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+//===- 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.
+
+static void DefaultPipeSignalFunction() {
+ exit(EX_IOERR);
+}
+
+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);
+static std::atomic<SignalHandlerFunctionType> PipeSignalFunction =
+ ATOMIC_VAR_INIT(DefaultPipeSignalFunction);
+
+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, SIGPIPE, 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);
+
+
+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);
+ 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);
+}
+
+// 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 (std::find(std::begin(IntSigs), std::end(IntSigs), Sig)
+ != std::end(IntSigs)) {
+ if (auto OldInterruptFunction = InterruptFunction.exchange(nullptr))
+ return OldInterruptFunction();
+
+ // Send a special return code that drivers can check for, from sysexits.h.
+ if (Sig == SIGPIPE)
+ if (SignalHandlerFunctionType CurrentPipeFunction = PipeSignalFunction)
+ CurrentPipeFunction();
+
+ 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::SetPipeSignalFunction(void (*Handler)()) {
+ PipeSignalFunction.exchange(Handler);
+ RegisterHandlers();
+}
+
+// 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
+}