1 files changed, 54 insertions, 0 deletions
diff --git a/ipc/mscom/VTableBuilder.c b/ipc/mscom/VTableBuilder.c
new file mode 100644
index 0000000000..48550503c2
--- /dev/null
+++ b/ipc/mscom/VTableBuilder.c
@@ -0,0 +1,54 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "VTableBuilder.h"
+
+#include <stdlib.h>
+
+static HRESULT STDMETHODCALLTYPE QueryInterfaceThunk(IUnknown* aThis,
+                                                     REFIID aIid,
+                                                     void** aOutInterface) {
+  void** table = (void**)aThis;
+  IUnknown* real = (IUnknown*)table[1];
+  return real->lpVtbl->QueryInterface(real, aIid, aOutInterface);
+}
+
+static ULONG STDMETHODCALLTYPE AddRefThunk(IUnknown* aThis) {
+  void** table = (void**)aThis;
+  IUnknown* real = (IUnknown*)table[1];
+  return real->lpVtbl->AddRef(real);
+}
+
+static ULONG STDMETHODCALLTYPE ReleaseThunk(IUnknown* aThis) {
+  void** table = (void**)aThis;
+  IUnknown* real = (IUnknown*)table[1];
+  return real->lpVtbl->Release(real);
+}
+
+IUnknown* BuildNullVTable(IUnknown* aUnk, uint32_t aVtblSize) {
+  void** table;
+
+  if (aVtblSize < 3) {
+    return NULL;
+  }
+
+  // We need to allocate slots for two additional pointers: The |lpVtbl|
+  // pointer, as well as |aUnk| which is needed to get |this| right when
+  // something calls through one of the IUnknown thunks.
+  table = calloc(aVtblSize + 2, sizeof(void*));
+
+  table[0] = &table[2];  // |lpVtbl|, points to the first entry of the vtable
+  table[1] = aUnk;       // |this|
+  // Now the actual vtable entries for IUnknown
+  table[2] = &QueryInterfaceThunk;
+  table[3] = &AddRefThunk;
+  table[4] = &ReleaseThunk;
+  // Remaining entries are NULL thanks to calloc zero-initializing everything.
+
+  return (IUnknown*)table;
+}
+
+void DeleteNullVTable(IUnknown* aUnk) { free(aUnk); }