path: root/core/vm/evm.go

// Copyright 2014 The go-ethereum Authors
// This file is part of the go-ethereum library.
//
// The go-ethereum library is free software: you can redistribute it and/or modify
// it under the terms of the GNU Lesser General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// The go-ethereum library is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
// GNU Lesser General Public License for more details.
//
// You should have received a copy of the GNU Lesser General Public License
// along with the go-ethereum library. If not, see <http://www.gnu.org/licenses/>.

package vm

import (
    "math/big"
    "sync/atomic"

    "github.com/ethereum/go-ethereum/common"
    "github.com/ethereum/go-ethereum/crypto"
    "github.com/ethereum/go-ethereum/params"
)

// emptyCodeHash is used by create to ensure deployment is disallowed to already
// deployed contract addresses (relevant after the account abstraction).
var emptyCodeHash = crypto.Keccak256Hash(nil)

type (
    CanTransferFunc func(StateDB, common.Address, *big.Int) bool
    TransferFunc    func(StateDB, common.Address, common.Address, *big.Int)
    // GetHashFunc returns the nth block hash in the blockchain
    // and is used by the BLOCKHASH EVM op code.
    GetHashFunc func(uint64) common.Hash
)

// run runs the given contract and takes care of running precompiles with a fallback to the byte code interpreter.
func run(evm *EVM, snapshot int, contract *Contract, input []byte) ([]byte, error) {
    if contract.CodeAddr != nil {
        precompiles := PrecompiledContractsHomestead
        if evm.ChainConfig().IsMetropolis(evm.BlockNumber) {
            precompiles = PrecompiledContractsMetropolis
        }
        if p := precompiles[*contract.CodeAddr]; p != nil {
            return RunPrecompiledContract(p, input, contract)
        }
    }
    return evm.interpreter.Run(snapshot, contract, input)
}

// Context provides the EVM with auxiliary information. Once provided
// it shouldn't be modified.
type Context struct {
    // CanTransfer returns whether the account contains
    // sufficient ether to transfer the value
    CanTransfer CanTransferFunc
    // Transfer transfers ether from one account to the other
    Transfer TransferFunc
    // GetHash returns the hash corresponding to n
    GetHash GetHashFunc

    // Message information
    Origin   common.Address // Provides information for ORIGIN
    GasPrice *big.Int       // Provides information for GASPRICE

    // Block information
    Coinbase    common.Address // Provides information for COINBASE
    GasLimit    *big.Int       // Provides information for GASLIMIT
    BlockNumber *big.Int       // Provides information for NUMBER
    Time        *big.Int       // Provides information for TIME
    Difficulty  *big.Int       // Provides information for DIFFICULTY
}

// EVM is the Ethereum Virtual Machine base object and provides
// the necessary tools to run a contract on the given state with
// the provided context. It should be noted that any error
// generated through any of the calls should be considered a
// revert-state-and-consume-all-gas operation, no checks on
// specific errors should ever be performed. The interpreter makes
// sure that any errors generated are to be considered faulty code.
//
// The EVM should never be reused and is not thread safe.
type EVM struct {
    // Context provides auxiliary blockchain related information
    Context
    // StateDB gives access to the underlying state
    StateDB StateDB
    // Depth is the current call stack
    depth int

    // chainConfig contains information about the current chain
    chainConfig *params.ChainConfig
    // chain rules contains the chain rules for the current epoch
    chainRules params.Rules
    // virtual machine configuration options used to initialise the
    // evm.
    vmConfig Config
    // global (to this context) ethereum virtual machine
    // used throughout the execution of the tx.
    interpreter *Interpreter
    // abort is used to abort the EVM calling operations
    // NOTE: must be set atomically
    abort int32
}

// NewEVM retutrns a new EVM . The returned EVM is not thread safe and should
// only ever be used *once*.
func NewEVM(ctx Context, statedb StateDB, chainConfig *params.ChainConfig, vmConfig Config) *EVM {
    evm := &EVM{
        Context:     ctx,
        StateDB:     statedb,
        vmConfig:    vmConfig,
        chainConfig: chainConfig,
        chainRules:  chainConfig.Rules(ctx.BlockNumber),
    }

    evm.interpreter = NewInterpreter(evm, vmConfig)
    return evm
}

// Cancel cancels any running EVM operation. This may be called concurrently and
// it's safe to be called multiple times.
func (evm *EVM) Cancel() {
    atomic.StoreInt32(&evm.abort, 1)
}

// Call executes the contract associated with the addr with the given input as
// parameters. It also handles any necessary value transfer required and takes
// the necessary steps to create accounts and reverses the state in case of an
// execution error or failed value transfer.
func (evm *EVM) Call(caller ContractRef, addr common.Address, input []byte, gas uint64, value *big.Int) (ret []byte, leftOverGas uint64, err error) {
    if evm.vmConfig.NoRecursion && evm.depth > 0 {
        return nil, gas, nil
    }

    // Fail if we're trying to execute above the call depth limit
    if evm.depth > int(params.CallCreateDepth) {
        return nil, gas, ErrDepth
    }
    // Fail if we're trying to transfer more than the available balance
    if !evm.Context.CanTransfer(evm.StateDB, caller.Address(), value) {
        return nil, gas, ErrInsufficientBalance
    }

    var (
        to       = AccountRef(addr)
        snapshot = evm.StateDB.Snapshot()
    )
    if !evm.StateDB.Exist(addr) {
        precompiles := PrecompiledContractsHomestead
        if evm.ChainConfig().IsMetropolis(evm.BlockNumber) {
            precompiles = PrecompiledContractsMetropolis
        }
        if precompiles[addr] == nil && evm.ChainConfig().IsEIP158(evm.BlockNumber) && value.Sign() == 0 {
            return nil, gas, nil
        }
        evm.StateDB.CreateAccount(addr)
    }
    evm.Transfer(evm.StateDB, caller.Address(), to.Address(), value)

    // initialise a new contract and set the code that is to be used by the
    // E The contract is a scoped environment for this execution context
    // only.
    contract := NewContract(caller, to, value, gas)
    contract.SetCallCode(&addr, evm.StateDB.GetCodeHash(addr), evm.StateDB.GetCode(addr))

    ret, err = run(evm, snapshot, contract, input)
    // When an error was returned by the EVM or when setting the creation code
    // above we revert to the snapshot and consume any gas remaining. Additionally
    // when we're in homestead this also counts for code storage gas errors.
    if err != nil {
        evm.StateDB.RevertToSnapshot(snapshot)
        if err != errExecutionReverted {
            contract.UseGas(contract.Gas)
        }
    }
    return ret, contract.Gas, err
}

// CallCode executes the contract associated with the addr with the given input
// as parameters. It also handles any necessary value transfer required and takes
// the necessary steps to create accounts and reverses the state in case of an
// execution error or failed value transfer.
//
// CallCode differs from Call in the sense that it executes the given address'
// code with the caller as context.
func (evm *EVM) CallCode(caller ContractRef, addr common.Address, input []byte, gas uint64, value *big.Int) (ret []byte, leftOverGas uint64, err error) {
    if evm.vmConfig.NoRecursion && evm.depth > 0 {
        return nil, gas, nil
    }

    // Fail if we're trying to execute above the call depth limit
    if evm.depth > int(params.CallCreateDepth) {
        return nil, gas, ErrDepth
    }
    // Fail if we're trying to transfer more than the available balance
    if !evm.CanTransfer(evm.StateDB, caller.Address(), value) {
        return nil, gas, ErrInsufficientBalance
    }

    var (
        snapshot = evm.StateDB.Snapshot()
        to       = AccountRef(caller.Address())
    )
    // initialise a new contract and set the code that is to be used by the
    // E The contract is a scoped evmironment for this execution context
    // only.
    contract := NewContract(caller, to, value, gas)
    contract.SetCallCode(&addr, evm.StateDB.GetCodeHash(addr), evm.StateDB.GetCode(addr))

    ret, err = run(evm, snapshot, contract, input)
    if err != nil {
        evm.StateDB.RevertToSnapshot(snapshot)
        if err != errExecutionReverted {
            contract.UseGas(contract.Gas)
        }
    }
    return ret, contract.Gas, err
}

// DelegateCall executes the contract associated with the addr with the given input
// as parameters. It reverses the state in case of an execution error.
//
// DelegateCall differs from CallCode in the sense that it executes the given address'
// code with the caller as context and the caller is set to the caller of the caller.
func (evm *EVM) DelegateCall(caller ContractRef, addr common.Address, input []byte, gas uint64) (ret []byte, leftOverGas uint64, err error) {
    if evm.vmConfig.NoRecursion && evm.depth > 0 {
        return nil, gas, nil
    }
    // Fail if we're trying to execute above the call depth limit
    if evm.depth > int(params.CallCreateDepth) {
        return nil, gas, ErrDepth
    }

    var (
        snapshot = evm.StateDB.Snapshot()
        to       = AccountRef(caller.Address())
    )

    // Initialise a new contract and make initialise the delegate values
    contract := NewContract(caller, to, nil, gas).AsDelegate()
    contract.SetCallCode(&addr, evm.StateDB.GetCodeHash(addr), evm.StateDB.GetCode(addr))

    ret, err = run(evm, snapshot, contract, input)
    if err != nil {
        evm.StateDB.RevertToSnapshot(snapshot)
        if err != errExecutionReverted {
            contract.UseGas(contract.Gas)
        }
    }
    return ret, contract.Gas, err
}

// StaticCall executes the contract associated with the addr with the given input
// as parameters while disallowing any modifications to the state during the call.
// Opcodes that attempt to perform such modifications will result in exceptions
// instead of performing the modifications.
func (evm *EVM) StaticCall(caller ContractRef, addr common.Address, input []byte, gas uint64) (ret []byte, leftOverGas uint64, err error) {
    if evm.vmConfig.NoRecursion && evm.depth > 0 {
        return nil, gas, nil
    }
    // Fail if we're trying to execute above the call depth limit
    if evm.depth > int(params.CallCreateDepth) {
        return nil, gas, ErrDepth
    }
    // Make sure the readonly is only set if we aren't in readonly yet
    // this makes also sure that the readonly flag isn't removed for
    // child calls.
    if !evm.interpreter.readOnly {
        evm.interpreter.readOnly = true
        defer func() { evm.interpreter.readOnly = false }()
    }

    var (
        to       = AccountRef(addr)
        snapshot = evm.StateDB.Snapshot()
    )
    // Initialise a new contract and set the code that is to be used by the
    // EVM. The contract is a scoped environment for this execution context
    // only.
    contract := NewContract(caller, to, new(big.Int), gas)
    contract.SetCallCode(&addr, evm.StateDB.GetCodeHash(addr), evm.StateDB.GetCode(addr))

    // When an error was returned by the EVM or when setting the creation code
    // above we revert to the snapshot and consume any gas remaining. Additionally
    // when we're in Homestead this also counts for code storage gas errors.
    ret, err = run(evm, snapshot, contract, input)
    if err != nil {
        evm.StateDB.RevertToSnapshot(snapshot)
        if err != errExecutionReverted {
            contract.UseGas(contract.Gas)
        }
    }
    return ret, contract.Gas, err
}

// Create creates a new contract using code as deployment code.
func (evm *EVM) Create(caller ContractRef, code []byte, gas uint64, value *big.Int) (ret []byte, contractAddr common.Address, leftOverGas uint64, err error) {
    if evm.vmConfig.NoRecursion && evm.depth > 0 {
        return nil, common.Address{}, gas, nil
    }

    // Depth check execution. Fail if we're trying to execute above the
    // limit.
    if evm.depth > int(params.CallCreateDepth) {
        return nil, common.Address{}, gas, ErrDepth
    }
    if !evm.CanTransfer(evm.StateDB, caller.Address(), value) {
        return nil, common.Address{}, gas, ErrInsufficientBalance
    }
    // Ensure there's no existing contract already at the designated address
    nonce := evm.StateDB.GetNonce(caller.Address())
    evm.StateDB.SetNonce(caller.Address(), nonce+1)

    contractAddr = crypto.CreateAddress(caller.Address(), nonce)
    contractHash := evm.StateDB.GetCodeHash(contractAddr)
    if evm.StateDB.GetNonce(contractAddr) != 0 || (contractHash != (common.Hash{}) && contractHash != emptyCodeHash) {
        return nil, common.Address{}, 0, ErrContractAddressCollision
    }
    // Create a new account on the state
    snapshot := evm.StateDB.Snapshot()
    evm.StateDB.CreateAccount(contractAddr)
    if evm.ChainConfig().IsEIP158(evm.BlockNumber) {
        evm.StateDB.SetNonce(contractAddr, 1)
    }
    evm.Transfer(evm.StateDB, caller.Address(), contractAddr, value)

    // initialise a new contract and set the code that is to be used by the
    // E The contract is a scoped evmironment for this execution context
    // only.
    contract := NewContract(caller, AccountRef(contractAddr), value, gas)
    contract.SetCallCode(&contractAddr, crypto.Keccak256Hash(code), code)

    ret, err = run(evm, snapshot, contract, nil)
    // check whether the max code size has been exceeded
    maxCodeSizeExceeded := evm.ChainConfig().IsEIP158(evm.BlockNumber) && len(ret) > params.MaxCodeSize
    // if the contract creation ran successfully and no errors were returned
    // calculate the gas required to store the code. If the code could not
    // be stored due to not enough gas set an error and let it be handled
    // by the error checking condition below.
    if err == nil && !maxCodeSizeExceeded {
        createDataGas := uint64(len(ret)) * params.CreateDataGas
        if contract.UseGas(createDataGas) {
            evm.StateDB.SetCode(contractAddr, ret)
        } else {
            err = ErrCodeStoreOutOfGas
        }
    }

    // When an error was returned by the EVM or when setting the creation code
    // above we revert to the snapshot and consume any gas remaining. Additionally
    // when we're in homestead this also counts for code storage gas errors.
    if maxCodeSizeExceeded || (err != nil && (evm.ChainConfig().IsHomestead(evm.BlockNumber) || err != ErrCodeStoreOutOfGas)) {
        evm.StateDB.RevertToSnapshot(snapshot)
        if err != errExecutionReverted {
            contract.UseGas(contract.Gas)
        }
    }
    // Assign err if contract code size exceeds the max while the err is still empty.
    if maxCodeSizeExceeded && err == nil {
        err = errMaxCodeSizeExceeded
    }
    return ret, contractAddr, contract.Gas, err
}

// ChainConfig returns the evmironment's chain configuration
func (evm *EVM) ChainConfig() *params.ChainConfig { return evm.chainConfig }

// Interpreter returns the EVM interpreter
func (evm *EVM) Interpreter() *Interpreter { return evm.interpreter }