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
36 namespace __refstring_imp {
37 namespace {
38 typedef int count_t;
39
40 struct _Rep_base {
41 std::size_t len;
42 std::size_t cap;
43 count_t count;
44 };
45
rep_from_data(const char * data_)46 inline _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
data_from_rep(_Rep_base * rep)51 inline 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)
compute_gcc_empty_string_storage()57 inline 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
get_gcc_empty_string_storage()67 inline 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
76 using namespace __refstring_imp;
77
__libcpp_refstring(const char * msg)78 inline __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
__libcpp_refstring(const __libcpp_refstring & s)89 inline __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
94 inline __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
~__libcpp_refstring()108 inline __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
__uses_refcount()117 inline 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