cat.asm

section .data
    error_msg db 'error while opening file', 10, 0 ;25 length 
    file      dd 0x2      ;stdin
    
section .bss
    buffer    resb 64
    
section .text
    global main
main:
    mov ebp, esp
    cmp dword [ebp+0x4], 1
    je main_loop
    
    ;open file
    mov ebx, [ebp+0x8]    
    mov ebx, [ebx+0x4]    ;filename = file path
    mov ecx, 0x0          ;flags    = O_RDONLY
    mov edx, 0x0000444    ;mode     = S_IRUSR | S_IRGRP | S_IROTH
    mov eax, 0x05         ;sys_open
    int 0x80
    mov dword [file], eax
    ;int 3
    cmp eax, 0
    jg main_loop
    
    ;print error
    mov ebx, 0x1          ;fd       = stdout
    mov ecx, error_msg    ;buf      = error_msg
    mov edx, 25           ;count    = 25
    mov eax, 0x4          ;sys_write
    int 0x80
    jmp end
    
main_loop:
    mov ebx, dword [file] ;fd       = file
    mov ecx, buffer       ;buf      = buffer
    mov edx, 64           ;count    = 64
    mov eax, 0x3          ;sys_read
    int 0x80
    test eax, eax
    jz end
    
    mov ebx, 0x1          ;fd       = stdout
    mov ecx, buffer       ;buf      = buffer
    mov edx, 64           ;count    = 64
    mov eax, 0x4          ;sys_write
    int 0x80
    jmp main_loop
end:
    xor eax, eax
    ret