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kconfiglib 14.1.0

Table of contents

News

Dependency loop with recent linux-next kernels
windows-curses is no longer automatically installed on Windows

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

News

Dependency loop with recent linux-next kernels
To fix issues with dependency loops on recent linux-next kernels, apply this
patch. Hopefully,
it will be in linux-next soon.

windows-curses is no longer automatically installed on Windows
Starting with Kconfiglib 13.0.0, the windows-curses package is no longer
automatically installed on Windows, and needs to be installed manually for the
terminal menuconfig to work.
This fixes installation of Kconfiglib on MSYS2, which is not compatible with
windows-curses. See this issue.
The menuconfig now shows a hint re. installing windows-curses when the
curses module can’t be imported on Windows.
Sorry if this change caused problems!

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, esp-idf, 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, 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 it’s 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. v14.1.0
(the latest version).
Semantic versioning is used. There’s been ten small
changes to the behavior of the API, a Windows packaging change, and a hashbang
change to use python3
(1,
2,
3,
4,
5,
6,
7,
8,
9,
10,
Windows packaging change,
Python 3 hashbang change),
which is why the major version is at 14 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, but the terminal menuconfig won’t work on Windows
unless a package like windows-curses is installed.

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

Install the library and the utilities.
Write Kconfig
files that describe the available configuration options. See this page for some
general Kconfig advice.
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.

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.

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).

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 other modules can be viewed in the same way (though a plain
--help will work when they’re run as executables):
$ pydoc(3) 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. Output for symbols appears in the order that they’re
defined, unlike in the C tools (where the order depends on the hash table
implementation).

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:
$ 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.