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 <__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
37namespace __refstring_imp { namespace {
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
58const 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
69inline
70const char*
71get_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
80using namespace __refstring_imp;
81
82inline
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
94inline
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
102inline
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
119inline
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
129inline
130bool __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