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> 17using namespace llvm; 18 19namespace { 20 21struct CrashRecoveryContextImpl; 22 23static ManagedStatic< 24 sys::ThreadLocal<const CrashRecoveryContextImpl> > CurrentContext; 25 26struct CrashRecoveryContextImpl { 27 // When threads are disabled, this links up all active 28 // CrashRecoveryContextImpls. When threads are enabled there's one thread 29 // per CrashRecoveryContext and CurrentContext is a thread-local, so only one 30 // CrashRecoveryContextImpl is active per thread and this is always null. 31 const CrashRecoveryContextImpl *Next; 32 33 CrashRecoveryContext *CRC; 34 ::jmp_buf JumpBuffer; 35 volatile unsigned Failed : 1; 36 unsigned SwitchedThread : 1; 37 38public: 39 CrashRecoveryContextImpl(CrashRecoveryContext *CRC) : CRC(CRC), 40 Failed(false), 41 SwitchedThread(false) { 42 Next = CurrentContext->get(); 43 CurrentContext->set(this); 44 } 45 ~CrashRecoveryContextImpl() { 46 if (!SwitchedThread) 47 CurrentContext->set(Next); 48 } 49 50 /// \brief Called when the separate crash-recovery thread was finished, to 51 /// indicate that we don't need to clear the thread-local CurrentContext. 52 void setSwitchedThread() { 53#if defined(LLVM_ENABLE_THREADS) && LLVM_ENABLE_THREADS != 0 54 SwitchedThread = true; 55#endif 56 } 57 58 void HandleCrash() { 59 // Eliminate the current context entry, to avoid re-entering in case the 60 // cleanup code crashes. 61 CurrentContext->set(Next); 62 63 assert(!Failed && "Crash recovery context already failed!"); 64 Failed = true; 65 66 // FIXME: Stash the backtrace. 67 68 // Jump back to the RunSafely we were called under. 69 longjmp(JumpBuffer, 1); 70 } 71}; 72 73} 74 75static ManagedStatic<sys::Mutex> gCrashRecoveryContextMutex; 76static bool gCrashRecoveryEnabled = false; 77 78static ManagedStatic<sys::ThreadLocal<const CrashRecoveryContext>> 79 tlIsRecoveringFromCrash; 80 81CrashRecoveryContextCleanup::~CrashRecoveryContextCleanup() {} 82 83CrashRecoveryContext::~CrashRecoveryContext() { 84 // Reclaim registered resources. 85 CrashRecoveryContextCleanup *i = head; 86 const CrashRecoveryContext *PC = tlIsRecoveringFromCrash->get(); 87 tlIsRecoveringFromCrash->set(this); 88 while (i) { 89 CrashRecoveryContextCleanup *tmp = i; 90 i = tmp->next; 91 tmp->cleanupFired = true; 92 tmp->recoverResources(); 93 delete tmp; 94 } 95 tlIsRecoveringFromCrash->set(PC); 96 97 CrashRecoveryContextImpl *CRCI = (CrashRecoveryContextImpl *) Impl; 98 delete CRCI; 99} 100 101bool CrashRecoveryContext::isRecoveringFromCrash() { 102 return tlIsRecoveringFromCrash->get() != nullptr; 103} 104 105CrashRecoveryContext *CrashRecoveryContext::GetCurrent() { 106 if (!gCrashRecoveryEnabled) 107 return nullptr; 108 109 const CrashRecoveryContextImpl *CRCI = CurrentContext->get(); 110 if (!CRCI) 111 return nullptr; 112 113 return CRCI->CRC; 114} 115 116void CrashRecoveryContext::registerCleanup(CrashRecoveryContextCleanup *cleanup) 117{ 118 if (!cleanup) 119 return; 120 if (head) 121 head->prev = cleanup; 122 cleanup->next = head; 123 head = cleanup; 124} 125 126void 127CrashRecoveryContext::unregisterCleanup(CrashRecoveryContextCleanup *cleanup) { 128 if (!cleanup) 129 return; 130 if (cleanup == head) { 131 head = cleanup->next; 132 if (head) 133 head->prev = nullptr; 134 } 135 else { 136 cleanup->prev->next = cleanup->next; 137 if (cleanup->next) 138 cleanup->next->prev = cleanup->prev; 139 } 140 delete cleanup; 141} 142 143#ifdef LLVM_ON_WIN32 144 145#include "Windows/WindowsSupport.h" 146 147// On Windows, we can make use of vectored exception handling to 148// catch most crashing situations. Note that this does mean 149// we will be alerted of exceptions *before* structured exception 150// handling has the opportunity to catch it. But that isn't likely 151// to cause problems because nowhere in the project is SEH being 152// used. 153// 154// Vectored exception handling is built on top of SEH, and so it 155// works on a per-thread basis. 156// 157// The vectored exception handler functionality was added in Windows 158// XP, so if support for older versions of Windows is required, 159// it will have to be added. 160// 161// If we want to support as far back as Win2k, we could use the 162// SetUnhandledExceptionFilter API, but there's a risk of that 163// being entirely overwritten (it's not a chain). 164 165static LONG CALLBACK ExceptionHandler(PEXCEPTION_POINTERS ExceptionInfo) 166{ 167 // Lookup the current thread local recovery object. 168 const CrashRecoveryContextImpl *CRCI = CurrentContext->get(); 169 170 if (!CRCI) { 171 // Something has gone horribly wrong, so let's just tell everyone 172 // to keep searching 173 CrashRecoveryContext::Disable(); 174 return EXCEPTION_CONTINUE_SEARCH; 175 } 176 177 // TODO: We can capture the stack backtrace here and store it on the 178 // implementation if we so choose. 179 180 // Handle the crash 181 const_cast<CrashRecoveryContextImpl*>(CRCI)->HandleCrash(); 182 183 // Note that we don't actually get here because HandleCrash calls 184 // longjmp, which means the HandleCrash function never returns. 185 llvm_unreachable("Handled the crash, should have longjmp'ed out of here"); 186} 187 188// Because the Enable and Disable calls are static, it means that 189// there may not actually be an Impl available, or even a current 190// CrashRecoveryContext at all. So we make use of a thread-local 191// exception table. The handles contained in here will either be 192// non-NULL, valid VEH handles, or NULL. 193static sys::ThreadLocal<const void> sCurrentExceptionHandle; 194 195void CrashRecoveryContext::Enable() { 196 sys::ScopedLock L(*gCrashRecoveryContextMutex); 197 198 if (gCrashRecoveryEnabled) 199 return; 200 201 gCrashRecoveryEnabled = true; 202 203 // We can set up vectored exception handling now. We will install our 204 // handler as the front of the list, though there's no assurances that 205 // it will remain at the front (another call could install itself before 206 // our handler). This 1) isn't likely, and 2) shouldn't cause problems. 207 PVOID handle = ::AddVectoredExceptionHandler(1, ExceptionHandler); 208 sCurrentExceptionHandle.set(handle); 209} 210 211void CrashRecoveryContext::Disable() { 212 sys::ScopedLock L(*gCrashRecoveryContextMutex); 213 214 if (!gCrashRecoveryEnabled) 215 return; 216 217 gCrashRecoveryEnabled = false; 218 219 PVOID currentHandle = const_cast<PVOID>(sCurrentExceptionHandle.get()); 220 if (currentHandle) { 221 // Now we can remove the vectored exception handler from the chain 222 ::RemoveVectoredExceptionHandler(currentHandle); 223 224 // Reset the handle in our thread-local set. 225 sCurrentExceptionHandle.set(NULL); 226 } 227} 228 229#else 230 231// Generic POSIX implementation. 232// 233// This implementation relies on synchronous signals being delivered to the 234// current thread. We use a thread local object to keep track of the active 235// crash recovery context, and install signal handlers to invoke HandleCrash on 236// the active object. 237// 238// This implementation does not to attempt to chain signal handlers in any 239// reliable fashion -- if we get a signal outside of a crash recovery context we 240// simply disable crash recovery and raise the signal again. 241 242#include <signal.h> 243 244static const int Signals[] = 245 { SIGABRT, SIGBUS, SIGFPE, SIGILL, SIGSEGV, SIGTRAP }; 246static const unsigned NumSignals = array_lengthof(Signals); 247static struct sigaction PrevActions[NumSignals]; 248 249static void CrashRecoverySignalHandler(int Signal) { 250 // Lookup the current thread local recovery object. 251 const CrashRecoveryContextImpl *CRCI = CurrentContext->get(); 252 253 if (!CRCI) { 254 // We didn't find a crash recovery context -- this means either we got a 255 // signal on a thread we didn't expect it on, the application got a signal 256 // outside of a crash recovery context, or something else went horribly 257 // wrong. 258 // 259 // Disable crash recovery and raise the signal again. The assumption here is 260 // that the enclosing application will terminate soon, and we won't want to 261 // attempt crash recovery again. 262 // 263 // This call of Disable isn't thread safe, but it doesn't actually matter. 264 CrashRecoveryContext::Disable(); 265 raise(Signal); 266 267 // The signal will be thrown once the signal mask is restored. 268 return; 269 } 270 271 // Unblock the signal we received. 272 sigset_t SigMask; 273 sigemptyset(&SigMask); 274 sigaddset(&SigMask, Signal); 275 sigprocmask(SIG_UNBLOCK, &SigMask, nullptr); 276 277 if (CRCI) 278 const_cast<CrashRecoveryContextImpl*>(CRCI)->HandleCrash(); 279} 280 281void CrashRecoveryContext::Enable() { 282 sys::ScopedLock L(*gCrashRecoveryContextMutex); 283 284 if (gCrashRecoveryEnabled) 285 return; 286 287 gCrashRecoveryEnabled = true; 288 289 // Setup the signal handler. 290 struct sigaction Handler; 291 Handler.sa_handler = CrashRecoverySignalHandler; 292 Handler.sa_flags = 0; 293 sigemptyset(&Handler.sa_mask); 294 295 for (unsigned i = 0; i != NumSignals; ++i) { 296 sigaction(Signals[i], &Handler, &PrevActions[i]); 297 } 298} 299 300void CrashRecoveryContext::Disable() { 301 sys::ScopedLock L(*gCrashRecoveryContextMutex); 302 303 if (!gCrashRecoveryEnabled) 304 return; 305 306 gCrashRecoveryEnabled = false; 307 308 // Restore the previous signal handlers. 309 for (unsigned i = 0; i != NumSignals; ++i) 310 sigaction(Signals[i], &PrevActions[i], nullptr); 311} 312 313#endif 314 315bool CrashRecoveryContext::RunSafely(function_ref<void()> Fn) { 316 // If crash recovery is disabled, do nothing. 317 if (gCrashRecoveryEnabled) { 318 assert(!Impl && "Crash recovery context already initialized!"); 319 CrashRecoveryContextImpl *CRCI = new CrashRecoveryContextImpl(this); 320 Impl = CRCI; 321 322 if (setjmp(CRCI->JumpBuffer) != 0) { 323 return false; 324 } 325 } 326 327 Fn(); 328 return true; 329} 330 331void CrashRecoveryContext::HandleCrash() { 332 CrashRecoveryContextImpl *CRCI = (CrashRecoveryContextImpl *) Impl; 333 assert(CRCI && "Crash recovery context never initialized!"); 334 CRCI->HandleCrash(); 335} 336 337// FIXME: Portability. 338static void setThreadBackgroundPriority() { 339#ifdef __APPLE__ 340 setpriority(PRIO_DARWIN_THREAD, 0, PRIO_DARWIN_BG); 341#endif 342} 343 344static bool hasThreadBackgroundPriority() { 345#ifdef __APPLE__ 346 return getpriority(PRIO_DARWIN_THREAD, 0) == 1; 347#else 348 return false; 349#endif 350} 351 352namespace { 353struct RunSafelyOnThreadInfo { 354 function_ref<void()> Fn; 355 CrashRecoveryContext *CRC; 356 bool UseBackgroundPriority; 357 bool Result; 358}; 359} 360 361static void RunSafelyOnThread_Dispatch(void *UserData) { 362 RunSafelyOnThreadInfo *Info = 363 reinterpret_cast<RunSafelyOnThreadInfo*>(UserData); 364 365 if (Info->UseBackgroundPriority) 366 setThreadBackgroundPriority(); 367 368 Info->Result = Info->CRC->RunSafely(Info->Fn); 369} 370bool CrashRecoveryContext::RunSafelyOnThread(function_ref<void()> Fn, 371 unsigned RequestedStackSize) { 372 bool UseBackgroundPriority = hasThreadBackgroundPriority(); 373 RunSafelyOnThreadInfo Info = { Fn, this, UseBackgroundPriority, false }; 374 llvm_execute_on_thread(RunSafelyOnThread_Dispatch, &Info, RequestedStackSize); 375 if (CrashRecoveryContextImpl *CRC = (CrashRecoveryContextImpl *)Impl) 376 CRC->setSwitchedThread(); 377 return Info.Result; 378} 379