1//===- Signals.cpp - Generic Unix Signals Implementation -----*- C++ -*-===//
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// This file defines some helpful functions for dealing with the possibility of
11// Unix signals occurring while your program is running.
12//
13//===----------------------------------------------------------------------===//
14
15#include "Unix.h"
16#include "llvm/ADT/STLExtras.h"
17#include "llvm/Support/Format.h"
18#include "llvm/Support/FileSystem.h"
19#include "llvm/Support/FileUtilities.h"
20#include "llvm/Support/MemoryBuffer.h"
21#include "llvm/Support/Mutex.h"
22#include "llvm/Support/Program.h"
23#include "llvm/Support/UniqueLock.h"
24#include "llvm/Support/raw_ostream.h"
25#include <algorithm>
26#include <string>
27#if HAVE_EXECINFO_H
28# include <execinfo.h>         // For backtrace().
29#endif
30#if HAVE_SIGNAL_H
31#include <signal.h>
32#endif
33#if HAVE_SYS_STAT_H
34#include <sys/stat.h>
35#endif
36#if HAVE_CXXABI_H
37#include <cxxabi.h>
38#endif
39#if HAVE_DLFCN_H
40#include <dlfcn.h>
41#endif
42#if HAVE_MACH_MACH_H
43#include <mach/mach.h>
44#endif
45#if HAVE_LINK_H
46#include <link.h>
47#endif
48
49using namespace llvm;
50
51static RETSIGTYPE SignalHandler(int Sig);  // defined below.
52
53static ManagedStatic<SmartMutex<true> > SignalsMutex;
54
55/// InterruptFunction - The function to call if ctrl-c is pressed.
56static void (*InterruptFunction)() = nullptr;
57
58static ManagedStatic<std::vector<std::string>> FilesToRemove;
59
60// IntSigs - Signals that represent requested termination. There's no bug
61// or failure, or if there is, it's not our direct responsibility. For whatever
62// reason, our continued execution is no longer desirable.
63static const int IntSigs[] = {
64  SIGHUP, SIGINT, SIGPIPE, SIGTERM, SIGUSR1, SIGUSR2
65};
66
67// KillSigs - Signals that represent that we have a bug, and our prompt
68// termination has been ordered.
69static const int KillSigs[] = {
70  SIGILL, SIGTRAP, SIGABRT, SIGFPE, SIGBUS, SIGSEGV, SIGQUIT
71#ifdef SIGSYS
72  , SIGSYS
73#endif
74#ifdef SIGXCPU
75  , SIGXCPU
76#endif
77#ifdef SIGXFSZ
78  , SIGXFSZ
79#endif
80#ifdef SIGEMT
81  , SIGEMT
82#endif
83};
84
85static unsigned NumRegisteredSignals = 0;
86static struct {
87  struct sigaction SA;
88  int SigNo;
89} RegisteredSignalInfo[(sizeof(IntSigs)+sizeof(KillSigs))/sizeof(KillSigs[0])];
90
91
92static void RegisterHandler(int Signal) {
93  assert(NumRegisteredSignals <
94         sizeof(RegisteredSignalInfo)/sizeof(RegisteredSignalInfo[0]) &&
95         "Out of space for signal handlers!");
96
97  struct sigaction NewHandler;
98
99  NewHandler.sa_handler = SignalHandler;
100  NewHandler.sa_flags = SA_NODEFER|SA_RESETHAND;
101  sigemptyset(&NewHandler.sa_mask);
102
103  // Install the new handler, save the old one in RegisteredSignalInfo.
104  sigaction(Signal, &NewHandler,
105            &RegisteredSignalInfo[NumRegisteredSignals].SA);
106  RegisteredSignalInfo[NumRegisteredSignals].SigNo = Signal;
107  ++NumRegisteredSignals;
108}
109
110static void RegisterHandlers() {
111  // We need to dereference the signals mutex during handler registration so
112  // that we force its construction. This is to prevent the first use being
113  // during handling an actual signal because you can't safely call new in a
114  // signal handler.
115  *SignalsMutex;
116
117  // If the handlers are already registered, we're done.
118  if (NumRegisteredSignals != 0) return;
119
120  for (auto S : IntSigs) RegisterHandler(S);
121  for (auto S : KillSigs) RegisterHandler(S);
122}
123
124static void UnregisterHandlers() {
125  // Restore all of the signal handlers to how they were before we showed up.
126  for (unsigned i = 0, e = NumRegisteredSignals; i != e; ++i)
127    sigaction(RegisteredSignalInfo[i].SigNo,
128              &RegisteredSignalInfo[i].SA, nullptr);
129  NumRegisteredSignals = 0;
130}
131
132
133/// RemoveFilesToRemove - Process the FilesToRemove list. This function
134/// should be called with the SignalsMutex lock held.
135/// NB: This must be an async signal safe function. It cannot allocate or free
136/// memory, even in debug builds.
137static void RemoveFilesToRemove() {
138  // Avoid constructing ManagedStatic in the signal handler.
139  // If FilesToRemove is not constructed, there are no files to remove.
140  if (!FilesToRemove.isConstructed())
141    return;
142
143  // We avoid iterators in case of debug iterators that allocate or release
144  // memory.
145  std::vector<std::string>& FilesToRemoveRef = *FilesToRemove;
146  for (unsigned i = 0, e = FilesToRemoveRef.size(); i != e; ++i) {
147    const char *path = FilesToRemoveRef[i].c_str();
148
149    // Get the status so we can determine if it's a file or directory. If we
150    // can't stat the file, ignore it.
151    struct stat buf;
152    if (stat(path, &buf) != 0)
153      continue;
154
155    // If this is not a regular file, ignore it. We want to prevent removal of
156    // special files like /dev/null, even if the compiler is being run with the
157    // super-user permissions.
158    if (!S_ISREG(buf.st_mode))
159      continue;
160
161    // Otherwise, remove the file. We ignore any errors here as there is nothing
162    // else we can do.
163    unlink(path);
164  }
165}
166
167// SignalHandler - The signal handler that runs.
168static RETSIGTYPE SignalHandler(int Sig) {
169  // Restore the signal behavior to default, so that the program actually
170  // crashes when we return and the signal reissues.  This also ensures that if
171  // we crash in our signal handler that the program will terminate immediately
172  // instead of recursing in the signal handler.
173  UnregisterHandlers();
174
175  // Unmask all potentially blocked kill signals.
176  sigset_t SigMask;
177  sigfillset(&SigMask);
178  sigprocmask(SIG_UNBLOCK, &SigMask, nullptr);
179
180  {
181    unique_lock<SmartMutex<true>> Guard(*SignalsMutex);
182    RemoveFilesToRemove();
183
184    if (std::find(std::begin(IntSigs), std::end(IntSigs), Sig)
185        != std::end(IntSigs)) {
186      if (InterruptFunction) {
187        void (*IF)() = InterruptFunction;
188        Guard.unlock();
189        InterruptFunction = nullptr;
190        IF();        // run the interrupt function.
191        return;
192      }
193
194      Guard.unlock();
195      raise(Sig);   // Execute the default handler.
196      return;
197   }
198  }
199
200  // Otherwise if it is a fault (like SEGV) run any handler.
201  llvm::sys::RunSignalHandlers();
202
203#ifdef __s390__
204  // On S/390, certain signals are delivered with PSW Address pointing to
205  // *after* the faulting instruction.  Simply returning from the signal
206  // handler would continue execution after that point, instead of
207  // re-raising the signal.  Raise the signal manually in those cases.
208  if (Sig == SIGILL || Sig == SIGFPE || Sig == SIGTRAP)
209    raise(Sig);
210#endif
211}
212
213void llvm::sys::RunInterruptHandlers() {
214  sys::SmartScopedLock<true> Guard(*SignalsMutex);
215  RemoveFilesToRemove();
216}
217
218void llvm::sys::SetInterruptFunction(void (*IF)()) {
219  {
220    sys::SmartScopedLock<true> Guard(*SignalsMutex);
221    InterruptFunction = IF;
222  }
223  RegisterHandlers();
224}
225
226// RemoveFileOnSignal - The public API
227bool llvm::sys::RemoveFileOnSignal(StringRef Filename,
228                                   std::string* ErrMsg) {
229  {
230    sys::SmartScopedLock<true> Guard(*SignalsMutex);
231    FilesToRemove->push_back(Filename);
232  }
233
234  RegisterHandlers();
235  return false;
236}
237
238// DontRemoveFileOnSignal - The public API
239void llvm::sys::DontRemoveFileOnSignal(StringRef Filename) {
240  sys::SmartScopedLock<true> Guard(*SignalsMutex);
241  std::vector<std::string>::reverse_iterator RI =
242    std::find(FilesToRemove->rbegin(), FilesToRemove->rend(), Filename);
243  std::vector<std::string>::iterator I = FilesToRemove->end();
244  if (RI != FilesToRemove->rend())
245    I = FilesToRemove->erase(RI.base()-1);
246}
247
248/// AddSignalHandler - Add a function to be called when a signal is delivered
249/// to the process.  The handler can have a cookie passed to it to identify
250/// what instance of the handler it is.
251void llvm::sys::AddSignalHandler(void (*FnPtr)(void *), void *Cookie) {
252  CallBacksToRun->push_back(std::make_pair(FnPtr, Cookie));
253  RegisterHandlers();
254}
255
256#if defined(HAVE_BACKTRACE) && defined(ENABLE_BACKTRACES) && HAVE_LINK_H &&    \
257    (defined(__linux__) || defined(__FreeBSD__) ||                             \
258     defined(__FreeBSD_kernel__) || defined(__NetBSD__))
259struct DlIteratePhdrData {
260  void **StackTrace;
261  int depth;
262  bool first;
263  const char **modules;
264  intptr_t *offsets;
265  const char *main_exec_name;
266};
267
268static int dl_iterate_phdr_cb(dl_phdr_info *info, size_t size, void *arg) {
269  DlIteratePhdrData *data = (DlIteratePhdrData*)arg;
270  const char *name = data->first ? data->main_exec_name : info->dlpi_name;
271  data->first = false;
272  for (int i = 0; i < info->dlpi_phnum; i++) {
273    const auto *phdr = &info->dlpi_phdr[i];
274    if (phdr->p_type != PT_LOAD)
275      continue;
276    intptr_t beg = info->dlpi_addr + phdr->p_vaddr;
277    intptr_t end = beg + phdr->p_memsz;
278    for (int j = 0; j < data->depth; j++) {
279      if (data->modules[j])
280        continue;
281      intptr_t addr = (intptr_t)data->StackTrace[j];
282      if (beg <= addr && addr < end) {
283        data->modules[j] = name;
284        data->offsets[j] = addr - info->dlpi_addr;
285      }
286    }
287  }
288  return 0;
289}
290
291/// If this is an ELF platform, we can find all loaded modules and their virtual
292/// addresses with dl_iterate_phdr.
293static bool findModulesAndOffsets(void **StackTrace, int Depth,
294                                  const char **Modules, intptr_t *Offsets,
295                                  const char *MainExecutableName,
296                                  StringSaver &StrPool) {
297  DlIteratePhdrData data = {StackTrace, Depth,   true,
298                            Modules,    Offsets, MainExecutableName};
299  dl_iterate_phdr(dl_iterate_phdr_cb, &data);
300  return true;
301}
302#else
303/// This platform does not have dl_iterate_phdr, so we do not yet know how to
304/// find all loaded DSOs.
305static bool findModulesAndOffsets(void **StackTrace, int Depth,
306                                  const char **Modules, intptr_t *Offsets,
307                                  const char *MainExecutableName,
308                                  StringSaver &StrPool) {
309  return false;
310}
311#endif // defined(HAVE_BACKTRACE) && defined(ENABLE_BACKTRACES) && ...
312
313// PrintStackTrace - In the case of a program crash or fault, print out a stack
314// trace so that the user has an indication of why and where we died.
315//
316// On glibc systems we have the 'backtrace' function, which works nicely, but
317// doesn't demangle symbols.
318void llvm::sys::PrintStackTrace(raw_ostream &OS) {
319#if defined(HAVE_BACKTRACE) && defined(ENABLE_BACKTRACES)
320  static void* StackTrace[256];
321  // Use backtrace() to output a backtrace on Linux systems with glibc.
322  int depth = backtrace(StackTrace,
323                        static_cast<int>(array_lengthof(StackTrace)));
324  if (printSymbolizedStackTrace(StackTrace, depth, OS))
325    return;
326#if HAVE_DLFCN_H && __GNUG__
327  int width = 0;
328  for (int i = 0; i < depth; ++i) {
329    Dl_info dlinfo;
330    dladdr(StackTrace[i], &dlinfo);
331    const char* name = strrchr(dlinfo.dli_fname, '/');
332
333    int nwidth;
334    if (!name) nwidth = strlen(dlinfo.dli_fname);
335    else       nwidth = strlen(name) - 1;
336
337    if (nwidth > width) width = nwidth;
338  }
339
340  for (int i = 0; i < depth; ++i) {
341    Dl_info dlinfo;
342    dladdr(StackTrace[i], &dlinfo);
343
344    OS << format("%-2d", i);
345
346    const char* name = strrchr(dlinfo.dli_fname, '/');
347    if (!name) OS << format(" %-*s", width, dlinfo.dli_fname);
348    else       OS << format(" %-*s", width, name+1);
349
350    OS << format(" %#0*lx", (int)(sizeof(void*) * 2) + 2,
351                 (unsigned long)StackTrace[i]);
352
353    if (dlinfo.dli_sname != nullptr) {
354      OS << ' ';
355#  if HAVE_CXXABI_H
356      int res;
357      char* d = abi::__cxa_demangle(dlinfo.dli_sname, nullptr, nullptr, &res);
358#  else
359      char* d = NULL;
360#  endif
361      if (!d) OS << dlinfo.dli_sname;
362      else    OS << d;
363      free(d);
364
365      // FIXME: When we move to C++11, use %t length modifier. It's not in
366      // C++03 and causes gcc to issue warnings. Losing the upper 32 bits of
367      // the stack offset for a stack dump isn't likely to cause any problems.
368      OS << format(" + %u",(unsigned)((char*)StackTrace[i]-
369                                      (char*)dlinfo.dli_saddr));
370    }
371    OS << '\n';
372  }
373#else
374  backtrace_symbols_fd(StackTrace, depth, STDERR_FILENO);
375#endif
376#endif
377}
378
379static void PrintStackTraceSignalHandler(void *) {
380  PrintStackTrace(llvm::errs());
381}
382
383void llvm::sys::DisableSystemDialogsOnCrash() {}
384
385/// PrintStackTraceOnErrorSignal - When an error signal (such as SIGABRT or
386/// SIGSEGV) is delivered to the process, print a stack trace and then exit.
387void llvm::sys::PrintStackTraceOnErrorSignal(bool DisableCrashReporting) {
388  AddSignalHandler(PrintStackTraceSignalHandler, nullptr);
389
390#if defined(__APPLE__) && defined(ENABLE_CRASH_OVERRIDES)
391  // Environment variable to disable any kind of crash dialog.
392  if (DisableCrashReporting || getenv("LLVM_DISABLE_CRASH_REPORT")) {
393    mach_port_t self = mach_task_self();
394
395    exception_mask_t mask = EXC_MASK_CRASH;
396
397    kern_return_t ret = task_set_exception_ports(self,
398                             mask,
399                             MACH_PORT_NULL,
400                             EXCEPTION_STATE_IDENTITY | MACH_EXCEPTION_CODES,
401                             THREAD_STATE_NONE);
402    (void)ret;
403  }
404#endif
405}
406
407
408/***/
409
410// On Darwin, raise sends a signal to the main thread instead of the current
411// thread. This has the unfortunate effect that assert() and abort() will end up
412// bypassing our crash recovery attempts. We work around this for anything in
413// the same linkage unit by just defining our own versions of the assert handler
414// and abort.
415
416#if defined(__APPLE__) && defined(ENABLE_CRASH_OVERRIDES)
417
418#include <signal.h>
419#include <pthread.h>
420
421int raise(int sig) {
422  return pthread_kill(pthread_self(), sig);
423}
424
425void __assert_rtn(const char *func,
426                  const char *file,
427                  int line,
428                  const char *expr) {
429  if (func)
430    fprintf(stderr, "Assertion failed: (%s), function %s, file %s, line %d.\n",
431            expr, func, file, line);
432  else
433    fprintf(stderr, "Assertion failed: (%s), file %s, line %d.\n",
434            expr, file, line);
435  abort();
436}
437
438void abort() {
439  raise(SIGABRT);
440  usleep(1000);
441  __builtin_trap();
442}
443
444#endif
445