Undefined reference errors when using External Library with k_msgq_* calls

[MaikVermeulen]

Describe the bug
I made a very simple library that includes two functions that use the message queue. However, I get this linking error:
undefined reference to 'z_impl_k_msgq_put'

I think it's due to 'z_impl_k_msgq_put' being declared as extern and that affects the linking, but I haven't found a solution. I tried replacing the k_msgq_* functions with LOG_INF, and then it works just fine.

I'm trying to put some code into libraries so that we can share those with external parties, without sharing our source code with them.

To Reproduce
I have created a simple minimal example of the problem.

Expected behavior
A clean build.

Impact
I can't librarize Zephyr code that includes calls to the message queue (and possibly similar code), hence I can't provide external parties with the modules they need without sharing our source code.

Logs and console output
Rebuilding ‘zephyr/zephyr_prebuilt.elf’ from solution 'build' in configuration 'Common' Compiling 'empty_file.c' Linking 'zephyr_prebuilt.elf' B 1 MB 2.67% B 448 KB 1.74% lib/liblib.a(lib.c.obj): in function 'k_msgq_put'': undefined reference to 'z_impl_k_msgq_put' ld returned 1 exit status B 2 KB 4.30% Build failed

Environment (please complete the following information):

• OS: Windows
• nRF Connect SDK v1.4.99-dev1

[pabigot]

Please look at 6b720cb3c56a198db19b1884e78385cb7a392b00 for a possible fix.

[MaikVermeulen]

@pabigot This pointed me in the right direction, thank you.
Simply linking the kernel library resulted in a strong component cycle error, so I included the dummy library as PRIVATE:
zephyr_library_link_libraries(kernel) target_link_libraries(app PRIVATE lib)

Now it works. Thanks!

[danderson-presonus]

Hi, I'm having the same problem linking an external library that makes Zephyr kernel calls. I tried adding the line "zephyr_library_link_libraries(kernel)" in my CMakeLists.txt and changed "target_link_libraries(app PUBLIC pep)" to "target_link_libraries(app PRIVATE pep)" but this had no effect. I think I must be making the change in the wrong spot... help?

[MaikVermeulen]

@danderson-presonus My CMakeLists.txt in the library folder containing the .a file:

zephyr_library_import(lib ${CMAKE_CURRENT_SOURCE_DIR}/liblib.a)
target_include_directories(app PUBLIC ${CMAKE_CURRENT_SOURCE_DIR})
target_link_libraries(lib INTERFACE kernel)
target_link_libraries(app PRIVATE lib)

[danderson-presonus]

Thanks! This got me up and running.

[CManigandan]

Please look at 6b720cb3c56a198db19b1884e78385cb7a392b00 for a possible fix.

@pabigot I am not able to locate this fix. Can you help?

Thanks in Advance.