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  1. ; Hello World in Assembly (Pure System Calls)
  2. section .data
  3.     msg1 db 'Testing 1, 2, 3, 4', 0Ah, 0h  ; original string
  4.  
  5. section .bss    ;reserver buffer to store string
  6.     reverse resb 256
  7.  
  8. section .text
  9.     global _start
  10.  
  11. _start:
  12.     mov eax, msg1
  13.     call string_rev
  14.     mov eax, reverse
  15.  
  16.     call printLF
  17.     call quit
  18.  
  19. string_rev:
  20.     push ebx
  21.     push ecx
  22.     push edx
  23.  
  24.     mov ebx, eax
  25.     call string_len
  26.     mov ecx, eax
  27.  
  28.     mov esi, ebx
  29.     mov edi, reverse
  30.     add esi, ecx
  31.     dec esi
  32.  
  33. rloop:
  34.     cmp ecx, 0
  35.     je reverse_done
  36.  
  37.     mov al, [esi]
  38.     mov [edi], al
  39.     inc edi
  40.     dec esi
  41.     dec ecx
  42.     jmp rloop
  43.  
  44. reverse_done:
  45.     mov byte [edi], 0
  46.     pop edx
  47.     pop ecx
  48.     pop ebx
  49.     ret
  50.  
  51.  
  52.  
  53. string_len:
  54.     push ebx
  55.     mov ebx, eax
  56.  
  57. next_char:
  58.     cmp byte [eax], 0
  59.     jz slen_done
  60.     inc eax
  61.     jmp next_char
  62.  
  63. slen_done:
  64.     sub eax, ebx
  65.     pop ebx
  66.     ret
  67.  
  68.  
  69.  
  70. printLF:
  71.     call print
  72.     push eax
  73.     mov eax, 0Ah
  74.     push eax
  75.     mov eax, esp
  76.     call print
  77.     pop eax
  78.     pop eax
  79.     ret
  80.  
  81. print:
  82.     push edx
  83.     push ecx
  84.     push ebx
  85.     push eax
  86.     call string_len
  87.  
  88.     mov edx, eax
  89.     pop eax
  90.     mov ecx, eax
  91.     mov ebx, 1
  92.     mov eax, 4
  93.     int 80h
  94.  
  95.     pop ebx
  96.     pop ecx
  97.     pop edx
  98.     ret
  99.  
  100. quit:
  101.     mov ebx, 0
  102.     mov eax, 1
  103.     int 80h
  104.     ret
Success #stdin #stdout 0s 5320KB
comments (?)
stdin 
Standard input is empty
stdout 
4 ,3 ,2 ,1 gnitseT
https://ideone.com/EyrfXH
language:
Assembler 32bit (nasm 2.14)
created:
20 hours ago
visibility:
public

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