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1//===----------------------------------------------------------------------===//2//3// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.4// See https://llvm.org/LICENSE.txt for license information.5// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception6//7//===----------------------------------------------------------------------===//8 9#ifndef _LIBCPP_REFSTRING_H10#define _LIBCPP_REFSTRING_H11 12#include "atomic_support.h"13#include <__config>14#include <cstddef>15#include <cstring>16#include <stdexcept>17 18// MacOS and iOS used to ship with libstdc++, and still support old applications19// linking against libstdc++. The libc++ and libstdc++ exceptions are supposed20// to be ABI compatible, such that they can be thrown from one library and caught21// in the other.22//23// For that reason, we must look for libstdc++ in the same process and if found,24// check the string stored in the exception object to see if it is the GCC empty25// string singleton before manipulating the reference count. This is done so that26// if an exception is created with a zero-length string in libstdc++, libc++abi27// won't try to delete the memory.28#if defined(__ENVIRONMENT_MAC_OS_X_VERSION_MIN_REQUIRED__) || defined(__ENVIRONMENT_IPHONE_OS_VERSION_MIN_REQUIRED__)29# define _LIBCPP_CHECK_FOR_GCC_EMPTY_STRING_STORAGE30# include <dlfcn.h>31# include <mach-o/dyld.h>32#endif33 34_LIBCPP_BEGIN_NAMESPACE_STD35 36namespace __refstring_imp {37namespace {38typedef int count_t;39 40struct _Rep_base {41 std::size_t len;42 std::size_t cap;43 count_t count;44};45 46inline _Rep_base* rep_from_data(const char* data_) noexcept {47 char* data = const_cast<char*>(data_);48 return reinterpret_cast<_Rep_base*>(data - sizeof(_Rep_base));49}50 51inline char* data_from_rep(_Rep_base* rep) noexcept {52 char* data = reinterpret_cast<char*>(rep);53 return data + sizeof(*rep);54}55 56#if defined(_LIBCPP_CHECK_FOR_GCC_EMPTY_STRING_STORAGE)57inline const char* compute_gcc_empty_string_storage() noexcept {58 void* handle = dlopen("/usr/lib/libstdc++.6.dylib", RTLD_NOLOAD);59 if (handle == nullptr)60 return nullptr;61 void* sym = dlsym(handle, "_ZNSs4_Rep20_S_empty_rep_storageE");62 if (sym == nullptr)63 return nullptr;64 return data_from_rep(reinterpret_cast<_Rep_base*>(sym));65}66 67inline const char* get_gcc_empty_string_storage() noexcept {68 static const char* p = compute_gcc_empty_string_storage();69 return p;70}71#endif72 73} // namespace74} // namespace __refstring_imp75 76using namespace __refstring_imp;77 78inline __libcpp_refstring::__libcpp_refstring(const char* msg) {79 std::size_t len = strlen(msg);80 _Rep_base* rep = static_cast<_Rep_base*>(::operator new(sizeof(*rep) + len + 1));81 rep->len = len;82 rep->cap = len;83 rep->count = 0;84 char* data = data_from_rep(rep);85 std::memcpy(data, msg, len + 1);86 __imp_ = data;87}88 89inline __libcpp_refstring::__libcpp_refstring(const __libcpp_refstring& s) noexcept : __imp_(s.__imp_) {90 if (__uses_refcount())91 __libcpp_atomic_add(&rep_from_data(__imp_)->count, 1);92}93 94inline __libcpp_refstring& __libcpp_refstring::operator=(__libcpp_refstring const& s) noexcept {95 bool adjust_old_count = __uses_refcount();96 struct _Rep_base* old_rep = rep_from_data(__imp_);97 __imp_ = s.__imp_;98 if (__uses_refcount())99 __libcpp_atomic_add(&rep_from_data(__imp_)->count, 1);100 if (adjust_old_count) {101 if (__libcpp_atomic_add(&old_rep->count, count_t(-1)) < 0) {102 ::operator delete(old_rep);103 }104 }105 return *this;106}107 108inline __libcpp_refstring::~__libcpp_refstring() {109 if (__uses_refcount()) {110 _Rep_base* rep = rep_from_data(__imp_);111 if (__libcpp_atomic_add(&rep->count, count_t(-1)) < 0) {112 ::operator delete(rep);113 }114 }115}116 117inline bool __libcpp_refstring::__uses_refcount() const {118#if defined(_LIBCPP_CHECK_FOR_GCC_EMPTY_STRING_STORAGE)119 return __imp_ != get_gcc_empty_string_storage();120#else121 return true;122#endif123}124 125_LIBCPP_END_NAMESPACE_STD126 127#endif // _LIBCPP_REFSTRING_H128