core: compile kernel_init and core_panic conditionally

[nmeum]

Contribution description

riotboot provides its own implementation of these functions in bootloaders/riotboot/main.c. Compiling them unconditionally causes two symbols with the same name to be present for core_panic and kernel_init, the linker will discard one of them.

Testing procedure

This was discovered during the implementation of link time reordering in #13176. Either test this using the aforementioned PR or read the code and check with tests/riotboot that both bootloaders/riotboot/main.c and core/kernel_init.c as well as core/panic.c are compiled and contain symbols with the same name.

Issues/PRs references

• Implement support for link time reordering #13176
• fe310: fix power management configuration #13229
• waspmote-pro: don't build the boards_common_atmega module #13230

[nmeum]

From Murdock:

--- result: BUILD FAILED!

--- static tests: failed!
dwqw: command timed out

What does this mean? What is dwqw?

[kaspar030]

What does this mean? What is dwqw?

dwqw is the tool that executes jobs on the worker. The message means that the job timed out (ran for more than 5 minutes).

[benpicco]

Makes sense and Murdock is happy.

[kaspar030]

I'm not happy with the RIOTBOOT defines.
I suggest the following:

• rename "kernel_init" "core_init"

• make it a default (sub-)module

• disable it for RIOTBOOT

• move the minimal "panic()" to panic.c

• make it selectable as module

I'll try how it looks and report back.

[kaspar030]

I think turning both kernel_init and core panic into submodules is cleaner.

[nmeum]

I prefer @kaspar030's solution closing this.