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}
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.
175static sys::ThreadLocal<const void> sCurrentExceptionHandle;
176
177void 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
193void 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
226static const int Signals[] = { SIGABRT, SIGBUS, SIGFPE, SIGILL, SIGSEGV, SIGTRAP };
227static const unsigned NumSignals = sizeof(Signals) / sizeof(Signals[0]);
228static struct sigaction PrevActions[NumSignals];
229
230static 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
262void 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
281void 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
296bool 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
312void CrashRecoveryContext::HandleCrash() {
313  CrashRecoveryContextImpl *CRCI = (CrashRecoveryContextImpl *) Impl;
314  assert(CRCI && "Crash recovery context never initialized!");
315  CRCI->HandleCrash();
316}
317
318const 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
327namespace {
328struct RunSafelyOnThreadInfo {
329  void (*UserFn)(void*);
330  void *UserData;
331  CrashRecoveryContext *CRC;
332  bool Result;
333};
334}
335
336static void RunSafelyOnThread_Dispatch(void *UserData) {
337  RunSafelyOnThreadInfo *Info =
338    reinterpret_cast<RunSafelyOnThreadInfo*>(UserData);
339  Info->Result = Info->CRC->RunSafely(Info->UserFn, Info->UserData);
340}
341bool 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