Commits on Dec 12, 2021

1. EVM: writeContract fixes, never return contract code as RETURNDATA …

   This fixes #867 "EIP-170 related consensus error at Goerli block 5080941", and
   equivalent on other networks.
   
   This combines a change on the EVM-caller side with an EVM-side change from
   @jangko 6548ff9 "fixes CREATE/CREATE2's `returndata` bug", making the caller
   EVM ignore any data except from `REVERT`.
   
   Either change works by itself.  The reason for both is to ensure we definitely
   comply with ambiguous EVMC expectations from either side of that boundary, and
   it makes the internal API clearer.
   
   As well as fixing a specific consensus issue, there are some other EVM logic
   changes too: Refactored `writeContract`, how `RETURNDATA` is handled inside the
   EVM, and changed behaviour with quirks before EIP-2 (Homestead).
   
   The fix allows sync to pass block 5080941 on Goerli, and probably equivalent on
   other networks.  Here's a trace at batch 5080897..5081088:
   
   ```
   TRC 2021-10-01 21:18:12.883+01:00 Persisting blocks                  file=persist_blocks.nim:43 fromBlock=5080897 toBlock=5081088
   ...
   DBG 2021-10-01 21:18:13.270+01:00 Contract code size exceeds EIP170  topics="vm computation" file=computation.nim:236 limit=24577 actual=31411
   DBG 2021-10-01 21:18:13.271+01:00 gasUsed neq cumulativeGasUsed      file=process_block.nim:68 block=5080941/0A3537BC5BDFC637349E1C77D9648F2F65E2BF973ABF7956618F854B769DF626 gasUsed=3129669 cumulativeGasUsed=3132615
   TRC 2021-10-01 21:18:13.271+01:00 peer disconnected                  file=blockchain_sync.nim:407 peer=<IP:PORT>
   ```
   
   Although it says "Contract code size" and "gasUsed", this bug is more general
   than either contract size or gas.  It's due to incorrect behaviour of EVM
   instructions `RETURNDATA` and `RETURNDATASIZE`.
   
   Sometimes when `writeContract` decides to reject writing the contract for any
   of several reasons (for example just insufficient gas), the unwritten contract
   code was being used as the "return data", and given to the caller.  If the
   caller used `RETURNDATA` or `RETURNDATASIZE` ops, those incorrectly reported
   the contract code that didn't get written.
   
   EIP-211 (https://eips.ethereum.org/EIPS/eip-211) describes `RETURNDATA`:
   > "`CREATE` and `CREATE2` are considered to return the empty buffer in the
   > success case and the failure data in the failure case".
   
   The language is ambiguous.  In fact "failure case" means when the contract uses
   `REVERT` to finish.  It doesn't mean other failures like out of gas, EIP-170
   limit, EIP-3541, etc.
   
   To be thorough, and to ensure we always do the right thing with real EVMC when
   that's finalised, this patch fixes the `RETURNDATA` issue in two places, either
   of which make Goerli block 5080941 pass.
   
   `writeContract` has been refactored to be caller, and so has where it's called.
   It sets an error in the usual way if contract writing is rejected -- that's
   anticipating EVMC, where we'll use different error codes later.
   
   Overall four behaviour changes:
   
   1. On the callee side, it doesn't set `c.outputData` except for `REVERT`.
   2. On the caller side, it doesn't read `child.outputData` except for `REVERT`.
   3. There was a bug in processing before Homestead fork (EIP-2).  We did not
      match the spec or other implementations; now we do.  When there's
      insufficient gas, before Homestead it's treated as success but with an empty
      contract.
   
      https://github.com/ethereum/pyethereum/blob/d117c8f3fd93359fc641fd850fa799436f7c43b5/ethereum/processblock.py#L304
      https://github.com/ethereum/go-ethereum/blob/401354976bb4/core/vm/instructions.go#L586
   
   4. The Byzantium check has been removed, as it's unnecessary.
   
   Signed-off-by: Jamie Lokier <[email protected]>

   

   jlokier authored and jangko committed Dec 12, 2021
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