Kernel Compilation

This guide will give you step by step instructions about compiling a kernel for ARM machines on the target platform. If you find something missing or unclear, please send a mail to the linux-arm list.

Here are some initial notes to help you understand the terminology and conventions used in this document:

• "bash$" and "bash#" are shell prompts, not commands to be typed.
• "host" means the machine you are building the ARM kernel on.
• "target" means the machine you are building the ARM kernel for.

1. Decide where to build your kernel

   Firstly, you need to decide where you are going to build your ARM Linux kernel. A good place to build the kernel is in your home directory, which we will refer to as $HOME thoughout this document. If you wish to use some other location, replace $HOME as appropriate.

   However, please note that building a kernel in /usr/src/linux is highly discouraged.

    

2. Deciding on a kernel version

   Firstly, you need to decide which version of the Linux kernel you wish to compile. Most people will want the latest stable kernel release. To help you identify a particular release, a system of version numbers is used by the kernel developers.

   For any kernel version x.y.z,

    

   • x - This is the major revision number
   • y - This is the minor revision number, where:
     Even numbers indicate "stable" kernel releases
     Odd numbers indicate "development" or "beta" kernel releases which may be less stable.
   • z - This is the patch level of the kernel

   This version number represents the main line kernel version.

   At the time of writing this document, the latest stable kernel on ARM is 2.6.6.

   Under the ARM kernel tree, you will find a suffix to the kernel version number: -rmkN, or -vrsN where 'N' is the patch release number. For instance, 2.4.26-vrs1. This indicates the version of the main ARM kernel patch which should be applied. (note: kernels later than 2.6.0-test2 do not require a -rmk or -vrs patch to be applied since ARM architecture support is already merged.)

   Other maintainers, such as Nicolas Pitre, may produce additional patches, and these will add an additional suffix to denote their version. Nicolas Pitre's patches add a -np suffix, eg 2.4.21-rmk2-np1.

   This means that 2.4.21-rmk2-np1 is based upon 2.4.21-rmk2, which in turn is based upon the 2.4.21 kernel. Therefore, to get the kernel source for 2.4.21-rmk2-np1, you need the 2.4.21 main line kernel source, the 2.4.21-rmk2 patch and the 2.4.21-rmk2-np1 patch.

   Therefore, if you need extra patches from other maintainers, you have to be careful to choose an appropriate kernel version. You will need to locate the maintainer patches first, and then work your way up through the version number towards the mainline kernel version.

3. Downloading the maintainer-specific patch.

   In some circumstances, you will need to patch the kernel with a maintainer specific patch. These patches add extra features or other device drivers which may be specific to various machines. However, as a general rule, maintainers forward upstream parts of their patches into the -rmk or -vrs trees as and when they are happy with the change.

   Please refer to the machine list for information concerning extra patches.

    

4. Downloading an ARM patch.

   (You only need this step if you are using a kernel prior to 2.6.0-test2. There are no -rmk or -vrs patches for later kernels.)

   You may need to download a kernel patch, which contains all the ARM specific updates for a particular kernel version. These can be found in ftp://ftp.arm.linux.org.uk/pub/armlinux/source/kernel-patches/. The kernel releases are separated out into directories corresponding to the major and minor version numbers of the kernel.

   The individual files are named patch-x.y.z-rmkN.gz or patch-x.y.z-vrsN.gz, where 'x', 'y', 'z' and 'N' are the version numbers mentioned above. You should select and download the latest patch for the kernel into the $HOME directory. This is the one which will have either the most features, or the most bug fixes in. You will need the version of the patch later when downloading the main kernel source.

   Note: Some files may be named (eg) pre-patch-x.y.z-rmkN.gz. These are alpha or beta patches, which are probably unstable. You should not use these unless you are sure that you know what you are doing, and you don't mind the target system being unstable. However, they are useful when new ideas need to be tested out.

   Note2: Some kernels are based on the Alan Cox series of kernels. These have names similar to patch-x.y.z-acm-rmkN.gz where x.y.z is Linus' version number and m is Alan's version number. In this case, you will need to obtain Alan Cox's corresponding patch from the kernel.org servers, in the directory /pub/linux/kernel/people/alan/linux-2.4/.