libcxx/include/__memory/array_cookie.h

   1 // -*- C++ -*-
   2 //===----------------------------------------------------------------------===//
   3 //
   4 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
   5 // See https://llvm.org/LICENSE.txt for license information.
   6 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
   7 //
   8 //===----------------------------------------------------------------------===//
   9
  10 #ifndef _LIBCPP___MEMORY_ARRAY_COOKIE_H
  11 #define _LIBCPP___MEMORY_ARRAY_COOKIE_H
  12
  13 #include <__config>
  14 #include <__configuration/abi.h>
  15 #include <__cstddef/size_t.h>
  16 #include <__type_traits/integral_constant.h>
  17 #include <__type_traits/is_trivially_destructible.h>
  18 #include <__type_traits/negation.h>
  19
  20 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
  21 #  pragma GCC system_header
  22 #endif
  23
  24 _LIBCPP_BEGIN_NAMESPACE_STD
  25
  26 // Trait representing whether a type requires an array cookie at the start of its allocation when
  27 // allocated as `new T[n]` and deallocated as `delete[] array`.
  28 //
  29 // Under the Itanium C++ ABI [1], we know that an array cookie is available unless `T` is trivially
  30 // destructible and the call to `operator delete[]` is not a sized operator delete. Under ABIs other
  31 // than the Itanium ABI, we assume there are no array cookies.
  32 //
  33 // [1]: https://itanium-cxx-abi.github.io/cxx-abi/abi.html#array-cookies
  34 #ifdef _LIBCPP_ABI_ITANIUM
  35 // TODO: Use a builtin instead
  36 // TODO: We should factor in the choice of the usual deallocation function in this determination.
  37 template <class _Tp>
  38 struct __has_array_cookie : _Not<is_trivially_destructible<_Tp> > {};
  39 #else
  40 template <class _Tp>
  41 struct __has_array_cookie : false_type {};
  42 #endif
  43
  44 template <class _Tp>
  45 // Avoid failures when -fsanitize-address-poison-custom-array-cookie is enabled
  46 _LIBCPP_HIDE_FROM_ABI _LIBCPP_NO_SANITIZE("address") size_t __get_array_cookie(_Tp const* __ptr) {
  47   static_assert(
  48       __has_array_cookie<_Tp>::value, "Trying to access the array cookie of a type that is not guaranteed to have one");
  49   size_t const* __cookie = reinterpret_cast<size_t const*>(__ptr) - 1; // TODO: Use a builtin instead
  50   return *__cookie;
  51 }
  52
  53 _LIBCPP_END_NAMESPACE_STD
  54
  55 #endif // _LIBCPP___MEMORY_ARRAY_COOKIE_H