1080 Snowboarding n64 decompilation

In progress 1080 Snowboarding decompilation, mostly driven by Claude. Uses https://github.com/djsaunde/decomp for n64 common tooling, Claude skills, etc.

Status

The build is ROM-exact (2026-06-10): make produces a tenshoe.z64 byte-identical to the original ROM (md5 fa27089c425dbab99f19245c5c997613), and make verify (part of the default target) hard-fails on any regression.

Twenty segments are being decompiled. USO overlays ship as a custom relocatable format (some Yay0-compressed); we match pre-relocation bytes by splatting at VRAM=0 with per-segment symbol prefixes (gl_func_, gui_func_, etc.).

Matched is the share of code bytes whose C body compiles to baserom byte-for-byte. Fuzzy is bytes-weighted partial credit: NM-wrapped C bodies that aren't byte-perfect contribute their per-instruction similarity (e.g., a 1 KB function at 80 % match adds ~800 bytes of fuzzy credit). Both metrics use a separate build/non_matching/ tree compiled with -DNON_MATCHING so partial decomp work shows up in the report.

Segment	Functions	Code matched	Matched	Fuzzy	Notes
kernel	136 / 201	21.8 KiB / 38.9 KiB	56.15 %	69.32 %	libultra + USO loader + audio (0x80000000)
bootup_uso	272 / 349	28.5 KiB / 81.6 KiB	34.99 %	83.75 %	Giles Goddard's libgdl engine
game_libs	1,322 / 1,904	144.6 KiB / 408.8 KiB	35.38 %	82.80 %	Support libraries (incl. statically-linked libultra)
gui_uso	16 / 39	1.7 KiB / 18.1 KiB	9.16 %	87.75 %	GUI/menu helpers
titproc_uso	41 / 46	5.9 KiB / 10.5 KiB	55.83 %	97.84 %	Title-screen process
arcproc_uso	45 / 59	5.2 KiB / 10.4 KiB	50.51 %	94.96 %	Arcade-mode process
h2hproc_uso	33 / 40	3.3 KiB / 6.8 KiB	49.02 %	96.67 %	Head-to-head process
eddproc_uso	15 / 15	1.1 KiB / 1.1 KiB	100.00 %	100.00 %	Edit-mode process
n64proc_uso	7 / 7	1.0 KiB / 1.0 KiB	100.00 %	100.00 %	N64-specific process
boarder1_uso	6 / 6	0.4 KiB / 0.4 KiB	100.00 %	100.00 %	Per-character snowboarder USO
boarder2_uso	6 / 6	0.4 KiB / 0.4 KiB	100.00 %	100.00 %	Per-character snowboarder USO
boarder3_uso	6 / 6	0.4 KiB / 0.4 KiB	100.00 %	100.00 %	Per-character snowboarder USO
boarder4_uso	6 / 6	0.4 KiB / 0.4 KiB	100.00 %	100.00 %	Per-character snowboarder USO
boarder5_uso	6 / 6	0.4 KiB / 0.4 KiB	100.00 %	100.00 %	Per-character snowboarder USO
mgrproc_uso	45 / 57	7.2 KiB / 13.0 KiB	55.09 %	96.67 %	Manager process (Yay0-decompressed)
game_uso	197 / 240	30.0 KiB / 70.8 KiB	42.40 %	90.29 %	Main game loop (Yay0-decompressed)
timproc_uso	266 / 315	32.0 KiB / 81.4 KiB	39.28 %	93.50 %	Timer process (Yay0; variants b1/b3/b5)
map4_data_uso_b2	3 / 3	0.2 KiB / 0.2 KiB	100.00 %	100.00 %	Map overlay code (remaining map assets are data)
Total	2,428 / 3,305	284.5 KiB / 744.5 KiB	38.22 %	85.04 %

Snapshot from report.json on 2026-09-12 (units grouped by source segment, including split files without category tags). Remaining Yay0-compressed USOs are splatted; code in map4_data_uso_b2 is tracked above, while pure data assets (audio banks, character meshes, textures) stay as bin segments.

Building

Requires: mips-linux-gnu binutils, Python 3, and IDO 7.1.

# 1. Place your 1080 Snowboarding (USA) ROM as baserom.z64
# 2. Extract IDO 7.1:
#    https://github.com/decompals/ido-static-recomp/releases/latest
#    Extract into tools/ido-static-recomp/build/7.1/out/
# 3. Extract asset bins from baserom via splat (one-time):
make setup
# 4. Build:
make

ROM-derived binary extracts (assets/*.bin) are not committed — they are regenerated from your local baserom by make setup.

The build uses IDO 7.1 with per-file optimization overrides: most libultra functions compile at -O1, game code at -O2.

Optional: Ghidra integration

A persistent Ghidra project at build/ghidra-project/tenshoe.gpr complements m2c for struct-recovery, xref discovery, and type-decorated decomp output. Setup (one-time, ~7 min):

# Tools (downloaded into ../tools/, gitignored):
#   - JDK 21 (Adoptium portable)
#   - Ghidra 12.x (NSA release)
#   - pyghidra-mcp (uv tool install pyghidra-mcp)
# See ~/.claude/projects/.../memory/feedback_pyghidra_mcp_setup_for_n64_decomp.md

bash scripts/setup-ghidra.sh           # build project + import 2,000+ symbols
bash scripts/ghidra-decompile-func.sh func_80008430   # one-shot decomp

Use Ghidra by trigger only (struct shape unknown, function family >3, stuck <50% fuzzy with structural unknowns) — m2c remains the default. See the /decompile skill for the trigger list.

References

• libreultra — libultra decomp reference; matching functions, structs, register keyword usage
• splat — ROM splitting tool
• asm-processor — Mixes C decompilation with INCLUDE_ASM stubs
• spimdisasm — MIPS disassembler (via splat)
• decomp.me / objdiff — Function-level matching, progress tracking, bytematch.dev integration

Game Structure

1080 Snowboarding uses a USO (Universal Shared Objects) overlay system loaded at runtime. The ROM has the kernel + two large always-resident USOs (bootup_uso, game_libs), then a bag of process-specific USOs (game_uso, gui_uso, *proc_uso, boarder*_uso, timproc_uso_b*) that are loaded/unloaded as gameplay state changes. Yay0-compressed USOs are decompressed at splat time.

• Kernel (39 KB, 213 functions, VRAM 0x80000000) — libultra, USO loader, audio
• bootup_uso (79 KB, 335 functions, VRAM 0) — libgdl game engine (C++, debug strings preserved)
• game_libs (411 KB, 1,483 functions, VRAM 0) — support libraries (stripped); biggest segment, the main grinding target
• game_uso (71 KB, 234 functions, VRAM 0) — main game loop (Yay0-decompressed)
• timproc_uso_b{1,3,5} (12+12+58 KB, 263 functions total) — timer-process variants (Yay0)
• Other process USOs (1–18 KB each) — gui_uso, titproc_uso, arcproc_uso, h2hproc_uso, eddproc_uso, n64proc_uso, mgrproc_uso, boarder{1..5}_uso, map4_data_uso_b2

All USOs splat at synthetic VRAM=0 to match unrelocated ROM bytes; distinct symbol prefixes (func_ vs gl_func_ vs gui_func_ vs game_uso_func_ vs <usoname>_func_) avoid linker collisions across USOs while letting each share its own internal label scope.