Rev U3d Dump skill

rev-u3d-dump - Unity IL2CPP Symbol Dumper

Extract C# method names, addresses, and type definitions from Unity IL2CPP builds for IDA/Ghidra analysis.

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Overview

Unity IL2CPP compiles C# to native code. The original class/method names are stripped from the binary but preserved in global-metadata.dat. This skill recovers the mapping between native function addresses and their original C# names.

Key Files in Unity Build

File	Location	Purpose
Native binary	iOS: Frameworks/UnityFramework.framework/UnityFramework Android: lib/{arch}/libil2cpp.so	Compiled C# code (Mach-O / ELF)
Metadata	Data/Managed/Metadata/global-metadata.dat	All type/method/string info

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Tool Selection

Il2CppDumper (recommended for metadata v39+)

Use the v39 fork for Unity 6+ builds:

• Repo: https://github.com/roytu/Il2CppDumper (branch: v39)
• Supports metadata v24–v39
• Outputs script.json with function addresses — ready for IDA/Ghidra import

The original Il2CppDumper (https://github.com/Perfare/Il2CppDumper) only supports up to v29.

Cpp2IL (alternative)

• Repo: https://github.com/SamboyCoding/Cpp2IL
• Supports metadata v39, but dummy DLLs lack [Address] attributes
• Useful for C# source reconstruction, not ideal for IDA import

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Step-by-Step Workflow

Step 1: Locate IL2CPP Files

iOS (IPA):

# Unzip IPA
unzip -o app.ipa -d .

# Binary
BINARY="Payload/<AppName>.app/Frameworks/UnityFramework.framework/UnityFramework"

# Metadata
METADATA="Payload/<AppName>.app/Data/Managed/Metadata/global-metadata.dat"

Android (APK):

# Unzip APK
unzip -o app.apk -d .

# Binary (pick target arch)
BINARY="lib/arm64-v8a/libil2cpp.so"

# Metadata
METADATA="assets/bin/Data/Managed/Metadata/global-metadata.dat"

Step 2: Check Metadata Version

# First 8 bytes: magic (4) + version (4), little-endian
xxd -l 8 "$METADATA"
# Expected: af1b b1fa 2700 0000  → magic OK, version = 0x27 = 39

Version	Unity	Tool
≤ 29	Unity 2021 and earlier	Original Il2CppDumper
31	Unity 2022	Original Il2CppDumper (partial)
39	Unity 6 (6000.x)	roytu/Il2CppDumper v39 fork

Step 3: Build & Run Il2CppDumper (v39 fork)

# Clone v39 fork
git clone -b v39 https://github.com/roytu/Il2CppDumper.git

# Build
cd Il2CppDumper
DOTNET_ROLL_FORWARD=LatestMajor dotnet build -c Release

# Run (use net8.0 framework)
DOTNET_ROLL_FORWARD=LatestMajor dotnet run \
  --project Il2CppDumper/Il2CppDumper.csproj \
  -c Release --framework net8.0 \
  -- "$BINARY" "$METADATA" output_dir

Notes:

• DOTNET_ROLL_FORWARD=LatestMajor allows running on .NET 9/10 even though the project targets .NET 6/8
• Exit code 134 is normal in non-interactive mode (caused by Console.ReadKey() at the end)
• On macOS, if the binary gets SIGKILL'd, ad-hoc sign it: codesign -s - <binary>

Step 4: Verify Output

Successful run produces these files in the output directory:

File	Size (typical)	Purpose
script.json	50–100 MB	Function addresses + names + signatures (IDA/Ghidra import)
dump.cs	10–30 MB	C# class dump with RVA/VA addresses
il2cpp.h	50–100 MB	C struct definitions for type import
ida_py3.py	~2 KB	IDA Python import script

Check script.json format:

{
  "ScriptMethod": [
    {
      "Address": 40865744,
      "Name": "ClassName$$MethodName",
      "Signature": "ReturnType ClassName__MethodName (args...);",
      "TypeSignature": "viii"
    }
  ]
}

Check dump.cs format:

// RVA: 0x1A2B3C4 Offset: 0x1A2B3C4 VA: 0x1A2B3C4
public void MethodName() { }

Step 5: Import into IDA

1. Open the native binary in IDA (UnityFramework / libil2cpp.so)
2. Place script.json and ida_py3.py in the same directory
3. File → Script file... → select ida_py3.py
4. The script reads script.json and renames all functions automatically
5. Optional: File → Load file → Parse C header file... → select il2cpp.h for struct types

Step 5 (alt): Import into Ghidra

1. Open the binary in Ghidra
2. Use the ghidra.py or ghidra_with_struct.py script from Il2CppDumper
3. Window → Script Manager → Run with script.json in the same directory

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Troubleshooting

Error	Cause	Fix
not a supported version[39]	Using original Il2CppDumper	Switch to roytu/Il2CppDumper v39 fork
Exit code 137 (SIGKILL)	macOS unsigned binary	codesign -s - <binary>
Cannot read keys (exit 134)	Non-interactive console	Ignore — dump completed successfully
DOTNET_ROLL_FORWARD error	.NET version mismatch	Set DOTNET_ROLL_FORWARD=LatestMajor
Empty output	Wrong binary/metadata pair	Verify both files are from the same build

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Output Usage Tips

• dump.cs is the quickest reference — search for class/method names with RVA addresses
• script.json Address values are decimal — convert to hex for IDA: hex(40865744) → 0x26F8FD0
• Field offsets in dump.cs (e.g., // 0x20) are relative to object base, useful for memory inspection with Frida