Minor cleanup in some waterbox memory functions

src/BizHawk.BizInvoke/CallingConventionAdapter.cs

@@ -3,6 +3,7 @@ using System.Collections.Generic;
 using System.IO;
 using System.Linq;
 using System.Runtime.InteropServices;
+using BizHawk.Common;
 
 namespace BizHawk.BizInvoke
 {
@@ -79,15 +80,17 @@ namespace BizHawk.BizInvoke
 		/// </summary>
 		public static ICallingConventionAdapter Native { get; } = new NativeConvention();
 
+		static CallingConventionAdapters()
+		{
+			Waterbox = OSTailoredCode.IsUnixHost
+				? (ICallingConventionAdapter)new SysVHostMsGuest()
+				: new NativeConvention();
+		}
+
 		/// <summary>
 		/// convention appropriate for waterbox guests
 		/// </summary>
-		public static ICallingConventionAdapter Waterbox { get; } =
-#if true
-			new NativeConvention();
-#else
-			new SysVHostMsGuest();
-#endif
+		public static ICallingConventionAdapter Waterbox { get; }
 
 		private class SysVHostMsGuest : ICallingConventionAdapter
 		{

src/BizHawk.BizInvoke/MemoryBlock.cs

@@ -50,7 +50,8 @@ namespace BizHawk.BizInvoke
 		/// <summary>get a page index within the block</summary>
 		protected int GetPage(ulong addr)
 		{
-			if (addr < Start || EndExclusive <= addr) throw new ArgumentOutOfRangeException(nameof(addr), addr, "invalid address");
+			if (addr < Start || EndExclusive <= addr)
+				throw new ArgumentOutOfRangeException(nameof(addr), addr, "invalid address");
 			return (int) ((addr - Start) >> WaterboxUtils.PageShift);
 		}
 
@@ -70,7 +71,7 @@ namespace BizHawk.BizInvoke
 				throw new ArgumentOutOfRangeException(nameof(start), start, "invalid address");
 			if (EndExclusive < start + length)
 				throw new ArgumentOutOfRangeException(nameof(length), length, "requested length implies invalid end address");
-			return new MemoryViewStream(!writer, writer, (long) start, (long) length, this);
+			return new MemoryViewStream(!writer, writer, (long)start, (long)length, this);
 		}
 
 		/// <summary>
@@ -90,7 +91,7 @@ namespace BizHawk.BizInvoke
 				throw new ArgumentOutOfRangeException(nameof(length), length, "requested length implies invalid end address");
 			if (_snapshot == null)
 				throw new InvalidOperationException("No snapshot taken!");
-			return new MemoryViewXorStream(!writer, writer, (long) start, (long) length, this, _snapshot, (long) (start - Start));
+			return new MemoryViewXorStream(!writer, writer, (long)start, (long)length, this, _snapshot, (long)(start - Start));
 		}
 
 		/// <summary>activate the memory block, swapping it in at the pre-specified address</summary>

src/BizHawk.BizInvoke/WaterboxUtils.cs

@@ -45,26 +45,24 @@ namespace BizHawk.BizInvoke
 		/// <summary>
 		/// system page size
 		/// </summary>
-		public static int PageSize { get; }
+		public const int PageSize = 4096;
 
 		/// <summary>
 		/// bitshift corresponding to PageSize
 		/// </summary>
-		public static int PageShift { get; }
+		public const int PageShift = 12;
 		/// <summary>
 		/// bitmask corresponding to PageSize
 		/// </summary>
-		public static ulong PageMask { get; }
+		public const ulong PageMask = 4095;
 
 		static WaterboxUtils()
 		{
-			int p = PageSize = Environment.SystemPageSize;
-			while (p != 1)
+			if (PageSize != Environment.SystemPageSize)
 			{
-				p >>= 1;
-				PageShift++;
+				// We can do it, but we'll have to change up some waterbox stuff
+				throw new InvalidOperationException("Wrong page size");
 			}
-			PageMask = (ulong)(PageSize - 1);
 		}
 
 		/// <summary>

src/BizHawk.Emulation.Cores/Waterbox/Heap.cs

@@ -36,11 +36,11 @@ namespace BizHawk.Emulation.Cores.Waterbox
 			Console.WriteLine("Created heap `{1}` at {0:x16}:{2:x16}", start, name, start + size);
 		}
 
-		private ulong EnsureAlignment(int align)
+		private ulong AlignForAllocation(int align)
 		{
 			if (align > 1)
 			{
-				ulong newused = ((Used - 1) | (ulong)(align - 1)) + 1;
+				ulong newused = ((Used - 1) | (ulong)((uint)align - 1)) + 1;
 				if (newused > Memory.Size)
 				{
 					throw new InvalidOperationException($"Failed to meet alignment {align} on heap {Name}");
@@ -55,7 +55,7 @@ namespace BizHawk.Emulation.Cores.Waterbox
 			if (Sealed)
 				throw new InvalidOperationException($"Attempt made to allocate from sealed heap {Name}");
 
-			ulong allocstart = EnsureAlignment(align);
+			ulong allocstart = AlignForAllocation(align);
 			ulong newused = allocstart + size;
 			if (newused > Memory.Size)
 			{
@@ -114,10 +114,25 @@ namespace BizHawk.Emulation.Cores.Waterbox
 				{
 					throw new InvalidOperationException($"Hash did not match for heap {Name}.  Is this the same rom with the same SyncSettings?");
 				}
+				var oldUsedAligned = WaterboxUtils.AlignUp(Used);
 				var usedAligned = WaterboxUtils.AlignUp(used);
+				if (usedAligned > oldUsedAligned)
+				{
+					// grow
+					var s = Memory.Start + oldUsedAligned;
+					var l = usedAligned - oldUsedAligned;
+					Memory.Protect(s, l, MemoryBlock.Protection.RW);
+				}
+				else if (usedAligned < oldUsedAligned)
+				{
+					// shrink
+					var s = Memory.Start + usedAligned;
+					var l = oldUsedAligned - usedAligned;
+					// like elsewhere, we zero on free to avoid nondeterminism if later reallocated
+					WaterboxUtils.ZeroMemory(Z.US(s), (long)l);
+					Memory.Protect(s, l, MemoryBlock.Protection.None);
+				}
 
-				Memory.Protect(Memory.Start, Memory.Size, MemoryBlock.Protection.None);
-				Memory.Protect(Memory.Start, used, MemoryBlock.Protection.RW);
 				var ms = Memory.GetXorStream(Memory.Start, usedAligned, true);
 				WaterboxUtils.CopySome(br.BaseStream, ms, (long)usedAligned);
 				Used = used;

src/BizHawk.Emulation.Cores/Waterbox/MapHeap.cs

@@ -40,9 +40,20 @@ namespace BizHawk.Emulation.Cores.Waterbox
 			return ((ulong)page << WaterboxUtils.PageShift) + Memory.Start;
 		}
 
+		/// <summary>
+		/// Sentinel value used to indicate unmapped pages.
+		/// Needed because mapped pages are allowed to be protected to None
+		/// </summary>
 		private const MemoryBlock.Protection FREE = (MemoryBlock.Protection)255;
 
+		/// <summary>
+		/// Bitmap of protections.  Similar to MemoryBlock._pageData (and unfortunately mirrors the same information),
+		/// but also handles FREE
+		/// </summary>
 		private readonly MemoryBlock.Protection[] _pages;
+		/// <summary>
+		/// alias of _pages used for serialization
+		/// </summary>
 		private readonly byte[] _pagesAsBytes;
 
 		public MapHeap(ulong start, ulong size, string name)
@@ -67,6 +78,7 @@ namespace BizHawk.Emulation.Cores.Waterbox
 		// used in realloc
 		private int FindConsecutiveFreePagesAssumingFreed(int count, int startPage, int numPages)
 		{
+			// TODO: I'm sure there are sublinear algorithms for this, if the right data is maintained
 			var starts = new List<int>();
 			var sizes = new List<int>();
 
@@ -86,6 +98,8 @@ namespace BizHawk.Emulation.Cores.Waterbox
 					currStart = i + 1;
 				}
 			}
+			// find smallest hole to reduce fragmentation
+			// TODO: Is this needed?
 			int bestIdx = -1;
 			int bestSize = int.MaxValue;
 			for (int i = 0; i < sizes.Count; i++)

src/BizHawk.Emulation.Cores/Waterbox/WaterboxUtils.cs

@@ -11,10 +11,10 @@ namespace BizHawk.Emulation.Cores.Waterbox
 		/// </summary>
 		public static void CopySome(Stream src, Stream dst, long len)
 		{
-			var buff = new byte[4096];
+			var buff = new byte[65536];
 			while (len > 0)
 			{
-				int r = src.Read(buff, 0, (int)Math.Min(len, 4096));
+				int r = src.Read(buff, 0, (int)Math.Min(len, 65536));
 				dst.Write(buff, 0, r);
 				len -= r;
 			}