fix op implemention about contract function call

[p0n1]

See contract comments.

pragma solidity ^0.4.18;

contract A {
    uint x;
    function a(uint input) public returns(uint) {
        require(input > 10);
        x = input;
        return x;
    }
}

contract B {
    uint x;
    address delegateAddress;
    function b(uint input) public {
        require(input > 10);
        x = input;
    }

    function b_call_a(uint input) public {
        A delegate = A(delegateAddress);
        var ret = delegate.a(input);
        // laser could not simulate these two branches
        // after library function call due to chaotic stack and memory
        if (ret > 20) {
            x = ret + 9;
        } else {
            x = ret + 10;
        }
    }
}

Two graph generated for comparison.

• call_ret_value.origin.graph.html

• call_ret_value.improved.graph.html

This commit do as follows:

• Add RETURNDATASIZE op: missing this caused misplaced stack after contract function call.

• Set output memory for CALL & CALLCODE op: should store call retval to memory, otherwise wrong value will be MLOAD from mem.

TODOs:

• [ ] Not sure this fix will break other code or not.

• [ ] This if branch is complicated and could forget to store retval to memory in several places.

[muellerberndt]

could forget to store retval to memory in several places.

Return values are not handled well currently because of the way calls are implemented. If there's multiple returns from the callee contract, only one return value (the last return simulated) will be used in the analysis.

This would have to be fixed buy moving call_stack into the global state and returning on exception/stop, however this would create a much larger state space.