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/ADT/SmallString.h" 12 #include "llvm/Config/config.h" 13 #include "llvm/Support/ErrorHandling.h" 14 #include "llvm/Support/ManagedStatic.h" 15 #include "llvm/Support/Mutex.h" 16 #include "llvm/Support/ThreadLocal.h" 17 #include <cstdio> 18 #include <setjmp.h> 19 using namespace llvm; 20 21 namespace { 22 23 struct CrashRecoveryContextImpl; 24 25 static ManagedStatic<sys::ThreadLocal<const CrashRecoveryContextImpl> > CurrentContext; 26 27 struct CrashRecoveryContextImpl { 28 CrashRecoveryContext *CRC; 29 std::string Backtrace; 30 ::jmp_buf JumpBuffer; 31 volatile unsigned Failed : 1; 32 unsigned SwitchedThread : 1; 33 34 public: 35 CrashRecoveryContextImpl(CrashRecoveryContext *CRC) : CRC(CRC), 36 Failed(false), 37 SwitchedThread(false) { 38 CurrentContext->set(this); 39 } 40 ~CrashRecoveryContextImpl() { 41 if (!SwitchedThread) 42 CurrentContext->erase(); 43 } 44 45 /// \brief Called when the separate crash-recovery thread was finished, to 46 /// indicate that we don't need to clear the thread-local CurrentContext. 47 void setSwitchedThread() { SwitchedThread = true; } 48 49 void HandleCrash() { 50 // Eliminate the current context entry, to avoid re-entering in case the 51 // cleanup code crashes. 52 CurrentContext->erase(); 53 54 assert(!Failed && "Crash recovery context already failed!"); 55 Failed = true; 56 57 // FIXME: Stash the backtrace. 58 59 // Jump back to the RunSafely we were called under. 60 longjmp(JumpBuffer, 1); 61 } 62 }; 63 64 } 65 66 static ManagedStatic<sys::Mutex> gCrashRecoveryContextMutex; 67 static bool gCrashRecoveryEnabled = false; 68 69 static ManagedStatic<sys::ThreadLocal<const CrashRecoveryContextCleanup> > 70 tlIsRecoveringFromCrash; 71 72 CrashRecoveryContextCleanup::~CrashRecoveryContextCleanup() {} 73 74 CrashRecoveryContext::~CrashRecoveryContext() { 75 // Reclaim registered resources. 76 CrashRecoveryContextCleanup *i = head; 77 tlIsRecoveringFromCrash->set(head); 78 while (i) { 79 CrashRecoveryContextCleanup *tmp = i; 80 i = tmp->next; 81 tmp->cleanupFired = true; 82 tmp->recoverResources(); 83 delete tmp; 84 } 85 tlIsRecoveringFromCrash->erase(); 86 87 CrashRecoveryContextImpl *CRCI = (CrashRecoveryContextImpl *) Impl; 88 delete CRCI; 89 } 90 91 bool CrashRecoveryContext::isRecoveringFromCrash() { 92 return tlIsRecoveringFromCrash->get() != 0; 93 } 94 95 CrashRecoveryContext *CrashRecoveryContext::GetCurrent() { 96 if (!gCrashRecoveryEnabled) 97 return 0; 98 99 const CrashRecoveryContextImpl *CRCI = CurrentContext->get(); 100 if (!CRCI) 101 return 0; 102 103 return CRCI->CRC; 104 } 105 106 void CrashRecoveryContext::registerCleanup(CrashRecoveryContextCleanup *cleanup) 107 { 108 if (!cleanup) 109 return; 110 if (head) 111 head->prev = cleanup; 112 cleanup->next = head; 113 head = cleanup; 114 } 115 116 void 117 CrashRecoveryContext::unregisterCleanup(CrashRecoveryContextCleanup *cleanup) { 118 if (!cleanup) 119 return; 120 if (cleanup == head) { 121 head = cleanup->next; 122 if (head) 123 head->prev = 0; 124 } 125 else { 126 cleanup->prev->next = cleanup->next; 127 if (cleanup->next) 128 cleanup->next->prev = cleanup->prev; 129 } 130 delete cleanup; 131 } 132 133 #ifdef LLVM_ON_WIN32 134 135 #include "Windows/Windows.h" 136 137 // On Windows, we can make use of vectored exception handling to 138 // catch most crashing situations. Note that this does mean 139 // we will be alerted of exceptions *before* structured exception 140 // handling has the opportunity to catch it. But that isn't likely 141 // to cause problems because nowhere in the project is SEH being 142 // used. 143 // 144 // Vectored exception handling is built on top of SEH, and so it 145 // works on a per-thread basis. 146 // 147 // The vectored exception handler functionality was added in Windows 148 // XP, so if support for older versions of Windows is required, 149 // it will have to be added. 150 // 151 // If we want to support as far back as Win2k, we could use the 152 // SetUnhandledExceptionFilter API, but there's a risk of that 153 // being entirely overwritten (it's not a chain). 154 155 static LONG CALLBACK ExceptionHandler(PEXCEPTION_POINTERS ExceptionInfo) 156 { 157 // Lookup the current thread local recovery object. 158 const CrashRecoveryContextImpl *CRCI = CurrentContext->get(); 159 160 if (!CRCI) { 161 // Something has gone horribly wrong, so let's just tell everyone 162 // to keep searching 163 CrashRecoveryContext::Disable(); 164 return EXCEPTION_CONTINUE_SEARCH; 165 } 166 167 // TODO: We can capture the stack backtrace here and store it on the 168 // implementation if we so choose. 169 170 // Handle the crash 171 const_cast<CrashRecoveryContextImpl*>(CRCI)->HandleCrash(); 172 173 // Note that we don't actually get here because HandleCrash calls 174 // longjmp, which means the HandleCrash function never returns. 175 llvm_unreachable("Handled the crash, should have longjmp'ed out of here"); 176 } 177 178 // Because the Enable and Disable calls are static, it means that 179 // there may not actually be an Impl available, or even a current 180 // CrashRecoveryContext at all. So we make use of a thread-local 181 // exception table. The handles contained in here will either be 182 // non-NULL, valid VEH handles, or NULL. 183 static sys::ThreadLocal<const void> sCurrentExceptionHandle; 184 185 void CrashRecoveryContext::Enable() { 186 sys::ScopedLock L(*gCrashRecoveryContextMutex); 187 188 if (gCrashRecoveryEnabled) 189 return; 190 191 gCrashRecoveryEnabled = true; 192 193 // We can set up vectored exception handling now. We will install our 194 // handler as the front of the list, though there's no assurances that 195 // it will remain at the front (another call could install itself before 196 // our handler). This 1) isn't likely, and 2) shouldn't cause problems. 197 PVOID handle = ::AddVectoredExceptionHandler(1, ExceptionHandler); 198 sCurrentExceptionHandle.set(handle); 199 } 200 201 void CrashRecoveryContext::Disable() { 202 sys::ScopedLock L(*gCrashRecoveryContextMutex); 203 204 if (!gCrashRecoveryEnabled) 205 return; 206 207 gCrashRecoveryEnabled = false; 208 209 PVOID currentHandle = const_cast<PVOID>(sCurrentExceptionHandle.get()); 210 if (currentHandle) { 211 // Now we can remove the vectored exception handler from the chain 212 ::RemoveVectoredExceptionHandler(currentHandle); 213 214 // Reset the handle in our thread-local set. 215 sCurrentExceptionHandle.set(NULL); 216 } 217 } 218 219 #else 220 221 // Generic POSIX implementation. 222 // 223 // This implementation relies on synchronous signals being delivered to the 224 // current thread. We use a thread local object to keep track of the active 225 // crash recovery context, and install signal handlers to invoke HandleCrash on 226 // the active object. 227 // 228 // This implementation does not to attempt to chain signal handlers in any 229 // reliable fashion -- if we get a signal outside of a crash recovery context we 230 // simply disable crash recovery and raise the signal again. 231 232 #include <signal.h> 233 234 static const int Signals[] = { 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, 0); 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], 0); 300 } 301 302 #endif 303 304 bool CrashRecoveryContext::RunSafely(void (*Fn)(void*), void *UserData) { 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(UserData); 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 // 334 335 namespace { 336 struct RunSafelyOnThreadInfo { 337 void (*UserFn)(void*); 338 void *UserData; 339 CrashRecoveryContext *CRC; 340 bool Result; 341 }; 342 } 343 344 static void RunSafelyOnThread_Dispatch(void *UserData) { 345 RunSafelyOnThreadInfo *Info = 346 reinterpret_cast<RunSafelyOnThreadInfo*>(UserData); 347 Info->Result = Info->CRC->RunSafely(Info->UserFn, Info->UserData); 348 } 349 bool CrashRecoveryContext::RunSafelyOnThread(void (*Fn)(void*), void *UserData, 350 unsigned RequestedStackSize) { 351 RunSafelyOnThreadInfo Info = { Fn, UserData, this, false }; 352 llvm_execute_on_thread(RunSafelyOnThread_Dispatch, &Info, RequestedStackSize); 353 if (CrashRecoveryContextImpl *CRC = (CrashRecoveryContextImpl *)Impl) 354 CRC->setSwitchedThread(); 355 return Info.Result; 356 } 357