N64 Decomp Workbench

Find the cause of late-stage MIPS decompilation mismatches.

Real output — decomp-workbench diagnose-dumps on the phase-shift fixture in this repository. From verdict to edit walks this exact screen from top to bottom.

You have an almost-matched function. Now what?

→ Read docs/START_HERE.md. A short guided tour, with every command runnable right now against fixtures in this repository — no ROM, no compiler, no toolchain, no AI.

It answers the three questions people actually arrive with:

• Do I need to isolate the function so asm-processor (the community preprocessor that lets hand-written MIPS assembly live inside C) stays out of it? No. Compare your normal full-TU build against the expected object; --function scopes it. Isolation changes codegen, so a harness is the wrong ground truth.
• Do I need a permuter or an agent to use this? No. The verdict names the mechanism, the next: footer names the lever, and the field guide gives you the C. The permuter is optional, and it is a hypothesis generator rather than a solver.
• Am I supposed to read trace.lst? Not yet, and probably not at all. Traces are the last resort for one verdict class, and only if your project built an instrumented compiler.

Three pages are the entire workflow:

Page	What it is for
Start here	One function, guided tour: diagnose → lever → repeat
Field guide	"The diff looks like X" → the C that moves it, with the measured effect
Backlog walkthrough	Thirty near matches: batch triage, and which classes to knock out first

Already at 100%? Then your question is a different one — whether the addresses in that matched ROM are references, so code and data can be inserted, removed or resized without a hardcoded pointer quietly surviving the move. Start at the shiftability campaign: five phases, the first two of which need only a linker map and a linked image, no build. Shiftability is the reference beside it.

Everything below is reference.

Try it in 60 seconds

Install from a checkout (Python 3.10 or newer; Python 3.10 installs one small TOML compatibility dependency). For a standalone command, pipx keeps the workbench isolated from system Python as recommended by the Python Packaging User Guide:

git clone https://github.com/akratch/n64-decomp-workbench.git
cd n64-decomp-workbench
pipx install .

Or, inside an activated virtual environment:

python3 -m pip install .

Compare two fixture dumps whose raw words differ only in relocated fields:

decomp-workbench compare-dumps \
  examples/fixtures/target.objdump \
  examples/fixtures/relocated-match.objdump \
  --fail-on-mismatch

verdict=instruction-exact aligned_total=   0 words=   0 raw=   2 opcodes=   0 gaps=   0 reloc_syms=   0 norm=   0 ...
raw difference classes: relocation_controlled=2
next: Instruction-exact: raw differences are linker-controlled relocation fields ...

words=0 is the relocation-aware result. raw=2 shows why a literal word comparison would have rejected the candidate.

Now diagnose a real residual—exactness and mechanism in one load, ending in a lever:

decomp-workbench diagnose-dumps \
  examples/fixtures/phase-shift-target.objdump \
  examples/fixtures/phase-shift-candidate.objdump \
  --function animStep

verdict: phase-shift  structural=0 schedule=0 register=6 constant=0 hunks=1 playbook=temp-fifo-phase
signature: prefix-exact@12 state-divergence@temp:5 register-first-divergence

Six register differences, one upstream cause. Start here walks the rest of that screen.

Is this for me?

Use it when:

• your candidate is close, but the remaining mismatch is hard to classify;
• you are compiling many source variants and need caching plus a durable ledger;
• a sweep needs row/function-scoped signals, baseline/differential controls, honest coverage, or a fresh auditable finish receipt;
• the instruction shape matches but register allocation does not;
• a function already matches and you want to remove fake-match machinery without losing exactness;
• you need to test whether uopt, ugen, or as1 (IDO's optimizer, code generator, and final assembler pass) owns a difference;
• your project is 100% matched and you need to know whether it is safe to shift, insert, or resize code and data without a hardcoded address quietly surviving the move.

You do not need a ROM or compiler to try the included fixtures. Real object comparison needs a GNU-compatible MIPS objdump. Compiler tracing and pass replay need binaries supplied by your project.

Use it in a decomp project

Preview a portable project config, then write it only after the inferred and explicit inputs look right:

decomp-workbench project init . \
  --target target.o --candidate candidate.o \
  --symbol function_name
# After reviewing the preview:
decomp-workbench project init . \
  --target target.o --candidate candidate.o \
  --symbol function_name --write
decomp-workbench project diagnose

Discovery recognizes objdiff, Splat, and common build metadata but refuses to guess which of many objects is authoritative. See project configuration. The same file can hold an explicit compile-one argv, sealed environment, and frontend/backend lineage for project campaign candidates/*.c; no generic Makefile is guessed into an executable campaign.

Compare one function out of your normal full-translation-unit build, or get exactness, mechanism, and the next lever in one invocation:

decomp-workbench compare target.o candidate.o --function function_name \
  --objdump /path/to/mips64-elf-objdump --show-diff
decomp-workbench diagnose target.o candidate.o --function function_name \
  --objdump /path/to/mips64-elf-objdump

diagnose --html report.html carries the same evidence — no scripts, no network, one file you can attach to a PR or a Discord thread.

As the work deepens, one command family per stage of a real campaign:

• public-match-check — before starting a function at all, ask whether decomp.me already has a verified match. Bind on the target's address and size, not its name. See gate 0.
• campaign target.o candidates/*.c --compile-command ... — run hundreds of source variants through your own compile wrapper, with caching, an append-only ledger, controls, and a fresh auditable finish receipt. See candidate campaigns.
• check-scratch, fetch-scratch, bundle-scratch — validate, download, and package decomp.me exports without guessing at context. See checking decomp.me exports. public-match-check and fetch-scratch are the only two commands that ever open a network connection; both are read-only and neither ever runs implicitly.
• object collateral — an exact function is only the first gate; compare the containing objects for .bss, GP-table, symbol, relocation, or neighboring-code collateral. See object comparison.
• shift audit, shift rehearse — a matched build proves the bytes at one layout, not that its addresses survive a resize. In one live gate, a hardcoded pointer that passed the project's own retail verifier was convicted by shift rehearse, by name. See shiftability and the shiftability campaign.
• handoff audit — before publishing a proof repository, check that every local dependency actually travels. See public handoff audits.
• install-skill codex|claude — an optional agent skill that runs the same commands you would.

Pick the next diagnostic

What the comparison says	Next move
structure-mismatch	Keep working at the C/control-flow level
constant-mismatch	Audit the flag/enum against the assembly, then re-derive fakes
commutative-order	Change the expression tree (x |= y), not the allocator
schedule-mismatch	Regroup statements; use -g0 to locate ownership, not to prove the C
allocation-mismatch	Run view to name the family, then decomp-workbench guide <playbook>
relocation-layout-mismatch	Check relocation metadata, then the project link/ROM check
exact=true	Run the project’s normal collateral and full-output verification

Whatever the verdict, --show-diff prints every differing site: no verdict suppresses evidence. The field guide turns each of these rows into the C that moves it, decomp-workbench guide <playbook|verdict|lever> prints the relevant part of it in the terminal, and from verdict to edit walks one case end to end.

Command reference

Run decomp-workbench commands for the annotated map of every command, grouped by journey (object, scratch, trace, probe, sweep, campaign, shift, ...), or decomp-workbench --help for the flat list. Two conventions hold everywhere:

• On every command that selects one function, --symbol and --function are the same option, and passing both with different values is refused rather than silently resolved.
• Every printed label is also the JSON key for that value; decomp-workbench --explain-keys prints the one registry of comparison, campaign, and aligned-view keys.

The name shapes — a bare verb reads objects, trace-* reads a compiler log, probe-* reads your C source, sweep <verb> writes a family of variants — are explained in Choose a workflow. decomp-workbench completion bash|zsh|fish|powershell prints a completion script.

Documentation

• Start here — an almost-matched function, end to end
• Field guide — the IDO codegen levers, with the C
• Backlog walkthrough — thirty near matches, in triage order
• Documentation index — every guide, with inputs, outputs, and reading order

Support boundary

Comparison, ranking, campaigns, scratch bundling, trace parsing, and pass replay are adapters: bring your own object files, objdump, compiler wrapper, scratch inputs, traces, or pass binaries. These workflows support explicit IRIX 4.x frontend cells and IDO 5.3/7.1 pipelines when the project supplies the corresponding toolchain; instrumentation remains profile-specific. See the IDO support matrix.

The packaged uopt patch profiles are intentionally narrower. They accept generated uopt.c from one pinned IDO 5.3 static-recomp revision, verify its SHA-256 and source anchors, and reject unknown input by default. The generic ugen instrumenter supports a broader but shallower call/free-list trace.

The repository contains no ROMs, target objects, proprietary compiler binaries, generated third-party contexts, extracted target assembly, or game assets. The CV64 campaign record retains aggregate measurements and a local regeneration recipe, while the uncleared scratch payloads remain excluded as recorded by its notice.

Development

python3 -m pip install -e ".[dev]"
python3 -m unittest discover -s tests -v
bandit -r src -ll
codespell README.md CHANGELOG.md CONTRIBUTING.md docs examples src tests
ruff check src tests
ruff format --check src tests
mypy src tests

The test runner is unittest, not pytest. pytest is not part of the dev extras; uv run pytest fails with collection errors unless you first run pip install -e ".[dev]" pytest.

See CONTRIBUTING.md before adding a relocation type, instrumentation profile, or trace format.

License

CC0-1.0. Third-party tools and user-supplied inputs keep their own terms.