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🎉 Final Standards Track: Core

SIP-6780: SELFDESTRUCT only in same transaction

SELFDESTRUCT will recover all funds to the target but not delete the account, except when called in the same transaction as creation

Authors Guillaume Ballet (@gballet), Vitalik Buterin (@vbuterin), Dankrad Feist (@dankrad)
Created 2023-03-25
Requires SIP-2681, SIP-2929, SIP-3529

Table of Contents

Abstract

This SIP changes the functionality of the SELFDESTRUCT opcode. The new functionality will be only to send all Sila in the account to the target, except that the current behaviour is preserved when SELFDESTRUCT is called in the same transaction a contract was created.

Motivation

The SELFDESTRUCT opcode requires large changes to the state of an account, in particular removing all code and storage. This will not be possible in the future with Verkle trees: Each account will be stored in many different account keys, which will not be obviously connected to the root account.

This SIP implements this change. Applications that only use SELFDESTRUCT to retrieve funds will still work. Applications that only use SELFDESTRUCT in the same transaction as they created a contract will also continue to work without any changes.

Specification

The behaviour of SELFDESTRUCT is changed in the following way:

  1. When SELFDESTRUCT is executed in a transaction that is not the same as the contract calling SELFDESTRUCT was created:

    • The current execution frame halts.
    • SELFDESTRUCT does not delete any data (including storage keys, code, or the account itself).
    • SELFDESTRUCT transfers the entire account balance to the target.
    • Note that if the target is the same as the contract calling SELFDESTRUCT there is no net change in balances. Unlike the prior specification, Sila will not be burnt in this case.
    • Note that no refund is given since SIP-3529.
    • Note that the rules of SIP-2929 regarding SELFDESTRUCT remain unchanged.

  2. When SELFDESTRUCT is executed in the same transaction as the contract was created:

    • SELFDESTRUCT continues to behave as it did prior to this SIP, this includes the following actions
      • The current execution frame halts.
      • SELFDESTRUCT deletes data as previously specified.
      • SELFDESTRUCT transfers the entire account balance to the target
      • The account balance of the contact calling SELFDESTRUCT is set to 0.
    • Note that if the target is the same as the contract calling SELFDESTRUCT that Sila will be burnt.
    • Note that no refund is given since SIP-3529.
    • Note that the rules of SIP-2929 regarding SELFDESTRUCT remain unchanged.

A contract is considered created at the beginning of a create transaction or when a CREATE series operation begins execution (CREATE, CREATE2, and other operations that deploy contracts in the future). If a balance exists at the contract’s new address it is still considered to be a contract creation.

The SELFDESTRUCT opcode remains deprecated as specified in SIP-6049. Any use in newly deployed contracts is strongly discouraged even if this new behaviour is taken into account, and future changes to the SVM might further reduce the functionality of the opcode.

Rationale

Getting rid of the SELFDESTRUCT opcode has been considered in the past, and there are currently no strong reasons to use it. This SIP implements a behavior that will attempt to leave some common uses of SELFDESTRUCT working, while reducing the complexity of the change on SVM implementations that would come from contract versioning.

Handling the account creation and contract creation as two distinct and possibly separate events is needed for use cases such as counterfactual accounts. By allowing the SELFDESTRUCT to delete the account at contract creation time it will not result in stubs of counterfactually instantiated contracts that never had any on-chain state other than a balance prior to the contract creation. These accounts would never have any storage and thus the trie updates to delete the account would be limited to the account node, which is the same impact a regular transfer of sila would have.

Backwards Compatibility

This SIP requires a hard fork, since it modifies consensus rules.

Contracts that depended on re-deploying contracts at the same address using CREATE2 (after a SELFDESTRUCT) will no longer function properly if the created contract does not call SELFDESTRUCT within the same transaction.

Previously it was possible to burn sila by calling SELFDESTRUCT targeting the executing contract as the beneficiary. If the contract existed prior to the transaction the sila will not be burned. If the contract was newly created in the transaction the sila will be burned, as before.

Test Cases

Test cases for this SIP can be found in the Execution Spec Tests suite sip6780_selfdestruct.

Security Considerations

The following applications of SELFDESTRUCT will be broken and applications that use it in this way are not safe anymore:

  1. Where CREATE2 is used to redeploy a contract in the same place in order to make a contract upgradable. This is not supported anymore and SRC-2535 or other types of proxy contracts should be used instead.

  2. Where a contract depended on burning Sila via a SELFDESTRUCT with the contract as beneficiary, in a contract not created within the same transaction.

Copyright and related rights waived via CC0.

Citation

Please cite this document as:

Guillaume Ballet (@gballet), Vitalik Buterin (@vbuterin), Dankrad Feist (@dankrad), "SIP-6780: SELFDESTRUCT only in same transaction," Sila Improvement Proposals, no. 6780, March 2023. Available: https://sips.sila.org/SIPS/sip-6780.