v1/__memory/array_cookie.h

0001 // -*- C++ -*-
0002 //===----------------------------------------------------------------------===//
0003 //
0004 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
0005 // See https://llvm.org/LICENSE.txt for license information.
0006 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
0007 //
0008 //===----------------------------------------------------------------------===//
0009
0010 #ifndef _LIBCPP___MEMORY_ARRAY_COOKIE_H
0011 #define _LIBCPP___MEMORY_ARRAY_COOKIE_H
0012
0013 #include <__config>
0014 #include <__configuration/abi.h>
0015 #include <__cstddef/size_t.h>
0016 #include <__type_traits/integral_constant.h>
0017 #include <__type_traits/is_trivially_destructible.h>
0018 #include <__type_traits/negation.h>
0019
0020 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
0021 #  pragma GCC system_header
0022 #endif
0023
0024 _LIBCPP_BEGIN_NAMESPACE_STD
0025
0026 // Trait representing whether a type requires an array cookie at the start of its allocation when
0027 // allocated as `new T[n]` and deallocated as `delete[] array`.
0028 //
0029 // Under the Itanium C++ ABI [1], we know that an array cookie is available unless `T` is trivially
0030 // destructible and the call to `operator delete[]` is not a sized operator delete. Under ABIs other
0031 // than the Itanium ABI, we assume there are no array cookies.
0032 //
0033 // [1]: https://itanium-cxx-abi.github.io/cxx-abi/abi.html#array-cookies
0034 #ifdef _LIBCPP_ABI_ITANIUM
0035 // TODO: Use a builtin instead
0036 // TODO: We should factor in the choice of the usual deallocation function in this determination.
0037 template <class _Tp>
0038 struct __has_array_cookie : _Not<is_trivially_destructible<_Tp> > {};
0039 #else
0040 template <class _Tp>
0041 struct __has_array_cookie : false_type {};
0042 #endif
0043
0044 template <class _Tp>
0045 // Avoid failures when -fsanitize-address-poison-custom-array-cookie is enabled
0046 _LIBCPP_HIDE_FROM_ABI _LIBCPP_NO_SANITIZE("address") size_t __get_array_cookie(_Tp const* __ptr) {
0047   static_assert(
0048       __has_array_cookie<_Tp>::value, "Trying to access the array cookie of a type that is not guaranteed to have one");
0049   size_t const* __cookie = reinterpret_cast<size_t const*>(__ptr) - 1; // TODO: Use a builtin instead
0050   return *__cookie;
0051 }
0052
0053 _LIBCPP_END_NAMESPACE_STD
0054
0055 #endif // _LIBCPP___MEMORY_ARRAY_COOKIE_H