fix #3726

src/BizHawk.BizInvoke/FPCtrl.cs

@@ -0,0 +1,67 @@
+using System;
+using System.IO;
+using System.Runtime.InteropServices;
+
+namespace BizHawk.BizInvoke
+{
+	// .NET is weird and sets the x87 control register to double precision
+	// It does this even on Linux which normally expects it set to extended x87 precision
+	// Even stranger is that this appears to be completely unneeded on x86-64
+	// On Windows, x87 registers are prohibited to be used in kernel code, and
+	// MSVC will not use the x87 registers (and presumably this extends to userland OS code)
+	// .NET presumbly follows MSVC and would not use the x87 registers (why would it? SSE is available! long double doesn't exist!)
+	// This thus only screws over code compiled with MinGW (which use extended x87 precision for long double)
+	// Or screws over any unmanaged code on Linux, which doubly includes all waterbox cores (!!!)
+	// Of course in practice, this only applies to any code using long double, which is rarely used typically
+	// But musl (used for waterbox cores) does end up using it for float formating in the printf family
+	// This can extend to issues in games: https://github.com/TASEmulators/BizHawk/issues/3726
+	public static class FPCtrl
+	{
+		private const CallingConvention cc = CallingConvention.Cdecl;
+
+		[UnmanagedFunctionPointer(cc)]
+		private delegate void FixFPCtrlDelegate();
+
+		private static readonly MemoryBlock? _memory;
+		private static readonly FixFPCtrlDelegate? _fixFpCtrl;
+
+		static FPCtrl()
+		{
+			// not usable outside of x64
+			if (RuntimeInformation.ProcessArchitecture != Architecture.X64)
+			{
+				return;
+			}
+
+			// generate assembly for fixing the x87 control register
+			_memory = new(4096);
+			_memory.Protect(_memory.Start, _memory.Size, MemoryBlock.Protection.RW);
+			var ss = _memory.GetStream(_memory.Start, 64, true);
+			var bw = new BinaryWriter(ss);
+
+			// FYI: The push/pop is only needed on Windows, but doesn't do any harm on Linux
+
+			bw.Write((byte)0x50); // push rax
+			bw.Write(0x06247CD9); // fnstcw word[rsp + 6]
+			bw.Write(0x07244C80); // or byte[rsp + 7], 3
+			bw.Write((byte)0x03);
+			bw.Write(0x06246CD9); // fldcw word[rsp + 6]
+			bw.Write((byte)0x58); // pop rax
+			bw.Write((byte)0xC3); // ret
+
+			_memory.Protect(_memory.Start, _memory.Size, MemoryBlock.Protection.RX);
+			_fixFpCtrl = Marshal.GetDelegateForFunctionPointer<FixFPCtrlDelegate>((IntPtr)_memory.Start);
+		}
+
+		public static void FixFPCtrl()
+		{
+			// not usable outside of x64
+			if (RuntimeInformation.ProcessArchitecture != Architecture.X64)
+			{
+				return;
+			}
+
+			_fixFpCtrl!();
+		}
+	}
+}

src/BizHawk.Client.EmuHawk/Program.cs

@@ -6,6 +6,7 @@ using System.Reflection;
 using System.Runtime.InteropServices;
 using System.Windows.Forms;
 
+using BizHawk.BizInvoke;
 using BizHawk.Bizware.BizwareGL;
 using BizHawk.Bizware.Graphics;
 using BizHawk.Common;
@@ -285,6 +286,8 @@ namespace BizHawk.Client.EmuHawk
 				}
 			}
 
+			FPCtrl.FixFPCtrl();
+
 			var exitCode = 0;
 			try
 			{

src/BizHawk.Emulation.Cores/Consoles/Nintendo/QuickNES/QuickNES.cs

@@ -1,6 +1,5 @@
 using System;
 using System.Collections.Generic;
-using System.Diagnostics;
 using System.IO;
 using System.Linq;
 using System.Runtime.InteropServices;
@@ -29,12 +28,6 @@ namespace BizHawk.Emulation.Cores.Consoles.Nintendo.QuickNES
 
 		[CoreConstructor(VSystemID.Raw.NES, Priority = CorePriority.Low)]
 		public QuickNES(byte[] file, QuickNESSettings settings, QuickNESSyncSettings syncSettings)
-		{
-			FP = OSTailoredCode.IsUnixHost
-				? (IFPCtrl) new Unix_FPCtrl()
-				: new Win32_FPCtrl();
-
-			using (FP.Save())
 		{
 			ServiceProvider = new BasicServiceProvider(this);
 			Context = QN.qn_new();
@@ -73,7 +66,6 @@ namespace BizHawk.Emulation.Cores.Consoles.Nintendo.QuickNES
 				throw;
 			}
 		}
-		}
 
 		private static readonly LibQuickNES QN;
 
@@ -83,40 +75,6 @@ namespace BizHawk.Emulation.Cores.Consoles.Nintendo.QuickNES
 
 		int IVideoLogicalOffsets.ScreenY => _settings.ClipTopAndBottom ? 8 : 0;
 
-		private interface IFPCtrl : IDisposable
-		{
-			IDisposable Save();
-		}
-
-		private class Win32_FPCtrl : IFPCtrl
-		{
-			[Conditional("DEBUG")]
-			public static void PrintCurrentFP() => Console.WriteLine($"Current FP word: 0x{Win32Imports._control87(0, 0):X8}");
-
-			private uint cw;
-
-			public IDisposable Save()
-			{
-				cw = Win32Imports._control87(0, 0);
-				Win32Imports._control87(0x00000, 0x30000);
-				return this;
-			}
-
-			public void Dispose()
-			{
-				Win32Imports._control87(cw, 0x30000);
-			}
-		}
-
-		private class Unix_FPCtrl : IFPCtrl
-		{
-			public IDisposable Save() => this;
-
-			public void Dispose() {}
-		}
-
-		private readonly IFPCtrl FP;
-
 		public ControllerDefinition ControllerDefinition { get; private set; }
 
 		private void SetControllerDefinition()
@@ -185,8 +143,7 @@ namespace BizHawk.Emulation.Cores.Consoles.Nintendo.QuickNES
 		public bool FrameAdvance(IController controller, bool render, bool rendersound = true)
 		{
 			CheckDisposed();
-			using (FP.Save())
+
-			{
 			if (controller.IsPressed("Power"))
 				QN.qn_reset(Context, true);
 			if (controller.IsPressed("Reset"))
@@ -213,7 +170,6 @@ namespace BizHawk.Emulation.Cores.Consoles.Nintendo.QuickNES
 
 			return true;
 		}
-		}
 
 		private IntPtr Context;
 		public int Frame { get; private set; }