• Home
  • Line#
  • Scopes#
  • Navigate#
  • Raw
  • Download
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:
CrashRecoveryContextImpl__anona80752490111::CrashRecoveryContextImpl33   CrashRecoveryContextImpl(CrashRecoveryContext *CRC) : CRC(CRC),
34                                                         Failed(false) {
35     CurrentContext.set(this);
36   }
~CrashRecoveryContextImpl__anona80752490111::CrashRecoveryContextImpl37   ~CrashRecoveryContextImpl() {
38     CurrentContext.erase();
39   }
40 
HandleCrash__anona80752490111::CrashRecoveryContextImpl41   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 
~CrashRecoveryContextCleanup()64 CrashRecoveryContextCleanup::~CrashRecoveryContextCleanup() {}
65 
~CrashRecoveryContext()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 
isRecoveringFromCrash()83 bool CrashRecoveryContext::isRecoveringFromCrash() {
84   return tlIsRecoveringFromCrash.get() != 0;
85 }
86 
GetCurrent()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 
registerCleanup(CrashRecoveryContextCleanup * cleanup)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
unregisterCleanup(CrashRecoveryContextCleanup * cleanup)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 
ExceptionHandler(PEXCEPTION_POINTERS ExceptionInfo)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 
Enable()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 
Disable()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 const 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 
CrashRecoverySignalHandler(int Signal)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 
Enable()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 
Disable()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 
RunSafely(void (* Fn)(void *),void * UserData)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 
HandleCrash()312 void CrashRecoveryContext::HandleCrash() {
313   CrashRecoveryContextImpl *CRCI = (CrashRecoveryContextImpl *) Impl;
314   assert(CRCI && "Crash recovery context never initialized!");
315   CRCI->HandleCrash();
316 }
317 
getBacktrace() const318 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 
RunSafelyOnThread_Dispatch(void * UserData)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 }
RunSafelyOnThread(void (* Fn)(void *),void * UserData,unsigned RequestedStackSize)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