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). For FHE-heavy contracts, use the Aster backend.

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

The Aster backend targets Aster Chain (Chain ID 1996), a purpose-built L1 with native FHE and ZK hardware acceleration.

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

Aster Deployment Workflow

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

covenant deploy   --network aster   --rpc https://tapi.asterdex.com/info   --chain-id 1996   --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