1 //===--- CrashRecoveryContext.cpp - Crash Recovery ------------------------===// 2 // 3 // The LLVM Compiler Infrastructure 4 // 5 // This file is distributed under the University of Illinois Open Source 6 // License. See LICENSE.TXT for details. 7 // 8 //===----------------------------------------------------------------------===// 9 10 #include "llvm/Support/CrashRecoveryContext.h" 11 #include "llvm/Config/config.h" 12 #include "llvm/Support/ErrorHandling.h" 13 #include "llvm/Support/ManagedStatic.h" 14 #include "llvm/Support/Mutex.h" 15 #include "llvm/Support/ThreadLocal.h" 16 #include <setjmp.h> 17 using namespace llvm; 18 19 namespace { 20 21 struct CrashRecoveryContextImpl; 22 23 static ManagedStatic< 24 sys::ThreadLocal<const CrashRecoveryContextImpl> > CurrentContext; 25 26 struct CrashRecoveryContextImpl { 27 CrashRecoveryContext *CRC; 28 std::string Backtrace; 29 ::jmp_buf JumpBuffer; 30 volatile unsigned Failed : 1; 31 unsigned SwitchedThread : 1; 32 33 public: 34 CrashRecoveryContextImpl(CrashRecoveryContext *CRC) : CRC(CRC), 35 Failed(false), 36 SwitchedThread(false) { 37 CurrentContext->set(this); 38 } 39 ~CrashRecoveryContextImpl() { 40 if (!SwitchedThread) 41 CurrentContext->erase(); 42 } 43 44 /// \brief Called when the separate crash-recovery thread was finished, to 45 /// indicate that we don't need to clear the thread-local CurrentContext. 46 void setSwitchedThread() { SwitchedThread = true; } 47 48 void HandleCrash() { 49 // Eliminate the current context entry, to avoid re-entering in case the 50 // cleanup code crashes. 51 CurrentContext->erase(); 52 53 assert(!Failed && "Crash recovery context already failed!"); 54 Failed = true; 55 56 // FIXME: Stash the backtrace. 57 58 // Jump back to the RunSafely we were called under. 59 longjmp(JumpBuffer, 1); 60 } 61 }; 62 63 } 64 65 static ManagedStatic<sys::Mutex> gCrashRecoveryContextMutex; 66 static bool gCrashRecoveryEnabled = false; 67 68 static ManagedStatic<sys::ThreadLocal<const CrashRecoveryContextCleanup> > 69 tlIsRecoveringFromCrash; 70 71 CrashRecoveryContextCleanup::~CrashRecoveryContextCleanup() {} 72 73 CrashRecoveryContext::~CrashRecoveryContext() { 74 // Reclaim registered resources. 75 CrashRecoveryContextCleanup *i = head; 76 tlIsRecoveringFromCrash->set(head); 77 while (i) { 78 CrashRecoveryContextCleanup *tmp = i; 79 i = tmp->next; 80 tmp->cleanupFired = true; 81 tmp->recoverResources(); 82 delete tmp; 83 } 84 tlIsRecoveringFromCrash->erase(); 85 86 CrashRecoveryContextImpl *CRCI = (CrashRecoveryContextImpl *) Impl; 87 delete CRCI; 88 } 89 90 bool CrashRecoveryContext::isRecoveringFromCrash() { 91 return tlIsRecoveringFromCrash->get() != nullptr; 92 } 93 94 CrashRecoveryContext *CrashRecoveryContext::GetCurrent() { 95 if (!gCrashRecoveryEnabled) 96 return nullptr; 97 98 const CrashRecoveryContextImpl *CRCI = CurrentContext->get(); 99 if (!CRCI) 100 return nullptr; 101 102 return CRCI->CRC; 103 } 104 105 void CrashRecoveryContext::registerCleanup(CrashRecoveryContextCleanup *cleanup) 106 { 107 if (!cleanup) 108 return; 109 if (head) 110 head->prev = cleanup; 111 cleanup->next = head; 112 head = cleanup; 113 } 114 115 void 116 CrashRecoveryContext::unregisterCleanup(CrashRecoveryContextCleanup *cleanup) { 117 if (!cleanup) 118 return; 119 if (cleanup == head) { 120 head = cleanup->next; 121 if (head) 122 head->prev = nullptr; 123 } 124 else { 125 cleanup->prev->next = cleanup->next; 126 if (cleanup->next) 127 cleanup->next->prev = cleanup->prev; 128 } 129 delete cleanup; 130 } 131 132 #ifdef LLVM_ON_WIN32 133 134 #include "Windows/WindowsSupport.h" 135 136 // On Windows, we can make use of vectored exception handling to 137 // catch most crashing situations. Note that this does mean 138 // we will be alerted of exceptions *before* structured exception 139 // handling has the opportunity to catch it. But that isn't likely 140 // to cause problems because nowhere in the project is SEH being 141 // used. 142 // 143 // Vectored exception handling is built on top of SEH, and so it 144 // works on a per-thread basis. 145 // 146 // The vectored exception handler functionality was added in Windows 147 // XP, so if support for older versions of Windows is required, 148 // it will have to be added. 149 // 150 // If we want to support as far back as Win2k, we could use the 151 // SetUnhandledExceptionFilter API, but there's a risk of that 152 // being entirely overwritten (it's not a chain). 153 154 static LONG CALLBACK ExceptionHandler(PEXCEPTION_POINTERS ExceptionInfo) 155 { 156 // Lookup the current thread local recovery object. 157 const CrashRecoveryContextImpl *CRCI = CurrentContext->get(); 158 159 if (!CRCI) { 160 // Something has gone horribly wrong, so let's just tell everyone 161 // to keep searching 162 CrashRecoveryContext::Disable(); 163 return EXCEPTION_CONTINUE_SEARCH; 164 } 165 166 // TODO: We can capture the stack backtrace here and store it on the 167 // implementation if we so choose. 168 169 // Handle the crash 170 const_cast<CrashRecoveryContextImpl*>(CRCI)->HandleCrash(); 171 172 // Note that we don't actually get here because HandleCrash calls 173 // longjmp, which means the HandleCrash function never returns. 174 llvm_unreachable("Handled the crash, should have longjmp'ed out of here"); 175 } 176 177 // Because the Enable and Disable calls are static, it means that 178 // there may not actually be an Impl available, or even a current 179 // CrashRecoveryContext at all. So we make use of a thread-local 180 // exception table. The handles contained in here will either be 181 // non-NULL, valid VEH handles, or NULL. 182 static sys::ThreadLocal<const void> sCurrentExceptionHandle; 183 184 void CrashRecoveryContext::Enable() { 185 sys::ScopedLock L(*gCrashRecoveryContextMutex); 186 187 if (gCrashRecoveryEnabled) 188 return; 189 190 gCrashRecoveryEnabled = true; 191 192 // We can set up vectored exception handling now. We will install our 193 // handler as the front of the list, though there's no assurances that 194 // it will remain at the front (another call could install itself before 195 // our handler). This 1) isn't likely, and 2) shouldn't cause problems. 196 PVOID handle = ::AddVectoredExceptionHandler(1, ExceptionHandler); 197 sCurrentExceptionHandle.set(handle); 198 } 199 200 void CrashRecoveryContext::Disable() { 201 sys::ScopedLock L(*gCrashRecoveryContextMutex); 202 203 if (!gCrashRecoveryEnabled) 204 return; 205 206 gCrashRecoveryEnabled = false; 207 208 PVOID currentHandle = const_cast<PVOID>(sCurrentExceptionHandle.get()); 209 if (currentHandle) { 210 // Now we can remove the vectored exception handler from the chain 211 ::RemoveVectoredExceptionHandler(currentHandle); 212 213 // Reset the handle in our thread-local set. 214 sCurrentExceptionHandle.set(NULL); 215 } 216 } 217 218 #else 219 220 // Generic POSIX implementation. 221 // 222 // This implementation relies on synchronous signals being delivered to the 223 // current thread. We use a thread local object to keep track of the active 224 // crash recovery context, and install signal handlers to invoke HandleCrash on 225 // the active object. 226 // 227 // This implementation does not to attempt to chain signal handlers in any 228 // reliable fashion -- if we get a signal outside of a crash recovery context we 229 // simply disable crash recovery and raise the signal again. 230 231 #include <signal.h> 232 233 static const int Signals[] = 234 { SIGABRT, SIGBUS, SIGFPE, SIGILL, SIGSEGV, SIGTRAP }; 235 static const unsigned NumSignals = sizeof(Signals) / sizeof(Signals[0]); 236 static struct sigaction PrevActions[NumSignals]; 237 238 static void CrashRecoverySignalHandler(int Signal) { 239 // Lookup the current thread local recovery object. 240 const CrashRecoveryContextImpl *CRCI = CurrentContext->get(); 241 242 if (!CRCI) { 243 // We didn't find a crash recovery context -- this means either we got a 244 // signal on a thread we didn't expect it on, the application got a signal 245 // outside of a crash recovery context, or something else went horribly 246 // wrong. 247 // 248 // Disable crash recovery and raise the signal again. The assumption here is 249 // that the enclosing application will terminate soon, and we won't want to 250 // attempt crash recovery again. 251 // 252 // This call of Disable isn't thread safe, but it doesn't actually matter. 253 CrashRecoveryContext::Disable(); 254 raise(Signal); 255 256 // The signal will be thrown once the signal mask is restored. 257 return; 258 } 259 260 // Unblock the signal we received. 261 sigset_t SigMask; 262 sigemptyset(&SigMask); 263 sigaddset(&SigMask, Signal); 264 sigprocmask(SIG_UNBLOCK, &SigMask, nullptr); 265 266 if (CRCI) 267 const_cast<CrashRecoveryContextImpl*>(CRCI)->HandleCrash(); 268 } 269 270 void CrashRecoveryContext::Enable() { 271 sys::ScopedLock L(*gCrashRecoveryContextMutex); 272 273 if (gCrashRecoveryEnabled) 274 return; 275 276 gCrashRecoveryEnabled = true; 277 278 // Setup the signal handler. 279 struct sigaction Handler; 280 Handler.sa_handler = CrashRecoverySignalHandler; 281 Handler.sa_flags = 0; 282 sigemptyset(&Handler.sa_mask); 283 284 for (unsigned i = 0; i != NumSignals; ++i) { 285 sigaction(Signals[i], &Handler, &PrevActions[i]); 286 } 287 } 288 289 void CrashRecoveryContext::Disable() { 290 sys::ScopedLock L(*gCrashRecoveryContextMutex); 291 292 if (!gCrashRecoveryEnabled) 293 return; 294 295 gCrashRecoveryEnabled = false; 296 297 // Restore the previous signal handlers. 298 for (unsigned i = 0; i != NumSignals; ++i) 299 sigaction(Signals[i], &PrevActions[i], nullptr); 300 } 301 302 #endif 303 304 bool CrashRecoveryContext::RunSafely(function_ref<void()> Fn) { 305 // If crash recovery is disabled, do nothing. 306 if (gCrashRecoveryEnabled) { 307 assert(!Impl && "Crash recovery context already initialized!"); 308 CrashRecoveryContextImpl *CRCI = new CrashRecoveryContextImpl(this); 309 Impl = CRCI; 310 311 if (setjmp(CRCI->JumpBuffer) != 0) { 312 return false; 313 } 314 } 315 316 Fn(); 317 return true; 318 } 319 320 void CrashRecoveryContext::HandleCrash() { 321 CrashRecoveryContextImpl *CRCI = (CrashRecoveryContextImpl *) Impl; 322 assert(CRCI && "Crash recovery context never initialized!"); 323 CRCI->HandleCrash(); 324 } 325 326 const std::string &CrashRecoveryContext::getBacktrace() const { 327 CrashRecoveryContextImpl *CRC = (CrashRecoveryContextImpl *) Impl; 328 assert(CRC && "Crash recovery context never initialized!"); 329 assert(CRC->Failed && "No crash was detected!"); 330 return CRC->Backtrace; 331 } 332 333 // FIXME: Portability. 334 static void setThreadBackgroundPriority() { 335 #ifdef __APPLE__ 336 setpriority(PRIO_DARWIN_THREAD, 0, PRIO_DARWIN_BG); 337 #endif 338 } 339 340 static bool hasThreadBackgroundPriority() { 341 #ifdef __APPLE__ 342 return getpriority(PRIO_DARWIN_THREAD, 0) == 1; 343 #else 344 return false; 345 #endif 346 } 347 348 namespace { 349 struct RunSafelyOnThreadInfo { 350 function_ref<void()> Fn; 351 CrashRecoveryContext *CRC; 352 bool UseBackgroundPriority; 353 bool Result; 354 }; 355 } 356 357 static void RunSafelyOnThread_Dispatch(void *UserData) { 358 RunSafelyOnThreadInfo *Info = 359 reinterpret_cast<RunSafelyOnThreadInfo*>(UserData); 360 361 if (Info->UseBackgroundPriority) 362 setThreadBackgroundPriority(); 363 364 Info->Result = Info->CRC->RunSafely(Info->Fn); 365 } 366 bool CrashRecoveryContext::RunSafelyOnThread(function_ref<void()> Fn, 367 unsigned RequestedStackSize) { 368 bool UseBackgroundPriority = hasThreadBackgroundPriority(); 369 RunSafelyOnThreadInfo Info = { Fn, this, UseBackgroundPriority, false }; 370 llvm_execute_on_thread(RunSafelyOnThread_Dispatch, &Info, RequestedStackSize); 371 if (CrashRecoveryContextImpl *CRC = (CrashRecoveryContextImpl *)Impl) 372 CRC->setSwitchedThread(); 373 return Info.Result; 374 } 375