1 //===--- CrashRecoveryContext.cpp - Crash Recovery ------------------------===//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
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"
21 struct CrashRecoveryContextImpl;
24 sys::ThreadLocal<const CrashRecoveryContextImpl> > CurrentContext;
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;
33 CrashRecoveryContext *CRC;
35 volatile unsigned Failed : 1;
36 unsigned SwitchedThread : 1;
39 CrashRecoveryContextImpl(CrashRecoveryContext *CRC) : CRC(CRC),
41 SwitchedThread(false) {
42 Next = CurrentContext->get();
43 CurrentContext->set(this);
45 ~CrashRecoveryContextImpl() {
47 CurrentContext->set(Next);
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;
59 // Eliminate the current context entry, to avoid re-entering in case the
60 // cleanup code crashes.
61 CurrentContext->set(Next);
63 assert(!Failed && "Crash recovery context already failed!");
66 // FIXME: Stash the backtrace.
68 // Jump back to the RunSafely we were called under.
69 longjmp(JumpBuffer, 1);
75 static ManagedStatic<sys::Mutex> gCrashRecoveryContextMutex;
76 static bool gCrashRecoveryEnabled = false;
78 static ManagedStatic<sys::ThreadLocal<const CrashRecoveryContext>>
79 tlIsRecoveringFromCrash;
81 CrashRecoveryContextCleanup::~CrashRecoveryContextCleanup() {}
83 CrashRecoveryContext::~CrashRecoveryContext() {
84 // Reclaim registered resources.
85 CrashRecoveryContextCleanup *i = head;
86 const CrashRecoveryContext *PC = tlIsRecoveringFromCrash->get();
87 tlIsRecoveringFromCrash->set(this);
89 CrashRecoveryContextCleanup *tmp = i;
91 tmp->cleanupFired = true;
92 tmp->recoverResources();
95 tlIsRecoveringFromCrash->set(PC);
97 CrashRecoveryContextImpl *CRCI = (CrashRecoveryContextImpl *) Impl;
101 bool CrashRecoveryContext::isRecoveringFromCrash() {
102 return tlIsRecoveringFromCrash->get() != nullptr;
105 CrashRecoveryContext *CrashRecoveryContext::GetCurrent() {
106 if (!gCrashRecoveryEnabled)
109 const CrashRecoveryContextImpl *CRCI = CurrentContext->get();
116 void CrashRecoveryContext::registerCleanup(CrashRecoveryContextCleanup *cleanup)
121 head->prev = cleanup;
122 cleanup->next = head;
127 CrashRecoveryContext::unregisterCleanup(CrashRecoveryContextCleanup *cleanup) {
130 if (cleanup == head) {
131 head = cleanup->next;
133 head->prev = nullptr;
136 cleanup->prev->next = cleanup->next;
138 cleanup->next->prev = cleanup->prev;
145 #include "Windows/WindowsSupport.h"
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
154 // Vectored exception handling is built on top of SEH, and so it
155 // works on a per-thread basis.
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.
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).
165 static LONG CALLBACK ExceptionHandler(PEXCEPTION_POINTERS ExceptionInfo)
167 // Lookup the current thread local recovery object.
168 const CrashRecoveryContextImpl *CRCI = CurrentContext->get();
171 // Something has gone horribly wrong, so let's just tell everyone
173 CrashRecoveryContext::Disable();
174 return EXCEPTION_CONTINUE_SEARCH;
177 // TODO: We can capture the stack backtrace here and store it on the
178 // implementation if we so choose.
181 const_cast<CrashRecoveryContextImpl*>(CRCI)->HandleCrash();
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");
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.
193 static sys::ThreadLocal<const void> sCurrentExceptionHandle;
195 void CrashRecoveryContext::Enable() {
196 sys::ScopedLock L(*gCrashRecoveryContextMutex);
198 if (gCrashRecoveryEnabled)
201 gCrashRecoveryEnabled = true;
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);
211 void CrashRecoveryContext::Disable() {
212 sys::ScopedLock L(*gCrashRecoveryContextMutex);
214 if (!gCrashRecoveryEnabled)
217 gCrashRecoveryEnabled = false;
219 PVOID currentHandle = const_cast<PVOID>(sCurrentExceptionHandle.get());
221 // Now we can remove the vectored exception handler from the chain
222 ::RemoveVectoredExceptionHandler(currentHandle);
224 // Reset the handle in our thread-local set.
225 sCurrentExceptionHandle.set(NULL);
231 // Generic POSIX implementation.
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.
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.
244 static const int Signals[] =
245 { SIGABRT, SIGBUS, SIGFPE, SIGILL, SIGSEGV, SIGTRAP };
246 static const unsigned NumSignals = array_lengthof(Signals);
247 static struct sigaction PrevActions[NumSignals];
249 static void CrashRecoverySignalHandler(int Signal) {
250 // Lookup the current thread local recovery object.
251 const CrashRecoveryContextImpl *CRCI = CurrentContext->get();
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
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.
263 // This call of Disable isn't thread safe, but it doesn't actually matter.
264 CrashRecoveryContext::Disable();
267 // The signal will be thrown once the signal mask is restored.
271 // Unblock the signal we received.
273 sigemptyset(&SigMask);
274 sigaddset(&SigMask, Signal);
275 sigprocmask(SIG_UNBLOCK, &SigMask, nullptr);
278 const_cast<CrashRecoveryContextImpl*>(CRCI)->HandleCrash();
281 void CrashRecoveryContext::Enable() {
282 sys::ScopedLock L(*gCrashRecoveryContextMutex);
284 if (gCrashRecoveryEnabled)
287 gCrashRecoveryEnabled = true;
289 // Setup the signal handler.
290 struct sigaction Handler;
291 Handler.sa_handler = CrashRecoverySignalHandler;
292 Handler.sa_flags = 0;
293 sigemptyset(&Handler.sa_mask);
295 for (unsigned i = 0; i != NumSignals; ++i) {
296 sigaction(Signals[i], &Handler, &PrevActions[i]);
300 void CrashRecoveryContext::Disable() {
301 sys::ScopedLock L(*gCrashRecoveryContextMutex);
303 if (!gCrashRecoveryEnabled)
306 gCrashRecoveryEnabled = false;
308 // Restore the previous signal handlers.
309 for (unsigned i = 0; i != NumSignals; ++i)
310 sigaction(Signals[i], &PrevActions[i], nullptr);
315 bool 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);
322 if (setjmp(CRCI->JumpBuffer) != 0) {
331 void CrashRecoveryContext::HandleCrash() {
332 CrashRecoveryContextImpl *CRCI = (CrashRecoveryContextImpl *) Impl;
333 assert(CRCI && "Crash recovery context never initialized!");
337 // FIXME: Portability.
338 static void setThreadBackgroundPriority() {
340 setpriority(PRIO_DARWIN_THREAD, 0, PRIO_DARWIN_BG);
344 static bool hasThreadBackgroundPriority() {
346 return getpriority(PRIO_DARWIN_THREAD, 0) == 1;
353 struct RunSafelyOnThreadInfo {
354 function_ref<void()> Fn;
355 CrashRecoveryContext *CRC;
356 bool UseBackgroundPriority;
361 static void RunSafelyOnThread_Dispatch(void *UserData) {
362 RunSafelyOnThreadInfo *Info =
363 reinterpret_cast<RunSafelyOnThreadInfo*>(UserData);
365 if (Info->UseBackgroundPriority)
366 setThreadBackgroundPriority();
368 Info->Result = Info->CRC->RunSafely(Info->Fn);
370 bool 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();