CISS-150 Project 5 – Assembly Language Syscalls

CISS-150 Project 5 (10 points)

(Updated October 13, 2024)

Overview

Use Linux syscalls to simulate Java method calls like Scanner’s nextLine() method and PrintWriter’s printf() method. (similar to fgets() and printf() in C).

Learning Outcomes

Understanding basic assembly instructions.
Understanding the connection of privileged calls and the Linux OS.
Understanding the basics of syscalls.

Getting Started

Begin by reviewing Assembly Language with NASM document.

This project continues with the examination of assembly language on the Ubuntu platform.

You will use two additional system calls in Linux to create a basic yet rudimentary interactive program. Since I/O operations are privileged, system calls (syscall) must be utilized for the OS to perform the privileged work on our behalf.

You will learn the complexity of harnessing the CPU in its most primitive form. This exercise uses the x86-64 call model and Linux system calls to move data around. There is much to learn about operating at this level – it is impossible to learn everything at this stage. The goal here is simply exposure to system calls and how some languages, like C, get translated to this code level.

The Code

Again, we are working in a terminal window and must move to the asm directory.

student@student-vm:~$ cd asm

Then, we will create a new shell program to build the project.

project5.sh

nasm -felf64 -g project5.asm && {
  ld project5.o -o project5
  chmod +x project5
  ./project5
}

Like Project 4, this script will build your program, link the pieces, and execute it. After creating that file, you need to change the permissions on it.

student@student-vm:~/asm$ chmod +x project5.sh

Here is a starting point for project 5.

project5.asm

  section .bss
  
name:    resb 32   ; 32 bytes for name

  section .data
  
; YOUR PROMPTS AND LENGTHS HERE

  section .text
  global _start

_start:

;
; YOUR CODE HERE!
;


exit:
  mov rax, 60    ; exit
  mov rdi, 0     ; return code
  syscall

What you need to do next

Your program will prompt the user for their name and then say hello to them using their name.

student@student-vm:~/asm$ ./project5.sh

For example, the output might look like:

Enter your name: Bill Jojo
Hello, Bill Jojo

The bold text was entered by the user.

Unlike the previous project, you will not have a library of routines to call upon for the printing and reading. You are manufacturing the complete setup and syscall.

After you complete the reading, remember that `.bss` is for your variables that will receive data and `.data` is for fixed information, like prompts.

The idea is to have fun with the assignment and experiment! Be sure to read up on how additional registers are utilized.

You can see an example starting point below.

p5ex.asm

  section .data

hello:  db "Hello, World!",0xa
len:    equ $ - hello

  section .text
  global _start

_start:
  mov rax, 1     ; write syscall
  mov rdi, 1     ; stdout
  mov rsi, hello ; text
  mov rdx, len   ; length
  syscall

exit:
  mov rax, 60    ; exit
  mov rdi, 0     ; return code
  syscall

Glossary of Assembly Language

db - Reserves declared byte space within the program.
equ - equate the name on the left with the expression on the right.
resb - reserve bytes, the value specifies the number of bytes to be reserved.

Submit a note in the Learning Management System when the project is completed.