Delegate Calls and Callcodes

Besides direct calls, the EVM also supports two other types of calls: DELEGATECALL and CALLCODE.

DelegateCall

DELEGATECALL execute the callee's bytecode in the caller's context. For example, if A sends a transaction to B, and B makes a DELEGATECALL to C, then:

• C's bytecode is being executed.

• A is msg.sender.
  

• B is address(this).
  

• B's storage will be used in any storage.
  

Similar to how we implemented the previous calls, we will define an external function, ICrossTx.delegateCall, for opDelegateCall to call.

For delegate calls, we now have 3 addresses to consider: that of the msg.sender, the caller (aka delegator), and the callee. All these can be passed to ICrossTx.delegateCall via the InternalInput structure.

CallCode

CALLCODE is similar to DELEGATECALL, with one distinguishing difference: the msg.sender is not preserved. For example, if A sends a transaction to B, and B makes a CALLCODE to C, then:

1. C's bytecode is being executed

2. B is msg.sender

3. B is address(this)

4. B's storage will be used in any storage operations

Because of how similar CALLCODE is to DELEGATECALL, CALLCODE can be implemented by simply calling ICrossTx.delegateCall.

Your Task

Implement DELEGATECALL by defining:

• opDelegateCall in contracts/libraries/Instructions.sol

• delegateCall in contracts/sEVM.sol
  

Then, implement CALLCODE by defining:

• opCallCode in contracts/libraries/Instructions.sol