Skip to content

ADR-007: EIP-6049 Implementation (Deprecate SELFDESTRUCT)

Status

Accepted

Context

EIP-6049 (https://eips.ethereum.org/EIPS/eip-6049) is an informational Ethereum Improvement Proposal that was activated as part of the Shanghai hard fork on Ethereum mainnet. For Ethereum Classic, this proposal is included in the Spiral hard fork (ECIP-1109: https://ecips.ethereumclassic.org/ECIPs/ecip-1109) at block 19,250,000 on mainnet and block 9,957,000 on Mordor testnet.

The proposal officially deprecates the SELFDESTRUCT opcode. Specifically:

  • Problem: The SELFDESTRUCT opcode (formerly known as SUICIDE) has several problematic characteristics:
  • It can be used to delete contract code and state
  • It transfers all remaining Ether to a beneficiary address
  • It complicates state management and consensus rules
  • It has been used in security exploits
  • It interacts poorly with various EIPs and future protocol changes

  • It creates unpredictable gas costs due to refund mechanisms

  • Solution: EIP-6049 officially deprecates SELFDESTRUCT and warns developers not to use it. However, the behavior remains unchanged in this EIP. This is a documentation-only change that:

  • Signals to developers that SELFDESTRUCT is deprecated
  • Warns that future EIPs may change or remove SELFDESTRUCT functionality
  • Encourages developers to design contracts without relying on SELFDESTRUCT

Important: EIP-6049 does NOT change the behavior of SELFDESTRUCT. The opcode continues to work exactly as before. Future EIPs (such as EIP-6780 in Ethereum's Cancun hard fork) will modify the behavior, but EIP-6049 itself is purely informational.

The deprecation affects: - Developer guidance and best practices - Code documentation and comments - Future protocol planning

This change does NOT affect: - Smart contract execution behavior - Gas costs - Transaction validity - Existing contract functionality - EVM bytecode interpretation

Decision

We implemented EIP-6049 in the Fukuii codebase with the following design decisions:

1. Documentation and Annotation

The SELFDESTRUCT opcode implementation in OpCode.scala is annotated with deprecation warnings:

/** SELFDESTRUCT opcode (0xff)
  * 
  * @deprecated As of EIP-6049 (Spiral fork), SELFDESTRUCT is officially deprecated.
  *             The behavior remains unchanged for now, but developers should avoid using
  *             this opcode in new contracts as future EIPs may change or remove its functionality.
  *             
  *             See: https://eips.ethereum.org/EIPS/eip-6049
  *             Activated with Spiral fork (ECIP-1109):
  *             - Block 19,250,000 on Ethereum Classic mainnet
  *             - Block 9,957,000 on Mordor testnet
  */
case object SELFDESTRUCT extends OpCode(0xff, 1, 0, _.G_selfdestruct) {
  // Implementation remains unchanged
}

2. Configuration Files

The Spiral fork configuration files already document the fork activation, but we add explicit mention of EIP-6049:

ETC Mainnet (etc-chain.conf): 

# Spiral EVM and Protocol Upgrades (ECIP-1109)
# Implements EIP-3855: PUSH0 instruction
# Implements EIP-3651: Warm COINBASE
# Implements EIP-3860: Limit and meter initcode
# Implements EIP-6049: Deprecate SELFDESTRUCT (informational - behavior unchanged)
# https://ecips.ethereumclassic.org/ECIPs/ecip-1109
spiral-block-number = "19250000"

Mordor Testnet (mordor-chain.conf): 

# Spiral EVM and Protocol Upgrades (ECIP-1109)
# Implements EIP-3855: PUSH0 instruction
# Implements EIP-3651: Warm COINBASE
# Implements EIP-3860: Limit and meter initcode
# Implements EIP-6049: Deprecate SELFDESTRUCT (informational - behavior unchanged)
# https://ecips.ethereumclassic.org/ECIPs/ecip-1109
spiral-block-number = "9957000"

3. Configuration Flag

While EIP-6049 does not change behavior, we add a configuration flag for tracking and documentation purposes:

case class EvmConfig(
    // ... other fields ...
    eip6049DeprecationEnabled: Boolean = false
)

This flag is set to true for the Spiral fork and later:

val SpiralConfigBuilder: EvmConfigBuilder = config =>
  MystiqueConfigBuilder(config).copy(
    opCodeList = SpiralOpCodes,
    eip3651Enabled = true,
    eip3860Enabled = true,
    eip6049DeprecationEnabled = true
  )

4. Fork Detection

A helper method is provided in BlockchainConfigForEvm to check if EIP-6049 deprecation is active:

def isEip6049DeprecationEnabled(etcFork: EtcFork): Boolean =
  etcFork >= EtcForks.Spiral

5. Implementation Rationale

No Behavior Changes

EIP-6049 is purely informational. The SELFDESTRUCT opcode implementation remains exactly as it was before. This means: - No changes to gas costs - No changes to state transitions - No changes to refund mechanisms - No changes to execution semantics

Documentation-Only Change

The primary purpose of EIP-6049 is to: 1. Signal to developers that SELFDESTRUCT is deprecated 2. Warn that future changes may modify or remove the opcode 3. Update documentation to reflect the deprecation status

Future-Proofing

By marking SELFDESTRUCT as deprecated now, we: - Prepare the ecosystem for future changes (like EIP-6780) - Give developers time to design contracts without SELFDESTRUCT - Maintain clear documentation of protocol evolution

Consequences

Positive

  1. Clear Developer Guidance: Developers are explicitly warned that SELFDESTRUCT is deprecated and should be avoided in new contracts.

  2. No Breaking Changes: Since behavior is unchanged, existing contracts continue to work exactly as before.

  3. Future Compatibility: Marking the opcode as deprecated prepares the ecosystem for future EIPs that may change SELFDESTRUCT behavior.

  4. Documentation Alignment: Keeps Ethereum Classic documentation aligned with Ethereum mainnet's Shanghai fork.

  5. Low Risk: This is a documentation-only change with no consensus impact or risk of chain splits.

Negative

  1. Limited Immediate Impact: Since behavior is unchanged, contracts can still use SELFDESTRUCT without technical consequences.

  2. Developer Confusion: Some developers may be confused about whether they can still use SELFDESTRUCT (answer: yes, but it's not recommended).

Neutral

  1. Ecosystem Awareness: The deprecation primarily serves to raise awareness in the developer community rather than enforce technical restrictions.

  2. Compiler Independence: Solidity and other compilers may add their own warnings about SELFDESTRUCT, independent of this EIP.

Implementation Details

Files Modified

  1. OpCode.scala:
  2. Added deprecation annotation to SELFDESTRUCT case object

  3. No behavior changes

  4. EvmConfig.scala:

  5. Added eip6049DeprecationEnabled flag to EvmConfig

  6. Updated SpiralConfigBuilder to set flag to true

  7. BlockchainConfigForEvm.scala:

  8. Added isEip6049DeprecationEnabled helper method

  9. Configuration files:

  10. Updated etc-chain.conf to document EIP-6049
  11. Updated mordor-chain.conf to document EIP-6049
  12. Updated other chain configs with comments

Testing Strategy

Since EIP-6049 does not change behavior, testing focuses on:

  1. Behavior Verification: Ensure SELFDESTRUCT continues to work exactly as before
  2. Verify gas costs remain unchanged
  3. Verify state transitions remain unchanged

  4. Verify refund mechanisms remain unchanged

  5. Fork Detection: Verify the eip6049DeprecationEnabled flag is set correctly

  6. true for Spiral fork and later

  7. false for pre-Spiral forks

  8. Existing Tests: Run existing SELFDESTRUCT test suite to ensure no regressions

  9. OpCodeFunSpec tests for SELFDESTRUCT
  10. CreateOpcodeSpec tests involving SELFDESTRUCT
  11. CallOpcodesSpec tests with SELFDESTRUCT
  12. Gas cost tests in OpCodeGasSpec

Test Coverage

The following existing test files cover SELFDESTRUCT behavior: - src/test/scala/com/chipprbots/ethereum/vm/OpCodeFunSpec.scala - src/test/scala/com/chipprbots/ethereum/vm/OpCodeGasSpec.scala - src/test/scala/com/chipprbots/ethereum/vm/OpCodeGasSpecPostEip161.scala - src/test/scala/com/chipprbots/ethereum/vm/OpCodeGasSpecPostEip2929.scala - src/test/scala/com/chipprbots/ethereum/vm/CallOpcodesSpec.scala - src/test/scala/com/chipprbots/ethereum/vm/CallOpcodesPostEip2929Spec.scala - src/test/scala/com/chipprbots/ethereum/vm/CreateOpcodeSpec.scala - src/test/scala/com/chipprbots/ethereum/vm/StaticCallOpcodeSpec.scala

All existing tests must continue to pass without modification.

Security Considerations

The EIP-6049 specification states:

Deprecating SELFDESTRUCT does not immediately change any security properties. However, it signals that developers should avoid relying on SELFDESTRUCT in new contracts.

Our implementation maintains security by:

  1. No Behavior Changes: Since behavior is unchanged, there are no new security implications from this EIP.

  2. Documentation: Clear documentation warns developers about the deprecation and encourages secure contract design without SELFDESTRUCT.

  3. Future Planning: The deprecation prepares for future EIPs that may improve security by modifying or removing SELFDESTRUCT.

  4. Existing Security Properties: All existing security properties of SELFDESTRUCT remain:

  5. Gas refunds are still calculated (though EIP-3529 reduced the refund amount)
  6. State is still cleared
  7. Ether is still transferred
  8. Access control still applies (cannot be called from static context)

References

Notes

  • This EIP was part of Ethereum's Shanghai hard fork (April 2023)
  • For ETC, this is part of the Spiral hard fork (ECIP-1109):
  • Mainnet activation: Block 19,250,000
  • Mordor testnet activation: Block 9,957,000
  • EIP-6049 is informational only - it does NOT change SELFDESTRUCT behavior
  • Future EIPs (like EIP-6780 in Ethereum's Cancun fork) will modify SELFDESTRUCT behavior
  • ETC may or may not adopt future changes to SELFDESTRUCT depending on community consensus
  • The deprecation warning serves primarily as developer guidance
  • Compilers like Solidity 0.8.18+ emit warnings when selfdestruct is used

EIP-3529: Reduction in Refunds

In the Mystique fork (before Spiral), EIP-3529 removed the gas refund for SELFDESTRUCT: - Previous: 24,000 gas refund - After EIP-3529: 0 gas refund

This made SELFDESTRUCT less economically attractive but didn't deprecate it.

EIP-6780: SELFDESTRUCT Only in Same Transaction (Future)

Ethereum's Cancun hard fork includes EIP-6780, which changes SELFDESTRUCT behavior: - SELFDESTRUCT only deletes code if called in the same transaction as contract creation - Otherwise, it only transfers Ether without deleting code - ETC has not yet decided whether to adopt EIP-6780

Why Deprecate SELFDESTRUCT?

  1. State Bloat: Allows contracts to be deleted, complicating state management
  2. Reentrancy: Can be used in complex reentrancy attacks
  3. Unpredictable Gas: Refunds make gas costs unpredictable
  4. Protocol Complexity: Interacts poorly with other EIPs (storage proofs, state expiry)
  5. Limited Use Cases: Most legitimate use cases can be achieved without SELFDESTRUCT

Migration Guidance for Developers

Developers should replace SELFDESTRUCT patterns with: 1. Transfer Ether: Use transfer() or call{value: amount}("") to send Ether 2. Disable Contract: Use a boolean flag to mark contract as disabled 3. Access Control: Use role-based access control instead of self-destruction 4. Upgradeability: Use proxy patterns instead of self-destruct and redeploy

Example: 

// Old pattern (deprecated)
function destroy() public onlyOwner {
    selfdestruct(payable(owner));
}

// New pattern (recommended)
bool public disabled;
function disable() public onlyOwner {
    disabled = true;
    payable(owner).transfer(address(this).balance);
}

Performance Implications

Since EIP-6049 does not change behavior, there are no performance implications: - Gas costs remain the same - Execution speed remains the same - State transitions remain the same

Conclusion

EIP-6049 is a documentation-only change that deprecates SELFDESTRUCT without modifying its behavior. The implementation in Fukuii adds clear deprecation warnings in code comments and configuration files, prepares for future protocol changes, and maintains full compatibility with existing contracts. This aligns Ethereum Classic with Ethereum mainnet's Shanghai hard fork while allowing the ETC community to independently decide on future changes to SELFDESTRUCT behavior.