Kernel

Freestanding AArch64 kernel written in Zig. No libc, no POSIX, and no existing guest OS in the boot path.

Boot

The AArch64 UEFI application loads KERNEL.BIN, passes the captured EFI memory map and handoff data, and transfers control to the kernel. The kernel exits UEFI Boot Services, installs its exception vectors and identity-mapped page tables, then initializes the devices it uses directly. The boot volume contains EFI/BOOT/BOOTAA64.EFI and KERNEL.BIN; applications and writable files are supplied through the host share.

The core

• Address translation: the kernel and its EL1-only identity map stay reachable under task roots; each process receives its own EL0 mappings.
• Exceptions: VBAR_EL1 points to the AArch64 vector table. Entry saves the general-purpose and FP/SIMD register state before dispatch, then restores the selected task's frame.
• Scheduling: a fixed pool of 16 task slots, with per-core ready rings; allocation is bounded and does not grow the pool dynamically.

Syscall seam

The syscall ABI is an append-only 128-slot table with 88 registered entries, slots 0–87. It covers process control and IPC, windows and events, files and networking, time, threads, anonymous mappings, filesystem metadata, native sockets, and the observability/pid surface. Reserved table entries return ENOSYS.

See Userspace & syscalls for the current numbered interface and kernel/src/syscall.zig for the implementation.

Identity & drivers

• virtio-gpu (virtio_gpu.zig): spec 2D path — GET_DISPLAY_INFO → CREATE_2D → ATTACH_BACKING → SET_SCANOUT → TRANSFER → FLUSH (4 KiB-aligned BSS framebuffer).
• virtio-net (virtio_net.zig): RX → ARP/ICMP/UDP/TCP (SYN..FIN, sliding window), TCP feature path on --net-tcp; UDP/TCP direct path.
• Host files: the same /host file API uses either the custom-virtio queue-5 channel (--cvc-file) or explicitly selected standard VirtioFS/FUSE (--virtio-fs). VirtioFS is opt-in; it does not change the boot default.
• virtio-input (virtio_input.zig): IRQ + snapshot ring → fixed-point pointer motion (the CG class gates).
• virtio-rng (virtio_rng.zig): the stack's only entropy source.
• Virtio-console (virtio_console.zig): --console-tcp <port> serves a real TCP listener at EL0; live-devcons boots 2 VMs and connects both directions.
• USB xHCI (xhci.zig): a bounded xHCI driver with a slot/context array, 32 doorbells, scratchpad allocator, transfer ring, and the LLGT low-level common-setup entry point (L4), with a class/subclass/protocol match table. Two class paths are live: HID boot protocol (input.zig — the keyboard/pointer behind --input; two known devices, no hubs, no full report-descriptor parser; gates live-usb, live-input) and mass storage (usb_msc.zig — Bulk-Only Transport + minimal SCSI over --usb-msd, raw sector write/read-back; gate live-usb-msc), with fat32_ro.zig providing the read-only FAT view.
• Storage today is the host share through the /host API — see storage for both transports and their limits.