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[] = {SIGHUP, SIGINT, SIGTERM, SIGUSR2};
212
213/// Signals that represent that we have a bug, and our prompt termination has
214/// been ordered.
215static const int KillSigs[] = {SIGILL,
216                               SIGTRAP,
217                               SIGABRT,
218                               SIGFPE,
219                               SIGBUS,
220                               SIGSEGV,
221                               SIGQUIT
222#ifdef SIGSYS
223                               ,
224                               SIGSYS
225#endif
226#ifdef SIGXCPU
227                               ,
228                               SIGXCPU
229#endif
230#ifdef SIGXFSZ
231                               ,
232                               SIGXFSZ
233#endif
234#ifdef SIGEMT
235                               ,
236                               SIGEMT
237#endif
238};
239
240/// Signals that represent requests for status.
241static const int InfoSigs[] = {SIGUSR1
242#ifdef SIGINFO
243                               ,
244                               SIGINFO
245#endif
246};
247
248static const size_t NumSigs = std::size(IntSigs) + std::size(KillSigs) +
249                              std::size(InfoSigs) + 1 /* SIGPIPE */;
250
251static std::atomic<unsigned> NumRegisteredSignals = ATOMIC_VAR_INIT(0);
252static struct {
253  struct sigaction SA;
254  int SigNo;
255} RegisteredSignalInfo[NumSigs];
256
257#if defined(HAVE_SIGALTSTACK)
258// Hold onto both the old and new alternate signal stack so that it's not
259// reported as a leak. We don't make any attempt to remove our alt signal
260// stack if we remove our signal handlers; that can't be done reliably if
261// someone else is also trying to do the same thing.
262static stack_t OldAltStack;
263LLVM_ATTRIBUTE_USED static void *NewAltStackPointer;
264
265static void CreateSigAltStack() {
266  const size_t AltStackSize = MINSIGSTKSZ + 64 * 1024;
267
268  // If we're executing on the alternate stack, or we already have an alternate
269  // signal stack that we're happy with, there's nothing for us to do. Don't
270  // reduce the size, some other part of the process might need a larger stack
271  // than we do.
272  if (sigaltstack(nullptr, &OldAltStack) != 0 ||
273      OldAltStack.ss_flags & SS_ONSTACK ||
274      (OldAltStack.ss_sp && OldAltStack.ss_size >= AltStackSize))
275    return;
276
277  stack_t AltStack = {};
278  AltStack.ss_sp = static_cast<char *>(safe_malloc(AltStackSize));
279  NewAltStackPointer = AltStack.ss_sp; // Save to avoid reporting a leak.
280  AltStack.ss_size = AltStackSize;
281  if (sigaltstack(&AltStack, &OldAltStack) != 0)
282    free(AltStack.ss_sp);
283}
284#else
285static void CreateSigAltStack() {}
286#endif
287
288static void RegisterHandlers() { // Not signal-safe.
289  // The mutex prevents other threads from registering handlers while we're
290  // doing it. We also have to protect the handlers and their count because
291  // a signal handler could fire while we're registeting handlers.
292  static ManagedStatic<sys::SmartMutex<true>> SignalHandlerRegistrationMutex;
293  sys::SmartScopedLock<true> Guard(*SignalHandlerRegistrationMutex);
294
295  // If the handlers are already registered, we're done.
296  if (NumRegisteredSignals.load() != 0)
297    return;
298
299  // Create an alternate stack for signal handling. This is necessary for us to
300  // be able to reliably handle signals due to stack overflow.
301  CreateSigAltStack();
302
303  enum class SignalKind { IsKill, IsInfo };
304  auto registerHandler = [&](int Signal, SignalKind Kind) {
305    unsigned Index = NumRegisteredSignals.load();
306    assert(Index < std::size(RegisteredSignalInfo) &&
307           "Out of space for signal handlers!");
308
309    struct sigaction NewHandler;
310
311    switch (Kind) {
312    case SignalKind::IsKill:
313      NewHandler.sa_handler = SignalHandler;
314      NewHandler.sa_flags = SA_NODEFER | SA_RESETHAND | SA_ONSTACK;
315      break;
316    case SignalKind::IsInfo:
317      NewHandler.sa_handler = InfoSignalHandler;
318      NewHandler.sa_flags = SA_ONSTACK;
319      break;
320    }
321    sigemptyset(&NewHandler.sa_mask);
322
323    // Install the new handler, save the old one in RegisteredSignalInfo.
324    sigaction(Signal, &NewHandler, &RegisteredSignalInfo[Index].SA);
325    RegisteredSignalInfo[Index].SigNo = Signal;
326    ++NumRegisteredSignals;
327  };
328
329  for (auto S : IntSigs)
330    registerHandler(S, SignalKind::IsKill);
331  for (auto S : KillSigs)
332    registerHandler(S, SignalKind::IsKill);
333  if (OneShotPipeSignalFunction)
334    registerHandler(SIGPIPE, SignalKind::IsKill);
335  for (auto S : InfoSigs)
336    registerHandler(S, SignalKind::IsInfo);
337}
338
339void sys::unregisterHandlers() {
340  // Restore all of the signal handlers to how they were before we showed up.
341  for (unsigned i = 0, e = NumRegisteredSignals.load(); i != e; ++i) {
342    sigaction(RegisteredSignalInfo[i].SigNo, &RegisteredSignalInfo[i].SA,
343              nullptr);
344    --NumRegisteredSignals;
345  }
346}
347
348/// Process the FilesToRemove list.
349static void RemoveFilesToRemove() {
350  FileToRemoveList::removeAllFiles(FilesToRemove);
351}
352
353void sys::CleanupOnSignal(uintptr_t Context) {
354  int Sig = (int)Context;
355
356  if (llvm::is_contained(InfoSigs, Sig)) {
357    InfoSignalHandler(Sig);
358    return;
359  }
360
361  RemoveFilesToRemove();
362
363  if (llvm::is_contained(IntSigs, Sig) || Sig == SIGPIPE)
364    return;
365
366  llvm::sys::RunSignalHandlers();
367}
368
369// The signal handler that runs.
370static void SignalHandler(int Sig) {
371  // Restore the signal behavior to default, so that the program actually
372  // crashes when we return and the signal reissues.  This also ensures that if
373  // we crash in our signal handler that the program will terminate immediately
374  // instead of recursing in the signal handler.
375  sys::unregisterHandlers();
376
377  // Unmask all potentially blocked kill signals.
378  sigset_t SigMask;
379  sigfillset(&SigMask);
380  sigprocmask(SIG_UNBLOCK, &SigMask, nullptr);
381
382  {
383    RemoveFilesToRemove();
384
385    if (Sig == SIGPIPE)
386      if (auto OldOneShotPipeFunction =
387              OneShotPipeSignalFunction.exchange(nullptr))
388        return OldOneShotPipeFunction();
389
390    bool IsIntSig = llvm::is_contained(IntSigs, Sig);
391    if (IsIntSig)
392      if (auto OldInterruptFunction = InterruptFunction.exchange(nullptr))
393        return OldInterruptFunction();
394
395    if (Sig == SIGPIPE || IsIntSig) {
396      raise(Sig); // Execute the default handler.
397      return;
398    }
399  }
400
401  // Otherwise if it is a fault (like SEGV) run any handler.
402  llvm::sys::RunSignalHandlers();
403
404#ifdef __s390__
405  // On S/390, certain signals are delivered with PSW Address pointing to
406  // *after* the faulting instruction.  Simply returning from the signal
407  // handler would continue execution after that point, instead of
408  // re-raising the signal.  Raise the signal manually in those cases.
409  if (Sig == SIGILL || Sig == SIGFPE || Sig == SIGTRAP)
410    raise(Sig);
411#endif
412}
413
414static void InfoSignalHandler(int Sig) {
415  SaveAndRestore SaveErrnoDuringASignalHandler(errno);
416  if (SignalHandlerFunctionType CurrentInfoFunction = InfoSignalFunction)
417    CurrentInfoFunction();
418}
419
420void llvm::sys::RunInterruptHandlers() { RemoveFilesToRemove(); }
421
422void llvm::sys::SetInterruptFunction(void (*IF)()) {
423  InterruptFunction.exchange(IF);
424  RegisterHandlers();
425}
426
427void llvm::sys::SetInfoSignalFunction(void (*Handler)()) {
428  InfoSignalFunction.exchange(Handler);
429  RegisterHandlers();
430}
431
432void llvm::sys::SetOneShotPipeSignalFunction(void (*Handler)()) {
433  OneShotPipeSignalFunction.exchange(Handler);
434  RegisterHandlers();
435}
436
437void llvm::sys::DefaultOneShotPipeSignalHandler() {
438  // Send a special return code that drivers can check for, from sysexits.h.
439  exit(EX_IOERR);
440}
441
442// The public API
443bool llvm::sys::RemoveFileOnSignal(StringRef Filename, std::string *ErrMsg) {
444  // Ensure that cleanup will occur as soon as one file is added.
445  static ManagedStatic<FilesToRemoveCleanup> FilesToRemoveCleanup;
446  *FilesToRemoveCleanup;
447  FileToRemoveList::insert(FilesToRemove, Filename.str());
448  RegisterHandlers();
449  return false;
450}
451
452// The public API
453void llvm::sys::DontRemoveFileOnSignal(StringRef Filename) {
454  FileToRemoveList::erase(FilesToRemove, Filename.str());
455}
456
457/// Add a function to be called when a signal is delivered to the process. The
458/// handler can have a cookie passed to it to identify what instance of the
459/// handler it is.
460void llvm::sys::AddSignalHandler(sys::SignalHandlerCallback FnPtr,
461                                 void *Cookie) { // Signal-safe.
462  insertSignalHandler(FnPtr, Cookie);
463  RegisterHandlers();
464}
465
466#if defined(HAVE_BACKTRACE) && ENABLE_BACKTRACES && HAVE_LINK_H &&             \
467    (defined(__linux__) || defined(__FreeBSD__) ||                             \
468     defined(__FreeBSD_kernel__) || defined(__NetBSD__))
469struct DlIteratePhdrData {
470  void **StackTrace;
471  int depth;
472  bool first;
473  const char **modules;
474  intptr_t *offsets;
475  const char *main_exec_name;
476};
477
478static int dl_iterate_phdr_cb(dl_phdr_info *info, size_t size, void *arg) {
479  DlIteratePhdrData *data = (DlIteratePhdrData *)arg;
480  const char *name = data->first ? data->main_exec_name : info->dlpi_name;
481  data->first = false;
482  for (int i = 0; i < info->dlpi_phnum; i++) {
483    const auto *phdr = &info->dlpi_phdr[i];
484    if (phdr->p_type != PT_LOAD)
485      continue;
486    intptr_t beg = info->dlpi_addr + phdr->p_vaddr;
487    intptr_t end = beg + phdr->p_memsz;
488    for (int j = 0; j < data->depth; j++) {
489      if (data->modules[j])
490        continue;
491      intptr_t addr = (intptr_t)data->StackTrace[j];
492      if (beg <= addr && addr < end) {
493        data->modules[j] = name;
494        data->offsets[j] = addr - info->dlpi_addr;
495      }
496    }
497  }
498  return 0;
499}
500
501/// If this is an ELF platform, we can find all loaded modules and their virtual
502/// addresses with dl_iterate_phdr.
503static bool findModulesAndOffsets(void **StackTrace, int Depth,
504                                  const char **Modules, intptr_t *Offsets,
505                                  const char *MainExecutableName,
506                                  StringSaver &StrPool) {
507  DlIteratePhdrData data = {StackTrace, Depth,   true,
508                            Modules,    Offsets, MainExecutableName};
509  dl_iterate_phdr(dl_iterate_phdr_cb, &data);
510  return true;
511}
512#else
513/// This platform does not have dl_iterate_phdr, so we do not yet know how to
514/// find all loaded DSOs.
515static bool findModulesAndOffsets(void **StackTrace, int Depth,
516                                  const char **Modules, intptr_t *Offsets,
517                                  const char *MainExecutableName,
518                                  StringSaver &StrPool) {
519  return false;
520}
521#endif // defined(HAVE_BACKTRACE) && ENABLE_BACKTRACES && ...
522
523#if ENABLE_BACKTRACES && defined(HAVE__UNWIND_BACKTRACE)
524static int unwindBacktrace(void **StackTrace, int MaxEntries) {
525  if (MaxEntries < 0)
526    return 0;
527
528  // Skip the first frame ('unwindBacktrace' itself).
529  int Entries = -1;
530
531  auto HandleFrame = [&](_Unwind_Context *Context) -> _Unwind_Reason_Code {
532    // Apparently we need to detect reaching the end of the stack ourselves.
533    void *IP = (void *)_Unwind_GetIP(Context);
534    if (!IP)
535      return _URC_END_OF_STACK;
536
537    assert(Entries < MaxEntries && "recursively called after END_OF_STACK?");
538    if (Entries >= 0)
539      StackTrace[Entries] = IP;
540
541    if (++Entries == MaxEntries)
542      return _URC_END_OF_STACK;
543    return _URC_NO_REASON;
544  };
545
546  _Unwind_Backtrace(
547      [](_Unwind_Context *Context, void *Handler) {
548        return (*static_cast<decltype(HandleFrame) *>(Handler))(Context);
549      },
550      static_cast<void *>(&HandleFrame));
551  return std::max(Entries, 0);
552}
553#endif
554
555// In the case of a program crash or fault, print out a stack trace so that the
556// user has an indication of why and where we died.
557//
558// On glibc systems we have the 'backtrace' function, which works nicely, but
559// doesn't demangle symbols.
560void llvm::sys::PrintStackTrace(raw_ostream &OS, int Depth) {
561#if ENABLE_BACKTRACES
562  static void *StackTrace[256];
563  int depth = 0;
564#if defined(HAVE_BACKTRACE)
565  // Use backtrace() to output a backtrace on Linux systems with glibc.
566  if (!depth)
567    depth = backtrace(StackTrace, static_cast<int>(std::size(StackTrace)));
568#endif
569#if defined(HAVE__UNWIND_BACKTRACE)
570  // Try _Unwind_Backtrace() if backtrace() failed.
571  if (!depth)
572    depth =
573        unwindBacktrace(StackTrace, static_cast<int>(std::size(StackTrace)));
574#endif
575  if (!depth)
576    return;
577  // If "Depth" is not provided by the caller, use the return value of
578  // backtrace() for printing a symbolized stack trace.
579  if (!Depth)
580    Depth = depth;
581  if (printSymbolizedStackTrace(Argv0, StackTrace, Depth, OS))
582    return;
583  OS << "Stack dump without symbol names (ensure you have llvm-symbolizer in "
584        "your PATH or set the environment var `LLVM_SYMBOLIZER_PATH` to point "
585        "to it):\n";
586#if HAVE_DLFCN_H && HAVE_DLADDR
587  int width = 0;
588  for (int i = 0; i < depth; ++i) {
589    Dl_info dlinfo;
590    dladdr(StackTrace[i], &dlinfo);
591    const char *name = strrchr(dlinfo.dli_fname, '/');
592
593    int nwidth;
594    if (!name)
595      nwidth = strlen(dlinfo.dli_fname);
596    else
597      nwidth = strlen(name) - 1;
598
599    if (nwidth > width)
600      width = nwidth;
601  }
602
603  for (int i = 0; i < depth; ++i) {
604    Dl_info dlinfo;
605    dladdr(StackTrace[i], &dlinfo);
606
607    OS << format("%-2d", i);
608
609    const char *name = strrchr(dlinfo.dli_fname, '/');
610    if (!name)
611      OS << format(" %-*s", width, dlinfo.dli_fname);
612    else
613      OS << format(" %-*s", width, name + 1);
614
615    OS << format(" %#0*lx", (int)(sizeof(void *) * 2) + 2,
616                 (unsigned long)StackTrace[i]);
617
618    if (dlinfo.dli_sname != nullptr) {
619      OS << ' ';
620      int res;
621      char *d = itaniumDemangle(dlinfo.dli_sname, nullptr, nullptr, &res);
622      if (!d)
623        OS << dlinfo.dli_sname;
624      else
625        OS << d;
626      free(d);
627
628      OS << format(" + %tu", (static_cast<const char *>(StackTrace[i]) -
629                              static_cast<const char *>(dlinfo.dli_saddr)));
630    }
631    OS << '\n';
632  }
633#elif defined(HAVE_BACKTRACE)
634  backtrace_symbols_fd(StackTrace, Depth, STDERR_FILENO);
635#endif
636#endif
637}
638
639static void PrintStackTraceSignalHandler(void *) {
640  sys::PrintStackTrace(llvm::errs());
641}
642
643void llvm::sys::DisableSystemDialogsOnCrash() {}
644
645/// When an error signal (such as SIGABRT or SIGSEGV) is delivered to the
646/// process, print a stack trace and then exit.
647void llvm::sys::PrintStackTraceOnErrorSignal(StringRef Argv0,
648                                             bool DisableCrashReporting) {
649  ::Argv0 = Argv0;
650
651  AddSignalHandler(PrintStackTraceSignalHandler, nullptr);
652
653#if defined(__APPLE__) && ENABLE_CRASH_OVERRIDES
654  // Environment variable to disable any kind of crash dialog.
655  if (DisableCrashReporting || getenv("LLVM_DISABLE_CRASH_REPORT")) {
656    mach_port_t self = mach_task_self();
657
658    exception_mask_t mask = EXC_MASK_CRASH;
659
660    kern_return_t ret = task_set_exception_ports(
661        self, mask, MACH_PORT_NULL,
662        EXCEPTION_STATE_IDENTITY | MACH_EXCEPTION_CODES, THREAD_STATE_NONE);
663    (void)ret;
664  }
665#endif
666}
667