EIP-4788: Beacon state root in EVM

Discussion thread for EIP-4788: Beacon state root in EVM.

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By including the ommersHash validation, clients can use existing code with only minimal changes (supplying the actual state root) during block production and verification.

Having the beacon state root value in the ommers field means that it is fairly straightforward to provide the value from the block data to the EVM execution context for client implementations as they stand today.

I would like to get validation from execution client teams that this is actually of meaningful value. It may be just as easy to completely remove the uncle validation code entirely as it would be to pseudo-replace it with this. If so, then I would strongly advocate for changing this into a single 32-byte hash rather than an array of 1 item.

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Should the storage address be added to warm addresses by default (EIP 2929?)

Correct me if I am wrong but this should also have a rule that if you CALL the storage address, this should not get removed from the state. I am pretty sure that accounts which have non-empty storage, but no code, nonce 0 and balance 0 are DEAD and should therefore get removed from the MPT (thus clearing the storage). The alternative could be to just send 1 wei to this address, but it should be noted in the EIP anyways.

A couple of things:

Epoch/slot/timestamp as a fork trigger requires support of two EL blocks at the same height with different consensus rules and/or structures. AFAIK, this is not currently supported by client implementations and might result in additional complexity.

I am echoing Vitalik’s comment on slot vs block number. Imagine an application that securely (with a proof) reads validator record from a beacon state, an interface of this app will have to do slot to block height translation to specify the right beacon block root for the proof verification process. Using slot number allows to avoid this complexity, reads will look like slot.validator(i).effective_balance. Though, this approach requires slots to be passed to EL block, perhaps slot numbers are suitable replacement for difficulty values.

For the reading of the value it would be possible to include code at the address, and require a CALL to be made to the address as opposed to a dedicated opcode. This would be similar to EIP-210.

This does raise the question why not also do the same for RANDAO(n) in EIP-4399: Supplant DIFFICULTY opcode with RANDOM.

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IIUC, the two arguments are:

  1. Changing the shape of the block makes it easier to differentiate between blocks of different eras as you can just look at the block’s shape to know “when” the block was from.
  2. Changing the shape of the block can break existing code that depends on block shape to decode.

I think the question we need to answer is which of these is likely to have a larger negative impact on the Ethereum ecosystem long term. If (1), then adding a new field to the end and (optionally, if we want to save 32 bytes per block) deleting OmmersHash from the middle is the ideal strategy. If (2), then changing the interpretation of OmmersHash to be BeaconRoot is the optimal strategy.