Replace the state-relabel-only round-robin with the SUB-OS "Weave"
scheduler backed by a genuine callee-saved context switch. Threads now
actually run on their own kernel stacks instead of merely having their
state field rewritten.
What was implemented:
- sub_ctx_switch(): per-arch assembly (arch/x86_64/cpu/switch.asm,
arch/aarch64/cpu/switch.S, arch/armv8i/cpu/switch.S) that saves/restores
the callee-saved register set (+ flags on x86_64) on each thread's own
stack, plus a first-run trampoline (sub_thread_trampoline) that launches
a freshly forged thread frame with entry/arg in callee-saved registers.
- task_forge_frame(): builds the initial saved-context frame per arch so
the very first switch into a new thread lands on the trampoline; task_t
gains a pointer-sized ctx_sp so the same struct works on 64- and 32-bit.
- Weave policy (kernel/sched.c): WEAVE_NLANES priority lanes, always
dispatch the lowest non-empty lane round-robin; a task that yields
voluntarily is woven UP a lane (interactive), one preempted after
burning its quantum is woven DOWN (CPU-bound). Cooperative switching
(sched_yield / task_exit) is always live; timer-driven preemption is
gated behind sched_set_preempt() and left disarmed for now.
- task_exit() now switches to the next runnable thread via
sched_exit_current() instead of spinning/halting.
- Boot-time weave_selftest() (x86_64) and sched_dump() diagnostics.
How it was verified:
- Builds clean for all three targets: x86_64 (CROSS_COMPILE=x86_64-linux-gnu-,
RUSTC="rustc --target x86_64-unknown-none"), aarch64, armv8i. No new
warnings; the new x86_64 asm carries a .note.GNU-stack section.
- Booted x86_64 under QEMU (TCG): the self-test runs three cooperative
kernel threads to completion on separate stacks with the expected
1->2->3 round-robin interleave, reports "20 real context switches,
3/3 workers exited", returns cleanly to the boot thread, and boot
proceeds normally to ring-3 init and the shell. No fault/panic.
Left unverified:
- The aarch64/armv8i sub_ctx_switch frames build and link but are not yet
boot-tested on their QEMU targets (tracked in docs/AUTODEV_ROADMAP.md).
- Timer preemption path is implemented but disarmed; exited kernel threads
currently leak their stack (reaper is next in the backlog).
Co-Authored-By: Claude Opus 4.8 <[email protected]>
Claude-Session: https://claude.ai/code/session_01Jk6K69yGS7zYgvoWd6nJxQ
SUB-OS had a syscall table and user GDT descriptors but nothing that could
actually leave ring 0: lazybox and the shell run as kernel code, and
syscall_handler() was never reachable from a user program. This adds the
missing path end to end on x86_64.
Address spaces (arch/x86_64/mm/vmspace.c)
- The boot page tables identity-map the low 4 GB off PML4[0] and leave the
rest empty, so userland is given its own PML4 slot (512 GiB) rather than
holes punched in the kernel's 2 MB huge-page map. A process PML4 shares
entry 0 with the kernel and privately owns entry 1.
- Frames outside the identity map are refused rather than written through an
unmapped pointer; lifting that needs a recursive map or a higher-half
direct map, which is noted in the file.
ELF loader (kernel/elf.c)
- Validates ELF64/little-endian/ET_EXEC/machine, bounds-checks every program
header against both the image and the user address range, and lays PT_LOAD
segments into an address space. Frames arrive zeroed, so .bss is covered.
Ring transition (arch/x86_64/cpu/usermode.asm)
- user_enter() drops to ring 3 via iretq after scrubbing every GPR, and
user_return() unwinds back to it when the process exits, so exec looks like
a call that blocks until the program finishes.
Syscalls
- INT 0x80 installed at DPL 3 with the Linux x86_64 register convention.
The process gets its own kernel stack for the trap, because TSS.rsp0 must
not point at the stack user_enter() is standing on.
- Every user pointer is range-checked before use. The process page tables are
still live during a syscall, so without that check a program could pass a
kernel address and have write(2) dump kernel text to the console. The new
/sbin/init asserts both a wild pointer and a kernel pointer are rejected.
- write(2) to stdout/stderr routes through the new console_write(), which
reuses printk's routing so output reaches serial and the framebuffer
console rather than only the VGA text buffer.
Faults
- A ring 3 exception now kills that process and reports CR2 instead of
panicking the machine.
Userland (userland/init/)
- /sbin/init is a real freestanding static executable, linked at the user
base and embedded in the kernel image by scripts/mkblob.py. It reports its
pid, verifies .bss was zeroed and .data is writable, checks the two pointer
rejections, and exits.
aarch64 and armv8i keep building: the loader and exec path are portable, and
those ports get honest vmspace stubs that fail cleanly rather than pretending
to run a program with kernel privileges.
Verified under QEMU: init loads at 0x80004000a0, reports pid 1, .bss zeroed,
.data writable, both bad pointers rejected, and exits 0 back into the shell.
Co-Authored-By: Claude Opus 5 <[email protected]>
Claude-Session: https://claude.ai/code/session_0161Jh7uCEMLYEMNPsjC1LKf
bochs_vbe_init switches the adapter into graphics mode at boot step [5/14], and
from that point the VGA text buffer is no longer scanned out. This kernel boots
to a TTY, so every message after that -- and the whole shell session -- was
invisible in the emulator window and reached only the serial line.
The console now moves to the framebuffer at that transition, which also makes
the nano editor render correctly: it positions with tty_set_cursor() rather than
escape sequences, and the TTY driver dispatches that to fbcon.
Co-Authored-By: Claude Opus 5 <[email protected]>
Claude-Session: https://claude.ai/code/session_01L5yKJT4Wo2cV3rfPrwY5MP
Pressing Esc left the desktop and started the shell, but nothing appeared in the
emulator window -- the session was only visible on the host terminal. Once the
VBE adapter is switched into graphics mode the VGA text buffer at 0xB8000 stops
being scanned out, so every printk after that point reached serial and the
dmesg ring but never the display.
Disabling the DISPI interface does not bring the text console back; QEMU keeps
presenting the last framebuffer surface. So rather than clawing the adapter back
to text mode, the console is now rendered into the framebuffer:
drivers/video/fbcon.c draws the console with the shared 8x8 font and carries a
VT100 subset -- SGR colours, cursor addressing, relative moves, erase-display,
erase-line and save/restore. It presents a fixed 80x25 grid, because that is
the geometry the userland assumes (nano pads its bars with %-80s, the shell
wraps at TTY_WIDTH), with the glyph cell scaled to fill the active resolution.
The TTY driver became the console dispatcher: tty_write, tty_clear and
tty_set_cursor route to fbcon while it owns the display. That last one is what
makes nano work -- it positions with tty_set_cursor() rather than escapes, so
its full-screen repaint was landing as an append-only stream.
Also in this change:
- `video=WIDTHxHEIGHT` on the kernel command line selects the display mode,
defaulting to 1280x720 so a 16:9 host panel is filled rather than pillarboxed
when QEMU goes fullscreen. Rejects modes the heap cannot back.
- `make run-fullscreen`, plus zoom-to-fit on the windowed target, so scaling
preserves the guest aspect ratio instead of stretching it.
- QEMU targets raise vgamem_mb, since a 1280x720 32-bit surface exceeds the
default VGA memory.
- bochs_vbe_disable()/fb_set_active() let the framebuffer be marked dormant so
drawing routines no-op after a mode teardown.
Co-Authored-By: Claude Opus 5 <[email protected]>
Claude-Session: https://claude.ai/code/session_01L5yKJT4Wo2cV3rfPrwY5MP
Boot logo (init/bootlogo.c, init/logo_data.c, scripts/mklogo.py):
The logo appears in two forms because the framebuffer does not exist for the
first third of boot. An ASCII rendition goes to the text console and serial
line from the first moments; once the video driver is up at step [5/14] the
real bitmap takes over as a graphical splash with a progress bar tied to the
actual boot stages.
The asset is 4-bit palette indexed, so 160x160 pixels cost 12.5 KB instead of
100 KB, and carries a transparency mask so the mark composites onto the
gradient rather than stamping a flat rectangle over it. scripts/mklogo.py
regenerates init/logo_data.c from the source PNG.
Boot reaches the desktop in well under a second, so the splash is held for a
minimum duration and the bar sweeps to 100% during the hold; without that the
logo would flash past unseen. `splashtime=<ms>` tunes it and `nosplash`,
`nogui` or `text` skip it.
Bootloader (boot/stage2.asm):
stage2 staged the whole kernel in conventional RAM before copying it to 1 MB,
which capped the kernel at roughly 576 KB before the load ran into video
memory at 0xA0000. The logo pushed it over that line and the kernel stopped
booting. Each 32 KB chunk now goes into one fixed low buffer and is copied
straight to its final address, using unreal mode for the 32-bit reach. The
ceiling is now the image itself, 1.375 MB.
Console font (lib/font8x8.c):
fb_draw_char was a stub that ignored its character argument and drew a filled
rectangle, which is why the splash rendered its text as solid blocks. It now
renders real glyphs, and the table it uses is shared: the framebuffer console,
the canvas rasterizer and the desktop compositor had three divergent private
copies, two of which still carried the `// \` line-continuation defect.
printk console sink (kernel/printk.c):
printk output can be redirected to a callback, so a caller can run a subsystem
that reports via printk and capture what it printed. Serial and the dmesg ring
still see everything, which keeps a captured run debuggable.
Shell builtins (userland/lazybox/shell.c):
The builtin chain is extracted into shell_execute_builtin(), so the kernel TTY
and the desktop terminal accept the same vocabulary instead of the GUI seeing
only the applet table. Callers that cannot be suspended pass allow_blocking =
false to refuse the animating ones.
Co-Authored-By: Claude Opus 5 <[email protected]>
Claude-Session: https://claude.ai/code/session_01L5yKJT4Wo2cV3rfPrwY5MP
Expands the kernel-and-TTY core with the primitives the higher layers have
been missing, plus an in-kernel harness that proves they work.
Data structures (lib/):
- rbtree.c: Linux-compatible red-black tree with parent pointers, full
insert/erase rebalancing, in-order iteration and an invariant validator.
- kfifo.c: power-of-two byte ring with free-running indices, so the wrap
path costs one mask instead of a branch per byte.
- hashtable.c: separately-chained table with FNV-1a hashing, string or
u64 keys, and rehash-on-growth at a 3/4 load factor.
Kernel subsystems:
- kernel/wait.c: wait queues and one-shot completion barriers, backed by a
static sleeper pool so a blocking path never re-enters the allocator.
- kernel/futex.c: 32-bucket futex hash with value re-check, requeue, and an
fmutex_t sleeping mutex built on the uncontended-fastpath protocol.
- kernel/rcu.c: tiny RCU with reader nesting, deferred callbacks, kfree_rcu
and rcu_assign_pointer/rcu_dereference publish barriers.
- mm/page_cache.c: write-back block page cache, 4 KB pages indexed by
(device, page), CLOCK second-chance eviction and dirty write-back.
- kernel/ktest.c: KUnit-style harness with 6 built-in suites, 21 cases and
735 assertions covering every subsystem above (all passing under QEMU).
LazyBox userland:
- coreutils.c: sort, uniq, cut, tr, rev, tac, nl, seq, diff, xxd, du,
factor, sum and truncate, reading through the VFS and handling the
zero-length synthetic nodes that procfs and sysfs expose.
- ktest, rcuinfo, futexinfo, waitinfo and pagecache diagnostics applets.
Co-Authored-By: Claude Opus 5 <[email protected]>
Claude-Session: https://claude.ai/code/session_01L5yKJT4Wo2cV3rfPrwY5MP
- Implement Intel 82574L / 82567LM / I217 / I219 PCIe Gigabit NIC driver with DMA ring buffers and auto-negotiation in drivers/net/e1000e.c and include/drivers/e1000e.h
- Implement VirtIO-GPU 2D hardware graphics display adapter driver with dirty rect flushing in drivers/virtio/virtio_gpu.c and include/drivers/virtio_gpu.h
- Implement Dynamic CPU Frequency Scaling and ACPI CPPC Power Governor with performance, powersave, ondemand, conservative, and schedutil policies in drivers/power/cpufreq.c and include/drivers/cpufreq.h
- Implement VirtIO-Input para-virtualized tablet/mouse event driver in drivers/virtio/virtio_input.c and include/drivers/virtio_input.h
- Expand stage2 kernel bootloader loading boundary to 768 KB (1536 sectors)
- Add LazyBox applets: 'cpufreq', 'gpuinfo', 'e1000e'
- Verified across x86_64, AArch64, and ARMv8i targets
- Add dedicated Linux-compatible Tree visualizer with UTF-8/ASCII branch tracking, -L depth filtering, human sizes, and permissions in userland/lazybox/tree.c
- Implement Hardware Invariant Timestamp Counter (TSC) calibration and microsecond delay timer in kernel/tsc.c and include/kernel/tsc.h
- Add Virtual Terminal color palette, live resource utilization bars, and logo banner in kernel/vt_art.c and include/kernel/vt_art.h
- Add LazyBox applets: 'tree', 'tscinfo', and 'vtart'
- Update README.md documentation and command matrix
- Implement modern freestanding C++17 containers (Vector<T>, UniquePtr<T>, String) in kernel/cpp/cpp_containers.hpp
- Implement object-oriented Device driver model (Device, BlockDevice, CharDevice, VirtualRamDiskDevice, VirtualNullDevice, VirtualZeroDevice, DeviceManager) in kernel/cpp/cpp_device.hpp and kernel/cpp/cpp_device.cpp
- Add C++ kernel performance microbenchmark suite in kernel/cpp/cpp_bench.cpp
- Export C-FFI bridges and add cross-architecture fallbacks in kernel/cpp/cpp_fallback.c and include/kernel/cpp_kernel.h
- Add LazyBox applets: 'cppdevs' and 'cppbench'
- Update README.md documentation and command matrix
- Implement flicker-free atomic double-buffered frame rendering and sub-tick input polling in userland/lazybox/snake.c
- Add multi-input support (PS/2 keyboard scancodes and serial ANSI arrow escape sequences)
- Add sound effects (food beep, game over chime) and live speed scaling (+/- keys, P to pause)
- Add POSIX /dev/shm shared memory subsystem in ipc/shm_posix.c and include/ipc/shm_posix.h
- Add DNS resolver cache with TTL tracking in net/ipv4/dns_cache.c and include/net/dns_cache.h
- Add audio tone and jingle synthesizer in sound/beep.c and include/sound/beep.h
- Add %o octal formatting support in lib/vsprintf.c
- Add LazyBox applets: 'shm', 'dnscache', and 'beep'
- Add freestanding C++17 runtime with operator new/delete, pure virtual handlers, and global constructor execution in kernel/cpp/cxx_runtime.cpp
- Implement C++ Object-Oriented telemetry and hardware services with polymorphism in kernel/cpp/cpp_module.cpp and include/kernel/cpp_kernel.h
- Add interactive ANSI Snake Game in userland/lazybox/snake.c with real-time keyboard control and automated simulation mode
- Initialize C++ subsystem during kernel boot step [8/14] in kernel/main.c
- Add LazyBox applets: 'snake', 'cppinfo', and 'cpptest'
- Add native .sb kernel modules in sub/ (signature.sb, power_governor.sb, benchmark.sb, easter_egg.sb)
- Implement in-kernel SUB Language VM and AST interpreter in kernel/sub/sub_vm.c
- Implement C-interop runtime in kernel/sub/sub_runtime.c and include/kernel/sub_lang.h
- Initialize SUB Language Engine in boot sequence step [8/14] in kernel/main.c
- Implement strtol in lib/string.c
- Add LazyBox applets: 'subinfo', 'subi', 'subpower', 'subbench', and 'subquote'
- Add 'clear' and 'cls' builtin handlers in LazyBox shell
- Output ANSI \033[2J\033[H sequence on tty_clear() to clear serial/UART terminals
- Support both ASCII 0x7F (DEL) and 0x08 (BS) for Backspace in shell and nano editor
- Connect 16550 serial input to keyboard_get_key() on x86_64 for headless terminals
- Add ANSI escape sequence decoding for arrow keys (Up/Down/Left/Right/Home/End/Del)
- Update Makefile 'make run' and 'make qemu' with -display none for smooth terminal execution
- Add 'make run-gui' target for optional graphical SDL/GTK window
Claude