lib/Support/CrashRecoveryContext.cpp

   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/System/Mutex.h"
  14 #include "llvm/System/ThreadLocal.h"
  15 #include <setjmp.h>
  16 #include <cstdio>
  17 using namespace llvm;
  18
  19 namespace {
  20
  21 struct CrashRecoveryContextImpl;
  22
  23 static sys::ThreadLocal<const CrashRecoveryContextImpl> CurrentContext;
  24
  25 struct CrashRecoveryContextImpl {
  26   CrashRecoveryContext *CRC;
  27   std::string Backtrace;
  28   ::jmp_buf JumpBuffer;
  29   volatile unsigned Failed : 1;
  30
  31 public:
  32   CrashRecoveryContextImpl(CrashRecoveryContext *CRC) : CRC(CRC),
  33                                                         Failed(false) {
  34     CurrentContext.set(this);
  35   }
  36   ~CrashRecoveryContextImpl() {
  37     CurrentContext.erase();
  38   }
  39
  40   void HandleCrash() {
  41     // Eliminate the current context entry, to avoid re-entering in case the
  42     // cleanup code crashes.
  43     CurrentContext.erase();
  44
  45     assert(!Failed && "Crash recovery context already failed!");
  46     Failed = true;
  47
  48     // FIXME: Stash the backtrace.
  49
  50     // Jump back to the RunSafely we were called under.
  51     longjmp(JumpBuffer, 1);
  52   }
  53 };
  54
  55 }
  56
  57 static sys::Mutex gCrashRecoveryContexMutex;
  58 static bool gCrashRecoveryEnabled = false;
  59
  60 CrashRecoveryContext::~CrashRecoveryContext() {
  61   CrashRecoveryContextImpl *CRCI = (CrashRecoveryContextImpl *) Impl;
  62   delete CRCI;
  63 }
  64
  65 CrashRecoveryContext *CrashRecoveryContext::GetCurrent() {
  66   const CrashRecoveryContextImpl *CRCI = CurrentContext.get();
  67   if (!CRCI)
  68     return 0;
  69
  70   return CRCI->CRC;
  71 }
  72
  73 #ifdef LLVM_ON_WIN32
  74
  75 // FIXME: No real Win32 implementation currently.
  76
  77 void CrashRecoveryContext::Enable() {
  78   sys::ScopedLock L(gCrashRecoveryContexMutex);
  79
  80   if (gCrashRecoveryEnabled)
  81     return;
  82
  83   gCrashRecoveryEnabled = true;
  84 }
  85
  86 void CrashRecoveryContext::Disable() {
  87   sys::ScopedLock L(gCrashRecoveryContexMutex);
  88
  89   if (!gCrashRecoveryEnabled)
  90     return;
  91
  92   gCrashRecoveryEnabled = false;
  93 }
  94
  95 #else
  96
  97 // Generic POSIX implementation.
  98 //
  99 // This implementation relies on synchronous signals being delivered to the
 100 // current thread. We use a thread local object to keep track of the active
 101 // crash recovery context, and install signal handlers to invoke HandleCrash on
 102 // the active object.
 103 //
 104 // This implementation does not to attempt to chain signal handlers in any
 105 // reliable fashion -- if we get a signal outside of a crash recovery context we
 106 // simply disable crash recovery and raise the signal again.
 107
 108 #include <signal.h>
 109
 110 static int Signals[] = { SIGABRT, SIGBUS, SIGFPE, SIGILL, SIGSEGV, SIGTRAP };
 111 static const unsigned NumSignals = sizeof(Signals) / sizeof(Signals[0]);
 112 static struct sigaction PrevActions[NumSignals];
 113
 114 static void CrashRecoverySignalHandler(int Signal) {
 115   // Lookup the current thread local recovery object.
 116   const CrashRecoveryContextImpl *CRCI = CurrentContext.get();
 117
 118   if (!CRCI) {
 119     // We didn't find a crash recovery context -- this means either we got a
 120     // signal on a thread we didn't expect it on, the application got a signal
 121     // outside of a crash recovery context, or something else went horribly
 122     // wrong.
 123     //
 124     // Disable crash recovery and raise the signal again. The assumption here is
 125     // that the enclosing application will terminate soon, and we won't want to
 126     // attempt crash recovery again.
 127     //
 128     // This call of Disable isn't thread safe, but it doesn't actually matter.
 129     CrashRecoveryContext::Disable();
 130     raise(Signal);
 131
 132     // The signal will be thrown once the signal mask is restored.
 133     return;
 134   }
 135
 136   // Unblock the signal we received.
 137   sigset_t SigMask;
 138   sigemptyset(&SigMask);
 139   sigaddset(&SigMask, Signal);
 140   sigprocmask(SIG_UNBLOCK, &SigMask, 0);
 141
 142   if (CRCI)
 143     const_cast<CrashRecoveryContextImpl*>(CRCI)->HandleCrash();
 144 }
 145
 146 void CrashRecoveryContext::Enable() {
 147   sys::ScopedLock L(gCrashRecoveryContexMutex);
 148
 149   if (gCrashRecoveryEnabled)
 150     return;
 151
 152   gCrashRecoveryEnabled = true;
 153
 154   // Setup the signal handler.
 155   struct sigaction Handler;
 156   Handler.sa_handler = CrashRecoverySignalHandler;
 157   Handler.sa_flags = 0;
 158   sigemptyset(&Handler.sa_mask);
 159
 160   for (unsigned i = 0; i != NumSignals; ++i) {
 161     sigaction(Signals[i], &Handler, &PrevActions[i]);
 162   }
 163 }
 164
 165 void CrashRecoveryContext::Disable() {
 166   sys::ScopedLock L(gCrashRecoveryContexMutex);
 167
 168   if (!gCrashRecoveryEnabled)
 169     return;
 170
 171   gCrashRecoveryEnabled = false;
 172
 173   // Restore the previous signal handlers.
 174   for (unsigned i = 0; i != NumSignals; ++i)
 175     sigaction(Signals[i], &PrevActions[i], 0);
 176 }
 177
 178 #endif
 179
 180 bool CrashRecoveryContext::RunSafely(void (*Fn)(void*), void *UserData) {
 181   // If crash recovery is disabled, do nothing.
 182   if (gCrashRecoveryEnabled) {
 183     assert(!Impl && "Crash recovery context already initialized!");
 184     CrashRecoveryContextImpl *CRCI = new CrashRecoveryContextImpl(this);
 185     Impl = CRCI;
 186
 187     if (setjmp(CRCI->JumpBuffer) != 0) {
 188       return false;
 189     }
 190   }
 191
 192   Fn(UserData);
 193   return true;
 194 }
 195
 196 void CrashRecoveryContext::HandleCrash() {
 197   CrashRecoveryContextImpl *CRCI = (CrashRecoveryContextImpl *) Impl;
 198   assert(CRCI && "Crash recovery context never initialized!");
 199   CRCI->HandleCrash();
 200 }
 201
 202 const std::string &CrashRecoveryContext::getBacktrace() const {
 203   CrashRecoveryContextImpl *CRC = (CrashRecoveryContextImpl *) Impl;
 204   assert(CRC && "Crash recovery context never initialized!");
 205   assert(CRC->Failed && "No crash was detected!");
 206   return CRC->Backtrace;
 207 }