docs/en/api-guides/build-system.rst
Build System
:link_to_translation:zh_CN:[中文]
This document explains the implementation of the ESP-IDF build system and the concept of "components". Read this document if you want to know how to organize and build a new ESP-IDF project or component.
An ESP-IDF project can be seen as an amalgamation of a number of components. For example, for a web server that shows the current humidity, there could be:
ESP-IDF makes these components explicit and configurable. To do that, when a project is compiled, the build system will look up all the components in the ESP-IDF directories, the project directories and (optionally) in additional custom component directories. It then allows the user to configure the ESP-IDF project using a text-based menu system to customize each component. After the components in the project are configured, the build system will compile the project.
A project is a directory that contains all the files and configuration to build a single app (executable), as well as additional supporting elements such as a partition table, data partitions or filesystem partitions, and a bootloader.
Project configuration is held in a single file called sdkconfig in the root directory of the project. This configuration file is modified via idf.py menuconfig to customize the configuration of the project. A single project contains exactly one project configuration.
An app is an executable that is built by ESP-IDF. A single project will usually build two apps - a "project app" (the main executable, ie your custom firmware) and a "bootloader app" (the initial bootloader program which launches the project app).
Components are modular pieces of standalone code that are compiled into static libraries (.a files) and linked to an app. Some are provided by ESP-IDF itself, others may be sourced from other places.
Target is the hardware for which an application is built. A full list of supported targets in your version of ESP-IDF can be seen by running idf.py --list-targets.
Some things are not part of the project:
ESP-IDF is not part of the project. Instead, it is standalone, and linked to the project via the IDF_PATH environment variable which holds the path of the esp-idf directory. This allows the ESP-IDF framework to be decoupled from your project.
The toolchain for compilation is not part of the project. The toolchain should be installed in the system command line PATH.
.. _idf.py:
The idf.py command-line tool provides a front-end for easily managing your project builds. It manages the following tools:
esptool_ for flashing the target.For more details about configuring the build system using idf.py, please refer to :doc:IDF Frontend <tools/idf-py>.
:ref:idf.py is a wrapper around CMake_ for convenience. However, you can also invoke CMake directly.
.. highlight:: bash
When idf.py does something, it prints each command that it runs for easy reference. For example, the idf.py build command is the same as running these commands in a bash shell (or similar commands for Windows Command Prompt)::
mkdir -p build cd build cmake .. -G Ninja # or 'Unix Makefiles' ninja
In the above list, the cmake command configures the project and generates build files for use with the final build tool. In this case, the final build tool is Ninja_: running ninja actually builds the project.
It's not necessary to run cmake more than once. After the first build, you only need to run ninja each time. ninja will automatically re-invoke cmake if the project needs reconfiguration.
If using CMake with ninja or make, there are also targets for more of the idf.py sub-commands. For example, running make menuconfig or ninja menuconfig in the build directory will work the same as idf.py menuconfig.
.. note::
If you're already familiar with CMake_, you may find the ESP-IDF CMake-based build system unusual because it wraps a lot of CMake's functionality to reduce boilerplate. See writing pure CMake components_ for some information about writing more "CMake style" components.
.. _flash-with-ninja-or-make:
Flashing with Ninja or Make ^^^^^^^^^^^^^^^^^^^^^^^^^^^
It's possible to build and flash directly from ninja or make by running a target like::
ninja flash
Or::
make app-flash
Available targets are: flash, app-flash (app only), bootloader-flash (bootloader only).
When flashing this way, optionally set the ESPPORT and ESPBAUD environment variables to specify the serial port and baud rate. You can set environment variables in your operating system or IDE project. Alternatively, set them directly on the command line::
ESPPORT=/dev/ttyUSB0 ninja flash
.. note::
Providing environment variables at the start of the command like this is Bash shell Syntax. It will work on Linux and macOS. It won't work when using Windows Command Prompt, but it will work when using Bash-like shells on Windows.
Or::
make -j3 app-flash ESPPORT=COM4 ESPBAUD=2000000
.. note::
Providing variables at the end of the command line is make syntax, and works for make on all platforms.
You can also use an IDE with CMake integration. The IDE will want to know the path to the project's CMakeLists.txt file. IDEs with CMake integration often provide their own build tools (CMake calls these "generators") to build the source files as part of the IDE.
When adding custom non-build steps like "flash" to the IDE, it is recommended to execute idf.py for these "special" commands.
For more detailed information about integrating ESP-IDF with CMake into an IDE, see Build System Metadata_.
.. _setting-python-interpreter:
ESP-IDF works well with Python version 3.10+.
idf.py and other Python scripts will run with the default Python interpreter, i.e., python. You can switch to a different one like python3 $IDF_PATH/tools/idf.py ..., or you can set up a shell alias or another script to simplify the command.
If using CMake directly, running cmake -D PYTHON=python3 ... will cause CMake to override the default Python interpreter.
If using an IDE with CMake, setting the PYTHON value as a CMake cache override in the IDE UI will override the default Python interpreter.
To manage the Python version more generally via the command line, check out the tools pyenv_ or virtualenv_. These let you change the default Python version.
.. _example-project-structure:
.. highlight:: none
An example project directory tree might look like this:
.. code-block:: none
- myProject/
- CMakeLists.txt
- sdkconfig
- dependencies.lock
- bootloader_components/ - boot_component/ - CMakeLists.txt
- Kconfig
- src1.c
- components/ - component1/ - CMakeLists.txt
- Kconfig
- src1.c
- component2/ - CMakeLists.txt
- Kconfig
- src1.c
- include/ - component2.h
- managed_components/ - namespace__component-name/ - CMakelists.txt
- src1.c
- idf_component.yml
- include/ - src1.h
- main/ - CMakeLists.txt
- src1.c
- src2.c
- idf_component.yml
- build/
This example "myProject" contains the following elements:
A top-level project CMakeLists.txt file. This is the primary file which CMake uses to learn how to build the project; and may set project-wide CMake variables. It includes the file :idf_file:/tools/cmake/project.cmake which implements the rest of the build system. Finally, it sets the project name and defines the project.
"sdkconfig" project configuration file. This file is created/updated when idf.py menuconfig runs, and holds the configuration for all of the components in the project (including ESP-IDF itself). The sdkconfig file may or may not be added to the source control system of the project. More information about this file can be found in the :ref:sdkconfig file <sdkconfig-file> section in the Configuration Guide.
"dependencies.lock" file contains the list of all managed components, and their versions, that are currently in used in the project. The dependencies.lock file is generated or updated automatically when IDF Component Manager is used to add or update project components. So this file should never be edited manually! If the project does not have idf_component.yml files in any of its components, dependencies.lock will not be created.
Optional "idf_component.yml" file contains metadata about the component and its dependencies. It is used by the IDF Component Manager to download and resolve these dependencies. More information about this file can be found in the idf_component.yml <https://docs.espressif.com/projects/idf-component-manager/en/latest/reference/manifest_file.html>_ section.
Optional "bootloader_components" directory contains components that need to be compiled and linked inside the bootloader project. A project does not have to contain custom bootloader components of this kind, but it can be useful in case the bootloader needs to be modified to embed new features.
Optional "components" directory contains components that are part of the project. A project does not have to contain custom components of this kind, but it can be useful for structuring reusable code or including third-party components that aren't part of ESP-IDF. Alternatively, EXTRA_COMPONENT_DIRS can be set in the top-level CMakeLists.txt to look for components in other places.
"main" directory is a special component that contains source code for the project itself. "main" is a default name, the CMake variable COMPONENT_DIRS includes this component but you can modify this variable. See the :ref:renaming main <rename-main> section for more info. If you have a lot of source files in your project, we recommend grouping most into components instead of putting them all in "main".
"build" directory is where the build output is created. This directory is created by idf.py if it doesn't already exist. CMake configures the project and generates interim build files in this directory. Then, after the main build process is run, this directory will also contain interim object files and libraries as well as final binary output files. This directory is usually not added to source control or distributed with the project source code.
"managed_components" directory is created by the IDF Component Manager to store components managed by this tool. Each managed component typically includes a idf_component.yml manifest file defining the component's metadata, such as version and dependencies. However, for components sourced from Git repositories, the manifest file is optional. Users should avoid manually modifying the contents of the "managed_components" directory. If alterations are needed, the component can be copied to the components directory. The "managed_components" directory is usually not versioned in Git and not distributed with the project source code.
Component directories each contain a component CMakeLists.txt file. This file contains variable definitions to control the build process of the component, and its integration into the overall project. See Component CMakeLists Files_ for more details.
Each component may also include a Kconfig file defining the component configuration_ options that can be set via menuconfig. Some components may also include Kconfig.projbuild and project_include.cmake files, which are special files for overriding parts of the project_.
Each project has a single top-level CMakeLists.txt file that contains build settings for the entire project. By default, the project CMakeLists can be quite minimal.
.. highlight:: cmake
Minimal project::
cmake_minimum_required(VERSION 3.22)
include($ENV{IDF_PATH}/tools/cmake/project.cmake)
project(myProject)
.. _project-mandatory-parts:
The inclusion of these three lines, in the order shown above, is necessary for every project:
cmake_minimum_required(VERSION 3.22) tells CMake the minimum version that is required to build the project. ESP-IDF is designed to work with CMake 3.22 or newer. This line must be the first line in the CMakeLists.txt file.include($ENV{IDF_PATH}/tools/cmake/project.cmake) pulls in the rest of the CMake functionality to configure the project, discover all the components, etc.project(myProject) creates the project itself, and specifies the project name. The project name is used for the final binary output files of the app - ie myProject.elf, myProject.bin. Only one project can be defined per CMakeLists file... _optional_project_variable:
These variables all have default values that can be overridden for custom behavior. Look in :idf_file:/tools/cmake/project.cmake for all of the implementation details.
COMPONENT_DIRS: Directories to search for components. Defaults to IDF_PATH/components, PROJECT_DIR/components, and EXTRA_COMPONENT_DIRS. Override this variable if you don't want to search for components in these places.
EXTRA_COMPONENT_DIRS: Optional list of additional directories to search for components. Paths can be relative to the project directory, or absolute.
COMPONENTS: A list of component names to build into the project. Defaults to all components found in the COMPONENT_DIRS directories. Use this variable to "trim down" the project for faster build times. Note that any component which "requires" another component via the REQUIRES or PRIV_REQUIRES arguments on component registration will automatically have it added to this list, so the COMPONENTS list can be very short. The MINIMAL_BUILD :ref:build property <cmake-build-properties> can be used as an alternative to specifying only the main component in COMPONENTS.
BOOTLOADER_IGNORE_EXTRA_COMPONENT: Optional list of components, placed in bootloader_components/, that should be ignored by the bootloader compilation. Use this variable if a bootloader component needs to be included conditionally inside the project.
BOOTLOADER_EXTRA_COMPONENT_DIRS: Optional list of additional directories to search for components to be compiled as part of the bootloader. Please note that this is a build property.
Any paths in these variables can be absolute paths, or set relative to the project directory.
To set these variables, use the cmake set command <cmake set_>_ ie set(VARIABLE "VALUE"). The set() commands should be placed after the cmake_minimum(...) line but before the include(...) line.
.. _rename-main:
main ComponentThe build system provides special treatment to the main component. It is a component that gets automatically added to the build provided that it is in the expected location, PROJECT_DIR/main. All other components in the build are also added as its dependencies, saving the user from hunting down dependencies and providing a build that works right out of the box. Renaming the main component causes the loss of these behind-the-scenes heavy lifting, requiring the user to specify the location of the newly renamed component and manually specify its dependencies. Specifically, the steps to renaming main are as follows:
main directory.EXTRA_COMPONENT_DIRS in the project CMakeLists.txt to include the renamed main directory.on component registration <cmake_minimal_component_cmakelists>... note::
A project without a main component cannot use the MINIMAL_BUILD :ref:build property <cmake-build-properties>, as this property explicitly relies on the presence of the main component. Ensure that the MINIMAL_BUILD build property is not set for projects that do not include a main component.
The build sets some global build specifications (compile flags, definitions, etc.) that gets used in compiling all sources from all components.
.. highlight:: cmake
For example, one of the default build specifications set is the compile option -Wextra. Suppose a user wants to use override this with -Wno-extra,
it should be done after project()::
cmake_minimum_required(VERSION 3.22)
include($ENV{IDF_PATH}/tools/cmake/project.cmake)
project(myProject)
idf_build_set_property(COMPILE_OPTIONS "-Wno-error" APPEND)
This ensures that the compile options set by the user won't be overridden by the default build specifications, since the latter are set inside project().
.. _component-directories:
Each project contains one or more components. Components can be part of ESP-IDF, part of the project's own components directory, or added from custom component directories (:ref:see above <component-directories>).
A component is any directory in the COMPONENT_DIRS list which contains a CMakeLists.txt file.
The list of directories in COMPONENT_DIRS is searched for the project's components. Directories in this list can either be components themselves (ie they contain a CMakeLists.txt file), or they can be top-level directories whose sub-directories are components.
When CMake runs to configure the project, it logs the components included in the build. This list can be useful for debugging the inclusion/exclusion of certain components.
.. _cmake-components-same-name:
When ESP-IDF is collecting all the components to compile, the search precedence is as follows (from highest to lowest):
EXTRA_COMPONENT_DIRSPROJECT_DIR/managed_components, unless the IDF Component Manager is disabled.IDF_PATH/components)If two or more of these directories contain component sub-directories with the same name, the component with higher precedence is used. This allows, for example, overriding ESP-IDF components with a modified version by copying that component from the ESP-IDF components directory to the project components directory and then modifying it there. If used in this way, the ESP-IDF directory itself can remain untouched.
.. note::
If a component is overridden in an existing project by moving it to a new location, the project will not automatically see the new component path. Run idf.py reconfigure (or delete the project build folder) and then build again.
.. _cmake_minimal_component_cmakelists:
.. highlight:: cmake
The minimal component CMakeLists.txt file simply registers the component to the build system using idf_component_register::
idf_component_register(SRCS "foo.c" "bar.c" INCLUDE_DIRS "include" REQUIRES mbedtls)
SRCS is a list of source files (*.c, *.cpp, *.cc, *.S). These source files will be compiled into the component library.INCLUDE_DIRS is a list of directories to add to the global include search path for any component which requires this component, and also the main source files.REQUIRES is not actually required, but it is very often required to declare what other components this component will use. See :ref:component requirements <component-requirements>.A library with the name of the component will be built and linked to the final app.
Directories are usually specified relative to the CMakeLists.txt file itself, although they can be absolute.
There are other arguments that can be passed to idf_component_register. These arguments are discussed :ref:here <cmake-component-register>.
See example component requirements_ and example component CMakeLists_ for more complete component CMakeLists.txt examples.
.. _preset_component_variables:
The following component-specific variables are available for use inside component CMakeLists, but should not be modified:
COMPONENT_DIR: The component directory. Evaluates to the absolute path of the directory containing CMakeLists.txt. The component path cannot contain spaces. This is the same as the CMAKE_CURRENT_SOURCE_DIR variable.COMPONENT_NAME: Name of the component. Same as the name of the component directory.COMPONENT_ALIAS: Alias of the library created internally by the build system for the component.COMPONENT_LIB: Name of the library created internally by the build system for the component.COMPONENT_VERSION: Component version specified by idf_component.yml and set by IDF Component Manager.The following variables are set at the project level, but available for use in component CMakeLists:
CONFIG_*: Each value in the project configuration has a corresponding variable available in cmake. All names begin with CONFIG_. More information on how the project configuration works, please visit :ref:Project Configuration Guide <project-configuration-guide>.ESP_PLATFORM: Set to 1 when the CMake file is processed within the ESP-IDF build system.The following are some project/build variables that are available as build properties and whose values can be queried using idf_build_get_property from the component CMakeLists.txt:
PROJECT_NAME: Name of the project, as set in project CMakeLists.txt file.
PROJECT_DIR: Absolute path of the project directory containing the project CMakeLists. Same as the CMAKE_SOURCE_DIR variable.
COMPONENTS: Names of all components that are included in this build, formatted as a semicolon-delimited CMake list.
IDF_VER: Git version of ESP-IDF (produced by git describe)
IDF_VERSION_MAJOR, IDF_VERSION_MINOR, IDF_VERSION_PATCH: Components of ESP-IDF version, to be used in conditional expressions. Note that this information is less precise than that provided by IDF_VER variable. v4.0-dev-*, v4.0-beta1, v4.0-rc1 and v4.0 will all have the same values of IDF_VERSION_* variables, but different IDF_VER values.
IDF_TARGET: Name of the target for which the project is being built.
PROJECT_VER: Project version.
CONFIG_APP_PROJECT_VER_FROM_CONFIG option is set, the value of :ref:CONFIG_APP_PROJECT_VER will be used.PROJECT_VER variable is set in project CMakeLists.txt file, its value will be used.PROJECT_DIR/version.txt exists, its contents will be used as PROJECT_VER.VERSION argument is passed to the project() call in the CMakeLists.txt file as project(... VERSION x.y.z.w ) then it will be used as PROJECT_VER. The VERSION argument must be compliant with the cmake standard <https://cmake.org/cmake/help/v3.22/command/project.html>_.PROJECT_VER will be "1".EXTRA_PARTITION_SUBTYPES: CMake list of extra partition subtypes. Each subtype description is a comma-separated string with type_name, subtype_name, numeric_value format. Components may add new subtypes by appending them to this list.
Other build properties are listed :ref:here <cmake-build-properties>.
.. _component_build_control:
.. highlight:: cmake
To pass compiler options when compiling source files belonging to a particular component, use the target_compile_options_ function::
target_compile_options(${COMPONENT_LIB} PRIVATE -Wno-unused-variable)
To apply the compilation flags to a single source file, use the CMake set_source_files_properties_ command::
set_source_files_properties(mysrc.c
PROPERTIES COMPILE_FLAGS
-Wno-unused-variable
)
This can be useful if there is upstream code that emits warnings.
.. note::
CMake `set_source_files_properties`_ command is not applicable when the source files have been populated with help of the ``SRC_DIRS`` variable in ``idf_component_register``. See :ref:`cmake-file-globbing` for more details.
When using these commands, place them after the call to idf_component_register in the component CMakeLists file.
.. _component-configuration:
Each component can also have a Kconfig file, alongside CMakeLists.txt. This contains configuration settings to add to the configuration menu for this component.
These settings are found under the "Component Settings" menu when menuconfig is run.
To create a component Kconfig file, it is easiest to start with one of the Kconfig files distributed with ESP-IDF.
For an example, see Adding conditional configuration_. For a more detailed guide, see :ref:Component Configuration Guide <component-configuration-guide>.
The ESP-IDF build system adds the following C preprocessor definitions on the command line:
ESP_PLATFORM : Can be used to detect that build happens within ESP-IDF.IDF_VER : Defined to a git version string. E.g. v2.0 for a tagged release or v1.0-275-g0efaa4f for an arbitrary commit... _component-requirements:
When compiling each component, the ESP-IDF build system recursively evaluates its dependencies. This means each component needs to declare the components that it depends on ("requires").
.. code-block:: cmake
idf_component_register(... REQUIRES mbedtls PRIV_REQUIRES console spiffs)
REQUIRES should be set to all components whose header files are #included from the public header files of this component.
PRIV_REQUIRES should be set to all components whose header files are #included from any source files in this component, unless already listed in REQUIRES. Also, any component which is required to be linked in order for this component to function correctly.
The values of REQUIRES and PRIV_REQUIRES should not depend on any configuration options (CONFIG_xxx macros). This is because requirements are expanded before the configuration is loaded. Other component variables (like include paths or source files) can depend on configuration options.
Not setting either or both REQUIRES variables is fine. If the component has no requirements except for the Common component requirements_ needed for RTOS, libc, etc.
If a component only supports some target chips (values of IDF_TARGET) then it can specify REQUIRED_IDF_TARGETS in the idf_component_register call to express these requirements. In this case, the build system will generate an error if the component is included in the build, but does not support the selected target.
.. note::
In CMake terms, REQUIRES & PRIV_REQUIRES are approximate wrappers around the CMake functions target_link_libraries(... PUBLIC ...) and target_link_libraries(... PRIVATE ...).
.. _example component requirements:
Imagine there is a car component, which uses the engine component, which uses the spark_plug component:
.. code-block:: none
- autoProject/
- CMakeLists.txt
- components/ - car/ - CMakeLists.txt
- car.c
- car.h
- engine/ - CMakeLists.txt
- engine.c
- include/ - engine.h
- spark_plug/ - CMakeLists.txt
- spark_plug.c
- spark_plug.h
Car Component ^^^^^^^^^^^^^
.. highlight:: c
The car.h header file is the public interface for the car component. This header includes engine.h directly because it uses some declarations from this header::
/* car.h */ #include "engine.h"
#ifdef ENGINE_IS_HYBRID #define CAR_MODEL "Hybrid" #endif
And car.c includes car.h as well::
/* car.c */ #include "car.h"
This means the car/CMakeLists.txt file needs to declare that car requires engine:
.. code-block:: cmake
idf_component_register(SRCS "car.c" INCLUDE_DIRS "." REQUIRES engine)
SRCS gives the list of source files in the car component.INCLUDE_DIRS gives the list of public include directories for this component. Because the public interface is car.h, the directory containing car.h is listed here.REQUIRES gives the list of components required by the public interface of this component. Because car.h is a public header and includes a header from engine, we include engine here. This makes sure that any other component which includes car.h will be able to recursively include the required engine.h also.Engine Component ^^^^^^^^^^^^^^^^
.. highlight:: c
The engine component also has a public header file include/engine.h, but this header is simpler::
/* engine.h */ #define ENGINE_IS_HYBRID
void engine_start(void);
The implementation is in engine.c::
/* engine.c */ #include "engine.h" #include "spark_plug.h"
...
In this component, engine depends on spark_plug but this is a private dependency. spark_plug.h is needed to compile engine.c, but not needed to include engine.h.
This means that the engine/CMakeLists.txt file can use PRIV_REQUIRES:
.. code-block:: cmake
idf_component_register(SRCS "engine.c" INCLUDE_DIRS "include" PRIV_REQUIRES spark_plug)
As a result, source files in the car component don't need the spark_plug include directories added to their compiler search path. This can speed up compilation, and stops compiler command lines from becoming longer than necessary.
Spark Plug Component ^^^^^^^^^^^^^^^^^^^^
The spark_plug component doesn't depend on anything else. It has a public header file spark_plug.h, but this doesn't include headers from any other components.
This means that the spark_plug/CMakeLists.txt file doesn't need any REQUIRES or PRIV_REQUIRES clauses:
.. code-block:: cmake
idf_component_register(SRCS "spark_plug.c" INCLUDE_DIRS ".")
Each component's source file is compiled with these include path directories, as specified in the passed arguments to idf_component_register:
.. code-block:: cmake
idf_component_register(.. INCLUDE_DIRS "include" PRIV_INCLUDE_DIRS "other")
INCLUDE_DIRS and PRIV_INCLUDE_DIRS.INCLUDE_DIRS belonging to all other components listed in the REQUIRES and PRIV_REQUIRES parameters (ie all the current component's public and private dependencies).INCLUDE_DIRS of those components REQUIRES lists (ie all public dependencies of this component's dependencies, recursively expanded).The component named main is special because it automatically requires all other components in the build. So it's not necessary to pass REQUIRES or PRIV_REQUIRES to this component. See :ref:renaming main <rename-main> for a description of what needs to be changed if no longer using the main component.
.. _component-common-requirements:
To avoid duplication, every component automatically requires some "common" IDF components even if they are not mentioned explicitly. Headers from these components can always be included.
The list of common components is: cxx, esp_libc, freertos, esp_hw_support, heap, log, soc, hal, esp_rom, esp_common, esp_system, xtensa/riscv.
.. _including-components-in-the-build:
By default, every component is included in the build.
If you set the COMPONENTS variable to a minimal list of components used directly by your project, then the build will expand to also include required components. The full list of components will be:
COMPONENTS.common components <component-common-requirements> that every component depends on.Setting COMPONENTS to the minimal list of required components can significantly reduce compile times.
The MINIMAL_BUILD :ref:build property <cmake-build-properties> can be set to ON, which acts as a shortcut to configure the COMPONENTS variable to include only the main component. This means that the build will include only the :ref:common components <component-common-requirements>, the main component, and all dependencies associated with it, both direct and indirect. If the COMPONENTS variable is defined while the MINIMAL_BUILD property is enabled, COMPONENTS will take precedence.
.. note::
Certain features and configurations, such as those provided by esp_psram or espcoredump components, may not be available to your project by default if the minimal list of components is used. When using the COMPONENTS variable, ensure that all necessary components are included. Similarly, when using the MINIMAL_BUILD build property, ensure that all required components are specified in the REQUIRES or PRIV_REQUIRES argument during component registration.
.. _component-circular-dependencies:
It's possible for a project to contain Component A that requires (REQUIRES or PRIV_REQUIRES) Component B, and Component B that requires Component A. This is known as a dependency cycle or a circular dependency.
CMake will usually handle circular dependencies automatically by repeating the component library names twice on the linker command line. However this strategy doesn't always work, and the build may fail with a linker error about "Undefined reference to ...", referencing a symbol defined by one of the components inside the circular dependency. This is particularly likely if there is a large circular dependency, i.e., A > B > C > D > A.
The best solution is to restructure the components to remove the circular dependency. In most cases, a software architecture without circular dependencies has desirable properties of modularity and clean layering and will be more maintainable in the long term. However, removing circular dependencies is not always possible.
To bypass a linker error caused by a circular dependency, the simplest workaround is to increase the CMake LINK_INTERFACE_MULTIPLICITY_ property of one of the component libraries. This causes CMake to repeat this library and its dependencies more than two times on the linker command line.
For example:
.. code-block:: cmake
set_property(TARGET ${COMPONENT_LIB} APPEND PROPERTY LINK_INTERFACE_MULTIPLICITY 3)
idf_component_register in the component CMakeLists.txt file.Advanced Workaround: Undefined Symbols ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
If only one or two symbols are causing a circular dependency, and all other dependencies are linear, then there is an alternative method to avoid linker errors: Specify the specific symbols required for the "reverse" dependency as undefined symbols at link time.
For example, if component A depends on component B but component B also needs to reference reverse_ops from component A (but nothing else), then you can add a line like the following to the component B CMakeLists.txt to resolve the cycle at link time:
.. code-block:: cmake
# This symbol is provided by 'Component A' at link time
target_link_libraries(${COMPONENT_LIB} INTERFACE "-u reverse_ops")
-u argument means that the linker will always include this symbol in the link, regardless of dependency ordering.idf_component_register in the component CMakeLists.txt file.REQUIRES from B to A. This further simplifies the component structure in the build system.See the target_link_libraries_ documentation for more information about this CMake function.
.. _component-requirements-implementation:
expand_requirements.cmake is run. This script does a partial evaluation of all component CMakeLists.txt files and builds a graph of component requirements (this :ref:graph may have cycles <component-circular-dependencies>). The graph is used to generate a file component_depends.cmake in the build directory.BUILD_COMPONENTS variable). The BUILD_COMPONENTS variable is sorted so dependencies are listed first, however, as the component dependency graph has cycles this cannot be guaranteed for all components. The order should be deterministic given the same set of components and component dependencies.BUILD_COMPONENTS is logged by CMake as "Component names: "Component Dependency Order ^^^^^^^^^^^^^^^^^^^^^^^^^^
The order of components in the BUILD_COMPONENTS variable determines other orderings during the build:
project_include.cmake files are included in the project.-I argument). (Note that for a given component's source files, only that component's dependency's header paths are passed to the compiler.)Adding Link-Time Dependencies ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
.. highlight:: cmake
The ESP-IDF CMake helper function idf_component_add_link_dependency adds a link-only dependency between one component and another. In almost all cases, it is better to use the PRIV_REQUIRES feature in idf_component_register to create a dependency. However, in some cases, it's necessary to add the link-time dependency of another component to this component, i.e., the reverse order to PRIV_REQUIRES (for example: :doc:/api-reference/peripherals/spi_flash/spi_flash_override_driver).
To make another component depend on this component at link time::
idf_component_add_link_dependency(FROM other_component)
Place this line after the line with idf_component_register.
It's also possible to specify both components by name::
idf_component_add_link_dependency(FROM other_component TO that_component)
.. _override_project_config:
.. _project_include.cmake:
For components that have build requirements that must be evaluated before any component CMakeLists files are evaluated, you can create a file called project_include.cmake in the component directory. This CMake file is included when project.cmake is evaluating the entire project.
project_include.cmake files are used inside ESP-IDF, for defining project-wide build features such as esptool command line arguments and the bootloader "special app".
Unlike component CMakeLists.txt files, when including a project_include.cmake file the current source directory (CMAKE_CURRENT_SOURCE_DIR and working directory) is the project directory. Use the variable COMPONENT_DIR for the absolute directory of the component.
Note that project_include.cmake isn't necessary for the most common component uses, such as adding include directories to the project, or LDFLAGS to the final linking step. These values can be customized via the CMakeLists.txt file itself. See Optional Project Variables_ for details.
project_include.cmake files are included in the order given in BUILD_COMPONENTS variable (as logged by CMake). This means that a component's project_include.cmake file will be included after it's all dependencies' project_include.cmake files, unless both components are part of a dependency cycle. This is important if a project_include.cmake file relies on variables set by another component. See also :ref:above <component-requirements-implementation>.
Take great care when setting variables or targets in a project_include.cmake file. As the values are included in the top-level project CMake pass, they can influence or break functionality across all components!
This is an equivalent to project_include.cmake for :ref:component-configuration Kconfig files. If you want to include configuration options at the top level of menuconfig, rather than inside the "Component Configuration" sub-menu, then these can be defined in the Kconfig.projbuild file alongside the CMakeLists.txt file.
Take care when adding configuration values in this file, as they will be included across the entire project configuration. Where possible, it's generally better to create a Kconfig file for :ref:component-configuration.
For more information, see :ref:Kconfig Files <kconfig-files> section in the Configuration Guide.
Thanks to the linker's wrap feature, it is possible to redefine or extend the behavior of an existing ESP-IDF function. To do so, you will need to provide the following CMake declaration in your project's CMakeLists.txt file:
.. code-block:: cmake
target_link_libraries(${COMPONENT_LIB} INTERFACE "-Wl,--wrap=function_to_redefine")
Where function_to_redefine is the name of the function to redefine or extend. This option will let the linker replace all the calls to function_to_redefine functions in the binary libraries with calls to __wrap_function_to_redefine function. Thus, you must define this new symbol in your application.
The linker will provide a new symbol named __real_function_to_redefine which points to the former implementation of the function to redefine. It can be called from the new implementation, making it an extension of the former one.
This mechanism is shown in the example :example:build_system/wrappers. Check :idf_file:examples/build_system/wrappers/README.md for more details.
Thanks to the optional bootloader_components directory present in your ESP-IDF project, it is possible to override the default ESP-IDF bootloader. To do so, a new bootloader_components/main component should be defined, which will make the project directory tree look like the following:
- myProject/
- CMakeLists.txt
- sdkconfig
- bootloader_components/ - main/ - CMakeLists.txt
- Kconfig
- my_bootloader.c
- main/ - CMakeLists.txt
- app_main.c
- build/
Here, the my_bootloader.c file becomes source code for the new bootloader, which means that it will need to perform all the required operations to set up and load the main application from flash.
It is also possible to conditionally replace the bootloader depending on a certain condition, such as the target for example. This can be achieved thanks to the BOOTLOADER_IGNORE_EXTRA_COMPONENT CMake variable. This list can be used to tell the ESP-IDF bootloader project to ignore and not compile the given components present in bootloader_components. For example, if one wants to use the default bootloader for ESP32 target, then myProject/CMakeLists.txt should look like the following::
include($ENV{IDF_PATH}/tools/cmake/project.cmake)
if(${IDF_TARGET} STREQUAL "esp32")
set(BOOTLOADER_IGNORE_EXTRA_COMPONENT "main")
endif()
project(main)
It is important to note that this can also be used for any other bootloader components than main. In all cases, the prefix bootloader_component must not be specified.
See :example:custom_bootloader/bootloader_override for an example of overriding the default bootloader.
Similarly to regular applications, it is possible to include external components, not placed in bootloader_component, as part of the bootloader build thanks to the build property BOOTLOADER_EXTRA_COMPONENT_DIRS. It can either refer to a directory that contains several components, or refer to a single component. For example:
include($ENV{IDF_PATH}/tools/cmake/project.cmake)
idf_build_set_property(BOOTLOADER_EXTRA_COMPONENT_DIRS "/path/to/extra/component/" APPEND)
project(main)
See :example:custom_bootloader/bootloader_extra_dir for an example of adding extra components to the bootloader build.
.. _config_only_component:
Special components which contain no source files, only Kconfig.projbuild and Kconfig, can have a one-line CMakeLists.txt file which calls the function idf_component_register() with no arguments specified. This function will include the component in the project build, but no library will be built and no header files will be added to any included paths.
For full details about CMake_ and CMake commands, see the CMake v3.22 documentation_.
Some tips for debugging the ESP-IDF CMake-based build system:
cmake -DDEBUG=1 will produce more verbose diagnostic output from the IDF build system.cmake with the --trace or --trace-expand options will give a lot of information about control flow. See the cmake command line documentation_.When included from a project CMakeLists file, the project.cmake file defines some utility modules and global variables and then sets IDF_PATH if it was not set in the system environment.
It also defines an overridden custom version of the built-in CMake_ project function. This function is overridden to add all of the ESP-IDF specific project functionality.
.. _warn-undefined-variables:
By default, the function of warnings on undefined variables is disabled.
To enable this function, we can pass the --warn-uninitialized flag to CMake_ or pass the --cmake-warn-uninitialized flag to idf.py so it will print a warning if an undefined variable is referenced in the build. This can be very useful to find buggy CMake files.
Browse the :idf_file:/tools/cmake/project.cmake file and supporting functions in :idf:/tools/cmake/ for more details.
.. _component_cmakelists_example:
Because the build environment tries to set reasonable defaults that will work most of the time, component CMakeLists.txt can be very small or even empty (see Minimal Component CMakeLists). However, overriding preset_component_variables is usually required for some functionality.
Here are some more advanced examples of component CMakeLists files.
.. _add_conditional_config:
The configuration system can be used to conditionally compile some files depending on the options selected in the project configuration.
.. highlight:: none
Kconfig::
config FOO_ENABLE_BAR
bool "Enable the BAR feature."
help
This enables the BAR feature of the FOO component.
CMakeLists.txt::
set(srcs "foo.c" "more_foo.c")
if(CONFIG_FOO_ENABLE_BAR)
list(APPEND srcs "bar.c")
endif()
idf_component_register(SRCS "${srcs}" ...)
This example makes use of the CMake if <cmake if_>_ function and list APPEND <cmake list_>_ function.
This can also be used to select or stub out an implementation, as such:
Kconfig::
config ENABLE_LCD_OUTPUT
bool "Enable LCD output."
help
Select this if your board has an LCD.
config ENABLE_LCD_CONSOLE
bool "Output console text to LCD"
depends on ENABLE_LCD_OUTPUT
help
Select this to output debugging output to the LCD
config ENABLE_LCD_PLOT
bool "Output temperature plots to LCD"
depends on ENABLE_LCD_OUTPUT
help
Select this to output temperature plots
.. highlight:: cmake
CMakeLists.txt::
if(CONFIG_ENABLE_LCD_OUTPUT)
set(srcs lcd-real.c lcd-spi.c)
else()
set(srcs lcd-dummy.c)
endif()
# We need font if either console or plot is enabled
if(CONFIG_ENABLE_LCD_CONSOLE OR CONFIG_ENABLE_LCD_PLOT)
list(APPEND srcs "font.c")
endif()
idf_component_register(SRCS "${srcs}"
...)
The current target is available to CMake files via IDF_TARGET variable.
In addition to that, if target xyz is used (IDF_TARGET=xyz), then Kconfig variable CONFIG_IDF_TARGET_XYZ will be set.
Note that component dependencies may depend on IDF_TARGET variable, but not on Kconfig variables. Also one can not use Kconfig variables in include statements in CMake files, but IDF_TARGET can be used in such context.
Some components will have a situation where a source file isn't supplied with the component itself but has to be generated from another file. Say our component has a header file that consists of the converted binary data of a BMP file, converted using a hypothetical tool called bmp2h. The header file is then included in as C source file called graphics_lib.c::
add_custom_command(OUTPUT logo.h
COMMAND bmp2h -i ${COMPONENT_DIR}/logo.bmp -o log.h
DEPENDS ${COMPONENT_DIR}/logo.bmp
VERBATIM)
add_custom_target(logo DEPENDS logo.h)
add_dependencies(${COMPONENT_LIB} logo)
set_property(DIRECTORY "${COMPONENT_DIR}" APPEND PROPERTY
ADDITIONAL_CLEAN_FILES logo.h)
This answer is adapted from the CMake FAQ entry <cmake faq generated files_>_, which contains some other examples that will also work with ESP-IDF builds.
In this example, logo.h will be generated in the current directory (the build directory) while logo.bmp comes with the component and resides under the component path. Because logo.h is a generated file, it should be cleaned when the project is cleaned. For this reason, it is added to the ADDITIONAL_CLEAN_FILES_ property.
.. note::
If generating files as part of the project CMakeLists.txt file, not a component CMakeLists.txt, then use build property PROJECT_DIR instead of ${COMPONENT_DIR} and ${PROJECT_NAME}.elf instead of ${COMPONENT_LIB}.)
If a a source file from another component included logo.h, then add_dependencies would need to be called to add a dependency between the two components, to ensure that the component source files were always compiled in the correct order.
.. _cmake_embed_data:
Sometimes you have a file with some binary or text data that you'd like to make available to your component, but you don't want to reformat the file as a C source.
You can specify argument EMBED_FILES in the component registration, giving space-delimited names of the files to embed::
idf_component_register(... EMBED_FILES server_root_cert.der)
Or if the file is a string, you can use the variable EMBED_TXTFILES. This will embed the contents of the text file as a null-terminated string::
idf_component_register(... EMBED_TXTFILES server_root_cert.pem)
.. highlight:: c
The file's contents will be added to the .rodata section in flash, and are available via symbol names as follows::
extern const uint8_t server_root_cert_pem_start[] asm("_binary_server_root_cert_pem_start"); extern const uint8_t server_root_cert_pem_end[] asm("_binary_server_root_cert_pem_end");
The names are generated from the full name of the file, as given in EMBED_FILES. Characters /, ., etc. are replaced with underscores. The _binary prefix in the symbol name is added by objcopy and is the same for both text and binary files.
.. highlight:: cmake
To embed a file into a project, rather than a component, you can call the function target_add_binary_data like this::
target_add_binary_data(myproject.elf "main/data.bin" TEXT)
Place this line after the project() line in your project CMakeLists.txt file. Replace myproject.elf with your project name. The final argument can be TEXT to embed a null-terminated string, or BINARY to embed the content as-is.
For an example of using this technique, see the "main" component of the file_serving example :example_file:protocols/http_server/file_serving/main/CMakeLists.txt - two files are loaded at build time and linked into the firmware.
.. highlight:: cmake
It is also possible to embed a generated file::
add_custom_command(OUTPUT my_processed_file.bin COMMAND my_process_file_cmd my_unprocessed_file.bin) target_add_binary_data(my_target "my_processed_file.bin" BINARY)
In the example above, my_processed_file.bin is generated from my_unprocessed_file.bin through some command my_process_file_cmd, then embedded into the target.
To specify a dependence on a target, use the DEPENDS argument::
add_custom_target(my_process COMMAND ...) target_add_binary_data(my_target "my_embed_file.bin" BINARY DEPENDS my_process)
The DEPENDS argument to target_add_binary_data ensures that the target executes first.
ESP-IDF has a feature called linker script generation that enables components to define where its code and data will be placed in memory through linker fragment files. These files are processed by the build system, and is used to augment the linker script used for linking app binary. See :doc:Linker Script Generation <linker-script-generation> for a quick start guide as well as a detailed discussion of the mechanism.
.. _component-build-full-override:
.. highlight:: cmake
Obviously, there are cases where all these recipes are insufficient for a certain component, for example when the component is basically a wrapper around another third-party component not originally intended to be compiled under this build system. In that case, it's possible to forego the ESP-IDF build system entirely by using a CMake feature called ExternalProject_. Example component CMakeLists::
externalproject_add(quirc_build PREFIX ${COMPONENT_DIR} SOURCE_DIR ${COMPONENT_DIR}/quirc CONFIGURE_COMMAND "" BUILD_IN_SOURCE 1 BUILD_COMMAND make CC=${CMAKE_C_COMPILER} libquirc.a INSTALL_COMMAND "" )
add_library(quirc STATIC IMPORTED GLOBAL) add_dependencies(quirc quirc_build)
set_target_properties(quirc PROPERTIES IMPORTED_LOCATION ${COMPONENT_DIR}/quirc/libquirc.a) set_target_properties(quirc PROPERTIES INTERFACE_INCLUDE_DIRECTORIES ${COMPONENT_DIR}/quirc/lib)
set_directory_properties( PROPERTIES ADDITIONAL_CLEAN_FILES "${COMPONENT_DIR}/quirc/libquirc.a")
(The above CMakeLists.txt can be used to create a component named quirc that builds the quirc_ project using its own Makefile.)
externalproject_add defines an external build system.
SOURCE_DIR, CONFIGURE_COMMAND, BUILD_COMMAND and INSTALL_COMMAND should always be set. CONFIGURE_COMMAND can be set to an empty string if the build system has no "configure" step. INSTALL_COMMAND will generally be empty for ESP-IDF builds.BUILD_IN_SOURCE means the build directory is the same as the source directory. Otherwise, you can set BUILD_DIR.externalproject_add()The second set of commands adds a library target, which points to the "imported" library file built by the external system. Some properties need to be set in order to add include directories and tell CMake where this file is.
Finally, the generated library is added to ADDITIONAL_CLEAN_FILES_. This means make clean will delete this library. (Note that the other object files from the build won't be deleted.)
.. _ADDITIONAL_CLEAN_FILES_note:
ExternalProject Dependencies and Clean Builds ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
CMake has some unusual behavior around external project builds:
ADDITIONAL_CLEAN_FILES_ only works when "make" or "ninja" is used as the build system. If an IDE build system is used, it won't delete these files when cleaning.
However, the ExternalProject_ configure & build commands will always be re-run after a clean is run.
Therefore, there are two alternative recommended ways to configure the external build command:
BUILD_COMMAND run a full clean compile of all sources. The build command will be run if any of the dependencies passed to externalproject_add with DEPENDS have changed, or if this is a clean build (ie any of idf.py clean, ninja clean, or make clean was run.)BUILD_COMMAND be an incremental build command. Pass the parameter BUILD_ALWAYS 1 to externalproject_add. This means the external project will be built each time a build is run, regardless of dependencies. This is only recommended if the external project has correct incremental build behavior, and doesn't take too long to run.The best of these approaches for building an external project will depend on the project itself, its build system, and whether you anticipate needing to frequently recompile the project.
.. _custom-sdkconfig-defaults:
.. note::
For more detailed information about sdkconfig.defaults file, please visit :ref:sdkconfig.defaults file <sdkconfig-defaults-file> in Project Configuration section.
For example projects or other projects where you don't want to specify a full sdkconfig configuration, but you do want to override some key values from the ESP-IDF defaults, it is possible to create a file sdkconfig.defaults in the project directory. This file will be used when creating a new config from scratch, or when any new config value hasn't yet been set in the sdkconfig file.
To override the name of this file or to specify multiple files, set the SDKCONFIG_DEFAULTS environment variable or set SDKCONFIG_DEFAULTS in top-level CMakeLists.txt. File names that are not specified as full paths are resolved relative to current project's directory.
When specifying multiple files, use a semicolon as the list separator. Files listed first will be applied first. If a particular key is defined in multiple files, the definition in the latter file will override definitions from former files.
Some of the IDF examples include a sdkconfig.ci file. This is part of the continuous integration (CI) test framework and is ignored by the normal build process.
If and only if an sdkconfig.defaults file exists, the build system will also attempt to load defaults from an sdkconfig.defaults.TARGET_NAME file, where TARGET_NAME is the value of IDF_TARGET. For example, for esp32 target, default settings will be taken from sdkconfig.defaults first, and then from sdkconfig.defaults.esp32. If there are no generic default settings, an empty sdkconfig.defaults still needs to be created if the build system should recognize any additional target-dependent sdkconfig.defaults.TARGET_NAME files.
If SDKCONFIG_DEFAULTS is used to override the name of defaults file/files, the name of target-specific defaults file will be derived from SDKCONFIG_DEFAULTS value/values using the rule above. When there are multiple files in SDKCONFIG_DEFAULTS, target-specific file will be applied right after the file bringing it in, before all latter files in SDKCONFIG_DEFAULTS
For example, if SDKCONFIG_DEFAULTS="sdkconfig.defaults;sdkconfig_devkit1", and there is a file sdkconfig.defaults.esp32 in the same folder, then the files will be applied in the following order: (1) sdkconfig.defaults (2) sdkconfig.defaults.esp32 (3) sdkconfig_devkit1.
You can find more detailed information on how the project configuration works in the :ref:Project Configuration Guide <project-configuration-guide>. In the :ref:Configuration Files Structure and Relationships <configuration-structure>, you can find lower-level information about the configuration files.
.. _flash_parameters:
There are some scenarios that we want to flash the target board without IDF. For this case we want to save the built binaries, esptool and esptool write-flash arguments. It's simple to write a script to save binaries and esptool.
After running a project build, the build directory contains binary output files (.bin files) for the project and also the following flashing data files:
flash_project_args contains arguments to flash the entire project (app, bootloader, partition table, PHY data if this is configured).flash_app_args contains arguments to flash only the app.flash_bootloader_args contains arguments to flash only the bootloader... highlight:: bash
You can pass any of these flasher argument files to esptool as follows::
esptool --chip esp32 write-flash @build/flash_project_args
Alternatively, it is possible to manually copy the parameters from the argument file and pass them on the command line.
The build directory also contains a generated file flasher_args.json which contains project flash information, in JSON format. This file is used by idf.py and can also be used by other tools which need information about the project build.
The bootloader is a special "subproject" inside :idf:/components/bootloader/subproject. It has its own project CMakeLists.txt file and builds separate .ELF and .BIN files to the main project. However, it shares its configuration and build directory with the main project.
The subproject is inserted as an external project from the top-level project, by the file :idf_file:/components/bootloader/project_include.cmake. The main build process runs CMake for the subproject, which includes discovering components (a subset of the main components) and generating a bootloader-specific config (derived from the main sdkconfig).
.. _write-pure-component:
The ESP-IDF build system "wraps" CMake with the concept of "components", and helper functions to automatically integrate these components into a project build.
However, underneath the concept of "components" is a full CMake build system. It is also possible to make a component which is pure CMake.
.. highlight:: cmake
Here is an example minimal "pure CMake" component CMakeLists file for a component named json::
add_library(json STATIC cJSON/cJSON.c cJSON/cJSON_Utils.c)
target_include_directories(json PUBLIC cJSON)
espressif/cjson <https://github.com/espressif/idf-extra-components/tree/master/cjson>_ managed component.CMake is used for a lot of open-source C and C++ projects — code that users can tap into for their applications. One of the benefits of having a CMake build system is the ability to import these third-party projects, sometimes even without modification! This allows for users to be able to get functionality that may not yet be provided by a component, or use another library for the same functionality.
.. highlight:: cmake
Importing a library might look like this for a hypothetical library foo to be used in the main component::
idf_component_register(...)
fooset(FOO_BUILD_STATIC OFF) set(FOO_BUILD_TESTS OFF)
add_subdirectory(foo)
foo to main componenttarget_link_libraries(main PUBLIC foo)
For an actual example, take a look at :example:build_system/cmake/import_lib. Take note that what needs to be done in order to import the library may vary. It is recommended to read up on the library's documentation for instructions on how to import it from other projects. Studying the library's CMakeLists.txt and build structure can also be helpful.
It is also possible to wrap a third-party library to be used as a component in this manner. For example, the :component:mbedtls component is a wrapper for Espressif's fork of mbedtls <https://github.com/Mbed-TLS/mbedtls>_. See its :component_file:component CMakeLists.txt <mbedtls/CMakeLists.txt>.
The CMake variable ESP_PLATFORM is set to 1 whenever the ESP-IDF build system is being used. Tests such as if (ESP_PLATFORM) can be used in generic CMake code if special IDF-specific logic is required.
The above example assumes that the external library foo (or tinyxml in the case of the import_lib example) doesn't need to use any ESP-IDF APIs apart from common APIs such as libc, libstdc++, etc. If the external library needs to use APIs provided by other ESP-IDF components, this needs to be specified in the external CMakeLists.txt file by adding a dependency on the library target idf::<componentname>.
For example, in the foo/CMakeLists.txt file::
add_library(foo bar.c fizz.cpp buzz.cpp)
if(ESP_PLATFORM) # On ESP-IDF, bar.c needs to include esp_flash.h from the spi_flash component target_link_libraries(foo PRIVATE idf::spi_flash) endif()
.. highlight:: cmake
Another possibility is that you have a prebuilt static library (.a file), built by some other build process.
The ESP-IDF build system provides a utility function add_prebuilt_library for users to be able to easily import and use prebuilt libraries::
add_prebuilt_library(target_name lib_path [REQUIRES req1 req2 ...] [PRIV_REQUIRES req1 req2 ...])
where:
target_name- name that can be used to reference the imported library, such as when linking to other targetslib_path- path to prebuilt library; may be an absolute or relative path to the component directoryOptional arguments REQUIRES and PRIV_REQUIRES specify dependency on other components. These have the same meaning as the arguments for idf_component_register.
Take note that the prebuilt library must have been compiled for the same target as the consuming project. Configuration relevant to the prebuilt library must also match. If not paid attention to, these two factors may contribute to subtle bugs in the app.
For an example, take a look at :example:build_system/cmake/import_prebuilt.
ESP-IDF provides a template CMake project for easily creating an application. However, in some instances the user might already have an existing CMake project or may want to create a custom one. In these cases it is desirable to be able to consume IDF components as libraries to be linked to the user's targets (libraries/executables).
It is possible to do so by using the :ref:build system APIs provided <cmake_buildsystem_api> by :idf_file:tools/cmake/idf.cmake. For example:
.. code-block:: cmake
cmake_minimum_required(VERSION 3.22) project(my_custom_app C)
include($ENV{IDF_PATH}/tools/cmake/idf.cmake)
idf_build_process(esp32)
add_executable(${CMAKE_PROJECT_NAME}.elf main.c) target_link_libraries(${CMAKE_PROJECT_NAME}.elf idf::esp_libc)
idf_build_executable(${CMAKE_PROJECT_NAME}.elf)
The example in :example:build_system/cmake/idf_as_lib demonstrates the creation of an application equivalent to :example:hello world application <get-started/hello_world> using a custom CMake project.
.. only:: esp32
.. note:: The IDF build system can only set compiler flags for source files that it builds. When an external CMakeLists.txt file is used and PSRAM is enabled, remember to add -mfix-esp32-psram-cache-issue to the C compiler arguments. See :ref:CONFIG_SPIRAM_CACHE_WORKAROUND for details of this flag.
.. _cmake_buildsystem_api:
.. code-block:: none
idf_build_get_property(var property [GENERATOR_EXPRESSION])
Retrieve a :ref:build property <cmake-build-properties> property and store it in var accessible from the current scope. Specifying GENERATOR_EXPRESSION will retrieve the generator expression string for that property, instead of the actual value, which can be used with CMake commands that support generator expressions.
.. code-block:: none
idf_build_set_property(property val [APPEND])
Set a :ref:build property <cmake-build-properties> property with value val. Specifying APPEND will append the specified value to the current value of the property. If the property does not previously exist or it is currently empty, the specified value becomes the first element/member instead.
.. code-block:: none
idf_build_component(component_dir [component_source])
Present a directory component_dir that contains a component to the build system. Relative paths are converted to absolute paths with respect to current directory.
An optional component_source argument can be specified to indicate the source of the component. (default: "project_components")
This argument determines the overriding priority for components with the same name. For detailed information, see :ref:cmake-components-same-name.
This argument supports the following values (from highest to lowest priority):
EXTRA_COMPONENT_DIRS/componentsFor instance, if a component named "json" is present as both "idf_components", and "project_components", the component as "project_components" takes precedence over the one as "idf_components".
.. warning::
All calls to this command must be performed before `idf_build_process`. This command does not guarantee that the component will be processed during build (see the `COMPONENTS` argument description for `idf_build_process`).
.. code-block:: none
idf_build_process(target [PROJECT_DIR project_dir] [PROJECT_VER project_ver] [PROJECT_NAME project_name] [SDKCONFIG sdkconfig] [SDKCONFIG_DEFAULTS sdkconfig_defaults] [BUILD_DIR build_dir] [COMPONENTS component1 component2 ...])
Performs the bulk of the behind-the-scenes magic for including ESP-IDF components such as component configuration, libraries creation, dependency expansion and resolution. Among these functions, perhaps the most important from a user's perspective is the libraries creation by calling each component's idf_component_register. This command creates the libraries for each component, which are accessible using aliases in the form idf::component_name.
These aliases can be used to link the components to the user's own targets, either libraries or executables.
The call requires the target chip to be specified with target argument. Optional arguments for the call include:
idf_build_component). This argument is used to trim the build.
Other components are automatically added if they are required in the dependency chain, i.e., the public and private requirements of the components in this list are automatically added, and in turn the public and private requirements of those requirements, so on and so forth. If not specified, all components known to the build system are processed... code-block:: none
idf_build_executable(executable)
Specify the executable executable for ESP-IDF build. This attaches additional targets such as dependencies related to flashing, generating additional binary files, etc. Should be called after idf_build_process.
.. code-block:: none
idf_build_get_config(var config [GENERATOR_EXPRESSION])
Get the value of the specified config. Much like build properties, specifying GENERATOR_EXPRESSION will retrieve the generator expression string for that config, instead of the actual value, which can be used with CMake commands that support generator expressions. Actual config values are only known after call to idf_build_process, however.
.. code-block:: none
idf_build_add_post_elf_dependency(elf_filename dep_target)
Register a dependency that must run after the ELF is linked (post-ELF) and before the binary image is generated. This is useful when a component needs to post‑process the ELF in place prior to elf2image execution (for example, inserting metadata, stripping sections, or generating additional symbol files). The dependency target dep_target must be a valid CMake target. If your rule reads or modifies the ELF, declare the ELF file as a DEPENDS of your custom command.
.. important::
When creating post‑ELF steps, ensure the build graph remains acyclic:
app.elf.post, app.elf.symbols, or a simple marker file).cmake -E touch). This ensures the output file has a newer timestamp than the modified ELF, so CMake considers the rule satisfied and won't re-run it on subsequent builds.Following these rules ensures the post‑ELF hook runs in the intended order without triggering infinite rebuild loops.
Example:
.. code-block:: cmake
# Create a custom command to process the ELF file after linking
idf_build_get_property(elf_target EXECUTABLE GENERATOR_EXPRESSION)
add_custom_command(
OUTPUT "${CMAKE_BINARY_DIR}/${CMAKE_PROJECT_NAME}.stripped_marker"
COMMAND ${CMAKE_OBJCOPY} --strip-debug
"$<TARGET_FILE:$<GENEX_EVAL:${elf_target}>>"
COMMAND ${CMAKE_COMMAND} -E touch
"${CMAKE_BINARY_DIR}/${CMAKE_PROJECT_NAME}.stripped_marker"
DEPENDS "$<TARGET_FILE:$<GENEX_EVAL:${elf_target}>>"
)
# Wrap it in a custom target
add_custom_target(strip_elf DEPENDS
"${CMAKE_BINARY_DIR}/${CMAKE_PROJECT_NAME}.stripped_marker"
)
# Register it to run after the ELF is linked but before the BIN is generated
idf_build_add_post_elf_dependency("${CMAKE_PROJECT_NAME}.elf" strip_elf)
.. code-block:: none
idf_build_get_post_elf_dependencies(elf_filename out_var)
Retrieve the list of post-ELF dependencies registered for the given ELF file and store it in out_var.
.. _cmake-build-properties:
These are properties that describe the build. Values of build properties can be retrieved by using the build command idf_build_get_property. For example, to get the Python interpreter used for the build:
.. code-block:: cmake
idf_build_get_property(python PYTHON) message(STATUS "The Python interpreter is: ${python}")
idf_build_process BUILD_DIR argumentidf_build_processidf_build_processdependencies.lock under the project path.idf_build_executableidf_build_executable0 it was disabled by the IDF_COMPONENT_MANAGER environment variableidf.cmakeidf_build_processidf_build_processidf_build_processmain component. By default, this property is disabled (set to OFF), but it can be enabled by setting it to ON.idf_build_process PROJECT_NAME argumentidf_build_process PROJECT_DIR argumentidf_build_process PROJECT_VER argumentidf_build_process SDKCONFIG argumentidf_build_process SDKCONFIG_DEFAULTS argumentidf_build_processidf_build_processidf_build_processidf_build_process.. code-block:: none
idf_component_get_property(var component property [GENERATOR_EXPRESSION])
Retrieve a specified component's :ref:component property <cmake-component-properties>, property and store it in var accessible from the current scope. Specifying GENERATOR_EXPRESSION will retrieve the generator expression string for that property, instead of the actual value, which can be used with CMake commands that support generator expressions.
.. code-block:: none
idf_component_set_property(component property val [APPEND])
Set a specified component's :ref:component property <cmake-component-properties>, property with value val. Specifying APPEND will append the specified value to the current value of the property. If the property does not previously exist or it is currently empty, the specified value becomes the first element/member instead.
.. _cmake-component-register:
.. code-block:: none
idf_component_register([[SRCS src1 src2 ...] | [[SRC_DIRS dir1 dir2 ...] [EXCLUDE_SRCS src1 src2 ...]] [INCLUDE_DIRS dir1 dir2 ...] [PRIV_INCLUDE_DIRS dir1 dir2 ...] [REQUIRES component1 component2 ...] [PRIV_REQUIRES component1 component2 ...] [LDFRAGMENTS ldfragment1 ldfragment2 ...] [REQUIRED_IDF_TARGETS target1 target2 ...] [EMBED_FILES file1 file2 ...] [EMBED_TXTFILES file1 file2 ...] [KCONFIG kconfig] [KCONFIG_PROJBUILD kconfig_projbuild] [WHOLE_ARCHIVE])
Register a component to the build system. Much like the project() CMake command, this should be called from the component's CMakeLists.txt directly (not through a function or macro) and is recommended to be called before any other command. Here are some guidelines on what commands can not be called before idf_component_register:
idf_build_get_property; although consider whether the property may not have been set yetCommands that set and operate on variables are generally okay to call before idf_component_register.
The arguments for idf_component_register include:
limitations of globbing in CMake <cmake-file-globbing>. Source files specified in EXCLUDE_SRCS are removed from the globbed files.-Wl,--whole-archive, -Wl,--no-whole-archive when linked. This has the same effect as setting WHOLE_ARCHIVE component property.The following are used for :ref:embedding data into the component <cmake_embed_data>, and is considered as source files when determining if a component is config-only. This means that even if the component does not specify source files, a static library is still created internally for the component if it specifies either:
.. _cmake-component-properties:
These are properties that describe a component. Values of component properties can be retrieved by using the build command idf_component_get_property. For example, to get the directory of the freertos component:
.. code-block:: cmake
idf_component_get_property(dir freertos COMPONENT_DIR) message(STATUS "The 'freertos' component directory is: ${dir}")
idf_build_component and alias library itself is created by idf_component_registeridf_build_componentthis component overrides another component <cmake-components-same-name>idf_build_component and library itself is created by idf_component_registeridf_build_component based on the component directory nameidf_component_register EMBED_FILES argumentidf_component_register EMBED_TXTFILES argumentidf_component_register INCLUDE_DIRS argumentidf_build_componentidf_build_componentidf_component_register LDFRAGMENTS argumentidf_component.yml manifest fileidf_component.yml manifest fileidf_component_register PRIV_INCLUDE_DIRS on components of type LIBRARYidf_component_register PRIV_REQUIRES argument and dependencies in idf_component.yml manifest fileidf_component_register REQUIRED_IDF_TARGETS argumentidf_component_register REQUIRES argument and dependencies in idf_component.yml manifest fileidf_component_registerTRUE (or any boolean "true" CMake value: 1, ON, YES, Y), the component library is surrounded by -Wl,--whole-archive, -Wl,--no-whole-archive when linked. This can be used to force the linker to include every object file into the executable, even if the object file doesn't resolve any references from the rest of the application. This is commonly used when a component contains plugins or modules which rely on link-time registration. This property is FALSE by default. It can be set to TRUE from the component CMakeLists.txt file... _cmake-file-globbing:
.. highlight:: cmake
The preferred way to include source files in an ESP-IDF component is to list them manually via SRCS argument to idf_component_register::
idf_component_register(SRCS library/a.c library/b.c platform/platform.c ...)
This preference reflects the CMake best practice <https://gist.github.com/mbinna/c61dbb39bca0e4fb7d1f73b0d66a4fd1/>_ of manually listing source files. This could, however, be inconvenient when there are lots of source files to add to the build. The ESP-IDF build system provides an alternative way for specifying source files using SRC_DIRS::
idf_component_register(SRC_DIRS library platform ...)
This uses globbing behind the scenes to find source files in the specified directories. Be aware, however, that if a new source file is added and this method is used, then CMake won't know to automatically re-run and this file won't be added to the build.
The trade-off is acceptable when you're adding the file yourself, because you can trigger a clean build or run idf.py reconfigure to manually re-run CMake_. However, the problem gets harder when you share your project with others who may check out a new version using a source control tool like Git...
For components which are part of ESP-IDF, we use a third party Git CMake integration module (:idf_file:/tools/cmake/third_party/GetGitRevisionDescription.cmake) which automatically re-runs CMake any time the repository commit changes. This means if you check out a new ESP-IDF version, CMake will automatically rerun.
For project components (not part of ESP-IDF), there are a few different options:
git_describe function in a component CMakeLists file in order to automatically trigger re-runs of CMake when the Git revision changes.idf.py reconfigure whenever a source file may change.SRCS argument to idf_component_register to list all source files in project components.The best option will depend on your particular project and its users.
.. _build_system_metadata:
For integration into IDEs and other build systems, when CMake runs the build process generates a number of metadata files in the build/ directory. To regenerate these files, run cmake or idf.py reconfigure (or any other idf.py build command).
compile_commands.json is a standard format JSON file which describes every source file which is compiled in the project. A CMake feature generates this file, and many IDEs know how to parse it.project_description.json contains some general information about the ESP-IDF project, configured paths, etc.flasher_args.json contains esptool arguments to flash the project's binary files. There are also flash_*_args files which can be used directly with esptool. See Flash arguments_.CMakeCache.txt is the CMake cache file which contains other information about the CMake process, toolchain, etc.config/sdkconfig.json is a JSON-formatted version of the project configuration values.config/kconfig_menus.json is a JSON-formatted version of the menus shown in menuconfig, for use in external IDE UIs.A tool called kconfserver is provided to allow IDEs to easily integrate with the configuration system logic. kconfserver is designed to run in the background and interact with a calling process by reading and writing JSON over process stdin & stdout.
You can run kconfserver from a project via idf.py confserver or ninja kconfserver, or a similar target triggered from a different build generator.
For more information about kconfserver, see the esp-idf-kconfig documentation <https://docs.espressif.com/projects/esp-idf-kconfig/en/latest/kconfserver/index.html>_.
The listfiles for the ESP-IDF build system reside in :idf:/tools/cmake. The modules which implement core build system functionality are as follows:
- build.cmake - Build related commands i.e., build initialization, retrieving/setting build properties, build processing.
- component.cmake - Component related commands i.e., adding components, retrieving/setting component properties, registering components.
- kconfig.cmake - Generation of configuration files (sdkconfig, sdkconfig.h, sdkconfig.cmake, etc.) from Kconfig files.
- ldgen.cmake - Generation of final linker script from linker fragment files.
- target.cmake - Setting build target and toolchain file.
- utilities.cmake - Miscellaneous helper commands.
Aside from these files, there are two other important CMake scripts in :idf:/tools/cmake:
- idf.cmake - Sets up the build and includes the core modules listed above. Included in CMake projects in order to access ESP-IDF build system functionality.
- project.cmake - Includes ``idf.cmake`` and provides a custom ``project()`` command that takes care of all the heavy lifting of building an executable. Included in the top-level CMakeLists.txt of standard ESP-IDF projects.
The rest of the files in :idf:/tools/cmake are support or third-party scripts used in the build process.
This section describes the standard ESP-IDF application build process. The build process can be broken down roughly into four phases:
.. blockdiag:: :scale: 100% :caption: ESP-IDF Build System Process :align: center
blockdiag idf-build-system-process {
Initialization -> Enumeration
Enumeration -> Processing
Processing -> Finalization
}
Initialization ^^^^^^^^^^^^^^
This phase sets up necessary parameters for the build.
- Upon inclusion of ``idf.cmake`` in ``project.cmake``, the following steps are performed:
- Set ``IDF_PATH`` from environment variable or inferred from path to ``project.cmake`` included in the top-level CMakeLists.txt.
- Add :idf:`/tools/cmake` to ``CMAKE_MODULE_PATH`` and include core modules plus the various helper/third-party scripts.
- Set build tools/executables such as default Python interpreter.
- Get ESP-IDF git revision and store as ``IDF_VER``.
- Set global build specifications i.e., compile options, compile definitions, include directories for all components in the build.
- Add components in :idf:`components` to the build.
- The initial part of the custom ``project()`` command performs the following steps:
- Set ``IDF_TARGET`` from environment variable or CMake cache and the corresponding ``CMAKE_TOOLCHAIN_FILE`` to be used.
- Add components in ``EXTRA_COMPONENT_DIRS`` to the build.
- Prepare arguments for calling command ``idf_build_process()`` from variables such as ``COMPONENTS``/``EXCLUDE_COMPONENTS``, ``SDKCONFIG``, ``SDKCONFIG_DEFAULTS``.
The call to idf_build_process() command marks the end of this phase.
Enumeration
^^^^^^^^^^^
This phase builds a final list of components to be processed in the build, and is performed in the first half of idf_build_process().
- Retrieve each component's public and private requirements. A child process is created which executes each component's CMakeLists.txt in script mode. The values of ``idf_component_register`` REQUIRES and PRIV_REQUIRES argument is returned to the parent build process. This is called early expansion. The variable ``CMAKE_BUILD_EARLY_EXPANSION`` is defined during this step.
- Recursively include components based on public and private requirements.
- Unless IDF Component Manager is disabled, it is called to resolve the dependencies of the components:
- Looks for manifests and dependencies contained in the project.
- Starts the version solving process to resolve the dependencies of the components.
- When the version solving process succeeds, the IDF Component Manager downloads dependencies, integrates them into the build, and creates a ``dependencies.lock`` file that contains a list of the exact versions of the dependencies installed by the IDF Component Manager.
Processing ^^^^^^^^^^
This phase processes the components in the build, and is the second half of idf_build_process().
project_include.cmake.idf_component_register which adds source files, include directories, creates component library, links dependencies, etc.Finalization
^^^^^^^^^^^^
This phase is everything after idf_build_process().
Browse :idf_file:/tools/cmake/project.cmake for more details.
.. _migrating_from_make:
Some aspects of the CMake-based ESP-IDF build system are very similar to the older GNU Make-based system. The developer needs to provide values the include directories, source files etc. There is a syntactical difference, however, as the developer needs to pass these as arguments to the registration command, idf_component_register.
An automatic project conversion tool is available in tools/cmake/convert_to_cmake.py in ESP-IDF v4.x releases. The script was removed in v5.0 because of its make build system dependency.
Some features are significantly different or removed in the CMake-based system. The following variables no longer exist in the CMake-based build system:
COMPONENT_BUILD_DIR: Use CMAKE_CURRENT_BINARY_DIR instead.COMPONENT_LIBRARY: Defaulted to $(COMPONENT_NAME).a, but the library name could be overridden by the component. The name of the component library can no longer be overridden by the component.CC, LD, AR, OBJCOPY: Full paths to each tool from the gcc xtensa cross-toolchain. Use CMAKE_C_COMPILER, CMAKE_C_LINK_EXECUTABLE, CMAKE_OBJCOPY, etc instead. Full list here <cmake language variables_>_.HOSTCC, HOSTLD, HOSTAR: Full names of each tool from the host native toolchain. These are no longer provided, external projects should detect any required host toolchain manually.COMPONENT_ADD_LDFLAGS: Used to override linker flags. Use the CMake target_link_libraries_ command instead.COMPONENT_ADD_LINKER_DEPS: List of files that linking should depend on. target_link_libraries_ will usually infer these dependencies automatically. For linker scripts, use the provided custom CMake function target_linker_scripts.COMPONENT_SUBMODULES: No longer used, the build system will automatically enumerate all submodules in the ESP-IDF repository.COMPONENT_EXTRA_INCLUDES: Used to be an alternative to COMPONENT_PRIV_INCLUDEDIRS for absolute paths. Use PRIV_INCLUDE_DIRS argument to idf_component_register for all cases now (can be relative or absolute).COMPONENT_OBJS: Previously, component sources could be specified as a list of object files. Now they can be specified as a list of source files via SRCS argument to idf_component_register.COMPONENT_OBJEXCLUDE: Has been replaced with EXCLUDE_SRCS argument to idf_component_register. Specify source files (as absolute paths or relative to component directory), instead.COMPONENT_EXTRA_CLEAN: Set property ADDITIONAL_CLEAN_FILES instead but note :ref:CMake has some restrictions around this functionality <ADDITIONAL_CLEAN_FILES_note>.COMPONENT_OWNBUILDTARGET & COMPONENT_OWNCLEANTARGET: Use CMake ExternalProject_ instead. See :ref:component-build-full-override for full details.COMPONENT_CONFIG_ONLY: Call idf_component_register without any arguments instead. See Configuration-Only Components_.CFLAGS, CPPFLAGS, CXXFLAGS: Use equivalent CMake commands instead. See Controlling Component Compilation_.Unlike in the legacy Make-based build system, the following have no default values:
COMPONENT_SRCDIRS variable in Make, SRC_DIRS argument to idf_component_register in CMake)COMPONENT_ADD_INCLUDEDIRS variable in Make, INCLUDE_DIRS argument to idf_component_register in CMake)COMPONENT_SRCDIRS if COMPONENT_SRCS is set. In CMake, the equivalent is not necessary i.e., specifying SRC_DIRS to idf_component_register if SRCS is also specified (in fact, SRCS is ignored if SRC_DIRS is specified).make flash and similar targets still work to build and flash. However, project sdkconfig no longer specifies serial port and baud rate. Environment variables can be used to override these. See :ref:flash-with-ninja-or-make for more details.
:example:build_system/wrappers demonstrates how to use a linker feature to redefine or override any public function in both ESP-IDF and the bootloader, allowing modification or extension of a function's default behavior.
:example:custom_bootloader/bootloader_override demonstrates how to override the second stage bootloader from a regular project, providing a custom bootloader that prints an extra message on startup, with the ability to conditionally override the bootloader based on certain conditions like target-dependency or Kconfig options.
:example:build_system/cmake/import_lib demonstrates how to import and use third-party libraries using ExternalProject CMake module.
:example:build_system/cmake/import_prebuilt demonstrates how to import a prebuilt static library into the ESP-IDF build system, build a component with dependencies, and link it to the main component, ultimately outputting the current running partition.
:example:build_system/cmake/idf_as_lib demonstrates the creation of an application equivalent to :example:hello world application <get-started/hello_world> using a custom CMake project.
:example:build_system/cmake/multi_config demonstrates how to build multiple configurations of a single application from a single codebase, it is useful for creating binaries for multiple similar products.
:example:build_system/cmake/plugins demonstrates features of the ESP-IDF build system related to link time registration of plugins, allowing you to add multiple implementations of a certain feature without the need to make the application aware of all these implementations.
.. _esp-idf-template: https://github.com/espressif/esp-idf-template .. _cmake: https://cmake.org .. _ninja: https://ninja-build.org .. _esptool: https://github.com/espressif/esptool/#readme .. _CMake v3.22 documentation: https://cmake.org/cmake/help/v3.22/index.html .. _cmake command line documentation: https://cmake.org/cmake/help/v3.22/manual/cmake.1.html#options .. _cmake add_library: https://cmake.org/cmake/help/v3.22/command/add_library.html .. _cmake if: https://cmake.org/cmake/help/v3.22/command/if.html .. _cmake list: https://cmake.org/cmake/help/v3.22/command/list.html .. _cmake project: https://cmake.org/cmake/help/v3.22/command/project.html .. _cmake set: https://cmake.org/cmake/help/v3.22/command/set.html .. _cmake string: https://cmake.org/cmake/help/v3.22/command/string.html .. _cmake faq generated files: https://gitlab.kitware.com/cmake/community/-/wikis/FAQ#how-can-i-generate-a-source-file-during-the-build .. _ADDITIONAL_CLEAN_FILES: https://cmake.org/cmake/help/v3.22/prop_dir/ADDITIONAL_CLEAN_FILES.html .. _ExternalProject: https://cmake.org/cmake/help/v3.22/module/ExternalProject.html .. _cmake language variables: https://cmake.org/cmake/help/v3.22/manual/cmake-variables.7.html#variables-for-languages .. _set_source_files_properties: https://cmake.org/cmake/help/v3.22/command/set_source_files_properties.html .. _target_compile_options: https://cmake.org/cmake/help/v3.22/command/target_compile_options.html .. _target_link_libraries: https://cmake.org/cmake/help/v3.22/command/target_link_libraries.html#command:target_link_libraries .. _cmake_toolchain_file: https://cmake.org/cmake/help/v3.22/variable/CMAKE_TOOLCHAIN_FILE.html .. _LINK_INTERFACE_MULTIPLICITY: https://cmake.org/cmake/help/v3.22/prop_tgt/LINK_INTERFACE_MULTIPLICITY.html .. _quirc: https://github.com/dlbeer/quirc .. _pyenv: https://github.com/pyenv/pyenv#readme .. _virtualenv: https://virtualenv.pypa.io/en/stable/