以太坊原始碼分析(29)core-vm原始碼分析

尹成發表於2018-05-14
原始碼
## contract.go
contract 代表了以太坊 state database裡面的一個合約。包含了合約程式碼，呼叫引數。


結構
    
    // ContractRef is a reference to the contract's backing object
    type ContractRef interface {
        Address() common.Address
    }
    
    // AccountRef implements ContractRef.
    //
    // Account references are used during EVM initialisation and
    // it's primary use is to fetch addresses. Removing this object
    // proves difficult because of the cached jump destinations which
    // are fetched from the parent contract (i.e. the caller), which
    // is a ContractRef.
    type AccountRef common.Address
    
    // Address casts AccountRef to a Address
    func (ar AccountRef) Address() common.Address { return (common.Address)(ar) }
    
    // Contract represents an ethereum contract in the state database. It contains
    // the the contract code, calling arguments. Contract implements ContractRef
    type Contract struct {
        // CallerAddress is the result of the caller which initialised this
        // contract. However when the "call method" is delegated this value
        // needs to be initialised to that of the caller's caller.
        // CallerAddress是初始化這個合約的人。 如果是delegate，這個值被設定為呼叫者的呼叫者。
        CallerAddress common.Address
        caller ContractRef
        self ContractRef
    
        jumpdests destinations // result of JUMPDEST analysis. JUMPDEST指令的分析
    
        Code []byte //程式碼
        CodeHash common.Hash //程式碼的HASH
        CodeAddr *common.Address //程式碼地址
        Input []byte // 入參
    
        Gas uint64       // 合約還有多少Gas
        value *big.Int
    
        Args []byte //好像沒有使用
    
        DelegateCall bool
    }

構造
    
    // NewContract returns a new contract environment for the execution of EVM.
    func NewContract(caller ContractRef, object ContractRef, value *big.Int, gas uint64) *Contract {
        c := &Contract{CallerAddress: caller.Address(), caller: caller, self: object, Args: nil}
    
        if parent, ok := caller.(*Contract); ok {
            // Reuse JUMPDEST analysis from parent context if available.
            // 如果 caller 是一個合約，說明是合約呼叫了我們。 jumpdests設定為caller的jumpdests
            c.jumpdests = parent.jumpdests
        } else {
            c.jumpdests = make(destinations)
        }
    
        // Gas should be a pointer so it can safely be reduced through the run
        // This pointer will be off the state transition
        c.Gas = gas
        // ensures a value is set
        c.value = value
    
        return c
    }

AsDelegate將合約設定為委託呼叫並返回當前合同（用於鏈式呼叫）

    // AsDelegate sets the contract to be a delegate call and returns the current
    // contract (for chaining calls)
    func (c *Contract) AsDelegate() *Contract {
        c.DelegateCall = true
        // NOTE: caller must, at all times be a contract. It should never happen
        // that caller is something other than a Contract.
        parent := c.caller.(*Contract)
        c.CallerAddress = parent.CallerAddress
        c.value = parent.value
    
        return c
    }
        
GetOp 用來獲取下一跳指令
    
    // GetOp returns the n'th element in the contract's byte array
    func (c *Contract) GetOp(n uint64) OpCode {
        return OpCode(c.GetByte(n))
    }
    
    // GetByte returns the n'th byte in the contract's byte array
    func (c *Contract) GetByte(n uint64) byte {
        if n < uint64(len(c.Code)) {
            return c.Code[n]
        }
    
        return 0
    }

    // Caller returns the caller of the contract.
    //
    // Caller will recursively call caller when the contract is a delegate
    // call, including that of caller's caller.
    func (c *Contract) Caller() common.Address {
        return c.CallerAddress
    }
UseGas使用Gas。
    
    // UseGas attempts the use gas and subtracts it and returns true on success
    func (c *Contract) UseGas(gas uint64) (ok bool) {
        if c.Gas < gas {
            return false
        }
        c.Gas -= gas
        return true
    }
    
    // Address returns the contracts address
    func (c *Contract) Address() common.Address {
        return c.self.Address()
    }
    
    // Value returns the contracts value (sent to it from it's caller)
    func (c *Contract) Value() *big.Int {
        return c.value
    }
SetCode ，SetCallCode 設定程式碼。

    // SetCode sets the code to the contract
    func (self *Contract) SetCode(hash common.Hash, code []byte) {
        self.Code = code
        self.CodeHash = hash
    }
    
    // SetCallCode sets the code of the contract and address of the backing data
    // object
    func (self *Contract) SetCallCode(addr *common.Address, hash common.Hash, code []byte) {
        self.Code = code
        self.CodeHash = hash
        self.CodeAddr = addr
    }


## evm.go

結構


    // Context provides the EVM with auxiliary information. Once provided
    // it shouldn't be modified.
    // 上下文為EVM提供輔助資訊。 一旦提供，不應該修改。
    type Context struct {
        // CanTransfer returns whether the account contains
        // sufficient ether to transfer the value
        // CanTransfer 函式返回賬戶是否有足夠的ether用來轉賬
        CanTransfer CanTransferFunc
        // Transfer transfers ether from one account to the other
        // Transfer 用來從一個賬戶給另一個賬戶轉賬
        Transfer TransferFunc
        // GetHash returns the hash corresponding to n
        // GetHash用來返回入參n對應的hash值
        GetHash GetHashFunc
    
        // Message information
        // 用來提供Origin的資訊 sender的地址
        Origin common.Address // Provides information for ORIGIN
        // 用來提供GasPrice資訊
        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.
    // EVM是以太坊虛擬機器基礎物件，並提供必要的工具，以使用提供的上下文執行給定狀態的合約。
    // 應該指出的是，任何呼叫產生的任何錯誤都應該被認為是一種回滾修改狀態和消耗所有GAS操作，
    // 不應該執行對具體錯誤的檢查。 直譯器確保生成的任何錯誤都被認為是錯誤的程式碼。
    // 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
        // 當前的呼叫堆疊
        depth int
    
        // chainConfig contains information about the current chain
        // 包含了當前的區塊鏈的資訊
        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
    }

建構函式
    
    // 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)
    }


合約建立 Create 會建立一個新的合約。

    
    // 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) {
    
        // 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
        // 確保特定的地址沒有合約存在
        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) { //如果已經存在
            return nil, common.Address{}, 0, ErrContractAddressCollision
        }
        // Create a new account on the state
        snapshot := evm.StateDB.Snapshot() //建立一個StateDB的快照，以便回滾
        evm.StateDB.CreateAccount(contractAddr) //建立賬戶
        if evm.ChainConfig().IsEIP158(evm.BlockNumber) {
            evm.StateDB.SetNonce(contractAddr, 1) //設定nonce
        }
        evm.Transfer(evm.StateDB, caller.Address(), contractAddr, value) //轉賬
    
        // 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)
    
        if evm.vmConfig.NoRecursion && evm.depth > 0 {
            return nil, contractAddr, gas, nil
        }
        ret, err = run(evm, snapshot, contract, nil) //執行合約的初始化程式碼
        // check whether the max code size has been exceeded
        // 檢查初始化生成的程式碼的長度不超過限制
        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.
        //如果合同建立成功並且沒有錯誤返回，則計算儲存程式碼所需的GAS。 如果由於沒有足夠的GAS而導致程式碼不能被儲存設定錯誤，並通過下面的錯誤檢查條件來處理。
        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.
        // 當錯誤返回我們回滾修改，
        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
    }


Call方法, 無論我們轉賬或者是執行合約程式碼都會呼叫到這裡， 同時合約裡面的call指令也會執行到這裡。

    
    // 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.
    
    // Call 執行與給定的input作為引數與addr相關聯的合約。
    // 它還處理所需的任何必要的轉賬操作，並採取必要的步驟來建立帳戶
    // 並在任意錯誤的情況下回滾所做的操作。

    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
        // 呼叫深度最多1024
        if evm.depth > int(params.CallCreateDepth) {
            return nil, gas, ErrDepth
        }
        // Fail if we're trying to transfer more than the available balance
        // 檢視我們的賬戶是否有足夠的金錢。
        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) { // 檢視指定地址是否存在
            // 如果地址不存在，檢視是否是 native go的合約， native go的合約在
            // contracts.go 檔案裡面
            precompiles := PrecompiledContractsHomestead
            if evm.ChainConfig().IsByzantium(evm.BlockNumber) {
                precompiles = PrecompiledContractsByzantium
            }
            if precompiles[addr] == nil && evm.ChainConfig().IsEIP158(evm.BlockNumber) && value.Sign() == 0 {
                // 如果不是指定的合約地址， 並且value的值為0那麼返回正常，而且這次呼叫沒有消耗Gas
                return nil, gas, nil
            }
            // 負責在本地狀態建立addr
            evm.StateDB.CreateAccount(addr)
        }
        // 執行轉賬
        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 {
                // 如果是由revert指令觸發的錯誤，因為ICO一般設定了人數限制或者資金限制
                // 在大家搶購的時候很可能會觸發這些限制條件，導致被抽走不少錢。這個時候
                // 又不能設定比較低的GasPrice和GasLimit。因為要速度快。
                // 那麼不會使用剩下的全部Gas，而是隻會使用程式碼執行的Gas
                // 不然會被抽走 GasLimit *GasPrice的錢，那可不少。
                contract.UseGas(contract.Gas)
            }
        }
        return ret, contract.Gas, err
    }


剩下的三個函式 CallCode, DelegateCall, 和 StaticCall，這三個函式不能由外部呼叫，只能由Opcode觸發。


CallCode

    // CallCode differs from Call in the sense that it executes the given address'
    // code with the caller as context.
    // CallCode與Call不同的地方在於它使用caller的context來執行給定地址的程式碼。
    
    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()) //這裡是最不同的地方 to的地址被修改為caller的地址了 而且沒有轉賬的行為
        )
        // 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

    // 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.
    // DelegateCall 和 CallCode不同的地方在於 caller被設定為 caller的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
        // 標識為AsDelete()
        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.
    // StaticCall不允許執行任何修改狀態的操作，
    
    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
    }




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