Procedures often need to allocate memory for local variables and perhaps space to save registers so they can pass parameters to other procedures. This space is allocated on the stack.

The general format of a stack frame is illustrated in Figure $3\mathrm{.}25$ on page $240$ of the text.

$($Figure $1)$

The procedure may need to save registers so it can set up calls to other procedures that require different parameters. It may also require local variables that cannot be maintained in registers, and may also require space for more than six procedure parameters.

The space for a procedure$$s stack frame is allocated by simply subtracting the appropriate value from $\%$rsp$.$ Individual elements of the frame are accessed by indexed references based on $\%$rsp$.$

Consider the following function and the function that calls it:

long array$\_$sum $($int $*$p$\_$array, int array$\_$size$)$

$\{$

long sum $=0$;

while $($array$\_$size$--)$

sum $+=*$p$\_$array$++$;

return sum;

$\}$

long caller $($void$)$

$\{$

int array$[10]$;

int a$\_$size $=10$;

long sum;

sum $=$ array$\_$sum $($array$,$ a$\_$size$)$;

return sum;

$\}$

Below is the assembly code. Note that caller$()$ allocated $48$ bytes of stack for local variables, the $10-$element integer array and apparently sum, even though it$$s never stored in memory.

Drag the correct register to the appropriate location in the code below. Not all labels will be used.