CMakeLists.txt: Link libkernel.a as whole-archive, like everything else

[pfalcon]

There was a report that a non-trivial application (MicroPython with
experimental LVGL bindings) errors out at link stage:

ld: libmicropython.a(main.o): in function k_timer_start': zephyr/include/generated/syscalls/kernel.h:55: undefined reference to z_impl_k_timer_start'
ld: libmicropython.a(main.o):(._k_timer.static.lvgl_timer+0xc):
undefined reference to `z_timer_expiration_handler'

These functions are of course defined and available in libkernel.a.

Investigating the link command, turned out that while all other
Zephyr constituent libraries are linked with --whole-archive flag,
libkernel.a isn't. Changing that fixed the issue above. Given that
it is in no way special than any other build process constituent
libs (the only difference is that it's always present, while presence
of other libs depends on configuration), this appears to be a
change which make sense.

Signed-off-by: Paul Sokolovsky [email protected]

[pfalcon]

@MaureenHelm, Please confirm whether it fixes the issue for you, it does for me.

That funky --whole-archive discrepancy is traceable to the original cmake advent, 12f8f76.

And well, while the report sit in my mailbox for a few weeks, only after repeating the exercise, I got a hunch that I saw a similar issue, where some symbol (again, that *_impl* stuff) was weirdly reported as undefined, while it definitely was there. Can't remember for sure what it was, but probably a test for #15602 or gettimeofday() I put up locally. Don't remember how it ended up either, likely I tweaked here and there, and it was gone.

[MaureenHelm]

@MaureenHelm, Please confirm whether it fixes the issue for you, it does for me.

Yes, it fixes the issue for me. Thank you!

[SebastianBoe]

The last time I tried to simplify the build by treating libkernel.a as any other library I discovered that as opposed to all other libraries, we don't use Kconfig as much to pick and choose kernel features.

This caused problems in various areas, hopefully CI will be able to demonstrate them. Because I can not recall the details.

[SebastianBoe]

How is libmicropython.a organized?

Would it be possible to move it into --whole-archive, e.g. with zephyr_library_import?

Or to have it explicitly link with the kernel, e.g. with zephyr_library_link_libraries(kernel) ?

[pfalcon]

How is libmicropython.a organized?

From Zephyr's build system point of view, as a black-box, generic 3rd-party library, which should be linked with.

[SebastianBoe]

Okay, if it were me, I'd look into zephyr_library_import then.

[nashif]

stale, closing. Reopen when there are updates...