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-exception
  6//
  7//===----------------------------------------------------------------------===//
  8
  9#ifndef _LIBCPP_REFSTRING_H
 10#define _LIBCPP_REFSTRING_H
 11
 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 applications
 19// linking against libstdc++. The libc++ and libstdc++ exceptions are supposed
 20// to be ABI compatible, such that they can be thrown from one library and caught
 21// 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 empty
 25// string singleton before manipulating the reference count. This is done so that
 26// if an exception is created with a zero-length string in libstdc++, libc++abi
 27// 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_STORAGE
 30#  include <dlfcn.h>
 31#  include <mach-o/dyld.h>
 32#endif
 33
 34_LIBCPP_BEGIN_NAMESPACE_STD
 35
 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#endif
 72
 73} // namespace
 74} // namespace __refstring_imp
 75
 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#else
121  return true;
122#endif
123}
124
125_LIBCPP_END_NAMESPACE_STD
126
127#endif // _LIBCPP_REFSTRING_H