path: root/core/vm/gas_table.go

// Copyright 2017 The go-ethereum Authors
// This file is part of the go-ethereum library.
//
// The go-ethereum library is free software: you can redistribute it and/or modify
// it under the terms of the GNU Lesser General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// The go-ethereum library is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
// GNU Lesser General Public License for more details.
//
// You should have received a copy of the GNU Lesser General Public License
// along with the go-ethereum library. If not, see <http://www.gnu.org/licenses/>.

package vm

import (
    "errors"

    "github.com/ethereum/go-ethereum/common"
    "github.com/ethereum/go-ethereum/common/math"
    "github.com/ethereum/go-ethereum/params"
)

// memoryGasCost calculates the quadratic gas for memory expansion. It does so
// only for the memory region that is expanded, not the total memory.
func memoryGasCost(mem *Memory, newMemSize uint64) (uint64, error) {
    if newMemSize == 0 {
        return 0, nil
    }
    // The maximum that will fit in a uint64 is max_word_count - 1. Anything above
    // that will result in an overflow. Additionally, a newMemSize which results in
    // a newMemSizeWords larger than 0xFFFFFFFF will cause the square operation to
    // overflow. The constant 0x1FFFFFFFE0 is the highest number that can be used
    // without overflowing the gas calculation.
    if newMemSize > 0x1FFFFFFFE0 {
        return 0, errGasUintOverflow
    }
    newMemSizeWords := toWordSize(newMemSize)
    newMemSize = newMemSizeWords * 32

    if newMemSize > uint64(mem.Len()) {
        square := newMemSizeWords * newMemSizeWords
        linCoef := newMemSizeWords * params.MemoryGas
        quadCoef := square / params.QuadCoeffDiv
        newTotalFee := linCoef + quadCoef

        fee := newTotalFee - mem.lastGasCost
        mem.lastGasCost = newTotalFee

        return fee, nil
    }
    return 0, nil
}

// memoryCopierGas creates the gas functions for the following opcodes, and takes
// the stack position of the operand which determines the size of the data to copy
// as argument:
// CALLDATACOPY (stack position 2)
// CODECOPY (stack position 2)
// EXTCODECOPY (stack poition 3)
// RETURNDATACOPY (stack position 2)
func memoryCopierGas(stackpos int) gasFunc {
    return func(evm *EVM, contract *Contract, stack *Stack, mem *Memory, memorySize uint64) (uint64, error) {
        // Gas for expanding the memory
        gas, err := memoryGasCost(mem, memorySize)
        if err != nil {
            return 0, err
        }
        // And gas for copying data, charged per word at param.CopyGas
        words, overflow := bigUint64(stack.Back(stackpos))
        if overflow {
            return 0, errGasUintOverflow
        }

        if words, overflow = math.SafeMul(toWordSize(words), params.CopyGas); overflow {
            return 0, errGasUintOverflow
        }

        if gas, overflow = math.SafeAdd(gas, words); overflow {
            return 0, errGasUintOverflow
        }
        return gas, nil
    }
}

var (
    gasCallDataCopy   = memoryCopierGas(2)
    gasCodeCopy       = memoryCopierGas(2)
    gasExtCodeCopy    = memoryCopierGas(3)
    gasReturnDataCopy = memoryCopierGas(2)
)

func gasSStore(evm *EVM, contract *Contract, stack *Stack, mem *Memory, memorySize uint64) (uint64, error) {
    var (
        y, x    = stack.Back(1), stack.Back(0)
        current = evm.StateDB.GetState(contract.Address(), common.BigToHash(x))
    )
    // The legacy gas metering only takes into consideration the current state
    // Legacy rules should be applied if we are in Petersburg (removal of EIP-1283)
    // OR Constantinople is not active
    if evm.chainRules.IsPetersburg || !evm.chainRules.IsConstantinople {
        // 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)
        switch {
        case current == (common.Hash{}) && y.Sign() != 0: // 0 => non 0
            return params.SstoreSetGas, nil
        case current != (common.Hash{}) && y.Sign() == 0: // non 0 => 0
            evm.StateDB.AddRefund(params.SstoreRefundGas)
            return params.SstoreClearGas, nil
        default: // non 0 => non 0 (or 0 => 0)
            return params.SstoreResetGas, nil
        }
    }
    // The new gas metering is based on net gas costs (EIP-1283):
    //
    // 1. If current value equals new value (this is a no-op), 200 gas is deducted.
    // 2. If current value does not equal new value
    //   2.1. If original value equals current value (this storage slot has not been changed by the current execution context)
    //     2.1.1. If original value is 0, 20000 gas is deducted.
    //     2.1.2. Otherwise, 5000 gas is deducted. If new value is 0, add 15000 gas to refund counter.
    //  2.2. If original value does not equal current value (this storage slot is dirty), 200 gas is deducted. Apply both of the following clauses.
    //    2.2.1. If original value is not 0
    //       2.2.1.1. If current value is 0 (also means that new value is not 0), remove 15000 gas from refund counter. We can prove that refund counter will never go below 0.
    //       2.2.1.2. If new value is 0 (also means that current value is not 0), add 15000 gas to refund counter.
    //    2.2.2. If original value equals new value (this storage slot is reset)
    //       2.2.2.1. If original value is 0, add 19800 gas to refund counter.
    //       2.2.2.2. Otherwise, add 4800 gas to refund counter.
    value := common.BigToHash(y)
    if current == value { // noop (1)
        return params.NetSstoreNoopGas, nil
    }
    original := evm.StateDB.GetCommittedState(contract.Address(), common.BigToHash(x))
    if original == current {
        if original == (common.Hash{}) { // create slot (2.1.1)
            return params.NetSstoreInitGas, nil
        }
        if value == (common.Hash{}) { // delete slot (2.1.2b)
            evm.StateDB.AddRefund(params.NetSstoreClearRefund)
        }
        return params.NetSstoreCleanGas, nil // write existing slot (2.1.2)
    }
    if original != (common.Hash{}) {
        if current == (common.Hash{}) { // recreate slot (2.2.1.1)
            evm.StateDB.SubRefund(params.NetSstoreClearRefund)
        } else if value == (common.Hash{}) { // delete slot (2.2.1.2)
            evm.StateDB.AddRefund(params.NetSstoreClearRefund)
        }
    }
    if original == value {
        if original == (common.Hash{}) { // reset to original inexistent slot (2.2.2.1)
            evm.StateDB.AddRefund(params.NetSstoreResetClearRefund)
        } else { // reset to original existing slot (2.2.2.2)
            evm.StateDB.AddRefund(params.NetSstoreResetRefund)
        }
    }
    return params.NetSstoreDirtyGas, nil
}

// 0. If *gasleft* is less than or equal to 2300, fail the current call.
// 1. If current value equals new value (this is a no-op), SSTORE_NOOP_GAS gas is deducted.
// 2. If current value does not equal new value:
//   2.1. If original value equals current value (this storage slot has not been changed by the current execution context):
//     2.1.1. If original value is 0, SSTORE_INIT_GAS gas is deducted.
//     2.1.2. Otherwise, SSTORE_CLEAN_GAS gas is deducted. If new value is 0, add SSTORE_CLEAR_REFUND to refund counter.
//   2.2. If original value does not equal current value (this storage slot is dirty), SSTORE_DIRTY_GAS gas is deducted. Apply both of the following clauses:
//     2.2.1. If original value is not 0:
//       2.2.1.1. If current value is 0 (also means that new value is not 0), subtract SSTORE_CLEAR_REFUND gas from refund counter. We can prove that refund counter will never go below 0.
//       2.2.1.2. If new value is 0 (also means that current value is not 0), add SSTORE_CLEAR_REFUND gas to refund counter.
//     2.2.2. If original value equals new value (this storage slot is reset):
//       2.2.2.1. If original value is 0, add SSTORE_INIT_REFUND to refund counter.
//       2.2.2.2. Otherwise, add SSTORE_CLEAN_REFUND gas to refund counter.
func gasSStoreEIP2200(evm *EVM, contract *Contract, stack *Stack, mem *Memory, memorySize uint64) (uint64, error) {
    // If we fail the minimum gas availability invariant, fail (0)
    if contract.Gas <= params.SstoreSentryGasEIP2200 {
        return 0, errors.New("not enough gas for reentrancy sentry")
    }
    // Gas sentry honoured, do the actual gas calculation based on the stored value
    var (
        y, x    = stack.Back(1), stack.Back(0)
        current = evm.StateDB.GetState(contract.Address(), common.BigToHash(x))
    )
    value := common.BigToHash(y)

    if current == value { // noop (1)
        return params.SstoreNoopGasEIP2200, nil
    }
    original := evm.StateDB.GetCommittedState(contract.Address(), common.BigToHash(x))
    if original == current {
        if original == (common.Hash{}) { // create slot (2.1.1)
            return params.SstoreInitGasEIP2200, nil
        }
        if value == (common.Hash{}) { // delete slot (2.1.2b)
            evm.StateDB.AddRefund(params.SstoreClearRefundEIP2200)
        }
        return params.SstoreCleanGasEIP2200, nil // write existing slot (2.1.2)
    }
    if original != (common.Hash{}) {
        if current == (common.Hash{}) { // recreate slot (2.2.1.1)
            evm.StateDB.SubRefund(params.SstoreClearRefundEIP2200)
        } else if value == (common.Hash{}) { // delete slot (2.2.1.2)
            evm.StateDB.AddRefund(params.SstoreClearRefundEIP2200)
        }
    }
    if original == value {
        if original == (common.Hash{}) { // reset to original inexistent slot (2.2.2.1)
            evm.StateDB.AddRefund(params.SstoreInitRefundEIP2200)
        } else { // reset to original existing slot (2.2.2.2)
            evm.StateDB.AddRefund(params.SstoreCleanRefundEIP2200)
        }
    }
    return params.SstoreDirtyGasEIP2200, nil // dirty update (2.2)
}

func makeGasLog(n uint64) gasFunc {
    return func(evm *EVM, contract *Contract, stack *Stack, mem *Memory, memorySize uint64) (uint64, error) {
        requestedSize, overflow := bigUint64(stack.Back(1))
        if overflow {
            return 0, errGasUintOverflow
        }

        gas, err := memoryGasCost(mem, memorySize)
        if err != nil {
            return 0, err
        }

        if gas, overflow = math.SafeAdd(gas, params.LogGas); overflow {
            return 0, errGasUintOverflow
        }
        if gas, overflow = math.SafeAdd(gas, n*params.LogTopicGas); overflow {
            return 0, errGasUintOverflow
        }

        var memorySizeGas uint64
        if memorySizeGas, overflow = math.SafeMul(requestedSize, params.LogDataGas); overflow {
            return 0, errGasUintOverflow
        }
        if gas, overflow = math.SafeAdd(gas, memorySizeGas); overflow {
            return 0, errGasUintOverflow
        }
        return gas, nil
    }
}

func gasSha3(evm *EVM, contract *Contract, stack *Stack, mem *Memory, memorySize uint64) (uint64, error) {
    gas, err := memoryGasCost(mem, memorySize)
    if err != nil {
        return 0, err
    }
    wordGas, overflow := bigUint64(stack.Back(1))
    if overflow {
        return 0, errGasUintOverflow
    }
    if wordGas, overflow = math.SafeMul(toWordSize(wordGas), params.Sha3WordGas); overflow {
        return 0, errGasUintOverflow
    }
    if gas, overflow = math.SafeAdd(gas, wordGas); overflow {
        return 0, errGasUintOverflow
    }
    return gas, nil
}

// pureMemoryGascost is used by several operations, which aside from their
// static cost have a dynamic cost which is solely based on the memory
// expansion
func pureMemoryGascost(evm *EVM, contract *Contract, stack *Stack, mem *Memory, memorySize uint64) (uint64, error) {
    return memoryGasCost(mem, memorySize)
}

var (
    gasReturn  = pureMemoryGascost
    gasRevert  = pureMemoryGascost
    gasMLoad   = pureMemoryGascost
    gasMStore8 = pureMemoryGascost
    gasMStore  = pureMemoryGascost
    gasCreate  = pureMemoryGascost
)

func gasCreate2(evm *EVM, contract *Contract, stack *Stack, mem *Memory, memorySize uint64) (uint64, error) {
    gas, err := memoryGasCost(mem, memorySize)
    if err != nil {
        return 0, err
    }
    wordGas, overflow := bigUint64(stack.Back(2))
    if overflow {
        return 0, errGasUintOverflow
    }
    if wordGas, overflow = math.SafeMul(toWordSize(wordGas), params.Sha3WordGas); overflow {
        return 0, errGasUintOverflow
    }
    if gas, overflow = math.SafeAdd(gas, wordGas); overflow {
        return 0, errGasUintOverflow
    }
    return gas, nil
}

func gasExpFrontier(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 * params.ExpByteFrontier // no overflow check required. Max is 256 * ExpByte gas
        overflow bool
    )
    if gas, overflow = math.SafeAdd(gas, params.ExpGas); overflow {
        return 0, errGasUintOverflow
    }
    return gas, nil
}

func gasExpEIP158(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 * params.ExpByteEIP158 // no overflow check required. Max is 256 * ExpByte gas
        overflow bool
    )
    if gas, overflow = math.SafeAdd(gas, params.ExpGas); overflow {
        return 0, errGasUintOverflow
    }
    return gas, nil
}

func gasCall(evm *EVM, contract *Contract, stack *Stack, mem *Memory, memorySize uint64) (uint64, error) {
    var (
        gas            uint64
        transfersValue = stack.Back(2).Sign() != 0
        address        = common.BigToAddress(stack.Back(1))
    )
    if evm.chainRules.IsEIP158 {
        if transfersValue && evm.StateDB.Empty(address) {
            gas += params.CallNewAccountGas
        }
    } else if !evm.StateDB.Exist(address) {
        gas += params.CallNewAccountGas
    }
    if transfersValue {
        gas += params.CallValueTransferGas
    }
    memoryGas, err := memoryGasCost(mem, memorySize)
    if err != nil {
        return 0, err
    }
    var overflow bool
    if gas, overflow = math.SafeAdd(gas, memoryGas); overflow {
        return 0, errGasUintOverflow
    }

    evm.callGasTemp, err = callGas(evm.chainRules.IsEIP150, contract.Gas, gas, stack.Back(0))
    if err != nil {
        return 0, err
    }
    if gas, overflow = math.SafeAdd(gas, evm.callGasTemp); overflow {
        return 0, errGasUintOverflow
    }
    return gas, nil
}

func gasCallCode(evm *EVM, contract *Contract, stack *Stack, mem *Memory, memorySize uint64) (uint64, error) {
    memoryGas, err := memoryGasCost(mem, memorySize)
    if err != nil {
        return 0, err
    }
    var (
        gas      uint64
        overflow bool
    )
    if stack.Back(2).Sign() != 0 {
        gas += params.CallValueTransferGas
    }
    if gas, overflow = math.SafeAdd(gas, memoryGas); overflow {
        return 0, errGasUintOverflow
    }
    evm.callGasTemp, err = callGas(evm.chainRules.IsEIP150, contract.Gas, gas, stack.Back(0))
    if err != nil {
        return 0, err
    }
    if gas, overflow = math.SafeAdd(gas, evm.callGasTemp); overflow {
        return 0, errGasUintOverflow
    }
    return gas, nil
}

func gasDelegateCall(evm *EVM, contract *Contract, stack *Stack, mem *Memory, memorySize uint64) (uint64, error) {
    gas, err := memoryGasCost(mem, memorySize)
    if err != nil {
        return 0, err
    }
    evm.callGasTemp, err = callGas(evm.chainRules.IsEIP150, contract.Gas, gas, stack.Back(0))
    if err != nil {
        return 0, err
    }
    var overflow bool
    if gas, overflow = math.SafeAdd(gas, evm.callGasTemp); overflow {
        return 0, errGasUintOverflow
    }
    return gas, nil
}

func gasStaticCall(evm *EVM, contract *Contract, stack *Stack, mem *Memory, memorySize uint64) (uint64, error) {
    gas, err := memoryGasCost(mem, memorySize)
    if err != nil {
        return 0, err
    }
    evm.callGasTemp, err = callGas(evm.chainRules.IsEIP150, contract.Gas, gas, stack.Back(0))
    if err != nil {
        return 0, err
    }
    var overflow bool
    if gas, overflow = math.SafeAdd(gas, evm.callGasTemp); overflow {
        return 0, errGasUintOverflow
    }
    return gas, nil
}

func gasSelfdestruct(evm *EVM, contract *Contract, stack *Stack, mem *Memory, memorySize uint64) (uint64, error) {
    var gas uint64
    // EIP150 homestead gas reprice fork:
    if evm.chainRules.IsEIP150 {
        gas = params.SelfdestructGasEIP150
        var address = common.BigToAddress(stack.Back(0))

        if evm.chainRules.IsEIP158 {
            // if empty and transfers value
            if evm.StateDB.Empty(address) && evm.StateDB.GetBalance(contract.Address()).Sign() != 0 {
                gas += params.CreateBySelfdestructGas
            }
        } else if !evm.StateDB.Exist(address) {
            gas += params.CreateBySelfdestructGas
        }
    }

    if !evm.StateDB.HasSuicided(contract.Address()) {
        evm.StateDB.AddRefund(params.SelfdestructRefundGas)
    }
    return gas, nil
}