Question

if I need to get the sum of 6 numbers, here is a C programming solution

int getSum(int number1, int number2, int number3, int number4, int number5, int number6);

and the function is:

int SUM;

sum = number1+number2+number3+number4+number5+number6;

return SUM;

this function is called in main, and the main looks like:

int totalSum;

totalSum=getSum(1,2,3,4,5,6);

while(1);

so how can I write this C programming code in ARM assembly code, can you please write the comment of each line so I can understand the code better, we only need to implement the function getSum(), which is called from the c code in main(). Please add some c code that is needed to call the function getSum().

Answer 1

The given C program is:

int getSum(int number1, int number2, int number3, int number4, int number5, int number6) {

    int SUM;

    SUM=number1+number2+number3+number4+number5+number6;

    return SUM;

}

main()

{

    int totalSum;

    totalSum=getSum(1,2,3,4,5,6);

}

The corresponding code in arm (arm64 gcc 6.4) assembly language is given below:

getSum:

        sub     sp, sp, #48 // stack space allocated

        str     w0, [sp, 28] // stores number 1

        str     w1, [sp, 24] // stores number 2

        str     w2, [sp, 20] // stores number 3

        str     w3, [sp, 16] // stores number 4

        str     w4, [sp, 12] // stores number 5

        str     w5, [sp, 8]  // stores number 6

        ldr     w1, [sp, 28]  // load number 1

        ldr     w0, [sp, 24]  // load number 2

        add     w1, w1, w0  // add numbers

        ldr     w0, [sp, 20] // load number 3

        add     w1, w1, w0  // add numbers

        ldr     w0, [sp, 16] // load number 4

        add     w1, w1, w0 // add numbers

        ldr     w0, [sp, 12] // load number 4

        add     w1, w1, w0 // add numbers

        ldr     w0, [sp, 8]  // load number 5

        add     w0, w1, w0 // add numbers

        str     w0, [sp, 44]

        ldr     w0, [sp, 44] // load number 6

        add     sp, sp, 48 //add numbers

        ret

main:

        stp     x29, x30, [sp, -32]!

        add     x29, sp, 0

        mov     w5, 6 //load 6

        mov     w4, 5 //load 5

        mov     w3, 4 //load 4

        mov     w2, 3 //load 3

        mov     w1, 2 //load 2

        mov     w0, 1 //load 1

        bl      getSum //call getSum()

        str     w0, [x29, 28] // final result

        mov     w0, 0

        ldp     x29, x30, [sp], 32

        ret