llvm.org GIT mirror llvm / stable lib / Support / CrashRecoveryContext.cpp
stable

Tree @stable (Download .tar.gz)

CrashRecoveryContext.cpp @stableraw · history · blame

  1
  2
  3
  4
  5
  6
  7
  8
  9
 10
 11
 12
 13
 14
 15
 16
 17
 18
 19
 20
 21
 22
 23
 24
 25
 26
 27
 28
 29
 30
 31
 32
 33
 34
 35
 36
 37
 38
 39
 40
 41
 42
 43
 44
 45
 46
 47
 48
 49
 50
 51
 52
 53
 54
 55
 56
 57
 58
 59
 60
 61
 62
 63
 64
 65
 66
 67
 68
 69
 70
 71
 72
 73
 74
 75
 76
 77
 78
 79
 80
 81
 82
 83
 84
 85
 86
 87
 88
 89
 90
 91
 92
 93
 94
 95
 96
 97
 98
 99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
//===--- CrashRecoveryContext.cpp - Crash Recovery ------------------------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//

#include "llvm/Support/CrashRecoveryContext.h"
#include "llvm/Config/llvm-config.h"
#include "llvm/Support/ErrorHandling.h"
#include "llvm/Support/ManagedStatic.h"
#include "llvm/Support/Mutex.h"
#include "llvm/Support/ThreadLocal.h"
#include <setjmp.h>
using namespace llvm;

namespace {

struct CrashRecoveryContextImpl;

static ManagedStatic<
    sys::ThreadLocal<const CrashRecoveryContextImpl> > CurrentContext;

struct CrashRecoveryContextImpl {
  // When threads are disabled, this links up all active
  // CrashRecoveryContextImpls.  When threads are enabled there's one thread
  // per CrashRecoveryContext and CurrentContext is a thread-local, so only one
  // CrashRecoveryContextImpl is active per thread and this is always null.
  const CrashRecoveryContextImpl *Next;

  CrashRecoveryContext *CRC;
  ::jmp_buf JumpBuffer;
  volatile unsigned Failed : 1;
  unsigned SwitchedThread : 1;

public:
  CrashRecoveryContextImpl(CrashRecoveryContext *CRC) : CRC(CRC),
                                                        Failed(false),
                                                        SwitchedThread(false) {
    Next = CurrentContext->get();
    CurrentContext->set(this);
  }
  ~CrashRecoveryContextImpl() {
    if (!SwitchedThread)
      CurrentContext->set(Next);
  }

  /// Called when the separate crash-recovery thread was finished, to
  /// indicate that we don't need to clear the thread-local CurrentContext.
  void setSwitchedThread() {
#if defined(LLVM_ENABLE_THREADS) && LLVM_ENABLE_THREADS != 0
    SwitchedThread = true;
#endif
  }

  void HandleCrash() {
    // Eliminate the current context entry, to avoid re-entering in case the
    // cleanup code crashes.
    CurrentContext->set(Next);

    assert(!Failed && "Crash recovery context already failed!");
    Failed = true;

    // FIXME: Stash the backtrace.

    // Jump back to the RunSafely we were called under.
    longjmp(JumpBuffer, 1);
  }
};

}

static ManagedStatic<sys::Mutex> gCrashRecoveryContextMutex;
static bool gCrashRecoveryEnabled = false;

static ManagedStatic<sys::ThreadLocal<const CrashRecoveryContext>>
       tlIsRecoveringFromCrash;

static void installExceptionOrSignalHandlers();
static void uninstallExceptionOrSignalHandlers();

CrashRecoveryContextCleanup::~CrashRecoveryContextCleanup() {}

CrashRecoveryContext::~CrashRecoveryContext() {
  // Reclaim registered resources.
  CrashRecoveryContextCleanup *i = head;
  const CrashRecoveryContext *PC = tlIsRecoveringFromCrash->get();
  tlIsRecoveringFromCrash->set(this);
  while (i) {
    CrashRecoveryContextCleanup *tmp = i;
    i = tmp->next;
    tmp->cleanupFired = true;
    tmp->recoverResources();
    delete tmp;
  }
  tlIsRecoveringFromCrash->set(PC);

  CrashRecoveryContextImpl *CRCI = (CrashRecoveryContextImpl *) Impl;
  delete CRCI;
}

bool CrashRecoveryContext::isRecoveringFromCrash() {
  return tlIsRecoveringFromCrash->get() != nullptr;
}

CrashRecoveryContext *CrashRecoveryContext::GetCurrent() {
  if (!gCrashRecoveryEnabled)
    return nullptr;

  const CrashRecoveryContextImpl *CRCI = CurrentContext->get();
  if (!CRCI)
    return nullptr;

  return CRCI->CRC;
}

void CrashRecoveryContext::Enable() {
  sys::ScopedLock L(*gCrashRecoveryContextMutex);
  // FIXME: Shouldn't this be a refcount or something?
  if (gCrashRecoveryEnabled)
    return;
  gCrashRecoveryEnabled = true;
  installExceptionOrSignalHandlers();
}

void CrashRecoveryContext::Disable() {
  sys::ScopedLock L(*gCrashRecoveryContextMutex);
  if (!gCrashRecoveryEnabled)
    return;
  gCrashRecoveryEnabled = false;
  uninstallExceptionOrSignalHandlers();
}

void CrashRecoveryContext::registerCleanup(CrashRecoveryContextCleanup *cleanup)
{
  if (!cleanup)
    return;
  if (head)
    head->prev = cleanup;
  cleanup->next = head;
  head = cleanup;
}

void
CrashRecoveryContext::unregisterCleanup(CrashRecoveryContextCleanup *cleanup) {
  if (!cleanup)
    return;
  if (cleanup == head) {
    head = cleanup->next;
    if (head)
      head->prev = nullptr;
  }
  else {
    cleanup->prev->next = cleanup->next;
    if (cleanup->next)
      cleanup->next->prev = cleanup->prev;
  }
  delete cleanup;
}

#if defined(_MSC_VER)
// If _MSC_VER is defined, we must have SEH. Use it if it's available. It's way
// better than VEH. Vectored exception handling catches all exceptions happening
// on the thread with installed exception handlers, so it can interfere with
// internal exception handling of other libraries on that thread. SEH works
// exactly as you would expect normal exception handling to work: it only
// catches exceptions if they would bubble out from the stack frame with __try /
// __except.

static void installExceptionOrSignalHandlers() {}
static void uninstallExceptionOrSignalHandlers() {}

bool CrashRecoveryContext::RunSafely(function_ref<void()> Fn) {
  if (!gCrashRecoveryEnabled) {
    Fn();
    return true;
  }

  bool Result = true;
  __try {
    Fn();
  } __except (1) { // Catch any exception.
    Result = false;
  }
  return Result;
}

#else // !_MSC_VER

#if defined(_WIN32)
// This is a non-MSVC compiler, probably mingw gcc or clang without
// -fms-extensions. Use vectored exception handling (VEH).
//
// On Windows, we can make use of vectored exception handling to catch most
// crashing situations.  Note that this does mean we will be alerted of
// exceptions *before* structured exception handling has the opportunity to
// catch it. Unfortunately, this causes problems in practice with other code
// running on threads with LLVM crash recovery contexts, so we would like to
// eventually move away from VEH.
//
// Vectored works on a per-thread basis, which is an advantage over
// SetUnhandledExceptionFilter. SetUnhandledExceptionFilter also doesn't have
// any native support for chaining exception handlers, but VEH allows more than
// one.
//
// The vectored exception handler functionality was added in Windows
// XP, so if support for older versions of Windows is required,
// it will have to be added.

#include "Windows/WindowsSupport.h"

static LONG CALLBACK ExceptionHandler(PEXCEPTION_POINTERS ExceptionInfo)
{
  // DBG_PRINTEXCEPTION_WIDE_C is not properly defined on all supported
  // compilers and platforms, so we define it manually.
  constexpr ULONG DbgPrintExceptionWideC = 0x4001000AL;
  switch (ExceptionInfo->ExceptionRecord->ExceptionCode)
  {
  case DBG_PRINTEXCEPTION_C:
  case DbgPrintExceptionWideC:
  case 0x406D1388:  // set debugger thread name
    return EXCEPTION_CONTINUE_EXECUTION;
  }

  // Lookup the current thread local recovery object.
  const CrashRecoveryContextImpl *CRCI = CurrentContext->get();

  if (!CRCI) {
    // Something has gone horribly wrong, so let's just tell everyone
    // to keep searching
    CrashRecoveryContext::Disable();
    return EXCEPTION_CONTINUE_SEARCH;
  }

  // TODO: We can capture the stack backtrace here and store it on the
  // implementation if we so choose.

  // Handle the crash
  const_cast<CrashRecoveryContextImpl*>(CRCI)->HandleCrash();

  // Note that we don't actually get here because HandleCrash calls
  // longjmp, which means the HandleCrash function never returns.
  llvm_unreachable("Handled the crash, should have longjmp'ed out of here");
}

// Because the Enable and Disable calls are static, it means that
// there may not actually be an Impl available, or even a current
// CrashRecoveryContext at all.  So we make use of a thread-local
// exception table.  The handles contained in here will either be
// non-NULL, valid VEH handles, or NULL.
static sys::ThreadLocal<const void> sCurrentExceptionHandle;

static void installExceptionOrSignalHandlers() {
  // We can set up vectored exception handling now.  We will install our
  // handler as the front of the list, though there's no assurances that
  // it will remain at the front (another call could install itself before
  // our handler).  This 1) isn't likely, and 2) shouldn't cause problems.
  PVOID handle = ::AddVectoredExceptionHandler(1, ExceptionHandler);
  sCurrentExceptionHandle.set(handle);
}

static void uninstallExceptionOrSignalHandlers() {
  PVOID currentHandle = const_cast<PVOID>(sCurrentExceptionHandle.get());
  if (currentHandle) {
    // Now we can remove the vectored exception handler from the chain
    ::RemoveVectoredExceptionHandler(currentHandle);

    // Reset the handle in our thread-local set.
    sCurrentExceptionHandle.set(NULL);
  }
}

#else // !_WIN32

// Generic POSIX implementation.
//
// This implementation relies on synchronous signals being delivered to the
// current thread. We use a thread local object to keep track of the active
// crash recovery context, and install signal handlers to invoke HandleCrash on
// the active object.
//
// This implementation does not to attempt to chain signal handlers in any
// reliable fashion -- if we get a signal outside of a crash recovery context we
// simply disable crash recovery and raise the signal again.

#include <signal.h>

static const int Signals[] =
    { SIGABRT, SIGBUS, SIGFPE, SIGILL, SIGSEGV, SIGTRAP };
static const unsigned NumSignals = array_lengthof(Signals);
static struct sigaction PrevActions[NumSignals];

static void CrashRecoverySignalHandler(int Signal) {
  // Lookup the current thread local recovery object.
  const CrashRecoveryContextImpl *CRCI = CurrentContext->get();

  if (!CRCI) {
    // We didn't find a crash recovery context -- this means either we got a
    // signal on a thread we didn't expect it on, the application got a signal
    // outside of a crash recovery context, or something else went horribly
    // wrong.
    //
    // Disable crash recovery and raise the signal again. The assumption here is
    // that the enclosing application will terminate soon, and we won't want to
    // attempt crash recovery again.
    //
    // This call of Disable isn't thread safe, but it doesn't actually matter.
    CrashRecoveryContext::Disable();
    raise(Signal);

    // The signal will be thrown once the signal mask is restored.
    return;
  }

  // Unblock the signal we received.
  sigset_t SigMask;
  sigemptyset(&SigMask);
  sigaddset(&SigMask, Signal);
  sigprocmask(SIG_UNBLOCK, &SigMask, nullptr);

  if (CRCI)
    const_cast<CrashRecoveryContextImpl*>(CRCI)->HandleCrash();
}

static void installExceptionOrSignalHandlers() {
  // Setup the signal handler.
  struct sigaction Handler;
  Handler.sa_handler = CrashRecoverySignalHandler;
  Handler.sa_flags = 0;
  sigemptyset(&Handler.sa_mask);

  for (unsigned i = 0; i != NumSignals; ++i) {
    sigaction(Signals[i], &Handler, &PrevActions[i]);
  }
}

static void uninstallExceptionOrSignalHandlers() {
  // Restore the previous signal handlers.
  for (unsigned i = 0; i != NumSignals; ++i)
    sigaction(Signals[i], &PrevActions[i], nullptr);
}

#endif // !_WIN32

bool CrashRecoveryContext::RunSafely(function_ref<void()> Fn) {
  // If crash recovery is disabled, do nothing.
  if (gCrashRecoveryEnabled) {
    assert(!Impl && "Crash recovery context already initialized!");
    CrashRecoveryContextImpl *CRCI = new CrashRecoveryContextImpl(this);
    Impl = CRCI;

    if (setjmp(CRCI->JumpBuffer) != 0) {
      return false;
    }
  }

  Fn();
  return true;
}

#endif // !_MSC_VER

void CrashRecoveryContext::HandleCrash() {
  CrashRecoveryContextImpl *CRCI = (CrashRecoveryContextImpl *) Impl;
  assert(CRCI && "Crash recovery context never initialized!");
  CRCI->HandleCrash();
}

// FIXME: Portability.
static void setThreadBackgroundPriority() {
#ifdef __APPLE__
  setpriority(PRIO_DARWIN_THREAD, 0, PRIO_DARWIN_BG);
#endif
}

static bool hasThreadBackgroundPriority() {
#ifdef __APPLE__
  return getpriority(PRIO_DARWIN_THREAD, 0) == 1;
#else
  return false;
#endif
}

namespace {
struct RunSafelyOnThreadInfo {
  function_ref<void()> Fn;
  CrashRecoveryContext *CRC;
  bool UseBackgroundPriority;
  bool Result;
};
}

static void RunSafelyOnThread_Dispatch(void *UserData) {
  RunSafelyOnThreadInfo *Info =
    reinterpret_cast<RunSafelyOnThreadInfo*>(UserData);

  if (Info->UseBackgroundPriority)
    setThreadBackgroundPriority();

  Info->Result = Info->CRC->RunSafely(Info->Fn);
}
bool CrashRecoveryContext::RunSafelyOnThread(function_ref<void()> Fn,
                                             unsigned RequestedStackSize) {
  bool UseBackgroundPriority = hasThreadBackgroundPriority();
  RunSafelyOnThreadInfo Info = { Fn, this, UseBackgroundPriority, false };
  llvm_execute_on_thread(RunSafelyOnThread_Dispatch, &Info, RequestedStackSize);
  if (CrashRecoveryContextImpl *CRC = (CrashRecoveryContextImpl *)Impl)
    CRC->setSwitchedThread();
  return Info.Result;
}