Arc

Introduction

Arc is a toy operating system for modern PCs with amd64 processors. It is written mostly in C11, with small amounts of Intel-style assembly where required. It can be loaded by any Multiboot 2-compliant boot loader, such as GNU GRUB.

Features

The current set of features, at a high level, is roughly:

• Symmetric multiprocessing (i.e. multiple processors/cores)
• Paging (and TLB shootdown)
• Physical memory allocation (several zones for DMA addressing limitations)
• Virtual memory allocation (in kernel- and user-space)
• Interrupt handling (dual 8259 PICs or local APIC)
• Interrupt routing (with I/O APIC and ACPI tables)
• Timing (8253/8254 PIT or local APIC)
• Processes (loaded as ELF64 Multiboot modules) and threads
• Scheduling (round-robin, preemptive)
• System calls (with SYSCALL/SYSRET)
• Fine-grained locking with spinlocks

Currently these are enough to boot up and execute some simple programs written in assembly language that directly make system calls to the kernel (there’s no C library yet!)

For example, the following ‘Hello, world!’ program can be seen running in the screenshot at the top of the page:

[section .text]
[global _start]
_start:
  ; sys_trace
  mov rax, 0
  mov rdi, hello_str
  syscall

  ; sys_exit
  mov rax, 1
  syscall
  jmp $

[section .data]
hello_str:
  db "hello, world"
  db 33, 10, 0

Source code

Arc is open-source software available under the terms of the ISC license, which is similar to the 2-clause BSD license. The source code is hosted on GitHub. The README file contains instructions for building and testing it.