wtf/StaticConstructors.h

   1 /*
   2  * Copyright (C) 2006 Apple Computer, Inc.
   3  *
   4  * This library is free software; you can redistribute it and/or
   5  * modify it under the terms of the GNU Library General Public
   6  * License as published by the Free Software Foundation; either
   7  * version 2 of the License, or (at your option) any later version.
   8  *
   9  * This library is distributed in the hope that it will be useful,
  10  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  11  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  12  * Library General Public License for more details.
  13  *
  14  * You should have received a copy of the GNU Library General Public License
  15  * along with this library; see the file COPYING.LIB.  If not, write to
  16  * the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
  17  * Boston, MA 02110-1301, USA.
  18  *
  19  */
  20
  21 #ifndef StaticConstructors_h
  22 #define StaticConstructors_h
  23
  24 // We need to avoid having static constructors. We achieve this
  25 // with two separate methods for GCC and MSVC. Both methods prevent the static
  26 // initializers from being registered and called on program startup. On GCC, we
  27 // declare the global objects with a different type that can be POD default
  28 // initialized by the linker/loader. On MSVC we use a special compiler feature
  29 // to have the CRT ignore our static initializers. The constructors will never
  30 // be called and the objects will be left uninitialized.
  31 //
  32 // With both of these approaches, we must define and explicitly call an init
  33 // routine that uses placement new to create the objects and overwrite the
  34 // uninitialized placeholders.
  35 //
  36 // This is not completely portable, but is what we have for now without
  37 // changing how a lot of code accesses these global objects.
  38
  39 #ifdef SKIP_STATIC_CONSTRUCTORS_ON_MSVC
  40 // - Assume that all includes of this header want ALL of their static
  41 //   initializers ignored. This is currently the case. This means that if
  42 //   a .cc includes this header (or it somehow gets included), all static
  43 //   initializers after the include will not be executed.
  44 // - We do this with a pragma, so that all of the static initializer pointers
  45 //   go into our own section, and the CRT won't call them. Eventually it would
  46 //   be nice if the section was discarded, because we don't want the pointers.
  47 //   See: http://msdn.microsoft.com/en-us/library/7977wcck(VS.80).aspx
  48 #pragma warning(disable:4075)
  49 #pragma init_seg(".unwantedstaticinits")
  50 #endif
  51
  52 #ifndef SKIP_STATIC_CONSTRUCTORS_ON_GCC
  53     // Define an global in the normal way.
  54 #if COMPILER(MSVC7_OR_LOWER)
  55 #define DEFINE_GLOBAL(type, name) \
  56     const type name;
  57 #elif COMPILER(WINSCW)
  58 #define DEFINE_GLOBAL(type, name, arg...) \
  59     const type name;
  60 #else
  61 #define DEFINE_GLOBAL(type, name, ...) \
  62     const type name;
  63 #endif
  64
  65 #else
  66 // Define an correctly-sized array of pointers to avoid static initialization.
  67 // Use an array of pointers instead of an array of char in case there is some alignment issue.
  68 #if COMPILER(MSVC7_OR_LOWER)
  69 #define DEFINE_GLOBAL(type, name) \
  70     void * name[(sizeof(type) + sizeof(void *) - 1) / sizeof(void *)];
  71 #elif COMPILER(WINSCW)
  72 #define DEFINE_GLOBAL(type, name, arg...) \
  73     void * name[(sizeof(type) + sizeof(void *) - 1) / sizeof(void *)];
  74 #else
  75 #define DEFINE_GLOBAL(type, name, ...) \
  76     void * name[(sizeof(type) + sizeof(void *) - 1) / sizeof(void *)];
  77 #endif
  78 #endif
  79
  80 #endif // StaticConstructors_h