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libcxx: backport llvm/llvm-project#160182
https://github.com/llvm/llvm-project/pull/160182
This commit is contained in:
Alex Rønne Petersen
parent
671428359e
commit
2357ae06dd
12
lib/libcxx/include/__configuration/abi.h
vendored
12
lib/libcxx/include/__configuration/abi.h
vendored
@ -30,8 +30,20 @@
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#elif _LIBCPP_ABI_FORCE_MICROSOFT
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# define _LIBCPP_ABI_MICROSOFT
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#else
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// Windows uses the Microsoft ABI
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# if defined(_WIN32) && defined(_MSC_VER)
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# define _LIBCPP_ABI_MICROSOFT
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// 32-bit ARM uses the Itanium ABI with a few differences (array cookies, etc),
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// and so does 64-bit ARM on Apple platforms.
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# elif defined(__arm__) || (defined(__APPLE__) && defined(__aarch64__))
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# define _LIBCPP_ABI_ITANIUM_WITH_ARM_DIFFERENCES
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// Non-Apple 64-bit ARM uses the vanilla Itanium ABI
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# elif defined(__aarch64__)
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# define _LIBCPP_ABI_ITANIUM
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// We assume that other architectures also use the vanilla Itanium ABI too
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# else
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# define _LIBCPP_ABI_ITANIUM
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# endif
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84
lib/libcxx/include/__memory/array_cookie.h
vendored
84
lib/libcxx/include/__memory/array_cookie.h
vendored
@ -13,6 +13,7 @@
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#include <__config>
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#include <__configuration/abi.h>
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#include <__cstddef/size_t.h>
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#include <__memory/addressof.h>
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#include <__type_traits/integral_constant.h>
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#include <__type_traits/is_trivially_destructible.h>
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#include <__type_traits/negation.h>
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@ -26,14 +27,15 @@ _LIBCPP_BEGIN_NAMESPACE_STD
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// Trait representing whether a type requires an array cookie at the start of its allocation when
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// allocated as `new T[n]` and deallocated as `delete[] array`.
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//
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// Under the Itanium C++ ABI [1], we know that an array cookie is available unless `T` is trivially
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// destructible and the call to `operator delete[]` is not a sized operator delete. Under ABIs other
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// than the Itanium ABI, we assume there are no array cookies.
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// Under the Itanium C++ ABI [1] and the ARM ABI which derives from it, we know that an array cookie is available
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// unless `T` is trivially destructible and the call to `operator delete[]` is not a sized operator delete. Under
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// other ABIs, we assume there are no array cookies.
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//
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// [1]: https://itanium-cxx-abi.github.io/cxx-abi/abi.html#array-cookies
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#ifdef _LIBCPP_ABI_ITANIUM
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#if defined(_LIBCPP_ABI_ITANIUM) || defined(_LIBCPP_ABI_ITANIUM_WITH_ARM_DIFFERENCES)
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// TODO: Use a builtin instead
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// TODO: We should factor in the choice of the usual deallocation function in this determination.
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// TODO: We should factor in the choice of the usual deallocation function in this determination:
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// a cookie may be available in more cases but we ignore those for now.
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template <class _Tp>
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struct __has_array_cookie : _Not<is_trivially_destructible<_Tp> > {};
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#else
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@ -41,13 +43,79 @@ template <class _Tp>
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struct __has_array_cookie : false_type {};
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#endif
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struct __itanium_array_cookie {
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size_t __element_count;
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};
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template <class _Tp>
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struct [[__gnu__::__aligned__(_LIBCPP_ALIGNOF(_Tp))]] __arm_array_cookie {
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size_t __element_size;
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size_t __element_count;
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};
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// Return the element count in the array cookie located before the given pointer.
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//
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// In the Itanium ABI [1]
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// ----------------------
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// The element count is stored immediately before the first element of the array. If the preferred alignment
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// of array elements (which is different from the ABI alignment) is more than that of size_t, additional
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// padding bytes exist before the array cookie. Assuming array elements of size and alignment 16 bytes, that
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// gives us the following layout:
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//
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// |ooooooooxxxxxxxxaaaaaaaaaaaaaaaabbbbbbbbbbbbbbbbccccccccccccccccdddddddddddddddd|
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// ^^^^^^^^ ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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// | ^^^^^^^^ |
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// | | array elements
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// padding |
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// element count
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//
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//
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// In the Itanium ABI with ARM differences [2]
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// -------------------------------------------
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// The array cookie is stored at the very start of the allocation and it has the following form:
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//
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// struct array_cookie {
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// std::size_t element_size; // element_size != 0
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// std::size_t element_count;
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// };
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//
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// Assuming elements of size and alignment 32 bytes, this gives us the following layout:
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//
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// |xxxxxxxxXXXXXXXXooooooooooooooooaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaabbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb|
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// ^^^^^^^^ ^^^^^^^^^^^^^^^^
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// | ^^^^^^^^ | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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// element size | padding |
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// element count array elements
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//
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// We must be careful to take into account the alignment of the array cookie, which may result in padding
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// bytes between the element count and the first element of the array. Note that for ARM, the compiler
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// aligns the array cookie using the ABI alignment, not the preferred alignment of array elements.
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//
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// [1]: https://itanium-cxx-abi.github.io/cxx-abi/abi.html#array-cookies
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// [2]: https://developer.apple.com/documentation/xcode/writing-arm64-code-for-apple-platforms#Handle-C++-differences
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template <class _Tp>
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// Avoid failures when -fsanitize-address-poison-custom-array-cookie is enabled
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_LIBCPP_HIDE_FROM_ABI _LIBCPP_NO_SANITIZE("address") size_t __get_array_cookie(_Tp const* __ptr) {
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_LIBCPP_HIDE_FROM_ABI _LIBCPP_NO_SANITIZE("address") size_t __get_array_cookie([[__maybe_unused__]] _Tp const* __ptr) {
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static_assert(
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__has_array_cookie<_Tp>::value, "Trying to access the array cookie of a type that is not guaranteed to have one");
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size_t const* __cookie = reinterpret_cast<size_t const*>(__ptr) - 1; // TODO: Use a builtin instead
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return *__cookie;
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#if defined(_LIBCPP_ABI_ITANIUM)
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using _ArrayCookie = __itanium_array_cookie;
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#elif defined(_LIBCPP_ABI_ITANIUM_WITH_ARM_DIFFERENCES)
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using _ArrayCookie = __arm_array_cookie<_Tp>;
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#else
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static_assert(false, "The array cookie layout is unknown on this ABI");
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struct _ArrayCookie { // dummy definition required to make the function parse
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size_t element_count;
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};
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#endif
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char const* __array_cookie_start = reinterpret_cast<char const*>(__ptr) - sizeof(_ArrayCookie);
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_ArrayCookie __cookie;
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// This is necessary to avoid violating strict aliasing. It's valid because _ArrayCookie is an
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// implicit lifetime type.
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__builtin_memcpy(std::addressof(__cookie), __array_cookie_start, sizeof(_ArrayCookie));
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return __cookie.__element_count;
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}
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_LIBCPP_END_NAMESPACE_STD
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