The symbol __rt_entry is the starting point for a program using the ARM C library. Control passes to __rt_entry after all scatter‑load regions have been relocated to their execution addresses.
The default implementation of __rt_entry:
Sets up the heap and stack.
Initializes the C library, by calling __rt_lib_init.
Calls main().
Shuts down the C library, by calling __rt_lib_shutdown.
Exits.
__rt_entry must end with a call to one of the following functions:
exit()Calls atexit()‑registered functions and shuts down the library.
__rt_exit()Shuts down the library but does not call atexit() functions.
_sys_exit()Exits directly to the execution environment. It does not shut down the library and does not call atexit() functions. See _sys_exit().