From ba2a3aa7c8cbc51f1b21f498592a6680dd6002aa Mon Sep 17 00:00:00 2001
From: Duncan Ogilvie <mr.exodia.tpodt@gmail.com>
Date: Wed, 15 Jul 2026 20:11:37 +0200
Subject: [PATCH] Complete orphaned breakpoint step-over reset when the stepped
 thread exits

If a thread is terminated (e.g. by ExitProcess) while it is in the middle of a
breakpoint step-over - its breakpoint temporarily removed and a restore pending on
its next single-step - the EXIT_THREAD handler cleared ThreadBeingProcessed but left
the reset state (ResetBPX/ResetHwBPX/ResetMemBPX) armed and the breakpoint removed.
The next thread's event then consumed that orphaned reset and was misinterpreted as a
step-over reset, producing a stray single-step that was passed to the debuggee
unhandled and crashed it. This was most visible with hardware breakpoints under
multi-thread contention. Complete the pending restore when the thread-being-processed
exits.
---
 .../TitanEngine.Debugger.DebugLoop.cpp        | 30 +++++++++++++++++++
 1 file changed, 30 insertions(+)

diff --git a/TitanEngine/TitanEngine.Debugger.DebugLoop.cpp b/TitanEngine/TitanEngine.Debugger.DebugLoop.cpp
index 4641709..942eb02 100644
--- a/TitanEngine/TitanEngine.Debugger.DebugLoop.cpp
+++ b/TitanEngine/TitanEngine.Debugger.DebugLoop.cpp
@@ -166,6 +166,36 @@ __declspec(dllexport) void TITCALL DebugLoop()
 
                     SuspendedThreads.clear();
                     ThreadBeingProcessed = 0;
+
+                    // The thread was in the middle of a breakpoint step-over (its
+                    // breakpoint was temporarily removed and a restore was pending on its
+                    // next single-step) but it is exiting before that single-step arrives.
+                    // Complete the restore now: otherwise the breakpoint is left removed
+                    // and the next thread's event would consume this dead thread's orphaned
+                    // reset state and be misinterpreted as a step-over reset, producing a
+                    // stray single-step that is passed to (and crashes) the debuggee.
+                    if(ResetBPX)
+                    {
+                        EnableBPX(ResetBPXAddressTo);
+                        ResetBPXAddressTo = 0;
+                        ResetBPX = false;
+                    }
+                    if(ResetHwBPX)
+                    {
+                        SetHardwareBreakPoint(DebugRegisterX.DrxBreakAddress, DebugRegisterXId, DebugRegisterX.DrxBreakPointType, DebugRegisterX.DrxBreakPointSize, (LPVOID)DebugRegisterX.DrxCallBack);
+                        ResetHwBPX = false;
+                    }
+                    if(ResetMemBPX)
+                    {
+                        ResetMemBpxCallback();
+                        if(ResetMemBpxExtraCallback != nullptr)
+                        {
+                            ResetMemBpxExtraCallback();
+                            ResetMemBpxExtraCallback = nullptr;
+                        }
+                        ResetMemBPX = false;
+                    }
+                    PushfBPX = false;
                 }
             }
         }