int pthread_create(pthread_t * thridptr, 
                         pthread_attr_t *attptr, 
                         void * (*(void *) start, 
                         void *arg);
   

Casting to the expected types only works if the arguments behave as those types.

For example, if a function has void return type but is cast as returning void *, problems may or may not occur depending on the calling protocol of the underlying machine.