A user-space process can now touch real hardware directly, capability-gated by
the device tree — the microkernel driver model.
- src/kernel/devsvc.zig: flattens the discovered device tree into an
id-indexed snapshot + a claim table at boot (devsvc.init from main.zig).
- Syscalls 11-13: dev_enumerate (snapshot the table), dev_claim (take
exclusive ownership), mmio_map (map a claimed device's MMIO window into the
caller's AS and return the register base). The claim is the capability:
mmio_map refuses any device the caller doesn't own.
- paging.mapUserDeviceInto: maps device MMIO strong-uncacheable (PCD|PWT) and
marks each leaf with a device_grant PTE bit; freeSubtree skips pmm.free on
those leaves, so tearing down a driver never returns MMIO frames to the RAM
pool (the teardown hazard). MMIO grants live in a distinct arena, PML4[226]
(Task.dev_map_next), so device pages widen no kernel mapping.
- lib/dev.zig: user enumerate/claim/mmioMap wrappers; shared DeviceDesc/ResDesc
in danos (root.zig). sbin/hpetd.zig: finds the HPET, claims it, maps its
registers, enables the counter (an MMIO write) and reads it (0xF0) — proving
read+write passthrough to real hardware.
- Tests: `hpet` (driver reads the counter advancing from ring 3) and `iopass`
(device-granted frame survives address-space teardown). Suite 33/33.
irq_bind/irq_ack (IRQ-as-message) are stubbed (-1) pending; notifyFromIsr (M7)
is the hook they'll use.
The payoff milestone: files are served by a user-space process, reached over
IPC — the kernel never sees a path or an fd.
- lib/vfs_proto.zig: the VFS wire protocol (Op, Request/Reply fixed header +
inline payload, Stat), shared by client and server; one message <= MSG_MAX.
- lib/ipc.zig: replyWait() — the server-side dual-return stub (length in rax,
badge in rdx via a "+{rdx}" read-write operand), deferred from M7.
- sbin/vfs.zig: the real VFS server — an in-heap ramfs (open creates a node)
with an IPC_ReplyWait dispatch loop serving open/read/write/stat/close.
Registers its endpoint under the well-known vfs id at startup.
- lib/unistd.zig: POSIX-style client API in rt — a per-process fd table +
open/close/read/write/lseek/stat, each an IPC_Call to the VFS. The kernel
knows nothing of fds; the table lives here.
- lib/stdio.zig: C stdio over unistd — FILE + fopen/fclose/fread/fwrite/
fseek/ftell/rewind/feof/ferror/fputs/fputc/fgetc (unbuffered for now).
- sbin/vfstest.zig: a client that opens/writes/seeks/reads a file and only
heartbeats "vfstest: ok" if the round trip matched. Packed in the initrd.
- New `vfs` test drives it end to end. initrd test relaxed to generic
liveness. Suite 31/31.
Ship more than one user binary: the bootloader now ferries an initrd bundle
(the VFS server + future drivers) alongside sbin/init, and the kernel unpacks
and spawns each program.
- src/user/proto/initrd.zig: the container format (Header{magic,count} +
Entry{name[32],offset,len} + blobs) with a validating Reader, shared by the
kernel and the packer.
- tools/mkinitrd.py: host-side packer (Python — trivial format, and sidesteps
the reworked Zig 0.16 std fs/args API). build.zig runs it on the built user
binaries via addSystemCommand and installs initrd.img to zig-out/bin + the
ESP root.
- BootInfo gains initrd_base/initrd_len; efi.zig loadInit refactored into a
shared loadFile, and loadInitrd ferries \initrd.img into surviving
LoaderData like init.
- main.zig startInitrdBinaries(): parse the image, spawn every entry (kernel-
spawns-all for now; init takes over via sys_spawn later).
- sbin/vfs.zig: a heartbeat stub (the real VFS server is M9), packed into the
initrd to prove the pipeline.
- New `initrd` test: parse + spawn + confirm the vfs stub reaches ring 3 and
heartbeats. Harness ships initrd.img on the ESP. Suite 30/30.
Add lib/ — the shared user-space runtime every user binary links against
(init now, servers/drivers later): syscall wrappers, the heap, IPC stub,
and the process start shim.
- lib/heap.zig: the kernel first-fit free-list ported to user space, grown
via the mmap syscall instead of pmm+mapPage. Dual API over one global free
list: extern "C" malloc/free/calloc/realloc (C ABI for future C code) and a
std.mem.Allocator adapter (with in-place resize) for Zig std containers.
- lib/syscall.zig + sys.zig: raw syscall0..5 (arg3 in r10) and typed
yield/write/sleep/exit/mmap/munmap over danos.Syscall.
- lib/start.zig: naked _start -> rt_start -> root.main() (SysV realign via
call), panic -> exit(127).
- lib/user.ld: the user link script, moved from sbin/linker.ld (shared by all
user binaries).
- build.zig: register the `rt` module; add an addUserBinary() helper that is
the one recipe for every user binary (freestanding, .large, use_lld,
user.ld, image_base), replacing the bespoke init block.
- sbin/init.zig: migrated onto rt; drops its hand-rolled syscall2/shims. Now
proves the heap (alloc -> write from a heap pointer -> free) before the
heartbeat loop. Serial shows "init: heap ok". Suite 28/28.
Start the user-space driver track (VFS + IPC + heap). This lays the
process/syscall foundation the runtime heap will grow on.
- Rename usermode.zig -> process.zig; drop the retired hello/ping blob and
its `user` test (subsumed by the real /sbin/init exerciser). Keep the
isolation-proof pf blob and the user-pf test.
- Add danos.Syscall as the single source of truth for syscall numbers, shared
by the kernel dispatcher and (later) the user runtime lib. Dispatch on the
enum. New calls: 1=yield, 4=mmap, 5=munmap. Widen debug_write's bounds
check to the whole user low half so heap buffers are writable.
- mmap grants zeroed RW+NX pages from a per-process bump arena
(Task.heap_next, PML4[224] above image+stack); munmap frees the frames.
Add paging.translateIn / unmapInto (+ arch.translate / unmapUserPageInto)
as the primitives munmap and future cross-AS copies need.
- New `usermem` test: grant three pages into a fresh AS, translate them,
release via the munmap path, tear down, and assert no frames leak.
Suite 28/28 (user -> usermem).
init is now a real scheduled ring-3 process: it prints a heartbeat and
sleeps, forever. The kernel spawns it at boot via spawnProcess (its own
address space, preemption on) and the boot context drops to idle — the
system's steady state is "kernel idle, init alive in ring 3", beating
~1 Hz. Adds the sleep(ms) syscall. The init/process tests are reshaped
around the heartbeat (repeated syscalls, still-alive, two concurrent
processes on distinct address spaces). Pins init to LLD and folds the
.large code model's .ltext/.lrodata/.ldata into the linker script so its
code segment is R+X. Removes the now-dead borrowed-thread ELF loader
(runInitElf); spawnProcess is the one path. Docs updated. Suite 28/28.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Per-core MSR setup (EFER.SCE, STAR, LSTAR, SFMASK) enables syscall; the
GDT layout was already chosen so sysret lands on CS 0x23 / SS 0x1B. A new
syscall_entry stub swaps in the kernel GS, switches to the task's kernel
stack via the per-CPU block, builds a CpuState frame identical to the
interrupt path's, and reuses interruptDispatch (vector 128) — then
sysretq back. enter_user now also publishes kernel_rsp so the borrowed
path's syscalls land on a good stack. /sbin/init uses the `syscall`
instruction. int 0x80 stays for the test blobs. Suite 27/27.
(Noted in the stub: sysretq #GPs in ring 0 on a non-canonical return
RIP — a hardening item once untrusted user code exists.)
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Ring 3 works: user GDT descriptors (sysret-ready layout), TSS.rsp0,
U/S-bit user mappings (W^X preserved), an int 0x80 syscall gate with a
mutable trap frame, and a setjmp-style enter/exit path. /sbin/init is a
real freestanding Zig binary built from sbin/, shipped on the ESP,
loaded by the bootloader (BootInfo.init_base/len), validated and mapped
by an in-kernel user-ELF loader, and run at CPL 3 — syscalls: exit,
ping, write. Tests: user, user-pf (U/S isolation proof, error code
0x5), init. Suite 27/27.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Daniel Samson
