fix(ERC1271InputGenerator): fix code start with ef error by adding 0x…

…ff as first byte

src/utils/ERC1271InputGenerator.sol

@@ -35,16 +35,18 @@ contract ERC1271InputGenerator {
     /// @param accountFactory  The factory that will be used to deploy the account (if not already deployed).
     /// @param factoryCalldata The calldata that will be used to deploy the account (if not already deployed).
     constructor(CoinbaseSmartWallet account, bytes32 hash, address accountFactory, bytes memory factoryCalldata) {
-        // This allows us to get a replay-safe hash on any deployed or undeployed account
-        // in a single eth_call, i.e. without deploying the contract. We do this by calling replaySafeHash on a deployed
-        // account,
-        // or by simulating the deployment of an undeployed account and then calling replaySafeHash on it.
+        // This allows us to get a replay-safe hash on any deployed or undeployed account in a single eth_call, i.e.
+        // without deploying the contract. We do this by calling replaySafeHash on a deployed account, or by simulating
+        // the deployment of an undeployed account and then calling replaySafeHash on it.
         bytes32 replaySafeHash = _coinbaseSmartWallet1271Input(account, hash, accountFactory, factoryCalldata);
         assembly {
-            // store replay safe hash
-            mstore(0x80, replaySafeHash)
-            // return replay safe hash
-            return(0x80, 0x20)
+            // Ensure the contract code does not start with ef (see https://eips.ethereum.org/EIPS/eip-3541).
+            mstore8(0x80, 0xff)
+            // Store replay safe hash.
+            mstore(0x81, replaySafeHash)
+            // Return 33 bytes corresponding to 0xff | replaySafeHash.
+            // Off-chain caller must skip the first byte (0xff) when interpreting the result.
+            return(0x80, 0x21)
         }
     }
 

test/ERC1271InputGenerator.t.sol

@@ -25,7 +25,7 @@ contract CoinbaseSmartWallet1271InputGeneratorTest is Test {
         bytes32 hash = 0x15fa6f8c855db1dccbb8a42eef3a7b83f11d29758e84aed37312527165d5eec5;
         bytes32 replaySafeHash = deployedAccount.replaySafeHash(hash);
         ERC1271InputGenerator generator = new ERC1271InputGenerator(deployedAccount, hash, address(0), "");
-        assertEq(bytes32(address(generator).code), replaySafeHash);
+        assertEq(_bytes32FromByteCode(address(generator).code), replaySafeHash);
     }
 
     function testGetReplaySafeHashForUndeployedAccount() public {
@@ -42,6 +42,13 @@ contract CoinbaseSmartWallet1271InputGeneratorTest is Test {
         // This is now deployed.
         bytes32 replaySafeHash = undeployedAccount.replaySafeHash(hash);
 
-        assertEq(bytes32(address(generator).code), replaySafeHash);
+        assertEq(_bytes32FromByteCode(address(generator).code), replaySafeHash);
+    }
+
+    function _bytes32FromByteCode(bytes memory bytecode) private pure returns (bytes32) {
+        bytes32 a = abi.decode(bytecode, (bytes32));
+        uint8 b = uint8(bytecode[bytecode.length - 1]);
+
+        return (a << 8) | bytes32(uint256(b));
     }
 }