__attribute__((constructor[(priority)]))

How exactly does __attribute__((constructor)) work?
GCC __attribute__((constructor)) is called before object constructor
C++ static initialization vs __attribute__((constructor))
__attribute__((constructor[(priority)])) function attribute
__attribute__((constructor(priority))) function attribute

__attribute__((init_priority(X)))

__attribute__((init_priority(X))) in GCC

__attribute__((weak))

__attribute__((weak)) and static libraries

void noOsSystickHandler() { } // empty 
void osSystickHandler() __attribute__((weak, alias("noOsSystickHandler")));