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// Copyright (C) 2021 The Qt Company Ltd.
// Copyright (C) 2019 Luxoft Sweden AB
// Copyright (C) 2018 Pelagicore AG
// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR GPL-3.0-only
#include "unixsignalhandler.h"
#include "logging.h"
#include <QSocketNotifier>
#include <QCoreApplication>
#include <errno.h>
#if defined(Q_OS_WIN)
# include <windows.h>
# include <synchapi.h>
#else
# include <sys/mman.h>
#endif
QT_BEGIN_NAMESPACE_AM
// sigmask() is not available on Windows
UnixSignalHandler::am_sigmask_t UnixSignalHandler::am_sigmask(int sig)
{
return ((am_sigmask_t(1)) << (((sig) - 1) % int(8 * sizeof(am_sigmask_t))));
}
UnixSignalHandler *UnixSignalHandler::s_instance = nullptr;
UnixSignalHandler::UnixSignalHandler()
{
#if defined(Q_OS_UNIX) && !defined(Q_OS_QNX)
// Setup alternate signal stack (to get backtrace for stack overflow)
// Canonical size might not be suffcient to get QML backtrace, so we double it
size_t stackSize = SIGSTKSZ * 2;
stack_t sigstack;
// ASAN and valgrind would report malloc() as a leak. In addition, we avoid the
// signal stack being close to a possibly corrupted heap this way.
sigstack.ss_sp = mmap(nullptr, stackSize, PROT_READ | PROT_WRITE, MAP_PRIVATE | MAP_ANON, -1, 0);
if (sigstack.ss_sp != MAP_FAILED) {
sigstack.ss_size = stackSize;
sigstack.ss_flags = 0;
sigaltstack(&sigstack, nullptr);
} else {
// this code runs before all other static constructors
qWarning("WARNING: UnixSignalHandler failed to allocate memory for an alternate signal stack.");
}
#endif
}
UnixSignalHandler *UnixSignalHandler::instance()
{
if (Q_UNLIKELY(!s_instance))
s_instance = new UnixSignalHandler();
return s_instance;
}
const char *UnixSignalHandler::signalName(int sig)
{
#if defined(Q_OS_UNIX)
#if __GLIBC__ >= 2 && __GLIBC_MINOR__ >= 32
return sigdescr_np(sig);
#else
return strsignal(sig); // not async-signal-safe
#endif
#else
Q_UNUSED(sig)
return "<unknown>";
#endif
}
void UnixSignalHandler::resetToDefault(int sig)
{
auto sigs = { sig };
resetToDefault(sigs);
}
void UnixSignalHandler::resetToDefault(const std::initializer_list<int> &sigs)
{
for (int sig : sigs) {
m_resetSignalMask |= am_sigmask(sig);
signal(sig, SIG_DFL);
}
}
bool UnixSignalHandler::install(Type handlerType, int sig, const std::function<void (int)> &handler)
{
auto sigs = { sig };
return install(handlerType, sigs, handler);
}
bool UnixSignalHandler::install(Type handlerType, const std::initializer_list<int> &sigs,
const std::function<void(int)> &handler)
{
auto sigHandler = [](int sig) {
// this lambda is the low-level signal handler multiplexer
auto that = UnixSignalHandler::instance();
that->m_currentSignal = sig;
for (const auto &h : std::as_const(that->m_handlers)) {
if ((h.m_signal == sig) && !h.m_disabled) {
if (!h.m_qt) {
h.m_handler(sig);
} else {
#if defined(Q_OS_UNIX)
auto dummy = write(that->m_pipe[1], &sig, sizeof(int));
Q_UNUSED(dummy)
#elif defined(Q_OS_WIN)
// we're running in a separate thread now
that->m_winLock.lock();
that->m_signalsForEventLoop << sig;
that->m_winLock.unlock();
PulseEvent(that->m_winEvent->handle());
#endif
}
}
}
if (that->m_resetSignalMask) {
// Someone called resetToDefault - now's a good time to handle it.
// We can not remove the entries in the list, because that would (a) allocate and (b)
// step on code that might be iterating over the list in the "Forwarded" handler.
for (const auto &h : std::as_const(that->m_handlers)) {
if (that->m_resetSignalMask & am_sigmask(h.m_signal))
h.m_disabled = true;
}
that->m_resetSignalMask = 0;
}
that->m_currentSignal = 0;
};
if (m_currentSignal) {
// installing a signal handler from within a signal handler shouldn't be necessary
return false;
}
if (handlerType == ForwardedToEventLoopHandler) {
#if defined(Q_OS_UNIX)
if ((m_pipe[0] == -1) && qApp) {
auto dummy = pipe(m_pipe);
Q_UNUSED(dummy)
auto sn = new QSocketNotifier(m_pipe[0], QSocketNotifier::Read, this);
connect(sn, &QSocketNotifier::activated, qApp, [this]() {
// this lambda is the "signal handler" multiplexer within the Qt event loop
int sig = 0;
if (read(m_pipe[0], &sig, sizeof(int)) != sizeof(int)) {
qCWarning(LogSystem) << "Error reading from signal handler:" << strerror(errno);;
return;
}
for (const auto &h : std::as_const(m_handlers)) {
if (h.m_qt && (h.m_signal == sig) && !h.m_disabled)
h.m_handler(sig);
}
});
}
#elif defined(Q_OS_WIN)
if (!m_winEvent) {
m_winEvent = new QWinEventNotifier(CreateEventW(nullptr, false, false, nullptr), this);
connect(m_winEvent, &QWinEventNotifier::activated, qApp, [this]() {
// this lambda is the "signal handler" multiplexer within the Qt event loop
m_winLock.lock();
for (const int &sig : std::as_const(m_signalsForEventLoop)) {
for (const auto &h : std::as_const(m_handlers)) {
if (h.m_qt && (h.m_signal == sig) && !h.m_disabled)
h.m_handler(sig);
}
}
m_signalsForEventLoop.clear();
m_winLock.unlock();
});
}
#else
qCWarning(LogSystem) << "Unix signal handling via 'ForwardedToEventLoopHandler' is not "
"supported on this platform";
return false;
#endif
}
// This is UB! We cannot guarantee that the signal handler is not currently executing and
// iterating over this list. In practice, this is a none-issue in the AM however, because all
// install() calls are done right at startup time.
// To do it right, we would need a lock-free list structure for m_handlers.
for (int sig : sigs)
m_handlers.emplace_back(sig, handlerType == ForwardedToEventLoopHandler, handler);
#if defined(Q_OS_UNIX) && !defined(Q_OS_QNX)
struct sigaction sigact;
sigact.sa_flags = SA_ONSTACK;
sigact.sa_handler = sigHandler;
sigemptyset(&sigact.sa_mask);
sigset_t unblockSet;
sigemptyset(&unblockSet);
for (int sig : sigs) {
sigaddset(&unblockSet, sig);
sigaction(sig, &sigact, nullptr);
m_resetSignalMask &= ~am_sigmask(sig); // cancel unfinished reset
}
sigprocmask(SIG_UNBLOCK, &unblockSet, nullptr);
#else
for (int sig : sigs)
signal(sig, sigHandler);
#endif
return true;
}
UnixSignalHandler::SigHandler::SigHandler(int signal, bool qt, const std::function<void (int)> &handler)
: m_signal(signal), m_qt(qt), m_handler(handler)
{ }
QT_END_NAMESPACE_AM
#include "moc_unixsignalhandler.cpp"
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