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.
37template <class _Tp>
38struct __has_array_cookie : _Not<is_trivially_destructible<_Tp> > {};
39#else
40template <class _Tp>
41struct __has_array_cookie : false_type {};
42#endif
43
44template <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
56