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 } 124
