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658 lines
22 KiB
658 lines
22 KiB
//===- Signals.cpp - Generic Unix Signals Implementation -----*- C++ -*-===//
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//
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// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
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// See https://llvm.org/LICENSE.txt for license information.
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// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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//
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//===----------------------------------------------------------------------===//
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//
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// This file defines some helpful functions for dealing with the possibility of
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// Unix signals occurring while your program is running.
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//
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//===----------------------------------------------------------------------===//
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//
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// This file is extremely careful to only do signal-safe things while in a
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// signal handler. In particular, memory allocation and acquiring a mutex
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// while in a signal handler should never occur. ManagedStatic isn't usable from
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// a signal handler for 2 reasons:
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//
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// 1. Creating a new one allocates.
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// 2. The signal handler could fire while llvm_shutdown is being processed, in
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// which case the ManagedStatic is in an unknown state because it could
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// already have been destroyed, or be in the process of being destroyed.
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//
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// Modifying the behavior of the signal handlers (such as registering new ones)
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// can acquire a mutex, but all this guarantees is that the signal handler
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// behavior is only modified by one thread at a time. A signal handler can still
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// fire while this occurs!
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//
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// Adding work to a signal handler requires lock-freedom (and assume atomics are
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// always lock-free) because the signal handler could fire while new work is
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// being added.
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//
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//===----------------------------------------------------------------------===//
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#include "Unix.h"
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#include "llvm/ADT/STLExtras.h"
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#include "llvm/Config/config.h"
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#include "llvm/Demangle/Demangle.h"
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#include "llvm/Support/ExitCodes.h"
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#include "llvm/Support/FileSystem.h"
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#include "llvm/Support/FileUtilities.h"
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#include "llvm/Support/Format.h"
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#include "llvm/Support/MemoryBuffer.h"
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#include "llvm/Support/Mutex.h"
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#include "llvm/Support/Program.h"
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#include "llvm/Support/SaveAndRestore.h"
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#include "llvm/Support/raw_ostream.h"
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#include <algorithm>
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#include <string>
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#ifdef HAVE_BACKTRACE
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# include BACKTRACE_HEADER // For backtrace().
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#endif
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#if HAVE_SIGNAL_H
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#include <signal.h>
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#endif
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#if HAVE_SYS_STAT_H
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#include <sys/stat.h>
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#endif
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#if HAVE_DLFCN_H
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#include <dlfcn.h>
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#endif
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#if HAVE_MACH_MACH_H
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#include <mach/mach.h>
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#endif
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#if HAVE_LINK_H
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#include <link.h>
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#endif
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#ifdef HAVE__UNWIND_BACKTRACE
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// FIXME: We should be able to use <unwind.h> for any target that has an
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// _Unwind_Backtrace function, but on FreeBSD the configure test passes
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// despite the function not existing, and on Android, <unwind.h> conflicts
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// with <link.h>.
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#ifdef __GLIBC__
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#include <unwind.h>
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#else
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#undef HAVE__UNWIND_BACKTRACE
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#endif
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#endif
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using namespace llvm;
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static RETSIGTYPE SignalHandler(int Sig); // defined below.
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static RETSIGTYPE InfoSignalHandler(int Sig); // defined below.
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using SignalHandlerFunctionType = void (*)();
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/// The function to call if ctrl-c is pressed.
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static std::atomic<SignalHandlerFunctionType> InterruptFunction =
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ATOMIC_VAR_INIT(nullptr);
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static std::atomic<SignalHandlerFunctionType> InfoSignalFunction =
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ATOMIC_VAR_INIT(nullptr);
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/// The function to call on SIGPIPE (one-time use only).
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static std::atomic<SignalHandlerFunctionType> OneShotPipeSignalFunction =
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ATOMIC_VAR_INIT(nullptr);
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namespace {
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/// Signal-safe removal of files.
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/// Inserting and erasing from the list isn't signal-safe, but removal of files
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/// themselves is signal-safe. Memory is freed when the head is freed, deletion
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/// is therefore not signal-safe either.
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class FileToRemoveList {
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std::atomic<char *> Filename = ATOMIC_VAR_INIT(nullptr);
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std::atomic<FileToRemoveList *> Next = ATOMIC_VAR_INIT(nullptr);
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FileToRemoveList() = default;
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// Not signal-safe.
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FileToRemoveList(const std::string &str) : Filename(strdup(str.c_str())) {}
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public:
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// Not signal-safe.
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~FileToRemoveList() {
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if (FileToRemoveList *N = Next.exchange(nullptr))
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delete N;
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if (char *F = Filename.exchange(nullptr))
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free(F);
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}
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// Not signal-safe.
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static void insert(std::atomic<FileToRemoveList *> &Head,
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const std::string &Filename) {
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// Insert the new file at the end of the list.
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FileToRemoveList *NewHead = new FileToRemoveList(Filename);
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std::atomic<FileToRemoveList *> *InsertionPoint = &Head;
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FileToRemoveList *OldHead = nullptr;
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while (!InsertionPoint->compare_exchange_strong(OldHead, NewHead)) {
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InsertionPoint = &OldHead->Next;
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OldHead = nullptr;
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}
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}
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// Not signal-safe.
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static void erase(std::atomic<FileToRemoveList *> &Head,
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const std::string &Filename) {
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// Use a lock to avoid concurrent erase: the comparison would access
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// free'd memory.
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static ManagedStatic<sys::SmartMutex<true>> Lock;
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sys::SmartScopedLock<true> Writer(*Lock);
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for (FileToRemoveList *Current = Head.load(); Current;
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Current = Current->Next.load()) {
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if (char *OldFilename = Current->Filename.load()) {
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if (OldFilename != Filename)
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continue;
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// Leave an empty filename.
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OldFilename = Current->Filename.exchange(nullptr);
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// The filename might have become null between the time we
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// compared it and we exchanged it.
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if (OldFilename)
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free(OldFilename);
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}
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}
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}
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// Signal-safe.
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static void removeAllFiles(std::atomic<FileToRemoveList *> &Head) {
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// If cleanup were to occur while we're removing files we'd have a bad time.
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// Make sure we're OK by preventing cleanup from doing anything while we're
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// removing files. If cleanup races with us and we win we'll have a leak,
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// but we won't crash.
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FileToRemoveList *OldHead = Head.exchange(nullptr);
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for (FileToRemoveList *currentFile = OldHead; currentFile;
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currentFile = currentFile->Next.load()) {
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// If erasing was occuring while we're trying to remove files we'd look
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// at free'd data. Take away the path and put it back when done.
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if (char *path = currentFile->Filename.exchange(nullptr)) {
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// Get the status so we can determine if it's a file or directory. If we
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// can't stat the file, ignore it.
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struct stat buf;
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if (stat(path, &buf) != 0)
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continue;
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// If this is not a regular file, ignore it. We want to prevent removal
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// of special files like /dev/null, even if the compiler is being run
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// with the super-user permissions.
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if (!S_ISREG(buf.st_mode))
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continue;
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// Otherwise, remove the file. We ignore any errors here as there is
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// nothing else we can do.
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unlink(path);
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// We're done removing the file, erasing can safely proceed.
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currentFile->Filename.exchange(path);
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}
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}
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// We're done removing files, cleanup can safely proceed.
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Head.exchange(OldHead);
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}
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};
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static std::atomic<FileToRemoveList *> FilesToRemove = ATOMIC_VAR_INIT(nullptr);
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/// Clean up the list in a signal-friendly manner.
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/// Recall that signals can fire during llvm_shutdown. If this occurs we should
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/// either clean something up or nothing at all, but we shouldn't crash!
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struct FilesToRemoveCleanup {
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// Not signal-safe.
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~FilesToRemoveCleanup() {
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FileToRemoveList *Head = FilesToRemove.exchange(nullptr);
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if (Head)
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delete Head;
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}
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};
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} // namespace
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static StringRef Argv0;
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/// Signals that represent requested termination. There's no bug or failure, or
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/// if there is, it's not our direct responsibility. For whatever reason, our
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/// continued execution is no longer desirable.
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static const int IntSigs[] = {
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SIGHUP, SIGINT, SIGTERM, SIGUSR2
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};
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/// Signals that represent that we have a bug, and our prompt termination has
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/// been ordered.
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static const int KillSigs[] = {
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SIGILL, SIGTRAP, SIGABRT, SIGFPE, SIGBUS, SIGSEGV, SIGQUIT
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#ifdef SIGSYS
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, SIGSYS
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#endif
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#ifdef SIGXCPU
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, SIGXCPU
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#endif
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#ifdef SIGXFSZ
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, SIGXFSZ
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#endif
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#ifdef SIGEMT
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, SIGEMT
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#endif
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};
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/// Signals that represent requests for status.
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static const int InfoSigs[] = {
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SIGUSR1
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#ifdef SIGINFO
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, SIGINFO
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#endif
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};
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static const size_t NumSigs =
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array_lengthof(IntSigs) + array_lengthof(KillSigs) +
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array_lengthof(InfoSigs) + 1 /* SIGPIPE */;
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static std::atomic<unsigned> NumRegisteredSignals = ATOMIC_VAR_INIT(0);
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static struct {
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struct sigaction SA;
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int SigNo;
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} RegisteredSignalInfo[NumSigs];
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#if defined(HAVE_SIGALTSTACK)
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// Hold onto both the old and new alternate signal stack so that it's not
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// reported as a leak. We don't make any attempt to remove our alt signal
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// stack if we remove our signal handlers; that can't be done reliably if
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// someone else is also trying to do the same thing.
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static stack_t OldAltStack;
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static void* NewAltStackPointer;
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static void CreateSigAltStack() {
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const size_t AltStackSize = MINSIGSTKSZ + 64 * 1024;
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// If we're executing on the alternate stack, or we already have an alternate
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// signal stack that we're happy with, there's nothing for us to do. Don't
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// reduce the size, some other part of the process might need a larger stack
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// than we do.
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if (sigaltstack(nullptr, &OldAltStack) != 0 ||
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OldAltStack.ss_flags & SS_ONSTACK ||
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(OldAltStack.ss_sp && OldAltStack.ss_size >= AltStackSize))
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return;
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stack_t AltStack = {};
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AltStack.ss_sp = static_cast<char *>(safe_malloc(AltStackSize));
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NewAltStackPointer = AltStack.ss_sp; // Save to avoid reporting a leak.
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AltStack.ss_size = AltStackSize;
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if (sigaltstack(&AltStack, &OldAltStack) != 0)
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free(AltStack.ss_sp);
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}
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#else
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static void CreateSigAltStack() {}
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#endif
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static void RegisterHandlers() { // Not signal-safe.
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// The mutex prevents other threads from registering handlers while we're
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// doing it. We also have to protect the handlers and their count because
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// a signal handler could fire while we're registeting handlers.
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static ManagedStatic<sys::SmartMutex<true>> SignalHandlerRegistrationMutex;
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sys::SmartScopedLock<true> Guard(*SignalHandlerRegistrationMutex);
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// If the handlers are already registered, we're done.
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if (NumRegisteredSignals.load() != 0)
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return;
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// Create an alternate stack for signal handling. This is necessary for us to
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// be able to reliably handle signals due to stack overflow.
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CreateSigAltStack();
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enum class SignalKind { IsKill, IsInfo };
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auto registerHandler = [&](int Signal, SignalKind Kind) {
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unsigned Index = NumRegisteredSignals.load();
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assert(Index < array_lengthof(RegisteredSignalInfo) &&
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"Out of space for signal handlers!");
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struct sigaction NewHandler;
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switch (Kind) {
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case SignalKind::IsKill:
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NewHandler.sa_handler = SignalHandler;
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NewHandler.sa_flags = SA_NODEFER | SA_RESETHAND | SA_ONSTACK;
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break;
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case SignalKind::IsInfo:
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NewHandler.sa_handler = InfoSignalHandler;
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NewHandler.sa_flags = SA_ONSTACK;
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break;
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}
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sigemptyset(&NewHandler.sa_mask);
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// Install the new handler, save the old one in RegisteredSignalInfo.
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sigaction(Signal, &NewHandler, &RegisteredSignalInfo[Index].SA);
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RegisteredSignalInfo[Index].SigNo = Signal;
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++NumRegisteredSignals;
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};
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for (auto S : IntSigs)
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registerHandler(S, SignalKind::IsKill);
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for (auto S : KillSigs)
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registerHandler(S, SignalKind::IsKill);
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if (OneShotPipeSignalFunction)
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registerHandler(SIGPIPE, SignalKind::IsKill);
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for (auto S : InfoSigs)
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registerHandler(S, SignalKind::IsInfo);
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}
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void sys::unregisterHandlers() {
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// Restore all of the signal handlers to how they were before we showed up.
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for (unsigned i = 0, e = NumRegisteredSignals.load(); i != e; ++i) {
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sigaction(RegisteredSignalInfo[i].SigNo,
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&RegisteredSignalInfo[i].SA, nullptr);
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--NumRegisteredSignals;
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}
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}
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/// Process the FilesToRemove list.
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static void RemoveFilesToRemove() {
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FileToRemoveList::removeAllFiles(FilesToRemove);
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}
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void sys::CleanupOnSignal(uintptr_t Context) {
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int Sig = (int)Context;
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if (llvm::is_contained(InfoSigs, Sig)) {
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InfoSignalHandler(Sig);
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return;
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}
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RemoveFilesToRemove();
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if (llvm::is_contained(IntSigs, Sig) || Sig == SIGPIPE)
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return;
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llvm::sys::RunSignalHandlers();
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}
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// The signal handler that runs.
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static RETSIGTYPE SignalHandler(int Sig) {
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// Restore the signal behavior to default, so that the program actually
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// crashes when we return and the signal reissues. This also ensures that if
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// we crash in our signal handler that the program will terminate immediately
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// instead of recursing in the signal handler.
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sys::unregisterHandlers();
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// Unmask all potentially blocked kill signals.
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sigset_t SigMask;
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sigfillset(&SigMask);
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sigprocmask(SIG_UNBLOCK, &SigMask, nullptr);
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{
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RemoveFilesToRemove();
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if (Sig == SIGPIPE)
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if (auto OldOneShotPipeFunction =
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OneShotPipeSignalFunction.exchange(nullptr))
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return OldOneShotPipeFunction();
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if (llvm::is_contained(IntSigs, Sig)) {
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if (auto OldInterruptFunction = InterruptFunction.exchange(nullptr))
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return OldInterruptFunction();
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raise(Sig); // Execute the default handler.
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return;
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}
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}
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// Otherwise if it is a fault (like SEGV) run any handler.
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llvm::sys::RunSignalHandlers();
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#ifdef __s390__
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// On S/390, certain signals are delivered with PSW Address pointing to
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// *after* the faulting instruction. Simply returning from the signal
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// handler would continue execution after that point, instead of
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// re-raising the signal. Raise the signal manually in those cases.
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if (Sig == SIGILL || Sig == SIGFPE || Sig == SIGTRAP)
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raise(Sig);
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#endif
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}
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static RETSIGTYPE InfoSignalHandler(int Sig) {
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SaveAndRestore<int> SaveErrnoDuringASignalHandler(errno);
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if (SignalHandlerFunctionType CurrentInfoFunction = InfoSignalFunction)
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CurrentInfoFunction();
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}
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void llvm::sys::RunInterruptHandlers() {
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RemoveFilesToRemove();
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}
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void llvm::sys::SetInterruptFunction(void (*IF)()) {
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InterruptFunction.exchange(IF);
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RegisterHandlers();
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}
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void llvm::sys::SetInfoSignalFunction(void (*Handler)()) {
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InfoSignalFunction.exchange(Handler);
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RegisterHandlers();
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}
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void llvm::sys::SetOneShotPipeSignalFunction(void (*Handler)()) {
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OneShotPipeSignalFunction.exchange(Handler);
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RegisterHandlers();
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}
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void llvm::sys::DefaultOneShotPipeSignalHandler() {
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// Send a special return code that drivers can check for, from sysexits.h.
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exit(EX_IOERR);
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}
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// The public API
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bool llvm::sys::RemoveFileOnSignal(StringRef Filename,
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std::string* ErrMsg) {
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// Ensure that cleanup will occur as soon as one file is added.
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static ManagedStatic<FilesToRemoveCleanup> FilesToRemoveCleanup;
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*FilesToRemoveCleanup;
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FileToRemoveList::insert(FilesToRemove, Filename.str());
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RegisterHandlers();
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return false;
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}
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// The public API
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void llvm::sys::DontRemoveFileOnSignal(StringRef Filename) {
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FileToRemoveList::erase(FilesToRemove, Filename.str());
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}
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/// Add a function to be called when a signal is delivered to the process. The
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/// handler can have a cookie passed to it to identify what instance of the
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/// handler it is.
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void llvm::sys::AddSignalHandler(sys::SignalHandlerCallback FnPtr,
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void *Cookie) { // Signal-safe.
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insertSignalHandler(FnPtr, Cookie);
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RegisterHandlers();
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}
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#if defined(HAVE_BACKTRACE) && ENABLE_BACKTRACES && HAVE_LINK_H && \
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(defined(__linux__) || defined(__FreeBSD__) || \
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defined(__FreeBSD_kernel__) || defined(__NetBSD__))
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struct DlIteratePhdrData {
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void **StackTrace;
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int depth;
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bool first;
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const char **modules;
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intptr_t *offsets;
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const char *main_exec_name;
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};
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static int dl_iterate_phdr_cb(dl_phdr_info *info, size_t size, void *arg) {
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DlIteratePhdrData *data = (DlIteratePhdrData*)arg;
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const char *name = data->first ? data->main_exec_name : info->dlpi_name;
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data->first = false;
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for (int i = 0; i < info->dlpi_phnum; i++) {
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const auto *phdr = &info->dlpi_phdr[i];
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if (phdr->p_type != PT_LOAD)
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continue;
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intptr_t beg = info->dlpi_addr + phdr->p_vaddr;
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intptr_t end = beg + phdr->p_memsz;
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for (int j = 0; j < data->depth; j++) {
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if (data->modules[j])
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continue;
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intptr_t addr = (intptr_t)data->StackTrace[j];
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if (beg <= addr && addr < end) {
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data->modules[j] = name;
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data->offsets[j] = addr - info->dlpi_addr;
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}
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}
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}
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return 0;
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}
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/// If this is an ELF platform, we can find all loaded modules and their virtual
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/// addresses with dl_iterate_phdr.
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static bool findModulesAndOffsets(void **StackTrace, int Depth,
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|
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, int Depth) {
|
|
#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 "Depth" is not provided by the caller, use the return value of
|
|
// backtrace() for printing a symbolized stack trace.
|
|
if (!Depth)
|
|
Depth = depth;
|
|
if (printSymbolizedStackTrace(Argv0, StackTrace, Depth, OS))
|
|
return;
|
|
OS << "Stack dump without symbol names (ensure you have llvm-symbolizer in "
|
|
"your PATH or set the environment var `LLVM_SYMBOLIZER_PATH` to point "
|
|
"to it):\n";
|
|
#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
|
|
}
|