1//===- Signals.cpp - Generic Unix Signals Implementation -----*- C++ -*-===//
2//
3// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4// See https://llvm.org/LICENSE.txt for license information.
5// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6//
7//===----------------------------------------------------------------------===//
8//
9// This file defines some helpful functions for dealing with the possibility of
10// Unix signals occurring while your program is running.
11//
12//===----------------------------------------------------------------------===//
13//
14// This file is extremely careful to only do signal-safe things while in a
15// signal handler. In particular, memory allocation and acquiring a mutex
16// while in a signal handler should never occur. ManagedStatic isn't usable from
17// a signal handler for 2 reasons:
18//
19//  1. Creating a new one allocates.
20//  2. The signal handler could fire while llvm_shutdown is being processed, in
21//     which case the ManagedStatic is in an unknown state because it could
22//     already have been destroyed, or be in the process of being destroyed.
23//
24// Modifying the behavior of the signal handlers (such as registering new ones)
25// can acquire a mutex, but all this guarantees is that the signal handler
26// behavior is only modified by one thread at a time. A signal handler can still
27// fire while this occurs!
28//
29// Adding work to a signal handler requires lock-freedom (and assume atomics are
30// always lock-free) because the signal handler could fire while new work is
31// being added.
32//
33//===----------------------------------------------------------------------===//
34
35#include "Unix.h"
36#include "llvm/ADT/STLExtras.h"
37#include "llvm/Config/config.h"
38#include "llvm/Demangle/Demangle.h"
39#include "llvm/Support/ExitCodes.h"
40#include "llvm/Support/FileSystem.h"
41#include "llvm/Support/FileUtilities.h"
42#include "llvm/Support/Format.h"
43#include "llvm/Support/MemoryBuffer.h"
44#include "llvm/Support/Mutex.h"
45#include "llvm/Support/Program.h"
46#include "llvm/Support/SaveAndRestore.h"
47#include "llvm/Support/raw_ostream.h"
48#include <algorithm>
49#include <string>
50#ifdef HAVE_BACKTRACE
51# include BACKTRACE_HEADER         // For backtrace().
52#endif
53#if HAVE_SIGNAL_H
54#include <signal.h>
55#endif
56#if HAVE_SYS_STAT_H
57#include <sys/stat.h>
58#endif
59#if HAVE_DLFCN_H
60#include <dlfcn.h>
61#endif
62#if HAVE_MACH_MACH_H
63#include <mach/mach.h>
64#endif
65#if HAVE_LINK_H
66#include <link.h>
67#endif
68#ifdef HAVE__UNWIND_BACKTRACE
69// FIXME: We should be able to use <unwind.h> for any target that has an
70// _Unwind_Backtrace function, but on FreeBSD the configure test passes
71// despite the function not existing, and on Android, <unwind.h> conflicts
72// with <link.h>.
73#ifdef __GLIBC__
74#include <unwind.h>
75#else
76#undef HAVE__UNWIND_BACKTRACE
77#endif
78#endif
79
80using namespace llvm;
81
82static void SignalHandler(int Sig);  // defined below.
83static void InfoSignalHandler(int Sig);  // defined below.
84
85using SignalHandlerFunctionType = void (*)();
86/// The function to call if ctrl-c is pressed.
87static std::atomic<SignalHandlerFunctionType> InterruptFunction =
88    ATOMIC_VAR_INIT(nullptr);
89static std::atomic<SignalHandlerFunctionType> InfoSignalFunction =
90    ATOMIC_VAR_INIT(nullptr);
91/// The function to call on SIGPIPE (one-time use only).
92static std::atomic<SignalHandlerFunctionType> OneShotPipeSignalFunction =
93    ATOMIC_VAR_INIT(nullptr);
94
95namespace {
96/// Signal-safe removal of files.
97/// Inserting and erasing from the list isn't signal-safe, but removal of files
98/// themselves is signal-safe. Memory is freed when the head is freed, deletion
99/// is therefore not signal-safe either.
100class FileToRemoveList {
101  std::atomic<char *> Filename = ATOMIC_VAR_INIT(nullptr);
102  std::atomic<FileToRemoveList *> Next = ATOMIC_VAR_INIT(nullptr);
103
104  FileToRemoveList() = default;
105  // Not signal-safe.
106  FileToRemoveList(const std::string &str) : Filename(strdup(str.c_str())) {}
107
108public:
109  // Not signal-safe.
110  ~FileToRemoveList() {
111    if (FileToRemoveList *N = Next.exchange(nullptr))
112      delete N;
113    if (char *F = Filename.exchange(nullptr))
114      free(F);
115  }
116
117  // Not signal-safe.
118  static void insert(std::atomic<FileToRemoveList *> &Head,
119                     const std::string &Filename) {
120    // Insert the new file at the end of the list.
121    FileToRemoveList *NewHead = new FileToRemoveList(Filename);
122    std::atomic<FileToRemoveList *> *InsertionPoint = &Head;
123    FileToRemoveList *OldHead = nullptr;
124    while (!InsertionPoint->compare_exchange_strong(OldHead, NewHead)) {
125      InsertionPoint = &OldHead->Next;
126      OldHead = nullptr;
127    }
128  }
129
130  // Not signal-safe.
131  static void erase(std::atomic<FileToRemoveList *> &Head,
132                    const std::string &Filename) {
133    // Use a lock to avoid concurrent erase: the comparison would access
134    // free'd memory.
135    static ManagedStatic<sys::SmartMutex<true>> Lock;
136    sys::SmartScopedLock<true> Writer(*Lock);
137
138    for (FileToRemoveList *Current = Head.load(); Current;
139         Current = Current->Next.load()) {
140      if (char *OldFilename = Current->Filename.load()) {
141        if (OldFilename != Filename)
142          continue;
143        // Leave an empty filename.
144        OldFilename = Current->Filename.exchange(nullptr);
145        // The filename might have become null between the time we
146        // compared it and we exchanged it.
147        if (OldFilename)
148          free(OldFilename);
149      }
150    }
151  }
152
153  // Signal-safe.
154  static void removeAllFiles(std::atomic<FileToRemoveList *> &Head) {
155    // If cleanup were to occur while we're removing files we'd have a bad time.
156    // Make sure we're OK by preventing cleanup from doing anything while we're
157    // removing files. If cleanup races with us and we win we'll have a leak,
158    // but we won't crash.
159    FileToRemoveList *OldHead = Head.exchange(nullptr);
160
161    for (FileToRemoveList *currentFile = OldHead; currentFile;
162         currentFile = currentFile->Next.load()) {
163      // If erasing was occuring while we're trying to remove files we'd look
164      // at free'd data. Take away the path and put it back when done.
165      if (char *path = currentFile->Filename.exchange(nullptr)) {
166        // Get the status so we can determine if it's a file or directory. If we
167        // can't stat the file, ignore it.
168        struct stat buf;
169        if (stat(path, &buf) != 0)
170          continue;
171
172        // If this is not a regular file, ignore it. We want to prevent removal
173        // of special files like /dev/null, even if the compiler is being run
174        // with the super-user permissions.
175        if (!S_ISREG(buf.st_mode))
176          continue;
177
178        // Otherwise, remove the file. We ignore any errors here as there is
179        // nothing else we can do.
180        unlink(path);
181
182        // We're done removing the file, erasing can safely proceed.
183        currentFile->Filename.exchange(path);
184      }
185    }
186
187    // We're done removing files, cleanup can safely proceed.
188    Head.exchange(OldHead);
189  }
190};
191static std::atomic<FileToRemoveList *> FilesToRemove = ATOMIC_VAR_INIT(nullptr);
192
193/// Clean up the list in a signal-friendly manner.
194/// Recall that signals can fire during llvm_shutdown. If this occurs we should
195/// either clean something up or nothing at all, but we shouldn't crash!
196struct FilesToRemoveCleanup {
197  // Not signal-safe.
198  ~FilesToRemoveCleanup() {
199    FileToRemoveList *Head = FilesToRemove.exchange(nullptr);
200    if (Head)
201      delete Head;
202  }
203};
204} // namespace
205
206static StringRef Argv0;
207
208/// Signals that represent requested termination. There's no bug or failure, or
209/// if there is, it's not our direct responsibility. For whatever reason, our
210/// continued execution is no longer desirable.
211static const int IntSigs[] = {
212  SIGHUP, SIGINT, SIGTERM, SIGUSR2
213};
214
215/// Signals that represent that we have a bug, and our prompt termination has
216/// been ordered.
217static const int KillSigs[] = {
218  SIGILL, SIGTRAP, SIGABRT, SIGFPE, SIGBUS, SIGSEGV, SIGQUIT
219#ifdef SIGSYS
220  , SIGSYS
221#endif
222#ifdef SIGXCPU
223  , SIGXCPU
224#endif
225#ifdef SIGXFSZ
226  , SIGXFSZ
227#endif
228#ifdef SIGEMT
229  , SIGEMT
230#endif
231};
232
233/// Signals that represent requests for status.
234static const int InfoSigs[] = {
235  SIGUSR1
236#ifdef SIGINFO
237  , SIGINFO
238#endif
239};
240
241static const size_t NumSigs =
242    array_lengthof(IntSigs) + array_lengthof(KillSigs) +
243    array_lengthof(InfoSigs) + 1 /* SIGPIPE */;
244
245
246static std::atomic<unsigned> NumRegisteredSignals = ATOMIC_VAR_INIT(0);
247static struct {
248  struct sigaction SA;
249  int SigNo;
250} RegisteredSignalInfo[NumSigs];
251
252#if defined(HAVE_SIGALTSTACK)
253// Hold onto both the old and new alternate signal stack so that it's not
254// reported as a leak. We don't make any attempt to remove our alt signal
255// stack if we remove our signal handlers; that can't be done reliably if
256// someone else is also trying to do the same thing.
257static stack_t OldAltStack;
258LLVM_ATTRIBUTE_USED static void *NewAltStackPointer;
259
260static void CreateSigAltStack() {
261  const size_t AltStackSize = MINSIGSTKSZ + 64 * 1024;
262
263  // If we're executing on the alternate stack, or we already have an alternate
264  // signal stack that we're happy with, there's nothing for us to do. Don't
265  // reduce the size, some other part of the process might need a larger stack
266  // than we do.
267  if (sigaltstack(nullptr, &OldAltStack) != 0 ||
268      OldAltStack.ss_flags & SS_ONSTACK ||
269      (OldAltStack.ss_sp && OldAltStack.ss_size >= AltStackSize))
270    return;
271
272  stack_t AltStack = {};
273  AltStack.ss_sp = static_cast<char *>(safe_malloc(AltStackSize));
274  NewAltStackPointer = AltStack.ss_sp; // Save to avoid reporting a leak.
275  AltStack.ss_size = AltStackSize;
276  if (sigaltstack(&AltStack, &OldAltStack) != 0)
277    free(AltStack.ss_sp);
278}
279#else
280static void CreateSigAltStack() {}
281#endif
282
283static void RegisterHandlers() { // Not signal-safe.
284  // The mutex prevents other threads from registering handlers while we're
285  // doing it. We also have to protect the handlers and their count because
286  // a signal handler could fire while we're registeting handlers.
287  static ManagedStatic<sys::SmartMutex<true>> SignalHandlerRegistrationMutex;
288  sys::SmartScopedLock<true> Guard(*SignalHandlerRegistrationMutex);
289
290  // If the handlers are already registered, we're done.
291  if (NumRegisteredSignals.load() != 0)
292    return;
293
294  // Create an alternate stack for signal handling. This is necessary for us to
295  // be able to reliably handle signals due to stack overflow.
296  CreateSigAltStack();
297
298  enum class SignalKind { IsKill, IsInfo };
299  auto registerHandler = [&](int Signal, SignalKind Kind) {
300    unsigned Index = NumRegisteredSignals.load();
301    assert(Index < array_lengthof(RegisteredSignalInfo) &&
302           "Out of space for signal handlers!");
303
304    struct sigaction NewHandler;
305
306    switch (Kind) {
307    case SignalKind::IsKill:
308      NewHandler.sa_handler = SignalHandler;
309      NewHandler.sa_flags = SA_NODEFER | SA_RESETHAND | SA_ONSTACK;
310      break;
311    case SignalKind::IsInfo:
312      NewHandler.sa_handler = InfoSignalHandler;
313      NewHandler.sa_flags = SA_ONSTACK;
314      break;
315    }
316    sigemptyset(&NewHandler.sa_mask);
317
318    // Install the new handler, save the old one in RegisteredSignalInfo.
319    sigaction(Signal, &NewHandler, &RegisteredSignalInfo[Index].SA);
320    RegisteredSignalInfo[Index].SigNo = Signal;
321    ++NumRegisteredSignals;
322  };
323
324  for (auto S : IntSigs)
325    registerHandler(S, SignalKind::IsKill);
326  for (auto S : KillSigs)
327    registerHandler(S, SignalKind::IsKill);
328  if (OneShotPipeSignalFunction)
329    registerHandler(SIGPIPE, SignalKind::IsKill);
330  for (auto S : InfoSigs)
331    registerHandler(S, SignalKind::IsInfo);
332}
333
334void sys::unregisterHandlers() {
335  // Restore all of the signal handlers to how they were before we showed up.
336  for (unsigned i = 0, e = NumRegisteredSignals.load(); i != e; ++i) {
337    sigaction(RegisteredSignalInfo[i].SigNo,
338              &RegisteredSignalInfo[i].SA, nullptr);
339    --NumRegisteredSignals;
340  }
341}
342
343/// Process the FilesToRemove list.
344static void RemoveFilesToRemove() {
345  FileToRemoveList::removeAllFiles(FilesToRemove);
346}
347
348void sys::CleanupOnSignal(uintptr_t Context) {
349  int Sig = (int)Context;
350
351  if (llvm::is_contained(InfoSigs, Sig)) {
352    InfoSignalHandler(Sig);
353    return;
354  }
355
356  RemoveFilesToRemove();
357
358  if (llvm::is_contained(IntSigs, Sig) || Sig == SIGPIPE)
359    return;
360
361  llvm::sys::RunSignalHandlers();
362}
363
364// The signal handler that runs.
365static void SignalHandler(int Sig) {
366  // Restore the signal behavior to default, so that the program actually
367  // crashes when we return and the signal reissues.  This also ensures that if
368  // we crash in our signal handler that the program will terminate immediately
369  // instead of recursing in the signal handler.
370  sys::unregisterHandlers();
371
372  // Unmask all potentially blocked kill signals.
373  sigset_t SigMask;
374  sigfillset(&SigMask);
375  sigprocmask(SIG_UNBLOCK, &SigMask, nullptr);
376
377  {
378    RemoveFilesToRemove();
379
380    if (Sig == SIGPIPE)
381      if (auto OldOneShotPipeFunction =
382              OneShotPipeSignalFunction.exchange(nullptr))
383        return OldOneShotPipeFunction();
384
385    bool IsIntSig = llvm::is_contained(IntSigs, Sig);
386    if (IsIntSig)
387      if (auto OldInterruptFunction = InterruptFunction.exchange(nullptr))
388        return OldInterruptFunction();
389
390    if (Sig == SIGPIPE || IsIntSig) {
391      raise(Sig); // Execute the default handler.
392      return;
393    }
394  }
395
396  // Otherwise if it is a fault (like SEGV) run any handler.
397  llvm::sys::RunSignalHandlers();
398
399#ifdef __s390__
400  // On S/390, certain signals are delivered with PSW Address pointing to
401  // *after* the faulting instruction.  Simply returning from the signal
402  // handler would continue execution after that point, instead of
403  // re-raising the signal.  Raise the signal manually in those cases.
404  if (Sig == SIGILL || Sig == SIGFPE || Sig == SIGTRAP)
405    raise(Sig);
406#endif
407}
408
409static void InfoSignalHandler(int Sig) {
410  SaveAndRestore<int> SaveErrnoDuringASignalHandler(errno);
411  if (SignalHandlerFunctionType CurrentInfoFunction = InfoSignalFunction)
412    CurrentInfoFunction();
413}
414
415void llvm::sys::RunInterruptHandlers() {
416  RemoveFilesToRemove();
417}
418
419void llvm::sys::SetInterruptFunction(void (*IF)()) {
420  InterruptFunction.exchange(IF);
421  RegisterHandlers();
422}
423
424void llvm::sys::SetInfoSignalFunction(void (*Handler)()) {
425  InfoSignalFunction.exchange(Handler);
426  RegisterHandlers();
427}
428
429void llvm::sys::SetOneShotPipeSignalFunction(void (*Handler)()) {
430  OneShotPipeSignalFunction.exchange(Handler);
431  RegisterHandlers();
432}
433
434void llvm::sys::DefaultOneShotPipeSignalHandler() {
435  // Send a special return code that drivers can check for, from sysexits.h.
436  exit(EX_IOERR);
437}
438
439// The public API
440bool llvm::sys::RemoveFileOnSignal(StringRef Filename,
441                                   std::string* ErrMsg) {
442  // Ensure that cleanup will occur as soon as one file is added.
443  static ManagedStatic<FilesToRemoveCleanup> FilesToRemoveCleanup;
444  *FilesToRemoveCleanup;
445  FileToRemoveList::insert(FilesToRemove, Filename.str());
446  RegisterHandlers();
447  return false;
448}
449
450// The public API
451void llvm::sys::DontRemoveFileOnSignal(StringRef Filename) {
452  FileToRemoveList::erase(FilesToRemove, Filename.str());
453}
454
455/// Add a function to be called when a signal is delivered to the process. The
456/// handler can have a cookie passed to it to identify what instance of the
457/// handler it is.
458void llvm::sys::AddSignalHandler(sys::SignalHandlerCallback FnPtr,
459                                 void *Cookie) { // Signal-safe.
460  insertSignalHandler(FnPtr, Cookie);
461  RegisterHandlers();
462}
463
464#if defined(HAVE_BACKTRACE) && ENABLE_BACKTRACES && HAVE_LINK_H &&    \
465    (defined(__linux__) || defined(__FreeBSD__) ||                             \
466     defined(__FreeBSD_kernel__) || defined(__NetBSD__))
467struct DlIteratePhdrData {
468  void **StackTrace;
469  int depth;
470  bool first;
471  const char **modules;
472  intptr_t *offsets;
473  const char *main_exec_name;
474};
475
476static int dl_iterate_phdr_cb(dl_phdr_info *info, size_t size, void *arg) {
477  DlIteratePhdrData *data = (DlIteratePhdrData*)arg;
478  const char *name = data->first ? data->main_exec_name : info->dlpi_name;
479  data->first = false;
480  for (int i = 0; i < info->dlpi_phnum; i++) {
481    const auto *phdr = &info->dlpi_phdr[i];
482    if (phdr->p_type != PT_LOAD)
483      continue;
484    intptr_t beg = info->dlpi_addr + phdr->p_vaddr;
485    intptr_t end = beg + phdr->p_memsz;
486    for (int j = 0; j < data->depth; j++) {
487      if (data->modules[j])
488        continue;
489      intptr_t addr = (intptr_t)data->StackTrace[j];
490      if (beg <= addr && addr < end) {
491        data->modules[j] = name;
492        data->offsets[j] = addr - info->dlpi_addr;
493      }
494    }
495  }
496  return 0;
497}
498
499/// If this is an ELF platform, we can find all loaded modules and their virtual
500/// addresses with dl_iterate_phdr.
501static bool findModulesAndOffsets(void **StackTrace, int Depth,
502                                  const char **Modules, intptr_t *Offsets,
503                                  const char *MainExecutableName,
504                                  StringSaver &StrPool) {
505  DlIteratePhdrData data = {StackTrace, Depth,   true,
506                            Modules,    Offsets, MainExecutableName};
507  dl_iterate_phdr(dl_iterate_phdr_cb, &data);
508  return true;
509}
510#else
511/// This platform does not have dl_iterate_phdr, so we do not yet know how to
512/// find all loaded DSOs.
513static bool findModulesAndOffsets(void **StackTrace, int Depth,
514                                  const char **Modules, intptr_t *Offsets,
515                                  const char *MainExecutableName,
516                                  StringSaver &StrPool) {
517  return false;
518}
519#endif // defined(HAVE_BACKTRACE) && ENABLE_BACKTRACES && ...
520
521#if ENABLE_BACKTRACES && defined(HAVE__UNWIND_BACKTRACE)
522static int unwindBacktrace(void **StackTrace, int MaxEntries) {
523  if (MaxEntries < 0)
524    return 0;
525
526  // Skip the first frame ('unwindBacktrace' itself).
527  int Entries = -1;
528
529  auto HandleFrame = [&](_Unwind_Context *Context) -> _Unwind_Reason_Code {
530    // Apparently we need to detect reaching the end of the stack ourselves.
531    void *IP = (void *)_Unwind_GetIP(Context);
532    if (!IP)
533      return _URC_END_OF_STACK;
534
535    assert(Entries < MaxEntries && "recursively called after END_OF_STACK?");
536    if (Entries >= 0)
537      StackTrace[Entries] = IP;
538
539    if (++Entries == MaxEntries)
540      return _URC_END_OF_STACK;
541    return _URC_NO_REASON;
542  };
543
544  _Unwind_Backtrace(
545      [](_Unwind_Context *Context, void *Handler) {
546        return (*static_cast<decltype(HandleFrame) *>(Handler))(Context);
547      },
548      static_cast<void *>(&HandleFrame));
549  return std::max(Entries, 0);
550}
551#endif
552
553// In the case of a program crash or fault, print out a stack trace so that the
554// user has an indication of why and where we died.
555//
556// On glibc systems we have the 'backtrace' function, which works nicely, but
557// doesn't demangle symbols.
558void llvm::sys::PrintStackTrace(raw_ostream &OS, int Depth) {
559#if ENABLE_BACKTRACES
560  static void *StackTrace[256];
561  int depth = 0;
562#if defined(HAVE_BACKTRACE)
563  // Use backtrace() to output a backtrace on Linux systems with glibc.
564  if (!depth)
565    depth = backtrace(StackTrace, static_cast<int>(array_lengthof(StackTrace)));
566#endif
567#if defined(HAVE__UNWIND_BACKTRACE)
568  // Try _Unwind_Backtrace() if backtrace() failed.
569  if (!depth)
570    depth = unwindBacktrace(StackTrace,
571                        static_cast<int>(array_lengthof(StackTrace)));
572#endif
573  if (!depth)
574    return;
575  // If "Depth" is not provided by the caller, use the return value of
576  // backtrace() for printing a symbolized stack trace.
577  if (!Depth)
578    Depth = depth;
579  if (printSymbolizedStackTrace(Argv0, StackTrace, Depth, OS))
580    return;
581  OS << "Stack dump without symbol names (ensure you have llvm-symbolizer in "
582        "your PATH or set the environment var `LLVM_SYMBOLIZER_PATH` to point "
583        "to it):\n";
584#if HAVE_DLFCN_H && HAVE_DLADDR
585  int width = 0;
586  for (int i = 0; i < depth; ++i) {
587    Dl_info dlinfo;
588    dladdr(StackTrace[i], &dlinfo);
589    const char* name = strrchr(dlinfo.dli_fname, '/');
590
591    int nwidth;
592    if (!name) nwidth = strlen(dlinfo.dli_fname);
593    else       nwidth = strlen(name) - 1;
594
595    if (nwidth > width) width = nwidth;
596  }
597
598  for (int i = 0; i < depth; ++i) {
599    Dl_info dlinfo;
600    dladdr(StackTrace[i], &dlinfo);
601
602    OS << format("%-2d", i);
603
604    const char* name = strrchr(dlinfo.dli_fname, '/');
605    if (!name) OS << format(" %-*s", width, dlinfo.dli_fname);
606    else       OS << format(" %-*s", width, name+1);
607
608    OS << format(" %#0*lx", (int)(sizeof(void*) * 2) + 2,
609                 (unsigned long)StackTrace[i]);
610
611    if (dlinfo.dli_sname != nullptr) {
612      OS << ' ';
613      int res;
614      char* d = itaniumDemangle(dlinfo.dli_sname, nullptr, nullptr, &res);
615      if (!d) OS << dlinfo.dli_sname;
616      else    OS << d;
617      free(d);
618
619      OS << format(" + %tu", (static_cast<const char*>(StackTrace[i])-
620                              static_cast<const char*>(dlinfo.dli_saddr)));
621    }
622    OS << '\n';
623  }
624#elif defined(HAVE_BACKTRACE)
625  backtrace_symbols_fd(StackTrace, Depth, STDERR_FILENO);
626#endif
627#endif
628}
629
630static void PrintStackTraceSignalHandler(void *) {
631  sys::PrintStackTrace(llvm::errs());
632}
633
634void llvm::sys::DisableSystemDialogsOnCrash() {}
635
636/// When an error signal (such as SIGABRT or SIGSEGV) is delivered to the
637/// process, print a stack trace and then exit.
638void llvm::sys::PrintStackTraceOnErrorSignal(StringRef Argv0,
639                                             bool DisableCrashReporting) {
640  ::Argv0 = Argv0;
641
642  AddSignalHandler(PrintStackTraceSignalHandler, nullptr);
643
644#if defined(__APPLE__) && ENABLE_CRASH_OVERRIDES
645  // Environment variable to disable any kind of crash dialog.
646  if (DisableCrashReporting || getenv("LLVM_DISABLE_CRASH_REPORT")) {
647    mach_port_t self = mach_task_self();
648
649    exception_mask_t mask = EXC_MASK_CRASH;
650
651    kern_return_t ret = task_set_exception_ports(self,
652                             mask,
653                             MACH_PORT_NULL,
654                             EXCEPTION_STATE_IDENTITY | MACH_EXCEPTION_CODES,
655                             THREAD_STATE_NONE);
656    (void)ret;
657  }
658#endif
659}
660