d-xo / ds-calls

ds-calls

ergonomic delegatecall wrapper

This implementation differs from solidity's in the following ways:

• reverts if the delegatecall fails
• reverts if the called address has no code
• reverts if insufficient gas has been provided
• propogates error messages from reverts during execution of the target contract

Usage

import 'ds-calls/calls.sol';

contract Delegator is DSDelegatecall {
    function delegate(address usr, bytes memory fax, uint gas)
        public
        returns (bytes memory)
    {
        return delegatecall(usr, fax, gas);
    }
}

Specification

The following is an executable K specification written in the klab act format. You can verify that the implementation in this repo correctly implements this specification by running dapp build && klab build && klab prove-all from the repo root.

The bare DSDelegateCall contract by itself is not very interesting as all functions are internal, so we instead write a specification for the simplest possible consumer contract: the Delegator defined in the usage section above.

Additionally we cannot use K to make statements about calls into arbitrary code. We therefore specify the behaviour of the Delegator when calling into various contracts that exercise the behaviour described in the features section above.

This limits the strength of the correctness claims that we can make about this component in isolation, and additional verification work specific to your particular context is encouraged.

Implementations of the Delegator and the various target contracts are provided in src/harness.sol

Trivial Call

We begin by describing a call into a contract that always returns 0.

behaviour delegate of Delegator
interface delegate(address usr, bytes fax, uint gas)

calls

  Trivial.returns_zero

iff
  fax == #generateSignature("returns_zero()")
  VCallDepth < 1024

returns 0

behaviour returns_zero of Trivial
interface returns_zero()

returns 0

TODO

• specify basic delegatecall behaviour
• specify handling of returndata
• specify calls to an EOA
• specify error message propogation
• specify gas semantics
• extend to include a call implementation