L3-Hungary - Operating System - Assembly 1

1.asm

section .data
    input db "abc", 0
    output db 0

section .text
    global _start

_start:
    ; Find the length of the string
    mov rsi, input       ; rsi points to the string
    xor rcx, rcx        ; counter for string length
    find_length:
        cmp byte [rsi + rcx], 0
        je  reverse_string
        inc rcx
        jmp find_length

    ; Reverse the string
    reverse_string:
        mov rdi, rcx        ; rdi points to the end of the string
        dec rdi             ; move rdi to the last character

    reverse_loop:
        cmp rsi, rdi
        jge print_result
        mov al, [rsi + rcx]
        mov ah, [rsi + rdi]
        mov [rsi + rcx], ah
        mov [rsi + rdi], al
        inc rsi
        dec rdi
        jmp reverse_loop

    print_result:
        ; Print reversed string
        mov eax, 1          ; syscall: write
        mov edi, 1          ; file descriptor: STDOUT
        mov edx, rcx        ; length of the reversed string
        sub edx, 1          ; exclude the null terminator
        mov rsi, input
        syscall             ; invoke syscall

        ; Exit the program
        mov eax, 60         ; syscall: exit
        xor edi, edi        ; status: 0
        syscall             ; invoke syscall

2.asm

section .data
    old_file db "source.txt", 0
    new_link db "hardlink.txt", 0

section .text
    global _start

_start:
    ; Create a hard link
    mov rax, 86         ; syscall: link
    mov rdi, old_file   ; source file
    mov rsi, new_link   ; new link file
    syscall             ; invoke syscall

    ; Exit the program
    mov rax, 60         ; syscall: exit
    xor rdi, rdi        ; status: 0
    syscall             ; invoke syscall

3.asm

section .data
    old_file db "source.txt", 0
    new_link db "symlink.txt", 0

section .text
    global _start

_start:
    ; Create a symbolic link
    mov rax, 88         ; syscall: symlink
    mov rdi, old_file   ; source file
    mov rsi, new_link   ; new link file
    syscall             ; invoke syscall

    ; Exit the program
    mov rax, 60         ; syscall: exit
    xor rdi, rdi        ; status: 0
    syscall             ; invoke syscall

4.asm

section .data
    prompt db "Enter first digit: ", 0
    prompt2 db "Enter second digit: ", 0
    larger_msg db "Larger digit: ", 0
    newline db 10
    buffer resb 5

section .text
    global _start

_start:
    ; Get the first digit
    mov rax, 1          ; syscall: write
    mov rdi, 1          ; file descriptor: STDOUT
    mov rsi, prompt
    mov rdx, 20         ; length of the prompt
    syscall             ; invoke syscall

    ; Read the first digit
    mov rax, 0          ; syscall: read
    mov rdi, 0          ; file descriptor: STDIN
    mov rsi, buffer
    mov rdx, 5          ; maximum number of bytes to read
    syscall             ; invoke syscall

    ; Convert ASCII to integer
    movzx rax, byte [buffer]
    sub rax, '0'
    mov rbx, rax        ; store the first digit

    ; Get the second digit
    mov rax, 1          ; syscall: write
    mov rdi, 1          ; file descriptor: STDOUT
    mov rsi, newline
    mov rdx, 1          ; length of newline
    syscall             ; invoke syscall

    mov rax, 1          ; syscall: write
    mov rdi, 1          ; file descriptor: STDOUT
    mov rsi, prompt2
    mov rdx, 20         ; length of the prompt
    syscall             ; invoke syscall

    ; Read the second digit
    mov rax, 0          ; syscall: read
    mov rdi, 0          ; file descriptor: STDIN
    mov rsi, buffer
    mov rdx, 5          ; maximum number of bytes to read
    syscall             ; invoke syscall

    ; Convert ASCII to integer
    movzx rax, byte [buffer]
    sub rax, '0'

    ; Compare and print the larger digit
    mov rax, 1          ; syscall: write
    mov rdi, 1          ; file descriptor: STDOUT
    mov rsi, larger_msg
    mov rdx, 13         ; length of the message
    syscall             ; invoke syscall

    cmp rax, rbx
    jge print_rax

    mov rax, rbx

print_rax:
    add rax, '0'
    mov rdi, rax

    ; Print the larger digit
    mov rax, 1          ; syscall: write
    mov rdi, 1          ; file descriptor: STDOUT
    mov rsi, rdi
    mov rdx, 1          ; length of the digit
    syscall             ; invoke syscall

    ; Exit the program
    mov rax, 60         ; syscall: exit
    xor rdi, rdi        ; status: 0
    syscall             ; invoke syscall

README.md

L3-Hungary - Operating System - Assembly 1

Guidelines

Assuming a x86-64 architecture

1. Write an assembly program that takes one string parameter and prints it the other way around. (so when started with abc, it would print cba
2. Write an assembly program that takes two parameters and it creates a hard link with the second parameter as the new name and the first parameter as the file that to be pointed
3. Write an assembly program that takes two parameters and it creates a symbolic link with the second parameter as the new name and the first parameter as the file that to be pointed
4. Create a program which gets two integer parameters (one digits only) and prints the larger