op-chain-ops: add legacy eth migration check

Very simple one for now

op-chain-ops/ether/cli.go

@@ -21,6 +21,10 @@ func getOVMETHTotalSupplySlot() common.Hash {
 	return key
 }
 
+func GetOVMETHTotalSupplySlot() common.Hash {
+	return getOVMETHTotalSupplySlot()
+}
+
 // getOVMETHBalance gets a user's OVM ETH balance from state by querying the
 // appropriate storage slot directly.
 func getOVMETHBalance(db *state.StateDB, addr common.Address) *big.Int {

op-chain-ops/genesis/check.go

 package genesis
 
 import (
+	"errors"
 	"fmt"
 	"math/big"
 
 	"github.com/ethereum-optimism/optimism/op-bindings/predeploys"
+	"github.com/ethereum-optimism/optimism/op-chain-ops/ether"
 	"github.com/ethereum/go-ethereum/common"
 	"github.com/ethereum/go-ethereum/core/rawdb"
 	"github.com/ethereum/go-ethereum/core/state"
@@ -41,6 +43,10 @@ func CheckMigratedDB(ldb ethdb.Database) error {
 		return err
 	}
 
+	if err := CheckLegacyETH(db); err != nil {
+		return err
+	}
+
 	return nil
 }
 
@@ -78,3 +84,14 @@ func CheckPredeploys(db vm.StateDB) error {
 	}
 	return nil
 }
+
+// CheckLegacyETH checks that the legacy eth migration was successful.
+// It currently only checks that the total supply was set to 0.
+func CheckLegacyETH(db vm.StateDB) error {
+	// Ensure total supply is set to 0
+	slot := db.GetState(predeploys.LegacyERC20ETHAddr, ether.GetOVMETHTotalSupplySlot())
+	if slot != (common.Hash{}) {
+		return errors.New("total supply not set to 0")
+	}
+	return nil
+}