rWasm is a ZK-friendly binary intermediate representation (IR) of WebAssembly (Wasm), designed for fast execution and efficient zero-knowledge proof generation. It preserves full semantic compatibility with Wasm while removing non-deterministic and hard-to-prove elements, making it the only WebAssembly runtime specifically optimized for blockchain and zero-knowledge applications.
- Flattened control flow: Eliminates complex branching structures by converting all control flow to simple
br,br_if, andbr_tableinstructions - No relative jump targets: Uses PC-relative branch targets instead of relative depth, eliminating a major ZK-proving bottleneck
- Simplified validation: No post-decode validation required, making it immediately executable and ZK-friendly
- 6x faster module loading compared to Wasmi in no-cache scenarios (common in blockchain environments)
- 484ns cached execution vs Wasmi's 341ns (competitive performance)
- 879ns no-cache execution vs Wasmi's 5379ns (significant advantage)
- Optimized for blockchain: Fast startup performance critical for smart contract execution
- Deterministic execution: Consistent behavior across all network nodes
- Fuel-based gas metering: Built-in resource management system
- Multiple execution backends: rWasm, Wasmtime, and Wasmi integration
- Semantic preservation: Every Wasm feature is either preserved or safely substituted
- Standard compilation: Compile from any language that targets WebAssembly
- Easy migration: Drop-in replacement for existing Wasm applications
| Feature | rWasm | Wasmtime | Wasmi | WAMR | V8 Wasm | WasmEdge | Wasmer |
|---|---|---|---|---|---|---|---|
| ZK-Friendly | ✅ | ❌ | ❌ | ❌ | ❌ | ❌ | ❌ |
| Fast Module Loading | ✅ | ✅ | ✅ | ✅ | ✅ | ✅ | ✅ |
| Blockchain Optimized | ✅ | ❌ | ❌ | ❌ | ❌ | ❌ | |
| No-Cache Performance | 6x faster | Standard | Baseline | Standard | Standard | Standard | Standard |
| Deterministic Execution | ✅ | ✅ | ❌ | ||||
| Gas Metering | ✅ | ❌ | ❌ | ❌ | ❌ | ❌ | ❌ |
Benchmark: fib(47) on Apple M3 MAX
| Engine | Cached Execution | No-Cache Execution | Use Case |
|---|---|---|---|
| Native | 12ns | 12ns | Baseline |
| rWasm | 484ns | 879ns | ZK/Blockchain |
| Wasmi | 341ns | 5379ns | Embedded/Blockchain |
Key Insights:
- No-cache scenarios (common in blockchain): rWasm is 6x faster than Wasmi
- ZK applications: Only rWasm provides flattened control flow suitable for ZK proofs
- Smart contracts: Fast module loading crucial for per-transaction execution
WebAssembly is an attractive binary format thanks to its structured control flow, clear memory model, and rich ecosystem support. However, its current binary design introduces complexity for ZK proving:
- Relative jump targets → Complex to trace in ZK circuits
- Indirect function calls → Non-deterministic execution paths
- Type-table indirection → Requires complex validation
- Imports/exports → Dynamic semantics unsuitable for ZK
- Flattened control flow → Simple, linear execution trace
- Embedded metadata → No external dependencies
- No validation overhead → Immediately executable
- Self-contained modules → Deterministic execution
- Functions are inlined into a flat bytecode section
- All branch targets are PC-relative
- Control structures (
block,loop,if) are desugared into explicitbrsequences
- Function types are validated at rWasm compile-time and inlined
- No external type section needed
- Module is immediately executable without prior type resolution
- rWasm is self-contained: no
importorexportsections required - All external dependencies must be pre-resolved
| Section | Purpose |
|---|---|
| Bytecode | Flat instruction stream |
| Memory | Merged memory and data segments |
| Element | Optional: Table segment placeholder |
All structured blocks are rewritten into br, br_if, and br_table with relative PC offsets:
Standard Wasm:
(block $label
...code...
br $label
)rWasm:
...code...
br @relative_pc_offset- rWasm: Custom interpreter optimized for flattened format
- Wasmtime: Integration with Bytecode Alliance runtime
- Wasmi: Lightweight interpreter integration
- Fuel-based execution: Gas metering system for resource management
- Syscall support: Integration with host environment functions
- Resumable execution: Support for interrupting and resuming execution
- 64-bit optimized opcodes: Specialized instructions for faster 64-bit operations
- Caching: Module compilation caching for improved performance
- Stack optimization: Improved stack handling and memory management
- Zero-Knowledge Proofs: Only runtime optimized for ZK circuit generation
- Blockchain Smart Contracts: Fast execution with deterministic behavior
- zkVMs: Efficient execution in zero-knowledge virtual machines
- Blended-VM Runtimes: Supporting EVM, SVM, and Wasm in unified runtime
- Per-transaction execution: Fast module loading for blockchain applications
- Consensus systems: Deterministic execution across network nodes
- Proof generation: Optimized for ZK-SNARK/STARK proof creation
# Clone the repository
git clone https://github.com/fluentlabs-xyz/rwasm.git
cd rwasm
# Build and run all tests
makerWasm is used in the Fluent project to execute smart contracts in a unified runtime that supports EVM, SVM, and Wasm logic in a ZK-friendly way.
rWasm is the only WebAssembly runtime specifically designed for zero-knowledge applications, combining:
- ZK-optimized binary format for efficient proof generation
- Blockchain-native features for smart contract execution
- Performance advantages where it matters most (module loading)
- Full Wasm compatibility for easy adoption
We welcome contributions to rWasm!
rWasm is open-source software licensed under LICENSE.
rWasm: The first and only ZK-friendly WebAssembly runtime, purpose-built for the future of blockchain and zero-knowledge applications.