LCOV - code coverage report
Current view: top level - lib/Support - CrashRecoveryContext.cpp (source / functions) Hit Total Coverage
Test: llvm-toolchain.info Lines: 81 101 80.2 %
Date: 2017-09-14 15:23:50 Functions: 14 18 77.8 %
Legend: Lines: hit not hit

          Line data    Source code
       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             :   // 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             : 
      38             : public:
      39        2436 :   CrashRecoveryContextImpl(CrashRecoveryContext *CRC) : CRC(CRC),
      40             :                                                         Failed(false),
      41        2436 :                                                         SwitchedThread(false) {
      42        4872 :     Next = CurrentContext->get();
      43        4872 :     CurrentContext->set(this);
      44        2436 :   }
      45        4872 :   ~CrashRecoveryContextImpl() {
      46        2436 :     if (!SwitchedThread)
      47           5 :       CurrentContext->set(Next);
      48        2436 :   }
      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        2431 :     SwitchedThread = true;
      55             : #endif
      56             :   }
      57             : 
      58          10 :   void HandleCrash() {
      59             :     // Eliminate the current context entry, to avoid re-entering in case the
      60             :     // cleanup code crashes.
      61          20 :     CurrentContext->set(Next);
      62             : 
      63             :     assert(!Failed && "Crash recovery context already failed!");
      64          10 :     Failed = true;
      65             : 
      66             :     // FIXME: Stash the backtrace.
      67             : 
      68             :     // Jump back to the RunSafely we were called under.
      69          10 :     longjmp(JumpBuffer, 1);
      70             :   }
      71             : };
      72             : 
      73             : }
      74             : 
      75             : static ManagedStatic<sys::Mutex> gCrashRecoveryContextMutex;
      76             : static bool gCrashRecoveryEnabled = false;
      77             : 
      78             : static ManagedStatic<sys::ThreadLocal<const CrashRecoveryContext>>
      79             :        tlIsRecoveringFromCrash;
      80             : 
      81             : static void installExceptionOrSignalHandlers();
      82             : static void uninstallExceptionOrSignalHandlers();
      83             : 
      84       10953 : CrashRecoveryContextCleanup::~CrashRecoveryContextCleanup() {}
      85             : 
      86        6974 : CrashRecoveryContext::~CrashRecoveryContext() {
      87             :   // Reclaim registered resources.
      88        3487 :   CrashRecoveryContextCleanup *i = head;
      89        6974 :   const CrashRecoveryContext *PC = tlIsRecoveringFromCrash->get();
      90        3487 :   tlIsRecoveringFromCrash->set(this);
      91        3518 :   while (i) {
      92          31 :     CrashRecoveryContextCleanup *tmp = i;
      93          31 :     i = tmp->next;
      94          31 :     tmp->cleanupFired = true;
      95          31 :     tmp->recoverResources();
      96          31 :     delete tmp;
      97             :   }
      98        6974 :   tlIsRecoveringFromCrash->set(PC);
      99             :   
     100        3487 :   CrashRecoveryContextImpl *CRCI = (CrashRecoveryContextImpl *) Impl;
     101        3487 :   delete CRCI;
     102        3487 : }
     103             : 
     104           0 : bool CrashRecoveryContext::isRecoveringFromCrash() {
     105           0 :   return tlIsRecoveringFromCrash->get() != nullptr;
     106             : }
     107             : 
     108       45786 : CrashRecoveryContext *CrashRecoveryContext::GetCurrent() {
     109       45786 :   if (!gCrashRecoveryEnabled)
     110             :     return nullptr;
     111             : 
     112       22018 :   const CrashRecoveryContextImpl *CRCI = CurrentContext->get();
     113       11009 :   if (!CRCI)
     114             :     return nullptr;
     115             : 
     116       10951 :   return CRCI->CRC;
     117             : }
     118             : 
     119         937 : void CrashRecoveryContext::Enable() {
     120        2811 :   sys::ScopedLock L(*gCrashRecoveryContextMutex);
     121             :   // FIXME: Shouldn't this be a refcount or something?
     122         937 :   if (gCrashRecoveryEnabled)
     123           0 :     return;
     124         937 :   gCrashRecoveryEnabled = true;
     125         937 :   installExceptionOrSignalHandlers();
     126             : }
     127             : 
     128           0 : void CrashRecoveryContext::Disable() {
     129           0 :   sys::ScopedLock L(*gCrashRecoveryContextMutex);
     130           0 :   if (!gCrashRecoveryEnabled)
     131           0 :     return;
     132           0 :   gCrashRecoveryEnabled = false;
     133           0 :   uninstallExceptionOrSignalHandlers();
     134             : }
     135             : 
     136       10953 : void CrashRecoveryContext::registerCleanup(CrashRecoveryContextCleanup *cleanup)
     137             : {
     138       10953 :   if (!cleanup)
     139             :     return;
     140       10953 :   if (head)
     141        8586 :     head->prev = cleanup;
     142       10953 :   cleanup->next = head;
     143       10953 :   head = cleanup;
     144             : }
     145             : 
     146             : void
     147       10922 : CrashRecoveryContext::unregisterCleanup(CrashRecoveryContextCleanup *cleanup) {
     148       10922 :   if (!cleanup)
     149             :     return;
     150       10922 :   if (cleanup == head) {
     151       10922 :     head = cleanup->next;
     152       10922 :     if (head)
     153        8564 :       head->prev = nullptr;
     154             :   }
     155             :   else {
     156           0 :     cleanup->prev->next = cleanup->next;
     157           0 :     if (cleanup->next)
     158           0 :       cleanup->next->prev = cleanup->prev;
     159             :   }
     160       10922 :   delete cleanup;
     161             : }
     162             : 
     163             : #if defined(_MSC_VER)
     164             : // If _MSC_VER is defined, we must have SEH. Use it if it's available. It's way
     165             : // better than VEH. Vectored exception handling catches all exceptions happening
     166             : // on the thread with installed exception handlers, so it can interfere with
     167             : // internal exception handling of other libraries on that thread. SEH works
     168             : // exactly as you would expect normal exception handling to work: it only
     169             : // catches exceptions if they would bubble out from the stack frame with __try /
     170             : // __except.
     171             : 
     172             : static void installExceptionOrSignalHandlers() {}
     173             : static void uninstallExceptionOrSignalHandlers() {}
     174             : 
     175             : bool CrashRecoveryContext::RunSafely(function_ref<void()> Fn) {
     176             :   if (!gCrashRecoveryEnabled) {
     177             :     Fn();
     178             :     return true;
     179             :   }
     180             : 
     181             :   bool Result = true;
     182             :   __try {
     183             :     Fn();
     184             :   } __except (1) { // Catch any exception.
     185             :     Result = false;
     186             :   }
     187             :   return Result;
     188             : }
     189             : 
     190             : #else // !_MSC_VER
     191             : 
     192             : #if defined(LLVM_ON_WIN32)
     193             : // This is a non-MSVC compiler, probably mingw gcc or clang without
     194             : // -fms-extensions. Use vectored exception handling (VEH).
     195             : //
     196             : // On Windows, we can make use of vectored exception handling to catch most
     197             : // crashing situations.  Note that this does mean we will be alerted of
     198             : // exceptions *before* structured exception handling has the opportunity to
     199             : // catch it. Unfortunately, this causes problems in practice with other code
     200             : // running on threads with LLVM crash recovery contexts, so we would like to
     201             : // eventually move away from VEH.
     202             : //
     203             : // Vectored works on a per-thread basis, which is an advantage over
     204             : // SetUnhandledExceptionFilter. SetUnhandledExceptionFilter also doesn't have
     205             : // any native support for chaining exception handlers, but VEH allows more than
     206             : // one.
     207             : //
     208             : // The vectored exception handler functionality was added in Windows
     209             : // XP, so if support for older versions of Windows is required,
     210             : // it will have to be added.
     211             : 
     212             : #include "Windows/WindowsSupport.h"
     213             : 
     214             : static LONG CALLBACK ExceptionHandler(PEXCEPTION_POINTERS ExceptionInfo)
     215             : {
     216             :   // DBG_PRINTEXCEPTION_WIDE_C is not properly defined on all supported
     217             :   // compilers and platforms, so we define it manually.
     218             :   constexpr ULONG DbgPrintExceptionWideC = 0x4001000AL;
     219             :   switch (ExceptionInfo->ExceptionRecord->ExceptionCode)
     220             :   {
     221             :   case DBG_PRINTEXCEPTION_C:
     222             :   case DbgPrintExceptionWideC:
     223             :   case 0x406D1388:  // set debugger thread name
     224             :     return EXCEPTION_CONTINUE_EXECUTION;
     225             :   }
     226             : 
     227             :   // Lookup the current thread local recovery object.
     228             :   const CrashRecoveryContextImpl *CRCI = CurrentContext->get();
     229             : 
     230             :   if (!CRCI) {
     231             :     // Something has gone horribly wrong, so let's just tell everyone
     232             :     // to keep searching
     233             :     CrashRecoveryContext::Disable();
     234             :     return EXCEPTION_CONTINUE_SEARCH;
     235             :   }
     236             : 
     237             :   // TODO: We can capture the stack backtrace here and store it on the
     238             :   // implementation if we so choose.
     239             : 
     240             :   // Handle the crash
     241             :   const_cast<CrashRecoveryContextImpl*>(CRCI)->HandleCrash();
     242             : 
     243             :   // Note that we don't actually get here because HandleCrash calls
     244             :   // longjmp, which means the HandleCrash function never returns.
     245             :   llvm_unreachable("Handled the crash, should have longjmp'ed out of here");
     246             : }
     247             : 
     248             : // Because the Enable and Disable calls are static, it means that
     249             : // there may not actually be an Impl available, or even a current
     250             : // CrashRecoveryContext at all.  So we make use of a thread-local
     251             : // exception table.  The handles contained in here will either be
     252             : // non-NULL, valid VEH handles, or NULL.
     253             : static sys::ThreadLocal<const void> sCurrentExceptionHandle;
     254             : 
     255             : static void installExceptionOrSignalHandlers() {
     256             :   // We can set up vectored exception handling now.  We will install our
     257             :   // handler as the front of the list, though there's no assurances that
     258             :   // it will remain at the front (another call could install itself before
     259             :   // our handler).  This 1) isn't likely, and 2) shouldn't cause problems.
     260             :   PVOID handle = ::AddVectoredExceptionHandler(1, ExceptionHandler);
     261             :   sCurrentExceptionHandle.set(handle);
     262             : }
     263             : 
     264             : static void uninstallExceptionOrSignalHandlers() {
     265             :   PVOID currentHandle = const_cast<PVOID>(sCurrentExceptionHandle.get());
     266             :   if (currentHandle) {
     267             :     // Now we can remove the vectored exception handler from the chain
     268             :     ::RemoveVectoredExceptionHandler(currentHandle);
     269             : 
     270             :     // Reset the handle in our thread-local set.
     271             :     sCurrentExceptionHandle.set(NULL);
     272             :   }
     273             : }
     274             : 
     275             : #else // !LLVM_ON_WIN32
     276             : 
     277             : // Generic POSIX implementation.
     278             : //
     279             : // This implementation relies on synchronous signals being delivered to the
     280             : // current thread. We use a thread local object to keep track of the active
     281             : // crash recovery context, and install signal handlers to invoke HandleCrash on
     282             : // the active object.
     283             : //
     284             : // This implementation does not to attempt to chain signal handlers in any
     285             : // reliable fashion -- if we get a signal outside of a crash recovery context we
     286             : // simply disable crash recovery and raise the signal again.
     287             : 
     288             : #include <signal.h>
     289             : 
     290             : static const int Signals[] =
     291             :     { SIGABRT, SIGBUS, SIGFPE, SIGILL, SIGSEGV, SIGTRAP };
     292             : static const unsigned NumSignals = array_lengthof(Signals);
     293             : static struct sigaction PrevActions[NumSignals];
     294             : 
     295          10 : static void CrashRecoverySignalHandler(int Signal) {
     296             :   // Lookup the current thread local recovery object.
     297          20 :   const CrashRecoveryContextImpl *CRCI = CurrentContext->get();
     298             : 
     299          10 :   if (!CRCI) {
     300             :     // We didn't find a crash recovery context -- this means either we got a
     301             :     // signal on a thread we didn't expect it on, the application got a signal
     302             :     // outside of a crash recovery context, or something else went horribly
     303             :     // wrong.
     304             :     //
     305             :     // Disable crash recovery and raise the signal again. The assumption here is
     306             :     // that the enclosing application will terminate soon, and we won't want to
     307             :     // attempt crash recovery again.
     308             :     //
     309             :     // This call of Disable isn't thread safe, but it doesn't actually matter.
     310           0 :     CrashRecoveryContext::Disable();
     311           0 :     raise(Signal);
     312             : 
     313             :     // The signal will be thrown once the signal mask is restored.
     314           0 :     return;
     315             :   }
     316             : 
     317             :   // Unblock the signal we received.
     318             :   sigset_t SigMask;
     319          10 :   sigemptyset(&SigMask);
     320          10 :   sigaddset(&SigMask, Signal);
     321          10 :   sigprocmask(SIG_UNBLOCK, &SigMask, nullptr);
     322             : 
     323             :   if (CRCI)
     324          10 :     const_cast<CrashRecoveryContextImpl*>(CRCI)->HandleCrash();
     325             : }
     326             : 
     327         937 : static void installExceptionOrSignalHandlers() {
     328             :   // Setup the signal handler.
     329             :   struct sigaction Handler;
     330         937 :   Handler.sa_handler = CrashRecoverySignalHandler;
     331         937 :   Handler.sa_flags = 0;
     332         937 :   sigemptyset(&Handler.sa_mask);
     333             : 
     334        6559 :   for (unsigned i = 0; i != NumSignals; ++i) {
     335        5622 :     sigaction(Signals[i], &Handler, &PrevActions[i]);
     336             :   }
     337         937 : }
     338             : 
     339             : static void uninstallExceptionOrSignalHandlers() {
     340             :   // Restore the previous signal handlers.
     341           0 :   for (unsigned i = 0; i != NumSignals; ++i)
     342           0 :     sigaction(Signals[i], &PrevActions[i], nullptr);
     343             : }
     344             : 
     345             : #endif // !LLVM_ON_WIN32
     346             : 
     347        3487 : bool CrashRecoveryContext::RunSafely(function_ref<void()> Fn) {
     348             :   // If crash recovery is disabled, do nothing.
     349        3487 :   if (gCrashRecoveryEnabled) {
     350             :     assert(!Impl && "Crash recovery context already initialized!");
     351        2436 :     CrashRecoveryContextImpl *CRCI = new CrashRecoveryContextImpl(this);
     352        2436 :     Impl = CRCI;
     353             : 
     354        2436 :     if (setjmp(CRCI->JumpBuffer) != 0) {
     355             :       return false;
     356             :     }
     357             :   }
     358             : 
     359             :   Fn();
     360             :   return true;
     361             : }
     362             : 
     363             : #endif // !_MSC_VER
     364             : 
     365           0 : void CrashRecoveryContext::HandleCrash() {
     366           0 :   CrashRecoveryContextImpl *CRCI = (CrashRecoveryContextImpl *) Impl;
     367             :   assert(CRCI && "Crash recovery context never initialized!");
     368           0 :   CRCI->HandleCrash();
     369             : }
     370             : 
     371             : // FIXME: Portability.
     372             : static void setThreadBackgroundPriority() {
     373             : #ifdef __APPLE__
     374             :   setpriority(PRIO_DARWIN_THREAD, 0, PRIO_DARWIN_BG);
     375             : #endif
     376             : }
     377             : 
     378             : static bool hasThreadBackgroundPriority() {
     379             : #ifdef __APPLE__
     380             :   return getpriority(PRIO_DARWIN_THREAD, 0) == 1;
     381             : #else
     382             :   return false;
     383             : #endif
     384             : }
     385             : 
     386             : namespace {
     387             : struct RunSafelyOnThreadInfo {
     388             :   function_ref<void()> Fn;
     389             :   CrashRecoveryContext *CRC;
     390             :   bool UseBackgroundPriority;
     391             :   bool Result;
     392             : };
     393             : }
     394             : 
     395        3482 : static void RunSafelyOnThread_Dispatch(void *UserData) {
     396        3482 :   RunSafelyOnThreadInfo *Info =
     397             :     reinterpret_cast<RunSafelyOnThreadInfo*>(UserData);
     398             : 
     399             :   if (Info->UseBackgroundPriority)
     400             :     setThreadBackgroundPriority();
     401             : 
     402        3482 :   Info->Result = Info->CRC->RunSafely(Info->Fn);
     403        3482 : }
     404        3482 : bool CrashRecoveryContext::RunSafelyOnThread(function_ref<void()> Fn,
     405             :                                              unsigned RequestedStackSize) {
     406        3482 :   bool UseBackgroundPriority = hasThreadBackgroundPriority();
     407        3482 :   RunSafelyOnThreadInfo Info = { Fn, this, UseBackgroundPriority, false };
     408        3482 :   llvm_execute_on_thread(RunSafelyOnThread_Dispatch, &Info, RequestedStackSize);
     409        3482 :   if (CrashRecoveryContextImpl *CRC = (CrashRecoveryContextImpl *)Impl)
     410             :     CRC->setSwitchedThread();
     411        3482 :   return Info.Result;
     412             : }

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