From ea0bbf084d0462340c9bd5d4c9990a5edfc853c7 Mon Sep 17 00:00:00 2001
From: Nate Beauregard <51711291+natebeauregard@users.noreply.github.com>
Date: Fri, 15 Mar 2024 06:38:03 -0400
Subject: [PATCH] Fix negative gas cost in debug_traceTransaction traces
 (#6831)

---
 .../Tracing/GethLikeTxMemoryTracerTests.cs    | 25 ++++++++++++++++++-
 .../Tracing/GethStyle/GethLikeTxTracer.cs     | 11 +++++++-
 2 files changed, 34 insertions(+), 2 deletions(-)

diff --git a/src/Nethermind/Nethermind.Evm.Test/Tracing/GethLikeTxMemoryTracerTests.cs b/src/Nethermind/Nethermind.Evm.Test/Tracing/GethLikeTxMemoryTracerTests.cs
index ae5ceab5c4b..878e1496570 100644
--- a/src/Nethermind/Nethermind.Evm.Test/Tracing/GethLikeTxMemoryTracerTests.cs
+++ b/src/Nethermind/Nethermind.Evm.Test/Tracing/GethLikeTxMemoryTracerTests.cs
@@ -16,7 +16,7 @@ namespace Nethermind.Evm.Test.Tracing;
 public class GethLikeTxMemoryTracerTests : VirtualMachineTestsBase
 {
     [Test]
-    public void Can_trace_gas()
+    public void Can_trace_gas_halt_with_stop()
     {
         byte[] code = Prepare.EvmCode
             .PushData("0x1")
@@ -38,6 +38,29 @@ public void Can_trace_gas()
         }
     }
 
+    [Test]
+    public void Can_trace_gas_halt_with_return()
+    {
+        byte[] code = Prepare.EvmCode
+            .PushData("0x1")
+            .PushData("0x2")
+            .Op(Instruction.ADD)
+            .Op(Instruction.RETURN)
+            .Done;
+
+        int[] gasCosts = new int[] { 3, 3, 3, 0 };
+
+        GethLikeTxTrace trace = ExecuteAndTrace(code);
+
+        int gasTotal = 0;
+        for (int i = 0; i < gasCosts.Length; i++)
+        {
+            Assert.That(trace.Entries[i].Gas, Is.EqualTo(79000 - gasTotal), $"gas[{i}]");
+            Assert.That(trace.Entries[i].GasCost, Is.EqualTo(gasCosts[i]), $"gasCost[{i}]");
+            gasTotal += gasCosts[i];
+        }
+    }
+
     [Test]
     [Todo("Verify the exact error string in Geth")]
     public void Can_trace_stack_underflow_failure()
diff --git a/src/Nethermind/Nethermind.Evm/Tracing/GethStyle/GethLikeTxTracer.cs b/src/Nethermind/Nethermind.Evm/Tracing/GethStyle/GethLikeTxTracer.cs
index 13f4f1c5707..3292c20b667 100644
--- a/src/Nethermind/Nethermind.Evm/Tracing/GethStyle/GethLikeTxTracer.cs
+++ b/src/Nethermind/Nethermind.Evm/Tracing/GethStyle/GethLikeTxTracer.cs
@@ -66,6 +66,7 @@ public override void MarkAsFailed(Address recipient, long gasSpent, byte[]? outp
     protected TEntry? CurrentTraceEntry { get; set; }
 
     protected GethLikeTxTracer(GethTraceOptions options) : base(options) { }
+    private bool _gasCostAlreadySetForCurrentOp;
 
     public override void StartOperation(int depth, long gas, Instruction opcode, int pc, bool isPostMerge = false)
     {
@@ -77,11 +78,19 @@ public override void StartOperation(int depth, long gas, Instruction opcode, int
         CurrentTraceEntry.Gas = gas;
         CurrentTraceEntry.Opcode = opcode.GetName(isPostMerge);
         CurrentTraceEntry.ProgramCounter = pc;
+        _gasCostAlreadySetForCurrentOp = false;
     }
 
     public override void ReportOperationError(EvmExceptionType error) => CurrentTraceEntry.Error = GetErrorDescription(error);
 
-    public override void ReportOperationRemainingGas(long gas) => CurrentTraceEntry.GasCost = CurrentTraceEntry.Gas - gas;
+    public override void ReportOperationRemainingGas(long gas)
+    {
+        if (!_gasCostAlreadySetForCurrentOp)
+        {
+            CurrentTraceEntry.GasCost = CurrentTraceEntry.Gas - gas;
+            _gasCostAlreadySetForCurrentOp = true;
+        }
+    }
 
     public override void SetOperationMemorySize(ulong newSize) => CurrentTraceEntry.UpdateMemorySize(newSize);