Save single byte to file

section .text
    global _start

_start:

    call openFileIn         ;open the org image
    call readFromFileIn     ;read the data
    call closeFileIn        ;close file

    call openFileOut        ;open output file
    call writeToFile        ;write the data in data
    call closeFileOut       ;close file

    call exitProg           ;exit process

openFileIn:
    ;opening the file roller1.raw
    mov eax, 5
    mov ebx, fileName
    mov edx, 0777
    int 0x80

    mov [fd_in], eax    ;get pointer to indexbuffer
    ret

openFileOut:
    ;opening the file roller1.raw
    mov eax, 5
    mov ebx, outName
    ;mov ecx, 1
    mov edx, 0777
    int 0x80

    mov [fd_out], eax   ;get pointer to indexbuffer
    ret

writeToFile:
    ;1. Put sys_write(), 4, in EAX
    ;2. Put fileDesc in EBX
    ;3. Put the pointer to data in ECX
    ;4. Put buffer size of data in EDX
    ;5. call kernel

    ;returns the actual nr of bytes written in EAX

    mov eax, 4
    mov ebx, [fd_out]
    mov ecx, info + 2      ;pointer to array + 2 bytes
    mov edx, 1             ;Nr of bytes to be printed
    int 0x80

    ret

readFromFileIn:
    ;Process: Read from file
    ;1. put the system call sys_read() number 3 in EAX
    ;2. Put the file descriptor in the EBX register
    ;3. Put the pointer to the input buffer in the ECX register
    ;4. Put the buffer size, in EDX
    ;5. call kernel


    ;the system call returns the number of bytes rad in the EAX
    ;register, in case of error code is in the EAX register

    ;read the file
    mov eax, 3
    mov ebx, [fd_in]    ;pointer to inputBuffer
    mov ecx, info       ;buffer size
    mov edx, IMAGE_SIZE
    int 0x80

    ret

readFromFileOut:
    ;Process: Read from file
    ;1. put the system call sys_read() number 3 in EAX
    ;2. Put the file descriptor in the EBX register
    ;3. Put the pointer to the input buffer in the ECX register
    ;4. Put the buffer size, in EDX
    ;5. call kernel


    ;the system call returns the number of bytes rad in the EAX
    ;register, in case of error code is in the EAX register

    ;read the file
    mov eax, 3
    mov ebx, [fd_in]    ;pointer to inputBuffer
    mov ecx, info       ;buffer size
    mov edx, IMAGE_SIZE
    int 0x80

    ret

printBuffer:
    ;1. put syscall sys_write to EAX
    ;2. put an argument in EBX
    ;3. put the data into ECX
    ;4. put the size of the segment in EDX
    ;5. call kernel
    mov eax, 4
    mov ebx, 1
    mov ecx, info
    mov edx, IMAGE_SIZE

    int 0x80
    ret

closeFileIn:
    ;Closing a file
    ;1.Put the system call sys_close(), 6, in the EAX register
    ;2.Put the file descriptor in the EBX register
    mov EAX, 6
    mov EBX, [fd_in]
    int 80h

    ;the system call returns error code in eax
    ret

closeFileOut:
    ;Closing a file
    ;1.Put the system call sys_close(), 6, in the EAX register
    ;2.Put the file descriptor in the EBX register
    mov EAX, 6
    mov EBX, [fd_out]
    int 80h

    ret

exitProg:
    ;call system exit
    mov eax, 1
    int 0x80

section .data
fileName db 'roller1.raw', 0 ;glöm förfan inte nollan
;lenfFileName equ $-fileName ; adress
outName db 'roller2.raw', 0
;lenOutName equ $-fileName
IMAGE_SIZE equ 64256

section .bss
fd_out resb 1
fd_in resb 1
info resb 64256