Compiler Targets

The Covenant compiler supports three first-class backends as of V0.8 GA, selected via the --target-chain flag:

covenant build --target-chain evm    ./src/Contract.cov   # default
covenant build --target-chain aster  ./src/Contract.cov   # Aster Chain
covenant build --target-chain wasm   ./src/Contract.cov   # V0.8 GA — deterministic

EVM Backend (default)

The EVM backend produces standard EVM bytecode deployable on Ethereum mainnet, all major L2s (Arbitrum, Optimism, Base, Scroll), and any EVM-compatible chain.

IR to EVM Opcode Mapping

Key mappings (IR opcode → EVM opcodes):

Gas Model

The EVM backend generates gas-optimal code for the standard EVM pricing model (EIP-1559, EIP-3529). The optimizer’s storage slot packing pass is particularly impactful: packing bool fields saves 15,000 gas per cold read.

FHE precompile costs on L1 are high (see ERC-8227 gas table). Budget precompile gas carefully for FHE-heavy contracts.

Metadata Format

The EVM artifact includes a CBOR-encoded metadata blob appended to the deployed bytecode (following Solidity convention). This blob contains:

• Compiler version
• Source hash
• ERC compliance profile (CL1–CL5)
• Audit report reference (OMEGA V4)
• IPFS hash of the full artifact JSON

Block explorers that understand Covenant contracts (AsterScan, etc.) use this CBOR blob for source verification.

Deployment Workflow

# Build
covenant build --target evm ./src/Token.cvt

# Deploy to Sepolia
covenant deploy   --network sepolia   --rpc https://rpc.sepolia.org   --private-key $DEPLOYER_KEY   ./out/Token.artifact.json

The covenant deploy command is a thin wrapper around cast send from Foundry. It reads the artifact, encodes the constructor call, and broadcasts the deployment transaction.

Aster Backend (deprecated — historical)

The Aster backend targeted Aster Chain (Chain ID 1996), a purpose-built L1 with native FHE and ZK hardware acceleration. Aster Chain is deprecated. The current featured deploy target is Robinhood Chain (Arbitrum Orbit L2, chainId 46630 / 0xB626), a standard EVM chain reached through the EVM backend. The section below is retained for historical reference; the native-hardware features it describes are specific to the deprecated Aster target and are not present on Robinhood.

Key Differences from EVM

Aster-Specific IR Lowering

When targeting Aster, the IR lowering transforms:

; EVM: FheAdd calls precompile 0x10
%result = FheAdd %a %b
  -> PUSH20 0x10  PUSH args  GAS  STATICCALL

; Aster: FheAdd is a single native opcode
%result = FheAdd %a %b
  -> ASTER_FHEADD  (1 opcode, ~400 pGas)

The Aster backend also enables:

• Account Privacy by default: Balance reads return ciphertexts unless the caller has a Viewer Pass
• Single-instruction batch FHE: The FheBatch IR opcode maps to a single Aster native opcode
• ZK proof generation via hardware: Off-chip ZK accelerators reduce proof time from seconds to milliseconds

Robinhood Deployment Workflow

covenant build --target evm ./src/Contract.cvt

covenant deploy   --network robinhood   --rpc https://rpc.testnet.chain.robinhood.com   --chain-id 46630   --private-key $DEPLOYER_KEY   ./out/Contract.artifact.json

Current state in V0.8 GA and V0.8.x roadmap

V0.8 GA ships the Aster foundation: chain ID 1996, precompile registry wiring, and placeholder artifacts with COV7\x01 magic. The --target-chain aster flag is a first-class target — it parses, type-checks, and emits auditable placeholder bytecode. Full Aster SDK lowering lands in V0.8.x:

• Full Aster SDK integration (native staking interaction, real per-opcode lowering)
• Aster Account Abstraction support
• pGas estimation in covenant build --estimate-gas
• Automatic Viewer Pass issuance for selective disclosure

WebAssembly Backend

Status: Stable as of V0.8 GA (April 2026). Deterministic, wasmparser::validate-clean output suitable for browsers and server-side sandboxes (wasmtime, wasmer).

The WASM backend compiles Covenant contracts to WebAssembly modules, enabling:

• Browser-side contract simulation (Covenant Playground)
• Off-chain computation for @prove_offchain circuits
• Deterministic server-side sandboxing via wasmtime / wasmer
• Testing without an EVM node

covenant build contract.cov --target-chain wasm
#   → contract.wasm (deterministic)
#   → contract.metadata.json (ABI, imports, exports, storage layout)

Determinism guarantees

The WASM backend emits byte-identical output for byte-identical inputs. No threads, no non-deterministic intrinsics, no floats in hot paths. Host-imports are narrow (storage get/put, keccak256, log emission) and fully enumerated in the metadata.json imports table.

FHE on WASM

V0.8 ships types and trap behavior for FHE operations on the WASM target. Real TFHE key-switching on WASM is gated on the 0x0128 precompile (or its WASM-host equivalent) and lands in V0.8.x. Until then, FHE ops in a WASM build will return a KeySwitchError::NotImplemented when exercised.

V0.8.x follow-ups

• Real TFHE key-switching on WASM (via 0x0128 precompile or host-import)
• Integration with the Covenant Playground (in-browser IDE)
• WASM contracts deployable to WASM-compatible chains (Cosmos CosmWasm, etc.)

Future Backends

The following backends are under consideration for V0.9+:

See Also

• Compiler Pipeline
• Diagnostics Catalog
• Example 15 — Deploy to Sepolia