EIP-7873 - EOF - TXCREATE and InitcodeTransaction type

Abstract

EVM Object Format (EOF) removes the possibility to create contracts using creation transactions (with an empty to field), CREATE or CREATE2 instructions. We introduce a new instruction: TXCREATE, as well as a new transaction type (InitcodeTransaction), to provide a way to create contracts using EOF containers in transaction data.

Motivation

This EIP uses terminology from the EIP-3540 which introduces the EOF format.

Creation transaction and creation instructions CREATE and CREATE2 are means provided by legacy EVM to deploy new code, but per requirement of removing code observability, they are not allowed to deploy EOF code. To allow Externally Owned Accounts (EOAs) to deploy EOF contracts, there must be a way to create EOF contracts using bytecode delivered in transaction data.

Additionally, the new instruction and transaction type introduced in this EIP enable contracts to create other contracts using initcode from the transaction data, which in legacy EVM is achieved via a combination of CREATE or CREATE2 and loading the initcode from calldata.

This mechanism complements EOFCREATE and RETURNCODE instructions from EIP-7620, and thus all use cases of contract creation that are available in legacy EVM are enabled for EOF.

Since TXCREATE is not restricted to EOF containers, it also serves the purpose of bootstrapping EOF contracts into the state.

Specification

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC 2119 and RFC 8174.

Parameters

Transaction Types

Introduce new transaction InitcodeTransaction (type INITCODE_TX_TYPE) which extends EIP-1559 (type 2) transaction by adding a new field initcodes: List[ByteList[MAX_INITCODE_SIZE], MAX_INITCODE_COUNT].

The initcodes can only be accessed via the TXCREATE instruction (see below), therefore InitcodeTransactions are intended to be sent to contracts including TXCREATE in their execution.

Gas schedule

initcodes items data costs the same as calldata: transaction gas of an InitcodeTransaction is extended to include tokens in initcodes alongside tokens in calldata. Using the conventions from EIP-7623, the transaction gas is calculated as:

STANDARD_TOKEN_COST = 4
TOTAL_COST_FLOOR_PER_TOKEN = 10

tokens_in_calldata = zero_bytes_in_calldata + nonzero_bytes_in_calldata * 4
tokens_in_initcodes = 0
for initcode in initcodes:
    tokens_in_initcodes += zero_bytes_in_initcode + nonzero_bytes_in_initcode * 4
tx.gasUsed = (
    21000
    +
    max(
        STANDARD_TOKEN_COST * (tokens_in_calldata + tokens_in_initcodes)
        + execution_gas_used,
        TOTAL_COST_FLOOR_PER_TOKEN * (tokens_in_calldata + tokens_in_initcodes)
    )
)

Transaction validation

• InitcodeTransaction is invalid if there are zero entries in initcodes, or if there are more than MAX_INITCODE_COUNT entries.
• InitcodeTransaction is invalid if any entry in initcodes is zero length, or if any entry exceeds MAX_INITCODE_SIZE.
• InitcodeTransaction is invalid if the to is nil.

Under transaction validation rules initcodes are not validated for conforming to the EOF specification. They are only validated when accessed via TXCREATE. This avoids potential DoS attacks of the mempool. If during the execution of an InitcodeTransaction no TXCREATE instruction is called, such transaction is still valid.

Other creation transactions that support contract creation (specifically type 0 "Frontier," type 1 "AccessList," type 2 "FeeMarket" transactions with an empty to field) will not attempt to parse EOF containers in their input field and will execute the code as non-EOF code. This will result in immediately executing the undefined 0xEF instruction and halting.

RLP and signature

Given the definitions from EIP-2718 the TransactionPayload for an InitcodeTransaction is the RLP serialization of:

[chain_id, nonce, max_priority_fee_per_gas, max_fee_per_gas, gas_limit, to, value, data, access_list, initcodes, y_parity, r, s]

TransactionType is INITCODE_TX_TYPE and the signature values y_parity, r, and s are calculated by constructing a secp256k1 signature over the following digest:

keccak256(INITCODE_TX_TYPE || rlp([chain_id, nonce, max_priority_fee_per_gas, max_fee_per_gas, gas_limit, to, value, data, access_list, initcodes]))

The EIP-2718 ReceiptPayload for this transaction is rlp([status, cumulative_transaction_gas_used, logs_bloom, logs]).

Execution Semantics

Wherever not explicitly listed, the rules of EOF contract creation, as well as the TXCREATE instruction, should be identical or analogous to those of CREATE2 instruction. This includes but is not limited to:

• behavior on accessed_addresses and address collision (EIP-684 and EIP-2929)
• EVM execution frame created for the TXCREATE initcode - memory, account context etc.
• nonce bumping of the account of newly created contract EIP-161
• balance checking and transfer for the creation endowment (value argument)

Introduce a new instruction on the same block number EIP-3540 is activated on: TXCREATE (0xed).

TXCREATE

• deduct TX_CREATE_COST gas
• halt with exceptional failure if the current frame is in static-mode.
• pop tx_initcode_hash, salt, input_offset, input_size, value from the operand stack
• perform (and charge for) memory expansion using [input_offset, input_size]
• load initcode EOF container from the transaction initcodes array which hashes to tx_initcode_hash
  • fails (returns 0 on the stack) if such initcode does not exist in the transaction, or if called from a transaction of TransactionType other than INITCODE_TX_TYPE
    • caller's nonce is not updated and gas for initcode execution is not consumed.
  • let initcontainer be that EOF container, and initcontainer_size its length in bytes
• check that current call depth is below STACK_DEPTH_LIMIT and that caller balance is enough to transfer value
  • in case of failure return 0 on the stack, caller's nonce is not updated and gas for initcode execution is not consumed.
• validate the initcode container and all its subcontainers recursively
  • unlike in general validation, initcontainer is additionally required to have data_size declared in the header equal to actual data_section size.
  • validation includes checking that the initcontainer does not contain RETURN or STOP
• fails (returns 0 on the stack) if container was invalid
  • caller’s nonce is not updated and gas for initcode execution is not consumed.
• caller's memory slice [input_offset:input_size] is used as calldata
• execute the container and deduct gas for execution. The 63/64th rule from EIP-150 applies.
• increment sender account's nonce
• calculate new_address as keccak256(0xff || sender32 || salt)[12:], where sender32 is the sender address left-padded to 32 bytes with zeros
• an unsuccessful execution of initcode results in pushing 0 onto the stack
  • can populate returndata if execution REVERTed
  • sender's nonce stays updated
• a successful execution ends with initcode executing RETURNCODE{deploy_container_index}(aux_data_offset, aux_data_size) instruction (see EIP-7620). After that:
  • load deploy EOF subcontainer at deploy_container_index in the container from which RETURNCODE is executed
  • concatenate data section with (aux_data_offset, aux_data_offset + aux_data_size) memory segment and update data size in the header
  • if updated deploy container size exceeds MAX_CODE_SIZE, instruction exceptionally aborts
  • set state[new_address].code to the updated deploy container
  • push new_address onto the stack
• deduct GAS_CODE_DEPOSIT * deployed_code_size gas

Note that the implementations are expected to cache the result of container validation for the time of current transaction execution, and therefore the cost of each container's validation is sufficiently covered by InitcodeTransaction intrinsic cost (initcodes charge).

Rationale

TXCREATE failure modes

TXCREATE has two "light" failure modes in case the initcontainer is not present and in case the EOF validation is unsuccessful. An alternative design where both cases led to a "hard" failure (consuming the entire gas available) was considered. We decided to have the more granular and forgiving failure modes in order to align the gas costs incurred to the actual work the EVM performs.

Allowing TXCREATE in legacy EVM

EOF contract creation requires an exceptional possibility of calling an EOF opcode in legacy code - TXCREATE, because otherwise neither legacy contracts nor create transactions can deploy EOF code to bootstrap. The alternative approach was to continue using legacy creation mechanisms, by either still relying on fetching the initcode from memory and not satisfy the overarching requirement of code non-observability, or to abuse the legacy creation transactions mechanism, or to introduce a predeployed Creator Contract into the state.

This also makes EIP-7698 (EOF - Creation transaction) no longer an essential requirement for deploying EOF contracts onto the chain. The EIP could be removed from EOFv1 and withdrawn.

New address hashing scheme

TXCREATE uses the scheme new_address = keccak256(0xff || sender32 || salt)[12:], same as EOFCREATE instruction. The decision whether to include initcontainer hash into salt is left to the TXCREATE caller. See EIP-7620 for detailed rationale.

EOF creation transactions vs deployment patterns

Relying on the EOF creation transactions as the alternative solution makes it impossible for smart contract wallets to deploy arbitrary EOF contracts (only EOAs can). At the same time, it is a use case current legacy creation rules allow, thanks to CREATE and CREATE2 instructions. A workaround where those arbitrary EOF contracts are first "uploaded" to a factory contract, and then deployed using an EXTDELEGATECALL-EOFCREATE sequence, is very expensive, as it requires the deployed contract to be put on-chain twice. Because of this, the approach proposed in this EIP is more compatible with the Account Abstraction (AA) roadmap, where smart contract wallets should have feature parity with EOAs.

On top of this, relying on nonce-based hashing scheme to obtain addresses of newly created contracts, like in the case of the EOF creation transactions, would prevent EOF contracts from being deployed counterfactually to deterministic, cross-chain addresses. Introduction of the TXCREATE instruction, supports this out of the box. ERCs can be written to provide toehold contracts which will cater for the deployment patterns, such as salt-less deployment and hashing in the sender's address as part of the salt.

Handling of 0xEF00 prefixed code in existing transaction types.

Three existing transaction types (type 0 "Frontier," type 1 "AccessList," type 2 "FeeMarket") accept code as part of their input data in certain configurations. This code can start with EF as it is initcode and not a deployed contract.

One possible way of handling potential EOF containers in these transactions is to make them invalid if they are attempting to execute an EOF container as initcode. Specifically the transactions is invalid if the input data begins with 0xef00 and if the to field is set to nil, signaling a contract creation transaction. This would make blocks containing these transactions invalid, whereas before the fork including this EIP they would have been valid.

One impact that would be seen by this would be block builders, as they would need to ensure that the transactions that are invalid are not included in a block. There is precedent for this, as EIP-7623 established a new floor for the gas limit in transactions, prior to its adoption the limit was lower. However, block builders have an existing check on gas limits and transactions and that change was adjusting the formula and constants.

We should also consider the treatment EIP-7702 delegation designations receive if they show up as code in a contract creation transaction. The transaction is valid, is executed as plain bytecode, ad the first operation executed is 0xEF, which is an invalid opcode and would cause the whole transaction to abort.

Letting the inputdata of a type 0, 1, and 2 contract creation transaction execute as plain EVM code irrespective of the magic 0xEF00 bytes keeps a consistent behavior in client code and keeps block builders from having to update their logic in older transaction types.

Backwards Compatibility

This change poses no risk to backwards compatibility, as it is introduced at the same time EIP-3540 is. Despite the new instruction being introduced for legacy bytecode (code which is not EOF formatted), there is little chance that a meaningful contract would unintentionally execute 0xed instruction with formally valid operands and inadvertently cause it to run EOF initcode (which would also require an InitcodeTransaction to be used, otherwise the initcode lookup will fail).

TXCREATE instruction introduction into legacy EVM does not affect JUMPDEST analysis, because instruction has no immediate arguments.

The transactions of the new type are invalid until this change activates.

Contract creation options do not change for legacy bytecode, including how existing transactions with to: nil behave when encountering code in their calldata that may look like an EOF container.

Security Considerations

Needs discussion.

Copyright

Copyright and related rights waived via CC0.