EOF - EXTCODEADDRESS instruction

Abstract

Add an instruction to EOF that reads code delegation designations from an account without requiring code introspection.

Motivation

EOFv1 as scoped in EIP-7692 removes code introspection capabilities from the EVM, preventing EOF from reading raw code values such as code delegation designations set by EIP-7702. There are a number of use cases where reading the delegation designation of EIP-7702 would allow contracts to be more proactive about user experience issues.

One example is a managed proxy contract. Such a contract may want to ensure security by not allowing the proxy to be updated to a delegated address. There are also safety concerns with pointing to a delegation, as the contract may be updated to non EOF code and EXTDELEGATECALL will no longer be able to call the contract, due to changes outside the control of the managed proxy contract.

Another example are contracts that need to ensure that the delegation has not changed over a limited scope of time, such as sponsorships. This will prevent a transaction from receiving gas sponsorship, changing the delegation, and performing an act different than what was approved. Sponsors can encode the delegation into the transaction data and verify wih this instruction.

Finally, there is the case where contracts may want to de-escalate risks and only accept a small number of delegations for any given contract. To enable this validation contracts will need to be able to resolve the actual address of delegtion, not just know that one exists.

To address this the essential task of the designation parsing is moved into a new opcode EXTCODEADDRESS, where the task of calculating the delegated address will be performed. For non-delegated accounts or empty accounts the address will be the same as the queried address.

Specification

Parameters

We introduce a new EOFv1 instruction EXTCODEADDRESS (0xea).

EOF code which contains this instruction prior to the fork activating this instruction is considered invalid. Beginning with the first block this EIP is activated in, this instruction is added to the set of valid EOFv1 instructions.

Execution Semantics

EXTCODEADDRESS

• Deduct GAS_WARM_ACCESS gas
• pop 1 argument target_address from the stack
• if target_address has any of the high 12 bytes set to a non-zero value (i.e. it does not contain a 20-byte address), then halt with an exceptional failure
  • Notice: Future expansion of the EVM address space may enlarge the number of valid addresses. Do not rely on this step always halting with the current restrictions.
• deduct GAS_COLD_ACCOUNT_ACCESS - GAS_WARM_ACCESS if target_address is not in accessed_addresses and add target_address to accessed_addresses
• Load the code from target_address and refer to it as loaded_code
• If loaded_code indicates a delegation designator (for example, prefixed with 0xef0100 as defined in EIP-7702) push the address of the designation onto the stack.
  • Notice: if EIP-7702 delegation designations are updated in a future fork (such as allowing chained delegations), then this section is expected to comply with any such hypothetical changes.
• Otherwise, push target_adress onto the stack.

Note: If target_address points to an account with a contract mid-creation, then target_address is returned. If delegation designator points to an account with a contract mid-creation, then address of the designation is returned.

Note: Only target_address is warmed. If a delegation is found the address that it is delegated to is not added to the accessed_addresses. Also, whether the delegated address is in accessed_addresses has no impact on the gas charged for the operation.

Note: This operation staddles the line between EIP-7702 code reading and code executing instructions. The operation steps work as a code reading instruction, but the value returned is the resolved address as through it is a code executing instruction.

Rationale

This EIP is very similar to EIP-7761, which introduces account type introspection. Its rationale is included by reference as they all apply to this situation.

Alternative: Return the whole designation, have contract parse

One alternative is to have a specially limited EXTCODECOPY that would return just delegation designations. Apart from the general objections to code introspection this would then lock in and limit delegation designation formats and capabilities that must be preserved in future forks. By allowing access to the effect of the delegation rather than the mechanism, EOF preserves space for the mechanism to be changed without breaking existing code.

Backwards Compatibility

EXTCODEADDRESS at 0xea can be introduced in a backwards compatible manner into EOFv1 (no bump to version), because 0xea has been rejected by EOF validation prior to the actication of this EIP, and there are no EOF contracts on-chain with an 0xea instruction which would have their behavior altered.

Security Considerations

EIP-7702 code delegation is a new feature that has not been made accessible to mainnet yet. EIP authors will keep abreast of any developments and reflect on their impact to this proposed instruction.

Copyright

Copyright and related rights waived via CC0