openethereum/ethcore/evm/src/interpreter/gasometer.rs

// Copyright 2015-2019 Parity Technologies (UK) Ltd.
// This file is part of Parity Ethereum.

// Parity Ethereum is free software: you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.

// Parity Ethereum 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 General Public License for more details.

// You should have received a copy of the GNU General Public License
// along with Parity Ethereum.  If not, see <http://www.gnu.org/licenses/>.

use super::u256_to_address;
use ethereum_types::{H256, U256};
use std::cmp;

use evm;
use instructions::{self, Instruction, InstructionInfo};
use interpreter::stack::Stack;
use vm::{self, Schedule};

macro_rules! overflowing {
    ($x: expr) => {{
        let (v, overflow) = $x;
        if overflow {
            return Err(vm::Error::OutOfGas);
        }
        v
    }};
}

enum Request<Cost: ::evm::CostType> {
    Gas(Cost),
    GasMem(Cost, Cost),
    GasMemProvide(Cost, Cost, Option<U256>),
    GasMemCopy(Cost, Cost, Cost),
}

pub struct InstructionRequirements<Cost> {
    pub gas_cost: Cost,
    pub provide_gas: Option<Cost>,
    pub memory_total_gas: Cost,
    pub memory_required_size: usize,
}

pub struct Gasometer<Gas> {
    pub current_gas: Gas,
    pub current_mem_gas: Gas,
}

impl<Gas: evm::CostType> Gasometer<Gas> {
    pub fn new(current_gas: Gas) -> Self {
        Gasometer {
            current_gas: current_gas,
            current_mem_gas: Gas::from(0),
        }
    }

    pub fn verify_gas(&self, gas_cost: &Gas) -> vm::Result<()> {
        match &self.current_gas < gas_cost {
            true => Err(vm::Error::OutOfGas),
            false => Ok(()),
        }
    }

    /// How much gas is provided to a CALL/CREATE, given that we need to deduct `needed` for this operation
    /// and that we `requested` some.
    pub fn gas_provided(
        &self,
        schedule: &Schedule,
        needed: Gas,
        requested: Option<U256>,
    ) -> vm::Result<Gas> {
        // Try converting requested gas to `Gas` (`U256/u64`)
        // but in EIP150 even if we request more we should never fail from OOG
        let requested = requested.map(Gas::from_u256);

        match schedule.sub_gas_cap_divisor {
            Some(cap_divisor) if self.current_gas >= needed => {
                let gas_remaining = self.current_gas - needed;
                let max_gas_provided = match cap_divisor {
                    64 => gas_remaining - (gas_remaining >> 6),
                    cap_divisor => gas_remaining - gas_remaining / Gas::from(cap_divisor),
                };

                if let Some(Ok(r)) = requested {
                    Ok(cmp::min(r, max_gas_provided))
                } else {
                    Ok(max_gas_provided)
                }
            }
            _ => {
                if let Some(r) = requested {
                    r
                } else if self.current_gas >= needed {
                    Ok(self.current_gas - needed)
                } else {
                    Ok(0.into())
                }
            }
        }
    }

    /// Determine how much gas is used by the given instruction, given the machine's state.
    ///
    /// We guarantee that the final element of the returned tuple (`provided`) will be `Some`
    /// iff the `instruction` is one of `CREATE`, or any of the `CALL` variants. In this case,
    /// it will be the amount of gas that the current context provides to the child context.
    pub fn requirements(
        &mut self,
        ext: &vm::Ext,
        instruction: Instruction,
        info: &InstructionInfo,
        stack: &Stack<U256>,
        current_mem_size: usize,
    ) -> vm::Result<InstructionRequirements<Gas>> {
        let schedule = ext.schedule();
        let tier = info.tier.idx();
        let default_gas = Gas::from(schedule.tier_step_gas[tier]);

        let cost = match instruction {
            instructions::JUMPDEST => Request::Gas(Gas::from(1)),
            instructions::SSTORE => {
                if schedule.eip1706 && self.current_gas <= Gas::from(schedule.call_stipend) {
                    return Err(vm::Error::OutOfGas);
                }
                let address = H256::from(stack.peek(0));
                let newval = stack.peek(1);
                let val = U256::from(&*ext.storage_at(&address)?);

                let gas = if schedule.eip1283 {
                    let orig = U256::from(&*ext.initial_storage_at(&address)?);
                    calculate_eip1283_sstore_gas(schedule, &orig, &val, &newval)
                } else {
                    if val.is_zero() && !newval.is_zero() {
                        schedule.sstore_set_gas
                    } else {
                        // Refund for below case is added when actually executing sstore
                        // !is_zero(&val) && is_zero(newval)
                        schedule.sstore_reset_gas
                    }
                };
                Request::Gas(Gas::from(gas))
            }
            instructions::SLOAD => Request::Gas(Gas::from(schedule.sload_gas)),
            instructions::BALANCE => Request::Gas(Gas::from(schedule.balance_gas)),
            instructions::EXTCODESIZE => Request::Gas(Gas::from(schedule.extcodesize_gas)),
            instructions::EXTCODEHASH => Request::Gas(Gas::from(schedule.extcodehash_gas)),
            instructions::SUICIDE => {
                let mut gas = Gas::from(schedule.suicide_gas);

                let is_value_transfer = !ext.origin_balance()?.is_zero();
                let address = u256_to_address(stack.peek(0));
                if (!schedule.no_empty && !ext.exists(&address)?)
                    || (schedule.no_empty
                        && is_value_transfer
                        && !ext.exists_and_not_null(&address)?)
                {
                    gas =
                        overflowing!(gas.overflow_add(schedule.suicide_to_new_account_cost.into()));
                }

                Request::Gas(gas)
            }
            instructions::MSTORE | instructions::MLOAD => {
                Request::GasMem(default_gas, mem_needed_const(stack.peek(0), 32)?)
            }
            instructions::MSTORE8 => {
                Request::GasMem(default_gas, mem_needed_const(stack.peek(0), 1)?)
            }
            instructions::RETURN | instructions::REVERT => {
                Request::GasMem(default_gas, mem_needed(stack.peek(0), stack.peek(1))?)
            }
            instructions::SHA3 => {
                let words = overflowing!(to_word_size(Gas::from_u256(*stack.peek(1))?));
                let gas = overflowing!(Gas::from(schedule.sha3_gas).overflow_add(overflowing!(
                    Gas::from(schedule.sha3_word_gas).overflow_mul(words)
                )));
                Request::GasMem(gas, mem_needed(stack.peek(0), stack.peek(1))?)
            }
            instructions::CALLDATACOPY | instructions::CODECOPY | instructions::RETURNDATACOPY => {
                Request::GasMemCopy(
                    default_gas,
                    mem_needed(stack.peek(0), stack.peek(2))?,
                    Gas::from_u256(*stack.peek(2))?,
                )
            }
            instructions::EXTCODECOPY => Request::GasMemCopy(
                schedule.extcodecopy_base_gas.into(),
                mem_needed(stack.peek(1), stack.peek(3))?,
                Gas::from_u256(*stack.peek(3))?,
            ),
            instructions::LOG0
            | instructions::LOG1
            | instructions::LOG2
            | instructions::LOG3
            | instructions::LOG4 => {
                let no_of_topics = instruction
                    .log_topics()
                    .expect("log_topics always return some for LOG* instructions; qed");
                let log_gas = schedule.log_gas + schedule.log_topic_gas * no_of_topics;

                let data_gas =
                    overflowing!(Gas::from_u256(*stack.peek(1))?
                        .overflow_mul(Gas::from(schedule.log_data_gas)));
                let gas = overflowing!(data_gas.overflow_add(Gas::from(log_gas)));
                Request::GasMem(gas, mem_needed(stack.peek(0), stack.peek(1))?)
            }
            instructions::CALL | instructions::CALLCODE => {
                let mut gas = Gas::from(schedule.call_gas);
                let mem = cmp::max(
                    mem_needed(stack.peek(5), stack.peek(6))?,
                    mem_needed(stack.peek(3), stack.peek(4))?,
                );

                let address = u256_to_address(stack.peek(1));
                let is_value_transfer = !stack.peek(2).is_zero();

                if instruction == instructions::CALL
                    && ((!schedule.no_empty && !ext.exists(&address)?)
                        || (schedule.no_empty
                            && is_value_transfer
                            && !ext.exists_and_not_null(&address)?))
                {
                    gas = overflowing!(gas.overflow_add(schedule.call_new_account_gas.into()));
                }

                if is_value_transfer {
                    gas = overflowing!(gas.overflow_add(schedule.call_value_transfer_gas.into()));
                }

                let requested = *stack.peek(0);

                Request::GasMemProvide(gas, mem, Some(requested))
            }
            instructions::DELEGATECALL | instructions::STATICCALL => {
                let gas = Gas::from(schedule.call_gas);
                let mem = cmp::max(
                    mem_needed(stack.peek(4), stack.peek(5))?,
                    mem_needed(stack.peek(2), stack.peek(3))?,
                );
                let requested = *stack.peek(0);

                Request::GasMemProvide(gas, mem, Some(requested))
            }
            instructions::CREATE => {
                let start = stack.peek(1);
                let len = stack.peek(2);

                let gas = Gas::from(schedule.create_gas);
                let mem = mem_needed(start, len)?;

                Request::GasMemProvide(gas, mem, None)
            }
            instructions::CREATE2 => {
                let start = stack.peek(1);
                let len = stack.peek(2);

                let base = Gas::from(schedule.create_gas);
                let word = overflowing!(to_word_size(Gas::from_u256(*len)?));
                let word_gas = overflowing!(Gas::from(schedule.sha3_word_gas).overflow_mul(word));
                let gas = overflowing!(base.overflow_add(word_gas));
                let mem = mem_needed(start, len)?;

                Request::GasMemProvide(gas, mem, None)
            }
            instructions::EXP => {
                let expon = stack.peek(1);
                let bytes = ((expon.bits() + 7) / 8) as usize;
                let gas = Gas::from(schedule.exp_gas + schedule.exp_byte_gas * bytes);
                Request::Gas(gas)
            }
            instructions::BLOCKHASH => Request::Gas(Gas::from(schedule.blockhash_gas)),
            _ => Request::Gas(default_gas),
        };

        Ok(match cost {
            Request::Gas(gas) => InstructionRequirements {
                gas_cost: gas,
                provide_gas: None,
                memory_required_size: 0,
                memory_total_gas: self.current_mem_gas,
            },
            Request::GasMem(gas, mem_size) => {
                let (mem_gas_cost, new_mem_gas, new_mem_size) =
                    self.mem_gas_cost(schedule, current_mem_size, &mem_size)?;
                let gas = overflowing!(gas.overflow_add(mem_gas_cost));
                InstructionRequirements {
                    gas_cost: gas,
                    provide_gas: None,
                    memory_required_size: new_mem_size,
                    memory_total_gas: new_mem_gas,
                }
            }
            Request::GasMemProvide(gas, mem_size, requested) => {
                let (mem_gas_cost, new_mem_gas, new_mem_size) =
                    self.mem_gas_cost(schedule, current_mem_size, &mem_size)?;
                let gas = overflowing!(gas.overflow_add(mem_gas_cost));
                let provided = self.gas_provided(schedule, gas, requested)?;
                let total_gas = overflowing!(gas.overflow_add(provided));

                InstructionRequirements {
                    gas_cost: total_gas,
                    provide_gas: Some(provided),
                    memory_required_size: new_mem_size,
                    memory_total_gas: new_mem_gas,
                }
            }
            Request::GasMemCopy(gas, mem_size, copy) => {
                let (mem_gas_cost, new_mem_gas, new_mem_size) =
                    self.mem_gas_cost(schedule, current_mem_size, &mem_size)?;
                let copy = overflowing!(to_word_size(copy));
                let copy_gas = overflowing!(Gas::from(schedule.copy_gas).overflow_mul(copy));
                let gas = overflowing!(gas.overflow_add(copy_gas));
                let gas = overflowing!(gas.overflow_add(mem_gas_cost));

                InstructionRequirements {
                    gas_cost: gas,
                    provide_gas: None,
                    memory_required_size: new_mem_size,
                    memory_total_gas: new_mem_gas,
                }
            }
        })
    }

    fn mem_gas_cost(
        &self,
        schedule: &Schedule,
        current_mem_size: usize,
        mem_size: &Gas,
    ) -> vm::Result<(Gas, Gas, usize)> {
        let gas_for_mem = |mem_size: Gas| {
            let s = mem_size >> 5;
            // s * memory_gas + s * s / quad_coeff_div
            let a = overflowing!(s.overflow_mul(Gas::from(schedule.memory_gas)));

            // Calculate s*s/quad_coeff_div
            assert_eq!(schedule.quad_coeff_div, 512);
            let b = overflowing!(s.overflow_mul_shr(s, 9));
            Ok(overflowing!(a.overflow_add(b)))
        };

        let current_mem_size = Gas::from(current_mem_size);
        let req_mem_size_rounded = overflowing!(to_word_size(*mem_size)) << 5;

        let (mem_gas_cost, new_mem_gas) = if req_mem_size_rounded > current_mem_size {
            let new_mem_gas = gas_for_mem(req_mem_size_rounded)?;
            (new_mem_gas - self.current_mem_gas, new_mem_gas)
        } else {
            (Gas::from(0), self.current_mem_gas)
        };

        Ok((mem_gas_cost, new_mem_gas, req_mem_size_rounded.as_usize()))
    }
}

#[inline]
fn mem_needed_const<Gas: evm::CostType>(mem: &U256, add: usize) -> vm::Result<Gas> {
    Gas::from_u256(overflowing!(mem.overflowing_add(U256::from(add))))
}

#[inline]
fn mem_needed<Gas: evm::CostType>(offset: &U256, size: &U256) -> vm::Result<Gas> {
    if size.is_zero() {
        return Ok(Gas::from(0));
    }

    Gas::from_u256(overflowing!(offset.overflowing_add(*size)))
}

#[inline]
fn add_gas_usize<Gas: evm::CostType>(value: Gas, num: usize) -> (Gas, bool) {
    value.overflow_add(Gas::from(num))
}

#[inline]
fn to_word_size<Gas: evm::CostType>(value: Gas) -> (Gas, bool) {
    let (gas, overflow) = add_gas_usize(value, 31);
    if overflow {
        return (gas, overflow);
    }

    (gas >> 5, false)
}

#[inline]
fn calculate_eip1283_sstore_gas<Gas: evm::CostType>(
    schedule: &Schedule,
    original: &U256,
    current: &U256,
    new: &U256,
) -> Gas {
    Gas::from(if current == new {
        // 1. If current value equals new value (this is a no-op), 200 gas is deducted.
        schedule.sload_gas
    } else {
        // 2. If current value does not equal new value
        if original == current {
            // 2.1. If original value equals current value (this storage slot has not been changed by the current execution context)
            if original.is_zero() {
                // 2.1.1. If original value is 0, 20000 gas is deducted.
                schedule.sstore_set_gas
            } else {
                // 2.1.2. Otherwise, 5000 gas is deducted.
                schedule.sstore_reset_gas

                // 2.1.2.1. If new value is 0, add 15000 gas to refund counter.
            }
        } else {
            // 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.
            schedule.sload_gas

            // 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.
        }
    })
}

pub fn handle_eip1283_sstore_clears_refund(
    ext: &mut vm::Ext,
    original: &U256,
    current: &U256,
    new: &U256,
) {
    let sstore_clears_schedule = ext.schedule().sstore_refund_gas;

    if current == new {
        // 1. If current value equals new value (this is a no-op), 200 gas is deducted.
    } else {
        // 2. If current value does not equal new value
        if original == current {
            // 2.1. If original value equals current value (this storage slot has not been changed by the current execution context)
            if original.is_zero() {
                // 2.1.1. If original value is 0, 20000 gas is deducted.
            } else {
                // 2.1.2. Otherwise, 5000 gas is deducted.
                if new.is_zero() {
                    // 2.1.2.1. If new value is 0, add 15000 gas to refund counter.
                    ext.add_sstore_refund(sstore_clears_schedule);
                }
            }
        } else {
            // 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.

            if !original.is_zero() {
                // 2.2.1. If original value is not 0
                if current.is_zero() {
                    // 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.
                    ext.sub_sstore_refund(sstore_clears_schedule);
                } else if new.is_zero() {
                    // 2.2.1.2. If new value is 0 (also means that current value is not 0), add 15000 gas to refund counter.
                    ext.add_sstore_refund(sstore_clears_schedule);
                }
            }

            if original == new {
                // 2.2.2. If original value equals new value (this storage slot is reset)
                if original.is_zero() {
                    // 2.2.2.1. If original value is 0, add 19800 gas to refund counter.
                    let refund = ext.schedule().sstore_set_gas - ext.schedule().sload_gas;
                    ext.add_sstore_refund(refund);
                } else {
                    // 2.2.2.2. Otherwise, add 4800 gas to refund counter.
                    let refund = ext.schedule().sstore_reset_gas - ext.schedule().sload_gas;
                    ext.add_sstore_refund(refund);
                }
            }
        }
    }
}

#[test]
fn test_mem_gas_cost() {
    // given
    let gasometer = Gasometer::<U256>::new(U256::zero());
    let schedule = Schedule::default();
    let current_mem_size = 5;
    let mem_size = !U256::zero();

    // when
    let result = gasometer.mem_gas_cost(&schedule, current_mem_size, &mem_size);

    // then
    if result.is_ok() {
        assert!(false, "Should fail with OutOfGas");
    }
}

#[test]
fn test_calculate_mem_cost() {
    // given
    let gasometer = Gasometer::<usize>::new(0);
    let schedule = Schedule::default();
    let current_mem_size = 0;
    let mem_size = 5;

    // when
    let (mem_cost, new_mem_gas, mem_size) = gasometer
        .mem_gas_cost(&schedule, current_mem_size, &mem_size)
        .unwrap();

    // then
    assert_eq!(mem_cost, 3);
    assert_eq!(new_mem_gas, 3);
    assert_eq!(mem_size, 32);
}