Allow manual heap deallocation with zerolib

src/zerolib/Internal/Startup.Efi.cs

@@ -143,7 +143,7 @@ unsafe readonly struct EFI_BOOT_SERVICES
         private readonly void* pad3;
         private readonly void* pad4;
         public readonly delegate*<int, nint, void**, ulong> AllocatePool;
-        private readonly void* pad6;
+        public readonly delegate*<void*, ulong> FreePool;
         private readonly void* pad7;
         private readonly void* pad8;
         private readonly void* pad9;

src/zerolib/Internal/Stubs.cs

@@ -131,6 +131,15 @@ public static unsafe void RhpAssignRef(void** dst, void* r)
             *dst = r;
         }
 
+        [RuntimeExport("RhSuppressFinalize")]
+        public static unsafe void RhSuppressFinalize(object obj)
+        {
+            fixed (MethodTable** mt = &obj.m_pMethodTable)
+            {
+                FreeObject(mt);
+            }
+        }
+
         static unsafe MethodTable** AllocObject(uint size)
         {
 #if WINDOWS
@@ -148,5 +157,20 @@ public static unsafe void RhpAssignRef(void** dst, void* r)
 
             return result;
         }
+
+        static unsafe void FreeObject(MethodTable** mt)
+        {
+#if WINDOWS
+            [DllImport("kernel32")]
+            static extern MethodTable** LocalFree(MethodTable** ptr);
+            LocalFree(mt);
+#elif LINUX
+            [DllImport("libSystem.Native")]
+            static extern void SystemNative_Free(MethodTable** ptr);
+            SystemNative_Free(mt);
+#elif UEFI
+            StartupCodeHelpers.s_efiSystemTable->BootServices->FreePool((void*)mt);
+#endif
+        }
     }
 }

src/zerolib/System/GC.cs

@@ -0,0 +1,18 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using Internal.Runtime.CompilerHelpers;
+
+namespace System
+{
+    public static class GC
+    {
+        public static void SuppressFinalize(object obj)
+        {
+            if (obj != null)
+            {
+                StartupCodeHelpers.RhSuppressFinalize(obj);
+            }
+        }
+    }
+}

src/zerolib/System/IDisposable.cs

@@ -0,0 +1,10 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+namespace System
+{
+    public interface IDisposable
+    {
+        void Dispose();
+    }
+}