xref: /llvm-project/libcxxabi/src/cxa_exception_storage.cpp (revision a06c89387621b0a040e6203e7f1a2d8243f5be33)
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 //  This file implements the storage for the "Caught Exception Stack"
9 //  https://itanium-cxx-abi.github.io/cxx-abi/abi-eh.html#cxx-exc-stack
10 //
11 //===----------------------------------------------------------------------===//
12 
13 #include "cxa_exception.h"
14 
15 #include <__thread/support.h>
16 
17 #if defined(_LIBCXXABI_HAS_NO_THREADS)
18 
19 namespace __cxxabiv1 {
20 extern "C" {
21     static __cxa_eh_globals eh_globals;
22     __cxa_eh_globals *__cxa_get_globals() { return &eh_globals; }
23     __cxa_eh_globals *__cxa_get_globals_fast() { return &eh_globals; }
24 } // extern "C"
25 } // namespace __cxxabiv1
26 
27 #elif __has_feature(cxx_thread_local)
28 
29 namespace __cxxabiv1 {
30 namespace {
31     __cxa_eh_globals *__globals() {
32         static thread_local __cxa_eh_globals eh_globals;
33         return &eh_globals;
34     }
35 } // namespace
36 
37 extern "C" {
38     __cxa_eh_globals *__cxa_get_globals() { return __globals(); }
39     __cxa_eh_globals *__cxa_get_globals_fast() { return __globals(); }
40 } // extern "C"
41 } // namespace __cxxabiv1
42 
43 #else
44 
45 #include "abort_message.h"
46 #include "fallback_malloc.h"
47 
48 #if defined(__ELF__) && defined(_LIBCXXABI_LINK_PTHREAD_LIB)
49 #pragma comment(lib, "pthread")
50 #endif
51 
52 //  In general, we treat all threading errors as fatal.
53 //  We cannot call std::terminate() because that will in turn
54 //  call __cxa_get_globals() and cause infinite recursion.
55 
56 namespace __cxxabiv1 {
57 namespace {
58     std::__libcpp_tls_key key_;
59     constinit std::__libcpp_exec_once_flag flag_ = _LIBCPP_EXEC_ONCE_INITIALIZER;
60 
61     void _LIBCPP_TLS_DESTRUCTOR_CC destruct_(void *p) {
62         __free_with_fallback(p);
63         if (0 != std::__libcpp_tls_set(key_, NULL))
64             __abort_message("cannot zero out thread value for __cxa_get_globals()");
65     }
66 
67     void construct_() {
68         if (0 != std::__libcpp_tls_create(&key_, destruct_))
69             __abort_message("cannot create thread specific key for __cxa_get_globals()");
70     }
71 } // namespace
72 
73 extern "C" {
74     __cxa_eh_globals *__cxa_get_globals() {
75         // Try to get the globals for this thread
76         __cxa_eh_globals *retVal = __cxa_get_globals_fast();
77 
78         // If this is the first time we've been asked for these globals, create them
79         if (NULL == retVal) {
80             retVal = static_cast<__cxa_eh_globals*>(
81                 __calloc_with_fallback(1, sizeof(__cxa_eh_globals)));
82             if (NULL == retVal)
83                 __abort_message("cannot allocate __cxa_eh_globals");
84             if (0 != std::__libcpp_tls_set(key_, retVal))
85                __abort_message("std::__libcpp_tls_set failure in __cxa_get_globals()");
86         }
87         return retVal;
88     }
89 
90     // Note that this implementation will reliably return NULL if not
91     // preceded by a call to __cxa_get_globals().  This is an extension
92     // to the Itanium ABI and is taken advantage of in several places in
93     // libc++abi.
94     __cxa_eh_globals *__cxa_get_globals_fast() {
95         // First time through, create the key.
96         if (0 != std::__libcpp_execute_once(&flag_, construct_))
97             __abort_message("execute once failure in __cxa_get_globals_fast()");
98         return static_cast<__cxa_eh_globals*>(std::__libcpp_tls_get(key_));
99     }
100 } // extern "C"
101 } // namespace __cxxabiv1
102 
103 #endif
104