fix(levm): sstore refund logic

[damiramirez]

Motivation

There was a discrepancies in gas usage and refunds. The issue was related to an improper management of gas refunds in sstore.

Description

There was an error when calculating the gas refund. Adjust the conditional logic to subtract refunds when reverting storage changes and adding refunds appropriately. Also, reordered refund and cost logic.

[JereSalo]

Nice!
I noticed that in execution specs they do this at the beginning of the opcode:

if evm.gas_left <= GAS_CALL_STIPEND:
     raise OutOfGasError

I think it is for avoiding accessing to the storage slot if we don't have enough gas, it feels like an optimization. Do you think we can add it here?

[damiramirez]

@JereSalo

Nice!
I noticed that in execution specs they do this at the beginning of the opcode:

if evm.gas_left <= GAS_CALL_STIPEND:
     raise OutOfGasError

I think it is for avoiding accessing to the storage slot if we don't have enough gas, it feels like an optimization. Do you think we can add it here?

We are doing that in the cost function:

pub fn sstore(
    storage_slot: &StorageSlot,
    new_value: U256,
    storage_slot_was_cold: bool,
    current_call_frame: &CallFrame,
) -> Result<u64, VMError> {
    // EIP-2200
    let gas_left = current_call_frame
        .gas_limit
        .checked_sub(current_call_frame.gas_used)
        .ok_or(OutOfGasError::ConsumedGasOverflow)?;
    if gas_left <= SSTORE_STIPEND {
        return Err(VMError::OutOfGas(OutOfGasError::MaxGasLimitExceeded));
    }
...

I can move it to the opcode function and if this case happens, we avoid doing extra calculations.

Done fce0d53

[JereSalo]

n1