[Testing] Integrate testing with `evm` in `go-ethereum`

[lialan]

go-ethereum provides a decent interface for executing EVM code. We could use it for our use of testing.
We will start with non-blockchain interacting correctness checking. In such cases, we compile a single function and feed it into evm and execute.
The compiled function takes a certain amount of arguments as input, plus the return address at the bottom of the stack. When function finishes executing, the last instruction will jump to the return address.
So to test the result and make sure the function returns correctly, we should push a return address onto stack before anything else. But that would alter the relocation offset.
One way to do this is to add an option to specify an offset to the relocation offset. Let’s say when we are fixing up a jump destination, and we have determined location at 0xabcd, and if we have specified -debug-offset-offset=2, then the 0xabcd will become 0xabcd + 2 = 0xabcf. By doing this we can acknowledge the prefix offsets added to test cases.

[lialan]

As for result checking:

The returned value is left on the top of the stack, the following instructions should be used when we want to return the instruction:

PUSH1 0x00
MSTORE
RETURN // returns the 32-byte values at memory 0x00

So in other words , we need to have a function dispatcher at the beginning to arrange arguments and return values. Here is an example of how we should add a prefix so we can get the return results.

PUSH1 0x5 // 0x00
PUSH1 0x0a // 0x02
JUMP  // 0x03
JUMPDEST // 0x04
PUSH1 0x0  // 0x06
MSTORE // 0x07
RETURN // 0x08
... // function body

[lialan]

This is the dispatcher for 1 argument, 1 return value function:

[1] PUSH1 0x08
[3] PUSH1 0x0A
[5] PUSH1 0xFF # this is the input value we wish to specify
[8] PUSH2 0x0013
[9] JUMP
[10] JUMPDEST
[12] PUSH1 0x00
[13] MSTORE
[15] PUSH1 0x20
[17] PUSH1 0x00
[18] RETURN
[19] JUMPDEST # Start of function body, in this case do nothing
[20] SWAP1
[21] JUMP

Binary:

6008600A60FF610013565b60005260206000f35b9056

[lialan]

Here is the example we perform 2 arguments 1 output function dispatching:

[1] PUSH1 0x0a
[3] PUSH1 0x0c
[5] PUSH1 0x11
[7] PUSH1 0x22
[10] PUSH2 0x0015
[11] JUMP
[12] JUMPDEST
[14] PUSH1 0x00
[15] MSTORE
[17] PUSH1 0x20
[19] PUSH1 0x00
[20] RETURN
[21] JUMPDEST
[22] ADD
[23] SWAP1
[24] JUMP

Binary:

600a600c60116022610015565b60005260206000f35b019056

[lialan]

Spent a bit of time refining a third party assembler: crytic/pyevmasm#36

We will use this little tool to inject a simple function dispatcher in our tests.

[lialan]

Another way to do this completely in Python is to use py-evm. Investigating the possibilities.