params: core, core/vm, miner: 64bit gas instructions

Reworked the EVM gas instructions to use 64bit integers rather than
arbitrary size big ints. All gas operations, be it additions,
multiplications or divisions, are checked and guarded against 64 bit
integer overflows.

In additon, most of the protocol paramaters in the params package have
been converted to uint64 and are now constants rather than variables.

* common/math: added overflow check ops
* core: vmenv, env renamed to evm
* eth, internal/ethapi, les: unmetered eth_call and cancel methods
* core/vm: implemented big.Int pool for evm instructions
* core/vm: unexported intPool methods & verification methods
* core/vm: added memoryGasCost overflow check and test

1 files changed, 50 insertions, 38 deletions

diff --git a/core/state_transition.go b/core/state_transition.go
index 3cb7e500c..98dc8d995 100644
--- a/core/state_transition.go
+++ b/core/state_transition.go
@@ -49,15 +49,16 @@ The state transitioning model does all all the necessary work to work out a vali
 6) Derive new state root
 */
 type StateTransition struct {
-	gp            *GasPool
-	msg           Message
-	gas, gasPrice *big.Int
-	initialGas    *big.Int
-	value         *big.Int
-	data          []byte
-	state         vm.StateDB
-
-	env *vm.EVM
+	gp         *GasPool
+	msg        Message
+	gas        uint64
+	gasPrice   *big.Int
+	initialGas *big.Int
+	value      *big.Int
+	data       []byte
+	state      vm.StateDB
+
+	evm *vm.EVM
 }
 
 // Message represents a message sent to a contract.
@@ -81,12 +82,14 @@ func MessageCreatesContract(msg Message) bool {
 
 // IntrinsicGas computes the 'intrinsic gas' for a message
 // with the given data.
+//
+// TODO convert to uint64
 func IntrinsicGas(data []byte, contractCreation, homestead bool) *big.Int {
 	igas := new(big.Int)
 	if contractCreation && homestead {
-		igas.Set(params.TxGasContractCreation)
+		igas.SetUint64(params.TxGasContractCreation)
 	} else {
-		igas.Set(params.TxGas)
+		igas.SetUint64(params.TxGas)
 	}
 	if len(data) > 0 {
 		var nz int64
@@ -96,27 +99,26 @@ func IntrinsicGas(data []byte, contractCreation, homestead bool) *big.Int {
 			}
 		}
 		m := big.NewInt(nz)
-		m.Mul(m, params.TxDataNonZeroGas)
+		m.Mul(m, new(big.Int).SetUint64(params.TxDataNonZeroGas))
 		igas.Add(igas, m)
 		m.SetInt64(int64(len(data)) - nz)
-		m.Mul(m, params.TxDataZeroGas)
+		m.Mul(m, new(big.Int).SetUint64(params.TxDataZeroGas))
 		igas.Add(igas, m)
 	}
 	return igas
 }
 
 // NewStateTransition initialises and returns a new state transition object.
-func NewStateTransition(env *vm.EVM, msg Message, gp *GasPool) *StateTransition {
+func NewStateTransition(evm *vm.EVM, msg Message, gp *GasPool) *StateTransition {
 	return &StateTransition{
 		gp:         gp,
-		env:        env,
+		evm:        evm,
 		msg:        msg,
-		gas:        new(big.Int),
 		gasPrice:   msg.GasPrice(),
 		initialGas: new(big.Int),
 		value:      msg.Value(),
 		data:       msg.Data(),
-		state:      env.StateDB,
+		state:      evm.StateDB,
 	}
 }
 
@@ -127,8 +129,8 @@ func NewStateTransition(env *vm.EVM, msg Message, gp *GasPool) *StateTransition
 // the gas used (which includes gas refunds) and an error if it failed. An error always
 // indicates a core error meaning that the message would always fail for that particular
 // state and would never be accepted within a block.
-func ApplyMessage(env *vm.EVM, msg Message, gp *GasPool) ([]byte, *big.Int, error) {
-	st := NewStateTransition(env, msg, gp)
+func ApplyMessage(evm *vm.EVM, msg Message, gp *GasPool) ([]byte, *big.Int, error) {
+	st := NewStateTransition(evm, msg, gp)
 
 	ret, _, gasUsed, err := st.TransitionDb()
 	return ret, gasUsed, err
@@ -157,21 +159,21 @@ func (self *StateTransition) to() vm.Account {
 	return self.state.GetAccount(*to)
 }
 
-func (self *StateTransition) useGas(amount *big.Int) error {
-	if self.gas.Cmp(amount) < 0 {
+func (self *StateTransition) useGas(amount uint64) error {
+	if self.gas < amount {
 		return vm.ErrOutOfGas
 	}
-	self.gas.Sub(self.gas, amount)
+	self.gas -= amount
 
 	return nil
 }
 
-func (self *StateTransition) addGas(amount *big.Int) {
-	self.gas.Add(self.gas, amount)
-}
-
 func (self *StateTransition) buyGas() error {
 	mgas := self.msg.Gas()
+	if mgas.BitLen() > 64 {
+		return vm.ErrOutOfGas
+	}
+
 	mgval := new(big.Int).Mul(mgas, self.gasPrice)
 
 	sender := self.from()
@@ -181,7 +183,8 @@ func (self *StateTransition) buyGas() error {
 	if err := self.gp.SubGas(mgas); err != nil {
 		return err
 	}
-	self.addGas(mgas)
+	self.gas += mgas.Uint64()
+
 	self.initialGas.Set(mgas)
 	sender.SubBalance(mgval)
 	return nil
@@ -209,7 +212,9 @@ func (self *StateTransition) preCheck() (err error) {
 	return nil
 }
 
-// TransitionDb will move the state by applying the message against the given environment.
+// TransitionDb will transition the state by applying the current message and returning the result
+// including the required gas for the operation as well as the used gas. It returns an error if it
+// failed. An error indicates a consensus issue.
 func (self *StateTransition) TransitionDb() (ret []byte, requiredGas, usedGas *big.Int, err error) {
 	if err = self.preCheck(); err != nil {
 		return
@@ -217,26 +222,32 @@ func (self *StateTransition) TransitionDb() (ret []byte, requiredGas, usedGas *b
 	msg := self.msg
 	sender := self.from() // err checked in preCheck
 
-	homestead := self.env.ChainConfig().IsHomestead(self.env.BlockNumber)
+	homestead := self.evm.ChainConfig().IsHomestead(self.evm.BlockNumber)
 	contractCreation := MessageCreatesContract(msg)
 	// Pay intrinsic gas
-	if err = self.useGas(IntrinsicGas(self.data, contractCreation, homestead)); err != nil {
+	// TODO convert to uint64
+	intrinsicGas := IntrinsicGas(self.data, contractCreation, homestead)
+	if intrinsicGas.BitLen() > 64 {
+		return nil, nil, nil, InvalidTxError(vm.ErrOutOfGas)
+	}
+
+	if err = self.useGas(intrinsicGas.Uint64()); err != nil {
 		return nil, nil, nil, InvalidTxError(err)
 	}
 
 	var (
-		vmenv = self.env
+		evm = self.evm
 		// vm errors do not effect consensus and are therefor
 		// not assigned to err, except for insufficient balance
 		// error.
 		vmerr error
 	)
 	if contractCreation {
-		ret, _, vmerr = vmenv.Create(sender, self.data, self.gas, self.value)
+		ret, _, self.gas, vmerr = evm.Create(sender, self.data, self.gas, self.value)
 	} else {
 		// Increment the nonce for the next transaction
 		self.state.SetNonce(sender.Address(), self.state.GetNonce(sender.Address())+1)
-		ret, vmerr = vmenv.Call(sender, self.to().Address(), self.data, self.gas, self.value)
+		ret, self.gas, vmerr = evm.Call(sender, self.to().Address(), self.data, self.gas, self.value)
 	}
 	if vmerr != nil {
 		glog.V(logger.Core).Infoln("vm returned with error:", err)
@@ -251,7 +262,7 @@ func (self *StateTransition) TransitionDb() (ret []byte, requiredGas, usedGas *b
 	requiredGas = new(big.Int).Set(self.gasUsed())
 
 	self.refundGas()
-	self.state.AddBalance(self.env.Coinbase, new(big.Int).Mul(self.gasUsed(), self.gasPrice))
+	self.state.AddBalance(self.evm.Coinbase, new(big.Int).Mul(self.gasUsed(), self.gasPrice))
 
 	return ret, requiredGas, self.gasUsed(), err
 }
@@ -260,20 +271,21 @@ func (self *StateTransition) refundGas() {
 	// Return eth for remaining gas to the sender account,
 	// exchanged at the original rate.
 	sender := self.from() // err already checked
-	remaining := new(big.Int).Mul(self.gas, self.gasPrice)
+	remaining := new(big.Int).Mul(new(big.Int).SetUint64(self.gas), self.gasPrice)
 	sender.AddBalance(remaining)
 
 	// Apply refund counter, capped to half of the used gas.
 	uhalf := remaining.Div(self.gasUsed(), common.Big2)
 	refund := common.BigMin(uhalf, self.state.GetRefund())
-	self.gas.Add(self.gas, refund)
+	self.gas += refund.Uint64()
+
 	self.state.AddBalance(sender.Address(), refund.Mul(refund, self.gasPrice))
 
 	// Also return remaining gas to the block gas counter so it is
 	// available for the next transaction.
-	self.gp.AddGas(self.gas)
+	self.gp.AddGas(new(big.Int).SetUint64(self.gas))
 }
 
 func (self *StateTransition) gasUsed() *big.Int {
-	return new(big.Int).Sub(self.initialGas, self.gas)
+	return new(big.Int).Sub(self.initialGas, new(big.Int).SetUint64(self.gas))
 }