Decompiling a Nintendo DS game is the process of converting the machine code (binary) stored on the cartridge back into a human-readable format (such as C or C++ source code). This is a reverse engineering process used for game preservation, creating fan translations, or fixing bugs in old games.
It is important to note that you cannot simply click a button and get the original source code. The process requires significant manual effort.
An NDS ROM is essentially a file system. Before decompiling code, you must unpack it.
No single tool performs full NDS decompilation. Instead, reverse engineers use a pipeline of tools.
2.1 Disassemblers: The First Step
Before decompilation comes disassembly. Tools like Ghidra (developed by the NSA) or IDA Pro load an NDS ROM, detect the ARM/Thumb instruction sets, and produce assembly language. Ghidra, with its open-source nature, has become a cornerstone of NDS reverse engineering. It can automatically split the ARM9 and ARM7 binaries and begin the process of labeling functions. However, assembly is still far from the original source. A typical line of ARM assembly:
STR R0, [R1, #0x14]
might be equivalent to:
gameState->score = currentScore;
2.2 Decompilers: Raising Abstraction The true decompiler (e.g., Ghidra’s built-in decompiler or the now-commercial Hex-Rays for IDA) attempts to lift assembly into a pseudo-C representation. For the NDS, this process is fraught with difficulty. The decompiler must identify function prologues and epilogues, reconstruct loops, infer data types, and recognize compiler idioms.
A successful decompilation from Ghidra for an NDS function might produce:
undefined4 FUN_0203a4c8(void)
int i;
for (i = 0; i < 4; i = i + 1)
FUN_0201b2e4(i);
return 0;
This is a massive improvement over raw hex, but it lacks semantic meaning. What does FUN_0201b2e4 do? What does the return value represent? The human reverse engineer must rename functions and variables, creating a Symbol Map.
2.3 The C++ Problem Most modern NDS games were written in C++, not C. Decompiling C++ is exponentially harder. Name mangling (where the compiler encodes class and namespace information into function names), virtual tables (vtables), inheritance hierarchies, and templates are nearly impossible to recover perfectly. An NDS decompiler can identify that a function is a constructor or a virtual call, but recovering the original class structure is a manual, detective process. Tools like Ghidra’s CPPAnalyzer plugin or retdec attempt to reconstruct classes, but they often produce approximations that require significant human correction.
2.4 Specialized NDS Tools Beyond general decompilers, the NDS scene has created specialized tools:
Summary
What it does well
Common limitations
Who should use it
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Related search suggestions (Function invoked)
This draft outlines a technical paper regarding the development and methodology of a Nintendo DS (NDS) decompiler, focusing on the challenges of the ARM9/ARM7 dual-core architecture.
Reverse Engineering the Dual-Screen Era: Design and Implementation of an NDS Decompiler
This paper presents the architectural design of a specialized decompiler for the Nintendo DS (NDS) handheld system. While general-purpose decompilers like Ghidra support ARM architectures, the NDS presents unique challenges, including a dual-core (ARM946E-S and ARM7TDMI) setup and complex memory-mapped I/O (MMIO). Our approach focuses on translating binary machine code back into human-readable C code while preserving hardware-specific function calls. 1. Introduction
The Nintendo DS remains a focal point for homebrew development and software preservation. Traditional reverse engineering involves reading raw assembly, which is time-consuming. An NDS-specific decompiler automates the recovery of high-level logic, enabling developers to understand legacy game engines and patch software for modern hardware. 2. System Architecture
A robust decompiler for this platform must handle the following components:
The Loader: Parses the NDS file format, which contains headers, ARM9/ARM7 binary blobs, and the NitroSDK filesystem. nds decompiler
Disassembly Engine: Decodes the 32-bit ARM and 16-bit Thumb instruction sets used by the system.
Control Flow Graph (CFG) Recovery: Identifies branches and loops to reconstruct the program's structural flow.
Type Inference: Guesses variable types (e.g., int, char*, or struct) based on how registers are manipulated. 3. Key Challenges
Dual-Core Synchronization: The ARM9 and ARM7 cores communicate via IPC (Inter-Process Communication) and shared memory. A decompiler must identify these communication points to provide context for cross-core logic.
Proprietary Graphics/Sound APIs: Much of the NDS's functionality relies on the NitroSDK. Integration with tools like NDS | Decompiler helps map MMIO addresses to recognizable SDK function names.
Code Obfuscation: Some late-generation titles use custom compression or anti-tamper measures that must be bypassed during the lifting phase. 4. Methodology
Binary Lifting: Converting machine code into an Intermediate Representation (IR).
Data Flow Analysis: Tracking register states to determine function arguments and return values.
Pattern Matching: Recognizing common compiler-generated code patterns (e.g., switch statements or for loops).
C-Code Generation: Emitting the final source code with comments referencing the original memory offsets. 5. Conclusion
By automating the transition from binary to source, an NDS decompiler serves as an essential tool for digital archeology. Future work involves integrating machine learning to improve variable naming and "symbolication" based on known open-source SDKs. Decompiling a Nintendo DS game is the process
Decompiling a Nintendo DS (NDS) game is a multi-step process that has become significantly more accessible with modern tools. Unlike simple "one-click" decompilers for high-level languages, NDS decompilation involves unpacking the ROM, decrypting its contents, and then using a reverse engineering suite to turn binary code back into readable C or assembly. 1. Essential Tools for Your Toolkit
To successfully decompile a DS game in 2026, you generally need a combination of these community-standard tools:
: A free, open-source reverse engineering suite developed by the NSA. It includes a powerful decompiler that can translate ARM machine code into C-like code. : A specialized Ghidra extension that allows you to load
ROM files directly into Ghidra, handling the complex memory mapping for you.
: A modern toolkit specifically designed to automate the setup of NDS decompilation projects, saving months of manual work by organizing code into translation units.
: Essential for decrypting retail DS cart images. You cannot analyze a ROM in Ghidra if it is still encrypted, as it will appear as "digital garbage".
: A versatile viewer and editor for NDS files. It is best used for extracting and converting non-code assets like images, text, and sounds. 2. The Decompilation Workflow
If you are looking to reverse engineer a specific title, the standard workflow follows these steps: AetiasHax/ds-decomp: Toolkit for decompiling DS games 3 Apr 2026 —
| Challenge | Description | |-----------|-------------| | Thumb/ARM interworking | Decompilers often misalign control flow at mode switches | | Inlined assembly | SDK macros use inline asm for speed; decompiler produces gibberish | | Overlays | Code loaded at runtime into same address space – static analysis misses cross-overlay calls | | Custom memory maps | NDS has 8+ distinct memory regions (Main RAM, VRAM, Shared WRAM, etc.) – pointers ambiguous | | Register banking | ARM9 has banked registers for IRQ/Supervisor modes – decompiler sees only user mode | | Binary differencing | Matching decompiled code to known SDK versions requires signature scanning |
Use Ghidra + manual memory map setup for free NDS reverse engineering.
Use IDA Pro + Hex-Rays only if you do NDS RE professionally.