you ready to generate your preferred image based on your customized kernel. If you prefer, you can build just the kernel running:

  Host    select

~/architech_sdk/architech/pengwyn/yocto/build$ bitbake linux-pengwyn

...

At the end of the build process, the output file (uImage.bin), along with the built kernel modules (modules-3.2.0-r0-pengwyn.tgz), will be placed under tmp/deploy/images/ inside your build directory, so, if you are building your system from the default directory, the destination directory will be /home/architech/architech_sdk/architech/pengwyn/yocto/build/tmp/deploy/images.

From sources

If you want to modify the Linux kernel sources instead, insert the following commands to create an image of the actual used sources:

  Host    select

~$ mkdir -p /home/architech/Documents/linux-kernel
~$ cd /home/architech/Documents/linux-kernel
~/Documents/linux-kernel$ cp /home/architech/architech_sdk/architech/pengwyn/yocto/poky/meta-silica/recipes-kernel/linux/linux-pengwyn-3.2/linux-pengwyn* .
~/Documents/linux-kernel$ tar -xzf linux-pengwyn_3.2.tar.gz
~/Documents/linux-kernel$ mv linux-pengwyn_3.2 a
~/Documents/linux-kernel$ patch -p1 -d a/ < linux-pengwyn_3.2.patch
patching file ...
...
~/Documents/linux-kernel$ cp -r a/ b/

Modify the sources contained inside directory b, than create your patch

  Host    select

~/Documents/linux-kernel$ diff -Naur a/ b/ > linux-pengwyn_3.2.mine.patch
~/Documents/linux-kernel$ cp linux-pengwyn_3.2.mine.patch /home/architech/architech_sdk/architech/pengwyn/yocto/poky/meta-silica/recipes-kernel/linux/linux-pengwyn-3.2/

Create a file named linux-pengwyn_3.2.bbappend inside directory /home/architech/architech_sdk/architech/pengwyn/yocto/poky/meta-silica/recipes-kernel/linux/ and write the following text inside the .bbappend file:

  Host    select

SRC_URI += "file://linux-pengwyn_3.2.mine.patch \
"

Clean and build:

  Host    select

bitbake linux-pengwyn -c cleanall
bitbake linux-pengwyn

Building kernel without bitbake

The following commands are used to build the kernel without bitbake. First of all, install the package uboot-mkimage:

  Host    select

apt-get install uboot-mkimage

and setup the environment:

  Host    select

export PATH="$PATH:/opt/poky/1.2.1/sysroots/i686-pokysdk-linux/usr/bin/armv5te-poky-linux-gnueabi"

After that, in linux kernel folder, set the kernel options:

  Host    select

make ARCH=arm CROSS_COMPILE=arm-poky-linux-gnueabi- menuconfig

and build the kernel:

  Host    select

make ARCH=arm CROSS_COMPILE=arm-poky-linux-gnueabi- uImage

It is not necessary using make clean to rebuild the kernel image after have modified source code.

Note

Use option -j with make to speed up the compilation

-j [jobs], –jobs[=jobs]

Specifies the number of jobs (commands) to run simultaneously. If there is more than one -j option, the last one is effective. If the -j option is given without an argument, make will not limit the number of jobs that can run simultaneously.

example: make -j 4 ARCH=arm CROSS_COMPILE=arm-poky-linux-gnueabi- uImage