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M4 boot integration development record

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M4 boot integration development record

Development reference and historical context. For current operating instructions, use the user manual. Acceptance applies only to the source and artifacts identified in each record.

The user has authorized the remaining software through M12. This page records M4 development decisions. Software validation is complete; see M4 evidence. Physical Pi validation remains deferred.

The Pi kernel overlay starts from the exact source commit and archive checksum in Void's pinned rpi5-kernel recipe (6.12.87). It uses bcm2712_defconfig plus the small FDS delta, verifies Kconfig actually applied that delta, and exports the Pi 5 Image, DTBs, overlays, and modules without modifying upstream Void files. The upstream Pi 5 16 KiB page configuration is retained.

Critical storage, EROFS, keyboard, console and VC4 display support are built in. VC4 also requires the SND/SND_SOC core to be built in; optional sound devices can remain modules. CH341 SPI is disabled for the Dasung companion bridge. Generic ARM VM drivers are built into this same kernel so we can exercise software boot without claiming to emulate Pi firmware or RP1. Debug/BTF artifacts are omitted; module authentication is part of immutable image/release authentication rather than random build-generated module keys.

make kernel uses the existing Void build container and cross compiler. Its additional host dependencies are Perl and Python for kernel generation, bc for build-time arithmetic, Bison/Flex for Kconfig, kmod for module indexes, OpenSSL headers for kernel build utilities, and archive tools. OpenSSL is a host build dependency, not a new Rust runtime dependency. The source and checksum are recorded in packages/fds-kernel/template.

Image builders use a separate project-local prefix at .host/image-tools for signed Void x86_64 erofs-utils, dosfstools and mtools, plus their resolved libraries. They create filesystem images without privileged loop mounts and do not mutate the shared kernel build container. Versions and cached inputs are recorded under out/manifests/image-tool-*; full input locking is M12 work.

Stage0 now has a Rust PID-1 implementation: direct filesystem syscalls, authenticated kernel uevents, explicit normal/recovery partition selection, early Dasung supervision, EROFS validation, mount transfer, and exec of native s6. Its normal path refuses to run outside root PID 1 on ramfs/tmpfs. The implementation reuses the locked libc crate for these Linux syscalls. The full initramfs matrix passed all four formats, missing-media USB insertion, ambiguous SYSTEM recovery, explicit recovery, invalid filesystems and foreign root rejection. A refreshed base package/rootfs build is being completed. QEMU uses its max CPU because the retained 16 KiB Pi kernel cannot execute on the old Cortex-A72 VM model.

The FAT32 boot builder verifies every file after reading it back with mtools. Directory timestamps are normalized as well as file timestamps; two consecutive builds from the same inputs produced the same complete image SHA-256. This narrow result is not a claim of complete offline or release reproducibility. Two complete kernel builds also produced identical kernel Image, Pi 5 DTB and XBPS package digests. The helper now reuses a build after checking recorded source inputs, its package and all exported files. --rebuild bypasses reuse.

The boot guide documents usable build commands, image boundaries, waiting-console commands, display policy, and remaining physical checks.

References: Raspberry Pi cross-compilation, Linux initramfs, and root handoff semantics.

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Maintained directly in the fds-os.wiki repository. Historical acceptance applies only to the source and artifacts identified in each record.