# qemu/ — the WardenOS device simulator

A QEMU virtual machine that boots the real forward-ported kernel (`build/` +
`patches/`) and real userspace, so the *device* — init, daemons, networking,
OTA, watchdog, display — can be tested off-hardware. The third simulator in
the stack, deliberately not named "sim":

- `lvglsim` (flare-edge) — SDL desktop build of the UI. Rendering only.
- `sim/` (this repo) — register-level Rust models of RV1106 blocks behind
  driver seams.
- `qemu/` (this) — the whole machine above the kernel entry point, running
  the real binaries.

Decision record: `docs/decisions/0006-qemu-device-sim.md`.

## The boundary (read this before trusting a green run)

There is no RV1106 machine model in QEMU and everything below the kernel is
closed rkbin blobs plus mask ROM, so the VM **enters at `-kernel zImage`** on
`-M virt,highmem=off` (single Cortex-A7, 256M — the RV1106G3's shape).

| Emulated / substituted | Not emulated (stays bench / `sim/` territory) |
|---|---|
| Kernel boot, init ordering, switch_root | BootROM, idblock/DDR-init, SPL, U-Boot |
| A/B *outcome* (`warden.slot=` cmdline) | Real BCB A/B selection, bootcount auto-revert |
| Storage: virtio-blk with the device's exact `blkdevparts=` layout + `/dev/block/by-name/` contract | eMMC controller itself |
| Network: virtio-net (slirp, hostfwd 22/80/28443) | GMAC, AIC8800 wifi, usb0 gadget |
| Display: virtio-gpu 720x720 via fbdev emulation | VOP/RGB666 pipeline, CH32V003 panel init, RGA blits |
| Touch: virtio-tablet (QMP `input-send-event`) | GT911 on I2C3 |
| Watchdog: i6300esb (PCI), `-action watchdog=reset` | DW watchdog @0xff5a0000, HPMCU supervisor |
| RS485: pci-serial chardev bridged to `sim/`'s `ModbusSlave` | Real UART4 timing/electrical behavior |
| RTC: PL031 (`--rtc` reproduces the no-RTC 2021-clock incident class) | The unpopulated backup-cell reality |

**"Boots/works under emulation" is never evidence of "works on silicon."**
The VM narrows which claims need a panel; on-device claims still need
on-device evidence. Conversely, the VM is the first environment that runs
production binaries on a non-RV1106 memory map — it found flare-edge #106
(fatal SIGBUS in flared's HPMCU probe) and #107 (Y2038 time_t truncation)
on its first two boots of real userspace.

Documented guest deviations from production, set by stage-2 init:
`WARDEN_FLARE_INSECURE=1` (the desk mock portal is plain HTTP) and
`WARDEN_HPMCU=0` (no mailbox SRAM on virt; flared >= flare-edge#106 fix
required, or the daemon dies of SIGBUS).

## Quick start

```sh
# 1. kernel: canonical build boots the VM as-is; the fragment variant adds
#    the scenario devices (PCI serial, watchdog, WireGuard, virtio-gpu/input)
WORK=$HOME/kbuild-out CROSS_COMPILE=arm-linux-gnueabihf- \
  WARDEN_KCONFIG_FRAGMENT=qemu/configs/virt.fragment bash build/build-kernel.sh

# 2. initramfs (sha256-pinned static busybox + qemu/rootfs/) and A/B disk
bash qemu/mkinitramfs.sh
bash qemu/mkimage.sh                  # options: --portal-url --state K=V --fw-version

# 3. run (see run.sh header for all flags)
bash qemu/run.sh --kernel $HOME/kbuild-out/linux-6.18.46/arch/arm/boot/zImage --shell
```

Payload: drop static musl armv7 binaries into `qemu/payload/` (see its
README) — `warden-flared`, `warden-modbus`, and `warden-ui` (the LVGL
fbdev+evdev build from flare-edge `tools/build-ui-vm.sh`) are started by
stage-2 init when present.

## Scenario tests (`qemu/tests/`)

- `boot-smoke.sh <zImage>` — sentinel-asserting boot; runs in CI inside the
  kernel-build job.
- `portal-scenario.sh <zImage>` (needs `FLARE_EDGE=<checkout>`) — the real
  flared in the VM against the desk mock portal: authenticated check-in,
  firmware desired-state pull, and download of a real signed tier-1 `.wfw`
  offer. Verify/stage/APPLYING run as a dry run (no `WARDEN_FW_ALLOW_APPLY`);
  flipping it on inside the VM is the documented stretch — apply writes
  `/dev/block/by-name/rootfs_b` inside disk.img, then `--slot _b` boots it.
- `ui-shot.sh <zImage>` — display+touch: boots headless with virtio-gpu,
  QMP-screendumps the 720x720 UI, taps the Metrics tab via `input-send-event`
  (a 200 ms hold — an instantaneous press+release lands inside one LVGL poll
  and never clicks), and asserts the frame changed. `qmp.py` is the tiny QMP
  client.
- Watchdog: `run.sh --watchdog`, arm `/dev/watchdog` in the guest, don't pet —
  the VM resets ~30 s later (verified). Do NOT combine with a flared payload
  expecting survival: flared pets only while the UI heartbeat is fresh.

## Gotchas that cost time (so they cost it once)

- AF_UNIX socket paths cap at ~108 chars — keep `--rs485`/`--qmp` paths short.
- A serial port that is closed discards incoming bytes: hold ONE fd open
  across write and read when scripting the guest side of the RS485 bridge.
- `highmem=off` and `-global virtio-mmio.force-legacy=false` are load-bearing
  (32-bit ECAM reach; virtio-1-only gpu/input) — both live ONLY in run.sh,
  which every script (boot smoke included) delegates to.
- Never pass `earlyprintk`: DEBUG_UART_PHYS is the RV1106's 0xff4c0000.

## Host requirements

`qemu-system-arm` (Debian 13 ships QEMU 10), `curl`, `cpio`, `mkfs.ext4`,
`gcc-arm-linux-gnueabihf` (kernel build), `python3` (+`cryptography` for the
portal scenario's `.wfw` signing). CI: the hosted `qemu-tools` job builds the
tooling; the boot smoke runs inside the (also hosted, dispatch-only)
`kernel-build` job, which apt-installs its own toolchain and qemu (ADR-0007).