Remove the limit on contract code size

Abstract

Remove the limit on the contract code size, i.e., only limit the contract code size by block gas limit, with minimal changes to existing code and proper gas metering adjustment to avoid possible attacks.

Motivation

The motivation is to remove the limit on the code size so that users can deploy a large-code contract without worrying about splitting the contract into several sub-contracts.

With the dramatic growth of dApplications, the functionalities of smart contracts are becoming more and more complicated, and thus, the sizes of newly developed contracts are steadily increasing. As a result, we are facing more and more issues with the 24576-bytes contract size limit. Although several techniques such as splitting a large contract into several sub-contracts can alleviate the issue, these techniques inevitably increase the burden of developing/deploying/maintaining smart contracts.

The proposal implements a solution to remove the existing 24576-bytes limit of the code size. Further, the proposal aims to minimize the changes in the client implementation (e.g., Geth) with

• proper gas metering to avoid abusing the node resources for contract-related opcodes, i.e, CODESIZE (0x38)/CODECOPY (0x39)/EXTCODESIZE (0x3B)/EXTCODECOPY (0x3C)/EXTCODEHASH (0x3F)/DELEGATECALL (0xF4)/CALL (0xF1)/CALLCODE (0xF2)/STATICCALL (0xFA)/CREATE (0xF0)/CREATE2 (0xF5); and
• no change to the existing structure of the Ethereum state.

Specification

Parameters

If block.number >= FORK_BLKNUM, the contract creation initialization can return data with any length, but the contract-related opcodes will take extra gas as defined below:

• For CODESIZE/CODECOPY/EXTCODESIZE/EXTCODEHASH, the gas is unchanged.

• For CREATE/CREATE2, if the newly created contract size > CODE_SIZE_UNIT, the opcodes will take extra write gas as

(CODE_SIZE - CODE_SIZE_UNIT) * CREATE_DATA_GAS.

• For EXTCODECOPY/CALL/CALLCODE/DELEGATECALL/STATICCALL, if the contract code size > CODE_SIZE_UNIT, then the opcodes will take extra gas as

(CODE_SIZE - 1) // CODE_SIZE_UNIT * COLD_ACCOUNT_CODE_ACCESS_COST_PER_UNIT

if the contract is not in accessed_code_in_addresses or 0 if the contract is in accessed_code_in_addresses, where // is the integer divide operator, and accessed_code_in_addresses: Set[Address] is a transaction-context-wide set similar to access_addresses and accessed_storage_keys.

When a transaction execution begins, accessed_code_in_addresses will include tx.sender, tx.to, and all precompiles.

When CREATE/CREATE2/EXTCODECOPY/CALL/CALLCODE/DELEGATECALL/STATICCALL is called, immediately add the address to accessed_code_in_addresses.

Rationale

Gas Metering

The goal is to measure the CPU/IO cost of the contract read/write operations reusing existing gas metering so that the resources will not be abused.

• For code-size-related opcodes (CODESIZE/EXTCODESIZE), we would expect the client to implement a mapping from the hash of code to the size, so reading the code size of a large contract should still be O(1).

• For CODECOPY, the data is already loaded in memory (as part of CALL/CALLCODE/DELEGATECALL/STATICCALL), so we do not charge extra gas.

• For EXTCODEHASH, the value is already in the account, so we do not charge extra gas.

• For EXTCODECOPY/CALL/CALLCODE/DELEGATECALL/STATICCALL, since it will read extra data from the database, we will additionally charge COLD_ACCOUNT_CODE_ACCESS_COST_PER_UNIT per extra CODE_SIZE_UNIT.

• For CREATE/CREATE2, since it will create extra data to the database, we will additionally charge CREATE_DATA_GAS per extra bytes.

Backwards Compatibility

All existing contracts will not be impacted by the proposal.

Only contracts deployed before EIP-170 could possibly be longer than the current max code size, and the reference implementation was able to successfully import all blocks before that fork.

Reference Implementation

The reference implementation on Geth is available at 0001-unlimit-code-size.patch.

Security Considerations

TBD

Copyright

Copyright and related rights waived via CC0.