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Case study

Kingdom Hearts 358/2 Days: a matching Nintendo DS decompilation

Reconstructs the ARM9 program and overlays of the EU Nintendo DS release of Kingdom Hearts 358/2 Days as C that recompiles byte for byte with CodeWarrior. README reports all 306 modules byte-identical, with about 99.5% of functions in real C and library assembly counted separately; the ARM7 binary is outside its scope. The repository holds no ROM, game assets or extracted disassembly and produces no playable build.

Requirements and limitations

  • README reports every function of the EU (YKGP) ARM9 program and its overlays matched and all initialized data reconstructed, with 306 of 306 rebuilt modules byte-identical; the remaining work is readability, such as shared structures, naming and file grouping. It counts 23,125 of about 23,233 functions as real C and tracks 108 assembly implementations (library routines and two game functions that need clz) separately. docs/ARM7.md states that the decomp covers the ARM9 only. This is a matching decompilation, not a port, and it produces no playable build or redistributable binary.
  • Requires the user’s own EU ROM dump, days.nds: 268,435,456 bytes, SHA-1 6fae8f5bbe80114b4e2535260eab5f4d0fc8a844 (CONTRIBUTING.md also lists SHA-256 and MD5). Other dumps will not line up with the committed addresses. The repository tracks no ROM, extracted data (including the extracted asm/ tree), build output or proprietary toolchain, and a pull-request check rejects added ROM, binary or asset files.
  • CONTRIBUTING.md lists Python 3 with capstone, pyelftools and ndspy, the dsd extraction and delinking tool, the proprietary CodeWarrior mwccarm 3.0 build 139 compiler (not supplied), arm-none-eabi-as and a Ninja-driven mwccarm/mwldarm build; its commands call tools/dsd.exe alongside Bash scripts. A few precompiled-middleware units use an older mwccarm through per-file compiler overrides.
  • dsd check modules compares each built module with the base ROM, verify_idx.py checks single functions including relocations, and the ROM round-trip script is expected to differ from the reference dump only in four non-functional CRC bytes. CONTRIBUTING notes that functions listed as known mismatches are kept out of the link and filled with original bytes. CI does not build the game; it rejects forbidden files and regenerates progress reports. decomp.dev reports YKGP 100.00% decompiled and fully linked at the reviewed commit, counting verified SDK assembly; this collection did not rerun these checks.
  • Contributors’ decompilation and tooling are dedicated to the public domain under CC0 1.0; the original game and its assets remain their owners’ property, and the CodeWarrior compiler is not distributed. DS Protect sources are reconstructed after taxicat1/dsprot, and the SDK identification harness compiles NitroSDK sources from pret/pokediamond. The reviewed sources disclose no REA or AI use, and no runtime reproduction is claimed; the separate khdays-port PC runtime is not covered.

About this entry

Type
Case study
Category
Independent reconstruction cases
Relationship
Independent reconstruction project
Targets
Game

Sources reviewed

The description was reviewed against primary sources. This does not establish runtime testing, security auditing or verified compatibility.

Primary sources

  1. README.md GitHub · Yokimitsuro/khdays-decomp · Revision 261a89e
  2. CONTRIBUTING.md GitHub · Yokimitsuro/khdays-decomp · Revision 261a89e
  3. PROGRESS.md GitHub · Yokimitsuro/khdays-decomp · Revision 261a89e
  4. docs/PROGRESS_POLICY.md GitHub · Yokimitsuro/khdays-decomp · Revision 261a89e
  5. docs/ARM7.md GitHub · Yokimitsuro/khdays-decomp · Revision 261a89e
  6. .github/workflows/checks.yml GitHub · Yokimitsuro/khdays-decomp · Revision 261a89e
  7. .github/workflows/report.yml GitHub · Yokimitsuro/khdays-decomp · Revision 261a89e
  8. LICENSE GitHub · Yokimitsuro/khdays-decomp · Revision 261a89e
  9. https://decomp.dev/Yokimitsuro/khdays-decomp