From 050f2426d881cd50d0819e341c5387596f7428bc Mon Sep 17 00:00:00 2001
From: rozbf <rozbf@users.noreply.github.com>
Date: Tue, 24 Jan 2023 23:36:38 +0100
Subject: [PATCH] Allow manual heap deallocation with zerolib

---
 src/zerolib/Internal/Startup.Efi.cs |  2 +-
 src/zerolib/Internal/Stubs.cs       | 24 ++++++++++++++++++++++++
 src/zerolib/System/GC.cs            | 18 ++++++++++++++++++
 src/zerolib/System/IDisposable.cs   | 10 ++++++++++
 4 files changed, 53 insertions(+), 1 deletion(-)
 create mode 100644 src/zerolib/System/GC.cs
 create mode 100644 src/zerolib/System/IDisposable.cs

diff --git a/src/zerolib/Internal/Startup.Efi.cs b/src/zerolib/Internal/Startup.Efi.cs
index 3377ec0..8832151 100644
--- a/src/zerolib/Internal/Startup.Efi.cs
+++ b/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;
diff --git a/src/zerolib/Internal/Stubs.cs b/src/zerolib/Internal/Stubs.cs
index 9307f18..4c2a42c 100644
--- a/src/zerolib/Internal/Stubs.cs
+++ b/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
+        }
     }
 }
diff --git a/src/zerolib/System/GC.cs b/src/zerolib/System/GC.cs
new file mode 100644
index 0000000..f59d0c2
--- /dev/null
+++ b/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);
+            }
+        }
+    }
+}
diff --git a/src/zerolib/System/IDisposable.cs b/src/zerolib/System/IDisposable.cs
new file mode 100644
index 0000000..33934c8
--- /dev/null
+++ b/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();
+    }
+}