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 56