/* --------------------------------------------------------------
   Show the pass-by-reference  in assembler 
   -------------------------------------------------------------- */

        .global main, Stop, CodeEnd, DataStart, DataEnd

        .global f, k

/* --------------------------------------------------
   Begin of the program instructions
   -------------------------------------------------- */
        .text
main:

        /* =========================================
           Pass k to f( ) by value
           ========================================= */
        movw	r0, #:lower16:k
        movt	r0, #:upper16:k		// r0 = address of k

        push  	{r0}			// Pass k by reference (pass k's address)

        bl    	f            		// Call function f             
        add   sp, sp, #4   		// Clean up parameter on the stack

        nop      
        nop

Stop:
        nop


/* ================================================
   Function f that gets a parameter by reference

   Stack frame of f( ):

	  FP-->	+-----------+
        	|  old FP   |   FP + 0
		+-----------+
        	|  ret addr |   FP + 4
		+-----------+
        	| addr of a |   FP + 8
		+-----------+
   ================================================ */
f:
        /* ****************************************
           Prelude: build stack frame
           **************************************** */
        push	{lr}	        // Save return address in LR
        push	{fp}	        // Save Frame Pointer in FP
        mov	fp, sp	        // Initialize my own FP
        sub	sp, sp, #0      // I create 0 local variable in stack

	/* =======================================
	   a = a + 1  
	   ======================================= */
	ldr	r0, [fp, #8]	// r0 = address of variable a
	ldr	r1, [r0]	// r0 = value of variable a
	add	r1, r1, #1	// r0 = a + 1
	ldr	r0, [fp, #8]	// r0 = address of variable a
	str	r1, [r0]	// Assign: a  = a + 1


        /* ************************************************
           Postlude: break down stack frame
           ************************************************ */
        mov	sp, fp		// De-allocate the local variables
        pop	{fp}		// Restore old FP

        pop	{pc}		// Return




CodeEnd:
        nop

/* --------------------------------------------------
   Begin of the permanent program variables
   -------------------------------------------------- */
        .data
DataStart:

k:	.4byte	7

DataEnd:

        .end