ipc/mscom/VTableBuilder.c

   1 /* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
   2 /* vim: set ts=8 sts=2 et sw=2 tw=80: */
   3 /* This Source Code Form is subject to the terms of the Mozilla Public
   4  * License, v. 2.0. If a copy of the MPL was not distributed with this
   5  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
   6
   7 #include "VTableBuilder.h"
   8
   9 #include <stdlib.h>
  10
  11 static HRESULT STDMETHODCALLTYPE QueryInterfaceThunk(IUnknown* aThis,
  12                                                      REFIID aIid,
  13                                                      void** aOutInterface) {
  14   void** table = (void**)aThis;
  15   IUnknown* real = (IUnknown*)table[1];
  16   return real->lpVtbl->QueryInterface(real, aIid, aOutInterface);
  17 }
  18
  19 static ULONG STDMETHODCALLTYPE AddRefThunk(IUnknown* aThis) {
  20   void** table = (void**)aThis;
  21   IUnknown* real = (IUnknown*)table[1];
  22   return real->lpVtbl->AddRef(real);
  23 }
  24
  25 static ULONG STDMETHODCALLTYPE ReleaseThunk(IUnknown* aThis) {
  26   void** table = (void**)aThis;
  27   IUnknown* real = (IUnknown*)table[1];
  28   return real->lpVtbl->Release(real);
  29 }
  30
  31 IUnknown* BuildNullVTable(IUnknown* aUnk, uint32_t aVtblSize) {
  32   void** table;
  33
  34   if (aVtblSize < 3) {
  35     return NULL;
  36   }
  37
  38   // We need to allocate slots for two additional pointers: The |lpVtbl|
  39   // pointer, as well as |aUnk| which is needed to get |this| right when
  40   // something calls through one of the IUnknown thunks.
  41   table = calloc(aVtblSize + 2, sizeof(void*));
  42
  43   table[0] = &table[2];  // |lpVtbl|, points to the first entry of the vtable
  44   table[1] = aUnk;       // |this|
  45   // Now the actual vtable entries for IUnknown
  46   table[2] = &QueryInterfaceThunk;
  47   table[3] = &AddRefThunk;
  48   table[4] = &ReleaseThunk;
  49   // Remaining entries are NULL thanks to calloc zero-initializing everything.
  50
  51   return (IUnknown*)table;
  52 }
  53
  54 void DeleteNullVTable(IUnknown* aUnk) { free(aUnk); }