Outpost-Kconfig

Outpost-Kconfig provides build system recipes for Meson and Cargo that handles kconfig and/or .config file. The aim is to ease kconfig usage across different languages and build systems.

Table of Contents

1. Meson Build System
2. Cargo
3. License

Meson Build system

Meson Buildsystem recipe collection that handles Kconfig and .config files.

This meson project can be used as a sub-project for every meson based project which uses Kconfig as configuration system. The top level Kconfig is parsed at configure time (i.e. during meson setup), the config file is checked and a build specific .config file is generated using oldconfig policy for missing Kconfig entry. During project configuration, two dependencies file are generated, one which listed all Kconfig files that are parsed, and the .config itself. Thus, if any of those file change (Kconfig new options and/or a manually run menuconfig), the project is automatically reconfigure by Meson. This project provides a meson configuration_data object containing all .config entries (field to y are converted to 1/0 boolean) and a config.h is generated using meson configure_file feature.

The provided configuration_data can be reused for Meson source_setconfiguration.

Options

• kconfig: Top level Kconfig file.
• config: input config file.

NOTE: This is up to the user to provide the input config file (e.g. from a defconfig, and/or after config fragment merge operation). This can be done w/ scripts/kconfig.py but this is out of scope of the meson configuration step.

Options got yield attribute and thus can be defined at top-level project and forwarded to sub projects seamlessly

Environment

Kconfig can use environment variables substitution in kconfig file and/or dotconfig. This recipe export a meson variable named kconfig_env to be used as env keyword argument value for meson function (see: https://mesonbuild.com/Reference-manual_returned_env.html).

Exported environment variables

• srctree: standard kconfig variable for top level source directory (a.k.a. meson global source tree).
• subprojects: helper to path to top level subprojects directory. This ease subprojects Kconfig files source from top level `Kconfig`` file.
• KCONFIG_CONFIG: Outputted dotconfig file path.

meson devenv

kconfig_env is also added to the meson devenv. Meson devenv is a python-virtual-env-like feature that allowed developers to enable the required variables for the project. Using this, one can activate the project devenv and directly use menuconfig from kconfiglib w/o the need of any helper or custom command.

e.g.

meson devenv -C builddir
menuconfig

Targets (deprecated)

There is a helper target called menuconfig for users who wants to edit the configuration during development. This target handles the path of top-level Kconfig and output .config.

• menuconfig: runs menuconfig inside the given builddir

TODO: Add oldconfig, savedefconfig targets

Meson variables

The following variables can be use by top level project to use Kconfig features. (see: https://mesonbuild.com/Reference-manual_returned_subproject.html)

• kconfig_env: environment variables set
• kconfig_data: kconfig meson configure_data w/ entry set to y converted as 1/0 boolean
• kconfig_h: C header generated at configure time by meson from processed kconfig_data
• kconfig_rustargs: Rust flags generated at configure time by meson from processed kconfig_data

Prerequisit

This project uses kconfiglib python package as Kconfig frontend. One could install it with the following:

pip3 install --user kconfiglib

Cargo

For Cargo build system, there is no handling of Kconfig itself nor any graphical frontend. We assumed that the .config file is well-formed.

As a pre requisite, we stated that kconfig entries must be build time evaluated in order to fail as soon as possible, and especially, not at runtime. Moreover, no external crates and no dead code are mandatory requirements too.

Thus, 2 crates are needed:

• kconfig_import: import and parse .config from a build script, i.e. build.rs.
• kconfig: provide helper getter macro

crate kconfig_import

This crate allows user to import a .config file, the file path is given through an environment variable config in order to stay coherent w/ meson option.

Blank lines and comments are trimmed and then, each kconfig entry is pushed in cargo config as boolean. This allows users to use conditional compile with #[cfg] attribute or cfg! macro using only the config entry name, i.e. means that the config is defined, whatever is type or value.

Entries w/ a specific value (i.e. int, hex and string) are pushed to the cargo environment. Due to some const limitation on string view manipulation, hex are converted to decimal integer at build time and an extra entry w/ _HEX_STR suffix is added, holding the original hexadecimal value (w/ 0x prefix) as string.

crate kconfig

This crate provide macro helper in order to get value (and converted to the right type) from Rust code at build time. As all environment variables are text, the get! macro takes a required parameter that is the config entry name and an optional parameter that is the integer type in which user wants to convert config entry. If no optional parameter, the raw string is accessed.

At build time, if the config entry does not exist, compiling process will panic. At build time, if the string to integer conversion fails, compiling process will panic.

For boolean value, rust #[cfg] and cfg! can be used.

usage

Cargo.toml

[dependencies]
kconfig

[build-dependencies]
kconfig_import

build.rs

fn main() {
    kconfig_import::import_dotconfig_from_script();
}

any.rs

use kconfig:

[...]

// conditional function compilation
#[cfg(CONFIG_EXTRA_UBER_FEATURE)]
fn my_extra_uber_function(...) {
    [...]
}

// u16 array size from KConfig `.config` file
const SOME_ARRAY_SIZE: u16 = kconfig::get!("CONFIG_SOME_ARRAY_SIZE", u16);

// string from KConfig `.config` file
const MOTD_BANNER: &str = kconfig::get!("CONFIG_MOTD");

LICENSE

Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with the License. You may obtain a copy of the License at

http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License.

NOTE: This project bundles a modified version kconfig.py from Zephyr project, licensed under ISC.