libgo/go/runtime/signal_unix.go - gofrontend - Git at Google

 // Copyright 2012 The Go Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.

 // +build aix darwin dragonfly freebsd linux netbsd openbsd solaris

 package runtime

 import (
 	"runtime/internal/sys"
 	"unsafe"
 )

 // For gccgo's C code to call:
 //go:linkname initsig runtime.initsig
 //go:linkname crash runtime.crash
 //go:linkname resetcpuprofiler runtime.resetcpuprofiler
 //go:linkname sigtrampgo runtime.sigtrampgo

 //go:linkname os_sigpipe os.sigpipe
 func os_sigpipe() {
 	systemstack(sigpipe)
 }

 func signame(sig uint32) string {
 	if sig >= uint32(len(sigtable)) {
 		return ""
 	}
 	return sigtable[sig].name
 }

 const (
 	_SIG_DFL uintptr = 0
 	_SIG_IGN uintptr = 1
 )

 // Stores the signal handlers registered before Go installed its own.
 // These signal handlers will be invoked in cases where Go doesn't want to
 // handle a particular signal (e.g., signal occurred on a non-Go thread).
 // See sigfwdgo() for more information on when the signals are forwarded.
 //
 // Signal forwarding is currently available only on Darwin and Linux.
 var fwdSig [_NSIG]uintptr

 // channels for synchronizing signal mask updates with the signal mask
 // thread
 var (
 	disableSigChan  chan uint32
 	enableSigChan   chan uint32
 	maskUpdatedChan chan struct{}
 )

 func init() {
 	// _NSIG is the number of signals on this operating system.
 	// sigtable should describe what to do for all the possible signals.
 	if len(sigtable) != _NSIG {
 		print("runtime: len(sigtable)=", len(sigtable), " _NSIG=", _NSIG, "\n")
 		throw("bad sigtable len")
 	}
 }

 var signalsOK bool

 // Initialize signals.
 // Called by libpreinit so runtime may not be initialized.
 //go:nosplit
 //go:nowritebarrierrec
 func initsig(preinit bool) {
 	if preinit {
 		// preinit is only passed as true if isarchive should be true.
 		isarchive = true
 	}

 	if !preinit {
 		// It's now OK for signal handlers to run.
 		signalsOK = true
 	}

 	// For c-archive/c-shared this is called by libpreinit with
 	// preinit == true.
 	if (isarchive || islibrary) && !preinit {
 		return
 	}

 	for i := uint32(0); i < _NSIG; i++ {
 		t := &sigtable[i]
 		if t.flags == 0 || t.flags&_SigDefault != 0 {
 			continue
 		}
 		fwdSig[i] = getsig(i)

 		if !sigInstallGoHandler(i) {
 			// Even if we are not installing a signal handler,
 			// set SA_ONSTACK if necessary.
 			if fwdSig[i] != _SIG_DFL && fwdSig[i] != _SIG_IGN {
 				setsigstack(i)
 			}
 			continue
 		}

 		t.flags |= _SigHandling
 		setsig(i, getSigtramp())
 	}
 }

 //go:nosplit
 //go:nowritebarrierrec
 func sigInstallGoHandler(sig uint32) bool {
 	// For some signals, we respect an inherited SIG_IGN handler
 	// rather than insist on installing our own default handler.
 	// Even these signals can be fetched using the os/signal package.
 	switch sig {
 	case _SIGHUP, _SIGINT:
 		if fwdSig[sig] == _SIG_IGN {
 			return false
 		}
 	}

 	t := &sigtable[sig]
 	if t.flags&_SigSetStack != 0 {
 		return false
 	}

 	// When built using c-archive or c-shared, only install signal
 	// handlers for synchronous signals.
 	if (isarchive || islibrary) && t.flags&_SigPanic == 0 {
 		return false
 	}

 	return true
 }

 func sigenable(sig uint32) {
 	if sig >= uint32(len(sigtable)) {
 		return
 	}

 	t := &sigtable[sig]
 	if t.flags&_SigNotify != 0 {
 		ensureSigM()
 		enableSigChan <- sig
 		<-maskUpdatedChan
 		if t.flags&_SigHandling == 0 {
 			t.flags |= _SigHandling
 			fwdSig[sig] = getsig(sig)
 			setsig(sig, getSigtramp())
 		}
 	}
 }

 func sigdisable(sig uint32) {
 	if sig >= uint32(len(sigtable)) {
 		return
 	}

 	t := &sigtable[sig]
 	if t.flags&_SigNotify != 0 {
 		ensureSigM()
 		disableSigChan <- sig
 		<-maskUpdatedChan

 		// If initsig does not install a signal handler for a
 		// signal, then to go back to the state before Notify
 		// we should remove the one we installed.
 		if !sigInstallGoHandler(sig) {
 			t.flags &^= _SigHandling
 			setsig(sig, fwdSig[sig])
 		}
 	}
 }

 func sigignore(sig uint32) {
 	if sig >= uint32(len(sigtable)) {
 		return
 	}

 	t := &sigtable[sig]
 	if t.flags&_SigNotify != 0 {
 		t.flags &^= _SigHandling
 		setsig(sig, _SIG_IGN)
 	}
 }

 func resetcpuprofiler(hz int32) {
 	var it _itimerval
 	if hz == 0 {
 		setitimer(_ITIMER_PROF, &it, nil)
 	} else {
 		it.it_interval.tv_sec = 0
 		it.it_interval.set_usec(1000000 / hz)
 		it.it_value = it.it_interval
 		setitimer(_ITIMER_PROF, &it, nil)
 	}
 	_g_ := getg()
 	_g_.m.profilehz = hz
 }

 func sigpipe() {
 	if sigsend(_SIGPIPE) {
 		return
 	}
 	dieFromSignal(_SIGPIPE)
 }

 // sigtrampgo is called from the signal handler function, sigtramp,
 // written in assembly code.
 // This is called by the signal handler, and the world may be stopped.
 //go:nosplit
 //go:nowritebarrierrec
 func sigtrampgo(sig uint32, info *_siginfo_t, ctx unsafe.Pointer) {
 	if sigfwdgo(sig, info, ctx) {
 		return
 	}
 	g := getg()
 	if g == nil {
 		c := sigctxt{info, ctx}
 		if sig == _SIGPROF {
 			_, pc := getSiginfo(info, ctx)
 			sigprofNonGo(pc)
 			return
 		}
 		badsignal(uintptr(sig), &c)
 		return
 	}

 	setg(g.m.gsignal)
 	sighandler(sig, info, ctx, g)
 	setg(g)
 }

 // sigpanic turns a synchronous signal into a run-time panic.
 // If the signal handler sees a synchronous panic, it arranges the
 // stack to look like the function where the signal occurred called
 // sigpanic, sets the signal's PC value to sigpanic, and returns from
 // the signal handler. The effect is that the program will act as
 // though the function that got the signal simply called sigpanic
 // instead.
 func sigpanic() {
 	g := getg()
 	if !canpanic(g) {
 		throw("unexpected signal during runtime execution")
 	}

 	switch g.sig {
 	case _SIGBUS:
 		if g.sigcode0 == _BUS_ADRERR && g.sigcode1 < 0x1000 {
 			panicmem()
 		}
 		// Support runtime/debug.SetPanicOnFault.
 		if g.paniconfault {
 			panicmem()
 		}
 		print("unexpected fault address ", hex(g.sigcode1), "\n")
 		throw("fault")
 	case _SIGSEGV:
 		if (g.sigcode0 == 0 || g.sigcode0 == _SEGV_MAPERR || g.sigcode0 == _SEGV_ACCERR) && g.sigcode1 < 0x1000 {
 			panicmem()
 		}
 		// Support runtime/debug.SetPanicOnFault.
 		if g.paniconfault {
 			panicmem()
 		}
 		print("unexpected fault address ", hex(g.sigcode1), "\n")
 		throw("fault")
 	case _SIGFPE:
 		switch g.sigcode0 {
 		case _FPE_INTDIV:
 			panicdivide()
 		case _FPE_INTOVF:
 			panicoverflow()
 		}
 		panicfloat()
 	}

 	if g.sig >= uint32(len(sigtable)) {
 		// can't happen: we looked up g.sig in sigtable to decide to call sigpanic
 		throw("unexpected signal value")
 	}
 	panic(errorString(sigtable[g.sig].name))
 }

 // dieFromSignal kills the program with a signal.
 // This provides the expected exit status for the shell.
 // This is only called with fatal signals expected to kill the process.
 //go:nosplit
 //go:nowritebarrierrec
 func dieFromSignal(sig uint32) {
 	setsig(sig, _SIG_DFL)
 	unblocksig(sig)
 	raise(sig)

 	// That should have killed us. On some systems, though, raise
 	// sends the signal to the whole process rather than to just
 	// the current thread, which means that the signal may not yet
 	// have been delivered. Give other threads a chance to run and
 	// pick up the signal.
 	osyield()
 	osyield()
 	osyield()

 	// If we are still somehow running, just exit with the wrong status.
 	exit(2)
 }

 // raisebadsignal is called when a signal is received on a non-Go
 // thread, and the Go program does not want to handle it (that is, the
 // program has not called os/signal.Notify for the signal).
 func raisebadsignal(sig uint32, c *sigctxt) {
 	if sig == _SIGPROF {
 		// Ignore profiling signals that arrive on non-Go threads.
 		return
 	}

 	var handler uintptr
 	if sig >= _NSIG {
 		handler = _SIG_DFL
 	} else {
 		handler = fwdSig[sig]
 	}

 	// Reset the signal handler and raise the signal.
 	// We are currently running inside a signal handler, so the
 	// signal is blocked. We need to unblock it before raising the
 	// signal, or the signal we raise will be ignored until we return
 	// from the signal handler. We know that the signal was unblocked
 	// before entering the handler, or else we would not have received
 	// it. That means that we don't have to worry about blocking it
 	// again.
 	unblocksig(sig)
 	setsig(sig, handler)

 	// If we're linked into a non-Go program we want to try to
 	// avoid modifying the original context in which the signal
 	// was raised. If the handler is the default, we know it
 	// is non-recoverable, so we don't have to worry about
 	// re-installing sighandler. At this point we can just
 	// return and the signal will be re-raised and caught by
 	// the default handler with the correct context.
 	if (isarchive || islibrary) && handler == _SIG_DFL && c.sigcode() != _SI_USER {
 		return
 	}

 	raise(sig)

 	// Give the signal a chance to be delivered.
 	// In almost all real cases the program is about to crash,
 	// so sleeping here is not a waste of time.
 	usleep(1000)

 	// If the signal didn't cause the program to exit, restore the
 	// Go signal handler and carry on.
 	//
 	// We may receive another instance of the signal before we
 	// restore the Go handler, but that is not so bad: we know
 	// that the Go program has been ignoring the signal.
 	setsig(sig, getSigtramp())
 }

 func crash() {
 	if GOOS == "darwin" {
 		// OS X core dumps are linear dumps of the mapped memory,
 		// from the first virtual byte to the last, with zeros in the gaps.
 		// Because of the way we arrange the address space on 64-bit systems,
 		// this means the OS X core file will be >128 GB and even on a zippy
 		// workstation can take OS X well over an hour to write (uninterruptible).
 		// Save users from making that mistake.
 		if sys.PtrSize == 8 {
 			return
 		}
 	}

 	dieFromSignal(_SIGABRT)
 }

 // ensureSigM starts one global, sleeping thread to make sure at least one thread
 // is available to catch signals enabled for os/signal.
 func ensureSigM() {
 	if maskUpdatedChan != nil {
 		return
 	}
 	maskUpdatedChan = make(chan struct{})
 	disableSigChan = make(chan uint32)
 	enableSigChan = make(chan uint32)
 	go func() {
 		// Signal masks are per-thread, so make sure this goroutine stays on one
 		// thread.
 		LockOSThread()
 		defer UnlockOSThread()
 		// The sigBlocked mask contains the signals not active for os/signal,
 		// initially all signals except the essential. When signal.Notify()/Stop is called,
 		// sigenable/sigdisable in turn notify this thread to update its signal
 		// mask accordingly.
 		var sigBlocked sigset
 		sigfillset(&sigBlocked)
 		for i := range sigtable {
 			if sigtable[i].flags&_SigUnblock != 0 {
 				sigdelset(&sigBlocked, i)
 			}
 		}
 		sigprocmask(_SIG_SETMASK, &sigBlocked, nil)
 		for {
 			select {
 			case sig := <-enableSigChan:
 				if sig > 0 {
 					sigdelset(&sigBlocked, int(sig))
 				}
 			case sig := <-disableSigChan:
 				if sig > 0 {
 					sigaddset(&sigBlocked, int(sig))
 				}
 			}
 			sigprocmask(_SIG_SETMASK, &sigBlocked, nil)
 			maskUpdatedChan <- struct{}{}
 		}
 	}()
 }

 // This is called when we receive a signal when there is no signal stack.
 // This can only happen if non-Go code calls sigaltstack to disable the
 // signal stack.
 func noSignalStack(sig uint32) {
 	println("signal", sig, "received on thread with no signal stack")
 	throw("non-Go code disabled sigaltstack")
 }

 // This is called if we receive a signal when there is a signal stack
 // but we are not on it. This can only happen if non-Go code called
 // sigaction without setting the SS_ONSTACK flag.
 func sigNotOnStack(sig uint32) {
 	println("signal", sig, "received but handler not on signal stack")
 	throw("non-Go code set up signal handler without SA_ONSTACK flag")
 }

 // This runs on a foreign stack, without an m or a g. No stack split.
 //go:nosplit
 //go:norace
 //go:nowritebarrierrec
 func badsignal(sig uintptr, c *sigctxt) {
 	needm(0)
 	if !sigsend(uint32(sig)) {
 		// A foreign thread received the signal sig, and the
 		// Go code does not want to handle it.
 		raisebadsignal(uint32(sig), c)
 	}
 	dropm()
 }

 // Determines if the signal should be handled by Go and if not, forwards the
 // signal to the handler that was installed before Go's. Returns whether the
 // signal was forwarded.
 // This is called by the signal handler, and the world may be stopped.
 //go:nosplit
 //go:nowritebarrierrec
 func sigfwdgo(sig uint32, info *_siginfo_t, ctx unsafe.Pointer) bool {
 	if sig >= uint32(len(sigtable)) {
 		return false
 	}
 	fwdFn := fwdSig[sig]

 	if !signalsOK {
 		// The only way we can get here is if we are in a
 		// library or archive, we installed a signal handler
 		// at program startup, but the Go runtime has not yet
 		// been initialized.
 		if fwdFn == _SIG_DFL {
 			dieFromSignal(sig)
 		} else {
 			sigfwd(fwdFn, sig, info, ctx)
 		}
 		return true
 	}

 	flags := sigtable[sig].flags

 	// If there is no handler to forward to, no need to forward.
 	if fwdFn == _SIG_DFL {
 		return false
 	}

 	// If we aren't handling the signal, forward it.
 	if flags&_SigHandling == 0 {
 		sigfwd(fwdFn, sig, info, ctx)
 		return true
 	}

 	// Only forward synchronous signals.
 	c := sigctxt{info, ctx}
 	if c.sigcode() == _SI_USER || flags&_SigPanic == 0 {
 		return false
 	}
 	// Determine if the signal occurred inside Go code. We test that:
 	//   (1) we were in a goroutine (i.e., m.curg != nil), and
 	//   (2) we weren't in CGO (i.e., m.curg.syscallsp == 0).
 	g := getg()
 	if g != nil && g.m != nil && g.m.curg != nil && g.m.curg.syscallsp == 0 {
 		return false
 	}
 	// Signal not handled by Go, forward it.
 	if fwdFn != _SIG_IGN {
 		sigfwd(fwdFn, sig, info, ctx)
 	}
 	return true
 }

 // msigsave saves the current thread's signal mask into mp.sigmask.
 // This is used to preserve the non-Go signal mask when a non-Go
 // thread calls a Go function.
 // This is nosplit and nowritebarrierrec because it is called by needm
 // which may be called on a non-Go thread with no g available.
 //go:nosplit
 //go:nowritebarrierrec
 func msigsave(mp *m) {
 	sigprocmask(_SIG_SETMASK, nil, &mp.sigmask)
 }

 // msigrestore sets the current thread's signal mask to sigmask.
 // This is used to restore the non-Go signal mask when a non-Go thread
 // calls a Go function.
 // This is nosplit and nowritebarrierrec because it is called by dropm
 // after g has been cleared.
 //go:nosplit
 //go:nowritebarrierrec
 func msigrestore(sigmask sigset) {
 	sigprocmask(_SIG_SETMASK, &sigmask, nil)
 }

 // sigblock blocks all signals in the current thread's signal mask.
 // This is used to block signals while setting up and tearing down g
 // when a non-Go thread calls a Go function.
 // The OS-specific code is expected to define sigset_all.
 // This is nosplit and nowritebarrierrec because it is called by needm
 // which may be called on a non-Go thread with no g available.
 //go:nosplit
 //go:nowritebarrierrec
 func sigblock() {
 	var set sigset
 	sigfillset(&set)
 	sigprocmask(_SIG_SETMASK, &set, nil)
 }

 // unblocksig removes sig from the current thread's signal mask.
 // This is nosplit and nowritebarrierrec because it is called from
 // dieFromSignal, which can be called by sigfwdgo while running in the
 // signal handler, on the signal stack, with no g available.
 //go:nosplit
 //go:nowritebarrierrec
 func unblocksig(sig uint32) {
 	var set sigset
 	sigemptyset(&set)
 	sigaddset(&set, int(sig))
 	sigprocmask(_SIG_UNBLOCK, &set, nil)
 }

 // minitSignals is called when initializing a new m to set the
 // thread's alternate signal stack and signal mask.
 func minitSignals() {
 	minitSignalStack()
 	minitSignalMask()
 }

 // minitSignalStack is called when initializing a new m to set the
 // alternate signal stack. If the alternate signal stack is not set
 // for the thread (the normal case) then set the alternate signal
 // stack to the gsignal stack. If the alternate signal stack is set
 // for the thread (the case when a non-Go thread sets the alternate
 // signal stack and then calls a Go function) then set the gsignal
 // stack to the alternate signal stack. Record which choice was made
 // in newSigstack, so that it can be undone in unminit.
 func minitSignalStack() {
 	_g_ := getg()
 	var st _stack_t
 	sigaltstack(nil, &st)
 	if st.ss_flags&_SS_DISABLE != 0 {
 		signalstack(_g_.m.gsignalstack, _g_.m.gsignalstacksize)
 		_g_.m.newSigstack = true
 	} else {
 		_g_.m.newSigstack = false
 	}
 }

 // minitSignalMask is called when initializing a new m to set the
 // thread's signal mask. When this is called all signals have been
 // blocked for the thread.  This starts with m.sigmask, which was set
 // either from initSigmask for a newly created thread or by calling
 // msigsave if this is a non-Go thread calling a Go function. It
 // removes all essential signals from the mask, thus causing those
 // signals to not be blocked. Then it sets the thread's signal mask.
 // After this is called the thread can receive signals.
 func minitSignalMask() {
 	nmask := getg().m.sigmask
 	for i := range sigtable {
 		if sigtable[i].flags&_SigUnblock != 0 {
 			sigdelset(&nmask, i)
 		}
 	}
 	sigprocmask(_SIG_SETMASK, &nmask, nil)
 }

 // unminitSignals is called from dropm, via unminit, to undo the
 // effect of calling minit on a non-Go thread.
 //go:nosplit
 //go:nowritebarrierrec
 func unminitSignals() {
 	if getg().m.newSigstack {
 		signalstack(nil, 0)
 	}
 }
	// Copyright 2012 The Go Authors. All rights reserved.
	// Use of this source code is governed by a BSD-style
	// license that can be found in the LICENSE file.

	// +build aix darwin dragonfly freebsd linux netbsd openbsd solaris

	package runtime

	import (
	"runtime/internal/sys"
	"unsafe"
	)

	// For gccgo's C code to call:
	//go:linkname initsig runtime.initsig
	//go:linkname crash runtime.crash
	//go:linkname resetcpuprofiler runtime.resetcpuprofiler
	//go:linkname sigtrampgo runtime.sigtrampgo

	//go:linkname os_sigpipe os.sigpipe
	func os_sigpipe() {
	systemstack(sigpipe)
	}

	func signame(sig uint32) string {
	if sig >= uint32(len(sigtable)) {
	return ""
	}
	return sigtable[sig].name
	}

	const (
	_SIG_DFL uintptr = 0
	_SIG_IGN uintptr = 1
	)

	// Stores the signal handlers registered before Go installed its own.
	// These signal handlers will be invoked in cases where Go doesn't want to
	// handle a particular signal (e.g., signal occurred on a non-Go thread).
	// See sigfwdgo() for more information on when the signals are forwarded.
	//
	// Signal forwarding is currently available only on Darwin and Linux.
	var fwdSig [_NSIG]uintptr

	// channels for synchronizing signal mask updates with the signal mask
	// thread
	var (
	disableSigChan chan uint32
	enableSigChan chan uint32
	maskUpdatedChan chan struct{}
	)

	func init() {
	// _NSIG is the number of signals on this operating system.
	// sigtable should describe what to do for all the possible signals.
	if len(sigtable) != _NSIG {
	print("runtime: len(sigtable)=", len(sigtable), " _NSIG=", _NSIG, "\n")
	throw("bad sigtable len")
	}
	}

	var signalsOK bool

	// Initialize signals.
	// Called by libpreinit so runtime may not be initialized.
	//go:nosplit
	//go:nowritebarrierrec
	func initsig(preinit bool) {
	if preinit {
	// preinit is only passed as true if isarchive should be true.
	isarchive = true
	}

	if !preinit {
	// It's now OK for signal handlers to run.
	signalsOK = true
	}

	// For c-archive/c-shared this is called by libpreinit with
	// preinit == true.
	if (isarchive \|\| islibrary) && !preinit {
	return
	}

	for i := uint32(0); i < _NSIG; i++ {
	t := &sigtable[i]
	if t.flags == 0 \|\| t.flags&_SigDefault != 0 {
	continue
	}
	fwdSig[i] = getsig(i)

	if !sigInstallGoHandler(i) {
	// Even if we are not installing a signal handler,
	// set SA_ONSTACK if necessary.
	if fwdSig[i] != _SIG_DFL && fwdSig[i] != _SIG_IGN {
	setsigstack(i)
	}
	continue
	}

	t.flags \|= _SigHandling
	setsig(i, getSigtramp())
	}
	}

	//go:nosplit
	//go:nowritebarrierrec
	func sigInstallGoHandler(sig uint32) bool {
	// For some signals, we respect an inherited SIG_IGN handler
	// rather than insist on installing our own default handler.
	// Even these signals can be fetched using the os/signal package.
	switch sig {
	case _SIGHUP, _SIGINT:
	if fwdSig[sig] == _SIG_IGN {
	return false
	}
	}

	t := &sigtable[sig]
	if t.flags&_SigSetStack != 0 {
	return false
	}

	// When built using c-archive or c-shared, only install signal
	// handlers for synchronous signals.
	if (isarchive \|\| islibrary) && t.flags&_SigPanic == 0 {
	return false
	}

	return true
	}

	func sigenable(sig uint32) {
	if sig >= uint32(len(sigtable)) {
	return
	}

	t := &sigtable[sig]
	if t.flags&_SigNotify != 0 {
	ensureSigM()
	enableSigChan <- sig
	<-maskUpdatedChan
	if t.flags&_SigHandling == 0 {
	t.flags \|= _SigHandling
	fwdSig[sig] = getsig(sig)
	setsig(sig, getSigtramp())
	}
	}
	}

	func sigdisable(sig uint32) {
	if sig >= uint32(len(sigtable)) {
	return
	}

	t := &sigtable[sig]
	if t.flags&_SigNotify != 0 {
	ensureSigM()
	disableSigChan <- sig
	<-maskUpdatedChan

	// If initsig does not install a signal handler for a
	// signal, then to go back to the state before Notify
	// we should remove the one we installed.
	if !sigInstallGoHandler(sig) {
	t.flags &^= _SigHandling
	setsig(sig, fwdSig[sig])
	}
	}
	}

	func sigignore(sig uint32) {
	if sig >= uint32(len(sigtable)) {
	return
	}

	t := &sigtable[sig]
	if t.flags&_SigNotify != 0 {
	t.flags &^= _SigHandling
	setsig(sig, _SIG_IGN)
	}
	}

	func resetcpuprofiler(hz int32) {
	var it _itimerval
	if hz == 0 {
	setitimer(_ITIMER_PROF, &it, nil)
	} else {
	it.it_interval.tv_sec = 0
	it.it_interval.set_usec(1000000 / hz)
	it.it_value = it.it_interval
	setitimer(_ITIMER_PROF, &it, nil)
	}
	_g_ := getg()
	_g_.m.profilehz = hz
	}

	func sigpipe() {
	if sigsend(_SIGPIPE) {
	return
	}
	dieFromSignal(_SIGPIPE)
	}

	// sigtrampgo is called from the signal handler function, sigtramp,
	// written in assembly code.
	// This is called by the signal handler, and the world may be stopped.
	//go:nosplit
	//go:nowritebarrierrec
	func sigtrampgo(sig uint32, info *_siginfo_t, ctx unsafe.Pointer) {
	if sigfwdgo(sig, info, ctx) {
	return
	}
	g := getg()
	if g == nil {
	c := sigctxt{info, ctx}
	if sig == _SIGPROF {
	_, pc := getSiginfo(info, ctx)
	sigprofNonGo(pc)
	return
	}
	badsignal(uintptr(sig), &c)
	return
	}

	setg(g.m.gsignal)
	sighandler(sig, info, ctx, g)
	setg(g)
	}

	// sigpanic turns a synchronous signal into a run-time panic.
	// If the signal handler sees a synchronous panic, it arranges the
	// stack to look like the function where the signal occurred called
	// sigpanic, sets the signal's PC value to sigpanic, and returns from
	// the signal handler. The effect is that the program will act as
	// though the function that got the signal simply called sigpanic
	// instead.
	func sigpanic() {
	g := getg()
	if !canpanic(g) {
	throw("unexpected signal during runtime execution")
	}

	switch g.sig {
	case _SIGBUS:
	if g.sigcode0 == _BUS_ADRERR && g.sigcode1 < 0x1000 {
	panicmem()
	}
	// Support runtime/debug.SetPanicOnFault.
	if g.paniconfault {
	panicmem()
	}
	print("unexpected fault address ", hex(g.sigcode1), "\n")
	throw("fault")
	case _SIGSEGV:
	if (g.sigcode0 == 0 \|\| g.sigcode0 == _SEGV_MAPERR \|\| g.sigcode0 == _SEGV_ACCERR) && g.sigcode1 < 0x1000 {
	panicmem()
	}
	// Support runtime/debug.SetPanicOnFault.
	if g.paniconfault {
	panicmem()
	}
	print("unexpected fault address ", hex(g.sigcode1), "\n")
	throw("fault")
	case _SIGFPE:
	switch g.sigcode0 {
	case _FPE_INTDIV:
	panicdivide()
	case _FPE_INTOVF:
	panicoverflow()
	}
	panicfloat()
	}

	if g.sig >= uint32(len(sigtable)) {
	// can't happen: we looked up g.sig in sigtable to decide to call sigpanic
	throw("unexpected signal value")
	}
	panic(errorString(sigtable[g.sig].name))
	}

	// dieFromSignal kills the program with a signal.
	// This provides the expected exit status for the shell.
	// This is only called with fatal signals expected to kill the process.
	//go:nosplit
	//go:nowritebarrierrec
	func dieFromSignal(sig uint32) {
	setsig(sig, _SIG_DFL)
	unblocksig(sig)
	raise(sig)

	// That should have killed us. On some systems, though, raise
	// sends the signal to the whole process rather than to just
	// the current thread, which means that the signal may not yet
	// have been delivered. Give other threads a chance to run and
	// pick up the signal.
	osyield()
	osyield()
	osyield()

	// If we are still somehow running, just exit with the wrong status.
	exit(2)
	}

	// raisebadsignal is called when a signal is received on a non-Go
	// thread, and the Go program does not want to handle it (that is, the
	// program has not called os/signal.Notify for the signal).
	func raisebadsignal(sig uint32, c *sigctxt) {
	if sig == _SIGPROF {
	// Ignore profiling signals that arrive on non-Go threads.
	return
	}

	var handler uintptr
	if sig >= _NSIG {
	handler = _SIG_DFL
	} else {
	handler = fwdSig[sig]
	}

	// Reset the signal handler and raise the signal.
	// We are currently running inside a signal handler, so the
	// signal is blocked. We need to unblock it before raising the
	// signal, or the signal we raise will be ignored until we return
	// from the signal handler. We know that the signal was unblocked
	// before entering the handler, or else we would not have received
	// it. That means that we don't have to worry about blocking it
	// again.
	unblocksig(sig)
	setsig(sig, handler)

	// If we're linked into a non-Go program we want to try to
	// avoid modifying the original context in which the signal
	// was raised. If the handler is the default, we know it
	// is non-recoverable, so we don't have to worry about
	// re-installing sighandler. At this point we can just
	// return and the signal will be re-raised and caught by
	// the default handler with the correct context.
	if (isarchive \|\| islibrary) && handler == _SIG_DFL && c.sigcode() != _SI_USER {
	return
	}

	raise(sig)

	// Give the signal a chance to be delivered.
	// In almost all real cases the program is about to crash,
	// so sleeping here is not a waste of time.
	usleep(1000)

	// If the signal didn't cause the program to exit, restore the
	// Go signal handler and carry on.
	//
	// We may receive another instance of the signal before we
	// restore the Go handler, but that is not so bad: we know
	// that the Go program has been ignoring the signal.
	setsig(sig, getSigtramp())
	}

	func crash() {
	if GOOS == "darwin" {
	// OS X core dumps are linear dumps of the mapped memory,
	// from the first virtual byte to the last, with zeros in the gaps.
	// Because of the way we arrange the address space on 64-bit systems,
	// this means the OS X core file will be >128 GB and even on a zippy
	// workstation can take OS X well over an hour to write (uninterruptible).
	// Save users from making that mistake.
	if sys.PtrSize == 8 {
	return
	}
	}

	dieFromSignal(_SIGABRT)
	}

	// ensureSigM starts one global, sleeping thread to make sure at least one thread
	// is available to catch signals enabled for os/signal.
	func ensureSigM() {
	if maskUpdatedChan != nil {
	return
	}
	maskUpdatedChan = make(chan struct{})
	disableSigChan = make(chan uint32)
	enableSigChan = make(chan uint32)
	go func() {
	// Signal masks are per-thread, so make sure this goroutine stays on one
	// thread.
	LockOSThread()
	defer UnlockOSThread()
	// The sigBlocked mask contains the signals not active for os/signal,
	// initially all signals except the essential. When signal.Notify()/Stop is called,
	// sigenable/sigdisable in turn notify this thread to update its signal
	// mask accordingly.
	var sigBlocked sigset
	sigfillset(&sigBlocked)
	for i := range sigtable {
	if sigtable[i].flags&_SigUnblock != 0 {
	sigdelset(&sigBlocked, i)
	}
	}
	sigprocmask(_SIG_SETMASK, &sigBlocked, nil)
	for {
	select {
	case sig := <-enableSigChan:
	if sig > 0 {
	sigdelset(&sigBlocked, int(sig))
	}
	case sig := <-disableSigChan:
	if sig > 0 {
	sigaddset(&sigBlocked, int(sig))
	}
	}
	sigprocmask(_SIG_SETMASK, &sigBlocked, nil)
	maskUpdatedChan <- struct{}{}
	}
	}()
	}

	// This is called when we receive a signal when there is no signal stack.
	// This can only happen if non-Go code calls sigaltstack to disable the
	// signal stack.
	func noSignalStack(sig uint32) {
	println("signal", sig, "received on thread with no signal stack")
	throw("non-Go code disabled sigaltstack")
	}

	// This is called if we receive a signal when there is a signal stack
	// but we are not on it. This can only happen if non-Go code called
	// sigaction without setting the SS_ONSTACK flag.
	func sigNotOnStack(sig uint32) {
	println("signal", sig, "received but handler not on signal stack")
	throw("non-Go code set up signal handler without SA_ONSTACK flag")
	}

	// This runs on a foreign stack, without an m or a g. No stack split.
	//go:nosplit
	//go:norace
	//go:nowritebarrierrec
	func badsignal(sig uintptr, c *sigctxt) {
	needm(0)
	if !sigsend(uint32(sig)) {
	// A foreign thread received the signal sig, and the
	// Go code does not want to handle it.
	raisebadsignal(uint32(sig), c)
	}
	dropm()
	}

	// Determines if the signal should be handled by Go and if not, forwards the
	// signal to the handler that was installed before Go's. Returns whether the
	// signal was forwarded.
	// This is called by the signal handler, and the world may be stopped.
	//go:nosplit
	//go:nowritebarrierrec
	func sigfwdgo(sig uint32, info *_siginfo_t, ctx unsafe.Pointer) bool {
	if sig >= uint32(len(sigtable)) {
	return false
	}
	fwdFn := fwdSig[sig]

	if !signalsOK {
	// The only way we can get here is if we are in a
	// library or archive, we installed a signal handler
	// at program startup, but the Go runtime has not yet
	// been initialized.
	if fwdFn == _SIG_DFL {
	dieFromSignal(sig)
	} else {
	sigfwd(fwdFn, sig, info, ctx)
	}
	return true
	}

	flags := sigtable[sig].flags

	// If there is no handler to forward to, no need to forward.
	if fwdFn == _SIG_DFL {
	return false
	}

	// If we aren't handling the signal, forward it.
	if flags&_SigHandling == 0 {
	sigfwd(fwdFn, sig, info, ctx)
	return true
	}

	// Only forward synchronous signals.
	c := sigctxt{info, ctx}
	if c.sigcode() == _SI_USER \|\| flags&_SigPanic == 0 {
	return false
	}
	// Determine if the signal occurred inside Go code. We test that:
	// (1) we were in a goroutine (i.e., m.curg != nil), and
	// (2) we weren't in CGO (i.e., m.curg.syscallsp == 0).
	g := getg()
	if g != nil && g.m != nil && g.m.curg != nil && g.m.curg.syscallsp == 0 {
	return false
	}
	// Signal not handled by Go, forward it.
	if fwdFn != _SIG_IGN {
	sigfwd(fwdFn, sig, info, ctx)
	}
	return true
	}

	// msigsave saves the current thread's signal mask into mp.sigmask.
	// This is used to preserve the non-Go signal mask when a non-Go
	// thread calls a Go function.
	// This is nosplit and nowritebarrierrec because it is called by needm
	// which may be called on a non-Go thread with no g available.
	//go:nosplit
	//go:nowritebarrierrec
	func msigsave(mp *m) {
	sigprocmask(_SIG_SETMASK, nil, &mp.sigmask)
	}

	// msigrestore sets the current thread's signal mask to sigmask.
	// This is used to restore the non-Go signal mask when a non-Go thread
	// calls a Go function.
	// This is nosplit and nowritebarrierrec because it is called by dropm
	// after g has been cleared.
	//go:nosplit
	//go:nowritebarrierrec
	func msigrestore(sigmask sigset) {
	sigprocmask(_SIG_SETMASK, &sigmask, nil)
	}

	// sigblock blocks all signals in the current thread's signal mask.
	// This is used to block signals while setting up and tearing down g
	// when a non-Go thread calls a Go function.
	// The OS-specific code is expected to define sigset_all.
	// This is nosplit and nowritebarrierrec because it is called by needm
	// which may be called on a non-Go thread with no g available.
	//go:nosplit
	//go:nowritebarrierrec
	func sigblock() {
	var set sigset
	sigfillset(&set)
	sigprocmask(_SIG_SETMASK, &set, nil)
	}

	// unblocksig removes sig from the current thread's signal mask.
	// This is nosplit and nowritebarrierrec because it is called from
	// dieFromSignal, which can be called by sigfwdgo while running in the
	// signal handler, on the signal stack, with no g available.
	//go:nosplit
	//go:nowritebarrierrec
	func unblocksig(sig uint32) {
	var set sigset
	sigemptyset(&set)
	sigaddset(&set, int(sig))
	sigprocmask(_SIG_UNBLOCK, &set, nil)
	}

	// minitSignals is called when initializing a new m to set the
	// thread's alternate signal stack and signal mask.
	func minitSignals() {
	minitSignalStack()
	minitSignalMask()
	}

	// minitSignalStack is called when initializing a new m to set the
	// alternate signal stack. If the alternate signal stack is not set
	// for the thread (the normal case) then set the alternate signal
	// stack to the gsignal stack. If the alternate signal stack is set
	// for the thread (the case when a non-Go thread sets the alternate
	// signal stack and then calls a Go function) then set the gsignal
	// stack to the alternate signal stack. Record which choice was made
	// in newSigstack, so that it can be undone in unminit.
	func minitSignalStack() {
	_g_ := getg()
	var st _stack_t
	sigaltstack(nil, &st)
	if st.ss_flags&_SS_DISABLE != 0 {
	signalstack(_g_.m.gsignalstack, _g_.m.gsignalstacksize)
	_g_.m.newSigstack = true
	} else {
	_g_.m.newSigstack = false
	}
	}

	// minitSignalMask is called when initializing a new m to set the
	// thread's signal mask. When this is called all signals have been
	// blocked for the thread. This starts with m.sigmask, which was set
	// either from initSigmask for a newly created thread or by calling
	// msigsave if this is a non-Go thread calling a Go function. It
	// removes all essential signals from the mask, thus causing those
	// signals to not be blocked. Then it sets the thread's signal mask.
	// After this is called the thread can receive signals.
	func minitSignalMask() {
	nmask := getg().m.sigmask
	for i := range sigtable {
	if sigtable[i].flags&_SigUnblock != 0 {
	sigdelset(&nmask, i)
	}
	}
	sigprocmask(_SIG_SETMASK, &nmask, nil)
	}

	// unminitSignals is called from dropm, via unminit, to undo the
	// effect of calling minit on a non-Go thread.
	//go:nosplit
	//go:nowritebarrierrec
	func unminitSignals() {
	if getg().m.newSigstack {
	signalstack(nil, 0)
	}
	}