Table of contents

• Overview
• Installation
  • Installation with pip
  • Manual installation
  • Installation for the Linux kernel
  • Python version compatibility (2.7/3.2+)
• Getting started
  • Using .config files as Make input
  • Useful helper macros
  • Incremental building
• Library documentation
• Library features
  • Kconfig extensions
• Other features
• Menuconfig interfaces
• Examples
  • Example scripts
  • Real-world examples
  • Sample make iscriptconfig session
• Test suite
• Notes
• Thanks
• License

Overview

Kconfiglib is a Kconfig implementation in Python 2/3. It started out as a helper library, but now has a enough functionality to also work well as a standalone Kconfig implementation (including terminal and GUI menuconfig interfaces and Kconfig extensions).

The entire library is contained in kconfiglib.py. The bundled scripts are implemented on top of it. Implementing your own scripts should be relatively easy, if needed.

Kconfiglib is used exclusively by e.g. the Zephyr and ACRN projects. It is also used for many small helper scripts in various projects.

Since Kconfiglib is based around a library, it can be used e.g. to generate a Kconfig cross-reference (note: heavy page), using the same robust Kconfig parser used for other Kconfig tools, instead of brittle ad-hoc parsing. The documentation generation script can be found here.

Kconfiglib implements the recently added Kconfig preprocessor. For backwards compatibility, environment variables can be referenced both as $(FOO) (the new syntax) and as $FOO (the old syntax). The old syntax is deprecated, but will probably be supported for a long time, as its needed to stay compatible with older Linux kernels. The major version will be increased if support is ever dropped. Using the old syntax with an undefined environment variable keeps the string as is.

Note: See this issue if you run into a "macro expanded to blank string" error with kernel 4.18+.

See this page for some Kconfig tips and best practices.

Installation

Installation with pip

Kconfiglib is available on PyPI and can be installed with e.g.

$ pip(3) install kconfiglib

Microsoft Windows is supported.

The pip installation will give you both the base library and the following executables. All but two (genconfig and setconfig) mirror functionality available in the C tools.

• menuconfig
• guiconfig
• oldconfig
• olddefconfig
• savedefconfig
• defconfig
• alldefconfig
• allnoconfig
• allmodconfig
• allyesconfig
• listnewconfig
• genconfig
• setconfig

genconfig is intended to be run at build time. It generates a C header from the configuration and (optionally) information that can be used to rebuild only files that reference Kconfig symbols that have changed value.

Starting with Kconfiglib version 12.2.0, all utilities are compatible with both Python 2 and Python 3. Previously, menuconfig.py only ran under Python 3 (i.e., it's now more backwards compatible than before).

Note: If you install Kconfiglib with pip's --user flag, make sure that your PATH includes the directory where the executables end up. You can list the installed files with pip(3) show -f kconfiglib.

All releases have a corresponding tag in the git repository, e.g. v12.14.0 (the latest version).

Semantic versioning is used. There's been ten small changes (1, 2, 3, 4, 5, 6, 7, 8, 9, 10) to the behavior of the API, which is why the major version is at 12 rather than 2. I do major version bumps for all behavior changes, even tiny ones, and most of these were fixes for baby issues in the early days of the Kconfiglib 2 API.

Manual installation

Just drop kconfiglib.py and the scripts you want somewhere. There are no third-party dependencies (except for the windows-curses package on Windows, when running the terminal menuconfig implementation).

Installation for the Linux kernel

See the module docstring at the top of kconfiglib.py.

Python version compatibility (2.7/3.2+)

Kconfiglib and all utilities run under both Python 2.7 and Python 3.2 and later. The code mostly uses basic Python features and has no third-party dependencies, so keeping it backwards-compatible is pretty low effort.

The 3.2 requirement comes from argparse. format() with unnumbered {} is used as well.

A recent Python 3 version is recommended if you have a choice, as it'll give you better Unicode handling.

Getting started

1. Install the library and the utilities.

2. Write Kconfig files that describe the available configuration options.

3. Generate an initial configuration with e.g. menuconfig/guiconfig or alldefconfig. The configuration is saved as .config by default.

   For more advanced projects, the defconfig utility can be used to generate the initial configuration from an existing configuration file. Usually, this existing configuration file would be a minimal configuration file, as generated by e.g. savedefconfig.

4. Run genconfig to generate a header file. By default, it is saved as config.h.

   Normally, genconfig would be run automatically as part of the build.

   Before writing a header file or other configuration output, Kconfiglib compares the old contents of the file against the new contents. If there's no change, the write is skipped. This avoids updating file metadata like the modification time, and might save work depending on your build setup.

   Adding new configuration output formats should be relatively straightforward. See the implementation of write_config() in kconfiglib.py. The documentation for the Symbol.config_string property has some tips as well.

5. To update an old .config file after the Kconfig files have changed (e.g. to add new options), run oldconfig (prompts for values for new options) or olddefconfig (gives new options their default value). Entering the menuconfig or guiconfig interface and saving the configuration will also update it (the configuration interfaces always prompt for saving on exit if it would modify the contents of the .config file).

   Due to Kconfig semantics, simply loading an old .config file performs an implicit olddefconfig, so building will normally not be affected by having an outdated configuration.

Whenever .config is overwritten, the previous version of the file is saved to .config.old (or, more generally, to $KCONFIG_CONFIG.old).

For some general Kconfig advice, see this page.

Using .config files as Make input

.config files use Make syntax and can be included directly in Makefiles to read configuration values from there. This is why n-valued bool/tristate values are written out as # CONFIG_FOO is not set (a Make comment) in .config, allowing them to be tested with ifdef in Make.

If you make use of this, you might want to pass --config-out <filename> to genconfig and include the configuration file it generates instead of including .config directly. This has the advantage that the generated configuration file will always be a "full" configuration file, even if .config is outdated. Otherwise, it might be necessary to run old(def)config or menuconfig/guiconfig before rebuilding with an outdated .config.

If you use --sync-deps to generate incremental build information, you can include deps/auto.conf instead, which is also a full configuration file.

Useful helper macros

The include/linux/kconfig.h header in the Linux kernel defines some useful helper macros for testing Kconfig configuration values.

IS_ENABLED() is generally useful, allowing configuration values to be tested in if statements with no runtime overhead.

Incremental building

See the docstring for Kconfig.sync_deps() in kconfiglib.py for hints on implementing incremental builds (rebuilding just source files that reference changed configuration values).

Running the scripts/basic/fixdep.c tool from the kernel on the output of gcc -MD <source file> might give you an idea of how it all fits together.

Library documentation

Kconfiglib comes with extensive documentation in the form of docstrings. To view it, run e.g. the following command:

$ pydoc(3) kconfiglib

For HTML output, add -w:

$ pydoc(3) -w kconfiglib

This will also work after installing Kconfiglib with pip(3).

Documentation for the menuconfig and guiconfig interfaces can be viewed in the same way:

$ pydoc3 menuconfig/guiconfig

A good starting point for learning the library is to read the module docstring (which you could also just read directly at the beginning of kconfiglib.py). It gives an introduction to symbol values, the menu tree, and expressions.

After reading the module docstring, a good next step is to read the Kconfig class documentation, and then the documentation for the Symbol, Choice, and MenuNode classes.

Please tell me if something is unclear or can be explained better.

Library features

Kconfiglib can do the following, among other things:

• Programmatically get and set symbol values

  See allnoconfig.py and allyesconfig.py, which are automatically verified to produce identical output to the standard make allnoconfig and make allyesconfig.

• Read and write .config and defconfig files

  The generated .config and defconfig (minimal configuration) files are character-for-character identical to what the C implementation would generate (except for the header comment). The test suite relies on this, as it compares the generated files.

• Write C headers

  The generated headers use the same format as include/generated/autoconf.h from the Linux kernel.

• Implement incremental builds

  This uses the same scheme as the include/config directory in the kernel: Symbols are translated into files that are touched when the symbol's value changes between builds, which can be used to avoid having to do a full rebuild whenever the configuration is changed.

  See the sync_deps() function for more information.

• Inspect symbols

  Printing a symbol or other item (which calls __str__()) returns its definition in Kconfig format. This also works for symbols defined in multiple locations.

  A helpful __repr__() is on all objects too.

  All __str__() and __repr__() methods are deliberately implemented with just public APIs, so all symbol information can be fetched separately as well.

• Inspect expressions

  Expressions use a simple tuple-based format that can be processed manually if needed. Expression printing and evaluation functions are provided, implemented with public APIs.

• Inspect the menu tree

  The underlying menu tree is exposed, including submenus created implicitly from symbols depending on preceding symbols. This can be used e.g. to implement menuconfig-like functionality.

  See menuconfig.py/guiconfig.py and the minimalistic menuconfig_example.py example.

Kconfig extensions

The following Kconfig extensions are available:

• source supports glob patterns and includes each matching file. A pattern is required to match at least one file.

  A separate osource statement is available for cases where it's okay for the pattern to match no files (in which case osource turns into a no-op).

• A relative source statement (rsource) is available, where file paths are specified relative to the directory of the current Kconfig file. An orsource statement is available as well, analogous to osource.

• Preprocessor user functions can be defined in Python, which makes it simple to integrate information from existing Python tools into Kconfig (e.g. to have Kconfig symbols depend on hardware information stored in some other format).

  See the Kconfig extensions section in the kconfiglib.py module docstring for more information.

• def_int, def_hex, and def_string are available in addition to def_bool and def_tristate, allowing int, hex, and string symbols to be given a type and a default at the same time.

  These can be useful in projects that make use of symbols defined in multiple locations, and remove some Kconfig inconsistency.

• Environment variables are expanded directly in e.g. source and mainmenu statements, meaning option env symbols are redundant.

  This is the standard behavior with the new Kconfig preprocessor, which Kconfiglib implements.

  option env symbols are accepted but ignored, which leads the caveat that they must have the same name as the environment variables they reference (Kconfiglib warns if the names differ). This keeps Kconfiglib compatible with older Linux kernels, where the name of the option env symbol always matched the environment variable. Compatibility with older Linux kernels is the main reason option env is still supported.

  The C tools have dropped support for option env.

• Two extra optional warnings can be enabled by setting environment variables, covering cases that are easily missed when making changes to Kconfig files:

  • KCONFIG_WARN_UNDEF: If set to y, warnings will be generated for all references to undefined symbols within Kconfig files. The only gotcha is that all hex literals must be prefixed with 0x or 0X, to make it possible to distinguish them from symbol references.

    Some projects (e.g. the Linux kernel) use multiple Kconfig trees with many shared Kconfig files, leading to some safe undefined symbol references. KCONFIG_WARN_UNDEF is useful in projects that only have a single Kconfig tree though.

    KCONFIG_STRICT is an older alias for this environment variable, supported for backwards compatibility.

  • KCONFIG_WARN_UNDEF_ASSIGN: If set to y, warnings will be generated for all assignments to undefined symbols within .config files. By default, no such warnings are generated.

    This warning can also be enabled/disabled by setting Kconfig.warn_assign_undef to True/False.

Other features

• Single-file implementation

  The entire library is contained in kconfiglib.py.

  The tools implemented on top of it are one file each.

• Robust and highly compatible with the C Kconfig tools

  The test suite automatically compares output from Kconfiglib and the C tools by diffing the generated .config files for the real kernel Kconfig and defconfig files, for all ARCHes.

  This currently involves comparing the output for 36 ARCHes and 498 defconfig files (or over 18000 ARCH/defconfig combinations in "obsessive" test suite mode). All tests are expected to pass.

  A comprehensive suite of selftests is included as well.

• Not horribly slow despite being a pure Python implementation

  The allyesconfig.py script currently runs in about 1.3 seconds on the Linux kernel on a Core i7 2600K (with a warm file cache), including the make overhead from make scriptconfig. Note that the Linux kernel Kconfigs are absolutely massive (over 14k symbols for x86) compared to most projects, and also have overhead from running shell commands via the Kconfig preprocessor.

  Kconfiglib is especially speedy in cases where multiple .config files need to be processed, because the Kconfig files will only need to be parsed once.

  For long-running jobs, PyPy gives a big performance boost. CPython is faster for short-running jobs as PyPy needs some time to warm up.

  Kconfiglib also works well with the multiprocessing module. No global state is kept.

• Generates more warnings than the C implementation

  Generates the same warnings as the C implementation, plus additional ones. Also detects dependency and source loops.

  All warnings point out the location(s) in the Kconfig files where a symbol is defined, where applicable.

• Unicode support

  Unicode characters in string literals in Kconfig and .config files are correctly handled. This support mostly comes for free from Python.

• Windows support

  Nothing Linux-specific is used. Universal newlines mode is used for both Python 2 and Python 3.

  The Zephyr project uses Kconfiglib to generate .config files and C headers on Linux as well as Windows.

• Internals that (mostly) mirror the C implementation

  While being simpler to understand and tweak.

Menuconfig interfaces

Three configuration interfaces are currently available:

• menuconfig.py is a terminal-based configuration interface implemented using the standard Python curses module. xconfig features like showing invisible symbols and showing symbol names are included, and it's possible to jump directly to a symbol in the menu tree (even if it's currently invisible).

  

  There is now also a show-help mode that shows the help text of the currently selected symbol in the help window at the bottom.

  Starting with Kconfiglib 12.2.0, menuconfig.py runs under both Python 2 and Python 3 (previously, it only ran under Python 3, so this was a backport). Running it under Python 3 provides better support for Unicode text entry (get_wch() is not available in the curses module on Python 2).

  There are no third-party dependencies on *nix. On Windows, the curses modules is not available by default, but support can be added by installing the windows-curses package (which is installed automatically when Kconfiglib is installed via pip on Windows):

  $ pip install windows-curses

  This uses wheels built from this repository, which is in turn based on Christoph Gohlke's Python Extension Packages for Windows.

  See the docstring at the top of menuconfig.py for more information about the terminal menuconfig implementation.

• guiconfig.py is a graphical configuration interface written in Tkinter. Like menuconfig.py, it supports showing all symbols (with invisible symbols in red) and jumping directly to symbols. Symbol values can also be changed directly from the jump-to dialog.

  When single-menu mode is enabled, a single menu is shown at a time, like in the terminal menuconfig. Only this mode distinguishes between symbols defined with config and symbols defined with menuconfig.

  guiconfig.py has been tested on X11, Windows, and macOS, and is compatible with both Python 2 and Python 3.

  Despite being part of the Python standard library, tkinter often isn't included by default in Python installations on Linux. These commands will install it on a few different distributions:

  • Ubuntu: sudo apt install python-tk/sudo apt install python3-tk
  • Fedora: dnf install python2-tkinter/dnf install python3-tkinter
  • Arch: sudo pacman -S tk
  • Clear Linux: sudo swupd bundle-add python3-tcl

  Screenshot below, with show-all mode enabled and the jump-to dialog open:

  

  To avoid having to carry around a bunch of GIFs, the image data is embedded in guiconfig.py. To use separate GIF files instead, change _USE_EMBEDDED_IMAGES to False in guiconfig.py. The image files can be found in the screenshots branch.

  I did my best with the images, but some are definitely only art adjacent. Touch-ups are welcome. :)

• pymenuconfig, built by RomaVis, is an older portable Python 2/3 TkInter menuconfig implementation.

  Screenshot below:

  

  While working on the terminal menuconfig implementation, I added a few APIs to Kconfiglib that turned out to be handy. pymenuconfig predates menuconfig.py and guiconfig.py, and so didn't have them available. Blame me for any workarounds.

Examples

Example scripts

The examples/ directory contains some simple example scripts. Among these are the following ones. Make sure you run them with the latest version of Kconfiglib, as they might make use of newly added features.

• eval_expr.py evaluates an expression in the context of a configuration.
• find_symbol.py searches through expressions to find references to a symbol, also printing a "backtrace" with parents for each reference found.
• help_grep.py searches for a string in all help texts.
• print_tree.py prints a tree of all configuration items.
• print_config_tree.py is similar to print_tree.py, but dumps the tree as it would appear in menuconfig, including values. This can be handy for visually diffing between .config files and different versions of Kconfig files.
• list_undefined.py finds references to symbols that are not defined by any architecture in the Linux kernel.
• merge_config.py merges configuration fragments to produce a complete .config, similarly to scripts/kconfig/merge_config.sh from the kernel.
• menuconfig_example.py implements a configuration interface that uses notation similar to make menuconfig. It's deliberately kept as simple as possible to demonstrate just the core concepts.

Real-world examples

• kconfig.py from the Zephyr project handles .config and header file generation, also doing configuration fragment merging
• genrest.py generates a Kconfig symbol cross-reference, which can be viewed here
• CMake and IDE integration from the ESP-IDF project, via a configuration server program.
• A script for turning on USB-related options, from the syzkaller project.
• Various automated checks, including a check for references to undefined Kconfig symbols in source code. See the KconfigCheck class.
• Various utilities from the ACRN project

These use the older Kconfiglib 1 API, which was clunkier and not as general (functions instead of properties, no direct access to the menu structure or properties, uglier __str__() output):

• genboardscfg.py from Das U-Boot generates some sort of legacy board database by pulling information from a newly added Kconfig-based configuration system (as far as I understand it :).
• gen-manual-lists.py generated listings for an appendix in the Buildroot manual. (The listing has since been removed.)
• gen_kconfig_doc.py from the esp-idf project generates documentation from Kconfig files.
• SConf builds an interactive configuration interface (like menuconfig) on top of Kconfiglib, for use e.g. with SCons.
• kconfig-diff.py -- a script by dubiousjim that compares kernel configurations.
• Originally, Kconfiglib was used in chapter 4 of my master's thesis to automatically generate a "minimal" kernel for a given system. Parts of it bother me a bit now, but that's how it goes with old work.

Sample make iscriptconfig session

The following log should give some idea of the functionality available in the API:

$ make iscriptconfig
A Kconfig instance 'kconf' for the architecture x86 has been created.
>>> kconf  # Calls Kconfig.__repr__()
<configuration with 13711 symbols, main menu prompt "Linux/x86 4.14.0-rc7 Kernel Configuration", srctree ".", config symbol prefix "CONFIG_", warnings enabled, undef. symbol assignment warnings disabled>
>>> kconf.mainmenu_text  # Expanded main menu text
'Linux/x86 4.14.0-rc7 Kernel Configuration'
>>> kconf.top_node  # The implicit top-level menu
<menu node for menu, prompt "Linux/x86 4.14.0-rc7 Kernel Configuration" (visibility y), deps y, 'visible if' deps y, has child, Kconfig:5>
>>> kconf.top_node.list  # First child menu node
<menu node for symbol SRCARCH, deps y, has next, Kconfig:7>
>>> print(kconf.top_node.list)  # Calls MenuNode.__str__()
config SRCARCH
    string
    option env="SRCARCH"
    default "x86"
>>> sym = kconf.top_node.list.next.item  # Item contained in next menu node
>>> print(sym)  # Calls Symbol.__str__()
config 64BIT
    bool "64-bit kernel" if ARCH = "x86"
    default ARCH != "i386"
    help
      Say yes to build a 64-bit kernel - formerly known as x86_64
      Say no to build a 32-bit kernel - formerly known as i386
>>> sym  # Calls Symbol.__repr__()
<symbol 64BIT, bool, "64-bit kernel", value y, visibility y, direct deps y, arch/x86/Kconfig:2>
>>> sym.assignable  # Currently assignable values (0, 1, 2 = n, m, y)
(0, 2)
>>> sym.set_value(0)  # Set it to n
True
>>> sym.tri_value  # Check the new value
0
>>> sym = kconf.syms["X86_MPPARSE"]  # Look up symbol by name
>>> print(sym)
config X86_MPPARSE
    bool "Enable MPS table" if (ACPI || SFI) && X86_LOCAL_APIC
    default y if X86_LOCAL_APIC
    help
      For old smp systems that do not have proper acpi support. Newer systems
      (esp with 64bit cpus) with acpi support, MADT and DSDT will override it
>>> default = sym.defaults[0]  # Fetch its first default
>>> sym = default[1]  # Fetch the default's condition (just a Symbol here)
>>> print(sym)
config X86_LOCAL_APIC
    bool
    default y
    select IRQ_DOMAIN_HIERARCHY
    select PCI_MSI_IRQ_DOMAIN if PCI_MSI
    depends on X86_64 || SMP || X86_32_NON_STANDARD || X86_UP_APIC || PCI_MSI
>>> sym.nodes  # Show the MenuNode(s) associated with it
[<menu node for symbol X86_LOCAL_APIC, deps n, has next, arch/x86/Kconfig:1015>]
>>> kconfiglib.expr_str(sym.defaults[0][1])  # Print the default's condition
'X86_64 || SMP || X86_32_NON_STANDARD || X86_UP_APIC || PCI_MSI'
>>> kconfiglib.expr_value(sym.defaults[0][1])  # Evaluate it (0 = n)
0
>>> kconf.syms["64BIT"].set_value(2)
True
>>> kconfiglib.expr_value(sym.defaults[0][1])  # Evaluate it again (2 = y)
2
>>> kconf.write_config("myconfig")  # Save a .config
>>> ^D
$ cat myconfig
# Generated by Kconfiglib (https://github.com/ulfalizer/Kconfiglib)
CONFIG_64BIT=y
CONFIG_X86_64=y
CONFIG_X86=y
CONFIG_INSTRUCTION_DECODER=y
CONFIG_OUTPUT_FORMAT="elf64-x86-64"
CONFIG_ARCH_DEFCONFIG="arch/x86/configs/x86_64_defconfig"
CONFIG_LOCKDEP_SUPPORT=y
CONFIG_STACKTRACE_SUPPORT=y
CONFIG_MMU=y
...

Test suite

The test suite is run with

$ python(3) Kconfiglib/testsuite.py

pypy works too, and is much speedier for everything except allnoconfig.py/allnoconfig_simpler.py/allyesconfig.py, where it doesn't have time to warm up since the scripts are run via make scriptconfig.

The test suite must be run from the top-level kernel directory. It requires that the Kconfiglib git repository has been cloned into it and that the makefile patch has been applied.

To get rid of warnings generated for the kernel Kconfig files, add 2>/dev/null to the command to discard stderr.

NOTE: Forgetting to apply the Makefile patch will cause some tests that compare generated configurations to fail

NOTE: The test suite overwrites .config in the kernel root, so make sure to back it up.

The test suite consists of a set of selftests and a set of compatibility tests that compare configurations generated by Kconfiglib with configurations generated by the C tools, for a number of cases. See testsuite.py for the available options.

The tests/reltest script runs the test suite and all the example scripts for both Python 2 and Python 3, verifying that everything works.

Rarely, the output from the C tools is changed slightly (most recently due to a change I added). If you get test suite failures, try running the test suite again against the linux-next tree, which has all the latest changes. I will make it clear if any non-backwards-compatible changes appear.

A lot of time is spent waiting around for make and the C utilities (which need to reparse all the Kconfig files for each defconfig test). Adding some multiprocessing to the test suite would make sense too.

Notes

• This is version 2 of Kconfiglib, which is not backwards-compatible with Kconfiglib 1. A summary of changes between Kconfiglib 1 and Kconfiglib 2 can be found here.

• I sometimes see people add custom output formats, which is pretty straightforward to do (see the implementations of write_autoconf() and write_config() for a template, and also the documentation of the Symbol.config_string property). If you come up with something you think might be useful to other people, I'm happy to take it in upstream. Batteries included and all that.

• Kconfiglib assumes the modules symbol is MODULES, which is backwards-compatible. A warning is printed by default if option modules is set on some other symbol.

  Let me know if you need proper option modules support. It wouldn't be that hard to add.

Thanks

• To RomaVis, for making pymenuconfig and suggesting the rsource keyword.
• To Mitja Horvat, for adding support for user-defined styles to the terminal menuconfig.
• To Philip Craig for adding support for the allnoconfig_y option and fixing an obscure issue with comments inside choices (that didn't affect correctness but made outputs differ). allnoconfig_y is used to force certain symbols to y during make allnoconfig to improve coverage.

License

See LICENSE.txt. SPDX license identifiers are used in the source code.