1 //===- Signals.cpp - Generic Unix Signals Implementation -----*- C++ -*-===//
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
7 //===----------------------------------------------------------------------===//
9 // This file defines some helpful functions for dealing with the possibility of
10 // Unix signals occurring while your program is running.
12 //===----------------------------------------------------------------------===//
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:
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.
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!
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
33 //===----------------------------------------------------------------------===//
36 #include "llvm/ADT/STLExtras.h"
37 #include "llvm/Config/config.h"
38 #include "llvm/Demangle/Demangle.h"
39 #include "llvm/Support/FileSystem.h"
40 #include "llvm/Support/FileUtilities.h"
41 #include "llvm/Support/Format.h"
42 #include "llvm/Support/MemoryBuffer.h"
43 #include "llvm/Support/Mutex.h"
44 #include "llvm/Support/Program.h"
45 #include "llvm/Support/SaveAndRestore.h"
46 #include "llvm/Support/raw_ostream.h"
51 # include BACKTRACE_HEADER // For backtrace().
63 #include <mach/mach.h>
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
76 #undef HAVE__UNWIND_BACKTRACE
82 static RETSIGTYPE SignalHandler(int Sig); // defined below.
83 static RETSIGTYPE InfoSignalHandler(int Sig); // defined below.
85 using SignalHandlerFunctionType = void (*)();
86 /// The function to call if ctrl-c is pressed.
87 static std::atomic<SignalHandlerFunctionType> InterruptFunction =
88 ATOMIC_VAR_INIT(nullptr);
89 static std::atomic<SignalHandlerFunctionType> InfoSignalFunction =
90 ATOMIC_VAR_INIT(nullptr);
91 /// The function to call on SIGPIPE (one-time use only).
92 static std::atomic<SignalHandlerFunctionType> OneShotPipeSignalFunction =
93 ATOMIC_VAR_INIT(nullptr);
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.
100 class FileToRemoveList {
101 std::atomic<char *> Filename = ATOMIC_VAR_INIT(nullptr);
102 std::atomic<FileToRemoveList *> Next = ATOMIC_VAR_INIT(nullptr);
104 FileToRemoveList() = default;
106 FileToRemoveList(const std::string &str) : Filename(strdup(str.c_str())) {}
110 ~FileToRemoveList() {
111 if (FileToRemoveList *N = Next.exchange(nullptr))
113 if (char *F = Filename.exchange(nullptr))
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;
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
135 static ManagedStatic<sys::SmartMutex<true>> Lock;
136 sys::SmartScopedLock<true> Writer(*Lock);
138 for (FileToRemoveList *Current = Head.load(); Current;
139 Current = Current->Next.load()) {
140 if (char *OldFilename = Current->Filename.load()) {
141 if (OldFilename != Filename)
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.
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);
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.
169 if (stat(path, &buf) != 0)
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))
178 // Otherwise, remove the file. We ignore any errors here as there is
179 // nothing else we can do.
182 // We're done removing the file, erasing can safely proceed.
183 currentFile->Filename.exchange(path);
187 // We're done removing files, cleanup can safely proceed.
188 Head.exchange(OldHead);
191 static std::atomic<FileToRemoveList *> FilesToRemove = ATOMIC_VAR_INIT(nullptr);
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!
196 struct FilesToRemoveCleanup {
198 ~FilesToRemoveCleanup() {
199 FileToRemoveList *Head = FilesToRemove.exchange(nullptr);
206 static StringRef Argv0;
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.
211 static const int IntSigs[] = {
212 SIGHUP, SIGINT, SIGTERM, SIGUSR2
215 /// Signals that represent that we have a bug, and our prompt termination has
217 static const int KillSigs[] = {
218 SIGILL, SIGTRAP, SIGABRT, SIGFPE, SIGBUS, SIGSEGV, SIGQUIT
233 /// Signals that represent requests for status.
234 static const int InfoSigs[] = {
241 static const size_t NumSigs =
242 array_lengthof(IntSigs) + array_lengthof(KillSigs) +
243 array_lengthof(InfoSigs) + 1 /* SIGPIPE */;
246 static std::atomic<unsigned> NumRegisteredSignals = ATOMIC_VAR_INIT(0);
250 } RegisteredSignalInfo[NumSigs];
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.
257 static stack_t OldAltStack;
258 static void* NewAltStackPointer;
260 static void CreateSigAltStack() {
261 const size_t AltStackSize = MINSIGSTKSZ + 64 * 1024;
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
267 if (sigaltstack(nullptr, &OldAltStack) != 0 ||
268 OldAltStack.ss_flags & SS_ONSTACK ||
269 (OldAltStack.ss_sp && OldAltStack.ss_size >= AltStackSize))
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);
280 static void CreateSigAltStack() {}
283 static 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);
290 // If the handlers are already registered, we're done.
291 if (NumRegisteredSignals.load() != 0)
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.
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!");
304 struct sigaction NewHandler;
307 case SignalKind::IsKill:
308 NewHandler.sa_handler = SignalHandler;
309 NewHandler.sa_flags = SA_NODEFER | SA_RESETHAND | SA_ONSTACK;
311 case SignalKind::IsInfo:
312 NewHandler.sa_handler = InfoSignalHandler;
313 NewHandler.sa_flags = SA_ONSTACK;
316 sigemptyset(&NewHandler.sa_mask);
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;
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);
334 static void 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;
343 /// Process the FilesToRemove list.
344 static void RemoveFilesToRemove() {
345 FileToRemoveList::removeAllFiles(FilesToRemove);
348 void sys::CleanupOnSignal(uintptr_t Context) {
349 int Sig = (int)Context;
351 if (llvm::is_contained(InfoSigs, Sig)) {
352 InfoSignalHandler(Sig);
356 RemoveFilesToRemove();
358 if (llvm::is_contained(IntSigs, Sig) || Sig == SIGPIPE)
361 llvm::sys::RunSignalHandlers();
364 // The signal handler that runs.
365 static RETSIGTYPE 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 UnregisterHandlers();
372 // Unmask all potentially blocked kill signals.
374 sigfillset(&SigMask);
375 sigprocmask(SIG_UNBLOCK, &SigMask, nullptr);
378 RemoveFilesToRemove();
381 if (auto OldOneShotPipeFunction =
382 OneShotPipeSignalFunction.exchange(nullptr))
383 return OldOneShotPipeFunction();
385 if (std::find(std::begin(IntSigs), std::end(IntSigs), Sig)
386 != std::end(IntSigs)) {
387 if (auto OldInterruptFunction = InterruptFunction.exchange(nullptr))
388 return OldInterruptFunction();
390 raise(Sig); // Execute the default handler.
395 // Otherwise if it is a fault (like SEGV) run any handler.
396 llvm::sys::RunSignalHandlers();
399 // On S/390, certain signals are delivered with PSW Address pointing to
400 // *after* the faulting instruction. Simply returning from the signal
401 // handler would continue execution after that point, instead of
402 // re-raising the signal. Raise the signal manually in those cases.
403 if (Sig == SIGILL || Sig == SIGFPE || Sig == SIGTRAP)
408 static RETSIGTYPE InfoSignalHandler(int Sig) {
409 SaveAndRestore<int> SaveErrnoDuringASignalHandler(errno);
410 if (SignalHandlerFunctionType CurrentInfoFunction = InfoSignalFunction)
411 CurrentInfoFunction();
414 void llvm::sys::RunInterruptHandlers() {
415 RemoveFilesToRemove();
418 void llvm::sys::SetInterruptFunction(void (*IF)()) {
419 InterruptFunction.exchange(IF);
423 void llvm::sys::SetInfoSignalFunction(void (*Handler)()) {
424 InfoSignalFunction.exchange(Handler);
428 void llvm::sys::SetOneShotPipeSignalFunction(void (*Handler)()) {
429 OneShotPipeSignalFunction.exchange(Handler);
433 void llvm::sys::DefaultOneShotPipeSignalHandler() {
434 // Send a special return code that drivers can check for, from sysexits.h.
439 bool llvm::sys::RemoveFileOnSignal(StringRef Filename,
440 std::string* ErrMsg) {
441 // Ensure that cleanup will occur as soon as one file is added.
442 static ManagedStatic<FilesToRemoveCleanup> FilesToRemoveCleanup;
443 *FilesToRemoveCleanup;
444 FileToRemoveList::insert(FilesToRemove, Filename.str());
450 void llvm::sys::DontRemoveFileOnSignal(StringRef Filename) {
451 FileToRemoveList::erase(FilesToRemove, Filename.str());
454 /// Add a function to be called when a signal is delivered to the process. The
455 /// handler can have a cookie passed to it to identify what instance of the
457 void llvm::sys::AddSignalHandler(sys::SignalHandlerCallback FnPtr,
458 void *Cookie) { // Signal-safe.
459 insertSignalHandler(FnPtr, Cookie);
463 #if defined(HAVE_BACKTRACE) && ENABLE_BACKTRACES && HAVE_LINK_H && \
464 (defined(__linux__) || defined(__FreeBSD__) || \
465 defined(__FreeBSD_kernel__) || defined(__NetBSD__))
466 struct DlIteratePhdrData {
470 const char **modules;
472 const char *main_exec_name;
475 static int dl_iterate_phdr_cb(dl_phdr_info *info, size_t size, void *arg) {
476 DlIteratePhdrData *data = (DlIteratePhdrData*)arg;
477 const char *name = data->first ? data->main_exec_name : info->dlpi_name;
479 for (int i = 0; i < info->dlpi_phnum; i++) {
480 const auto *phdr = &info->dlpi_phdr[i];
481 if (phdr->p_type != PT_LOAD)
483 intptr_t beg = info->dlpi_addr + phdr->p_vaddr;
484 intptr_t end = beg + phdr->p_memsz;
485 for (int j = 0; j < data->depth; j++) {
486 if (data->modules[j])
488 intptr_t addr = (intptr_t)data->StackTrace[j];
489 if (beg <= addr && addr < end) {
490 data->modules[j] = name;
491 data->offsets[j] = addr - info->dlpi_addr;
498 /// If this is an ELF platform, we can find all loaded modules and their virtual
499 /// addresses with dl_iterate_phdr.
500 static bool findModulesAndOffsets(void **StackTrace, int Depth,
501 const char **Modules, intptr_t *Offsets,
502 const char *MainExecutableName,
503 StringSaver &StrPool) {
504 DlIteratePhdrData data = {StackTrace, Depth, true,
505 Modules, Offsets, MainExecutableName};
506 dl_iterate_phdr(dl_iterate_phdr_cb, &data);
510 /// This platform does not have dl_iterate_phdr, so we do not yet know how to
511 /// find all loaded DSOs.
512 static bool findModulesAndOffsets(void **StackTrace, int Depth,
513 const char **Modules, intptr_t *Offsets,
514 const char *MainExecutableName,
515 StringSaver &StrPool) {
518 #endif // defined(HAVE_BACKTRACE) && ENABLE_BACKTRACES && ...
520 #if ENABLE_BACKTRACES && defined(HAVE__UNWIND_BACKTRACE)
521 static int unwindBacktrace(void **StackTrace, int MaxEntries) {
525 // Skip the first frame ('unwindBacktrace' itself).
528 auto HandleFrame = [&](_Unwind_Context *Context) -> _Unwind_Reason_Code {
529 // Apparently we need to detect reaching the end of the stack ourselves.
530 void *IP = (void *)_Unwind_GetIP(Context);
532 return _URC_END_OF_STACK;
534 assert(Entries < MaxEntries && "recursively called after END_OF_STACK?");
536 StackTrace[Entries] = IP;
538 if (++Entries == MaxEntries)
539 return _URC_END_OF_STACK;
540 return _URC_NO_REASON;
544 [](_Unwind_Context *Context, void *Handler) {
545 return (*static_cast<decltype(HandleFrame) *>(Handler))(Context);
547 static_cast<void *>(&HandleFrame));
548 return std::max(Entries, 0);
552 // In the case of a program crash or fault, print out a stack trace so that the
553 // user has an indication of why and where we died.
555 // On glibc systems we have the 'backtrace' function, which works nicely, but
556 // doesn't demangle symbols.
557 void llvm::sys::PrintStackTrace(raw_ostream &OS) {
558 #if ENABLE_BACKTRACES
559 static void *StackTrace[256];
561 #if defined(HAVE_BACKTRACE)
562 // Use backtrace() to output a backtrace on Linux systems with glibc.
564 depth = backtrace(StackTrace, static_cast<int>(array_lengthof(StackTrace)));
566 #if defined(HAVE__UNWIND_BACKTRACE)
567 // Try _Unwind_Backtrace() if backtrace() failed.
569 depth = unwindBacktrace(StackTrace,
570 static_cast<int>(array_lengthof(StackTrace)));
575 if (printSymbolizedStackTrace(Argv0, StackTrace, depth, OS))
577 #if HAVE_DLFCN_H && HAVE_DLADDR
579 for (int i = 0; i < depth; ++i) {
581 dladdr(StackTrace[i], &dlinfo);
582 const char* name = strrchr(dlinfo.dli_fname, '/');
585 if (!name) nwidth = strlen(dlinfo.dli_fname);
586 else nwidth = strlen(name) - 1;
588 if (nwidth > width) width = nwidth;
591 for (int i = 0; i < depth; ++i) {
593 dladdr(StackTrace[i], &dlinfo);
595 OS << format("%-2d", i);
597 const char* name = strrchr(dlinfo.dli_fname, '/');
598 if (!name) OS << format(" %-*s", width, dlinfo.dli_fname);
599 else OS << format(" %-*s", width, name+1);
601 OS << format(" %#0*lx", (int)(sizeof(void*) * 2) + 2,
602 (unsigned long)StackTrace[i]);
604 if (dlinfo.dli_sname != nullptr) {
607 char* d = itaniumDemangle(dlinfo.dli_sname, nullptr, nullptr, &res);
608 if (!d) OS << dlinfo.dli_sname;
612 OS << format(" + %tu", (static_cast<const char*>(StackTrace[i])-
613 static_cast<const char*>(dlinfo.dli_saddr)));
617 #elif defined(HAVE_BACKTRACE)
618 backtrace_symbols_fd(StackTrace, depth, STDERR_FILENO);
623 static void PrintStackTraceSignalHandler(void *) {
624 sys::PrintStackTrace(llvm::errs());
627 void llvm::sys::DisableSystemDialogsOnCrash() {}
629 /// When an error signal (such as SIGABRT or SIGSEGV) is delivered to the
630 /// process, print a stack trace and then exit.
631 void llvm::sys::PrintStackTraceOnErrorSignal(StringRef Argv0,
632 bool DisableCrashReporting) {
635 AddSignalHandler(PrintStackTraceSignalHandler, nullptr);
637 #if defined(__APPLE__) && ENABLE_CRASH_OVERRIDES
638 // Environment variable to disable any kind of crash dialog.
639 if (DisableCrashReporting || getenv("LLVM_DISABLE_CRASH_REPORT")) {
640 mach_port_t self = mach_task_self();
642 exception_mask_t mask = EXC_MASK_CRASH;
644 kern_return_t ret = task_set_exception_ports(self,
647 EXCEPTION_STATE_IDENTITY | MACH_EXCEPTION_CODES,