eth/tracers: fix codehash in prestate diffmode (#34675)

Fixes https://github.com/ethereum/go-ethereum/issues/34648.

eth/tracers/internal/tracetest/testdata/prestate_tracer_with_diff_mode/eip7702_deauth.json

@@ -0,0 +1,98 @@
+{
+  "genesis": {
+    "blobGasUsed": "0",
+    "difficulty": "0",
+    "excessBlobGas": "0",
+    "extraData": "0x",
+    "gasLimit": "11511229",
+    "hash": "0x455b93a512baa4ed5e117508b184a6bb03904b94d665ce38931728eca9cdd8fe",
+    "miner": "0x71562b71999873db5b286df957af199ec94617f7",
+    "mixHash": "0x042877c4fab9f022d29590ae83bad89d6181afb1d6e107619911ea52e5901364",
+    "nonce": "0x0000000000000000",
+    "number": "1",
+    "parentBeaconBlockRoot": "0x0000000000000000000000000000000000000000000000000000000000000000",
+    "stateRoot": "0xc8688ad6433e6b9f4edeb82360d2b99c8e919f493a01cacbe7c4a97184f5d043",
+    "timestamp": "1775654796",
+    "alloc": {
+      "0x71562b71999873db5b286df957af199ec94617f7": {
+        "balance": "0xffffffffffffffffffffffffffffffffffffffffffffffffffffdb64910c3bf7",
+        "nonce": "1"
+      },
+      "0xe85a1c0e9d5b1c9b417c6c1b34c22cd77f623f50": {
+        "balance": "0x0",
+        "code": "0xef0100d313d93607c016a85e63e557a11ca5ab0b53ad83",
+        "codeHash": "0x9eea9f41ed2b35e6234d1e1c14e88c1136f85d56ed1f32a7efc0096d998dad3d",
+        "nonce": "1"
+      }
+    },
+    "config": {
+      "chainId": 1337,
+      "homesteadBlock": 0,
+      "eip150Block": 0,
+      "eip155Block": 0,
+      "eip158Block": 0,
+      "byzantiumBlock": 0,
+      "constantinopleBlock": 0,
+      "petersburgBlock": 0,
+      "istanbulBlock": 0,
+      "muirGlacierBlock": 0,
+      "berlinBlock": 0,
+      "londonBlock": 0,
+      "arrowGlacierBlock": 0,
+      "grayGlacierBlock": 0,
+      "shanghaiTime": 0,
+      "cancunTime": 0,
+      "pragueTime": 0,
+      "terminalTotalDifficulty": 0,
+      "blobSchedule": {
+        "cancun": {
+          "target": 3,
+          "max": 6,
+          "baseFeeUpdateFraction": 3338477
+        },
+        "prague": {
+          "target": 6,
+          "max": 9,
+          "baseFeeUpdateFraction": 5007716
+        }
+      }
+    }
+  },
+  "context": {
+    "number": "2",
+    "difficulty": "0",
+    "timestamp": "1775654797",
+    "gasLimit": "11522469",
+    "miner": "0x71562b71999873db5b286df957af199ec94617f7",
+    "baseFeePerGas": "766499147"
+  },
+  "input": "0x04f8cd82053901843b9aca008477359400830186a09471562b71999873db5b286df957af199ec94617f78080c0f85ef85c8205399400000000000000000000000000000000000000000101a011fc0271f2566e7ebe5ddbff6d48ea97a19afa248452a392781096b7e3b89177a0020107ecefe99c90429b416fe4d1eead5a7fa253761e85cd7cdc7df6e5032d7f80a098495fb16c904f0b67b49afe868b28b0159c8df07522bed99ef6ff2cc2ac2935a048857a9c385d91735a9fdccabc66de7a5ea1897f523a5b9a352e281642a76e6b",
+  "tracerConfig": {
+    "diffMode": true
+  },
+  "result": {
+    "post": {
+      "0x71562b71999873db5b286df957af199ec94617f7": {
+        "balance": "0xffffffffffffffffffffffffffffffffffffffffffffffffffffc1bd12c85eb7",
+        "nonce": 2
+      },
+      "0xe85a1c0e9d5b1c9b417c6c1b34c22cd77f623f50": {
+        "code": "0x",
+        "codeHash": "0xc5d2460186f7233c927e7db2dcc703c0e500b653ca82273b7bfad8045d85a470",
+        "nonce": 2
+      }
+    },
+    "pre": {
+      "0x71562b71999873db5b286df957af199ec94617f7": {
+        "balance": "0xffffffffffffffffffffffffffffffffffffffffffffffffffffdb64910c3bf7",
+        "nonce": 1
+      },
+      "0xe85a1c0e9d5b1c9b417c6c1b34c22cd77f623f50": {
+        "balance": "0x0",
+        "code": "0xef0100d313d93607c016a85e63e557a11ca5ab0b53ad83",
+        "codeHash": "0x9eea9f41ed2b35e6234d1e1c14e88c1136f85d56ed1f32a7efc0096d998dad3d",
+        "nonce": 1
+      }
+    }
+  }
+}

eth/tracers/native/gen_account_json.go

@@ -16,14 +16,14 @@ var _ = (*accountMarshaling)(nil)
 func (a account) MarshalJSON() ([]byte, error) {
 	type account struct {
 		Balance  *hexutil.Big                `json:"balance,omitempty"`
-		Code     hexutil.Bytes               `json:"code,omitempty"`
+		Code     *hexutil.Bytes              `json:"code,omitempty"`
 		CodeHash *common.Hash                `json:"codeHash,omitempty"`
 		Nonce    uint64                      `json:"nonce,omitempty"`
 		Storage  map[common.Hash]common.Hash `json:"storage,omitempty"`
 	}
 	var enc account
 	enc.Balance = (*hexutil.Big)(a.Balance)
-	enc.Code = a.Code
+	enc.Code = (*hexutil.Bytes)(a.Code)
 	enc.CodeHash = a.CodeHash
 	enc.Nonce = a.Nonce
 	enc.Storage = a.Storage
@@ -47,7 +47,7 @@ func (a *account) UnmarshalJSON(input []byte) error {
 		a.Balance = (*big.Int)(dec.Balance)
 	}
 	if dec.Code != nil {
-		a.Code = *dec.Code
+		a.Code = (*[]byte)(dec.Code)
 	}
 	if dec.CodeHash != nil {
 		a.CodeHash = dec.CodeHash

eth/tracers/native/prestate.go

@@ -44,21 +44,24 @@ func init() {
 type stateMap = map[common.Address]*account
 
 type account struct {
-	Balance  *big.Int                    `json:"balance,omitempty"`
-	Code     []byte                      `json:"code,omitempty"`
+	Balance *big.Int `json:"balance,omitempty"`
+	// Code is a pointer so omitempty can omit unchanged code (nil) while
+	// still emitting "0x" when code is cleared (e.g. EIP-7702 deauth).
+	Code     *[]byte                     `json:"code,omitempty"`
 	CodeHash *common.Hash                `json:"codeHash,omitempty"`
 	Nonce    uint64                      `json:"nonce,omitempty"`
 	Storage  map[common.Hash]common.Hash `json:"storage,omitempty"`
-	empty    bool
+
+	empty bool
 }
 
 func (a *account) exists() bool {
-	return a.Nonce > 0 || len(a.Code) > 0 || len(a.Storage) > 0 || (a.Balance != nil && a.Balance.Sign() != 0)
+	return a.Nonce > 0 || (a.Code != nil && len(*a.Code) > 0) || len(a.Storage) > 0 || (a.Balance != nil && a.Balance.Sign() != 0)
 }
 
 type accountMarshaling struct {
 	Balance *hexutil.Big
-	Code    hexutil.Bytes
+	Code    *hexutil.Bytes
 }
 
 type prestateTracer struct {
@@ -266,24 +269,28 @@ func (t *prestateTracer) processDiffState() {
 			modified = true
 			postAccount.Nonce = newNonce
 		}
-		prevCodeHash := common.Hash{}
+		// Empty code hashes are excluded from the prestate, so default
+		// to EmptyCodeHash to match what GetCodeHash returns for codeless accounts.
+		prevCodeHash := types.EmptyCodeHash
 		if t.pre[addr].CodeHash != nil {
 			prevCodeHash = *t.pre[addr].CodeHash
 		}
-		// Empty code hashes are excluded from the prestate. Normalize
-		// the empty code hash to a zero hash to make it comparable.
-		if newCodeHash == types.EmptyCodeHash {
-			newCodeHash = common.Hash{}
-		}
 		if newCodeHash != prevCodeHash {
 			modified = true
 			postAccount.CodeHash = &newCodeHash
 		}
 		if !t.config.DisableCode {
 			newCode := t.env.StateDB.GetCode(addr)
-			if !bytes.Equal(newCode, t.pre[addr].Code) {
+			var prevCode []byte
+			if t.pre[addr].Code != nil {
+				prevCode = *t.pre[addr].Code
+			}
+			if !bytes.Equal(newCode, prevCode) {
 				modified = true
-				postAccount.Code = newCode
+				if newCode == nil {
+					newCode = []byte{}
+				}
+				postAccount.Code = &newCode
 			}
 		}
 
@@ -323,10 +330,13 @@ func (t *prestateTracer) lookupAccount(addr common.Address) {
 		return
 	}
 
+	code := t.env.StateDB.GetCode(addr)
 	acc := &account{
 		Balance: t.env.StateDB.GetBalance(addr).ToBig(),
 		Nonce:   t.env.StateDB.GetNonce(addr),
-		Code:    t.env.StateDB.GetCode(addr),
+	}
+	if len(code) > 0 {
+		acc.Code = &code
 	}
 	codeHash := t.env.StateDB.GetCodeHash(addr)
 	// If the code is empty, we don't need to store it in the prestate.