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