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Opcode Differences

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Modified Opcodes

OpcodeSolidity equivalentBehaviour
COINBASEblock.coinbaseValue is set by the sequencer. Currently returns the OVM_SequencerFeeVault address (0x420…011).
DIFFICULTYblock.difficultyAlways returns zero.
BASEFEEblock.basefeeCurrently unsupported.

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Added Opcodes

OpcodeBehavior
L1BLOCKNUMBERReturns the block number of the last L1 block known by the L2 system. Typically, this block number will lag up to 15 minutes behind the latest L1 block number.

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Block Numbers and Timestamps

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Block production is not constant

  • On Ethereum, the NUMBER opcode (block.number in Solidity) corresponds to the current Ethereum block number. Similarly, in Lollipop, block.number corresponds to the current L2 block number. However, each transaction on L2 is placed in a separate block and blocks are NOT produced at a constant rate.
  • This is important because it means that block.number is currently NOT a reliable source of timing information. If you want access to the current time, you should use block.timestamp (the TIMESTAMP opcode) instead.

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Timestamps

  • The TIMESTAMP opcode (block.timestamp in Solidity) uses the timestamp of the transaction itself.

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Address Aliasing

  • Because of the behaviour of the CREATE opcode, a user can create a contract on L1 and on L2 that share the same address but have different bytecode. This can break trust assumptions because one contract may be trusted and another be untrusted (see below).
  • To prevent this problem, the behaviour of the ORIGIN and CALLER opcodes (tx.origin and msg.sender) differs slightly between L1 and L2.
  • The value of tx.origin is determined as follows:
Call sourcetx.origin
L1 user (Externally Owned Account)The user’s address (same as in Ethereum)
L2 user (Externally Owned Account)The user’s address (same as in Ethereum)
  • The value of msg.sender at the top-level (the very first contract being called) is always equal to tx.origin. Therefore, if the value of tx.origin is affected by the rules defined above, the top-level value of msg.sender will also be impacted.
In general, tx.origin should not be used for authorization (https://docs.soliditylang.org/en/latest/security-considerations.html#tx-origin). However, that is a separate issue from address aliasing because address aliasing also affects msg.sender.