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 } 169 170 // Because the Enable and Disable calls are static, it means that 171 // there may not actually be an Impl available, or even a current 172 // CrashRecoveryContext at all. So we make use of a thread-local 173 // exception table. The handles contained in here will either be 174 // non-NULL, valid VEH handles, or NULL. 175 static sys::ThreadLocal<const void> sCurrentExceptionHandle; 176 177 void CrashRecoveryContext::Enable() { 178 sys::ScopedLock L(gCrashRecoveryContexMutex); 179 180 if (gCrashRecoveryEnabled) 181 return; 182 183 gCrashRecoveryEnabled = true; 184 185 // We can set up vectored exception handling now. We will install our 186 // handler as the front of the list, though there's no assurances that 187 // it will remain at the front (another call could install itself before 188 // our handler). This 1) isn't likely, and 2) shouldn't cause problems. 189 PVOID handle = ::AddVectoredExceptionHandler(1, ExceptionHandler); 190 sCurrentExceptionHandle.set(handle); 191 } 192 193 void CrashRecoveryContext::Disable() { 194 sys::ScopedLock L(gCrashRecoveryContexMutex); 195 196 if (!gCrashRecoveryEnabled) 197 return; 198 199 gCrashRecoveryEnabled = false; 200 201 PVOID currentHandle = const_cast<PVOID>(sCurrentExceptionHandle.get()); 202 if (currentHandle) { 203 // Now we can remove the vectored exception handler from the chain 204 ::RemoveVectoredExceptionHandler(currentHandle); 205 206 // Reset the handle in our thread-local set. 207 sCurrentExceptionHandle.set(NULL); 208 } 209 } 210 211 #else 212 213 // Generic POSIX implementation. 214 // 215 // This implementation relies on synchronous signals being delivered to the 216 // current thread. We use a thread local object to keep track of the active 217 // crash recovery context, and install signal handlers to invoke HandleCrash on 218 // the active object. 219 // 220 // This implementation does not to attempt to chain signal handlers in any 221 // reliable fashion -- if we get a signal outside of a crash recovery context we 222 // simply disable crash recovery and raise the signal again. 223 224 #include <signal.h> 225 226 static int Signals[] = { SIGABRT, SIGBUS, SIGFPE, SIGILL, SIGSEGV, SIGTRAP }; 227 static const unsigned NumSignals = sizeof(Signals) / sizeof(Signals[0]); 228 static struct sigaction PrevActions[NumSignals]; 229 230 static void CrashRecoverySignalHandler(int Signal) { 231 // Lookup the current thread local recovery object. 232 const CrashRecoveryContextImpl *CRCI = CurrentContext.get(); 233 234 if (!CRCI) { 235 // We didn't find a crash recovery context -- this means either we got a 236 // signal on a thread we didn't expect it on, the application got a signal 237 // outside of a crash recovery context, or something else went horribly 238 // wrong. 239 // 240 // Disable crash recovery and raise the signal again. The assumption here is 241 // that the enclosing application will terminate soon, and we won't want to 242 // attempt crash recovery again. 243 // 244 // This call of Disable isn't thread safe, but it doesn't actually matter. 245 CrashRecoveryContext::Disable(); 246 raise(Signal); 247 248 // The signal will be thrown once the signal mask is restored. 249 return; 250 } 251 252 // Unblock the signal we received. 253 sigset_t SigMask; 254 sigemptyset(&SigMask); 255 sigaddset(&SigMask, Signal); 256 sigprocmask(SIG_UNBLOCK, &SigMask, 0); 257 258 if (CRCI) 259 const_cast<CrashRecoveryContextImpl*>(CRCI)->HandleCrash(); 260 } 261 262 void CrashRecoveryContext::Enable() { 263 sys::ScopedLock L(gCrashRecoveryContexMutex); 264 265 if (gCrashRecoveryEnabled) 266 return; 267 268 gCrashRecoveryEnabled = true; 269 270 // Setup the signal handler. 271 struct sigaction Handler; 272 Handler.sa_handler = CrashRecoverySignalHandler; 273 Handler.sa_flags = 0; 274 sigemptyset(&Handler.sa_mask); 275 276 for (unsigned i = 0; i != NumSignals; ++i) { 277 sigaction(Signals[i], &Handler, &PrevActions[i]); 278 } 279 } 280 281 void CrashRecoveryContext::Disable() { 282 sys::ScopedLock L(gCrashRecoveryContexMutex); 283 284 if (!gCrashRecoveryEnabled) 285 return; 286 287 gCrashRecoveryEnabled = false; 288 289 // Restore the previous signal handlers. 290 for (unsigned i = 0; i != NumSignals; ++i) 291 sigaction(Signals[i], &PrevActions[i], 0); 292 } 293 294 #endif 295 296 bool CrashRecoveryContext::RunSafely(void (*Fn)(void*), void *UserData) { 297 // If crash recovery is disabled, do nothing. 298 if (gCrashRecoveryEnabled) { 299 assert(!Impl && "Crash recovery context already initialized!"); 300 CrashRecoveryContextImpl *CRCI = new CrashRecoveryContextImpl(this); 301 Impl = CRCI; 302 303 if (setjmp(CRCI->JumpBuffer) != 0) { 304 return false; 305 } 306 } 307 308 Fn(UserData); 309 return true; 310 } 311 312 void CrashRecoveryContext::HandleCrash() { 313 CrashRecoveryContextImpl *CRCI = (CrashRecoveryContextImpl *) Impl; 314 assert(CRCI && "Crash recovery context never initialized!"); 315 CRCI->HandleCrash(); 316 } 317 318 const std::string &CrashRecoveryContext::getBacktrace() const { 319 CrashRecoveryContextImpl *CRC = (CrashRecoveryContextImpl *) Impl; 320 assert(CRC && "Crash recovery context never initialized!"); 321 assert(CRC->Failed && "No crash was detected!"); 322 return CRC->Backtrace; 323 } 324 325 // 326 327 namespace { 328 struct RunSafelyOnThreadInfo { 329 void (*UserFn)(void*); 330 void *UserData; 331 CrashRecoveryContext *CRC; 332 bool Result; 333 }; 334 } 335 336 static void RunSafelyOnThread_Dispatch(void *UserData) { 337 RunSafelyOnThreadInfo *Info = 338 reinterpret_cast<RunSafelyOnThreadInfo*>(UserData); 339 Info->Result = Info->CRC->RunSafely(Info->UserFn, Info->UserData); 340 } 341 bool CrashRecoveryContext::RunSafelyOnThread(void (*Fn)(void*), void *UserData, 342 unsigned RequestedStackSize) { 343 RunSafelyOnThreadInfo Info = { Fn, UserData, this, false }; 344 llvm_execute_on_thread(RunSafelyOnThread_Dispatch, &Info, RequestedStackSize); 345 return Info.Result; 346 } 347