//===- Signals.cpp - Generic Unix Signals Implementation -----*- C++ -*-===//

//

// 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

//

//===----------------------------------------------------------------------===//

//

// This file defines some helpful functions for dealing with the possibility of

// Unix signals occurring while your program is running.

//

//===----------------------------------------------------------------------===//

//

// This file is extremely careful to only do signal-safe things while in a

// signal handler. In particular, memory allocation and acquiring a mutex

// while in a signal handler should never occur. ManagedStatic isn't usable from

// a signal handler for 2 reasons:

//

//  1. Creating a new one allocates.

//  2. The signal handler could fire while llvm_shutdown is being processed, in

//     which case the ManagedStatic is in an unknown state because it could

//     already have been destroyed, or be in the process of being destroyed.

//

// Modifying the behavior of the signal handlers (such as registering new ones)

// can acquire a mutex, but all this guarantees is that the signal handler

// behavior is only modified by one thread at a time. A signal handler can still

// fire while this occurs!

//

// Adding work to a signal handler requires lock-freedom (and assume atomics are

// always lock-free) because the signal handler could fire while new work is

// being added.

//

//===----------------------------------------------------------------------===//

#include "Unix.h"

#include "llvm/ADT/STLExtras.h"

#include "llvm/Config/config.h"

#include "llvm/Demangle/Demangle.h"

#include "llvm/Support/FileSystem.h"

#include "llvm/Support/FileUtilities.h"

#include "llvm/Support/Format.h"

#include "llvm/Support/MemoryBuffer.h"

#include "llvm/Support/Mutex.h"

#include "llvm/Support/Program.h"

#include "llvm/Support/SaveAndRestore.h"

#include "llvm/Support/raw_ostream.h"

#include <algorithm>

#include <string>

#include <sysexits.h>

#ifdef HAVE_BACKTRACE

# include BACKTRACE_HEADER         // For backtrace().

#endif

#if HAVE_SIGNAL_H

#include <signal.h>

#endif

#if HAVE_SYS_STAT_H

#include <sys/stat.h>

#endif

#if HAVE_DLFCN_H

#include <dlfcn.h>

#endif

#if HAVE_MACH_MACH_H

#include <mach/mach.h>

#endif

#if HAVE_LINK_H

#include <link.h>

#endif

#ifdef HAVE__UNWIND_BACKTRACE

// FIXME: We should be able to use <unwind.h> for any target that has an

// _Unwind_Backtrace function, but on FreeBSD the configure test passes

// despite the function not existing, and on Android, <unwind.h> conflicts

// with <link.h>.

#ifdef __GLIBC__

#include <unwind.h>

#else

#undef HAVE__UNWIND_BACKTRACE

#endif

#endif

using namespace llvm;

static RETSIGTYPE SignalHandler(int Sig);  // defined below.

static RETSIGTYPE InfoSignalHandler(int Sig);  // defined below.

using SignalHandlerFunctionType = void (*)();

/// The function to call if ctrl-c is pressed.

static std::atomic<SignalHandlerFunctionType> InterruptFunction =

    ATOMIC_VAR_INIT(nullptr);

static std::atomic<SignalHandlerFunctionType> InfoSignalFunction =

    ATOMIC_VAR_INIT(nullptr);

/// The function to call on SIGPIPE (one-time use only).

static std::atomic<SignalHandlerFunctionType> OneShotPipeSignalFunction =

    ATOMIC_VAR_INIT(nullptr);

namespace {

/// Signal-safe removal of files.

/// Inserting and erasing from the list isn't signal-safe, but removal of files

/// themselves is signal-safe. Memory is freed when the head is freed, deletion

/// is therefore not signal-safe either.

class FileToRemoveList {

  std::atomic<char *> Filename = ATOMIC_VAR_INIT(nullptr);

  std::atomic<FileToRemoveList *> Next = ATOMIC_VAR_INIT(nullptr);

  FileToRemoveList() = default;

  // Not signal-safe.

  FileToRemoveList(const std::string &str) : Filename(strdup(str.c_str())) {}

public:

  // Not signal-safe.

  ~FileToRemoveList() {

    if (FileToRemoveList *N = Next.exchange(nullptr))

      delete N;

    if (char *F = Filename.exchange(nullptr))

      free(F);

  }

  // Not signal-safe.

  static void insert(std::atomic<FileToRemoveList *> &Head,

                     const std::string &Filename) {

    // Insert the new file at the end of the list.

    FileToRemoveList *NewHead = new FileToRemoveList(Filename);

    std::atomic<FileToRemoveList *> *InsertionPoint = &Head;

    FileToRemoveList *OldHead = nullptr;

    while (!InsertionPoint->compare_exchange_strong(OldHead, NewHead)) {

      InsertionPoint = &OldHead->Next;

      OldHead = nullptr;

    }

  }

  // Not signal-safe.

  static void erase(std::atomic<FileToRemoveList *> &Head,

                    const std::string &Filename) {

    // Use a lock to avoid concurrent erase: the comparison would access

    // free'd memory.

    static ManagedStatic<sys::SmartMutex<true>> Lock;

    sys::SmartScopedLock<true> Writer(*Lock);

    for (FileToRemoveList *Current = Head.load(); Current;

         Current = Current->Next.load()) {

      if (char *OldFilename = Current->Filename.load()) {

        if (OldFilename != Filename)

          continue;

        // Leave an empty filename.

        OldFilename = Current->Filename.exchange(nullptr);

        // The filename might have become null between the time we

        // compared it and we exchanged it.

        if (OldFilename)

          free(OldFilename);

      }

    }

  }

  // Signal-safe.

  static void removeAllFiles(std::atomic<FileToRemoveList *> &Head) {

    // If cleanup were to occur while we're removing files we'd have a bad time.

    // Make sure we're OK by preventing cleanup from doing anything while we're

    // removing files. If cleanup races with us and we win we'll have a leak,

    // but we won't crash.

    FileToRemoveList *OldHead = Head.exchange(nullptr);

    for (FileToRemoveList *currentFile = OldHead; currentFile;

         currentFile = currentFile->Next.load()) {

      // If erasing was occuring while we're trying to remove files we'd look

      // at free'd data. Take away the path and put it back when done.

      if (char *path = currentFile->Filename.exchange(nullptr)) {

        // Get the status so we can determine if it's a file or directory. If we

        // can't stat the file, ignore it.

        struct stat buf;

        if (stat(path, &buf) != 0)

          continue;

        // If this is not a regular file, ignore it. We want to prevent removal

        // of special files like /dev/null, even if the compiler is being run

        // with the super-user permissions.

        if (!S_ISREG(buf.st_mode))

          continue;

        // Otherwise, remove the file. We ignore any errors here as there is

        // nothing else we can do.

        unlink(path);

        // We're done removing the file, erasing can safely proceed.

        currentFile->Filename.exchange(path);

      }

    }

    // We're done removing files, cleanup can safely proceed.

    Head.exchange(OldHead);

  }

};

static std::atomic<FileToRemoveList *> FilesToRemove = ATOMIC_VAR_INIT(nullptr);

/// Clean up the list in a signal-friendly manner.

/// Recall that signals can fire during llvm_shutdown. If this occurs we should

/// either clean something up or nothing at all, but we shouldn't crash!

struct FilesToRemoveCleanup {

  // Not signal-safe.

  ~FilesToRemoveCleanup() {

    FileToRemoveList *Head = FilesToRemove.exchange(nullptr);

    if (Head)

      delete Head;

  }

};

} // namespace

static StringRef Argv0;

/// Signals that represent requested termination. There's no bug or failure, or

/// if there is, it's not our direct responsibility. For whatever reason, our

/// continued execution is no longer desirable.

static const int IntSigs[] = {

  SIGHUP, SIGINT, SIGTERM, SIGUSR2

};

/// Signals that represent that we have a bug, and our prompt termination has

/// been ordered.

static const int KillSigs[] = {

  SIGILL, SIGTRAP, SIGABRT, SIGFPE, SIGBUS, SIGSEGV, SIGQUIT

#ifdef SIGSYS

  , SIGSYS

#endif

#ifdef SIGXCPU

  , SIGXCPU

#endif

#ifdef SIGXFSZ

  , SIGXFSZ

#endif

#ifdef SIGEMT

  , SIGEMT

#endif

};

/// Signals that represent requests for status.

static const int InfoSigs[] = {

  SIGUSR1

#ifdef SIGINFO

  , SIGINFO

#endif

};

static const size_t NumSigs =

    array_lengthof(IntSigs) + array_lengthof(KillSigs) +

    array_lengthof(InfoSigs) + 1 /* SIGPIPE */;

static std::atomic<unsigned> NumRegisteredSignals = ATOMIC_VAR_INIT(0);

static struct {

  struct sigaction SA;

  int SigNo;

} RegisteredSignalInfo[NumSigs];

#if defined(HAVE_SIGALTSTACK)

// Hold onto both the old and new alternate signal stack so that it's not

// reported as a leak. We don't make any attempt to remove our alt signal

// stack if we remove our signal handlers; that can't be done reliably if

// someone else is also trying to do the same thing.

static stack_t OldAltStack;

static void* NewAltStackPointer;

static void CreateSigAltStack() {

  const size_t AltStackSize = MINSIGSTKSZ + 64 * 1024;

  // If we're executing on the alternate stack, or we already have an alternate

  // signal stack that we're happy with, there's nothing for us to do. Don't

  // reduce the size, some other part of the process might need a larger stack

  // than we do.

  if (sigaltstack(nullptr, &OldAltStack) != 0 ||

      OldAltStack.ss_flags & SS_ONSTACK ||

      (OldAltStack.ss_sp && OldAltStack.ss_size >= AltStackSize))

    return;

  stack_t AltStack = {};

  AltStack.ss_sp = static_cast<char *>(safe_malloc(AltStackSize));

  NewAltStackPointer = AltStack.ss_sp; // Save to avoid reporting a leak.

  AltStack.ss_size = AltStackSize;

  if (sigaltstack(&AltStack, &OldAltStack) != 0)

    free(AltStack.ss_sp);

}

#else

static void CreateSigAltStack() {}

#endif

static void RegisterHandlers() { // Not signal-safe.

  // The mutex prevents other threads from registering handlers while we're

  // doing it. We also have to protect the handlers and their count because

  // a signal handler could fire while we're registeting handlers.

  static ManagedStatic<sys::SmartMutex<true>> SignalHandlerRegistrationMutex;

  sys::SmartScopedLock<true> Guard(*SignalHandlerRegistrationMutex);

  // If the handlers are already registered, we're done.

  if (NumRegisteredSignals.load() != 0)

    return;

  // Create an alternate stack for signal handling. This is necessary for us to

  // be able to reliably handle signals due to stack overflow.

  CreateSigAltStack();

  enum class SignalKind { IsKill, IsInfo };

  auto registerHandler = [&](int Signal, SignalKind Kind) {

    unsigned Index = NumRegisteredSignals.load();

    assert(Index < array_lengthof(RegisteredSignalInfo) &&

           "Out of space for signal handlers!");

    struct sigaction NewHandler;

    switch (Kind) {

    case SignalKind::IsKill:

      NewHandler.sa_handler = SignalHandler;

      NewHandler.sa_flags = SA_NODEFER | SA_RESETHAND | SA_ONSTACK;

      break;

    case SignalKind::IsInfo:

      NewHandler.sa_handler = InfoSignalHandler;

      NewHandler.sa_flags = SA_ONSTACK;

      break;

    }

    sigemptyset(&NewHandler.sa_mask);

    // Install the new handler, save the old one in RegisteredSignalInfo.

    sigaction(Signal, &NewHandler, &RegisteredSignalInfo[Index].SA);

    RegisteredSignalInfo[Index].SigNo = Signal;

    ++NumRegisteredSignals;

  };

  for (auto S : IntSigs)

    registerHandler(S, SignalKind::IsKill);

  for (auto S : KillSigs)

    registerHandler(S, SignalKind::IsKill);

  if (OneShotPipeSignalFunction)

    registerHandler(SIGPIPE, SignalKind::IsKill);

  for (auto S : InfoSigs)

    registerHandler(S, SignalKind::IsInfo);

}

static void UnregisterHandlers() {

  // Restore all of the signal handlers to how they were before we showed up.

  for (unsigned i = 0, e = NumRegisteredSignals.load(); i != e; ++i) {

    sigaction(RegisteredSignalInfo[i].SigNo,

              &RegisteredSignalInfo[i].SA, nullptr);

    --NumRegisteredSignals;

  }

}

/// Process the FilesToRemove list.

static void RemoveFilesToRemove() {

  FileToRemoveList::removeAllFiles(FilesToRemove);

}

void sys::CleanupOnSignal(uintptr_t Context) {

  int Sig = (int)Context;

  if (llvm::is_contained(InfoSigs, Sig)) {

    InfoSignalHandler(Sig);

    return;

  }

  RemoveFilesToRemove();

  if (llvm::is_contained(IntSigs, Sig) || Sig == SIGPIPE)

    return;

  llvm::sys::RunSignalHandlers();

}

// The signal handler that runs.

static RETSIGTYPE SignalHandler(int Sig) {

  // Restore the signal behavior to default, so that the program actually

  // crashes when we return and the signal reissues.  This also ensures that if

  // we crash in our signal handler that the program will terminate immediately

  // instead of recursing in the signal handler.

  UnregisterHandlers();

  // Unmask all potentially blocked kill signals.

  sigset_t SigMask;

  sigfillset(&SigMask);

  sigprocmask(SIG_UNBLOCK, &SigMask, nullptr);

  {

    RemoveFilesToRemove();

    if (Sig == SIGPIPE)

      if (auto OldOneShotPipeFunction =

              OneShotPipeSignalFunction.exchange(nullptr))

        return OldOneShotPipeFunction();

    if (std::find(std::begin(IntSigs), std::end(IntSigs), Sig)

        != std::end(IntSigs)) {

      if (auto OldInterruptFunction = InterruptFunction.exchange(nullptr))

        return OldInterruptFunction();

      raise(Sig);   // Execute the default handler.

      return;

   }

  }

  // Otherwise if it is a fault (like SEGV) run any handler.

  llvm::sys::RunSignalHandlers();

#ifdef __s390__

  // On S/390, certain signals are delivered with PSW Address pointing to

  // *after* the faulting instruction.  Simply returning from the signal

  // handler would continue execution after that point, instead of

  // re-raising the signal.  Raise the signal manually in those cases.

  if (Sig == SIGILL || Sig == SIGFPE || Sig == SIGTRAP)

    raise(Sig);

#endif

}

static RETSIGTYPE InfoSignalHandler(int Sig) {

  SaveAndRestore<int> SaveErrnoDuringASignalHandler(errno);

  if (SignalHandlerFunctionType CurrentInfoFunction = InfoSignalFunction)

    CurrentInfoFunction();

}

void llvm::sys::RunInterruptHandlers() {

  RemoveFilesToRemove();

}

void llvm::sys::SetInterruptFunction(void (*IF)()) {

  InterruptFunction.exchange(IF);

  RegisterHandlers();

}

void llvm::sys::SetInfoSignalFunction(void (*Handler)()) {

  InfoSignalFunction.exchange(Handler);

  RegisterHandlers();

}

void llvm::sys::SetOneShotPipeSignalFunction(void (*Handler)()) {

  OneShotPipeSignalFunction.exchange(Handler);

  RegisterHandlers();

}

void llvm::sys::DefaultOneShotPipeSignalHandler() {

  // Send a special return code that drivers can check for, from sysexits.h.

  exit(EX_IOERR);

}

// The public API

bool llvm::sys::RemoveFileOnSignal(StringRef Filename,

                                   std::string* ErrMsg) {

  // Ensure that cleanup will occur as soon as one file is added.

  static ManagedStatic<FilesToRemoveCleanup> FilesToRemoveCleanup;

  *FilesToRemoveCleanup;

  FileToRemoveList::insert(FilesToRemove, Filename.str());

  RegisterHandlers();

  return false;

}

// The public API

void llvm::sys::DontRemoveFileOnSignal(StringRef Filename) {

  FileToRemoveList::erase(FilesToRemove, Filename.str());

}

/// Add a function to be called when a signal is delivered to the process. The

/// handler can have a cookie passed to it to identify what instance of the

/// handler it is.

void llvm::sys::AddSignalHandler(sys::SignalHandlerCallback FnPtr,

                                 void *Cookie) { // Signal-safe.

  insertSignalHandler(FnPtr, Cookie);

  RegisterHandlers();

}

#if defined(HAVE_BACKTRACE) && ENABLE_BACKTRACES && HAVE_LINK_H &&    \

    (defined(__linux__) || defined(__FreeBSD__) ||                             \

     defined(__FreeBSD_kernel__) || defined(__NetBSD__))

struct DlIteratePhdrData {

  void **StackTrace;

  int depth;

  bool first;

  const char **modules;

  intptr_t *offsets;

  const char *main_exec_name;

};

static int dl_iterate_phdr_cb(dl_phdr_info *info, size_t size, void *arg) {

  DlIteratePhdrData *data = (DlIteratePhdrData*)arg;

  const char *name = data->first ? data->main_exec_name : info->dlpi_name;

  data->first = false;

  for (int i = 0; i < info->dlpi_phnum; i++) {

    const auto *phdr = &info->dlpi_phdr[i];

    if (phdr->p_type != PT_LOAD)

      continue;

    intptr_t beg = info->dlpi_addr + phdr->p_vaddr;

    intptr_t end = beg + phdr->p_memsz;

    for (int j = 0; j < data->depth; j++) {

      if (data->modules[j])

        continue;

      intptr_t addr = (intptr_t)data->StackTrace[j];

      if (beg <= addr && addr < end) {

        data->modules[j] = name;

        data->offsets[j] = addr - info->dlpi_addr;

      }

    }

  }

  return 0;

}

/// If this is an ELF platform, we can find all loaded modules and their virtual

/// addresses with dl_iterate_phdr.

static bool findModulesAndOffsets(void **StackTrace, int Depth,

                                  const char **Modules, intptr_t *Offsets,

                                  const char *MainExecutableName,

                                  StringSaver &StrPool) {

  DlIteratePhdrData data = {StackTrace, Depth,   true,

                            Modules,    Offsets, MainExecutableName};

  dl_iterate_phdr(dl_iterate_phdr_cb, &data);

  return true;

}

#else

/// This platform does not have dl_iterate_phdr, so we do not yet know how to

/// find all loaded DSOs.

static bool findModulesAndOffsets(void **StackTrace, int Depth,

                                  const char **Modules, intptr_t *Offsets,

                                  const char *MainExecutableName,

                                  StringSaver &StrPool) {

  return false;

}

#endif // defined(HAVE_BACKTRACE) && ENABLE_BACKTRACES && ...

#if ENABLE_BACKTRACES && defined(HAVE__UNWIND_BACKTRACE)

static int unwindBacktrace(void **StackTrace, int MaxEntries) {

  if (MaxEntries < 0)

    return 0;

  // Skip the first frame ('unwindBacktrace' itself).

  int Entries = -1;

  auto HandleFrame = [&](_Unwind_Context *Context) -> _Unwind_Reason_Code {

    // Apparently we need to detect reaching the end of the stack ourselves.

    void *IP = (void *)_Unwind_GetIP(Context);

    if (!IP)

      return _URC_END_OF_STACK;

    assert(Entries < MaxEntries && "recursively called after END_OF_STACK?");

    if (Entries >= 0)

      StackTrace[Entries] = IP;

    if (++Entries == MaxEntries)

      return _URC_END_OF_STACK;

    return _URC_NO_REASON;

  };

  _Unwind_Backtrace(

      [](_Unwind_Context *Context, void *Handler) {

        return (*static_cast<decltype(HandleFrame) *>(Handler))(Context);

      },

      static_cast<void *>(&HandleFrame));

  return std::max(Entries, 0);

}

#endif

// In the case of a program crash or fault, print out a stack trace so that the

// user has an indication of why and where we died.

//

// On glibc systems we have the 'backtrace' function, which works nicely, but

// doesn't demangle symbols.

void llvm::sys::PrintStackTrace(raw_ostream &OS) {

#if ENABLE_BACKTRACES

  static void *StackTrace[256];

  int depth = 0;

#if defined(HAVE_BACKTRACE)

  // Use backtrace() to output a backtrace on Linux systems with glibc.

  if (!depth)

    depth = backtrace(StackTrace, static_cast<int>(array_lengthof(StackTrace)));

#endif

#if defined(HAVE__UNWIND_BACKTRACE)

  // Try _Unwind_Backtrace() if backtrace() failed.

  if (!depth)

    depth = unwindBacktrace(StackTrace,

                        static_cast<int>(array_lengthof(StackTrace)));

#endif

  if (!depth)

    return;

  if (printSymbolizedStackTrace(Argv0, StackTrace, depth, OS))

    return;

#if HAVE_DLFCN_H && HAVE_DLADDR

  int width = 0;

  for (int i = 0; i < depth; ++i) {

    Dl_info dlinfo;

    dladdr(StackTrace[i], &dlinfo);

    const char* name = strrchr(dlinfo.dli_fname, '/');

    int nwidth;

    if (!name) nwidth = strlen(dlinfo.dli_fname);

    else       nwidth = strlen(name) - 1;

    if (nwidth > width) width = nwidth;

  }

  for (int i = 0; i < depth; ++i) {

    Dl_info dlinfo;

    dladdr(StackTrace[i], &dlinfo);

    OS << format("%-2d", i);

    const char* name = strrchr(dlinfo.dli_fname, '/');

    if (!name) OS << format(" %-*s", width, dlinfo.dli_fname);

    else       OS << format(" %-*s", width, name+1);

    OS << format(" %#0*lx", (int)(sizeof(void*) * 2) + 2,

                 (unsigned long)StackTrace[i]);

    if (dlinfo.dli_sname != nullptr) {

      OS << ' ';

      int res;

      char* d = itaniumDemangle(dlinfo.dli_sname, nullptr, nullptr, &res);

      if (!d) OS << dlinfo.dli_sname;

      else    OS << d;

      free(d);

      OS << format(" + %tu", (static_cast<const char*>(StackTrace[i])-

                              static_cast<const char*>(dlinfo.dli_saddr)));

    }

    OS << '\n';

  }

#elif defined(HAVE_BACKTRACE)

  backtrace_symbols_fd(StackTrace, depth, STDERR_FILENO);

#endif

#endif

}

static void PrintStackTraceSignalHandler(void *) {

  sys::PrintStackTrace(llvm::errs());

}

void llvm::sys::DisableSystemDialogsOnCrash() {}

/// When an error signal (such as SIGABRT or SIGSEGV) is delivered to the

/// process, print a stack trace and then exit.

void llvm::sys::PrintStackTraceOnErrorSignal(StringRef Argv0,

                                             bool DisableCrashReporting) {

  ::Argv0 = Argv0;

  AddSignalHandler(PrintStackTraceSignalHandler, nullptr);

#if defined(__APPLE__) && ENABLE_CRASH_OVERRIDES

  // Environment variable to disable any kind of crash dialog.

  if (DisableCrashReporting || getenv("LLVM_DISABLE_CRASH_REPORT")) {

    mach_port_t self = mach_task_self();

    exception_mask_t mask = EXC_MASK_CRASH;

    kern_return_t ret = task_set_exception_ports(self,

                             mask,

                             MACH_PORT_NULL,

                             EXCEPTION_STATE_IDENTITY | MACH_EXCEPTION_CODES,

                             THREAD_STATE_NONE);

    (void)ret;

  }

#endif

}