- C 90.2%
- Makefile 3.2%
- PowerShell 2.3%
- Shell 1.7%
- Python 1.3%
- Other 1.2%
| Filename | Latest commit message | Latest commit date |
|---|---|---|
3fd1cc5279
docs/plan/ldls.md milestone L3b. ldls/ko.c, btf.c and stub.c were written
freestanding so they would build unchanged on both sides; cmd/ldlsd collects
that promise -- the same three files, linked against lib/ instead of a libc,
in an ordinary SchOS process.
# ldlsd /lib/modules/8139too.ko /lib/modules/btf
module 8139too license GPL wants 94 symbols
defused 6 %gs stack-guard reference(s)
calling init_module
1 _printk(...)
| 8139too: 8139too Fast Ethernet driver 0.9.28
2 __pci_register_driver(...)
btf 122279 types
layout pci_driver.probe +16 pci_dev 2680 bytes
driver "8139too" devices it claims: 10ec:8139 ... and 18 more
calling probe
1 alloc_etherdev_mqs(0x368, 0x1)
probe returned -12 after 1 stub call(s)
Byte for byte the host harness's behaviour, which is what the shared source
was for. Two earlier predictions came good with no work: a process's mmap area
starts at 0x40000000, inside the window R_X86_64_32S needs, and the kernel
never sets EFER.NXE so every mapping is executable. The second is a gap rather
than a feature and is now recorded as one -- LDLS is relying on the absence of
a protection an OS should have.
One thing did not just work. The first run faulted before probe's first call,
err 5 -- present, read, user -- at a kernel address, with the rip resolving to
mov %gs:0x0(%rip),%rax # rtl8139_init_one+0x26
Modules are built -mstack-protector-guard-reg=gs, so the canary comes through
the GS segment, and that is an ABI between the kernel and its own per-CPU area
which a host that is not that kernel cannot provide. ko_defuse_gs() rewrites
those references to xor %reg,%reg.
There are two forms and the second is easy to miss: the prologue loads the
guard with mov (8b) and the epilogue compares it with sub (2b) before a jne to
__stack_chk_fail. xor is right for both -- it zeroes the saved canary and sets
ZF, so the epilogue's branch falls through exactly as a passing check does. Six
sites in 8139too.
It checks every site before patching any and refuses the whole operation on
anything it does not recognise. That refusal is what found the sub form, by
declining to guess -- a loader that half-understands an instruction should not
be editing it.
make ldls-stage/ldls-unstage put a module and its kernel's BTF into the local
sysroot and take them out again. Not part of `all`, and .gitignore refuses
*.ko, so an image only carries somebody else's GPL code between two commands
you typed on purpose.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01VQ7Qx8E1q1M1bbCq8QLHS2
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| .claude/memory | ||
| boot | ||
| 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.