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>
18using namespace llvm;
19
20namespace {
21
22struct CrashRecoveryContextImpl;
23
24static sys::ThreadLocal<const CrashRecoveryContextImpl> CurrentContext;
25
26struct CrashRecoveryContextImpl {
27  CrashRecoveryContext *CRC;
28  std::string Backtrace;
29  ::jmp_buf JumpBuffer;
30  volatile unsigned Failed : 1;
31
32public:
33  CrashRecoveryContextImpl(CrashRecoveryContext *CRC) : CRC(CRC),
34                                                        Failed(false) {
35    CurrentContext.set(this);
36  }
37  ~CrashRecoveryContextImpl() {
38    CurrentContext.erase();
39  }
40
41  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
58static sys::Mutex gCrashRecoveryContexMutex;
59static bool gCrashRecoveryEnabled = false;
60
61static sys::ThreadLocal<const CrashRecoveryContextCleanup>
62       tlIsRecoveringFromCrash;
63
64CrashRecoveryContextCleanup::~CrashRecoveryContextCleanup() {}
65
66CrashRecoveryContext::~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
83bool CrashRecoveryContext::isRecoveringFromCrash() {
84  return tlIsRecoveringFromCrash.get() != 0;
85}
86
87CrashRecoveryContext *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
98void 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
108void
109CrashRecoveryContext::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
147static 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  return EXCEPTION_CONTINUE_SEARCH;
169}
170
171// Because the Enable and Disable calls are static, it means that
172// there may not actually be an Impl available, or even a current
173// CrashRecoveryContext at all.  So we make use of a thread-local
174// exception table.  The handles contained in here will either be
175// non-NULL, valid VEH handles, or NULL.
176static sys::ThreadLocal<const void> sCurrentExceptionHandle;
177
178void CrashRecoveryContext::Enable() {
179  sys::ScopedLock L(gCrashRecoveryContexMutex);
180
181  if (gCrashRecoveryEnabled)
182    return;
183
184  gCrashRecoveryEnabled = true;
185
186  // We can set up vectored exception handling now.  We will install our
187  // handler as the front of the list, though there's no assurances that
188  // it will remain at the front (another call could install itself before
189  // our handler).  This 1) isn't likely, and 2) shouldn't cause problems.
190  PVOID handle = ::AddVectoredExceptionHandler(1, ExceptionHandler);
191  sCurrentExceptionHandle.set(handle);
192}
193
194void CrashRecoveryContext::Disable() {
195  sys::ScopedLock L(gCrashRecoveryContexMutex);
196
197  if (!gCrashRecoveryEnabled)
198    return;
199
200  gCrashRecoveryEnabled = false;
201
202  PVOID currentHandle = const_cast<PVOID>(sCurrentExceptionHandle.get());
203  if (currentHandle) {
204    // Now we can remove the vectored exception handler from the chain
205    ::RemoveVectoredExceptionHandler(currentHandle);
206
207    // Reset the handle in our thread-local set.
208    sCurrentExceptionHandle.set(NULL);
209  }
210}
211
212#else
213
214// Generic POSIX implementation.
215//
216// This implementation relies on synchronous signals being delivered to the
217// current thread. We use a thread local object to keep track of the active
218// crash recovery context, and install signal handlers to invoke HandleCrash on
219// the active object.
220//
221// This implementation does not to attempt to chain signal handlers in any
222// reliable fashion -- if we get a signal outside of a crash recovery context we
223// simply disable crash recovery and raise the signal again.
224
225#include <signal.h>
226
227static int Signals[] = { SIGABRT, SIGBUS, SIGFPE, SIGILL, SIGSEGV, SIGTRAP };
228static const unsigned NumSignals = sizeof(Signals) / sizeof(Signals[0]);
229static struct sigaction PrevActions[NumSignals];
230
231static void CrashRecoverySignalHandler(int Signal) {
232  // Lookup the current thread local recovery object.
233  const CrashRecoveryContextImpl *CRCI = CurrentContext.get();
234
235  if (!CRCI) {
236    // We didn't find a crash recovery context -- this means either we got a
237    // signal on a thread we didn't expect it on, the application got a signal
238    // outside of a crash recovery context, or something else went horribly
239    // wrong.
240    //
241    // Disable crash recovery and raise the signal again. The assumption here is
242    // that the enclosing application will terminate soon, and we won't want to
243    // attempt crash recovery again.
244    //
245    // This call of Disable isn't thread safe, but it doesn't actually matter.
246    CrashRecoveryContext::Disable();
247    raise(Signal);
248
249    // The signal will be thrown once the signal mask is restored.
250    return;
251  }
252
253  // Unblock the signal we received.
254  sigset_t SigMask;
255  sigemptyset(&SigMask);
256  sigaddset(&SigMask, Signal);
257  sigprocmask(SIG_UNBLOCK, &SigMask, 0);
258
259  if (CRCI)
260    const_cast<CrashRecoveryContextImpl*>(CRCI)->HandleCrash();
261}
262
263void CrashRecoveryContext::Enable() {
264  sys::ScopedLock L(gCrashRecoveryContexMutex);
265
266  if (gCrashRecoveryEnabled)
267    return;
268
269  gCrashRecoveryEnabled = true;
270
271#ifdef ENABLE_SIGNAL_OVERRIDES
272  // Setup the signal handler.
273  struct sigaction Handler;
274  Handler.sa_handler = CrashRecoverySignalHandler;
275  Handler.sa_flags = 0;
276  sigemptyset(&Handler.sa_mask);
277
278  for (unsigned i = 0; i != NumSignals; ++i) {
279    sigaction(Signals[i], &Handler, &PrevActions[i]);
280  }
281#endif
282}
283
284void CrashRecoveryContext::Disable() {
285  sys::ScopedLock L(gCrashRecoveryContexMutex);
286
287  if (!gCrashRecoveryEnabled)
288    return;
289
290  gCrashRecoveryEnabled = false;
291
292#ifdef ENABLE_SIGNAL_OVERRIDES
293  // Restore the previous signal handlers.
294  for (unsigned i = 0; i != NumSignals; ++i)
295    sigaction(Signals[i], &PrevActions[i], 0);
296#endif
297}
298
299#endif
300
301bool CrashRecoveryContext::RunSafely(void (*Fn)(void*), void *UserData) {
302  // If crash recovery is disabled, do nothing.
303  if (gCrashRecoveryEnabled) {
304    assert(!Impl && "Crash recovery context already initialized!");
305    CrashRecoveryContextImpl *CRCI = new CrashRecoveryContextImpl(this);
306    Impl = CRCI;
307
308    if (setjmp(CRCI->JumpBuffer) != 0) {
309      return false;
310    }
311  }
312
313  Fn(UserData);
314  return true;
315}
316
317void CrashRecoveryContext::HandleCrash() {
318  CrashRecoveryContextImpl *CRCI = (CrashRecoveryContextImpl *) Impl;
319  assert(CRCI && "Crash recovery context never initialized!");
320  CRCI->HandleCrash();
321}
322
323const std::string &CrashRecoveryContext::getBacktrace() const {
324  CrashRecoveryContextImpl *CRC = (CrashRecoveryContextImpl *) Impl;
325  assert(CRC && "Crash recovery context never initialized!");
326  assert(CRC->Failed && "No crash was detected!");
327  return CRC->Backtrace;
328}
329
330//
331
332namespace {
333struct RunSafelyOnThreadInfo {
334  void (*UserFn)(void*);
335  void *UserData;
336  CrashRecoveryContext *CRC;
337  bool Result;
338};
339}
340
341static void RunSafelyOnThread_Dispatch(void *UserData) {
342  RunSafelyOnThreadInfo *Info =
343    reinterpret_cast<RunSafelyOnThreadInfo*>(UserData);
344  Info->Result = Info->CRC->RunSafely(Info->UserFn, Info->UserData);
345}
346bool CrashRecoveryContext::RunSafelyOnThread(void (*Fn)(void*), void *UserData,
347                                             unsigned RequestedStackSize) {
348  RunSafelyOnThreadInfo Info = { Fn, UserData, this, false };
349  llvm_execute_on_thread(RunSafelyOnThread_Dispatch, &Info, RequestedStackSize);
350  return Info.Result;
351}
352