MacBook M1 Assembly Programming

 What do I need to code in assembly on my MacBook Air M1?

ChatGPT said:

To code in assembly on your MacBook Air M1, you need a few tools and knowledge to get started, as Apple's M1 chip is based on the ARM architecture (specifically ARM64, also called AArch64). Here’s a step-by-step guide to setting up your environment for ARM64 assembly programming:

1. Install a Text Editor or IDE

• Text Editors: You can use any text editor to write assembly code. Some popular ones include:
  • Visual Studio Code: Highly customizable with syntax highlighting for assembly.
  • Sublime Text: Lightweight and easy to use.
  • Nano/Vim: Terminal-based editors if you prefer using the command line.
• IDEs: Xcode can be configured to work with assembly code, though it's more often used for higher-level languages.

2. Install Developer Tools

• Xcode Command Line Tools: You’ll need the Xcode command line tools to access essential compilers and linkers.
  • Open Terminal and run:

    bash
    xcode-select --install
    

3. Write ARM64 Assembly Code

• Write your assembly code in a text file with the .s extension (e.g., my_program.s).
• A simple ARM64 assembly program might look like this:

  assembly
  .global _start
  _start:
      mov x0, #1         // Exit code
      mov x8, #93        // syscall number for exit on AArch64
      svc 0              // invoke the syscall
  

You said:

how to run the my_program.s?

ChatGPT said:

To run your assembly program (my_program.s) on your MacBook Air M1 (ARM64 architecture), you’ll need to assemble, link, and execute it. Here's how you can do this using command-line tools:

1. Assemble the Code

• You will need the as assembler (part of the Xcode Command Line Tools) to convert your assembly code into an object file.

bash
as -o my_program.o my_program.s

This command assembles my_program.s into an object file called my_program.o.

2. Link the Object File

• You need to link the object file to create an executable. You can use ld (the linker) to do this. On macOS, you may also want to link against system libraries like libSystem.

bash
ld -o my_program my_program.o -lSystem

This creates an executable named my_program.

3. Run the Program

• Once the program is linked, you can run it directly from the terminal:

bash
./my_program

4. Debugging (Optional)

• If you encounter issues, you can use a debugger like lldb (the default debugger for Xcode) to run and step through your assembly program:

bash
lldb ./my_program

---

By following these steps, you'll be able to assemble, link, and run your assembly code on macOS with an ARM64 (M1) architecture.

You said:

is there a command line editor I can use?

ChatGPT said:

Yes, there are several command-line editors available on macOS that you can use to write and edit your assembly code. Here are some of the most popular ones:

1. Nano

• Nano is a simple, easy-to-use text editor that is pre-installed on macOS.
• To edit your assembly file using Nano, you can use:

  bash
  nano my_program.s
  

• Basic usage:
  • Ctrl + O: Save the file.
  • Ctrl + X: Exit the editor.
  • Ctrl + W: Search for text.

2. Vim

• Vim is a powerful and more complex text editor that is also pre-installed on macOS. It offers many advanced features like syntax highlighting and customization.
• To edit your file in Vim:

  bash
  vim my_program.s
  

• Basic usage:
  • Press i to enter insert mode and start editing.
  • Press Esc to exit insert mode.
  • Type :wq to save and exit.
  • Type :q! to quit without saving.

3. Emacs

• Emacs is another powerful text editor available on the command line, though you may need to install it using Homebrew:

  bash
  brew install emacs
  

• To open your file with Emacs:

  bash
  emacs my_program.s
  

• Basic usage:
  • Ctrl + X, Ctrl + S: Save the file.
  • Ctrl + X, Ctrl + C: Exit the editor.

4. Micro

• Micro is a modern terminal-based text editor that is designed to be user-friendly. You can install it using Homebrew:

  bash
  brew install micro
  

• To edit your file with Micro:

  bash
  micro my_program.s
  

• Basic usage:
  • Ctrl + S: Save the file.
  • Ctrl + Q: Quit the editor.

---

For simplicity and ease of use, Nano is a great choice for beginners, while Vim and Emacs offer more advanced features for those who need them.

Write a simple assembly code to display "Hello Helmi!" on screen.

ChatGPT said:

Here’s a simple assembly code that displays "Hello Helmi!" on the screen using the ARM64 (AArch64) assembly language, which is appropriate for your MacBook Air M1.

assembly
    .section    __TEXT,__text,regular,pure_instructions
    .globl      _main                    // Declare the entry point as main
    .align      2

_main:                                   // Entry point
    // Write system call (syscall number 0x20)
    mov     x0, #1                       // File descriptor (1 = stdout)
    ldr     x1, =message                 // Load the address of the message
    mov     x2, #12                      // Message length (12 characters)
    mov     x8, #0x40                    // Syscall number for 'write' in ARM64
    svc     #0                           // Make the system call

    // Exit system call (syscall number 0x5D)
    mov     x0, #0                       // Return 0 status
    mov     x8, #0x5D                    // Syscall number for 'exit' in ARM64
    svc     #0                           // Make the system call

    .data                                // Data section
message:
    .ascii  "Hello Helmi!\n"              // The message to print

Explanation:

1. mov x0, #1: This moves the file descriptor for stdout (1) into register x0.
2. ldr x1, =message: This loads the address of the string message into register x1.
3. mov x2, #12: The number of characters in the string is loaded into register x2. "Hello Helmi!\n" has 12 characters, including the newline.
4. mov x8, #0x40: This moves the syscall number for write (which is 0x40 in ARM64) into x8.
5. svc #0: This triggers the system call to display the message.
6. mov x8, #0x5D: This sets up the exit syscall (which is 0x5D in ARM64).
7. svc #0: This triggers the system call to exit the program.

How to Assemble and Run:

1. Save this code to a file called hello_helmi.s.
2. Open a terminal and assemble the code:

   bash
   as -o hello_helmi.o hello_helmi.s
   

3. Link the object file to create an executable:

   bash
   ld -o hello_helmi hello_helmi.o -lSystem
   

4. Run the program:

   bash
   ./hello_helmi
   

This should print:

Hello Helmi!

ld: library 'System' not found
The error message ld: library 'System' not found is happening because ld is looking for the libSystem library in a way that's not compatible with macOS. On macOS, the libSystem library is implicitly linked, so you don't need to manually specify it. Instead, you can use a different approach for linking with the system's standard libraries.
Here's how you can modify the linking step to avoid this error:
Updated Linking Command:
bash
ld -o hello_helmi hello_helmi.o -lSystem -syslibroot `xcrun --show-sdk-path` -e _main
Explanation of new options:
-syslibroot \xcrun --show-sdk-path`: This option points ld` to the correct SDK path for macOS.
-e _main: This tells the linker that _main is the entry point for your program.
Full Steps:
Assemble the Code:
bash
as -o hello_helmi.o hello_helmi.s
Link the Object File:
bash
ld -o hello_helmi hello_helmi.o -lSystem -syslibroot `xcrun --show-sdk-path` -e _main
Run the Program:
bash
./hello_helmi
This should successfully link and run the program, displaying the message "Hello Helmi!" on your terminal.
Let me know if you encounter any further issues!