core/vm: improved EVM run loop & instruction calling (#3378)

The run loop, which previously contained custom opcode executes have been
removed and has been simplified to a few checks.

Each operation consists of 4 elements: execution function, gas cost function,
stack validation function and memory size function. The execution function
implements the operation's runtime behaviour, the gas cost function implements
the operation gas costs function and greatly depends on the memory and stack,
the stack validation function validates the stack and makes sure that enough
items can be popped off and pushed on and the memory size function calculates
the memory required for the operation and returns it.

This commit also allows the EVM to go unmetered. This is helpful for offline
operations such as contract calls.

1 files changed, 246 insertions, 0 deletions

diff --git a/core/vm/gas_table.go b/core/vm/gas_table.go
new file mode 100644
index 000000000..4d2c4e94a
--- /dev/null
+++ b/core/vm/gas_table.go
@@ -0,0 +1,246 @@
+package vm
+
+import (
+	"math/big"
+
+	"github.com/ethereum/go-ethereum/common"
+	"github.com/ethereum/go-ethereum/params"
+)
+
+func memoryGasCost(mem *Memory, newMemSize *big.Int) *big.Int {
+	gas := new(big.Int)
+	if newMemSize.Cmp(common.Big0) > 0 {
+		newMemSizeWords := toWordSize(newMemSize)
+
+		if newMemSize.Cmp(u256(int64(mem.Len()))) > 0 {
+			// be careful reusing variables here when changing.
+			// The order has been optimised to reduce allocation
+			oldSize := toWordSize(big.NewInt(int64(mem.Len())))
+			pow := new(big.Int).Exp(oldSize, common.Big2, Zero)
+			linCoef := oldSize.Mul(oldSize, params.MemoryGas)
+			quadCoef := new(big.Int).Div(pow, params.QuadCoeffDiv)
+			oldTotalFee := new(big.Int).Add(linCoef, quadCoef)
+
+			pow.Exp(newMemSizeWords, common.Big2, Zero)
+			linCoef = linCoef.Mul(newMemSizeWords, params.MemoryGas)
+			quadCoef = quadCoef.Div(pow, params.QuadCoeffDiv)
+			newTotalFee := linCoef.Add(linCoef, quadCoef)
+
+			fee := newTotalFee.Sub(newTotalFee, oldTotalFee)
+			gas.Add(gas, fee)
+		}
+	}
+	return gas
+}
+
+func constGasFunc(gas *big.Int) gasFunc {
+	return func(gt params.GasTable, env *EVM, contract *Contract, stack *Stack, mem *Memory, memorySize *big.Int) *big.Int {
+		return gas
+	}
+}
+
+func gasCalldataCopy(gt params.GasTable, env *EVM, contract *Contract, stack *Stack, mem *Memory, memorySize *big.Int) *big.Int {
+	gas := memoryGasCost(mem, memorySize)
+	gas.Add(gas, GasFastestStep)
+	words := toWordSize(stack.Back(2))
+
+	return gas.Add(gas, words.Mul(words, params.CopyGas))
+}
+
+func gasSStore(gt params.GasTable, env *EVM, contract *Contract, stack *Stack, mem *Memory, memorySize *big.Int) *big.Int {
+	var (
+		y, x = stack.Back(1), stack.Back(0)
+		val  = env.StateDB.GetState(contract.Address(), common.BigToHash(x))
+	)
+	// This checks for 3 scenario's and calculates gas accordingly
+	// 1. From a zero-value address to a non-zero value         (NEW VALUE)
+	// 2. From a non-zero value address to a zero-value address (DELETE)
+	// 3. From a non-zero to a non-zero                         (CHANGE)
+	if common.EmptyHash(val) && !common.EmptyHash(common.BigToHash(y)) {
+		// 0 => non 0
+		return new(big.Int).Set(params.SstoreSetGas)
+	} else if !common.EmptyHash(val) && common.EmptyHash(common.BigToHash(y)) {
+		env.StateDB.AddRefund(params.SstoreRefundGas)
+
+		return new(big.Int).Set(params.SstoreClearGas)
+	} else {
+		// non 0 => non 0 (or 0 => 0)
+		return new(big.Int).Set(params.SstoreResetGas)
+	}
+}
+
+func makeGasLog(n uint) gasFunc {
+	return func(gt params.GasTable, env *EVM, contract *Contract, stack *Stack, mem *Memory, memorySize *big.Int) *big.Int {
+		mSize := stack.Back(1)
+
+		gas := new(big.Int).Add(memoryGasCost(mem, memorySize), params.LogGas)
+		gas.Add(gas, new(big.Int).Mul(big.NewInt(int64(n)), params.LogTopicGas))
+		gas.Add(gas, new(big.Int).Mul(mSize, params.LogDataGas))
+		return gas
+	}
+}
+
+func gasSha3(gt params.GasTable, env *EVM, contract *Contract, stack *Stack, mem *Memory, memorySize *big.Int) *big.Int {
+	gas := memoryGasCost(mem, memorySize)
+	gas.Add(gas, params.Sha3Gas)
+	words := toWordSize(stack.Back(1))
+	return gas.Add(gas, words.Mul(words, params.Sha3WordGas))
+}
+
+func gasCodeCopy(gt params.GasTable, env *EVM, contract *Contract, stack *Stack, mem *Memory, memorySize *big.Int) *big.Int {
+	gas := memoryGasCost(mem, memorySize)
+	gas.Add(gas, GasFastestStep)
+	words := toWordSize(stack.Back(2))
+
+	return gas.Add(gas, words.Mul(words, params.CopyGas))
+}
+
+func gasExtCodeCopy(gt params.GasTable, env *EVM, contract *Contract, stack *Stack, mem *Memory, memorySize *big.Int) *big.Int {
+	gas := memoryGasCost(mem, memorySize)
+	gas.Add(gas, gt.ExtcodeCopy)
+	words := toWordSize(stack.Back(3))
+
+	return gas.Add(gas, words.Mul(words, params.CopyGas))
+}
+
+func gasMLoad(gt params.GasTable, env *EVM, contract *Contract, stack *Stack, mem *Memory, memorySize *big.Int) *big.Int {
+	return new(big.Int).Add(GasFastestStep, memoryGasCost(mem, memorySize))
+}
+
+func gasMStore8(gt params.GasTable, env *EVM, contract *Contract, stack *Stack, mem *Memory, memorySize *big.Int) *big.Int {
+	return new(big.Int).Add(GasFastestStep, memoryGasCost(mem, memorySize))
+}
+
+func gasMStore(gt params.GasTable, env *EVM, contract *Contract, stack *Stack, mem *Memory, memorySize *big.Int) *big.Int {
+	return new(big.Int).Add(GasFastestStep, memoryGasCost(mem, memorySize))
+}
+
+func gasCreate(gt params.GasTable, env *EVM, contract *Contract, stack *Stack, mem *Memory, memorySize *big.Int) *big.Int {
+	return new(big.Int).Add(params.CreateGas, memoryGasCost(mem, memorySize))
+}
+
+func gasBalance(gt params.GasTable, env *EVM, contract *Contract, stack *Stack, mem *Memory, memorySize *big.Int) *big.Int {
+	return gt.Balance
+}
+
+func gasExtCodeSize(gt params.GasTable, env *EVM, contract *Contract, stack *Stack, mem *Memory, memorySize *big.Int) *big.Int {
+	return gt.ExtcodeSize
+}
+
+func gasSLoad(gt params.GasTable, env *EVM, contract *Contract, stack *Stack, mem *Memory, memorySize *big.Int) *big.Int {
+	return gt.SLoad
+}
+
+func gasExp(gt params.GasTable, env *EVM, contract *Contract, stack *Stack, mem *Memory, memorySize *big.Int) *big.Int {
+	expByteLen := int64((stack.data[stack.len()-2].BitLen() + 7) / 8)
+	gas := big.NewInt(expByteLen)
+	gas.Mul(gas, gt.ExpByte)
+	return gas.Add(gas, GasSlowStep)
+}
+
+func gasCall(gt params.GasTable, env *EVM, contract *Contract, stack *Stack, mem *Memory, memorySize *big.Int) *big.Int {
+	gas := new(big.Int).Set(gt.Calls)
+
+	transfersValue := stack.Back(2).BitLen() > 0
+	var (
+		address = common.BigToAddress(stack.Back(1))
+		eip158  = env.ChainConfig().IsEIP158(env.BlockNumber)
+	)
+	if eip158 {
+		if env.StateDB.Empty(address) && transfersValue {
+			gas.Add(gas, params.CallNewAccountGas)
+		}
+	} else if !env.StateDB.Exist(address) {
+		gas.Add(gas, params.CallNewAccountGas)
+	}
+	if transfersValue {
+		gas.Add(gas, params.CallValueTransferGas)
+	}
+	gas.Add(gas, memoryGasCost(mem, memorySize))
+
+	cg := callGas(gt, contract.Gas, gas, stack.data[stack.len()-1])
+	// Replace the stack item with the new gas calculation. This means that
+	// either the original item is left on the stack or the item is replaced by:
+	// (availableGas - gas) * 63 / 64
+	// We replace the stack item so that it's available when the opCall instruction is
+	// called. This information is otherwise lost due to the dependency on *current*
+	// available gas.
+	stack.data[stack.len()-1] = cg
+
+	return gas.Add(gas, cg)
+}
+
+func gasCallCode(gt params.GasTable, env *EVM, contract *Contract, stack *Stack, mem *Memory, memorySize *big.Int) *big.Int {
+	gas := new(big.Int).Set(gt.Calls)
+	if stack.Back(2).BitLen() > 0 {
+		gas.Add(gas, params.CallValueTransferGas)
+	}
+	gas.Add(gas, memoryGasCost(mem, memorySize))
+
+	cg := callGas(gt, contract.Gas, gas, stack.data[stack.len()-1])
+	// Replace the stack item with the new gas calculation. This means that
+	// either the original item is left on the stack or the item is replaced by:
+	// (availableGas - gas) * 63 / 64
+	// We replace the stack item so that it's available when the opCall instruction is
+	// called. This information is otherwise lost due to the dependency on *current*
+	// available gas.
+	stack.data[stack.len()-1] = cg
+
+	return gas.Add(gas, cg)
+}
+
+func gasReturn(gt params.GasTable, env *EVM, contract *Contract, stack *Stack, mem *Memory, memorySize *big.Int) *big.Int {
+	return memoryGasCost(mem, memorySize)
+}
+
+func gasSuicide(gt params.GasTable, env *EVM, contract *Contract, stack *Stack, mem *Memory, memorySize *big.Int) *big.Int {
+	gas := new(big.Int)
+	// EIP150 homestead gas reprice fork:
+	if env.ChainConfig().IsEIP150(env.BlockNumber) {
+		gas.Set(gt.Suicide)
+		var (
+			address = common.BigToAddress(stack.Back(0))
+			eip158  = env.ChainConfig().IsEIP158(env.BlockNumber)
+		)
+
+		if eip158 {
+			// if empty and transfers value
+			if env.StateDB.Empty(address) && env.StateDB.GetBalance(contract.Address()).BitLen() > 0 {
+				gas.Add(gas, gt.CreateBySuicide)
+			}
+		} else if !env.StateDB.Exist(address) {
+			gas.Add(gas, gt.CreateBySuicide)
+		}
+	}
+
+	if !env.StateDB.HasSuicided(contract.Address()) {
+		env.StateDB.AddRefund(params.SuicideRefundGas)
+	}
+	return gas
+}
+
+func gasDelegateCall(gt params.GasTable, env *EVM, contract *Contract, stack *Stack, mem *Memory, memorySize *big.Int) *big.Int {
+	gas := new(big.Int).Add(gt.Calls, memoryGasCost(mem, memorySize))
+
+	cg := callGas(gt, contract.Gas, gas, stack.data[stack.len()-1])
+	// Replace the stack item with the new gas calculation. This means that
+	// either the original item is left on the stack or the item is replaced by:
+	// (availableGas - gas) * 63 / 64
+	// We replace the stack item so that it's available when the opCall instruction is
+	// called.
+	stack.data[stack.len()-1] = cg
+
+	return gas.Add(gas, cg)
+}
+
+func gasPush(gt params.GasTable, env *EVM, contract *Contract, stack *Stack, mem *Memory, memorySize *big.Int) *big.Int {
+	return GasFastestStep
+}
+
+func gasSwap(gt params.GasTable, env *EVM, contract *Contract, stack *Stack, mem *Memory, memorySize *big.Int) *big.Int {
+	return GasFastestStep
+}
+
+func gasDup(gt params.GasTable, env *EVM, contract *Contract, stack *Stack, mem *Memory, memorySize *big.Int) *big.Int {
+	return GasFastestStep
+}