systick problem

hi i am trying to display the execution time with the systick :
i read that there is a limitation to the size of this timer so i tried to add this function many times ,i though of summing the result to get the hole execution time however it's the same NO Displaying time
is there an other solution ? or did i do smething wrong ?
SysTick->CTRL =0 ; SysTick->LOAD=0xFFFFFFFF ; SysTick->VAL=0; SysTick->CTRL =0x5
... istructions
stop=SysTick->VAL; printf("start %d---stop %d---dur %d",starttime,stop, starttime-stop);