warning: "x" macro redefined

[alexpaschoaletto]

TL:DR

How does Zephyr deal with redefinition of macros? How to properly work with those on kernel implementations?

Context

Proceeding to the next step in the journey of implementing a new kernel feature which I started here, I'm now struggling to understand how do the tracing subsystems fare with the redefinition of macros. In fact I'll catch the same example as the previous discussion, since it's the one I'm trying to work with right now.

Here's a snippet found in zephyr/include/zephyr/tracing.h:

/**
 * @brief Called before a thread has been selected to run
 */
#define sys_port_trace_k_thread_switched_out()

And this is the snippet found in 3 different header files - zephyr/subsys/tracing/ctf/tracing_ctf.h for example:

#define sys_port_trace_k_thread_switched_out() sys_trace_k_thread_switched_out()

What's the underlying magic happening here that allows both defines to coexist without triggering the warning: "sys_port_trace_k_thread_switched_out" redefined when building the file? If I try to do this in my own new subsystem, however, it WILL give the warnign and the execution will be messed up.

Thank you once again for your time and attention.