craftdex

Work in progress.

craftdex is a tool that turns .smali files into .dex bytecode — written in Zig.

It's a small, low-level project that focuses on understanding and generating the core of Android apps: the classes.dex file.

You don't need Android Studio, JDK, or NDK — just a .smali file and zig.

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🔧 What it does

• Parses a .smali file with a custom lexer and parser
• Builds internal IR (intermediate representation)
• Supports common instruction formats: 10x, 21c, 35c
• Emits valid .dex files with:
  • string data
  • type/method/proto/class tables
  • code sections
  • headers, checksums, and signature

It works on real Android devices — the .dex loads and runs.

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📸 Screenshots

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🚀 How to use

0. Generate signing keys (only once):

openssl genpkey -algorithm RSA -pkeyopt rsa_keygen_bits:2048 -out key.pem
openssl pkcs8 -topk8 -inform PEM -outform DER -nocrypt -in key.pem -out key.pk8
openssl req -new -x509 -key key.pem -out key.x509.pem -days 365 -subj "/CN=helloworld"

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For the next steps you can also use the build_hello.sh script.

1. Build

zig build

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2. Convert smali to dex

mkdir -p examples/HelloWorld/apk/
zig-out/bin/craftdex dex examples/HelloWorld/HelloActivity.smali -o examples/HelloWorld/apk/classes.dex

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3. Make an APK (temporary method)

Install marco via nimble install and use it to convert XML to some binary XML

nimble install marco
~/.nimble/bin/marco < examples/HelloWorld/AndroidManifest.xml > examples/HelloWorld/apk/AndroidManifest.xml

Install basia via go install and use it to make an apk archive and sign it

basia -i=examples/HelloWorld/apk/ -o=examples/HelloWorld/hello.apk -c=key.x509.pem -k=key.pk8

marco and basia are planned to be replaced by Zig code.

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🛠 TODO

Plans to evolve craftdex from a single .smali emitter into a full toolchain:

🔧 Code & architecture

• Refactor internal layout planner and offset assignment
• Make internal IR more expressive and modular
• Clean up DexEmitter structure for better testability and reuse

📜 Smali parsing

• Extend smali grammar (fields, annotations, register ranges, labels)
• Improve error messages and robustness
• Add support for .locals, .registers, labels, and branching

🧱 Instruction formats & bytecode

• Implement more instruction formats (22c, 3rc, 10t, etc.)
• Add support for control flow, field access, arrays
• Support exception handling and method attributes

📦 Packaging and tooling

• Replace marco with a native Zig binary XML writer
• Replace basia with a native Zig APK builder and signer
• Add support for resources.arsc and proper ZIP layout

🎮 End-to-end example goal: run Flappy Bird

• Add support for minimal Android views and layout
• Draw with SurfaceView
• Implement enough bytecode to run a game loop
• Build and launch a Flappy Bird demo

✨ Long-term goals

• Support compilation from Zig AIR, like SPIR-V codegen
• Make it possible to write Android apps entirely in Zig and emit .dex directly
• Support Android libc (bionic) for cross-compilation

Much more is needed...

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Some links

• https://formats.kaitai.io/dex/
• https://source.android.com/docs/core/runtime/dalvik-bytecode
• https://source.android.com/docs/core/runtime/constraints
• https://github.com/google/smali

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Thanks

Special thanks to akavel for the inspiration and motivation.
I’ll add more credits as the project evolves. Contributions are welcome — feel free to open issues, send PRs, or just share ideas.