External libs are always placed after libkernel on linker command line

[jasal82]

Describe the bug

I want to link external static libraries to my app target. These external libraries were built with Conan and use Zephyr kernel functions. I made sure that the Conan build uses the same (generated) headers as the Zephyr build itself. I added the CMakeDeps generator path to the Zephyr build by adding a -DCMAKE_PREFIX_PATH argument so that I can use the find_package macros to discover the Conan imported library targets inside my Zephyr app CMakeLists. Now the problem is that when I do

find_package(conanlib1 CONFIG REQUIRED)
target_link_libraries(app conanlib1::conanlib1)

the Conan library always ends up after the zephyr/kernel/libkernel.a in the linker command line. That makes the linker drop the unused symbols from libkernel.a which are then reported as undefined symbols when linking conanlib1.

I already tried a myriad of things to get this running somehow, including trying to understand the zephyr cmake internals, but nothing seems to work. I found a suggestion to make the imported lib link against zephyr or zephyr_interface, but that didn't help either.

To Reproduce

You can reproduce this with the external_lib sample project. There the external lib is also added after the kernel lib on the command line.

Expected behavior

The external libs are placed after the whole-archive section but before libkernel.a.

Impact

Showstopper for our Conan/Zephyr integration project.

Logs and console output

n/a

Environment (please complete the following information):

• OS: Linux
• Zephyr 4.1.0-rc3, SDK 0.17.0

Additional context

n/a

[github-actions]

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[jasal82]

I found a solution that seems to fix the problem. If I do

def package_info(self):
  if self.settings.os == "Zephyr":
    self.cpp_info.system_libs.append("kernel")

in my conanfile.py the CMakeDeps generator will add kernel at the end of the INTERFACE_LINK_LIBRARIES for my library and then the linker command in Zephyr gets an extra zephyr/kernel/libkernel.a after the Conan library. I found no way to do that in the Zephyr CMakeLists, however. Do you think that this solution is robust enough or is there a chance that the kernel CMake target is renamed in the future? This would break our build.

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