jumptable. 是一个 [256]operation 的数据结构. 每个下标对应了一种指令, 使用operation来存储了指令对应的处理逻辑, gas消耗, 堆栈验证方法, memory使用的大小等功能.
数据结构operation存储了一条指令的所需要的函数.
type operation struct {
// op is the operation function 执行函数
execute executionFunc
// gasCost is the gas function and returns the gas required for execution gas消耗函数
gasCost gasFunc
// validateStack validates the stack (size) for the operation 堆栈大小验证函数
validateStack stackValidationFunc
// memorySize returns the memory size required for the operation 需要的内存大小
memorySize memorySizeFunc
halts bool // indicates whether the operation shoult halt further execution 表示操作是否停止进一步执行
jumps bool // indicates whether the program counter should not increment 指示程序计数器是否不增加
writes bool // determines whether this a state modifying operation 确定这是否是一个状态修改操作
valid bool // indication whether the retrieved operation is valid and known 指示检索到的操作是否有效并且已知
reverts bool // determines whether the operation reverts state (implicitly halts)确定操作是否恢复状态（隐式停止）
returns bool // determines whether the opertions sets the return data content 确定操作是否设置了返回数据内容
}
指令集, 下面定义了三种指令集,针对三种不同的以太坊版本,
var ( frontierInstructionSet = NewFrontierInstructionSet() homesteadInstructionSet = NewHomesteadInstructionSet() byzantiumInstructionSet = NewByzantiumInstructionSet() )
NewByzantiumInstructionSet 拜占庭版本首先调用NewHomesteadInstructionSet创造了前一个版本的指令,然后增加自己特有的指令.STATICCALL ,RETURNDATASIZE ,RETURNDATACOPY ,REVERT
// NewByzantiumInstructionSet returns the frontier, homestead and
// byzantium instructions.
func NewByzantiumInstructionSet() [256]operation {
// instructions that can be executed during the homestead phase.
instructionSet := NewHomesteadInstructionSet()
instructionSet[STATICCALL] = operation{
execute: opStaticCall,
gasCost: gasStaticCall,
validateStack: makeStackFunc(6, 1),
memorySize: memoryStaticCall,
valid: true,
returns: true,
}
instructionSet[RETURNDATASIZE] = operation{
execute: opReturnDataSize,
gasCost: constGasFunc(GasQuickStep),
validateStack: makeStackFunc(0, 1),
valid: true,
}
instructionSet[RETURNDATACOPY] = operation{
execute: opReturnDataCopy,
gasCost: gasReturnDataCopy,
validateStack: makeStackFunc(3, 0),
memorySize: memoryReturnDataCopy,
valid: true,
}
instructionSet[REVERT] = operation{
execute: opRevert,
gasCost: gasRevert,
validateStack: makeStackFunc(2, 0),
memorySize: memoryRevert,
valid: true,
reverts: true,
returns: true,
}
return instructionSet
}
NewHomesteadInstructionSet
// NewHomesteadInstructionSet returns the frontier and homestead
// instructions that can be executed during the homestead phase.
func NewHomesteadInstructionSet() [256]operation {
instructionSet := NewFrontierInstructionSet()
instructionSet[DELEGATECALL] = operation{
execute: opDelegateCall,
gasCost: gasDelegateCall,
validateStack: makeStackFunc(6, 1),
memorySize: memoryDelegateCall,
valid: true,
returns: true,
}
return instructionSet
}
因为指令很多,所以不一一列出来, 只列举几个例子. 虽然组合起来的功能可以很复杂,但是单个指令来说,还是比较直观的.
func opPc(pc *uint64, evm *EVM, contract *Contract, memory *Memory, stack *Stack) ([]byte, error) {
stack.push(evm.interpreter.intPool.get().SetUint64(*pc))
return nil, nil
}
func opMsize(pc *uint64, evm *EVM, contract *Contract, memory *Memory, stack *Stack) ([]byte, error) {
stack.push(evm.interpreter.intPool.get().SetInt64(int64(memory.Len())))
return nil, nil
}
gas_table返回了各种指令消耗的gas的函数 这个函数的返回值基本上只有errGasUintOverflow 整数溢出的错误.
func gasBalance(gt params.GasTable, evm *EVM, contract *Contract, stack *Stack, mem *Memory, memorySize uint64) (uint64, error) {
return gt.Balance, nil
}
func gasExtCodeSize(gt params.GasTable, evm *EVM, contract *Contract, stack *Stack, mem *Memory, memorySize uint64) (uint64, error) {
return gt.ExtcodeSize, nil
}
func gasSLoad(gt params.GasTable, evm *EVM, contract *Contract, stack *Stack, mem *Memory, memorySize uint64) (uint64, error) {
return gt.SLoad, nil
}
func gasExp(gt params.GasTable, evm *EVM, contract *Contract, stack *Stack, mem *Memory, memorySize uint64) (uint64, error) {
expByteLen := uint64((stack.data[stack.len()-2].BitLen() + 7) / 8)
var (
gas = expByteLen * gt.ExpByte // no overflow check required. Max is 256 * ExpByte gas
overflow bool
)
if gas, overflow = math.SafeAdd(gas, GasSlowStep); overflow {
return 0, errGasUintOverflow
}
return gas, nil
}
数据结构
// Config are the configuration options for the Interpreter
type Config struct {
// Debug enabled debugging Interpreter options
Debug bool
// EnableJit enabled the JIT VM
EnableJit bool
// ForceJit forces the JIT VM
ForceJit bool
// Tracer is the op code logger
Tracer Tracer
// NoRecursion disabled Interpreter call, callcode,
// delegate call and create.
NoRecursion bool
// Disable gas metering
DisableGasMetering bool
// Enable recording of SHA3/keccak preimages
EnablePreimageRecording bool
// JumpTable contains the EVM instruction table. This
// may be left uninitialised and will be set to the default
// table.
JumpTable [256]operation
}
// Interpreter is used to run Ethereum based contracts and will utilise the
// passed evmironment to query external sources for state information.
// The Interpreter will run the byte code VM or JIT VM based on the passed
// configuration.
type Interpreter struct {
evm *EVM
cfg Config
gasTable params.GasTable // 标识了很多操作的Gas价格
intPool *intPool
readOnly bool // Whether to throw on stateful modifications
returnData []byte // Last CALL's return data for subsequent reuse 最后一个函数的返回值
}
构造函数
// NewInterpreter returns a new instance of the Interpreter.
func NewInterpreter(evm *EVM, cfg Config) *Interpreter {
// We use the STOP instruction whether to see
// the jump table was initialised. If it was not
// we'll set the default jump table.
// 用一个STOP指令测试JumpTable是否已经被初始化了, 如果没有被初始化,那么设置为默认值
if !cfg.JumpTable[STOP].valid {
switch {
case evm.ChainConfig().IsByzantium(evm.BlockNumber):
cfg.JumpTable = byzantiumInstructionSet
case evm.ChainConfig().IsHomestead(evm.BlockNumber):
cfg.JumpTable = homesteadInstructionSet
default:
cfg.JumpTable = frontierInstructionSet
}
}
return &Interpreter{
evm: evm,
cfg: cfg,
gasTable: evm.ChainConfig().GasTable(evm.BlockNumber),
intPool: newIntPool(),
}
}
解释器一共就两个方法enforceRestrictions方法和Run方法.
func (in *Interpreter) enforceRestrictions(op OpCode, operation operation, stack *Stack) error {
if in.evm.chainRules.IsByzantium {
if in.readOnly {
// If the interpreter is operating in readonly mode, make sure no
// state-modifying operation is performed. The 3rd stack item
// for a call operation is the value. Transferring value from one
// account to the others means the state is modified and should also
// return with an error.
if operation.writes || (op == CALL && stack.Back(2).BitLen() > 0) {
return errWriteProtection
}
}
}
return nil
}
// Run loops and evaluates the contract's code with the given input data and returns
// the return byte-slice and an error if one occurred.
// 用给定的入参循环执行合约的代码，并返回返回的字节片段，如果发生错误则返回错误。
// It's important to note that any errors returned by the interpreter should be
// considered a revert-and-consume-all-gas operation. No error specific checks
// should be handled to reduce complexity and errors further down the in.
// 重要的是要注意，解释器返回的任何错误都会消耗全部gas。 为了减少复杂性,没有特别的错误处理流程。
func (in *Interpreter) Run(snapshot int, contract *Contract, input []byte) (ret []byte, err error) {
// Increment the call depth which is restricted to 1024
in.evm.depth++
defer func() { in.evm.depth-- }()
// Reset the previous call's return data. It's unimportant to preserve the old buffer
// as every returning call will return new data anyway.
in.returnData = nil
// Don't bother with the execution if there's no code.
if len(contract.Code) == 0 {
return nil, nil
}
codehash := contract.CodeHash // codehash is used when doing jump dest caching
if codehash == (common.Hash{}) {
codehash = crypto.Keccak256Hash(contract.Code)
}
var (
op OpCode // current opcode
mem = NewMemory() // bound memory
stack = newstack() // local stack
// For optimisation reason we're using uint64 as the program counter.
// It's theoretically possible to go above 2^64. The YP defines the PC
// to be uint256. Practically much less so feasible.
pc = uint64(0) // program counter
cost uint64
// copies used by tracer
stackCopy = newstack() // stackCopy needed for Tracer since stack is mutated by 63/64 gas rule
pcCopy uint64 // needed for the deferred Tracer
gasCopy uint64 // for Tracer to log gas remaining before execution
logged bool // deferred Tracer should ignore already logged steps
)
contract.Input = input
defer func() {
if err != nil && !logged && in.cfg.Debug {
in.cfg.Tracer.CaptureState(in.evm, pcCopy, op, gasCopy, cost, mem, stackCopy, contract, in.evm.depth, err)
}
}()
// The Interpreter main run loop (contextual). This loop runs until either an
// explicit STOP, RETURN or SELFDESTRUCT is executed, an error occurred during
// the execution of one of the operations or until the done flag is set by the
// parent context.
// 解释器的主要循环， 直到遇到STOP，RETURN，SELFDESTRUCT指令被执行，或者是遇到任意错误，或者说done 标志被父context设置。
for atomic.LoadInt32(&in.evm.abort) == 0 {
// Get the memory location of pc
// 难道下一个需要执行的指令
op = contract.GetOp(pc)
if in.cfg.Debug {
logged = false
pcCopy = uint64(pc)
gasCopy = uint64(contract.Gas)
stackCopy = newstack()
for _, val := range stack.data {
stackCopy.push(val)
}
}
// get the operation from the jump table matching the opcode
// 通过JumpTable拿到对应的operation
operation := in.cfg.JumpTable[op]
// 这里检查了只读模式下面不能执行writes指令
// staticCall的情况下会设置为readonly模式
if err := in.enforceRestrictions(op, operation, stack); err != nil {
return nil, err
}
// if the op is invalid abort the process and return an error
if !operation.valid { //检查指令是否非法
return nil, fmt.Errorf("invalid opcode 0x%x", int(op))
}
// validate the stack and make sure there enough stack items available
// to perform the operation
// 检查是否有足够的堆栈空间。 包括入栈和出栈
if err := operation.validateStack(stack); err != nil {
return nil, err
}
var memorySize uint64
// calculate the new memory size and expand the memory to fit
// the operation
if operation.memorySize != nil { // 计算内存使用量，需要收费
memSize, overflow := bigUint64(operation.memorySize(stack))
if overflow {
return nil, errGasUintOverflow
}
// memory is expanded in words of 32 bytes. Gas
// is also calculated in words.
if memorySize, overflow = math.SafeMul(toWordSize(memSize), 32); overflow {
return nil, errGasUintOverflow
}
}
if !in.cfg.DisableGasMetering { //这个参数在本地模拟执行的时候比较有用，可以不消耗或者检查GAS执行交易并得到返回结果
// consume the gas and return an error if not enough gas is available.
// cost is explicitly set so that the capture state defer method cas get the proper cost
// 计算gas的Cost 并使用，如果不够，就返回OutOfGas错误。
cost, err = operation.gasCost(in.gasTable, in.evm, contract, stack, mem, memorySize)
if err != nil || !contract.UseGas(cost) {
return nil, ErrOutOfGas
}
}
if memorySize > 0 { //扩大内存范围
mem.Resize(memorySize)
}
if in.cfg.Debug {
in.cfg.Tracer.CaptureState(in.evm, pc, op, gasCopy, cost, mem, stackCopy, contract, in.evm.depth, err)
logged = true
}
// execute the operation
// 执行命令
res, err := operation.execute(&pc, in.evm, contract, mem, stack)
// verifyPool is a build flag. Pool verification makes sure the integrity
// of the integer pool by comparing values to a default value.
if verifyPool {
verifyIntegerPool(in.intPool)
}
// if the operation clears the return data (e.g. it has returning data)
// set the last return to the result of the operation.
if operation.returns { //如果有返回值，那么就设置返回值。 注意只有最后一个返回有效果。
in.returnData = res
}
switch {
case err != nil:
return nil, err
case operation.reverts:
return res, errExecutionReverted
case operation.halts:
return res, nil
case !operation.jumps:
pc++
}
}
return nil, nil
}