(gdb) x/s $rdi
0x7fffffffe410:	 "almost every pro"
(gdb)
0x7fffffffe421:	 "rammer should know memset!"

##############################################
char str_t[] = "almost every programmer should know memset!";
        test("memset", strcmp(memset_(str_t,'-',6), "------ every programmer should know memset!") == 0);