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(s: msg);
80 _Rep_base* rep = static_cast<_Rep_base*>(::operator new(sz: 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(dest: data, src: msg, n: 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(val: &rep_from_data(data_: __imp_)->count, a: 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(data_: __imp_);
97 __imp_ = s.__imp_;
98 if (__uses_refcount())
99 __libcpp_atomic_add(val: &rep_from_data(data_: __imp_)->count, a: 1);
100 if (adjust_old_count) {
101 if (__libcpp_atomic_add(val: &old_rep->count, a: count_t(-1)) < 0) {
102 ::operator delete(p: 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(data_: __imp_);
111 if (__libcpp_atomic_add(val: &rep->count, a: count_t(-1)) < 0) {
112 ::operator delete(p: 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
128