Add live debugger frontend and mutex stall recovery (#383)

src/SharpEmu.Core/Cpu/CpuDispatcher.cs

@@ -3,6 +3,7 @@
 
 using System.Buffers.Binary;
 using System.Text;
+using SharpEmu.Core.Cpu.Debugging;
 using SharpEmu.Core.Cpu.Native;
 using SharpEmu.Core.Loader;
 using SharpEmu.Core.Memory;
@@ -272,7 +273,23 @@ public sealed class CpuDispatcher : ICpuDispatcher, IDisposable
             entryFrameDiagnostic,
             Environment.NewLine,
             "CpuEngine: native-only");
+        // Frame boundaries an attached debugger observes; null hook = a branch.
+        var debugHook = executionOptions.DebugHook;
+        var debugFrame = debugHook is null
+            ? null
+            : new CpuContextDebugFrame(
+                frameKind == EntryFrameKind.ProcessEntry
+                    ? CpuDebugFrameKind.ProcessEntry
+                    : CpuDebugFrameKind.ModuleInitializer,
+                entryPoint,
+                processImageName,
+                context,
+                effectiveImportStubs);
+        debugHook?.OnFrameEnter(debugFrame!);
+
         _nativeCpuBackend ??= new DirectExecutionBackend(_moduleManager);
+        // Let backend stall reports reference the same frame as entry.
+        (_nativeCpuBackend as DirectExecutionBackend)?.SetActiveDebugFrame(debugFrame);
         if (_nativeCpuBackend.TryExecute(
                 context,
                 entryPoint,
@@ -282,6 +299,7 @@ public sealed class CpuDispatcher : ICpuDispatcher, IDisposable
                 executionOptions,
                 out var nativeResult))
         {
+            debugHook?.OnFrameExit(debugFrame!, nativeResult);
             LastSessionSummary = new CpuSessionSummary(
                 nativeResult,
                 nativeResult == OrbisGen2Result.ORBIS_GEN2_OK
@@ -296,6 +314,8 @@ public sealed class CpuDispatcher : ICpuDispatcher, IDisposable
             return nativeResult;
         }
 
+        debugHook?.OnFrameExit(debugFrame!, OrbisGen2Result.ORBIS_GEN2_ERROR_NOT_IMPLEMENTED);
+
         var backendName = string.IsNullOrWhiteSpace(_nativeCpuBackend.BackendName)
             ? "native-backend"
             : _nativeCpuBackend.BackendName;

src/SharpEmu.Core/Cpu/CpuExecutionOptions.cs

@@ -1,15 +1,26 @@
 // Copyright (C) 2026 SharpEmu Emulator Project
 // SPDX-License-Identifier: GPL-2.0-or-later
 
+using SharpEmu.Core.Cpu.Debugging;
+
 namespace SharpEmu.Core.Cpu;
 
 public readonly struct CpuExecutionOptions
 {
     public bool EnableDisasmDiagnostics { get; init; }
-    
+
     public CpuExecutionEngine CpuEngine { get; init; }
 
     public bool StrictDynlibResolution { get; init; }
 
     public int ImportTraceLimit { get; init; }
+
+    /// <summary>
+    /// An optional debugger attached to this execution session. When set, the
+    /// dispatcher notifies it at each frame boundary via
+    /// <see cref="ICpuDebugHook.OnFrameEnter"/> / <see cref="ICpuDebugHook.OnFrameExit"/>.
+    /// Null when no debugger is attached, which is the default and imposes no
+    /// runtime cost.
+    /// </summary>
+    public ICpuDebugHook? DebugHook { get; init; }
 }

src/SharpEmu.Core/Cpu/Debugging/CpuContextDebugFrame.cs

@@ -0,0 +1,66 @@
+// Copyright (C) 2026 SharpEmu Emulator Project
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+using SharpEmu.HLE;
+
+namespace SharpEmu.Core.Cpu.Debugging;
+
+/// <summary>
+/// Adapts a live <see cref="CpuContext"/> to <see cref="ICpuDebugFrame"/>. The
+/// dispatcher creates one of these around the guest context it is about to run
+/// and passes it to the attached <see cref="ICpuDebugHook"/>; every accessor
+/// forwards directly to the underlying context.
+/// </summary>
+internal sealed class CpuContextDebugFrame : ICpuDebugFrame
+{
+    private readonly CpuContext _context;
+
+    internal CpuContextDebugFrame(
+        CpuDebugFrameKind kind,
+        ulong entryPoint,
+        string label,
+        CpuContext context,
+        IReadOnlyDictionary<ulong, string> importStubs)
+    {
+        Kind = kind;
+        EntryPoint = entryPoint;
+        Label = label ?? string.Empty;
+        _context = context ?? throw new ArgumentNullException(nameof(context));
+        ImportStubs = importStubs ?? new Dictionary<ulong, string>();
+    }
+
+    public CpuDebugFrameKind Kind { get; }
+
+    public Generation Generation => _context.TargetGeneration;
+
+    public ulong EntryPoint { get; }
+
+    public string Label { get; }
+
+    public ICpuMemory Memory => _context.Memory;
+
+    public ulong GetRegister(CpuRegister register) => _context[register];
+
+    public void SetRegister(CpuRegister register, ulong value) => _context[register] = value;
+
+    public ulong Rip
+    {
+        get => _context.Rip;
+        set => _context.Rip = value;
+    }
+
+    public ulong Rflags
+    {
+        get => _context.Rflags;
+        set => _context.Rflags = value;
+    }
+
+    public ulong FsBase => _context.FsBase;
+
+    public ulong GsBase => _context.GsBase;
+
+    public void GetXmm(int registerIndex, out ulong low, out ulong high)
+        => _context.GetXmmRegister(registerIndex, out low, out high);
+
+    public IReadOnlyDictionary<ulong, string> ImportStubs { get; }
+}

src/SharpEmu.Core/Cpu/Debugging/CpuDebugFrameKind.cs

@@ -0,0 +1,18 @@
+// Copyright (C) 2026 SharpEmu Emulator Project
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+namespace SharpEmu.Core.Cpu.Debugging;
+
+/// <summary>
+/// Identifies the kind of guest entry frame a debugger is observing. The
+/// dispatcher enters a fresh frame for the process entry point and for every
+/// module initializer, so the debug layer can label stops accordingly.
+/// </summary>
+public enum CpuDebugFrameKind
+{
+    /// <summary>The guest process entry point (<c>eboot.bin</c> start).</summary>
+    ProcessEntry,
+
+    /// <summary>A module DT_INIT / initializer routine.</summary>
+    ModuleInitializer,
+}

src/SharpEmu.Core/Cpu/Debugging/CpuStallInfo.cs

@@ -0,0 +1,70 @@
+// Copyright (C) 2026 SharpEmu Emulator Project
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+namespace SharpEmu.Core.Cpu.Debugging;
+
+/// <summary>The kind of execution stall the backend detected.</summary>
+public enum CpuStallKind
+{
+    /// <summary>
+    /// The guest is repeatedly re-dispatching the same import with no forward
+    /// progress — most commonly a spin on a mutex lock/unlock pair.
+    /// </summary>
+    ImportLoop,
+}
+
+/// <summary>
+/// Details of a detected stall handed to <see cref="ICpuDebugHook.OnStall"/>.
+/// Reported from the emulation thread at the point the backend recognises the
+/// livelock, before it forces the guest out of the loop.
+/// </summary>
+public readonly struct CpuStallInfo
+{
+    public CpuStallInfo(
+        CpuStallKind kind,
+        string? nid,
+        ulong instructionPointer,
+        long dispatchIndex,
+        ulong argument0,
+        ulong argument1,
+        string detail,
+        string? libraryName = null,
+        string? functionName = null)
+    {
+        Kind = kind;
+        Nid = nid;
+        InstructionPointer = instructionPointer;
+        DispatchIndex = dispatchIndex;
+        Argument0 = argument0;
+        Argument1 = argument1;
+        Detail = detail ?? string.Empty;
+        LibraryName = libraryName;
+        FunctionName = functionName;
+    }
+
+    public CpuStallKind Kind { get; }
+
+    /// <summary>The NID of the import being spun on, when known.</summary>
+    public string? Nid { get; }
+
+    /// <summary>The guest return address of the looping import dispatch.</summary>
+    public ulong InstructionPointer { get; }
+
+    /// <summary>The import dispatch counter at detection time.</summary>
+    public long DispatchIndex { get; }
+
+    /// <summary>The first two guest ABI arguments at stall detection.</summary>
+    public ulong Argument0 { get; }
+
+    public ulong Argument1 { get; }
+
+    /// <summary>The resolved HLE export, when the NID is registered.</summary>
+    public string? LibraryName { get; }
+
+    public string? FunctionName { get; }
+
+    public bool IsResolved => !string.IsNullOrWhiteSpace(FunctionName);
+
+    /// <summary>A human-readable one-line summary of the stall.</summary>
+    public string Detail { get; }
+}

src/SharpEmu.Core/Cpu/Debugging/ICpuDebugFrame.cs

@@ -0,0 +1,66 @@
+// Copyright (C) 2026 SharpEmu Emulator Project
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+using SharpEmu.HLE;
+
+namespace SharpEmu.Core.Cpu.Debugging;
+
+/// <summary>
+/// A live view of the guest CPU state at a dispatch boundary, handed to an
+/// <see cref="ICpuDebugHook"/> so a debugger can read and mutate registers and
+/// guest memory without taking a dependency on the concrete
+/// <c>CpuContext</c>/<c>CpuDispatcher</c> types.
+/// </summary>
+/// <remarks>
+/// The frame instance is only valid for the duration of the hook call that
+/// receives it (between <see cref="ICpuDebugHook.OnFrameEnter"/> and the
+/// matching <see cref="ICpuDebugHook.OnFrameExit"/>). Reads and writes are
+/// forwarded straight to the underlying guest context, so mutations made from
+/// a hook are observed by the CPU backend when it resumes the frame.
+/// </remarks>
+public interface ICpuDebugFrame
+{
+    /// <summary>The kind of frame being executed.</summary>
+    CpuDebugFrameKind Kind { get; }
+
+    /// <summary>The guest ABI generation this frame targets.</summary>
+    Generation Generation { get; }
+
+    /// <summary>The guest virtual address the frame begins executing at.</summary>
+    ulong EntryPoint { get; }
+
+    /// <summary>
+    /// A human-readable label for the frame (process image name or module name).
+    /// </summary>
+    string Label { get; }
+
+    /// <summary>Guest-addressable memory for this frame.</summary>
+    ICpuMemory Memory { get; }
+
+    /// <summary>Reads a general-purpose register.</summary>
+    ulong GetRegister(CpuRegister register);
+
+    /// <summary>Overwrites a general-purpose register.</summary>
+    void SetRegister(CpuRegister register, ulong value);
+
+    /// <summary>The instruction pointer.</summary>
+    ulong Rip { get; set; }
+
+    /// <summary>The flags register.</summary>
+    ulong Rflags { get; set; }
+
+    /// <summary>The FS segment base (guest TLS pointer).</summary>
+    ulong FsBase { get; }
+
+    /// <summary>The GS segment base.</summary>
+    ulong GsBase { get; }
+
+    /// <summary>Reads the 128-bit value of an XMM register.</summary>
+    void GetXmm(int registerIndex, out ulong low, out ulong high);
+
+    /// <summary>
+    /// The import stubs (guest address to NID) resolved for this frame, so a
+    /// debugger can annotate calls into HLE exports.
+    /// </summary>
+    IReadOnlyDictionary<ulong, string> ImportStubs { get; }
+}

src/SharpEmu.Core/Cpu/Debugging/ICpuDebugHook.cs

@@ -0,0 +1,49 @@
+// Copyright (C) 2026 SharpEmu Emulator Project
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+using SharpEmu.HLE;
+
+namespace SharpEmu.Core.Cpu.Debugging;
+
+/// <summary>
+/// The seam the CPU dispatcher uses to notify an attached debugger when guest
+/// execution crosses a frame boundary. Implemented outside of Core (for
+/// example by <c>SharpEmu.Debugger</c>) and supplied through
+/// <see cref="CpuExecutionOptions.DebugHook"/>.
+/// </summary>
+/// <remarks>
+/// This is intentionally coarse-grained: it exposes the entry and exit of each
+/// dispatched frame rather than per-instruction stepping. Per-instruction
+/// control requires cooperation from the native execution backend and is layered
+/// on top of this seam as the backend gains support; keeping the dispatcher-level
+/// contract stable lets the debugger infrastructure exist independently of that
+/// work. Implementations must be thread-safe: frames may be dispatched from the
+/// dedicated emulation thread while a debug server services clients on its own
+/// threads.
+/// </remarks>
+public interface ICpuDebugHook
+{
+    /// <summary>
+    /// Invoked immediately before the native backend begins executing a frame.
+    /// The debugger may inspect or mutate <paramref name="frame"/> and may block
+    /// the calling thread (for example, to honour a pause request) before
+    /// returning to allow execution to proceed.
+    /// </summary>
+    void OnFrameEnter(ICpuDebugFrame frame);
+
+    /// <summary>
+    /// Invoked after a frame completes, whether it returned to the host or
+    /// terminated with an error. <paramref name="frame"/> reflects the final
+    /// guest state.
+    /// </summary>
+    void OnFrameExit(ICpuDebugFrame frame, OrbisGen2Result result);
+
+    /// <summary>
+    /// Invoked from the emulation thread when the backend detects an execution
+    /// stall (for example a mutex spin loop) in the running frame, before it
+    /// forces the guest out of the loop. As with <see cref="OnFrameEnter"/>, the
+    /// implementation may inspect <paramref name="frame"/> and block to honour a
+    /// break before returning to let the backend proceed.
+    /// </summary>
+    void OnStall(ICpuDebugFrame frame, CpuStallInfo info);
+}

src/SharpEmu.Core/Cpu/Native/DirectExecutionBackend.Imports.cs

@@ -10,6 +10,7 @@ using System.Runtime.InteropServices;
 using System.Security.Cryptography;
 using System.Text;
 using System.Threading;
+using SharpEmu.Core.Cpu.Debugging;
 using SharpEmu.Core.Cpu;
 using SharpEmu.HLE;
 using SharpEmu.Libs.Kernel;
@@ -316,11 +317,15 @@ public sealed partial class DirectExecutionBackend
 		}
 		if (!isGuestWorker &&
 			!ActiveForcedGuestExit &&
-			ShouldForceGuestExitOnImportLoop(in importStubEntry, num7, num, value, value2) &&
-			TryForceGuestExitToHostStub(argPackPtr, num, num7, importStubEntry.Nid))
+			ShouldForceGuestExitOnImportLoop(in importStubEntry, num7, num, value, value2))
 		{
-			cpuContext[CpuRegister.Rax] = 1uL;
-			return 1uL;
+			// Break before the forced exit so the loop state is still live.
+			NotifyDebuggerStall(CpuStallKind.ImportLoop, in importStubEntry, num7, num, value, value2);
+			if (TryForceGuestExitToHostStub(argPackPtr, num, num7, importStubEntry.Nid))
+			{
+				cpuContext[CpuRegister.Rax] = 1uL;
+				return 1uL;
+			}
 		}
 		bool flag0 = importStubEntry.SuppressStrlenTrace;
 		bool flag = num7 >= 2156221920u && num7 <= 2156225024u;

src/SharpEmu.Core/Cpu/Native/DirectExecutionBackend.cs

@@ -9,6 +9,7 @@ using System.Linq;
 using System.Runtime.InteropServices;
 using System.Threading;
 using SharpEmu.Core.Cpu;
+using SharpEmu.Core.Cpu.Debugging;
 using SharpEmu.Core.Loader;
 using SharpEmu.Core.Memory;
 using SharpEmu.HLE;
@@ -235,6 +236,11 @@ public sealed unsafe partial class DirectExecutionBackend : INativeCpuBackend, I
 
 	private CpuContext? _cpuContext;
 
+	// Debugger seam; both null when no debugger is attached.
+	private ICpuDebugHook? _debugHook;
+
+	private ICpuDebugFrame? _activeDebugFrame;
+
 	[ThreadStatic]
 	private static DirectExecutionBackend? _activeExecutionBackend;
 
@@ -890,6 +896,49 @@ public sealed unsafe partial class DirectExecutionBackend : INativeCpuBackend, I
 
 	private bool HasActiveExecutionThread => ReferenceEquals(_activeExecutionBackend, this);
 
+	/// <summary>
+	/// Binds the debug frame view the dispatcher created for the frame about to
+	/// run, so stall notifications reference the same frame the debugger saw at
+	/// entry. Set to null when no debugger is attached.
+	/// </summary>
+	internal void SetActiveDebugFrame(ICpuDebugFrame? frame) => _activeDebugFrame = frame;
+
+	/// <summary>
+	/// Notifies an attached debugger of a detected execution stall. No-op when no
+	/// debugger is attached or no frame is bound. The debugger may block here to
+	/// present a break before the backend forces the guest out of the loop.
+	/// </summary>
+	private void NotifyDebuggerStall(
+		CpuStallKind kind,
+		in ImportStubEntry import,
+		ulong instructionPointer,
+		long dispatchIndex,
+		ulong argument0,
+		ulong argument1)
+	{
+		var hook = _debugHook;
+		var frame = _activeDebugFrame;
+		if (hook is null || frame is null)
+		{
+			return;
+		}
+
+		var export = import.Export;
+		var exportDescription = export is null ? "unresolved" : $"{export.LibraryName}:{export.Name}";
+		var detail = $"kind={kind}, nid={import.Nid}, export={exportDescription}, dispatch#{dispatchIndex}, " +
+			$"rip=0x{instructionPointer:X16}, arg0=0x{argument0:X16}, arg1=0x{argument1:X16}";
+		hook.OnStall(frame, new CpuStallInfo(
+			kind,
+			import.Nid,
+			instructionPointer,
+			dispatchIndex,
+			argument0,
+			argument1,
+			detail,
+			export?.LibraryName,
+			export?.Name));
+	}
+
 	private CpuContext? ActiveCpuContext => HasActiveExecutionThread ? _activeCpuContext : _cpuContext;
 
 	private ulong ActiveEntryReturnSentinelRip
@@ -1051,6 +1100,7 @@ public sealed unsafe partial class DirectExecutionBackend : INativeCpuBackend, I
 		Console.Error.WriteLine(_moduleManager.TryGetExport("L-Q3LEjIbgA", out ExportedFunction export2) ? ("[LOADER][INFO] ExportCheck map_direct: " + export2.LibraryName + ":" + export2.Name) : "[LOADER][INFO] ExportCheck map_direct: MISSING");
 		_entryPoint = entryPoint;
 		_cpuContext = context;
+		_debugHook = executionOptions.DebugHook;
 		_returnFallbackTarget = context[CpuRegister.Rsi];
 		Volatile.Write(ref _globalFallbackTarget, _returnFallbackTarget);
 		Volatile.Write(ref _globalUnresolvedReturnStub, (ulong)_unresolvedReturnStub);