Operating System written for me

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Daniel Samson 73df864fd2 threads(M2): thread_spawn/thread_exit + runtime.Thread.spawn A thread is a task sharing the caller's address space. New private syscalls thread_spawn(entry, stack_top, arg)=37 and thread_exit=38: thread_spawn goes through scheduler.spawnThread (retains the shared aspace), thread_exit ends the task like a process exit(0) (terminateCurrent -> releaseAspace, so the space survives while siblings hold it). The closure pointer reaches the new thread in rdi via a new jump_to_user_arg asm path and a per-task user_arg (0 for a normal process, whose _start ignores it) - so the runtime trampoline is a plain C-ABI Zig function, no naked asm. runtime.Thread (library/runtime/thread.zig) mirrors std.Thread.spawn: mmap a stack, heap-allocate the args closure, hand the kernel the trampoline + closure. addThreadedUserBinary opts a binary into single_threaded=false; thread-test is the first, and proves a worker runs in the shared address space via a shared global the main thread polls. Gate thread-spawn PASS; 16 guardrail cases green (incl. args/init/process on the new jump_to_user_arg path) + aspace-refcount; build + host tests clean.		2026-07-20 21:04:23 +01:00
boot	serial: make the log sink a build option, off by default	2026-07-13 22:05:08 +01:00
docs	threads(M2): thread_spawn/thread_exit + runtime.Thread.spawn	2026-07-20 21:04:23 +01:00
library	threads(M2): thread_spawn/thread_exit + runtime.Thread.spawn	2026-07-20 21:04:23 +01:00
system	threads(M2): thread_spawn/thread_exit + runtime.Thread.spawn	2026-07-20 21:04:23 +01:00
test	threads(M2): thread_spawn/thread_exit + runtime.Thread.spawn	2026-07-20 21:04:23 +01:00
tools	build: release-x86-64 — the flashable hybrid ISO (Etcher/dd + optical), built in-repo	2026-07-20 13:37:10 +01:00
usr/share/fonts	assets: add font families under usr/share/fonts	2026-07-14 18:39:23 +01:00
.editorconfig	editorconfig	2026-07-12 16:09:11 +01:00
.gitattributes	gitattributes	2026-07-12 16:09:18 +01:00
.gitignore	gitignore: ignore .claude/ and .github/	2026-07-10 14:09:38 +01:00
README.md	update README.md	2026-07-20 13:39:03 +01:00
build.zig	threads(M2): thread_spawn/thread_exit + runtime.Thread.spawn	2026-07-20 21:04:23 +01:00
build.zig.zon	started project with basic efi setup	2026-07-01 18:32:56 +01:00

README.md

DanOS

Codename: Shodan

A very small resilient operating system.

Zen of DanOS:

Resilient Micro-Kernel Architecture.
- Every process run in an isolated user space not kernel space.
- Processes cannot take down the entire OS with it when they die or is killed
Stable public runtime library, private OS ABI.
- Keeps a stable runtime for user space processes between OS versions (great for backwards compatibility)
- Allows the underlying OS to be changed without effecting applications
- Provides a boundary to enable compatibility between OS's e.g. POSIX, MUSL etc
Drivers are just isolated processes in user space.
- Thin binaries that can be restarted like applications.
- Useful during driver development.
- Drivers can claim MMIO / ports
- Driver resources (e.g. IRQ/Port/MMIO) claims are automatically cleaned up if the driver dies or is killed
- Drivers can also hook into the process lifecycle to clean up or reset hardware
No legacy to deal with
- Zig code uses a clean coding style (Zen of Zig)
- Favor reading code over writing code.
- No magic numbers.
- No shortened names unless its for ABI compatibility or acronyms
Inter-Process Communication (IPC)
- Publish and subscribe to Asynchronous Messages
- Talk to services and processes synchronously

Prerequisites

Zig 0.16.x — the build is pinned to this line (.zig-version); other minor versions are rejected, because Zig makes breaking changes between releases pre-1.0. A toolchain manager such as zvm or zigup will pick up .zig-version automatically.
QEMU (qemu-system-x86_64) — to run and test the kernel. On macOS, brew install qemu also bundles the OVMF firmware below.
OVMF UEFI firmware — the edk2-ovmf package (Arch), ovmf (Debian/Ubuntu), or edk2-ovmf (Fedora); on macOS it ships inside the Homebrew qemu formula. Both the build and the test harness probe the known Arch/Debian/Fedora/macOS layouts and use the first that exists, so no configuration is normally needed. Override with -Dovmf-code= / -Dovmf-vars= (build) if yours lives elsewhere.
Python 3 — for the QEMU integration test harness.

Build

zig build

Produces a FHS-shaped zig-out/ that is the danos filesystem and the boot volume: the UEFI bootloader at zig-out/EFI/BOOT/BOOTX64.efi, the kernel at zig-out/system/kernel, init at zig-out/system/services/init, drivers under zig-out/system/drivers/, and the initial-ramdisk at zig-out/boot/.

Release media

zig build release-x86-64

Produces zig-out/danos-x86-64.iso, a hybrid ISO that boots flashed raw to a USB stick (balenaEtcher, dd) or burned to optical media — see docs/release-iso.md. zig build check-iso-image validates it without booting.

Run

Boot it in QEMU with OVMF (opens a display window):

zig build run-x86-64
# distro with OVMF elsewhere:
zig build run-x86-64 -Dovmf-code=/path/OVMF_CODE.fd -Dovmf-vars=/path/OVMF_VARS.fd

Test

zig build test            # host unit tests (the platform-independent shared code)
python3 test/qemu_test.py  # QEMU integration tests: boots the kernel and asserts
                           # on its serial output (see docs/testing.md)

The integration harness builds and boots the kernel once per test case, checking memory, the frame allocator, paging (incl. NX and the null guard), the heap, interrupts, and exception handling. It exits non-zero on any failure, so it drops straight into CI.

Documentation

Design notes explaining why behind the code live in docs/ — start with docs/README.md.

For the hardware needed to run DanOS — minimum specs plus a plain-language guide matching Intel/AMD CPU generations by name — see docs/system-requirements.md.

Logo

San Serif Text "Dan OS" with a black karate belt around it.