The Kconfig System

The Kconfig system is an additional tool for users to change configuration options of TF-M.

../_images/kconfig_header_file_system.png

It handles dependencies and validations automatically when you change configurations so that the generated configuration options are always valid.

It consists of The Kconfig tool and the The Kconfig files.

The Kconfig tool

The Kconfig tool is a python script based on Kconfiglib to launch the menuconfig interfaces and generate the following config files:

CMake config file

Contains CMake cache variables of building options. This file should be passed to the build system via command line option TFM_EXTRA_CONFIG_PATH.
Header file

Contains component options in the header file system. This file should be passed to the build system via the command line option PROJECT_CONFIG_HEADER_FILE. Component options are gathered together in a seperate menu TF-M component configs in The Kconfig files.
The .config and .config.old files

The .config file which contains all the above configurations in the Kconfig format. It will be created after the first execution of the script. It is only used to allow users to make adjustments basing on the previous settings. The Kconfig tool will load it if it exists and .config.old will be created to save the previous configurations.

How To Use

The script takes four arguments at maximum.

‘-k’, ‘–kconfig-file’

Required. The root Kconfig file.
‘-u’, ‘–ui’

Optional. The menuconfig interface to launch, gui or tui. Refer to Menuconfig interfaces for interface details. Only the first two are supported. If no UI is selected, the tool generates config files with default values.
‘-o’, ‘–output_path’

Required. The output directory to hold the generated files.
‘-p’, ‘–platform-path’

Optional. The platform specific Kconfig or defconfig files.

Here is an example:

cd trusted-firmware-m
python3 tools/kconfig/tfm_kconfig.py -k Kconfig -o <output_path> -u tui

# If the platform path has defconfig or Kconfig, use '-p' to load them.
python3 tools/kconfig/tfm_kconfig.py -k Kconfig -o <output_path> -p platform/ext/target/arm/mps2/an521

The script can be used as a standalone tool. You can pass the config files to build system via command line option TFM_EXTRA_CONFIG_PATH and PROJECT_CONFIG_HEADER_FILE respectively, as mentioned above.

# Pass the files generated by script.
<cmake build command> -DTFM_EXTRA_CONFIG_PATH=<output_path>/project_config.cmake \
                      -DPROJECT_CONFIG_HEADER_FILE=<output_path>/project_config.h

The TF-M build system has also integrated the tool. You only need to set USE_KCONFIG_TOOL to ON/TRUE/1 in commande line and CMake will launch the GUI menuconfig for users to adjust configurations and automatically load the generated config files.

Note

Only GUI menuconfig can be launched by CMake for the time being.
Due to the current limitation of the tool, you are not allowed to change the values of build options that of which platforms have customized values. And there is no prompt messages either.

The Kconfig files

The Kconfig files are the files written by the Kconfig language to describe config options. They also uses some Kconfiglib extensions such as optional source osource and relative source rsource so they can only work with the Kconfiglib.