mkimage -p only places the FIRST payload. The rest are packed contiguously, and
U-Boot reads each by dividing its data-position by the 512-byte block size with a
truncating divide -- so a payload that is not block-aligned is read from the
wrong offset. Measured: without -B this script emitted the kernel at 0x9A94,
data-position % 512 = 148, which is exactly the failing shape.
That failure is on record. flare-edge 9387cff (2026-09-01) hit it on a boot_b
FIT: "unaligned sub-images fail the RESC loader's sha256 and the logo silently
falls back to 'No resource file'". It landed on -B 0x200, inferred from noticing
the proven image was "512-aligned" without checking for a larger factor.
The proven images are aligned to 0x800, not merely to 512. Measured on the pair
that boots this board today: boot.img fdt/kernel/resource at 0x800 / 0x12800 /
0x3A7800, recovery.img at 0x800 / 0x12800 / 0x3F8800 -- every one a multiple of
2048. So 0x800 satisfies everything 0x200 does, since every 0x800 multiple is a
0x200 multiple, and additionally reproduces the vendor layout exactly. The cost
is at most 2 KiB of padding. Where a remembered rule and a booting image
disagree, match the image.
The alignment is now also asserted at build time rather than trusted. It runs on
every build because the failure it catches is silent -- a wrong offset does not
fail the build, it fails on a panel, and only sometimes visibly.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01T2D2KtdgwbhbF6Mo64eUrn
Two gaps between "this SDK builds a kernel" and "this SDK can replace the
vendor SDK for the device".
BOOT IMAGE. build-kernel.sh emitted a zImage and a dtb and stopped, so
producing something the board's U-Boot would actually boot still meant going
through the vendor tree. mk-bootimg.sh packages the pair the way M2 bring-up
established (kernel/docs/m2-boot-on-c8a3.md): an EXTERNAL-DATA FIT
(mkimage -E -p 0x800), a mandatory `resource` multi sub-image carrying
rk-kernel.dtb plus any logos, and the sysmem sentinel load addresses. Each of
those was learned from a specific failure -- an embedded-data FIT is "No fit
blob", a missing resource image is "Failed to load DTB, ret=-19", real load
addresses collide -- so the script also ASSERTS the metadata stayed small,
because an embedded-data FIT looks perfectly fine until a panel will not come
back.
NETWORKING. Diffing this defconfig's expansion against the kernel actually
shipping on the panel found three whole subsystems missing, none of which fail
at build time and none of which are visible until the unit is in the field:
- WIREGUARD + NET_UDP_TUNNEL: flared's mesh to FLARE. Without it wg0 never
comes up.
- VLAN_8021Q: the MikroTik app configures tagged ports the panel terminates.
- NETFILTER and legacy iptables: every rule in S35iptables, and NAT for
router mode.
The netfilter half carried a trap worth naming. 6.18 split the legacy tables
out behind NETFILTER_XTABLES_LEGACY and IP_NF_IPTABLES_LEGACY, symbols that do
not exist in 5.10 -- so copying the vendor kernel's symbol list verbatim gives
a kernel where IP_NF_FILTER and IP_NF_NAT silently stay off and `iptables` has
no filter or nat table at all. Our userspace drives legacy iptables, not nft.
The result now shows ZERO regressions against the shipping 5.10 kernel across
mesh, gadget, firewall, VLAN, storage, net core, display/input, RGA/NPU,
wifi/BT and watchdog.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01T2D2KtdgwbhbF6Mo64eUrn
