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

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);
+}