Integration

This document is a guide listing detailed steps to integrate fhevm-go into go-ethereum or any other implementations that follow the same architecture.

This document is based on go-ethereum v1.13.5

Steps

Step 1: update core/state_transition.go

func IntrinsicGas(data []byte, accessList types.AccessList, isContractCreation bool, isHomestead, isEIP2028 bool, isEIP3860 bool) (uint64, error)

replace the last return with:

return fhevm.TxDataFractionalGas(gas), nil

which will impact tests as the returned gas won’t be the same.

Step 2: update core/vm/contracts.go

update the PrecompiledContract interface to:

type PrecompileAccessibleState interface {
    Interpreter() *EVMInterpreter
}

type PrecompiledContract interface {
    RequiredGas(accessibleState PrecompileAccessibleState, input []byte) uint64
    Run(accessibleState PrecompileAccessibleState, caller common.Address, addr common.Address, input []byte, readOnly bool) ([]byte, error)
}

Update all previous uses of this interface

Add:

common.BytesToAddress([]byte{93}): &fheLib{}

to all precompiled contract maps (e.g. PrecompiledContractsHomestead )

We used 93 as the address of the precompile here, but you can choose any other address as far as client libraries know where to find it.

Implement the fheLib precompile

// fheLib calls into the different precompile functions available in the fhevm
type fheLib struct{}

func (c *fheLib) RequiredGas(accessibleState PrecompileAccessibleState, input []byte) uint64 {
    return fhevm.FheLibRequiredGas(accessibleState.Interpreter().evm.FhevmEnvironment(), input)
}

func (c *fheLib) Run(accessibleState PrecompileAccessibleState, caller common.Address, addr common.Address, input []byte, readOnly bool) ([]byte, error) {
    return fhevm.FheLibRun(accessibleState.Interpreter().evm.FhevmEnvironment(), caller, addr, input, readOnly)
}

Rewrite RunPrecompiledContract

func RunPrecompiledContract(p PrecompiledContract, accessibleState PrecompileAccessibleState, caller common.Address, addr common.Address, input []byte, suppliedGas uint64) (ret []byte, remainingGas uint64, err error) {
    gasCost := p.RequiredGas(accessibleState, input)
    if suppliedGas < gasCost {
        return nil, 0, ErrOutOfGas
    }

    suppliedGas -= gasCost
    output, err := p.Run(accessibleState, caller, addr, input, accessibleState.Interpreter().readOnly)

    return output, suppliedGas, err
}

Step 3: update core/vm/errors.go

Register errors at initialization in fhevm-go to be recognized at runtime

func init() {
    fhevm.RegisterErrors(ErrOutOfGas, ErrCodeStoreOutOfGas, ErrDepth, ErrInsufficientBalance,
        ErrContractAddressCollision, ErrExecutionReverted, ErrMaxInitCodeSizeExceeded, ErrMaxCodeSizeExceeded,
        ErrInvalidJump, ErrWriteProtection, ErrReturnDataOutOfBounds, ErrGasUintOverflow, ErrInvalidCode,
        ErrNonceUintOverflow, nil, nil, nil)
}

Step 4: update core/vm/evm.go

Update EVM struct with new fields

fhevmEnvironment FhevmImplementation
isGasEstimation  bool
isEthCall        bool

While implementing fhevmEnvironment as:

type FhevmImplementation struct {
    interpreter *EVMInterpreter
    data        fhevm.FhevmData
    logger      fhevm.Logger
    params      fhevm.FhevmParams
}

Update NewEVM

In:

func NewEVM(blockCtx BlockContext, txCtx TxContext, statedb StateDB, chainConfig *params.ChainConfig, config Config) *EVM

• Initialize isGasEstimation using config.IsGasEstimation

• Initialize isEthCall using config.IsEthCall

• Initialize fhevmEnvironment with FhevmImplementation{interpreter: nil, logger: &fhevm.DefaultLogger{}, data: fhevm.NewFhevmData(), params: fhevm.DefaultFhevmParams()}

• After initializing evm.interpreter make sure to point fhevmEnvironment to it evm.fhevmEnvironment.interpreter = evm.interpreter then initialize it fhevm.InitFhevm(&evm.fhevmEnvironment)

Update RunPrecompiledContract

After changing precompiled contract interface in 2, we have to change usages of:

RunPrecompiledContract(p, input, gas)

to:

RunPrecompiledContract(p, evm, caller.Address(), addr, input, gas)

Implement EVMEnvironment interface

Now implement the fhevm.EVMEnvironment interface for FhevmImplementation:

func (evm *EVM) FhevmEnvironment() fhevm.EVMEnvironment { return &evm.fhevmEnvironment }

// If you are using OpenTelemetry, you can return a context that the precompiled fhelib will use
// to trace its internal functions. Otherwise, just return nil
func (evm *FhevmImplementation) OtelContext() context.Context {
       return nil
}

func (evm *FhevmImplementation) GetState(addr common.Address, hash common.Hash) common.Hash {
    return evm.interpreter.evm.StateDB.GetState(addr, hash)
}

func (evm *FhevmImplementation) SetState(addr common.Address, hash common.Hash, input common.Hash) {
    evm.interpreter.evm.StateDB.SetState(addr, hash, input)
}

func (evm *FhevmImplementation) GetNonce(addr common.Address) uint64 {
    return evm.interpreter.evm.StateDB.GetNonce(addr)
}

func (evm *FhevmImplementation) AddBalance(addr common.Address, value *big.Int) {
    evm.interpreter.evm.StateDB.AddBalance(addr, value)
}

func (evm *FhevmImplementation) GetBalance(addr common.Address) *big.Int {
    return evm.interpreter.evm.StateDB.GetBalance(addr)
}

func (evm *FhevmImplementation) Suicide(addr common.Address) bool {
    evm.interpreter.evm.StateDB.SelfDestruct(addr)
    return evm.interpreter.evm.StateDB.HasSelfDestructed(addr)
}

func (evm *FhevmImplementation) GetDepth() int {
    return evm.interpreter.evm.depth
}

func (evm *FhevmImplementation) IsCommitting() bool {
    return !evm.interpreter.evm.isGasEstimation
}

func (evm *FhevmImplementation) IsEthCall() bool {
    return evm.interpreter.evm.isEthCall
}

func (evm *FhevmImplementation) IsReadOnly() bool {
    return evm.interpreter.readOnly
}

func (evm *FhevmImplementation) GetLogger() fhevm.Logger {
    return evm.logger
}

func (evm *FhevmImplementation) FhevmData() *fhevm.FhevmData {
    return &evm.data
}

func (evm *FhevmImplementation) FhevmParams() *fhevm.FhevmParams {
    return &evm.params
}

func (evm *FhevmImplementation) CreateContract(caller common.Address, code []byte, gas uint64, value *big.Int, address common.Address) ([]byte, common.Address, uint64, error) {
    return evm.interpreter.evm.create(AccountRef(caller), &codeAndHash{code: code}, gas, value, address, CREATE)
}

func (evm *FhevmImplementation) CreateContract2(caller common.Address, code []byte, codeHash common.Hash, gas uint64, value *big.Int, address common.Address) ([]byte, common.Address, uint64, error) {
    return evm.interpreter.evm.create(AccountRef(caller), &codeAndHash{code: code, hash: codeHash}, gas, value, address, CREATE2)
}

Step 5: update core/vm/instructions.go

Update opSstore

Rewrite opSstore by a call to their fhevm implementation:

func opSstore(pc *uint64, interpreter *EVMInterpreter, scope *ScopeContext) ([]byte, error) {
    return fhevm.OpSstore(pc, interpreter.evm.FhevmEnvironment(), scope)
}

Step 6: update core/vm/interpreter.go

Update Config struct with new fields

IsEthCall               bool
IsGasEstimation         bool

Implements the GetMemory, GetStack and GetContract methods

func (s *ScopeContext) GetMemory() fhevm.Memory {
    return s.Memory
}

func (s *ScopeContext) GetStack() fhevm.Stack {
    return s.Stack
}

func (s *ScopeContext) GetContract() fhevm.Contract {
    return s.Contract
}

Update Run method

In:

func (in *EVMInterpreter) Run(contract *Contract, input []byte, readOnly bool) (ret []byte, err error)

Step 7: update core/vm/stack.go

Implement the following methods

func (st *Stack) Pop() uint256.Int {
    return st.pop()
}

func (st *Stack) Peek() *uint256.Int {
    return st.peek()
}

Step 8: update core/vm/operations_acl.go

Implement gas cost for storing a ciphertext

In func makeGasSStoreFunc(clearingRefund uint64) gasFunc {

Just before original := evm.StateDB.GetCommittedState(contract.Address(), x.Bytes32()), add this block to increase SSTORE gas cost for storing a ciphertext:

ct := fhevm.GetCiphertextFromMemory(evm.FhevmEnvironment(), value)
if ct != nil {
    cost += evm.fhevmEnvironment.params.GasCosts.FheStorageSstoreGas[ct.Type()]
}

Step 9: update internal/ethapi/api.go

• Add isGasEstimation, isEthCall bool arguments to func doCall and pass them in vm.Config during EVM creation:

evm, vmError := b.GetEVM(ctx, msg, state, header, &vm.Config{NoBaseFee: true, IsGasEstimation: isGasEstimation, IsEthCall: isEthCall}, &blockCtx)

• Add isGasEstimation, isEthCall bool arguments to func DoCall and forward them in the call to doCall

• Update usages of doCall and DoCall by simply setting IsEthCall to true when it’s a call, and IsGasEstimation to true when it’s estimating gas

Step 10: update graphql/graphql.go

Update usages of doCall and DoCall by simply setting IsEthCall to true when it’s a call, and IsGasEstimation to true when it’s estimating gas