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| Filename | Latest commit message | Latest commit date |
|---|---|---|
35ea398334
The first piece of real-hardware work, and it is three bugs that QEMU cannot show you. The report was an ASUS laptop -- Ryzen 7000-series APU, Radeon integrated, RTX discrete -- booting to a white underscore on a black screen, and unable to be offered 1920x1080. **The framebuffer address was truncated.** The loader handed over `(UINT32)gop->Mode->FrameBufferBase` and the kernel read a 32-bit field out of a VBE mode-info block -- a *BIOS* structure the UEFI path had been filling in because the kernel already knew how to read one. A machine that puts its aperture above 4 GB, which is ordinary on a laptop with a discrete GPU, got a plausible-looking address pointing at nothing. The splash went into it, the kernel was handed it, and the firmware's own cursor kept blinking on an otherwise black screen. Every step in that sequence succeeded on a number that was wrong, which is why there is no error message anywhere in it. SCHBOOT_FB_BASE is the loader's own display block: 64-bit address, 64-bit size, 32-bit width, height and stride, and the pixel format. The VBE block is still written for the BIOS loader, but anything that does not fit is left at zero rather than wrapped -- a truncated address is this bug, and a zero is at least honest. The kernel then has a problem the loader does not: its direct map covers the low 4 GB, so a framebuffer above it needs ioremap(), which needs kpdpt, which kvmalloc() has not allocated when the early console starts. A low framebuffer is attached exactly as before; a high one is attached immediately after kvmalloc(), still thousands of lines before anything else. **There was more than one adapter, and the first one was taken.** LocateProtocol answers with *a* GOP and the specification says nothing about which. QEMU with a stdvga and a virtio-gpu has **three** handles and two of them are Blt-only with a framebuffer address of zero -- so this is not a hardware-only hazard, it was a one-in-three chance of drawing into address 0 that happened to keep coming up heads. Every handle is scored now: no aperture, no candidacy; a readable current mode beats one that needs changing; size breaks the tie. **mode_usable() rejected modes real machines have.** A padded scanline (every GPU that aligns its rows -- and very likely the reason 1920x1080 could not be offered), a width not divisible by eight (1366x768, which is half the laptops in the world), and anything below 800x600 (the only mode some firmware gives over a KVM). All three passed on QEMU, which is why they survived. The mode list now offers 1366x768 and 640x480 where it did not. The loader also prints what it found, to the firmware's text console, which is cleared before the splash: invisible on a boot that works, and the only thing on the screen on a boot that dies before the splash. One process note, recorded because it cost a wrong test: `make UEFI_KEEP=1` ships the loader that is already built. Its own comment says "a build that quietly ships a stale bootloader is how you spend an evening debugging code that is not running", and that is exactly what happened -- a regression run that looked clean had tested the old loader. Loader work gets a full build. Both supported configurations verified after a clean build: one boot each, no traps, no panics, socktest and memfdtest green, and the adapter report shows the right one being chosen out of three. Co-Authored-By: Claude Opus 5 <noreply@anthropic.com> |
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A 64-bit operating system, written from the metal up.
SMP · copy-on-write filesystem · TCP/IP · PCI, USB and virtio drivers · TrueType text · Linux syscall ABI
SchOS began as xv6 and is now mostly something else. The scheduler, the memory manager and the trap path have been rewritten for x86-64 and for more than one processor; the filesystem has been replaced outright; the syscall table speaks Linux numbering so that real software — musl, toybox, mksh — runs unmodified.
It is a hobby system built by one person, and it is honest about that: what works below has been run, not inferred, and the gaps are listed as plainly as the features.
The pieces
| Layer | Name | What it is |
|---|---|---|
| System | SchOS | The distribution — kernel, userland, tooling |
| Kernel | SchIFT | Multi-core x86-64 kernel with a modular VFS |
| Filesystem | SchFS | Transactional, copy-on-write, the root filesystem |
| API | SchAPI | System programming interface — the stable surface |
| Compositor | SchCom | Display compositor (planned) |
| Window manager | SchWM | (planned) |
| Desktop | SchDE | (planned) |
uname -s reports SchIFT, the way every Unix reports its kernel rather than
its distribution.
What works
Kernel — Long mode, 4-level paging, preemptive multitasking. SMP: one, two and four processors all boot, with CPU enumeration from the ACPI MADT rather than the 1994 MP table. Memory sized from the E820 map, so it runs in tens of megabytes rather than demanding hundreds.
Filesystem — SchFS is the root: a copy-on-write B-tree with a
uberblock ring, so a crash leaves either the old tree or the new one and there
is nothing to repair. Free space is derived from the tree rather than stored
beside it, which removes a whole class of disagreement. /proc/schfs shows the
generation counter advancing as writes commit.
Processes — fork, exec, wait, pipes, signals, sessions and process groups,
mmap (anonymous and file-backed), POSIX shared memory, Unix domain sockets,
poll.
Devices — PCI enumeration with a bus-agnostic device model at
/proc/devices. Drivers for e1000 networking, virtio-gpu and stdvga
displays, xHCI USB with HID, hub and mass-storage class drivers, IDE, PS/2,
serial. /dev/fb0 speaks the Linux fbdev interface.
Networking — ARP, IPv4, ICMP, UDP, TCP and DHCP, on lwIP behind a
driver-agnostic interface class. Verified end to end from the host, both
directions, rather than by inspection. Names resolve, so wget http://host/
works; httpd serves a directory back the other way.
Userland — musl, toybox, mksh and zsh, built from source. 268 applets:
ls, cat, ps, top, wc, cp, mount, awk, bc, diff and the rest
behave the way you expect, because they are the real programs. edit is
kilo — arrow keys, Ctrl-S, Ctrl-Q, nothing
to learn.
Text — a TrueType rasteriser (glyf outlines, composite glyphs, cmap
format 4) replacing the 8×16 cell grid. JetBrains Mono for the terminal, Roboto
for the desktop layer to come.
When it dies — PSOGM, the Purple Screen of Guru Meditation: stop code, fault address, call chain, and a QR code containing a text copy of the whole report.
Quick start
make # kernel + UEFI loader + root filesystem
make qemu # build it and boot it
make iso # a bootable ISO for VMware or real hardware
Builds on Linux, macOS, FreeBSD/OpenBSD/NetBSD and Windows (Git Bash). The toolchain is clang + lld everywhere — it is a cross-compiler by construction, so one LLVM install targets the bare-metal kernel, the 16-bit boot code and musl userland from any host. See docs/guides/building.md for prerequisites per platform, and docs/history/moving-to-linux.md for moving a checkout between machines.
Testing
Booting to a prompt proves nothing: a filesystem can mount and still fail the first real command, and that has happened here. So the test harness drives the serial console and asserts on what comes back.
tools/windows/bootcheck.ps1 # boot, run real commands, check the answers
tools/windows/bootcheck.ps1 -Tty -Ps # terminal behaviour, process enumeration
make schfs-check # SchFS B-tree, object and image suites
bootcheck is PowerShell because pwsh runs on every supported host.
Layout
kernel/ arch/ core/ dev/ drivers/ fs/ net/ proc/ sys/
fs/schfs/ the filesystem -- same source the host tools compile
include/ kernel and userland headers
boot/ uefi/ (PE loader) common/ (shared loader UI)
lib/ cmd/ first-party userland runtime and programs
ports/ third-party software built from source
tools/ windows/ (.ps1) posix/ (.sh) python/ (.py) and .c/.pl
docs/ architecture/ (what it is) plan/ (what's next)
guides/ (how to work on it) history/ (why it's like this)
docs/README.md is the index. If you are reading the tree for the first time, docs/architecture/README.md is the system layer by layer.
One rule worth knowing: the kernel and the host tools compile the same SchFS
source. mkschfs cannot disagree with the kernel about the on-disk format,
because there is only one implementation — found and fixed on the host, where a
test takes a second instead of a boot.
Another: syscalls are declared in exactly one place,
kernel/sys/table.inc. Everything else is generated from it.
Not there yet
- No desktop. Schcom composites and routes input; the plan is now to put it on Wayland and delete the homegrown protocol. See docs/plan/wayland.md.
- No descriptor passing. No
sendmsg/recvmsg, so noSCM_RIGHTS— which is what the GUI work stops at. docs/plan/foundations.md. - No dynamic linking.
exechandles staticET_EXEConly. - No page cache, so writable
MAP_SHAREDof a file is refused rather than faked. - A USB disk cannot be booted from — the root device is compiled in rather than selectable.
- SchFS has no Linux driver yet; the plan is on-disk format version first, then FUSE, then a kernel module.
- CFF/OpenType outlines and TrueType hinting are deliberately out of scope.
Licensing
Apache-2.0, copyright Nexoniarz. See LICENSE.
The kernel derives from xv6, which is MIT — see LICENSE.MIT. Third-party code redistributed in a built image (musl, toybox, mksh, zsh, kilo, the fonts) keeps its own licence; NOTICE carries the attributions. All of it is permissive — there is no GPL in an image this builds, which is why the userland is toybox and not BusyBox and the editor is kilo and not nano. See docs/licensing.md.
Drivers may be adapted from BSD sources, which are compatible. Linux drivers are not: GPL-2.0-only and Apache-2.0 cannot be combined and redistributed. Reading Linux to understand hardware is fine; translating a driver is not. Best of all is the public specification — xHCI, virtio, AHCI, e1000 — which carries no licence on what you write from it.