Function nrf_modem_os_alloc 

#[unsafe(no_mangle)]
pub extern "C" fn nrf_modem_os_alloc(
    num_bytes_requested: usize,
) -> *mut u8

The Modem library needs to dynamically allocate memory (a heap) for proper functioning. This memory is used to store the internal data structures that are used to manage the communication between the application core and the modem core. This memory is never shared with the modem core and hence, it can be located anywhere in the application core’s RAM instead of the shared memory regions. This function allocates dynamic memory for the library.