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| Filename | Latest commit message | Latest commit date |
|---|---|---|
7a7c7611e0
docs/plan/ldls.md milestone L1. Every undefined symbol resolves to a
trampoline -- twenty generated bytes that load the symbol's index and jump to
a shared thunk, which saves the argument registers and reports the call. Then
init_module is simply called.
$ ldls-run 8139too.ko
module 8139too
license GPL
wants 94 symbols
calling init_module at 0x416fc020
1 _printk(0x416fb6c0, 0, 0)
| 8139too: 8139too Fast Ethernet driver 0.9.28
2 __pci_register_driver(0x416fb400, 0x416fff80, 0x416fbdbb)
init_module returned 0 after 2 stub call(s)
That second line is the driver's own banner, printed through a _printk that
is ours, from a string in the module's own .rodata that a relocation put
there. There is no stronger evidence that a load worked than the loaded thing
speaking.
Stubs return zero rather than stopping, which departs from what the milestone
originally said and does so deliberately: stopping at the first call tells you
one name, carrying on tells you the sequence, and the sequence is the thing a
symbol table cannot give you. A driver that then dereferences the zero faults,
and that is a result too -- it says how far it got before it needed the kernel
to have really done something.
The first run failed on neither of those. It failed on a relocation:
ldls-run: relocate: a signed 32-bit relocation does not fit
A module is compiled -mcmodel=kernel, so the compiler emits R_X86_64_32S for
anything it believes lives in the top 2 GB, and an ordinary mmap at 0x7f...
has nowhere to put it. Linux gives modules a region within 2 GB of the kernel
text; the harness uses MAP_32BIT to reach the same window from the other end.
On SchOS this costs nothing -- a process's mmap area starts at 0x40000000 and
is already inside it -- but it is a real constraint on where the host may load
a module, and a loader that did not check its own arithmetic would have found
it much later and much more confusingly.
Swept over 500 stock modules: 449 ran init to completion, 22 faulted on a
stub's zero, 29 have no init_module, and zero hit a loader error.
Recorded honestly in "what it will not do": running init is not working. Every
symbol is a stub, so what has been shown is that drivers ask for things in a
readable order, not that anything answers. Also recorded: every undefined
symbol in a module is NOTYPE, so the stubs cannot tell jiffies from
pci_iomap and both get a trampoline -- BTF distinguishes VAR from FUNC and
that is where the fix belongs rather than in a guess.
make ldls-check is 23 checks now, five of them L1's, all against
ldls/test/refmod.c which is ours and now has an init_module of its own.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01VQ7Qx8E1q1M1bbCq8QLHS2
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| cmd | ||
| docs | ||
| etc | ||
| include | ||
| kernel | ||
| ldls | ||
| lib | ||
| ports | ||
| projects | ||
| 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.
Userland — musl, toybox and mksh, built from source. ls, cat, ps,
top, wc, cp, mount and the rest behave the way you expect, because they
are the real programs.
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, the fonts) keeps its own licence; NOTICE carries the attributions.
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.