mfbt/Poison.h

   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 /*
   8  * A poison value that can be used to fill a memory space with
   9  * an address that leads to a safe crash when dereferenced.
  10  */
  11
  12 #ifndef mozilla_Poison_h
  13 #define mozilla_Poison_h
  14
  15 #include "mozilla/Assertions.h"
  16 #include "mozilla/Types.h"
  17
  18 #include <stdint.h>
  19
  20 MOZ_BEGIN_EXTERN_C
  21
  22 extern MFBT_DATA uintptr_t gMozillaPoisonValue;
  23
  24 /**
  25  * @return the poison value.
  26  */
  27 inline uintptr_t mozPoisonValue()
  28 {
  29   return gMozillaPoisonValue;
  30 }
  31
  32 /**
  33  * Overwrite the memory block of aSize bytes at aPtr with the poison value.
  34  * aPtr MUST be aligned at a sizeof(uintptr_t) boundary.
  35  * Only an even number of sizeof(uintptr_t) bytes are overwritten, the last
  36  * few bytes (if any) is not overwritten.
  37  */
  38 inline void mozWritePoison(void* aPtr, size_t aSize)
  39 {
  40   const uintptr_t POISON = mozPoisonValue();
  41   char* p = (char*)aPtr;
  42   char* limit = p + aSize;
  43   MOZ_ASSERT((uintptr_t)aPtr % sizeof(uintptr_t) == 0, "bad alignment");
  44   MOZ_ASSERT(aSize >= sizeof(uintptr_t), "poisoning this object has no effect");
  45   for (; p < limit; p += sizeof(uintptr_t)) {
  46     *((uintptr_t*)p) = POISON;
  47   }
  48 }
  49
  50 /**
  51  * Initialize the poison value.
  52  * This should only be called once.
  53  */
  54 extern MFBT_API void mozPoisonValueInit();
  55
  56 /* Values annotated by CrashReporter */
  57 extern MFBT_DATA uintptr_t gMozillaPoisonBase;
  58 extern MFBT_DATA uintptr_t gMozillaPoisonSize;
  59
  60 MOZ_END_EXTERN_C
  61
  62 #endif /* mozilla_Poison_h */