CODEWITHSUNDEEP
assemblyarm64
jp.lasanas
jp.lasanas

Reputation: 1

Can't print sum in ARMv8 Assembly

I've been trying to print my sum in ARMv8 but I can't seem to get it to work. I can compile and run but no output is showing.

This is my code:

       .balign 4
       .global main
main:
        stp     x29, x30, [sp, -16]! 
        mov     x29, sp              

        mov     x19, 1              
        mov     x20, 2
        add     x21, x20, x19

        mov     w0, 0                
        ldp     x29, x30, [sp], 16   
        ret

Upvotes: 0

Views: 1537

Answers (1)

InfinitelyManic
InfinitelyManic

Reputation: 822

As indicated by @Michael, you are not using any instructions to "print" your sum to the screen. You may use syscalls or printf. The sample ARMv8 code below uses printf and some simple simple macros; which are not necessary.

May I suggest you study ARMv7 since there are plenty of tutorials out there then review the ARMv8 Instruction Set Overview and the ARM Procedure Call Standard for AArch64. 

1 /*
  2         David @InfinitelyManic
  3         http://stackoverflow.com/questions/39845288/cant-print-sum-in-armv8-assembly
  4         $ uname -a
  5         Linux alarm 3.10.65-4-pine64-longsleep #16 SMP PREEMPT Sun Apr 3 10:56:40 CEST 2016 aarch64 GNU/Linux
  6         $ cat /etc/os-release
  7         NAME="Arch Linux ARM"
  8         gcc -g print_sum.s -o print_sum
  9 */
 10 .bss
 11 .data
 12         fmt:    .asciz  "%d + %d = %d\n"
 13 .text
 14         .global main
 15
 16         // macros
 17         // push2
 18         .macro push2, xreg1, xreg2
 19         .push2\@:
 20                 stp     \xreg1, \xreg2, [sp, #-16]!
 21         .endm
 22
 23         // pop2
 24         .macro  pop2, xreg1, xreg2
 25         .pop2\@:
 26                 ldp     \xreg1, \xreg2, [sp], #16
 27         .endm
 28
 29         // exit
 30         .macro _exit
 31         .exit\@:
 32                 mov x8, #93             // exit see /usr/include/asm-generic/unistd.h
 33                 svc 0
 34         .endm
 35
 36 main:
 37         mov x1, 1
 38         mov x2, 2
 39         add x3, x1, x2
 40         bl write
 41
 42 _exit
 43
 44 write:
 45         push2 x29, x30
 46         ldr x0,=fmt
 47         bl printf
 48         pop2 x29, x30
 49         ret

OUTPUT:

 $./print_sum
1 + 2 = 3

Upvotes: 1

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