Don't use mmap in the frozen object manager for WASM

src/coreclr/nativeaot/System.Private.CoreLib/src/Internal/Runtime/FrozenObjectHeapManager.Wasm.cs

@@ -0,0 +1,33 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+#pragma warning disable IDE0060 // Remove unused parameter
+
+using System.Runtime.InteropServices;
+
+namespace Internal.Runtime
+{
+    internal unsafe partial class FrozenObjectHeapManager
+    {
+        private static void* ClrVirtualReserve(nuint size)
+        {
+            void* alloc = Interop.Sys.AlignedAlloc(8, size);
+            if (alloc != null)
+            {
+                NativeMemory.Clear(alloc, size);
+            }
+            return alloc;
+        }
+
+        private static void* ClrVirtualCommit(void* pBase, nuint size)
+        {
+            // Already 'commited'.
+            return pBase;
+        }
+
+        private static void ClrVirtualFree(void* pBase, nuint size)
+        {
+            // This will only be called before an OOM. We have no way do a partial unmap, so do not try.
+        }
+    }
+}

src/coreclr/nativeaot/System.Private.CoreLib/src/Internal/Runtime/FrozenObjectHeapManager.cs

@@ -19,8 +19,13 @@ internal unsafe partial class FrozenObjectHeapManager
         private readonly LowLevelLock m_Crst = new LowLevelLock();
         private FrozenObjectSegment m_CurrentSegment;
 
+#if TARGET_WASM
+        // WASM doesn't support reserving memory so we use a smaller size.
+        private const nuint FOH_SEGMENT_DEFAULT_SIZE = 64 * 1024;
+#else
         // Default size to reserve for a frozen segment
         private const nuint FOH_SEGMENT_DEFAULT_SIZE = 4 * 1024 * 1024;
+#endif
         // Size to commit on demand in that reserved space
         private const nuint FOH_COMMIT_SIZE = 64 * 1024;
 
@@ -119,7 +124,7 @@ public FrozenObjectSegment(nuint sizeHint)
             {
                 m_Size = sizeHint;
 
-                Debug.Assert(m_Size > FOH_COMMIT_SIZE);
+                Debug.Assert(m_Size >= FOH_COMMIT_SIZE);
                 Debug.Assert(m_Size % FOH_COMMIT_SIZE == 0);
 
                 void* alloc = ClrVirtualReserve(m_Size);

src/coreclr/nativeaot/System.Private.CoreLib/src/System.Private.CoreLib.csproj

@@ -307,7 +307,8 @@
     <Compile Include="System\Threading\ThreadPoolCallbackWrapper.NativeAot.cs" />
   </ItemGroup>
   <ItemGroup Condition="'$(TargetsUnix)'=='true' or '$(TargetsBrowser)'=='true' or '$(TargetsWasi)'=='true'">
-    <Compile Include="Internal\Runtime\FrozenObjectHeapManager.Unix.cs" />
+    <Compile Include="Internal\Runtime\FrozenObjectHeapManager.Unix.cs" Condition="'$(TargetsWasm)' != 'true'" />
+    <Compile Include="Internal\Runtime\FrozenObjectHeapManager.Wasm.cs" Condition="'$(TargetsWasm)' == 'true'" />
     <Compile Include="System\Environment.NativeAot.Unix.cs" />
     <Compile Include="System\Runtime\InteropServices\NativeLibrary.NativeAot.Unix.cs" />
     <Compile Include="System\Runtime\InteropServices\PInvokeMarshal.Unix.cs" />