[Review] Restore opcode gas costs from Ethereum

[gastonponti]

Simple Summary

Restore the gas cost of the SLOAD, *CALL, BALANCE, EXT* and SELFDESTRUCT opcodes which diverged from Ethereum.

Abstract

Apply the EIP-1884 gas cost changes, that will restore the costs applied in the EIP-2929. Our CIP-48 was created to apply the last one, with reduced costs.

Motivation

EIP-1884 was not applied in the past, because the CELO state was small in comparison to Ethereum’s. This has changed already, and not only do we need to cover ourselves from possible attacks of underpriced operations, but also not having the same gas cost table than Ethereum, generates two issues:

• We are not fully compatible with Ethereum
• Increases the complexity of the codebase

In our new pursue of maintaining the execution layer as close as Ethereum to be able to merge new versions from upstream as soon as possible, this change not only brings us closer to that objective, but also simplifies our e2e tests to verify that everything works as expected.

Specification

Copy the specification of EIP-2929 restoring the changes added in the EIP-1884:

Parameters

Constant	Espresso Value	Restored Value
COLD_ACCOUNT_ACCESS_COST	900	2600
COLD_SLOAD_COST	800	2100
WARM_STORAGE_READ_COST	100	100

SStore

As the SSTORE_CLEARS_SCHEDULE changes in the EIP-3529, using the values of the EIP-2929, which also depended of the EIP-1884.

The new SSTORE_CLEARS_SCHEDULE changes from 6100 to 4800

Constant	Calculation	Espresso Value	Restored Value
SSTORE_CLEARS_SCHEDULE	SSTORE_RESET_GAS + ACCESS_LIST_STORAGE_KEY_COST	6100	4800

Rationale

There is no specific need to restore the same numbers, and we could discuss a better tuning to reach a more specific gas cost per opcode, but mimicking the same numbers of Ethereum will simplify the code base and reduce the divergence from upstream geth, thereby making Celo clients more maintainable.

Backwards Compatibility

• This needs to be added as part of a hardfork.
• These gas cost increases may potentially break contracts that depend on fixed gas costs.

Security Considerations

As with any gas cost increasing EIP/CIP, there are three possible cases where it could cause applications to break:

1. Fixed gas limits to sub-calls in contracts
2. Applications relying on contract calls that consume close to the full gas limit
3. The 2300 base limit given to the callee by ETH-transferring calls

There are two ways to look at these risks. First, we can note that as of today developers have had years of warning; gas cost increases on storage-accessing opcodes have been discussed for a long time, with multiple statements made including to major dApp developers around the likelihood of such changes. EIP-1884 itself, EIP-2929, or even CIP-48 provided an important wake-up call. Hence, we can argue that risks this time will be significantly lower than the previous CIP-48.

License

This work is licensed under the Apache License, Version 2.0.