60 lines
1.6 KiB
NASM
60 lines
1.6 KiB
NASM
bits 32 ; assembling for the 32 bits architecture
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; declare the EntryPoint (a label defining the very first instruction of the program)
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global start
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; declare external functions needed by our program
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extern exit ; tell nasm that exit exists even if we won't be defining it
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import exit msvcrt.dll ; exit is a function that ends the calling process. It is defined in msvcrt.dll
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; msvcrt.dll contains exit, printf and all the other important C-runtime specific functions
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; our data is declared here (the variables needed by our program)
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segment data use32 class=data
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; ...
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s1 db 12h,78h
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l1 equ $-s1
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s2 db 34h,0ABh
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l2 equ $-s2
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s3 resb l1+l2
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l3 equ $-s3
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; our code starts here
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segment code use32 class=code
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start:
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; ...
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mov ECX,l3
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mov ESI,0
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mov EDX,0
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mov EDI,s3
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cld
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label:
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mov AL,0FFh
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cmp ESI,l1
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jge a
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mov AL,[s1+ESI]
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a:
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mov BL,0FFh
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cmp EDX,l1
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jge b
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mov BL,[s2+EDX]
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b:
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cmp AL,BL
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jb less
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mov AL,BL
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inc EDX
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STOSB
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dec ECX
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jmp comp
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less:
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inc ESI
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dec ECX
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STOSB
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jmp comp
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comp:
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cmp ECX,0
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jg label
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; exit(0)
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push dword 0 ; push the parameter for exit onto the stack
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call [exit] ; call exit to terminate the program
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