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. 36static 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. 43static 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. 59extern "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. 63extern "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. 72extern const PIMAGE_TLS_CALLBACK p_thread_callback_dllmain_typical_entry; 73const 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") 81PIMAGE_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. 88NOINLINE 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. 94BOOL 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 112static 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