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llvm-project/llvm/lib/Support/Unix/Signals.inc

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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.
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
}
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