Reserve `EXTENSION (0xae)` opcode

The five-minute read

One action, walked through

1. Open EIP 8163 and read the status line before the examples.
2. Write down the rule in one sentence. A fair version of that sentence is: Reserve an opcode EXTENSION (0xae) which will be guaranteed to not become a valid opcode on Ethereum L1 EVM, but which will be available to be used in other EVMs as a prefix to encode extension instructions.
3. Name the object that changes: EXTENSION, EVM, MUST.
4. Ask what an old client, an old contract, or an offline counterparty does. If the document is silent, the silence is part of the design.

The argument, unpacked

What has to be true

• You are implementing EIP 8163 at the status the text itself states: Review.
• The object that has to change is EXTENSION, EVM, MUST. A neighbouring document with a similar name is not this one.
• Constants in the text can be superseded by a later fork. Cite the EIP number and the fork you mean.

What happened after the paper

The source marks this review. It is not a live consensus rule just because it has a number. Later documents can narrow, replace, or ignore this one. Cite the number you mean.

What to check before you use the idea

• What does Reserve `EXTENSION (0xae)` opcode charge, reject, or redefine on the first touch versus a later one?
• Does a reverted subcall roll the change back?
• Can you point at the object in a client: EXTENSION, EVM, MUST?

Terms

EIP 8163

The public text titled Reserve `EXTENSION (0xae)` opcode.

Review

The document's own label for how finished the text is. It is not a market fact.

The problem the paper names

An underpriced or ambiguous EVM rule is not a feature. It is a block that takes longer than the gas limit claimed, or a client that disagrees about the result.

What the design proposes

• Reserve an opcode EXTENSION (0xae) which will be guaranteed to not become a valid opcode on Ethereum L1 EVM, but which will be available to be used in other EVMs as a prefix to encode extension instructions.
• Currently, non-Ethereum-L1 EVM chains cannot innovate on the EVM by introducing new instructions, because they run a risk of becoming incompatible with the Ethereum L1 EVM and the EVMs on other chains, in the event that these decide to implement new features using overlapping opcodes.
• By setting aside a single opcode and agreeing that it will never become a valid instruction on Ethereum L1 EVM, we open up to extensions which can be implemented on other EVM chains.

How the mechanism is specified

• Taken from the specification, the next constraint is: Currently, non-Ethereum-L1 EVM chains cannot innovate on the EVM by introducing new instructions, because they run a risk of becoming incompatible with the Ethereum L1 EVM and the EVMs on other chains, in the event that these decide to implement new features using overlapping opcodes.
• Locate EXTENSION, EVM, MUST in EIP 8163 and apply it to one transaction or call.
• Then check the failure the class of rule always has: a node that did not upgrade, a reverted call, a replayed signature, or a peer that does not speak the message.

What this page does not treat as proven

• A gas or opcode change is not a throughput benchmark. It is a relative price and a validity rule.
• Constants in the text can be superseded by a later fork. Cite the EIP number and the fork you mean.
• The source marks this review. It is not a live consensus rule just because it has a number.

Why a venture studio still reads it

Use EIP 8163 when a pitch says 'Reserve `EXTENSION (0xae)` opcode' without saying whether the rule is consensus, policy, or an interface. The number is the citation. The pitch is not.