92 lines
4.2 KiB
Markdown
92 lines
4.2 KiB
Markdown
# Findings log
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One entry per claim. Every claim carries evidence (kernel source reference or
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blob offset + observed bytes). Claims that cannot be evidenced are registered
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in the Unknowns section instead. Blobs referenced by filename are the
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linux-firmware copies listed in `manifest.json` (SHA-256 TBD in fixtures).
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Blobs observed: mt7981/mt7915/mt7916/mt7986 × {wm, wa, rom_patch}
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(linux-firmware snapshot 2026-04-20, Debian).
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## F1 — Connac2 RAM container layout
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`[region data, packed from offset 0 in table order][optional hidden trailer
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(see F2)][n_region × 40-byte region table][36-byte trailer at EOF]`
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Evidence: `mt76_connac_mcu.c` `mt76_connac2_load_ram()` +
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`mt76_connac2_send_ram()` (region data streamed sequentially from offset 0;
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table and trailer located from EOF); `mt76_connac_mcu.h`
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`struct mt76_connac2_fw_region` / `_fw_trailer`. Confirmed by exact layout
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match on 8 RAM blobs (sum(region.len) + table + trailer (+ hidden trailer) ==
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file size).
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Region fields: `decomp_crc/decomp_len/decomp_blk_sz` (MCU-side decompression,
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unused when decomp_len==0 — all observed blobs), `addr`, `len`,
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`feature_set`, `type`.
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## F2 — Hidden second trailer carries the full build string
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Between region data and the kernel-parsed table sits a trailer the upstream
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loader never reads. WM blobs: 100 bytes; WA blobs: 36 bytes (no string).
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Observed family-wide (all 4 chips).
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WM hidden trailer = 16×'#' + `40 00 00 00` + 1-byte string length + flags +
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full build string + '#'-padding. Recovered strings:
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- mt7981_wm: `t-neptune-main-mt7915-1953-MT7981_MP2111_IMP-20240823161204`
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- mt7916_wm: `t-neptune-main-mt7915-1953-MT7916_MP2111_IMP-20240823170147`
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- mt7986_wm: `t-neptune-main-mt7915-1953-MT7986_MP2111_IMP-20240823160608`
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- mt7915_wm: `t-neptune-mp-mt7915-2045-MT7915_MP_7_4_2045-20220929103802`
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Significance: the kernel-visible trailer's `fw_ver[10]` is stripped
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(`____000000` WM / `DEV_000000` WA); the hidden trailer restores branch
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("main"/"mp"), internal build number (1953/2045), MP tag, and build
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timestamp. This is the version metadata the changelog tooling keys on.
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Evidence: bytes at offset `sum(region.len)` in each blob (see
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`manifest.json` → `hidden_trailer.raw_head`).
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## F3 — region `type` is a content tag used by some loaders
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All parsed mt79-family blobs: `type == 0` (`FW_TYPE_DEFAULT`). It is not
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ignored upstream: mt7921's loader selects
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`feature_set & FW_FEATURE_NON_DL && type == FW_TYPE_CLC` regions as
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country/location-calibration data instead of downloading them to the MCU.
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Evidence: `mt7921/mcu.c` CLC handling; `FW_TYPE_CLC` definition in
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`mt76_connac_mcu.h`.
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## F4 — Patch container format
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92-byte big-endian header (16-byte build date, 4-byte platform tag —
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"ALPS" on all four — hw_sw_ver, patch_ver, checksum, descriptor), 64-byte BE
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section table, plaintext section data at explicit offsets. All observed
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patch sections: `enc_type == 0` (plaintext).
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Evidence: `mt76_connac2_load_patch()` + `struct mt76_connac2_patch_hdr/_sec`
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in `mt76_connac_mcu.h`; exact parse of 4 patch blobs.
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Section counts: mt7915 patch = 2 sections, all others = 1; section `type`
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constant `0x30002` on every observed section (loader downloads all sections
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regardless; field semantics otherwise unobserved).
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## Unknowns registry
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- **U1 — `feature_set` bit 7 (0x80):** observed only on WM regions at
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`0xf0xxxxxx` addresses (mt7981 r7–r10, mt7986 equivalents). Upstream
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defines bits 0–6 only; vendor-SDK search found no definition (2026-08-20).
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Correlation with address family noted; semantics undetermined. May relate
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to a second download destination or content class.
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- **U2 — hidden-trailer non-string fields:** the `40 00 00 00` and flag
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bytes before/around the string (F2) are uninterpreted.
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- **U3 — WO container:** `mt7981_wo.bin` uses the mtk_wed loader
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(`mtk_wed_mcu.c`), a different format; not yet parsed.
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## Related verified facts
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- NDS32LE target: `GCC: (2018-10-23_nds32le-elf-mculib-v3) 4.9.4` string in
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mt7981_wa region data; FreeRTOS v10.0.0 + `portable/GCC/NDS32/port.c`
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strings in mt7981_wo.
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- No per-region encryption in any observed blob (`FW_FEATURE_SET_ENCRYPT`
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clear; patch `enc_type == 0`). Optional protocol support exists in the
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loader (key from EFUSE path) but is not exercised by shipped images.
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