solvm: The EVM inside the EVM

WTF?

A (slightly) stripped down version of the EVM implemented on top of the EVM using yul and solidity.

Why?

idk, for fun. Its a fun memory-management challenge. Also I've always wanted scripting in solidity and this is a step in that direction.

How?

A dynamic in-memory array is used as a jump table for ops. A dynamic in-memory array is used for the simulated EVM's stack variables. The simulated EVM's memory is held at a moveable offset and can move if needed (unlikely unless stack is forced to move).

Limits

Currently no context switching opcodes (all flavors of call). We can simulate a lot of these in memory if want though, just haven't gotten around to it.

Also bugs. Probably many bugs.

And gas. There are large one-time gas costs, that get amortized with more ops (but not a ton).

Example

contract EvmTest is DSTest {
    function testMul() public {
        Evm evm;
        // pass in raw bytecode and it evaluates it
        // does 1 * 3 and returns it
        (bool succ, bytes memory ret) = evm.evaluate(hex"600160030260205260206000F3");
        (uint256 r) = abi.decode(ret, (uint256));
        assertTrue(succ);
        assertEq(r, 3);
    }
}