QuantumOS on Firecracker

QuantumOS boots as a Firecracker microVM through the PVH boot protocol (x86_64; verified with Firecracker v1.16.1 on a KVM host, 2026-09-06).

Firecracker cannot load Multiboot images. kernel/src/boot.S therefore carries a .note.Xen ELF note (XEN_ELFNOTE_PHYS32_ENTRY) pointing at _pvh_start, a 32-bit stub that reads hvm_start_info and synthesizes the Multiboot1 info block the kernel already understands (memory map, command line, mem_lower/mem_upper), then joins the normal _start path. The kernel stays Multiboot1-only (ADR-0021); nothing above the boot stub changes. kernel/link.ld keeps the note in its own PT_NOTE segment.

Run

Use the ELF64 image (build/x86_64/kernel.elf); the .elf32 copy is for GRUB and qemu -kernel, which cannot take this path (QEMU's loader finds the Multiboot header first and refuses 64-bit images).

{
  "boot-source": { "kernel_image_path": "/path/to/build/x86_64/kernel.elf", "boot_args": "quiet" },
  "drives": [],
  "machine-config": { "vcpu_count": 1, "mem_size_mib": 128 },
  "logger": { "level": "Error", "log_path": "/tmp/qos-fc.log" }
}

firecracker --no-api --config-file qos.json     # serial console (COM1) on stdio

Boot reaches qsh in about a minute on a CPU-only host; the holographic field works inside the microVM:

qsh> imprint a cat sat on the mat
FIELD: imprinted slot 0
qsh> recall a cxt sxt on thx mat
FIELD: winner="a cat sat on the mat" slot=0 score=15975 n=1

What the microVM does not have

Firecracker exposes no VGA, no PCI and no ATA, and only virtio-mmio devices. So: the text-mode console writes to 0xB8000 land in plain RAM (harmless); the rtl8139 NIC and ATA disk are absent (httpd: no network -- idle); COM2 is unbacked (the swarm bridge stays idle). Firecracker's logger reports the VGA CRTC and COM2 port writes as MissingAddressRange at Warning level, which is why the config above sets Error. Networking and storage inside Firecracker need virtio-mmio drivers, which QuantumOS does not have yet.