HIP-26: Migrate Smart Contract Service EVM to Hyperledger Besu EVM
|Author||Daniel Ivanov, Danno Ferrin|
|Needs Council Approval||Yes|
Table of Contents
- User stories
- Backwards Compatibility
- Security Implications
- Reference Implementation
- Rejected Ideas
- Open Issues
Replace the Ethereum Virtual Machine (EVM) engine in Hedera Services, moving from an EthereumJ based engine to a Hyperledger Besu based engine
The current codebase that implements EVM Smart Contract transactions is out of date. It is based on EthereumJ and the upstream project has not implemented any hard forks since the St. Petersburg hard fork in early 2019. Some changes to opcodes and precompiled contracts make support of newer Solidity versions difficult. The integration also required inclusion of the entire EthereumJ codebase, as the EVM was not fully segregated from the client code.
Hyperledger Besu is an Ethereum Mainnet compatible EVM client with an EVM that is severable from the codebase. It is also supported by an active maintainer community and is a “Graduated Project” from the Hyperledger Project. The codebase is also up-to-date with current Ethereum Mainnet hard forks (London as of the writing of this HIP) and has a roadmap aiming to support future Ethereum features such as Proof of Stake migration and MEV integration.
With Besu’s current maintainers it will be possible to extract the EVM code needed to form a reusable library and not include any unneeded support code such as Ethereum networking and merkle tree support. Going forward it will be easier to maintain parity with Ethereum Mainnet evolutions such as the EVM container formats and new opcodes/precompiled contracts.
As a developer I want to execute EVM contracts with current versions of Solidity and with an EVM that is more compatible with Ethereum Mainnet than our current EVM.
This release targets a swap between EthereumJ and Besu with a minimum of compatibility changes.
EthereumJ dependency is to be removed from the codebase and Hedera
optimised fork of
Besu based on the upcoming 21.10.0 release is to be
introduced as a dependency. The
Besu integrations will be configured to use
the “London” hard fork of Ethereum Mainnet with some necessary changes outlined
in [Backwards Compatibility].
All operations (transition logics) in the Smart Contract Service will be refactored to a new model-based design.
SmartContractRequestHandler is to be removed along with the
related EthereumJ execution logic. Instead, two new components will be
HederaWorldUpdater. The executor will be
preparing and running the
MessageFrames of the EVM until halt.
Account and State access (read/write) will be provided to Besu through
implementation of a
WorldUpdater. The updater will expose an API to Besu. The
component will utilise Postgres for bytecode and storage persistence (same as
the current EthereumJ integration).
The Smart Contract internal logic will be updated to more fully conform to Hedera’s account abstractions.
1) Addresses in Hedera are utilising sequence number design compared to the hash
based design in the default EVM implementation.
2) Hedera’s account abstraction requires a
expiry for every
The following changes will be made to Besu in order to mitigate the fundamental changes described above:
HederaCreateoperation in Besu will be introduced to support the
CREATEopcode. The operation will compute new contract addresses based on
sequence numbers, and matches existing behavior with EthereumJ.
AbstractWorldUpdaterwill be extended to handle
MessageFramereverts to reclaim the allocated
MutableAccountwill be extended to support
Changes unrelated to “London” hard fork
The following changes will be made to the Opcodes, outside of London hard fork support. These are done to better reflect the nature of the Hedera platform.
CREATE2 operation will not be supported and return an illegal opcode
failure. The implementation in hedera of
CREATE2 are identical,
and this creates a usability problem with contracts that expect
operate in the specified manner. This stems from the differences in Hedera’s and
Ethereum’s account mapping.
COINBASE operation will return the funding account (Hedera Fee collecting
account which on mainnet is
0.0.98). The implementation at the moment returns
0.0.0 account and
0x0 EVM address.
GASLIMIT operation will return the
gasLimit of the transaction. The
gasLimit will be the lowest of the gas limit requested in the
transaction or a global upper gas limit configured for all smart contracts. The
current maximum configured gas limit per transaction is 300,000 gas.
Enumerating created contracts in ContractCreateResult
ContractCreateResult responses we would list sub-contracts
created as a part of the
ContractCreate operation in the
field, but not the contract that was directly created as part of the call. Now
all contracts that are created as a consequence of the
ContractCreate call are
enumerated, including the primary new contract.
Self Destruct during Contract Creation
If a contract was being created and the new contract called
the initcode we would not mark the
isDeleted field as true. If
SELFDESTRUCT was called as part of a function call we would mark it as
Now regardless of whether the call to
SELFDESTRUCT occurred in initcode or in
a function call the
isDeleted field is set to true.
Errors moving from PreCheck errors to Transaction Errors
Code relating to validation errors has been cleaned up. Only errors detectable in GRPC objects will cause precheck errors and all other errors will be reported as part of the transaction.
The following errors in contract creation are moving out of precheck errors and
into transaction errors:
The following errors in contract call are moving out of precheck errors and into
Deprecated HAPI properties
fileID property in the
ContractUpdate operation (found in the
ContractUpdateTransactionBody protobuf) will be deprecated. The wording of the field implies it updates the contract code while the comments indicate that it the assertion of where the initcode originated from will be changed. Ethereum contracts are expected to be immutable once deployed and so neither variation is appropriate, hence the field will be deprecated.
maxResultSize property in the
ContractCallLocal operation (found in the
ContractCallLocalQuery) will be deprecated. In order to calculate the effective result size the entire operation needs to be executed, and then at the last moment an error is returned if the result is too large. The result is not stored in server ram nor is it stored in storage, so there is no fees associated with larger queries. Because of this any errors that setting it is hoping to avoid would still occur on the server and different errors would be returned instead. The limitations of Ethereum Gas already provide a reasonable limitation on unexpectedly large results. Hence this property will be ignored if specified and all results will be returned.
Upgrade to “London” Hard Fork
The smart contract platform will be upgraded to support the EVM visible changes for the “London” hard fork. This includes changes introduced in the “Istanbul” and “Berlin” hard forks. Changes relating to block production and data serialization (such as the fee market, intrinsic gas costs, and transaction formats) will not be implemented because they are not relevant to Hedera’s architecture.
BASEFEE opcode will return zero. Hedera does not use the Fee Market
mechanism this is designed to support.
Reject Contracts starting with
ContractCreate transactions and
CREATE opcode calls will fail if the
first bytes of the smart contract is
0xFE. Extending this to
ContractCreate transaction mirrors how Ethereum contract deployments
This opcode will operate as expected with no change from Ethereum Mainnet.
CHAINID opcode will return
0x0127) for mainnet,
0x0128) for testnet, and
0x0129) for previewnet.
Blake2 compression function F precompile
The precompiled contract operates the same as on Ethereum Mainnet.
Gas Schedule Changes
The Smart Contract Service will use the Gas Schedule from the “London” hard fork. Notable changes include warm/cold account access and refund reductions.
Warm and Cold Account and Slot Access
Berlin introduced the notion of warm and cold accounts and storage slots. The first access to an account or storage slot in a transaction will need to pay the “cold” costs and all subsequent calls will pay the lower “warm” access costs. EIP-2929 contains the full details of the new cost scheduling.
Hedera does not at this time allow for “pre-warming” addresses and storage slots as part of the transaction as seen in EIP-2930. Future HIPs may support this scheme.
Gas Refund Reductions and Eliminations
In the London gas schedule the amount of gas that can be returned from storage
access usage patterns has been significantly reduced. Account refunds
SELFDESTRUCT have been completely removed.
Table of Gas Cost Changes
|Operation||Current Hedera||London Cost||HIP-26 Cost|
|Code deposit||Floating Hedera
Storage Cost per byte
|200 * bytes||Max of London
|EXP||10 + 10/byte||10 + 50/byte||10 + 50/byte|
|20 + Mem||2600 + Mem||2600 + Mem|
|20 + Mem||100 + Mem||100 + Mem|
|LOG0, LOG1, LOG2,
Ram Cost per byte
|375 + 375*topics
+ data Mem
|Max of London
Storage Cost per byte
|22,100||Max of London
|CALL et al.
|CALL et al.
|CALL et al.
Hbar/Eth Transfer Surcharge
|CALL et al.
New Account Surcharge
The terms ‘warm’ and ‘cold’ in the above table correspond with whether the account or storage slot has been read or written to within the current smart contract transaction, even if within a child call frame.
‘CALL et al.’ includes with limitation CALL, CALLCODE, DELEGATECALL, and STATICCALL
Between Besu and EthereumJ there is no material difference in the security attack surfaces. The same specifications and Hedera integrations will exist.
Hedera Services PR #2208
Migration to another Smart Contract VM
The EVM is not the only smart contract platform, however it is the platform that has the most widespread use in terms of total users and total numbers of DLTs supporting the EVM. One alternative of note is WASM and eWASM. The Ethereum Foundation’s eWASM project has stagnated over the last two years and is not under active development. It also did not achieve the performance goals it had set, often running slower than optimized EVM implementations. WASM as a standalone technology lacks determinism in some instructions it supports (mostly floating point operations) as well as lacking resource metering and limitations.
Other leading smart contract platforms (TEAL, Michelson, MoveVM, etc.) are strongly tied to their host chain and are not used with other chains and have not gained cross-DLT support. A few chains that have custom smart contract platforms have added EVM compatability layers or libraries for their systems too (Aurora/NEAR and Arbitrum most notably).
Apart from EVM being one of the best choices there are also issues relating to migrating to other smart contract systems that staying with EVM avoids. While there may be future changes in supported services keeping the Smart Contract Service on the EVM provides the least amount of backwards compatibility issues.
Eliminating Smart Contract Service Support
Eliminating the EVM as a whole would foreclose future growth of the Hedera Platform in the “on-chain” smart contract arena.
Currently, no open issues.
This document is licensed under the Apache License, Version 2.0 – see LICENSE or (https://www.apache.org/licenses/LICENSE-2.0)
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