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1 // Copyright (c) 2012 The Chromium Authors. All rights reserved. | |
2 // Use of this source code is governed by a BSD-style license that can be | |
3 // found in the LICENSE file. | |
4 | |
5 // Windows doesn't support pthread_key_create's destr_function, and in fact | |
6 // it's a bit tricky to get code to run when a thread exits. This is | |
7 // cargo-cult magic from http://www.codeproject.com/threads/tls.asp. | |
8 // We are trying to be compatible with both a LoadLibrary style invocation, as | |
9 // well as static linking. This code only needs to be included if we use | |
10 // LoadLibrary, but it hooks into the "standard" set of TLS callbacks that are | |
11 // provided for static linking. | |
12 | |
13 // This code is deliberately written to match the style of calls seen in | |
14 // base/threading/thread_local_storage_win.cc. Please keep the two in sync if | |
15 // coding conventions are changed. | |
16 | |
17 // WARNING: Do *NOT* try to include this in the construction of the base | |
18 // library, even though it potentially drives code in | |
19 // base/threading/thread_local_storage_win.cc. If you do, some users will end | |
20 // up getting duplicate definition of DllMain() in some of their later links. | |
21 | |
22 // Force a reference to _tls_used to make the linker create the TLS directory | |
23 // if it's not already there (that is, even if __declspec(thread) is not used). | |
24 // Force a reference to p_thread_callback_dllmain_typical_entry to prevent whole | |
25 // program optimization from discarding the variables. | |
26 | |
27 #include <windows.h> | |
28 | |
29 #include "base/compiler_specific.h" | |
30 #include "base/win/win_util.h" | |
31 | |
32 // Indicate if another service is scanning the callbacks. When this becomes | |
33 // set to true, then DllMain() will stop supporting the callback service. This | |
34 // value is set to true the first time any of our callbacks are called, as that | |
35 // shows that some other service is handling callbacks. | |
36 static bool linker_notifications_are_active = false; | |
37 | |
38 // This will be our mostly no-op callback that we'll list. We won't | |
39 // deliberately call it, and if it is called, that means we don't need to do any | |
40 // of the callbacks anymore. We expect such a call to arrive via a | |
41 // THREAD_ATTACH message, long before we'd have to perform our THREAD_DETACH | |
42 // callbacks. | |
43 static void NTAPI on_callback(PVOID h, DWORD reason, PVOID reserved); | |
44 | |
45 #ifdef _WIN64 | |
46 | |
47 #pragma comment(linker, "/INCLUDE:_tls_used") | |
48 #pragma comment(linker, "/INCLUDE:p_thread_callback_dllmain_typical_entry") | |
49 | |
50 #else // _WIN64 | |
51 | |
52 #pragma comment(linker, "/INCLUDE:__tls_used") | |
53 #pragma comment(linker, "/INCLUDE:_p_thread_callback_dllmain_typical_entry") | |
54 | |
55 #endif // _WIN64 | |
56 | |
57 // Explicitly depend on VC\crt\src\tlssup.c variables | |
58 // to bracket the list of TLS callbacks. | |
59 extern "C" PIMAGE_TLS_CALLBACK __xl_a, __xl_z; | |
60 | |
61 // extern "C" suppresses C++ name mangling so we know the symbol names for the | |
62 // linker /INCLUDE:symbol pragmas above. | |
63 extern "C" { | |
64 #ifdef _WIN64 | |
65 | |
66 // .CRT section is merged with .rdata on x64 so it must be constant data. | |
67 #pragma data_seg(push, old_seg) | |
68 // Use a typical possible name in the .CRT$XL? list of segments. | |
69 #pragma const_seg(".CRT$XLB") | |
70 // When defining a const variable, it must have external linkage to be sure the | |
71 // linker doesn't discard it. | |
72 extern const PIMAGE_TLS_CALLBACK p_thread_callback_dllmain_typical_entry; | |
73 const PIMAGE_TLS_CALLBACK p_thread_callback_dllmain_typical_entry = on_callback; | |
74 #pragma data_seg(pop, old_seg) | |
75 | |
76 #else // _WIN64 | |
77 | |
78 #pragma data_seg(push, old_seg) | |
79 // Use a typical possible name in the .CRT$XL? list of segments. | |
80 #pragma data_seg(".CRT$XLB") | |
81 PIMAGE_TLS_CALLBACK p_thread_callback_dllmain_typical_entry = on_callback; | |
82 #pragma data_seg(pop, old_seg) | |
83 | |
84 #endif // _WIN64 | |
85 } // extern "C" | |
86 | |
87 // Custom crash code to get a unique entry in crash reports. | |
88 NOINLINE static void CrashOnProcessDetach() { | |
89 *static_cast<volatile int*>(0) = 0x356; | |
90 } | |
91 | |
92 // Make DllMain call the listed callbacks. This way any third parties that are | |
93 // linked in will also be called. | |
94 BOOL WINAPI DllMain(PVOID h, DWORD reason, PVOID reserved) { | |
95 if (DLL_PROCESS_DETACH == reason && base::win::ShouldCrashOnProcessDetach()) | |
96 CrashOnProcessDetach(); | |
97 | |
98 if (DLL_THREAD_DETACH != reason && DLL_PROCESS_DETACH != reason) | |
99 return true; // We won't service THREAD_ATTACH calls. | |
100 | |
101 if (linker_notifications_are_active) | |
102 return true; // Some other service is doing this work. | |
103 | |
104 for (PIMAGE_TLS_CALLBACK* it = &__xl_a; it < &__xl_z; ++it) { | |
105 if (*it == NULL || *it == on_callback) | |
106 continue; // Don't bother to call our own callback. | |
107 (*it)(h, reason, reserved); | |
108 } | |
109 return true; | |
110 } | |
111 | |
112 static void NTAPI on_callback(PVOID h, DWORD reason, PVOID reserved) { | |
113 // Do nothing. We were just a place holder in the list used to test that we | |
114 // call all items. | |
115 // If we are called, it means that some other system is scanning the callbacks | |
116 // and we don't need to do so in DllMain(). | |
117 linker_notifications_are_active = true; | |
118 // Note: If some other routine some how plays this same game... we could both | |
119 // decide not to do the scanning <sigh>, but this trick should suppress | |
120 // duplicate calls on Vista, where the runtime takes care of the callbacks, | |
121 // and allow us to do the callbacks on XP, where we are currently devoid of | |
122 // callbacks (due to an explicit LoadLibrary call). | |
123 } | |
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