The ArbSys Precompiled Contract

ArbSys is a precompiled contract that exists in every Arbitrum Chain. As its name would imply, ArbSys provides systems functionality useful to some Arbitrum contracts. Any contract running on an Arbitrum Chain can call the chain's ArbSys.

ArbSys lives at address 0x0000000000000000000000000000000000000064 on every Arbitrum chain. To call it, write something like this:

uint256 txCount = ArbSys(address(100)).getTransactionCount();

Here is the interface offered by ArbSys:

/**
* @title Precompiled contract that exists in every Arbitrum chain at address(100), 0x0000000000000000000000000000000000000064. Exposes a variety of system-level functionality.
 */
interface ArbSys {
    /**
    * @notice Get internal version number identifying an ArbOS build
    * @return version number as int
     */
    function arbOSVersion() external pure returns (uint);

    /**
    * @notice Get Arbitrum block number (distinct from L1 block number; Arbitrum genesis block has block number 0)
    * @return block number as int
     */
    function arbBlockNumber() external view returns (uint);

    /**
    * @notice Send given amount of Eth to dest from sender.
    * This is a convenience function, which is equivalent to calling sendTxToL1 with empty calldataForL1.
    * @param destination recipient address on L1
    * @return unique identifier for this L2-to-L1 transaction.
    */
    function withdrawEth(address destination) external payable returns(uint);

    /**
    * @notice Send a transaction to L1
    * @param destination recipient address on L1
    * @param calldataForL1 (optional) calldata for L1 contract call
    * @return a unique identifier for this L2-to-L1 transaction.
    */
    function sendTxToL1(address destination, bytes calldata calldataForL1) external payable returns(uint);



    /**
    * @notice get the number of transactions issued by the given external account or the account sequence number of the given contract
    * @param account target account
    * @return the number of transactions issued by the given external account or the account sequence number of the given contract
    */
    function getTransactionCount(address account) external view returns(uint256);

    /**
    * @notice get the value of target L2 storage slot
    * This function is only callable from address 0 to prevent contracts from being able to call it
    * @param account target account
    * @param index target index of storage slot
    * @return stotage value for the given account at the given index
    */
    function getStorageAt(address account, uint256 index) external view returns (uint256);

    /**
    * @notice check if current call is coming from l1
    * @return true if the caller of this was called directly from L1
    */
    function isTopLevelCall() external view returns (bool);

    event EthWithdrawal(address indexed destAddr, uint amount);

    event L2ToL1Transaction(address caller, address indexed destination, uint indexed uniqueId,
                            uint indexed batchNumber, uint indexInBatch,
                            uint arbBlockNum, uint ethBlockNum, uint timestamp,
                            uint callvalue, bytes data);
}