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 EVM context or state opcodes (address, balance, caller, origin, callvalue, calldataload, etc.). We can simulate a lot of these in memory if want though, just haven't gotten around to it.

A bunch of opcodes haven't been implemented.

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);
    }
}