tendermint/vm/vm.go

package vm

import (
	"bytes"
	"errors"
	"fmt"
	"math/big"

	. "github.com/tendermint/tendermint/common"
	"github.com/tendermint/tendermint/events"
	ptypes "github.com/tendermint/tendermint/permission/types"
	"github.com/tendermint/tendermint/types"
	"github.com/tendermint/tendermint/vm/sha3"
)

var (
	ErrUnknownAddress      = errors.New("Unknown address")
	ErrInsufficientBalance = errors.New("Insufficient balance")
	ErrInvalidJumpDest     = errors.New("Invalid jump dest")
	ErrInsufficientGas     = errors.New("Insuffient gas")
	ErrMemoryOutOfBounds   = errors.New("Memory out of bounds")
	ErrCodeOutOfBounds     = errors.New("Code out of bounds")
	ErrInputOutOfBounds    = errors.New("Input out of bounds")
	ErrCallStackOverflow   = errors.New("Call stack overflow")
	ErrCallStackUnderflow  = errors.New("Call stack underflow")
	ErrDataStackOverflow   = errors.New("Data stack overflow")
	ErrDataStackUnderflow  = errors.New("Data stack underflow")
	ErrInvalidContract     = errors.New("Invalid contract")
)

type ErrPermission struct {
	typ string
}

func (err ErrPermission) Error() string {
	return fmt.Sprintf("Contract does not have permission to %s", err.typ)
}

type Debug bool

const (
	dataStackCapacity       = 1024
	callStackCapacity       = 100         // TODO ensure usage.
	memoryCapacity          = 1024 * 1024 // 1 MB
	dbg               Debug = true
)

func (d Debug) Printf(s string, a ...interface{}) {
	if d {
		fmt.Printf(s, a...)
	}
}

type VM struct {
	appState AppState
	params   Params
	origin   Word256
	txid     []byte

	callDepth int

	evc events.Fireable
}

func NewVM(appState AppState, params Params, origin Word256, txid []byte) *VM {
	return &VM{
		appState:  appState,
		params:    params,
		origin:    origin,
		callDepth: 0,
		txid:      txid,
	}
}

// satisfies events.Eventable
func (vm *VM) SetFireable(evc events.Fireable) {
	vm.evc = evc
}

// CONTRACT: it is the duty of the contract writer to call known permissions
// we do not convey if a permission is not set
// (unlike in state/execution, where we guarantee HasPermission is called
// on known permissions and panics else)
// If the perm is not defined in the acc nor set by default in GlobalPermissions,
// prints a log warning and returns false.
func HasPermission(appState AppState, acc *Account, perm ptypes.PermFlag) bool {
	v, err := acc.Permissions.Base.Get(perm)
	if _, ok := err.(ptypes.ErrValueNotSet); ok {
		if appState == nil {
			log.Warn(Fmt("\n\n***** Unknown permission %b! ********\n\n", perm))
			return false
		}
		return HasPermission(nil, appState.GetAccount(ptypes.GlobalPermissionsAddress256), perm)
	}
	return v
}

func (vm *VM) fireCallEvent(exception *string, output *[]byte, caller, callee *Account, input []byte, value int64, gas *int64) {
	// fire the post call event (including exception if applicable)
	if vm.evc != nil {
		vm.evc.FireEvent(types.EventStringAccCall(callee.Address.Postfix(20)), types.EventMsgCall{
			&types.CallData{caller.Address.Postfix(20), callee.Address.Postfix(20), input, value, *gas},
			vm.origin.Postfix(20),
			vm.txid,
			*output,
			*exception,
		})
	}
}

// CONTRACT appState is aware of caller and callee, so we can just mutate them.
// value: To be transferred from caller to callee. Refunded upon error.
// gas:   Available gas. No refunds for gas.
// code: May be nil, since the CALL opcode may be used to send value from contracts to accounts
func (vm *VM) Call(caller, callee *Account, code, input []byte, value int64, gas *int64) (output []byte, err error) {

	exception := new(string)
	// fire the post call event (including exception if applicable)
	defer vm.fireCallEvent(exception, &output, caller, callee, input, value, gas)

	if err = transfer(caller, callee, value); err != nil {
		*exception = err.Error()
		return
	}

	if len(code) > 0 {
		vm.callDepth += 1
		output, err = vm.call(caller, callee, code, input, value, gas)
		vm.callDepth -= 1
		if err != nil {
			*exception = err.Error()
			err := transfer(callee, caller, value)
			if err != nil {
				// data has been corrupted in ram
				PanicCrisis("Could not return value to caller")
			}
		}
	}

	return
}

// Try to deduct gasToUse from gasLeft.  If ok return false, otherwise
// set err and return true.
func useGasNegative(gasLeft *int64, gasToUse int64, err *error) bool {
	if *gasLeft >= gasToUse {
		*gasLeft -= gasToUse
		return false
	} else if *err == nil {
		*err = ErrInsufficientGas
	}
	return true
}

// Just like Call() but does not transfer 'value' or modify the callDepth.
func (vm *VM) call(caller, callee *Account, code, input []byte, value int64, gas *int64) (output []byte, err error) {
	dbg.Printf("(%d) (%X) %X (code=%d) gas: %v (d) %X\n", vm.callDepth, caller.Address[:4], callee.Address, len(callee.Code), *gas, input)

	var (
		pc     int64 = 0
		stack        = NewStack(dataStackCapacity, gas, &err)
		memory       = make([]byte, memoryCapacity)
	)

	for {

		// Use BaseOp gas.
		if useGasNegative(gas, GasBaseOp, &err) {
			return nil, err
		}

		var op = codeGetOp(code, pc)
		dbg.Printf("(pc) %-3d (op) %-14s (st) %-4d ", pc, op.String(), stack.Len())

		switch op {

		case STOP: // 0x00
			return nil, nil

		case ADD: // 0x01
			x, y := stack.Pop(), stack.Pop()
			xb := new(big.Int).SetBytes(x[:])
			yb := new(big.Int).SetBytes(y[:])
			sum := new(big.Int).Add(xb, yb)
			res := LeftPadWord256(U256(sum).Bytes())
			stack.Push(res)
			dbg.Printf(" %v + %v = %v (%X)\n", xb, yb, sum, res)

		case MUL: // 0x02
			x, y := stack.Pop(), stack.Pop()
			xb := new(big.Int).SetBytes(x[:])
			yb := new(big.Int).SetBytes(y[:])
			prod := new(big.Int).Mul(xb, yb)
			res := LeftPadWord256(U256(prod).Bytes())
			stack.Push(res)
			dbg.Printf(" %v * %v = %v (%X)\n", xb, yb, prod, res)

		case SUB: // 0x03
			x, y := stack.Pop(), stack.Pop()
			xb := new(big.Int).SetBytes(x[:])
			yb := new(big.Int).SetBytes(y[:])
			diff := new(big.Int).Sub(xb, yb)
			res := LeftPadWord256(U256(diff).Bytes())
			stack.Push(res)
			dbg.Printf(" %v - %v = %v (%X)\n", xb, yb, diff, res)

		case DIV: // 0x04
			x, y := stack.Pop(), stack.Pop()
			if y.IsZero() {
				stack.Push(Zero256)
				dbg.Printf(" %x / %x = %v\n", x, y, 0)
			} else {
				xb := new(big.Int).SetBytes(x[:])
				yb := new(big.Int).SetBytes(y[:])
				div := new(big.Int).Div(xb, yb)
				res := LeftPadWord256(U256(div).Bytes())
				stack.Push(res)
				dbg.Printf(" %v / %v = %v (%X)\n", xb, yb, div, res)
			}

		case SDIV: // 0x05
			x, y := stack.Pop(), stack.Pop()
			if y.IsZero() {
				stack.Push(Zero256)
				dbg.Printf(" %x / %x = %v\n", x, y, 0)
			} else {
				xb := S256(new(big.Int).SetBytes(x[:]))
				yb := S256(new(big.Int).SetBytes(y[:]))
				div := new(big.Int).Div(xb, yb)
				res := LeftPadWord256(U256(div).Bytes())
				stack.Push(res)
				dbg.Printf(" %v / %v = %v (%X)\n", xb, yb, div, res)
			}

		case MOD: // 0x06
			x, y := stack.Pop(), stack.Pop()
			if y.IsZero() {
				stack.Push(Zero256)
				dbg.Printf(" %v %% %v = %v\n", x, y, 0)
			} else {
				xb := new(big.Int).SetBytes(x[:])
				yb := new(big.Int).SetBytes(y[:])
				mod := new(big.Int).Mod(xb, yb)
				res := LeftPadWord256(U256(mod).Bytes())
				stack.Push(res)
				dbg.Printf(" %v %% %v = %v (%X)\n", xb, yb, mod, res)
			}

		case SMOD: // 0x07
			x, y := stack.Pop(), stack.Pop()
			if y.IsZero() {
				stack.Push(Zero256)
				dbg.Printf(" %v %% %v = %v\n", x, y, 0)
			} else {
				xb := S256(new(big.Int).SetBytes(x[:]))
				yb := S256(new(big.Int).SetBytes(y[:]))
				mod := new(big.Int).Mod(xb, yb)
				res := LeftPadWord256(U256(mod).Bytes())
				stack.Push(res)
				dbg.Printf(" %v %% %v = %v (%X)\n", xb, yb, mod, res)
			}

		case ADDMOD: // 0x08
			x, y, z := stack.Pop(), stack.Pop(), stack.Pop()
			if z.IsZero() {
				stack.Push(Zero256)
				dbg.Printf(" %v %% %v = %v\n", x, y, 0)
			} else {
				xb := new(big.Int).SetBytes(x[:])
				yb := new(big.Int).SetBytes(y[:])
				zb := new(big.Int).SetBytes(z[:])
				add := new(big.Int).Add(xb, yb)
				mod := new(big.Int).Mod(add, zb)
				res := LeftPadWord256(U256(mod).Bytes())
				stack.Push(res)
				dbg.Printf(" %v + %v %% %v = %v (%X)\n",
					xb, yb, zb, mod, res)
			}

		case MULMOD: // 0x09
			x, y, z := stack.Pop(), stack.Pop(), stack.Pop()
			if z.IsZero() {
				stack.Push(Zero256)
				dbg.Printf(" %v %% %v = %v\n", x, y, 0)
			} else {
				xb := new(big.Int).SetBytes(x[:])
				yb := new(big.Int).SetBytes(y[:])
				zb := new(big.Int).SetBytes(z[:])
				mul := new(big.Int).Mul(xb, yb)
				mod := new(big.Int).Mod(mul, zb)
				res := LeftPadWord256(U256(mod).Bytes())
				stack.Push(res)
				dbg.Printf(" %v * %v %% %v = %v (%X)\n",
					xb, yb, zb, mod, res)
			}

		case EXP: // 0x0A
			x, y := stack.Pop(), stack.Pop()
			xb := new(big.Int).SetBytes(x[:])
			yb := new(big.Int).SetBytes(y[:])
			pow := new(big.Int).Exp(xb, yb, big.NewInt(0))
			res := LeftPadWord256(U256(pow).Bytes())
			stack.Push(res)
			dbg.Printf(" %v ** %v = %v (%X)\n", xb, yb, pow, res)

		case SIGNEXTEND: // 0x0B
			back := stack.Pop()
			backb := new(big.Int).SetBytes(back[:])
			if backb.Cmp(big.NewInt(31)) < 0 {
				bit := uint(backb.Uint64()*8 + 7)
				num := stack.Pop()
				numb := new(big.Int).SetBytes(num[:])
				mask := new(big.Int).Lsh(big.NewInt(1), bit)
				mask.Sub(mask, big.NewInt(1))
				if numb.Bit(int(bit)) == 1 {
					numb.Or(numb, mask.Not(mask))
				} else {
					numb.Add(numb, mask)
				}
				res := LeftPadWord256(U256(numb).Bytes())
				dbg.Printf(" = %v (%X)", numb, res)
				stack.Push(res)
			}

		case LT: // 0x10
			x, y := stack.Pop(), stack.Pop()
			xb := new(big.Int).SetBytes(x[:])
			yb := new(big.Int).SetBytes(y[:])
			if xb.Cmp(yb) < 0 {
				stack.Push64(1)
				dbg.Printf(" %v < %v = %v\n", xb, yb, 1)
			} else {
				stack.Push(Zero256)
				dbg.Printf(" %v < %v = %v\n", xb, yb, 0)
			}

		case GT: // 0x11
			x, y := stack.Pop(), stack.Pop()
			xb := new(big.Int).SetBytes(x[:])
			yb := new(big.Int).SetBytes(y[:])
			if xb.Cmp(yb) > 0 {
				stack.Push64(1)
				dbg.Printf(" %v > %v = %v\n", xb, yb, 1)
			} else {
				stack.Push(Zero256)
				dbg.Printf(" %v > %v = %v\n", xb, yb, 0)
			}

		case SLT: // 0x12
			x, y := stack.Pop(), stack.Pop()
			xb := S256(new(big.Int).SetBytes(x[:]))
			yb := S256(new(big.Int).SetBytes(y[:]))
			if xb.Cmp(yb) < 0 {
				stack.Push64(1)
				dbg.Printf(" %v < %v = %v\n", xb, yb, 1)
			} else {
				stack.Push(Zero256)
				dbg.Printf(" %v < %v = %v\n", xb, yb, 0)
			}

		case SGT: // 0x13
			x, y := stack.Pop(), stack.Pop()
			xb := S256(new(big.Int).SetBytes(x[:]))
			yb := S256(new(big.Int).SetBytes(y[:]))
			if xb.Cmp(yb) > 0 {
				stack.Push64(1)
				dbg.Printf(" %v > %v = %v\n", xb, yb, 1)
			} else {
				stack.Push(Zero256)
				dbg.Printf(" %v > %v = %v\n", xb, yb, 0)
			}

		case EQ: // 0x14
			x, y := stack.Pop(), stack.Pop()
			if bytes.Equal(x[:], y[:]) {
				stack.Push64(1)
				dbg.Printf(" %X == %X = %v\n", x, y, 1)
			} else {
				stack.Push(Zero256)
				dbg.Printf(" %X == %X = %v\n", x, y, 0)
			}

		case ISZERO: // 0x15
			x := stack.Pop()
			if x.IsZero() {
				stack.Push64(1)
				dbg.Printf(" %v == 0 = %v\n", x, 1)
			} else {
				stack.Push(Zero256)
				dbg.Printf(" %v == 0 = %v\n", x, 0)
			}

		case AND: // 0x16
			x, y := stack.Pop(), stack.Pop()
			z := [32]byte{}
			for i := 0; i < 32; i++ {
				z[i] = x[i] & y[i]
			}
			stack.Push(z)
			dbg.Printf(" %X & %X = %X\n", x, y, z)

		case OR: // 0x17
			x, y := stack.Pop(), stack.Pop()
			z := [32]byte{}
			for i := 0; i < 32; i++ {
				z[i] = x[i] | y[i]
			}
			stack.Push(z)
			dbg.Printf(" %X | %X = %X\n", x, y, z)

		case XOR: // 0x18
			x, y := stack.Pop(), stack.Pop()
			z := [32]byte{}
			for i := 0; i < 32; i++ {
				z[i] = x[i] ^ y[i]
			}
			stack.Push(z)
			dbg.Printf(" %X ^ %X = %X\n", x, y, z)

		case NOT: // 0x19
			x := stack.Pop()
			z := [32]byte{}
			for i := 0; i < 32; i++ {
				z[i] = ^x[i]
			}
			stack.Push(z)
			dbg.Printf(" !%X = %X\n", x, z)

		case BYTE: // 0x1A
			idx, val := stack.Pop64(), stack.Pop()
			res := byte(0)
			if idx < 32 {
				res = val[idx]
			}
			stack.Push64(int64(res))
			dbg.Printf(" => 0x%X\n", res)

		case SHA3: // 0x20
			if useGasNegative(gas, GasSha3, &err) {
				return nil, err
			}
			offset, size := stack.Pop64(), stack.Pop64()
			data, ok := subslice(memory, offset, size)
			if !ok {
				return nil, firstErr(err, ErrMemoryOutOfBounds)
			}
			data = sha3.Sha3(data)
			stack.PushBytes(data)
			dbg.Printf(" => (%v) %X\n", size, data)

		case ADDRESS: // 0x30
			stack.Push(callee.Address)
			dbg.Printf(" => %X\n", callee.Address)

		case BALANCE: // 0x31
			addr := stack.Pop()
			if useGasNegative(gas, GasGetAccount, &err) {
				return nil, err
			}
			acc := vm.appState.GetAccount(addr)
			if acc == nil {
				return nil, firstErr(err, ErrUnknownAddress)
			}
			balance := acc.Balance
			stack.Push64(balance)
			dbg.Printf(" => %v (%X)\n", balance, addr)

		case ORIGIN: // 0x32
			stack.Push(vm.origin)
			dbg.Printf(" => %X\n", vm.origin)

		case CALLER: // 0x33
			stack.Push(caller.Address)
			dbg.Printf(" => %X\n", caller.Address)

		case CALLVALUE: // 0x34
			stack.Push64(value)
			dbg.Printf(" => %v\n", value)

		case CALLDATALOAD: // 0x35
			offset := stack.Pop64()
			data, ok := subslice(input, offset, 32)
			if !ok {
				return nil, firstErr(err, ErrInputOutOfBounds)
			}
			res := LeftPadWord256(data)
			stack.Push(res)
			dbg.Printf(" => 0x%X\n", res)

		case CALLDATASIZE: // 0x36
			stack.Push64(int64(len(input)))
			dbg.Printf(" => %d\n", len(input))

		case CALLDATACOPY: // 0x37
			memOff := stack.Pop64()
			inputOff := stack.Pop64()
			length := stack.Pop64()
			data, ok := subslice(input, inputOff, length)
			if !ok {
				return nil, firstErr(err, ErrInputOutOfBounds)
			}
			dest, ok := subslice(memory, memOff, length)
			if !ok {
				return nil, firstErr(err, ErrMemoryOutOfBounds)
			}
			copy(dest, data)
			dbg.Printf(" => [%v, %v, %v] %X\n", memOff, inputOff, length, data)

		case CODESIZE: // 0x38
			l := int64(len(code))
			stack.Push64(l)
			dbg.Printf(" => %d\n", l)

		case CODECOPY: // 0x39
			memOff := stack.Pop64()
			codeOff := stack.Pop64()
			length := stack.Pop64()
			data, ok := subslice(code, codeOff, length)
			if !ok {
				return nil, firstErr(err, ErrCodeOutOfBounds)
			}
			dest, ok := subslice(memory, memOff, length)
			if !ok {
				return nil, firstErr(err, ErrMemoryOutOfBounds)
			}
			copy(dest, data)
			dbg.Printf(" => [%v, %v, %v] %X\n", memOff, codeOff, length, data)

		case GASPRICE_DEPRECATED: // 0x3A
			stack.Push(Zero256)
			dbg.Printf(" => %X (GASPRICE IS DEPRECATED)\n")

		case EXTCODESIZE: // 0x3B
			addr := stack.Pop()
			if useGasNegative(gas, GasGetAccount, &err) {
				return nil, err
			}
			acc := vm.appState.GetAccount(addr)
			if acc == nil {
				return nil, firstErr(err, ErrUnknownAddress)
			}
			code := acc.Code
			l := int64(len(code))
			stack.Push64(l)
			dbg.Printf(" => %d\n", l)

		case EXTCODECOPY: // 0x3C
			addr := stack.Pop()
			if useGasNegative(gas, GasGetAccount, &err) {
				return nil, err
			}
			acc := vm.appState.GetAccount(addr)
			if acc == nil {
				return nil, firstErr(err, ErrUnknownAddress)
			}
			code := acc.Code
			memOff := stack.Pop64()
			codeOff := stack.Pop64()
			length := stack.Pop64()
			data, ok := subslice(code, codeOff, length)
			if !ok {
				return nil, firstErr(err, ErrCodeOutOfBounds)
			}
			dest, ok := subslice(memory, memOff, length)
			if !ok {
				return nil, firstErr(err, ErrMemoryOutOfBounds)
			}
			copy(dest, data)
			dbg.Printf(" => [%v, %v, %v] %X\n", memOff, codeOff, length, data)

		case BLOCKHASH: // 0x40
			stack.Push(Zero256)
			dbg.Printf(" => 0x%X (NOT SUPPORTED)\n", stack.Peek().Bytes())

		case COINBASE: // 0x41
			stack.Push(Zero256)
			dbg.Printf(" => 0x%X (NOT SUPPORTED)\n", stack.Peek().Bytes())

		case TIMESTAMP: // 0x42
			time := vm.params.BlockTime
			stack.Push64(int64(time))
			dbg.Printf(" => 0x%X\n", time)

		case BLOCKHEIGHT: // 0x43
			number := int64(vm.params.BlockHeight)
			stack.Push64(number)
			dbg.Printf(" => 0x%X\n", number)

		case GASLIMIT: // 0x45
			stack.Push64(vm.params.GasLimit)
			dbg.Printf(" => %v\n", vm.params.GasLimit)

		case POP: // 0x50
			popped := stack.Pop()
			dbg.Printf(" => 0x%X\n", popped)

		case MLOAD: // 0x51
			offset := stack.Pop64()
			data, ok := subslice(memory, offset, 32)
			if !ok {
				return nil, firstErr(err, ErrMemoryOutOfBounds)
			}
			stack.Push(LeftPadWord256(data))
			dbg.Printf(" => 0x%X\n", data)

		case MSTORE: // 0x52
			offset, data := stack.Pop64(), stack.Pop()
			dest, ok := subslice(memory, offset, 32)
			if !ok {
				return nil, firstErr(err, ErrMemoryOutOfBounds)
			}
			copy(dest, data[:])
			dbg.Printf(" => 0x%X\n", data)

		case MSTORE8: // 0x53
			offset, val := stack.Pop64(), byte(stack.Pop64()&0xFF)
			if len(memory) <= int(offset) {
				return nil, firstErr(err, ErrMemoryOutOfBounds)
			}
			memory[offset] = val
			dbg.Printf(" => [%v] 0x%X\n", offset, val)

		case SLOAD: // 0x54
			loc := stack.Pop()
			data := vm.appState.GetStorage(callee.Address, loc)
			stack.Push(data)
			dbg.Printf(" {0x%X : 0x%X}\n", loc, data)

		case SSTORE: // 0x55
			loc, data := stack.Pop(), stack.Pop()
			if useGasNegative(gas, GasStorageUpdate, &err) {
				return nil, err
			}
			vm.appState.SetStorage(callee.Address, loc, data)
			dbg.Printf(" {0x%X : 0x%X}\n", loc, data)

		case JUMP: // 0x56
			err = jump(code, stack.Pop64(), &pc)
			continue

		case JUMPI: // 0x57
			pos, cond := stack.Pop64(), stack.Pop()
			if !cond.IsZero() {
				err = jump(code, pos, &pc)
				continue
			}
			dbg.Printf(" ~> false\n")

		case PC: // 0x58
			stack.Push64(pc)

		case MSIZE: // 0x59
			stack.Push64(int64(len(memory)))

		case GAS: // 0x5A
			stack.Push64(*gas)
			dbg.Printf(" => %X\n", *gas)

		case JUMPDEST: // 0x5B
			dbg.Printf("\n")
			// Do nothing

		case PUSH1, PUSH2, PUSH3, PUSH4, PUSH5, PUSH6, PUSH7, PUSH8, PUSH9, PUSH10, PUSH11, PUSH12, PUSH13, PUSH14, PUSH15, PUSH16, PUSH17, PUSH18, PUSH19, PUSH20, PUSH21, PUSH22, PUSH23, PUSH24, PUSH25, PUSH26, PUSH27, PUSH28, PUSH29, PUSH30, PUSH31, PUSH32:
			a := int64(op - PUSH1 + 1)
			codeSegment, ok := subslice(code, pc+1, a)
			if !ok {
				return nil, firstErr(err, ErrCodeOutOfBounds)
			}
			res := LeftPadWord256(codeSegment)
			stack.Push(res)
			pc += a
			dbg.Printf(" => 0x%X\n", res)
			//stack.Print(10)

		case DUP1, DUP2, DUP3, DUP4, DUP5, DUP6, DUP7, DUP8, DUP9, DUP10, DUP11, DUP12, DUP13, DUP14, DUP15, DUP16:
			n := int(op - DUP1 + 1)
			stack.Dup(n)
			dbg.Printf(" => [%d] 0x%X\n", n, stack.Peek().Bytes())

		case SWAP1, SWAP2, SWAP3, SWAP4, SWAP5, SWAP6, SWAP7, SWAP8, SWAP9, SWAP10, SWAP11, SWAP12, SWAP13, SWAP14, SWAP15, SWAP16:
			n := int(op - SWAP1 + 2)
			stack.Swap(n)
			dbg.Printf(" => [%d] %X\n", n, stack.Peek())
			//stack.Print(10)

		case LOG0, LOG1, LOG2, LOG3, LOG4:
			n := int(op - LOG0)
			topics := make([]Word256, n)
			offset, size := stack.Pop64(), stack.Pop64()
			for i := 0; i < n; i++ {
				topics[i] = stack.Pop()
			}
			data, ok := subslice(memory, offset, size)
			if !ok {
				return nil, firstErr(err, ErrMemoryOutOfBounds)
			}
			log := &Log{
				callee.Address,
				topics,
				data,
				vm.params.BlockHeight,
			}
			vm.appState.AddLog(log)
			if vm.evc != nil {
				eventId := types.EventStringLogEvent(callee.Address.Postfix(20))
				fmt.Printf("eventId: %s\n", eventId)
				vm.evc.FireEvent(eventId, log)
			}
			// Using sol-log for this as well since 'log' will print garbage.
			dbg.Printf(" => T:%X D:%X\n", log.Topics, log.Data)

		case CREATE: // 0xF0
			if !HasPermission(vm.appState, callee, ptypes.CreateContract) {
				return nil, ErrPermission{"create_contract"}
			}
			contractValue := stack.Pop64()
			offset, size := stack.Pop64(), stack.Pop64()
			input, ok := subslice(memory, offset, size)
			if !ok {
				return nil, firstErr(err, ErrMemoryOutOfBounds)
			}

			// Check balance
			if callee.Balance < contractValue {
				return nil, firstErr(err, ErrInsufficientBalance)
			}

			// TODO charge for gas to create account _ the code length * GasCreateByte

			newAccount := vm.appState.CreateAccount(callee)
			// Run the input to get the contract code.
			ret, err_ := vm.Call(callee, newAccount, input, input, contractValue, gas)
			if err_ != nil {
				stack.Push(Zero256)
			} else {
				newAccount.Code = ret // Set the code
				stack.Push(newAccount.Address)
			}

		case CALL, CALLCODE: // 0xF1, 0xF2
			if !HasPermission(vm.appState, callee, ptypes.Call) {
				return nil, ErrPermission{"call"}
			}
			gasLimit := stack.Pop64()
			addr, value := stack.Pop(), stack.Pop64()
			inOffset, inSize := stack.Pop64(), stack.Pop64()   // inputs
			retOffset, retSize := stack.Pop64(), stack.Pop64() // outputs
			dbg.Printf(" => %X\n", addr)

			// Get the arguments from the memory
			args, ok := subslice(memory, inOffset, inSize)
			if !ok {
				return nil, firstErr(err, ErrMemoryOutOfBounds)
			}

			// Ensure that gasLimit is reasonable
			if *gas < gasLimit {
				return nil, firstErr(err, ErrInsufficientGas)
			} else {
				*gas -= gasLimit
				// NOTE: we will return any used gas later.
			}

			// Begin execution
			var ret []byte
			var err error
			if nativeContract := registeredNativeContracts[addr]; nativeContract != nil {
				// Native contract
				ret, err = nativeContract(vm.appState, callee, args, &gasLimit)

				// for now we fire the Call event. maybe later we'll fire more particulars
				var exception string
				if err != nil {
					exception = err.Error()
				}
				vm.fireCallEvent(&exception, &ret, callee, &Account{Address: addr}, args, value, gas)
			} else {
				// EVM contract
				if useGasNegative(gas, GasGetAccount, &err) {
					return nil, err
				}
				acc := vm.appState.GetAccount(addr)
				// since CALL is used also for sending funds,
				// acc may not exist yet. This is an error for
				// CALLCODE, but not for CALL, though I don't think
				// ethereum actually cares
				if op == CALLCODE {
					if acc == nil {
						return nil, firstErr(err, ErrUnknownAddress)
					}
					ret, err = vm.Call(callee, callee, acc.Code, args, value, gas)
				} else {
					if acc == nil {
						// nil account means we're sending funds to a new account
						if !HasPermission(vm.appState, caller, ptypes.CreateAccount) {
							return nil, ErrPermission{"create_account"}
						}
						acc = &Account{Address: addr}
						vm.appState.UpdateAccount(acc)
						// send funds to new account
						ret, err = vm.Call(callee, acc, acc.Code, args, value, gas)
					} else {
						// call standard contract
						ret, err = vm.Call(callee, acc, acc.Code, args, value, gas)
					}
				}
			}

			// Push result
			if err != nil {
				dbg.Printf("error on call: %s\n", err.Error())
				stack.Push(Zero256)
			} else {
				stack.Push(One256)
				dest, ok := subslice(memory, retOffset, retSize)
				if !ok {
					return nil, firstErr(err, ErrMemoryOutOfBounds)
				}
				copy(dest, ret)
			}

			// Handle remaining gas.
			*gas += gasLimit

			dbg.Printf("resume %X (%v)\n", callee.Address, gas)

		case RETURN: // 0xF3
			offset, size := stack.Pop64(), stack.Pop64()
			ret, ok := subslice(memory, offset, size)
			if !ok {
				return nil, firstErr(err, ErrMemoryOutOfBounds)
			}
			dbg.Printf(" => [%v, %v] (%d) 0x%X\n", offset, size, len(ret), ret)
			return ret, nil

		case SUICIDE: // 0xFF
			addr := stack.Pop()
			if useGasNegative(gas, GasGetAccount, &err) {
				return nil, err
			}
			// TODO if the receiver is , then make it the fee.
			receiver := vm.appState.GetAccount(addr)
			if receiver == nil {
				return nil, firstErr(err, ErrUnknownAddress)
			}
			balance := callee.Balance
			receiver.Balance += balance
			vm.appState.UpdateAccount(receiver)
			vm.appState.RemoveAccount(callee)
			dbg.Printf(" => (%X) %v\n", addr[:4], balance)
			fallthrough

		default:
			dbg.Printf("(pc) %-3v Invalid opcode %X\n", pc, op)
			return nil, fmt.Errorf("Invalid opcode %X", op)
		}

		pc++

	}
}

func subslice(data []byte, offset, length int64) (ret []byte, ok bool) {
	size := int64(len(data))
	if size < offset {
		return nil, false
	} else if size < offset+length {
		ret, ok = data[offset:], true
		ret = RightPadBytes(ret, 32)
	} else {
		ret, ok = data[offset:offset+length], true
	}

	return
}

func rightMostBytes(data []byte, n int) []byte {
	size := MinInt(len(data), n)
	offset := len(data) - size
	return data[offset:]
}

func codeGetOp(code []byte, n int64) OpCode {
	if int64(len(code)) <= n {
		return OpCode(0) // stop
	} else {
		return OpCode(code[n])
	}
}

func jump(code []byte, to int64, pc *int64) (err error) {
	dest := codeGetOp(code, to)
	if dest != JUMPDEST {
		dbg.Printf(" ~> %v invalid jump dest %v\n", to, dest)
		return ErrInvalidJumpDest
	}
	dbg.Printf(" ~> %v\n", to)
	*pc = to
	return nil
}

func firstErr(errA, errB error) error {
	if errA != nil {
		return errA
	} else {
		return errB
	}
}

func transfer(from, to *Account, amount int64) error {
	if from.Balance < amount {
		return ErrInsufficientBalance
	} else {
		from.Balance -= amount
		to.Balance += amount
		return nil
	}
}