How to forward ZephyrConfig.cmake location to Sub-Builds in multi_image.cmake

[TorstenRobitzki]

Hello,
so far my Zephyr build works for my first project. Now, I want to add a bootloader (MCUboot). I've included ZephyrConfig.cmake into CMake, by loading the module with a hint:

find_package(Zephyr REQUIRED HINTS ${CMAKE_CURRENT_LIST_DIR}/../zephyr)

project(firmware
    VERSION 0.0.0
    LANGUAGES C CXX ASM)

This way, I get always the version of Zephyr, which was checked out by west in a relative position to the current checkout of the project.

Now, I've enabled MCUboot, by adding CONFIG_BOOTLOADER_MCUBOOT=y to my project configuration. In multi_image.cmake is a recursive invocation of CMake, which then opens the CMakeLists.txt of MCUboot, which tries to load the Zephyr module by:

find_package(Zephyr REQUIRED HINTS $ENV{ZEPHYR_BASE})
project(NONE)

If that variable is requires, why isn't the Zephyr build system not setting that variable, when spawning subprocesses? Any idea, how to work around this, without redundantly setting the environment variable?

[tejlmand]

I've included ZephyrConfig.cmake into CMake, by loading the module with a hint:
...
This way, I get always the version of Zephyr, which was checked out by west in a relative position to the current checkout of the project.

This should not be needed, then find_package(Zephyr) will always prefer to use the Zephyr within the same workspace as your application.
Only out-of-workspace applications need some extra knowledge in case you have multiple versions of Zephyr installed.

Read more here: https://docs.zephyrproject.org/latest/build/zephyr_cmake_package.html#zephyr-cmake-package-search-order

In multi_image.cmake is a recursive invocation of CMake, which then opens the CMakeLists.txt of MCUboot, which tries to load the Zephyr module by:

Are you perhaps using the nRF Connect SDK (which is including Zephyr) and not a pure Zephyr ?

Zephyr itself has no multi_image.cmake file.

find_package(Zephyr REQUIRED HINTS $ENV{ZEPHYR_BASE})
project(NONE)

If that variable is requires

I assume you refer to $ENV{ZEPHYR_BASE} ?
And no, that variable is not required, notice the HINTS in front (see also https://cmake.org/cmake/help/latest/command/find_package.html#config-mode-search-procedure).

The find_package will look for Zephyr as described in the Zephyr doc link above, but if ZEPHYR_BASE is set in environment, then that setting will be honored and used.
The reason for ZEPHYR_BASE as environment variable is partly for historic reasons / backward compatibility from a time when ZEPHYR_BASE was required to be set, but also to allow users to explicitly point to a given Zephyr installation.
Reasons could be just for a desire to have explicit control or for test purposes. Personally I never set Zephyr base in environment, as there is no need.

[TorstenRobitzki]

Hi @tejlmand,
thank you very much for your reply! :-) Indeed, I forgot to mention that I'm using the Nordic flavor of Zephyr (when I wrote the above, I was not even aware, that this is a Nordic flavor-only feature).

I have a single project repository, that contains a west.yml file that mainly contains a reference to sdk-nrf. The hint, that I give CMake to find the Zephyr package is relative to the CMakeLists.txt file itself, which allows me to checkout the repository at any location without setting the ZEPHYR_BASE environment variable:

    find_package(Zephyr REQUIRED HINTS ${CMAKE_CURRENT_LIST_DIR}/../zephyr)

The multi image build then fails, due to ZEPHYR_BASE not being set, which comes to a surprise, as it seems to be part of Zephyr (or the CMake Zephyr package):

=== child image b0n - CPUNET (inherited) begin ===
loading initial cache file /Users/todi/yyyyyyyyy/zephyr-workspace/xxxxxxx/build/hci_ipc/b0n/child_image_preload.cmake
CMake Error at CMakeLists.txt:9 (find_package):
  Could not find a package configuration file provided by "Zephyr" with any
  of the following names:

    ZephyrConfig.cmake
    zephyr-config.cmake

  Add the installation prefix of "Zephyr" to CMAKE_PREFIX_PATH or set
  "Zephyr_DIR" to a directory containing one of the above files.  If "Zephyr"
  provides a separate development package or SDK, be sure it has been
  installed.


-- Configuring incomplete, errors occurred!
CMake Error at /Users/todi/yyyyyyyyy/zephyr-workspace/nrf/cmake/multi_image.cmake:450 (message):
  CMake generation for b0n failed, aborting.  Command: 1
Call Stack (most recent call first):
  /Users/todi/yyyyyyyyy/zephyr-workspace/nrf/cmake/multi_image.cmake:178 (add_child_image_from_source)
  /Users/todi/yyyyyyyyy/zephyr-workspace/nrf/samples/CMakeLists.txt:13 (add_child_image)


-- Configuring incomplete, errors occurred!
CMake Error at /Users/todi/yyyyyyyyy/zephyr-workspace/nrf/cmake/multi_image.cmake:450 (message):
  CMake generation for hci_ipc failed, aborting.  Command: 1
Call Stack (most recent call first):
  /Users/todi/yyyyyyyyy/zephyr-workspace/nrf/cmake/multi_image.cmake:178 (add_child_image_from_source)
  /Users/todi/yyyyyyyyy/zephyr-workspace/nrf/samples/CMakeLists.txt:148 (add_child_image)

My workaround for this, is to set the environment variable to the required hint:

# add_child_image_from_source() in multi_image.cmake creates sub processes running
# cmake to build other images, which might fail to find the Zephyr package if this
# environment variable is not set.
set(ENV{ZEPHYR_BASE} ${CMAKE_CURRENT_LIST_DIR}/../zephyr)

find_package(Zephyr REQUIRED HINTS ${CMAKE_CURRENT_LIST_DIR}/../zephyr)

Which works fine for me.