fix(levm): change in extcodehash (#1503)

**Motivation**

The `extcodehash` opcode was not handling certain edge cases correctly.

**Description**

- Return `U256::zero` for non-existent accounts and empty accounts.
Right now we are checking if the account is empty.
- Properly compute code hashes for accounts with bytecode.

**References**
[EIP-161](https://eips.ethereum.org/EIPS/eip-161): _An account is
considered empty when it has no code and zero nonce and zero balance._
[EIP-1052](https://eips.ethereum.org/EIPS/eip-1052): _In case the
account does not exist or is empty, 0 is pushed to the stack._

crates/vm/levm/src/opcode_handlers/environment.rs

@@ -424,10 +424,14 @@ impl VM {
 
         self.increase_consumed_gas(current_call_frame, gas_cost::extcodehash(address_was_cold)?)?;
 
-        current_call_frame.stack.push(U256::from_big_endian(
-            keccak(account_info.bytecode).as_fixed_bytes(),
-        ))?;
+        // An account is considered empty when it has no code and zero nonce and zero balance. [EIP-161]
+        if account_info.is_empty() {
+            current_call_frame.stack.push(U256::zero())?;
+            return Ok(OpcodeSuccess::Continue);
+        }
 
+        let hash = U256::from_big_endian(keccak(account_info.bytecode).as_fixed_bytes());
+        current_call_frame.stack.push(hash)?;
         Ok(OpcodeSuccess::Continue)
     }
 }

crates/vm/levm/tests/tests.rs

@@ -3873,7 +3873,7 @@ fn create_happy_path() {
 #[test]
 fn caller_op() {
     let caller = Address::from_low_u64_be(0x100);
-    let address_that_has_the_code = Address::from_low_u64_be(0x42);
+    let address_that_has_the_code = Address::from_low_u64_be(213);
 
     let operations = [Operation::Caller, Operation::Stop];
 
@@ -3915,7 +3915,7 @@ fn caller_op() {
 
 #[test]
 fn origin_op() {
-    let address_that_has_the_code = Address::from_low_u64_be(0x42);
+    let address_that_has_the_code = Address::from_low_u64_be(213);
     let msg_sender = Address::from_low_u64_be(0x999);
 
     let operations = [Operation::Origin, Operation::Stop];
@@ -3986,7 +3986,7 @@ fn balance_op() {
 
 #[test]
 fn address_op() {
-    let address_that_has_the_code = Address::from_low_u64_be(0x42);
+    let address_that_has_the_code = Address::from_low_u64_be(123);
 
     let operations = [Operation::Address, Operation::Stop];
 
@@ -4028,7 +4028,7 @@ fn address_op() {
 
 #[test]
 fn selfbalance_op() {
-    let address_that_has_the_code = Address::from_low_u64_be(0x42);
+    let address_that_has_the_code = Address::from_low_u64_be(123);
     let balance = U256::from(999);
 
     let operations = [Operation::SelfBalance, Operation::Stop];
@@ -4075,7 +4075,7 @@ fn selfbalance_op() {
 
 #[test]
 fn callvalue_op() {
-    let address_that_has_the_code = Address::from_low_u64_be(0x42);
+    let address_that_has_the_code = Address::from_low_u64_be(123);
     let value = U256::from(0x1234);
 
     let operations = [Operation::Callvalue, Operation::Stop];
@@ -4119,7 +4119,7 @@ fn callvalue_op() {
 
 #[test]
 fn codesize_op() {
-    let address_that_has_the_code = Address::from_low_u64_be(0x42);
+    let address_that_has_the_code = Address::from_low_u64_be(123);
 
     let operations = [Operation::Codesize, Operation::Stop];
 
@@ -4161,7 +4161,7 @@ fn codesize_op() {
 
 #[test]
 fn gasprice_op() {
-    let address_that_has_the_code = Address::from_low_u64_be(0x42);
+    let address_that_has_the_code = Address::from_low_u64_be(123);
     let operations = [Operation::Gasprice, Operation::Stop];
 
     let mut db = Db::default();
@@ -4204,7 +4204,7 @@ fn gasprice_op() {
 #[test]
 fn codecopy_op() {
     // Copies two bytes of the code, with offset 2, and loads them beginning at offset 3 in memory.
-    let address_that_has_the_code = Address::from_low_u64_be(0x42);
+    let address_that_has_the_code = Address::from_low_u64_be(123);
     // https://www.evm.codes/playground?fork=cancun&unit=Wei&codeType=Mnemonic&code=%27~2z~2z~3zCODECOPY%27~PUSH1%200x0z%5Cn%01z~_
     let operations = [
         Operation::Push((1, 0x02.into())), // size
@@ -4269,7 +4269,7 @@ fn codecopy_op() {
 
 #[test]
 fn extcodesize_existing_account() {
-    let address_with_code = Address::from_low_u64_be(0x42);
+    let address_with_code = Address::from_low_u64_be(123);
     let operations = [
         Operation::Push((20, address_with_code.as_bytes().into())),
         Operation::ExtcodeSize,
@@ -4297,7 +4297,7 @@ fn extcodesize_existing_account() {
 fn extcodesize_non_existing_account() {
     // EVM Playground: https://www.evm.codes/playground?fork=cancun&unit=Wei&codeType=Mnemonic&code='PUSH20%200x42%5CnEXTCODESIZE%5CnSTOP'_
     let operations = [
-        Operation::Push((20, "0x42".into())),
+        Operation::Push((20, U256::from(0xABCD))),
         Operation::ExtcodeSize,
         Operation::Stop,
     ];
@@ -4315,7 +4315,7 @@ fn extcodesize_non_existing_account() {
 
 #[test]
 fn extcodecopy_existing_account() {
-    let address_with_code = Address::from_low_u64_be(0x42);
+    let address_with_code = Address::from_low_u64_be(213);
     let size: usize = 1;
 
     let operations = [
@@ -4358,7 +4358,7 @@ fn extcodecopy_non_existing_account() {
         Operation::Push((1, size.into())),
         Operation::Push0, // offset
         Operation::Push0, // destOffset
-        Operation::Push((20, "0x42".into())),
+        Operation::Push((20, U256::from(213))),
         Operation::ExtcodeCopy,
         Operation::Stop,
     ];
@@ -4380,16 +4380,17 @@ fn extcodecopy_non_existing_account() {
 }
 
 #[test]
-fn extcodehash_account_with_empty_code() {
-    let address_with_code = Address::from_low_u64_be(0x42);
+fn extcodehash_account_with_zero_bytecode_but_not_empty() {
+    let address = Address::from_low_u64_be(213);
     let operations = [
-        Operation::Push((20, address_with_code.as_bytes().into())),
+        Operation::Push((20, address.as_bytes().into())),
         Operation::ExtcodeHash,
         Operation::Stop,
     ];
 
     let mut db = Db::default();
-    db.add_accounts(vec![(address_with_code, Account::default())]);
+    let account = Account::default().with_balance(U256::one()); // Add balance to avoid empty account
+    db.add_accounts(vec![(address, account)]);
 
     let mut vm = new_vm_with_ops_db(&operations, db).unwrap();
 
@@ -4405,8 +4406,9 @@ fn extcodehash_account_with_empty_code() {
 #[test]
 fn extcodehash_non_existing_account() {
     // EVM Playground: https://www.evm.codes/playground?fork=cancun&unit=Wei&codeType=Mnemonic&code='PUSH20%200x42%5CnEXTCODEHASH%5CnSTOP'_
+    let random_address = Address::from_low_u64_be(12345);
     let operations = [
-        Operation::Push((20, "0x42".into())),
+        Operation::Push((20, random_address.as_bytes().into())),
         Operation::ExtcodeHash,
         Operation::Stop,
     ];
@@ -4417,7 +4419,7 @@ fn extcodehash_non_existing_account() {
     vm.execute(&mut current_call_frame).unwrap();
     assert_eq!(
         vm.current_call_frame_mut().unwrap().stack.pop().unwrap(),
-        "c5d2460186f7233c927e7db2dcc703c0e500b653ca82273b7bfad8045d85a470".into()
+        U256::zero()
     );
     assert_eq!(current_call_frame.gas_used, 2603.into());
 }