michael@0: /* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
michael@0: /* vim: set ts=8 sts=2 et sw=2 tw=80: */
michael@0: /* This Source Code Form is subject to the terms of the Mozilla Public
michael@0:  * License, v. 2.0. If a copy of the MPL was not distributed with this
michael@0:  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
michael@0: 
michael@0: /*
michael@0:  * A poison value that can be used to fill a memory space with
michael@0:  * an address that leads to a safe crash when dereferenced.
michael@0:  */
michael@0: 
michael@0: #ifndef mozilla_Poison_h
michael@0: #define mozilla_Poison_h
michael@0: 
michael@0: #include "mozilla/Assertions.h"
michael@0: #include "mozilla/Types.h"
michael@0: 
michael@0: #include <stdint.h>
michael@0: 
michael@0: MOZ_BEGIN_EXTERN_C
michael@0: 
michael@0: extern MFBT_DATA uintptr_t gMozillaPoisonValue;
michael@0: 
michael@0: /**
michael@0:  * @return the poison value.
michael@0:  */
michael@0: inline uintptr_t mozPoisonValue()
michael@0: {
michael@0:   return gMozillaPoisonValue;
michael@0: }
michael@0: 
michael@0: /**
michael@0:  * Overwrite the memory block of aSize bytes at aPtr with the poison value.
michael@0:  * aPtr MUST be aligned at a sizeof(uintptr_t) boundary.
michael@0:  * Only an even number of sizeof(uintptr_t) bytes are overwritten, the last
michael@0:  * few bytes (if any) is not overwritten.
michael@0:  */
michael@0: inline void mozWritePoison(void* aPtr, size_t aSize)
michael@0: {
michael@0:   const uintptr_t POISON = mozPoisonValue();
michael@0:   char* p = (char*)aPtr;
michael@0:   char* limit = p + aSize;
michael@0:   MOZ_ASSERT((uintptr_t)aPtr % sizeof(uintptr_t) == 0, "bad alignment");
michael@0:   MOZ_ASSERT(aSize >= sizeof(uintptr_t), "poisoning this object has no effect");
michael@0:   for (; p < limit; p += sizeof(uintptr_t)) {
michael@0:     *((uintptr_t*)p) = POISON;
michael@0:   }
michael@0: }
michael@0: 
michael@0: /**
michael@0:  * Initialize the poison value.
michael@0:  * This should only be called once.
michael@0:  */
michael@0: extern MFBT_API void mozPoisonValueInit();
michael@0: 
michael@0: /* Values annotated by CrashReporter */
michael@0: extern MFBT_DATA uintptr_t gMozillaPoisonBase;
michael@0: extern MFBT_DATA uintptr_t gMozillaPoisonSize;
michael@0: 
michael@0: MOZ_END_EXTERN_C
michael@0: 
michael@0: #endif /* mozilla_Poison_h */