Zephyr package modules

[tejlmand]

This is a complete Zephyr CMake package and CMake modules overhaul.

The intention with this major cleanup is to make the build system more modular in a way so that it can easier be reused through the Zephyr package mechanism.

Use-cases for this work is:

• The sysbuild proposal: Zephyr sysbuild / multi image #40555
  In Zephyr sysbuild / multi image #40555 it will remove the need for a boilerplate file like this: https://github.com/zephyrproject-rtos/zephyr/blob/641b86999750f1ed71fffda1da7c47387db22c23/sysbuild/cmake/boilerplate.cmake as this can now be handled as part of Zephyr package loading.
• Possibility to run Zephyr CMake configure stages individually, for example dts or kconfig.
  This will allow twister to generate the zephyr.dts tree and do filtering and not invoking a complete CMake configuration.
  This opens for the use-case referenced by @mbolivar-nordic on Discord https://discord.com/channels/720317445772017664/733037738068148335/914952860192632852
  See a PR for this work: cmake: package_helper CMake script #41302
• Cleanup of find_package(ZephyrUnittest) as that can simply be loaded as specific module like: find_package(Zephyr COMPONENTS unittest)

With the improved Zephyr CMake package, it is now possible to do:
find_package(Zephyr) : Will load a standard build setup as always
find_package(Zephyr COMPONENTS unittest): Load specific unittest build setup
find_package(Zephyr COMPONENTS dts): Load only dts module (and its direct dependencies)
find_package(Zephyr COMPONENTS extensions west zephyr_module): Load specific modules(and their direct dependencies), for example sysbuild use-case/

[carlescufi]

Excellent initiative!

The only thing I would like to ask is that you fully qualify "Zephyr module" vs "CMake module" in every instance of each that could be prone to confusion with the other.

[henrikbrixandersen]

Perhaps kernel.cmake is a bit misleading as we often refer to a subset of the Zephyr repository codebase as the "kernel", whereas this CMake module is not specific to that part of the codebase?

[tejlmand]

I tend to agree with you that it would be nice to have the kernel name referring to a specific sub-part of the Zephyr repo.
I'm very open to other proposals, but so far kernel.cmake was the best I could find that refers to the overall build of the system and the final executable.

We use the term kernel in a lot of places outside the kernel code base itself, for example:
The project name:

zephyr/cmake/app/boilerplate.cmake

Line 591 in 5fda6a3

project(Zephyr-Kernel VERSION ${PROJECT_VERSION})

zephyr/cmake/app/boilerplate.cmake

Line 611 in 5fda6a3

set(KERNEL_NAME ${CONFIG_KERNEL_BIN_NAME})

In Kconfig:

zephyr/Kconfig.zephyr

Lines 96 to 103 in 5fda6a3

	hex "Kernel load offset" if !USE_DT_CODE_PARTITION
	default $(dt_chosen_reg_addr_hex,$(DT_CHOSEN_Z_CODE_PARTITION)) if USE_DT_CODE_PARTITION
	default 0
	help
	This option specifies the byte offset from the beginning of flash that
	the kernel should be loaded into. Changing this value from zero will
	affect the Zephyr image's link, and will decrease the total amount of
	flash available for use by application code.

zephyr/Kconfig.zephyr

Line 109 in 5fda6a3

hex "Kernel load size" if !USE_DT_CODE_PARTITION

zephyr/Kconfig.zephyr

Lines 361 to 362 in 5fda6a3

	config KERNEL_BIN_NAME
	string "The kernel binary name"

Because we are already using the term kernel to also refer to the overall project / image then I felt kernel was the best I could come up with, but other proposals are more than welcome.

[mbolivar-nordic]

Because we are already using the term kernel to also refer to the overall project / image then I felt kernel was the best I could come up with, but other proposals are more than welcome.

How about "core"?

[tejlmand]

Excellent initiative!

Thanks.

The only thing I would like to ask is that you fully qualify "Zephyr module" vs "CMake module" in every instance of each that could be prone to confusion with the other.

Good point, and done.

To everyone else, the reason for using the name CMake module here is because it's the official term used in CMake, ref:
https://cmake.org/cmake/help/latest/command/include.html#command:include

Load and run CMake code from a file or module.

include(<file|module> [OPTIONAL] [RESULT_VARIABLE <var>]
                      [NO_POLICY_SCOPE])

[carlescufi]

Looks great now!