laos -- LAm Operating System

A personal study on operating systems, with help from the OSDev Wiki. A long-term weekend side project.

Quick start

Make sure to have QEMU and GNU make installed.

# Fetch Limine (bootloader) dependency.
git submodule update --init

# Build Limine (this build is separate from the kernel build)
make limine

# Build and run in QEMU (run_iso target also available)
sudo make run_hdd

# Cleanup
sudo make limine-clean clean

More advanced usage

# Run with extra logging and debug flags.
sudo make DEBUG=1 run_hdd

# Run all tests.
sudo make RUNTEST=all run_hdd

# Run tests that match the specified pattern.
sudo make RUNTEST=^slab.,^phys. run_hdd

# Run specified tests with debug flags.
sudo make RUNTEST

# Run interactively with gdb and debug flags/logging. Run these in separate
# terminal emulators, and make sure the variants match exactly.
sudo make RUNTEST=^list. DEBUG=i run_hdd
make RUNTEST=^list. DEBUG=i run_gdb

Each RUNTEST value creates a different build variant to avoid inconsistent builds. Specifying DEBUG also creates a different build variant. Output binaries, intermediate files, and test results will be written to out<build_variant>/.

TODO(jlam55555): Note that headers are not correctly considered as dependencies, and the debug mode still has the -O2 flag because there are problems building with -O0.

Features

• Limine bootloader (forked to jlam55555/limine to enable VGA text mode 3 by default)
• PS/2 Keyboard driver: read scancodes, translate to keycodes/ASCII and pass to input subsystem
• TTY subsystem: basic line discipline, buffering core utilities, tty driver
• Console driver: write text to screen, with scrollback; interpret special characters like ^H, ^M, ^J
• Simple shell: run simple hardcoded commands
• Synchronization primitives: mask interrupts/save IRQ state, spinlocks (for multicore)
• Memory management: page fault handler, page table representation, page allocator, library functions for heap allocation
• Processes: TODO

See also TODO.md.

Directory structure

• src:
  • src/limine: Limine bootloader submodule.
  • src/kernel:
    • src/kernel/arch: Architecture-specific code. There shouldn't be many direct references to architecture-specific code from outside this directory. If there are ever multiple references to the same architecture-specific interface, this should be abstracted away in some architecture-agnostic interface.
    • src/kernel/common: Utility code and definitions, to be used anywhere.
    • src/kernel/diag: Diagnostic printing code. (deprecated; I'm trying to get rid of this in favor of other ways of dumping diagnostics once we get to userspace processes.)
    • src/kernel/drivers: Hardware drivers.
    • src/kernel/mem: Memory allocators and virtual memory definitions.
    • src/kernel/proc: Userspace utilities.
    • src/kernel/sched: Thread scheduling utilities.
    • src/kernel/test: Unit tests.

Learning goals

I.e., interest points.

• The bootloader
• Memory and cache management (e.g., fences, cache coherence policies, etc.)
• Scheduling on a multiprocessor system, especially focusing on latencies and power requirements on a RTS-like system
• Operating characteristics of popular ARM processors (e.g., ARM Cortex R52); tracing and observing real latencies at high precision. (However, an initial port to x86-64 may be simpler)
• Interrupt handling and latencies
• Integrating Rust as a systems language

There are some Markdown notes in the docs/ directory. This isn't done in a systematic way, and I may also write up some more cohesive notes in blog posts.

Non-goals

• Creating a userspace application environment
• POSIX compliance (or any other compliance)
• UI system (except maybe an X clone)
• Becoming the next Linux (or Windows, or Mac OS)

Other things with this name

• Latency Aware Operating System
• the country