From 7a528c2da91cb413d3e423f803d653de9e095bf2 Mon Sep 17 00:00:00 2001
From: jonny rhea <jonathan.rhea@gmail.com>
Date: Thu, 15 Jan 2026 15:51:57 -0600
Subject: [PATCH] core/vm: changes made to reflect the updates to the spec that
 specify behavior at the end of code

---
 core/vm/instructions.go      | 24 ++++++++++-----------
 core/vm/instructions_test.go | 42 +++++++++++++++++++++++-------------
 2 files changed, 39 insertions(+), 27 deletions(-)

diff --git a/core/vm/instructions.go b/core/vm/instructions.go
index 6b04a2daff..8813325634 100644
--- a/core/vm/instructions.go
+++ b/core/vm/instructions.go
@@ -945,11 +945,11 @@ func opDupN(pc *uint64, evm *EVM, scope *ScopeContext) ([]byte, error) {
 	code := scope.Contract.Code
 	i := *pc + 1
 
-	// Ensure an immediate byte exists after DUPN
-	if i >= uint64(len(code)) {
-		return nil, &ErrInvalidOpCode{opcode: INVALID}
+	// If the immediate byte is missing, treat as 0x00 (same convention as PUSHn).
+	var x byte
+	if i < uint64(len(code)) {
+		x = code[i]
 	}
-	x := code[i]
 
 	// This range is excluded to preserve compatibility with existing opcodes.
 	if x > 90 && x < 128 {
@@ -972,11 +972,11 @@ func opSwapN(pc *uint64, evm *EVM, scope *ScopeContext) ([]byte, error) {
 	code := scope.Contract.Code
 	i := *pc + 1
 
-	// Ensure an immediate byte exists after SWAPN
-	if i >= uint64(len(code)) {
-		return nil, &ErrInvalidOpCode{opcode: INVALID}
+	// If the immediate byte is missing, treat as 0x00 (same convention as PUSHn).
+	var x byte
+	if i < uint64(len(code)) {
+		x = code[i]
 	}
-	x := code[i]
 
 	// This range is excluded to preserve compatibility with existing opcodes.
 	if x > 90 && x < 128 {
@@ -1001,11 +1001,11 @@ func opExchange(pc *uint64, evm *EVM, scope *ScopeContext) ([]byte, error) {
 	code := scope.Contract.Code
 	i := *pc + 1
 
-	// Ensure an immediate byte exists after EXCHANGE
-	if i >= uint64(len(code)) {
-		return nil, &ErrInvalidOpCode{opcode: INVALID}
+	// If the immediate byte is missing, treat as 0x00 (same convention as PUSHn).
+	var x byte
+	if i < uint64(len(code)) {
+		x = code[i]
 	}
-	x := code[i]
 
 	// This range is excluded both to preserve compatibility with existing opcodes
 	// and to keep decode_pair’s 16-aligned arithmetic mapping valid (0–79, 128–255).
diff --git a/core/vm/instructions_test.go b/core/vm/instructions_test.go
index f38da7fb22..5c8052243e 100644
--- a/core/vm/instructions_test.go
+++ b/core/vm/instructions_test.go
@@ -1027,6 +1027,15 @@ func TestEIP8024_Execution(t *testing.T) {
 				1,
 			},
 		},
+		{
+			name:    "DUPN_MISSING_IMMEDIATE",
+			codeHex: "60016000808080808080808080808080808080e6",
+			wantVals: []uint64{
+				1,
+				0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+				1,
+			},
+		},
 		{
 			name:    "SWAPN",
 			codeHex: "600160008080808080808080808080808080806002e700",
@@ -1036,11 +1045,29 @@ func TestEIP8024_Execution(t *testing.T) {
 				2,
 			},
 		},
+		{
+			name:    "SWAPN_MISSING_IMMEDIATE",
+			codeHex: "600160008080808080808080808080808080806002e7",
+			wantVals: []uint64{
+				1,
+				0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+				2,
+			},
+		},
 		{
 			name:     "EXCHANGE",
 			codeHex:  "600060016002e801",
 			wantVals: []uint64{2, 0, 1},
 		},
+		{
+			name:    "EXCHANGE_MISSING_IMMEDIATE",
+			codeHex: "600060006000600060006000600060006000600060006000600060006000600060006000600060006000600060006000600060006000600060016002e8",
+			wantVals: []uint64{
+				2,
+				0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+				1,
+			},
+		},
 		{
 			name:    "INVALID_SWAPN_LOW",
 			codeHex: "e75b",
@@ -1092,21 +1119,6 @@ func TestEIP8024_Execution(t *testing.T) {
 			codeHex: "60016002e801", // (n,m)=(1,2), need 3 items, have 2
 			wantErr: true,
 		},
-		{
-			name:    "MISSING_IMMEDIATE_DUPN",
-			codeHex: "e6", // no operand
-			wantErr: true,
-		},
-		{
-			name:    "MISSING_IMMEDIATE_SWAPN",
-			codeHex: "e7", // no operand
-			wantErr: true,
-		},
-		{
-			name:    "MISSING_IMMEDIATE_EXCHANGE",
-			codeHex: "e8", // no operand
-			wantErr: true,
-		},
 		{
 			name:     "PC_INCREMENT",
 			codeHex:  "600060006000e80115",