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Section 10.4 Programming Exercise

1.

Modify the assembly language program in Listing 10.3.1 so that it prints “Hello, yourName!” on the screen. Remember to change the documentation such that it accurately describes your program.

Solution
@ helloBob.s
@ Hello Bob program, in assembly language.
@ 2017-09-29: Bob Plantz

@ Define my Raspberry Pi
        .cpu    cortex-a53
        .fpu    neon-fp-armv8
        .syntax unified         @ modern syntax

@ Useful source code constant
        .equ    STDOUT,1

@ Constant program data
        .section  .rodata
        .align  2
helloMsg:
        .asciz	 "Hello, Bob!\n"
        .equ    helloLngth,.-helloMsg

@ Program code
        .text
        .align  2
        .global main
        .type   main, %function
main:
        sub     sp, sp, 8       @ space for fp, lr
        str     fp, [sp, 0]     @ save fp
        str     lr, [sp, 4]     @   and lr
        add     fp, sp, 4       @ set our frame pointer

        mov     r0, STDOUT      @ file number to write to
        ldr     r1, helloMsgAddr   @ pointer to message
        mov     r2, helloLngth  @ number of bytes to write
        bl      write           @ write the message
        
        mov     r0, 0           @ return 0;
        ldr     fp, [sp, 0]     @ restore caller fp
        ldr     lr, [sp, 4]     @       lr
        add     sp, sp, 8       @   and sp
        bx      lr              @ return
        
        .align  2
helloMsgAddr:
        .word   helloMsg