I was trying to write a code that will have an array and a potr variable that will show which element you are on the array that will be edited right know. In the code after ; --- Add --- ; and ; --- Sub --- ; it adds or subtracts some value from the potrth element in the array. After ; --- Right --- ; and ; --- Left --- ; it adds or subtracts 1 from the potr variable. And after ; --- Print --- ; it prints the value of the potrth element in the array.
So I was doing things like adding some things to the first element printing it and going to the next element adding some things and printing it. But when I try to print twice it just didn't print it. Things got weirder when I try to add or subtract some stuff after printing a value, it started giving Segmentation Fault errors and printing �.
For example this code,
BITS 64
section .data
arr: times 30000 db 0
potr: db 0
output: db 0
section .text
global _start
_start:
; --- Add --- ;
mov rax, [potr]
mov rdi, [arr+rax]
add rdi, 49
mov [arr+rax], rdi
; --- Print --- ;
mov rax, [potr]
mov rdi, [arr+rax]
mov [output], rdi
mov rax, 1
mov rdi, 1
mov rsi, output
mov rdx, 1
syscall
; --- Right --- ;
mov rax, [potr]
add rax, 1
mov [potr], rax
; --- Add --- ;
mov rax, [potr]
mov rdi, [arr+rax]
add rdi, 48
mov [arr+rax], rdi
; --- Print --- ;
mov rax, [potr]
mov rdi, [arr+rax]
mov [output], rdi
mov rax, 1
mov rdi, 1
mov rsi, output
mov rdx, 1
syscall
; --- Exit --- ;
mov rax, 60
mov rdi, 0
syscall
works perfectly and writes 10.
But this code,
BITS 64
section .data
arr: times 30000 db 0
potr: db 0
output: db 0
section .text
global _start
_start:
; --- Add --- ;
mov rax, [potr]
mov rdi, [arr+rax]
add rdi, 49
mov [arr+rax], rdi
; --- Print --- ;
mov rax, [potr]
mov rdi, [arr+rax]
mov [output], rdi
mov rax, 1
mov rdi, 1
mov rsi, output
mov rdx, 1
syscall
; --- Sub --- ;
mov rax, [potr]
mov rdi, [arr+rax]
sub rdi, 1
mov [arr+rax], rdi
; --- Print --- ;
mov rax, [potr]
mov rdi, [arr+rax]
mov [output], rdi
mov rax, 1
mov rdi, 1
mov rsi, output
mov rdx, 1
syscall
; --- Right --- ;
mov rax, [potr]
add rax, 1
mov [potr], rax
; --- Add --- ;
mov rax, [potr]
mov rdi, [arr+rax]
add rdi, 48
mov [arr+rax], rdi
; --- Print --- ;
mov rax, [potr]
mov rdi, [arr+rax]
mov [output], rdi
mov rax, 1
mov rdi, 1
mov rsi, output
mov rdx, 1
syscall
; --- Exit --- ;
mov rax, 60
mov rdi, 0
syscall
prints 1�Segmentation fault.
And if you run this code without the
; --- Sub --- ;
mov rax, [potr]
mov rdi, [arr+rax]
sub rdi, 1
mov [arr+rax], rdi
part it prints 10 but it should have printed 110.
So what's the problem here? Why doesn't it print twice?
Note: I'm using $ nasm -felf64 -o output.o output.asm and $ ld -o output output.o to compile.
