Abstract

With the PUSH0 opcode (EIP-3855), introduced with the Shanghai upgrade, we optimized the previous Minimal Proxy Contract (ERC-1167) by 200 gas at deployment and 5 gas at runtime, while retaining the same functionality.

Motivation

1. Reduce the contract bytecode size by 1 byte by removing a redundant SWAP opcode.
2. Reduce the runtime gas by replacing two DUP (cost 3 gas each) with two PUSH0 (cost 2 gas each).
3. Increase the readability of the proxy contract by redesigning it from first principles with PUSH0.

Specification

Standard Proxy Contract

The exact runtime code for the minimal proxy contract with PUSH0 is:

365f5f375f5f365f73bebebebebebebebebebebebebebebebebebebebe5af43d5f5f3e5f3d91602a57fd5bf3

where the bytes at indices 9 - 28 (inclusive) are replaced with the 20-byte address of the master implementation contract. The length of the runtime code is 44 bytes.

The disassembly of the new minimal proxy contract code is:

pc	op	opcode	stack
[00]	36	CALLDATASIZE	cds
[01]	5f	PUSH0	0 cds
[02]	5f	PUSH0	0 0 cds
[03]	37	CALLDATACOPY
[04]	5f	PUSH0	0
[05]	5f	PUSH0	0 0
[06]	36	CALLDATASIZE	cds 0 0
[07]	5f	PUSH0	0 cds 0 0
[08]	73bebe.	PUSH20 0xbebe.	0xbebe. 0 cds 0 0
[1d]	5a	GAS	gas 0xbebe. 0 cds 0 0
[1e]	f4	DELEGATECALL	suc
[1f]	3d	RETURNDATASIZE	rds suc
[20]	5f	PUSH0	0 rds suc
[21]	5f	PUSH0	0 0 rds suc
[22]	3e	RETURNDATACOPY	suc
[23]	5f	PUSH0	0 suc
[24]	3d	RETURNDATASIZE	rds 0 suc
[25]	91	SWAP2	suc 0 rds
[26]	602a	PUSH1 0x2a	0x2a suc 0 rds
[27]	57	JUMPI	0 rds
[29]	fd	REVERT
[2a]	5b	JUMPDEST	0 rds
[2b]	f3	RETURN

Minimal Creation Code

The minimal creation code of the minimal proxy contract is:

602c8060095f395ff3365f5f375f5f365f73bebebebebebebebebebebebebebebebebebebebe5af43d5f5f3e5f3d91602a57fd5bf3

where the first 9 bytes are the initcode:

602c8060095f395ff3

And the rest are runtime/contract code of the proxy. The length of the creation code is 53 bytes.

Deploy with Solidity

The minimal proxy contract can be deployed with Solidity using the following contract:

// SPDX-License-Identifier: CC0-1.0
pragma solidity ^0.8.20;

// Note: this contract requires `PUSH0`, which is available in solidity > 0.8.20 and EVM version > Shanghai
contract Clone0Factory {
    error FailedCreateClone();

    receive() external payable {}

    /**
     * @dev Deploys and returns the address of a clone0 (Minimal Proxy Contract with `PUSH0`) that mimics the behaviour of `implementation`.
     *
     * This function uses the create opcode, which should never revert.
     */
    function clone0(address impl) public payable returns (address addr) {
        // first 18 bytes of the creation code 
        bytes memory data1 = hex"602c8060095f395ff3365f5f375f5f365f73";
        // last 15 bytes of the creation code
        bytes memory data2 = hex"5af43d5f5f3e5f3d91602a57fd5bf3";
        // complete the creation code of Clone0
        bytes memory _code = abi.encodePacked(data1, impl, data2);

        // deploy with create op
        assembly {
            // create(v, p, n)
            addr := create(callvalue(), add(_code, 0x20), mload(_code))
        }

        if (addr == address(0)) {
            revert FailedCreateClone();
        }
    }
}

Rationale

The optimized contract is constructed with essential components of the proxy contract and incorporates the recently added PUSH0 opcode. The core elements of the minimal proxy include:

1. Copy the calldata with CALLDATACOPY.
2. Forward the calldata to the implementation contract using DELEGATECALL.
3. Copy the returned data from the DELEGATECALL.
4. Return the results or revert the transaction based on whether the DELEGATECALL is successful.

Step 1: Copy the Calldata

To copy the calldata, we need to provide the arguments for the CALLDATACOPY opcodes, which are [0, 0, cds], where cds represents calldata size.

pc	op	opcode	stack
[00]	36	CALLDATASIZE	cds
[01]	5f	PUSH0	0 cds
[02]	5f	PUSH0	0 0 cds
[03]	37	CALLDATACOPY

Step 2: Delegatecall

To forward the calldata to the delegate call, we need to prepare arguments for the DELEGATECALL opcodes, which are [gas 0xbebe. 0 cds 0 0], where gas represents the remaining gas, 0xbebe. represents the address of the implementation contract, and suc represents whether the delegatecall is successful.

pc	op	opcode	stack
[04]	5f	PUSH0	0
[05]	5f	PUSH0	0 0
[06]	36	CALLDATASIZE	cds 0 0
[07]	5f	PUSH0	0 cds 0 0
[08]	73bebe.	PUSH20 0xbebe.	0xbebe. 0 cds 0 0
[1d]	5a	GAS	gas 0xbebe. 0 cds 0 0
[1e]	f4	DELEGATECALL	suc

Step 3: Copy the Returned Data from the DELEGATECALL

To copy the returndata, we need to provide the arguments for the RETURNDATACOPY opcodes, which are [0, 0, red], where rds represents size of returndata from the DELEGATECALL.

pc	op	opcode	stack
[1f]	3d	RETURNDATASIZE	rds suc
[20]	5f	PUSH0	0 rds suc
[21]	5f	PUSH0	0 0 rds suc
[22]	3e	RETURNDATACOPY	suc

Step 4: Return or Revert

Lastly, we need to return the data or revert the transaction based on whether the DELEGATECALL is successful. There is no if/else in opcodes, so we need to use JUMPI and JUMPDEST instead. The arguments for JUMPI is [0x2a, suc], where 0x2a is the destination of the conditional jump.

We also need to prepare the argument [0, rds] for REVERT and RETURN opcodes before the JUMPI, otherwise we have to prepare them twice. We cannot avoid the SWAP operation, because we can only get rds after the DELEGATECALL.

pc	op	opcode	stack
[23]	5f	PUSH0	0 suc
[24]	3d	RETURNDATASIZE	rds 0 suc
[25]	91	SWAP2	suc 0 rds
[26]	602a	PUSH1 0x2a	0x2a suc 0 rds
[27]	57	JUMPI	0 rds
[29]	fd	REVERT
[2a]	5b	JUMPDEST	0 rds
[2b]	f3	RETURN

In the end, we arrived at the runtime code for Minimal Proxy Contract with PUSH0:

365f5f375f5f365f73bebebebebebebebebebebebebebebebebebebebe5af43d5f5f3e5f3d91602a57fd5bf3

The length of the runtime code is 44 bytes, which reduced 1 byte from the previous Minimal Proxy Contract. Moreover, it replaced the RETURNDATASIZE and DUP operations with PUSH0, which saves gas and increases the readability of the code. In summary, the new Minimal Proxy Contract reduces 200 gas at deployment and 5 gas at runtime, while remaining the same functionalities as the old one.

Backwards Compatibility

Because the new minimal proxy contract uses PUSH0 opcode, it can only be deployed after the Shanghai Upgrade. It behaves the same as the previous Minimal Proxy Contract.

Security Considerations

The new proxy contract standard is identical to the previous one (ERC-1167). Here are the security considerations when using minimal proxy contracts:

1. Non-Upgradability: Minimal Proxy Contracts delegate their logic to another contract (often termed the "implementation" or "logic" contract). This delegation is fixed upon deployment, meaning you can't change which implementation contract the proxy delegates to after its creation.

2. Initialization Concerns: Proxy contracts lack constructors, so you need to use an initialization function after deployment. Skipping this step could leave the contract unsafe.

3. Safety of Logic Contract: Vulnerabilities in the logic contract affect all associated proxy contracts.

4. Transparency Issues: Because of its complexity, users might see the proxy as an empty contract, making it challenging to trace back to the actual logic contract.

Copyright

Copyright and related rights waived via CC0.