gas.md
July 29, 2018 · View on GitHub
gas
Gas, 是Ethereum里对所有活动进行消耗资源计量的单位。这里的活动是泛化的概念，包括但不限于：转帐，合约的创建，合约指令的执行，执行中内存的扩展等等。所以Gas可以想象成现实中的汽油或者燃气。Gas是Ethereum系统的血液。一切资源，活动，交互的开销，都以Gas为计量单元。如果定义了一个GasPrice，那么所有的Gas消耗亦可等价于以太币Ether。
关于 gas 的计算:
// schema: [opcode, pop, push, gasUsed, halts, jumps, writes, valid, reverts, returns]
halts bool // 是否会停止之后的执行
jumps bool // pc计数器是否需要增长
writes bool // 是否会修改state
valid bool // 是否是合法的操作
reverts bool // 是否会revert state会隐式地停止之后的操作
returns bool // 是否会返回数据
// 没有填写的均为false
var opcodes = {
// arithmetic
0x00: ["STOP", 0, 0, 0, halts: true, valid: true], // 不对栈进行操作，停止执行代码
0x01: ["ADD", 2, 1, 3, valid: true], // 取出栈顶两个元素x,*y（x表示pop，*y表示返回栈顶元素指针，以下均同此）,y = x + *y
0x02: ["MUL", 2, 1, 5, valid: true], // 取出栈顶两个元素x,y，push(x*y)
0x03: ["SUB", 2, 1, 3, valid: true], // 取出栈顶两个元素x,*y，y = x - *y
0x04: ["DIV", 2, 1, 5, valid: true], // 取出栈顶两个元素x，*y，y = x / *y
0x05: ["SDIV", 2, 1, 5, valid: true], // x, y;TODO
0x06: ["MOD", 2, 1, 5, valid: true], // x, y; push x % y
0x07: ["SMOD", 2, 1, 5, valid: true], // TODO
0x08: ["ADDMOD", 3, 1, 8, valid: true], // x, y, z; push (x + y) % z
0x09: ["MULMOD", 3, 1, 8, valid: true], // x, y, z; push (x * y) % z
0x0a: ["EXP", 2, 1, gasExp, valid: true], // evm-tools中显示为10; x, y; push x ^ y
0x0b: ["SIGNEXTEND", 2, 1, 5, valid: true], // x; TODO
// boolean
0x10: ["LT", 2, 1, 3, valid: true], // x, *y; if x < *y; *y = 1; else *y = 0;
0x11: ["GT", 2, 1, 3, valid: true], // x, *y; if x > *y; *y = 1; else *y = 0;
0x12: ["SLT", 2, 1, 3, valid: true], // x, *y;TODO
0x13: ["SGT", 2, 1, 3, valid: true], // x, *y:TODO
0x14: ["EQ", 2, 1, 3, valid: true], // x, *y; if x == *y *y = 1; else *y = 0;
0x15: ["ISZERO", 1, 1, 3, valid: true], // *x; if *x > 0 ; *x = 0; else *x = 1;
0x16: ["AND", 2, 1, 3, valid: true], // x, y; push x and y
0x17: ["OR", 2, 1, 3, valid: true], // x, *y; *y = x or *y
0x18: ["XOR", 2, 1, 3, valid: true], // x, *y; *y = x xor *y
0x19: ["NOT", 1, 1, 3, valid: true], // *x; *x = not *x
0x1a: ["BYTE", 2, 1, 3, valid: true], // x, *y; TODO
0x1b: ["SHL", 2, 1, 3], //
0x1c: ["SHR", 2, 1, 3],
0x1d: ["SAR", 2, 1, 3],
// crypto
0x20: ["SHA3", 2, 1, gasSha3, valid: true], // evm-tools中显示为30; x, y; data = memory(offset: x, size: y), push Hash(data)
// contract context
0x30: ["ADDRESS", 0, 1, 2, valid: true], // push contract.address
0x31: ["BALANCE", 1, 1, 400, valid: true], // Homestead为20；EIP150/EIP158为400； *x; *x = balance(*x);
0x32: ["ORIGIN", 0, 1, 2, valid: true], // push origin
0x33: ["CALLER", 0, 1, 2, valid: true], // push caller
0x34: ["CALLVALUE", 0, 1, 2, valid: true], // push contract.value
0x35: ["CALLDATALOAD", 1, 1, 3, valid: true], // x; inputData[x:x+32],inputData需先转为byte数组
0x36: ["CALLDATASIZE", 0, 1, 2, valid: true], // push input.length
0x37: ["CALLDATACOPY", 3, 0, gasCallDataCopy, valid: true], // evm-tools中显示为3; x, y, z;memory[x:x+z] = inputData[y:y+z]
0x38: ["CODESIZE", 0, 1, 2, valid: true], // push contract.code.length
0x39: ["CODECOPY", 3, 0, gasCodeCopy, valid: true], // evm-tool中显示为3; x, y, z;memory[x: x+z]=code[y:y+z]
0x3a: ["GASPRICE", 0, 1, 2, valid: true], // push gasPrice
0x3b: ["EXTCODESIZE", 1, 1, 700, valid: true], // Homestead为20；EIP150/EIP158为700；*x; *x = codesize(*x)
0x3c: ["EXTCODECOPY", 4, 0, gasExtCodeCopy, valid: true], // evm-tools中显示为20;x, y, z, g; memory[y:y+g] = code(x)[z:z+g]
0x3d: ["RETURNDATASIZE", 0, 1, 2, valid: true], // push len(returnData)
0x3f: ["RETURNDATACOPY", 3, 0, gasReturnDataCopy, valid: true], // x, y, z; memeory[x:x+z] = returnData[y:y+z];
// blockchain context
0x40: ["BLOCKHASH", 1, 1, 20, valid: true], // x; push(hash(x));x必须在最近的257块之内
0x41: ["COINBASE", 0, 1, 2, valid: true], // push coinbase
0x42: ["TIMESTAMP", 0, 1, 2, valid: true], // push time
0x43: ["NUMBER", 0, 1, 2, valid: true], // push blockNumber
0x44: ["DIFFICULTY", 0, 1, 2, valid: true], // push difficulty
0x45: ["GASLIMIT", 0, 1, 2, valid: true], // push gasLimit
// storage and execution
0x50: ["POP", 1, 0, 2, valid: true], // x;
0x51: ["MLOAD", 1, 1, gasMLoad, valid: true], // evm-tools中显示为3; x; push memory[x:x+32]
0x52: ["MSTORE", 2, 0, gasMStore, valid: true], // evm-tools中显示为3; x, y; memory[x:x+32] = y;
0x53: ["MSTORE8", 2, 0, gasMStore8, valid: true], // evm-tools中显示为3; x, y; memory[x] = y;
0x54: ["SLOAD", 1, 1, 200, valid: true], // Homestead为50；EIP150/EIP158为200； x; push( stateOf(hash(x)) );
0x55: ["SSTORE", 2, 0, gasSStore, writes: true, valid: true], // evm-tools中显示为0; x, y; setState(hash(x), hash(y));
0x56: ["JUMP", 1, 0, 8, jumps: true, valid: true], // pos; pc = pos;
0x57: ["JUMPI", 2, 0, 10, valid: true], // pos, cond; if cond != 0 pc = pos; else pc++;
0x58: ["PC", 0, 1, 2, valid: true], // push pc;
0x59: ["MSIZE", 0, 1, 2, valid: true], // push memory.length
0x5a: ["GAS", 0, 1, 2, valid: true], // push contract.gas
0x5b: ["JUMPDEST", 0, 0, 1, valid: true], // do nothing
// logging
0xa0: ["LOG0", 2, 0, makeGasLog(0), writes: true, valid: true], // evm-tools中显示为375
0xa1: ["LOG1", 3, 0, makeGasLog(1), writes: true, valid: true], // evm-tools中显示为750
0xa2: ["LOG2", 4, 0, makeGasLog(2), writes: true, valid: true], // evm-tools中显示为1125
0xa3: ["LOG3", 5, 0, makeGasLog(3), writes: true, valid: true], // evm-tools中显示为1500
0xa4: ["LOG4", 6, 0, makeGasLog(4), writes: true, valid: true], // evm-tools中显示为1875
// makeGasLog(size)
// mStart, mSize; for i:=0; i<size; i++ { topics[i]=stack.pop } log.topics = topics; log.data = memory[mStart:mSize];
// unofficial opcodes used for parsing
0xb0: ["PUSH"],
0xb1: ["DUP"],
0xb2: ["SWAP"],
// closures
0xf0: ["CREATE", 3, 1, gasCreate32000, writes: true, valid: true, returns: true], // vlaue, offset, size; input = memory[offset:offset+size]; createContract
0xf1: ["CALL", 7, 1, gasCall40, valid: true, returns: true], // _, addr, value, inOffset, inSize, retOffset, retSize; call;
0xf2: ["CALLCODE", 7, 1, gasCallCode40, valid: true, returns: true], // _, addr, value, inOffset, inSize, retOffset, retSize; callCode;
0xf3: ["RETURN", 2, 0, gasReturn0, halts: true, valid: true, returns: ], // offset, size; return memory[offset:offset+size]
0xf4: ["DELEGATECALL", 6, 1, gasDelegateCall, valid: true, returns: true], // _, addr, inOffset, inSize, retOffset, retSize; delegateCall;
0xfa: ["STATICCALL", 6, 1, gasStaticCall, valid: true, returns: true], // _, addr, inOffset, inSize, retOffset, retSize; staticCall;
0xfd: ["REVERT", 2, 0, gasRevert ,valid: true, returns: true, reverts: true], // offset, size; return memory[offset:offset+size]
0xff: ["SELFDESTRUCT", 1, 0, gasSuicide, halts: true, writes: true, valid: true], // x; addBalance(hash(x), contract.balance)
// arbitrary length storage (proposal for metropolis hardfork)
0xe1: ["SLOADBYTES", 3, 0, 50], // not use now
0xe2: ["SSTOREBYTES", 3, 0, 0], // not use now
0xe3: ["SSIZE", 1, 1, 50], // not use now
}
// i 代表是一个字节个数，如PUSH1代表压入1个单字节的数，PUSH2代表压入一个双字节的数，下面同此。
for i := 1; i <= 32; i++ {
opcodes[0x60 + i - 1] = ["PUSH" + string(i), 0, 1, 3]; // push x;
}
for i := 1; i <= 16; i++ {
opcodes[0x80 + i - 1] = ["DUP" + string(i), i, i+1, 3] // push stack[stack.len - i];
opcodes[0x90 + i - 1] = ["SWP" + string(i), i+1, i+1, 3] // stack[stack.len - (i + 1)], stack[stack.len - 1] = stack[stack.len - 1], stack[stack.len - (i + 1)]
}
交易时，计算的gas，主要分为IntrinsicGas，执行evm的gas，最后会进行refund操作，所以交易费基本等于=(IntrinsicGas+evmGas-refundGas) * gasPrice:
IntrinsicGas:
func IntrinsicGas(data []byte, contractCreation, homestead bool) (uint64, error) {
// Set the starting gas for the raw transaction
var gas uint64
// 判断是否为创建合约交易，所需的gas不一致
if contractCreation && homestead {
gas = params.TxGasContractCreation
} else {
gas = params.TxGas
}
// Bump the required gas by the amount of transactional data
if len(data) > 0 {
// Zero and non-zero bytes are priced differently
var nz uint64
// 计算非0的数据个数
for _, byt := range data {
if byt != 0 {
nz++
}
}
// Make sure we don't exceed uint64 for all data combinations
if (math.MaxUint64-gas)/params.TxDataNonZeroGas < nz {
return 0, vm.ErrOutOfGas
}
gas += nz * params.TxDataNonZeroGas
// 计算0的数据个数
z := uint64(len(data)) - nz
if (math.MaxUint64-gas)/params.TxDataZeroGas < z {
return 0, vm.ErrOutOfGas
}
gas += z * params.TxDataZeroGas
}
// 总的来说 gas = 交易类型的gas + 0数据的gas×0数据的size + 非0数据的gas×非0数据的size
return gas, nil
}
refundGas:
func (st *StateTransition) refundGas() {
// refund的数量为使用gas的一半
refund := st.gasUsed() / 2
// 取refund和GetRefund()中较小的一个
// GetRefund()在evm执行过程中，仅有两个操作可能会增加该部分的值：
// 1. SstoreRefundGas： 15000，执行Sstore操作，删除一个地址
// 2. SuicideRefundGas： 合约自毁24000
if refund > st.state.GetRefund() {
refund = st.state.GetRefund()
}
// 当前剩余gas加上refund的gas
st.gas += refund
// 计算需要退回的金额
remaining := new(big.Int).Mul(new(big.Int).SetUint64(st.gas), st.gasPrice)
// 把这部分金额退还给发送交易的地址
st.state.AddBalance(st.msg.From(), remaining)
// 将剩下的gas加到全局的gas中，保证下一条交易使用的数据是对的。
st.gp.AddGas(st.gas)
}
// run runs the given contract and takes care of running precompiles with a fallback to the byte code interpreter.
func run(evm *EVM, contract *Contract, input []byte) ([]byte, error) {
if contract.CodeAddr != nil {
precompiles := PrecompiledContractsHomestead
if evm.ChainConfig().IsByzantium(evm.BlockNumber) {
precompiles = PrecompiledContractsByzantium
}
if p := precompiles[*contract.CodeAddr]; p != nil {
return RunPrecompiledContract(p, input, contract)
}
}
return evm.interpreter.Run(contract, input)
}
// PrecompiledContractsHomestead contains the default set of pre-compiled Ethereum
// contracts used in the Frontier and Homestead releases.
var PrecompiledContractsHomestead = map[common.Address]PrecompiledContract{ // 默认的预编译合约
common.BytesToAddress([]byte{1}): &ecrecover{},
common.BytesToAddress([]byte{2}): &sha256hash{},
common.BytesToAddress([]byte{3}): &ripemd160hash{},
common.BytesToAddress([]byte{4}): &dataCopy{},
}
// RunPrecompiledContract runs and evaluates the output of a precompiled contract.
func RunPrecompiledContract(p PrecompiledContract, input []byte, contract *Contract) (ret []byte, err error) {
gas := p.RequiredGas(input) // 计算预编译合约所需 gas
if contract.UseGas(gas) {
return p.Run(input)
}
return nil, ErrOutOfGas
}
// Precompiled contract gas prices 具体预编译合约的 gas
EcrecoverGas uint64 = 3000 // Elliptic curve sender recovery gas price
Sha256BaseGas uint64 = 60 // Base price for a SHA256 operation
Sha256PerWordGas uint64 = 12 // Per-word price for a SHA256 operation
Ripemd160BaseGas uint64 = 600 // Base price for a RIPEMD160 operation