CS 456 - Systems Programming Spring 2024

Displaying ./code/asm/close.asm

; Close
; Compile with: nasm -f elf close.asm
; Link with (64 bit systems require elf_i386 option): ld -m elf_i386 close.o -o close
; Run with: ./close
 
%include    'functions.asm'
 
SECTION .data
filename db 'readme.txt', 0h    ; the filename to create
contents db 'Hello world!', 0h  ; the contents to write
 
SECTION .bss
fileContents resb 255,          ; variable to store file contents
 
SECTION .text
global  _start
 
_start:
 
    mov     ecx, 0777o          ; Create file from lesson 22
    mov     ebx, filename
    mov     eax, 8
    int     80h
 
    mov     edx, 12             ; Write contents to file from lesson 23
    mov     ecx, contents
    mov     ebx, eax
    mov     eax, 4
    int     80h
 
    mov     ecx, 0              ; Open file from lesson 24
    mov     ebx, filename
    mov     eax, 5
    int     80h
 
    mov     edx, 12             ; Read file from lesson 25
    mov     ecx, fileContents
    mov     ebx, eax
    mov     eax, 3
    int     80h
 
    mov     eax, fileContents
    call    sprintLF
 
    mov     ebx, ebx            ; not needed but used to demonstrate that SYS_CLOSE takes a file descriptor from EBX
    mov     eax, 6              ; invoke SYS_CLOSE (kernel opcode 6)
    int     80h                 ; call the kernel
 
    call    quit                ; call our quit function