WindowsPageAllocator: Fix allocation issues on macOS

On macOS (if using e.g. Crossover), VirtualQuery can report a memory address as free but still fail to reserve the memory with VirtualAlloc (fails with error code 0x170C240 for some reason).

To fix this, memory is now reserved directly in the loop to ensure it can be reserved. If reservation fails, the next address is tried.

Author: ghorsington

BepInEx.IL2CPP/Hook/Allocator/WindowsPageAllocator.cs

@@ -12,7 +12,7 @@ namespace BepInEx.IL2CPP.Hook.Allocator;
 internal class WindowsPageAllocator : PageAllocator
 {
     [MethodImpl(MethodImplOptions.AggressiveInlining)]
-    private static nint RoundUp(nint num, nint unit) => (num + unit - 1) & ~ (unit - 1);
+    private static nint RoundUp(nint num, nint unit) => (num + unit - 1) & ~(unit - 1);
 
     private static Win32Exception Win32Error(string message = null, int code = -1)
     {
@@ -23,6 +23,7 @@ private static Win32Exception Win32Error(string message = null, int code = -1)
 
     protected override nint AllocateChunk(nint hint)
     {
+        nint chunk;
         while (true)
         {
             if (WinApi.VirtualQuery(hint, out var mbi) == 0)
@@ -38,7 +39,17 @@ protected override nint AllocateChunk(nint hint)
                 var d = nextAddress - mbi.BaseAddress;
                 if (d >= 0 && mbi.RegionSize - d >= ALLOCATION_UNIT)
                 {
+                    Logger.Log(LogLevel.Debug, $"Found free chunk at 0x{(long) nextAddress:X8}");
                     hint = nextAddress;
+
+                    chunk = WinApi.VirtualAlloc(hint, ALLOCATION_UNIT, WinApi.AllocationType.MEM_RESERVE,
+                                                WinApi.ProtectConstant.PAGE_NOACCESS);
+                    if (chunk == 0)
+                    {
+                        Logger.Log(LogLevel.Debug, $"Failed to reserve address: 0x{(long) hint:X8}: {Win32Error()}");
+                        goto next;
+                    }
+
                     break;
                 }
             }
@@ -47,10 +58,6 @@ protected override nint AllocateChunk(nint hint)
             hint = mbi.BaseAddress + mbi.RegionSize;
         }
 
-        var chunk = WinApi.VirtualAlloc(hint, ALLOCATION_UNIT, WinApi.AllocationType.MEM_RESERVE,
-                                        WinApi.ProtectConstant.PAGE_NOACCESS);
-        if (chunk == 0)
-            throw Win32Error($"Failed to reserve address: 0x{(long) hint:X8}");
         var addr = WinApi.VirtualAlloc(chunk, PAGE_SIZE, WinApi.AllocationType.MEM_COMMIT,
                                        WinApi.ProtectConstant.PAGE_READWRITE);
         if (addr == 0)