kbuild-template

This is a project template, that uses the Linux Kernel build system Kbuild.

Kbuild was originially developed to be used with the Linux Kernel. It implements a powerfull configuration and build infrastructure that allowes you to build a project with only the sources, that are really needed to fit your configuration.

But Kbuild can not only be used along with the Linux kernel. Lots of other projects use the Kbuild system as well. A few famos examples:

• buildroot -- https://buildroot.org/
• zephyr -- https://www.zephyrproject.org/
• U-Boot -- http://www.denx.de/wiki/U-Boot

This project showes you that Kbuild is a makefile framework for writing simple makefiles for complex and configurable tasks that you can easily use for your own purposes.

How it works

The top Makefile reads the .config file, which comes from the application configuration process.

The top Makefile is responsible for building building the application It builds this goal by recursively descending into the subdirectories of the application source tree. The list of subdirectories which are visited depends upon the application configuration. The top Makefile can include several other Makefiles that supply function specific information to the top Makefile.

Each subdirectory has a kbuild Makefile which carries out the commands passed down from above. The kbuild Makefile uses information from the .config file to construct various file lists used by kbuild to build any built-in targets.

scripts/Makefile.* contains all the definitions/rules etc. that are used to build the application based on the kbuild makefiles.

Sample project

This project combines a pretty simple application with the Kbuild environment. The Kbuild system itself was copied from the Linux Kernel. Next, the Makefiles and scripts where simplified and most of the kernel specific rules and targets where removed or replaced by out own application specific targets.

All changes to the Makefiles and scripts are logged in this git repository.

Building

Building the sample application is quite simple.

First configure it, then just call make to build it.

    make menconfig # Create the ".config" file
    make           # Build the application

These steps generate a small executable myapp, which just print some messages to the console.

You can save default configurations into the configs/ directory. There are two sample default configurations one with all options enabled (all-y-defconfig) and one with no option enabled (all-n-defconfig)

You can configure the project with a default configuration by calling e.g.

    make all-y-defconfig

The full list of configuration and build targets is available by:

    make help

How to use and modify this template for your own applications?

The application sources can easily be replaced and extended by your own files.

Currently the sources are located in the following directories:

• main/ -- Main application source
• lib/ -- A sample logging library, that will be compiled into a .a file
• include/ -- This directory holds all include files.

All you need to to is to modify the following files, according to your needs:

• Kconfig in the top and all sub-directories
• Makefile in the top and all sub-directories

Eventually also

• Kbuild

To get a starting point, just search for the string myapp in all Makefiles and Kconfig files. As a first task, replace these strings with your own application name.

It should be quite obvious how to extend this example to your needs.

You can add more subdirectories by adding to objs-y or libs-y variables of the top-level Makefile.

In our sample, these variables are set to:

    objs-y          := main
    libs-y          := lib

You can also add further sub-sub directories, as you like.

Kbuild documentation

The original Kbuild documentation is located at

Learn about the kconfig language: Documentation/kbuild/kconfig-language.txt.

Learn how to write makefiles: Documentation/kbuild/makefiles.txt.

This is the original documentation from the Linux Kernel