1 //===------------------------ __refstring ---------------------------------===//
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 <__config>
13 #include <stdexcept>
14 #include <cstddef>
15 #include <cstring>
16 #include "atomic_support.h"
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__) || \
29 defined(__ENVIRONMENT_IPHONE_OS_VERSION_MIN_REQUIRED__)
30 # define _LIBCPP_CHECK_FOR_GCC_EMPTY_STRING_STORAGE
31 # include <dlfcn.h>
32 # include <mach-o/dyld.h>
33 #endif
34
35 _LIBCPP_BEGIN_NAMESPACE_STD
36
37 namespace __refstring_imp { 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)
57 inline
compute_gcc_empty_string_storage()58 const char* compute_gcc_empty_string_storage() _NOEXCEPT
59 {
60 void* handle = dlopen("/usr/lib/libstdc++.6.dylib", RTLD_NOLOAD);
61 if (handle == nullptr)
62 return nullptr;
63 void* sym = dlsym(handle, "_ZNSs4_Rep20_S_empty_rep_storageE");
64 if (sym == nullptr)
65 return nullptr;
66 return data_from_rep(reinterpret_cast<_Rep_base *>(sym));
67 }
68
69 inline
70 const char*
get_gcc_empty_string_storage()71 get_gcc_empty_string_storage() _NOEXCEPT
72 {
73 static const char* p = compute_gcc_empty_string_storage();
74 return p;
75 }
76 #endif
77
78 }} // namespace __refstring_imp
79
80 using namespace __refstring_imp;
81
82 inline
__libcpp_refstring(const char * msg)83 __libcpp_refstring::__libcpp_refstring(const char* msg) {
84 std::size_t len = strlen(msg);
85 _Rep_base* rep = static_cast<_Rep_base *>(::operator new(sizeof(*rep) + len + 1));
86 rep->len = len;
87 rep->cap = len;
88 rep->count = 0;
89 char *data = data_from_rep(rep);
90 std::memcpy(data, msg, len + 1);
91 __imp_ = data;
92 }
93
94 inline
__libcpp_refstring(const __libcpp_refstring & s)95 __libcpp_refstring::__libcpp_refstring(const __libcpp_refstring &s) _NOEXCEPT
96 : __imp_(s.__imp_)
97 {
98 if (__uses_refcount())
99 __libcpp_atomic_add(&rep_from_data(__imp_)->count, 1);
100 }
101
102 inline
103 __libcpp_refstring& __libcpp_refstring::operator=(__libcpp_refstring const& s) _NOEXCEPT {
104 bool adjust_old_count = __uses_refcount();
105 struct _Rep_base *old_rep = rep_from_data(__imp_);
106 __imp_ = s.__imp_;
107 if (__uses_refcount())
108 __libcpp_atomic_add(&rep_from_data(__imp_)->count, 1);
109 if (adjust_old_count)
110 {
111 if (__libcpp_atomic_add(&old_rep->count, count_t(-1)) < 0)
112 {
113 ::operator delete(old_rep);
114 }
115 }
116 return *this;
117 }
118
119 inline
~__libcpp_refstring()120 __libcpp_refstring::~__libcpp_refstring() {
121 if (__uses_refcount()) {
122 _Rep_base* rep = rep_from_data(__imp_);
123 if (__libcpp_atomic_add(&rep->count, count_t(-1)) < 0) {
124 ::operator delete(rep);
125 }
126 }
127 }
128
129 inline
__uses_refcount()130 bool __libcpp_refstring::__uses_refcount() const {
131 #if defined(_LIBCPP_CHECK_FOR_GCC_EMPTY_STRING_STORAGE)
132 return __imp_ != get_gcc_empty_string_storage();
133 #else
134 return true;
135 #endif
136 }
137
138 _LIBCPP_END_NAMESPACE_STD
139
140 #endif //_LIBCPP_REFSTRING_H
141