build/pure_virtual/pure_virtual.c

   1 /* This Source Code Form is subject to the terms of the Mozilla Public
   2  * License, v. 2.0. If a copy of the MPL was not distributed with this
   3  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
   4
   5 #include <mozilla/Assertions.h>
   6
   7 // This function is used in vtables to point at pure virtual methods.
   8 // The implementation in the standard library usually aborts, but
   9 // the function is normally never called (a call would be a bug).
  10 // Each of these entries in vtables, however, require an unnecessary
  11 // dynamic relocation. Defining our own function makes the linker
  12 // point the vtables here instead of the standard library, replacing
  13 // the dynamic relocations with relative relocations.
  14 //
  15 // On Windows, it doesn't really make a difference, but on macOS it
  16 // can be packed better, saving about 10KB in libxul, and on 64-bits
  17 // ELF systems, with packed relative relocations, it saves 140KB.
  18 //
  19 // Another advantage of having our own is that we can use MOZ_CRASH
  20 // instead of the system's abort.
  21 #ifdef _MSC_VER
  22 int __cdecl _purecall() { MOZ_CRASH("pure virtual call"); }
  23 #else
  24 __attribute__((visibility("hidden"))) void __cxa_pure_virtual() {
  25   MOZ_CRASH("pure virtual call");
  26 }
  27 #endif