CS 456 - Systems Programming Spring 2024

Displaying ./code/asm/read.asm

; Read
; Compile with: nasm -f elf read.asm
; Link with (64 bit systems require elf_i386 option): ld -m elf_i386 read.o -o read
; Run with: ./read
 
%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             ; number of bytes to read - one for each letter of the file contents
    mov     ecx, fileContents   ; move the memory address of our file contents variable into ecx
    mov     ebx, eax            ; move the opened file descriptor into EBX
    mov     eax, 3              ; invoke SYS_READ (kernel opcode 3)
    int     80h                 ; call the kernel
 
    mov     eax, fileContents   ; move the memory address of our file contents variable into eax for printing
    call    sprintLF            ; call our string printing function
 
    call    quit                ; call our quit function