At the moment you would have to port solidity code (ETH) to C++ (EOS). 

In the future [EOS will support the Ethereum virtual machine][1] so it could be possible to use existing solidity codebases with minimal changes.

From an [earlier version of the EOS whitepaper][2]:

> Ethereum Virtual Machine (EVM) This virtual machine has been used for
> most existing smart contracts and could be adapted to work within an
> EOS.IO blockchain. It is conceivable that EVM contracts could be run
> within their own sandbox inside an EOS.IO blockchain and that with
> some adaptation EVM contracts could communicate with other EOS.IO
> blockchain applications.


  [1]: https://github.com/EOSIO/Documentation/blob/master/TechnicalWhitePaper.md#scripts--virtual-machines
  [2]: https://github.com/EOSIO/Documentation/blob/477bac64dfaa953e1b5188fca390c8d99ec4714f/TechnicalWhitePaper.md#ethereum-virtual-machine-evm