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bcd4d4e2bd
Two reports, and the first one was not an F8 bug at all.
**Choosing "Boot SchOS (verbose)" appeared to do nothing.** The menu worked,
the flag crossed, and the kernel really did boot verbose -- and then the
machine *reset* partway through and the second boot was quiet. So what anybody
ended up looking at was an ordinary boot, which reads as "verbose is broken".
PROBE before startothers, ncpu=2 <- verbose boot
SchOS UEFI loader <- the firmware, again
PROBE before startothers, ncpu=2 <- quiet boot
PROBE after startothers
mpmain() opened with
kinfo("cpu%d: starting\n", cpunum());
enable_sse();
idtinit();
and the order is the bug. enable_sse() clears CR0.EM; until it runs, *any* SSE
instruction on that CPU faults, and the kernel is not built with -mno-sse, so
the compiler emits them freely for struct copies and inline memset. idtinit()
loads that CPU's IDT; until it runs there is nowhere for a fault to go. So the
#UD is not a panic -- it is a double fault with no handler, then a triple
fault, then the firmware comes back up. A triple fault prints nothing, which is
why there was no last line to go on.
**Why only on a verbose boot**, which is what disguised it as an F8 problem:
kinfo() is log-only when the boot is quiet, so the work is a few bytes into a
ring and no XMM is involved. A verbose boot renders that same line through the
TrueType rasteriser, and that is where the SSE lands.
Setup first, announcement second. The general rule, stated where the next
person will meet it: a processor announces that it is up after it is able to
run, not before.
Verbose now boots once and puts the whole log on the screen -- `verbose boot:`
lines, `cpu1: starting`, the mount, `schinit: ready`, the jobs starting -- which
is what F8 was for and what a machine with no serial port needs.
**And vgpud drew a test card.** Three colour bands, four gradients, a
checkerboard, and the driver's own pid in binary along the bottom edge. That
was scaffolding for hybrid.md's H2 and H3: a screenshot had to answer "did a
*userspace process* put this here", and "did the driver come back" needed a
restarted instance to look different from one that never stopped. Both
milestones closed a while ago and the test card stayed, so a second display
showed something garish with nothing to explain it.
It draws the Shift mark on SCH_BG now, from the same include/logo.h the loader
splash and the kernel console use. That answers the same question a black
screen cannot -- something is driving this device -- as the system rather than
as a test rig.
Also: vgpud's "no control socket" line is vputs, not puts. It is progress, not
news, and it was printing on the console of every quiet boot.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
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| include | ||
| kernel | ||
| ldls | ||
| lib | ||
| ports | ||
| projects | ||
| srv | ||
| tools | ||
| .gdbinit | ||
| .gitattributes | ||
| .gitignore | ||
| LICENSE | ||
| LICENSE.MIT | ||
| Makefile | ||
| NOTICE | ||
| README.md | ||
| run.ps1 | ||
| shell.nix | ||
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.