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

src/SharpEmu.Debugger/Session/DebugStopEvent.cs

@@ -0,0 +1,69 @@
+// Copyright (C) 2026 SharpEmu Emulator Project
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+using SharpEmu.Core.Cpu.Debugging;
+using SharpEmu.Debugger.Breakpoints;
+using SharpEmu.HLE;
+
+namespace SharpEmu.Debugger.Session;
+
+/// <summary>
+/// Describes a stop delivered to debugger clients: why the target stopped,
+/// where, and the register snapshot at that point.
+/// </summary>
+public sealed class DebugStopEvent
+{
+    public DebugStopEvent(
+        DebugStopReason reason,
+        DebugRegisterFile registers,
+        CpuDebugFrameKind frameKind,
+        string frameLabel,
+        Breakpoint? breakpoint = null,
+        OrbisGen2Result? result = null,
+        string? detail = null,
+        string? opcodeBytes = null,
+        CpuStallInfo? stallInfo = null)
+    {
+        Reason = reason;
+        Registers = registers;
+        FrameKind = frameKind;
+        FrameLabel = frameLabel ?? string.Empty;
+        Breakpoint = breakpoint;
+        Result = result;
+        Detail = detail;
+        OpcodeBytes = opcodeBytes;
+        StallInfo = stallInfo;
+    }
+
+    public DebugStopReason Reason { get; }
+
+    /// <summary>The instruction pointer where the target stopped.</summary>
+    public ulong Address => Registers.Rip;
+
+    public DebugRegisterFile Registers { get; }
+
+    public CpuDebugFrameKind FrameKind { get; }
+
+    public string FrameLabel { get; }
+
+    /// <summary>The breakpoint responsible for the stop, when applicable.</summary>
+    public Breakpoint? Breakpoint { get; }
+
+    /// <summary>
+    /// The frame result for a <see cref="DebugStopReason.Fault"/> stop; null for
+    /// non-fault stops.
+    /// </summary>
+    public OrbisGen2Result? Result { get; }
+
+    /// <summary>A human-readable summary of a fault, when applicable.</summary>
+    public string? Detail { get; }
+
+    /// <summary>
+    /// A hex preview of the bytes at <see cref="Address"/> (the faulting
+    /// instruction), when the stop is a fault and the bytes were readable.
+    /// </summary>
+    public string? OpcodeBytes { get; }
+
+    /// <summary>Structured backend evidence for a stall stop.</summary>
+    public CpuStallInfo? StallInfo { get; }
+}

src/SharpEmu.Debugger/Session/DebugStopReason.cs

@@ -0,0 +1,32 @@
+// Copyright (C) 2026 SharpEmu Emulator Project
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+namespace SharpEmu.Debugger.Session;
+
+/// <summary>Why the target stopped and handed control to the debugger.</summary>
+public enum DebugStopReason
+{
+    /// <summary>Stopped at the configured entry point before running any frame.</summary>
+    EntryPoint,
+
+    /// <summary>An execution breakpoint was hit.</summary>
+    Breakpoint,
+
+    /// <summary>A data watchpoint was hit.</summary>
+    Watchpoint,
+
+    /// <summary>A single-step (frame step) request completed.</summary>
+    Step,
+
+    /// <summary>A client-requested pause took effect.</summary>
+    Pause,
+
+    /// <summary>The guest raised a fault or trap.</summary>
+    Fault,
+
+    /// <summary>
+    /// The backend detected an execution stall (for example a mutex spin loop /
+    /// livelock) with no forward progress.
+    /// </summary>
+    Stall,
+}

src/SharpEmu.Debugger/Session/DebuggerRunState.cs

@@ -0,0 +1,23 @@
+// Copyright (C) 2026 SharpEmu Emulator Project
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+namespace SharpEmu.Debugger.Session;
+
+/// <summary>The execution state of a debugged target as seen by the debugger.</summary>
+public enum DebuggerRunState
+{
+    /// <summary>No guest frame has entered the debugger yet.</summary>
+    Detached,
+
+    /// <summary>The guest is executing and cannot be inspected safely.</summary>
+    Running,
+
+    /// <summary>
+    /// The guest is parked at a frame boundary. Registers and memory can be
+    /// read and written, and breakpoints can be edited.
+    /// </summary>
+    Paused,
+
+    /// <summary>The guest has finished; no further frames will run.</summary>
+    Terminated,
+}

src/SharpEmu.Debugger/Session/DebuggerSession.cs

@@ -0,0 +1,425 @@
+// Copyright (C) 2026 SharpEmu Emulator Project
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+using SharpEmu.Core.Cpu.Debugging;
+using SharpEmu.Debugger.Breakpoints;
+using SharpEmu.HLE;
+using SharpEmu.Logging;
+
+namespace SharpEmu.Debugger.Session;
+
+/// <summary>
+/// The default <see cref="IDebuggerSession"/>. It plugs into the CPU dispatcher
+/// as an <see cref="ICpuDebugHook"/>: when a frame boundary warrants a stop it
+/// parks the emulation thread inside <see cref="ICpuDebugHook.OnFrameEnter"/>
+/// while a debug client inspects and edits state, then releases it on
+/// continue/step.
+/// </summary>
+/// <remarks>
+/// Pausing works by blocking the emulation thread on <see cref="_resumeGate"/>
+/// from within the hook call. Because that thread is the one that owns the guest
+/// context, register and memory accessors are safe to serve from other threads
+/// only while it is parked — which is exactly the <see cref="DebuggerRunState.Paused"/>
+/// window the accessors gate on.
+/// </remarks>
+public sealed class DebuggerSession : IDebuggerSession, ICpuDebugHook
+{
+    private static readonly SharpEmuLogger Log = SharpEmuLog.For("SharpEmu.Debugger");
+
+    private readonly object _sync = new();
+    private readonly ManualResetEventSlim _resumeGate = new(initialState: false);
+    private readonly DebuggerSessionOptions _options;
+
+    private ICpuDebugFrame? _currentFrame;
+    private DebuggerRunState _state = DebuggerRunState.Detached;
+    private DebugStopEvent? _lastStop;
+    private bool _seenFirstFrame;
+    private bool _pausePending;
+    private bool _stepPending;
+
+    public DebuggerSession(DebuggerSessionOptions? options = null)
+    {
+        _options = options ?? new DebuggerSessionOptions();
+        Breakpoints = new BreakpointStore();
+    }
+
+    public BreakpointStore Breakpoints { get; }
+
+    public ICpuDebugHook Hook => this;
+
+    public event EventHandler<DebugStopEvent>? Stopped;
+
+    public event EventHandler? Resumed;
+
+    public event EventHandler? Terminated;
+
+    public DebuggerRunState State
+    {
+        get
+        {
+            lock (_sync)
+            {
+                return _state;
+            }
+        }
+    }
+
+    public DebugStopEvent? LastStop
+    {
+        get
+        {
+            lock (_sync)
+            {
+                return _lastStop;
+            }
+        }
+    }
+
+    void ICpuDebugHook.OnFrameEnter(ICpuDebugFrame frame)
+    {
+        DebugStopEvent? stop;
+        lock (_sync)
+        {
+            _currentFrame = frame;
+            var firstFrame = !_seenFirstFrame;
+            _seenFirstFrame = true;
+
+            var reason = ResolveStopReason(frame, firstFrame, out var breakpoint);
+            if (reason is null)
+            {
+                _state = DebuggerRunState.Running;
+                return;
+            }
+
+            _state = DebuggerRunState.Paused;
+            _lastStop = new DebugStopEvent(
+                reason.Value,
+                DebugRegisterFile.Capture(frame),
+                frame.Kind,
+                frame.Label,
+                breakpoint);
+            stop = _lastStop;
+            _resumeGate.Reset();
+        }
+
+        Log.Debug($"Debugger stop: {stop!.Reason} at 0x{stop.Address:X16} ({stop.FrameLabel})");
+        Stopped?.Invoke(this, stop);
+
+        // Park the emulation thread until a client resumes the target. The frame
+        // stays live and inspectable for the whole wait.
+        _resumeGate.Wait();
+
+        lock (_sync)
+        {
+            if (_state != DebuggerRunState.Terminated)
+            {
+                _state = DebuggerRunState.Running;
+            }
+        }
+
+        Resumed?.Invoke(this, EventArgs.Empty);
+    }
+
+    void ICpuDebugHook.OnFrameExit(ICpuDebugFrame frame, OrbisGen2Result result)
+    {
+        DebugStopEvent? stop = null;
+        lock (_sync)
+        {
+            if (_options.BreakOnFault &&
+                result != OrbisGen2Result.ORBIS_GEN2_OK &&
+                _state != DebuggerRunState.Terminated)
+            {
+                // Parking here keeps the post-fault frame inspectable.
+                _currentFrame = frame;
+                _state = DebuggerRunState.Paused;
+                _lastStop = BuildFaultStop(frame, result);
+                stop = _lastStop;
+                _resumeGate.Reset();
+            }
+        }
+
+        if (stop is not null)
+        {
+            Log.Debug($"Debugger fault stop: {stop.Result} at 0x{stop.Address:X16} ({stop.FrameLabel})");
+            Stopped?.Invoke(this, stop);
+            _resumeGate.Wait();
+            Resumed?.Invoke(this, EventArgs.Empty);
+        }
+
+        lock (_sync)
+        {
+            if (ReferenceEquals(_currentFrame, frame))
+            {
+                _currentFrame = null;
+            }
+
+            if (_state != DebuggerRunState.Terminated)
+            {
+                _state = DebuggerRunState.Running;
+            }
+        }
+    }
+
+    void ICpuDebugHook.OnStall(ICpuDebugFrame frame, CpuStallInfo info)
+    {
+        if (!_options.BreakOnStall)
+        {
+            return;
+        }
+
+        DebugStopEvent? stop = null;
+        lock (_sync)
+        {
+            if (_state == DebuggerRunState.Terminated)
+            {
+                return;
+            }
+
+            _currentFrame = frame;
+            _state = DebuggerRunState.Paused;
+            _lastStop = new DebugStopEvent(
+                DebugStopReason.Stall,
+                DebugRegisterFile.Capture(frame),
+                frame.Kind,
+                frame.Label,
+                breakpoint: null,
+                result: null,
+                detail: info.Detail,
+                opcodeBytes: ReadOpcodePreview(frame, info.InstructionPointer, 16),
+                stallInfo: info);
+            stop = _lastStop;
+            _resumeGate.Reset();
+        }
+
+        Log.Debug($"Debugger stall stop: {info.Kind} nid={info.Nid} at 0x{info.InstructionPointer:X16}");
+        Stopped?.Invoke(this, stop);
+        _resumeGate.Wait();
+
+        lock (_sync)
+        {
+            if (ReferenceEquals(_currentFrame, frame))
+            {
+                _currentFrame = null;
+            }
+
+            if (_state != DebuggerRunState.Terminated)
+            {
+                _state = DebuggerRunState.Running;
+            }
+        }
+
+        Resumed?.Invoke(this, EventArgs.Empty);
+    }
+
+    private static DebugStopEvent BuildFaultStop(ICpuDebugFrame frame, OrbisGen2Result result)
+    {
+        var opcodeBytes = ReadOpcodePreview(frame, frame.Rip, 16);
+        var detail = $"result={result}";
+        if (opcodeBytes is not null)
+        {
+            detail += $", bytes={opcodeBytes}";
+        }
+
+        return new DebugStopEvent(
+            DebugStopReason.Fault,
+            DebugRegisterFile.Capture(frame),
+            frame.Kind,
+            frame.Label,
+            breakpoint: null,
+            result: result,
+            detail: detail,
+            opcodeBytes: opcodeBytes);
+    }
+
+    private static string? ReadOpcodePreview(ICpuDebugFrame frame, ulong address, int maxBytes)
+    {
+        Span<byte> buffer = stackalloc byte[maxBytes];
+        var count = 0;
+        for (; count < maxBytes; count++)
+        {
+            if (!frame.Memory.TryRead(address + (ulong)count, buffer.Slice(count, 1)))
+            {
+                break;
+            }
+        }
+
+        return count == 0 ? null : Convert.ToHexString(buffer[..count]);
+    }
+
+    /// <summary>
+    /// Signals that the whole guest run has finished. Releases any parked
+    /// emulation thread and moves the session to
+    /// <see cref="DebuggerRunState.Terminated"/>.
+    /// </summary>
+    public void NotifyTerminated()
+    {
+        lock (_sync)
+        {
+            _state = DebuggerRunState.Terminated;
+            _currentFrame = null;
+        }
+
+        _resumeGate.Set();
+        Terminated?.Invoke(this, EventArgs.Empty);
+    }
+
+    private DebugStopReason? ResolveStopReason(ICpuDebugFrame frame, bool firstFrame, out Breakpoint? breakpoint)
+    {
+        breakpoint = null;
+        if (_pausePending)
+        {
+            _pausePending = false;
+            return DebugStopReason.Pause;
+        }
+
+        if (_stepPending)
+        {
+            _stepPending = false;
+            return DebugStopReason.Step;
+        }
+
+        var hit = Breakpoints.FindExecuteHit(frame.EntryPoint);
+        if (hit is not null)
+        {
+            breakpoint = hit;
+            return DebugStopReason.Breakpoint;
+        }
+
+        if (_options.StopAtEntry && firstFrame)
+        {
+            return DebugStopReason.EntryPoint;
+        }
+
+        return null;
+    }
+
+    public bool TryGetRegisters(out DebugRegisterFile registers)
+    {
+        lock (_sync)
+        {
+            if (!IsPausedWithFrame(out var frame))
+            {
+                registers = default;
+                return false;
+            }
+
+            registers = DebugRegisterFile.Capture(frame);
+            return true;
+        }
+    }
+
+    public bool TrySetRegister(DebugRegisterId id, ulong value)
+    {
+        lock (_sync)
+        {
+            if (!IsPausedWithFrame(out var frame))
+            {
+                return false;
+            }
+
+            if (id.IsGeneralPurpose())
+            {
+                frame.SetRegister(id.ToCpuRegister(), value);
+                return true;
+            }
+
+            switch (id)
+            {
+                case DebugRegisterId.Rip:
+                    frame.Rip = value;
+                    return true;
+                case DebugRegisterId.Rflags:
+                    frame.Rflags = value;
+                    return true;
+                default:
+                    // FS/GS bases are owned by the TLS setup and are read-only here.
+                    return false;
+            }
+        }
+    }
+
+    public bool TryReadMemory(ulong address, Span<byte> destination)
+    {
+        lock (_sync)
+        {
+            return IsPausedWithFrame(out var frame) && frame.Memory.TryRead(address, destination);
+        }
+    }
+
+    public bool TryWriteMemory(ulong address, ReadOnlySpan<byte> source)
+    {
+        lock (_sync)
+        {
+            return IsPausedWithFrame(out var frame) && frame.Memory.TryWrite(address, source);
+        }
+    }
+
+    public bool TryReadXmm(int registerIndex, out ulong low, out ulong high)
+    {
+        lock (_sync)
+        {
+            if (!IsPausedWithFrame(out var frame) || (uint)registerIndex >= 16)
+            {
+                low = 0;
+                high = 0;
+                return false;
+            }
+
+            frame.GetXmm(registerIndex, out low, out high);
+            return true;
+        }
+    }
+
+    public bool Continue()
+    {
+        lock (_sync)
+        {
+            if (_state != DebuggerRunState.Paused)
+            {
+                return false;
+            }
+
+            _resumeGate.Set();
+            return true;
+        }
+    }
+
+    public bool StepFrame()
+    {
+        lock (_sync)
+        {
+            if (_state != DebuggerRunState.Paused)
+            {
+                return false;
+            }
+
+            _stepPending = true;
+            _resumeGate.Set();
+            return true;
+        }
+    }
+
+    public void RequestPause()
+    {
+        lock (_sync)
+        {
+            if (_state == DebuggerRunState.Running)
+            {
+                _pausePending = true;
+            }
+        }
+    }
+
+    private bool IsPausedWithFrame(out ICpuDebugFrame frame)
+    {
+        // Callers must hold _sync.
+        if (_state == DebuggerRunState.Paused && _currentFrame is not null)
+        {
+            frame = _currentFrame;
+            return true;
+        }
+
+        frame = null!;
+        return false;
+    }
+}

src/SharpEmu.Debugger/Session/DebuggerSessionOptions.cs

@@ -0,0 +1,31 @@
+// Copyright (C) 2026 SharpEmu Emulator Project
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+namespace SharpEmu.Debugger.Session;
+
+/// <summary>Configuration for a <see cref="DebuggerSession"/>.</summary>
+public sealed class DebuggerSessionOptions
+{
+    /// <summary>
+    /// When true, the session pauses at the first frame it observes so a client
+    /// can attach breakpoints before the guest runs. Defaults to true, matching
+    /// the "stop at entry" behaviour most debuggers expose.
+    /// </summary>
+    public bool StopAtEntry { get; init; } = true;
+
+    /// <summary>
+    /// When true, the session pauses when a frame ends with a non-OK result (a
+    /// CPU trap, memory fault, or unimplemented path) so a client can inspect the
+    /// post-fault register/memory state before the frame is torn down. Defaults
+    /// to true. The stop reports <see cref="DebugStopReason.Fault"/>.
+    /// </summary>
+    public bool BreakOnFault { get; init; } = true;
+
+    /// <summary>
+    /// When true, the session pauses when the backend detects an execution stall
+    /// (a mutex spin loop / livelock) before the guest is forced out of the loop,
+    /// so a client can inspect the stalled state. Defaults to true. The stop
+    /// reports <see cref="DebugStopReason.Stall"/>.
+    /// </summary>
+    public bool BreakOnStall { get; init; } = true;
+}

src/SharpEmu.Debugger/Session/IDebugTarget.cs

@@ -0,0 +1,51 @@
+// Copyright (C) 2026 SharpEmu Emulator Project
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+namespace SharpEmu.Debugger.Session;
+
+/// <summary>
+/// The inspection and control surface a debugger front-end (for example a
+/// network server) drives. Register and memory accessors succeed only while the
+/// target is <see cref="DebuggerRunState.Paused"/>; they return <c>false</c>
+/// otherwise so callers never read torn state from a running guest.
+/// </summary>
+public interface IDebugTarget
+{
+    /// <summary>The current execution state.</summary>
+    DebuggerRunState State { get; }
+
+    /// <summary>The most recent stop, or null if the target has not stopped yet.</summary>
+    DebugStopEvent? LastStop { get; }
+
+    /// <summary>Reads the integer register file. Fails unless paused.</summary>
+    bool TryGetRegisters(out DebugRegisterFile registers);
+
+    /// <summary>Writes a single register. Fails unless paused.</summary>
+    bool TrySetRegister(DebugRegisterId id, ulong value);
+
+    /// <summary>Reads guest memory into <paramref name="destination"/>. Fails unless paused.</summary>
+    bool TryReadMemory(ulong address, Span<byte> destination);
+
+    /// <summary>Writes guest memory from <paramref name="source"/>. Fails unless paused.</summary>
+    bool TryWriteMemory(ulong address, ReadOnlySpan<byte> source);
+
+    /// <summary>Reads a 128-bit XMM register. Fails unless paused.</summary>
+    bool TryReadXmm(int registerIndex, out ulong low, out ulong high);
+
+    /// <summary>
+    /// Resumes a paused target. Returns false when the target was not paused.
+    /// </summary>
+    bool Continue();
+
+    /// <summary>
+    /// Resumes a paused target and stops again at the next frame boundary.
+    /// Returns false when the target was not paused.
+    /// </summary>
+    bool StepFrame();
+
+    /// <summary>
+    /// Requests that a running target stop at the next frame boundary. Has no
+    /// effect if the target is already paused or terminated.
+    /// </summary>
+    void RequestPause();
+}

src/SharpEmu.Debugger/Session/IDebuggerSession.cs

@@ -0,0 +1,43 @@
+// Copyright (C) 2026 SharpEmu Emulator Project
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+using SharpEmu.Core.Cpu.Debugging;
+using SharpEmu.Debugger.Breakpoints;
+
+namespace SharpEmu.Debugger.Session;
+
+/// <summary>
+/// The debugger's coordination point. It bridges the CPU dispatcher seam
+/// (<see cref="Hook"/>) to the inspection surface (<see cref="IDebugTarget"/>),
+/// owns breakpoint state, and raises lifecycle events that a server relays to
+/// connected clients.
+/// </summary>
+public interface IDebuggerSession : IDebugTarget
+{
+    /// <summary>The breakpoints armed for this session.</summary>
+    BreakpointStore Breakpoints { get; }
+
+    /// <summary>
+    /// The dispatcher-facing hook. Assign this to
+    /// <c>SharpEmuRuntimeOptions.DebugHook</c> so guest frames are routed through
+    /// the session.
+    /// </summary>
+    ICpuDebugHook Hook { get; }
+
+    /// <summary>Raised on the emulation thread each time the target stops.</summary>
+    event EventHandler<DebugStopEvent>? Stopped;
+
+    /// <summary>Raised when a paused target resumes.</summary>
+    event EventHandler? Resumed;
+
+    /// <summary>Raised once the target has terminated.</summary>
+    event EventHandler? Terminated;
+
+    /// <summary>
+    /// Signals that the guest run has finished. Releases any parked emulation
+    /// thread and transitions the session to
+    /// <see cref="DebuggerRunState.Terminated"/>. Hosts call this after the
+    /// runtime returns.
+    /// </summary>
+    void NotifyTerminated();
+}