2018-23-01 Paul Thomas <pault@gcc.gnu.org>

[official-gcc.git] / libgo / go / runtime / signal_unix.go

// 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/atomic"
        "unsafe"
)

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

// sigTabT is the type of an entry in the global sigtable array.
// sigtable is inherently system dependent, and appears in OS-specific files,
// but sigTabT is the same for all Unixy systems.
// The sigtable array is indexed by a system signal number to get the flags
// and printable name of each signal.
type sigTabT struct {
        flags int32
        name  string
}

//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.
//
// This is read by the signal handler; accesses should use
// atomic.Loaduintptr and atomic.Storeuintptr.
var fwdSig [_NSIG]uintptr

// handlingSig is indexed by signal number and is non-zero if we are
// currently handling the signal. Or, to put it another way, whether
// the signal handler is currently set to the Go signal handler or not.
// This is uint32 rather than bool so that we can use atomic instructions.
var handlingSig [_NSIG]uint32

// 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
                }

                // We don't need to use atomic operations here because
                // there shouldn't be any other goroutines running yet.
                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
                }

                handlingSig[i] = 1
                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 atomic.Loaduintptr(&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 and SIGPIPE.
        if (isarchive || islibrary) && t.flags&_SigPanic == 0 && sig != _SIGPIPE {
                return false
        }

        return true
}

// sigenable enables the Go signal handler to catch the signal sig.
// It is only called while holding the os/signal.handlers lock,
// via os/signal.enableSignal and signal_enable.
func sigenable(sig uint32) {
        if sig >= uint32(len(sigtable)) {
                return
        }

        // SIGPROF is handled specially for profiling.
        if sig == _SIGPROF {
                return
        }

        t := &sigtable[sig]
        if t.flags&_SigNotify != 0 {
                ensureSigM()
                enableSigChan <- sig
                <-maskUpdatedChan
                if atomic.Cas(&handlingSig[sig], 0, 1) {
                        atomic.Storeuintptr(&fwdSig[sig], getsig(sig))
                        setsig(sig, getSigtramp())
                }
        }
}

// sigdisable disables the Go signal handler for the signal sig.
// It is only called while holding the os/signal.handlers lock,
// via os/signal.disableSignal and signal_disable.
func sigdisable(sig uint32) {
        if sig >= uint32(len(sigtable)) {
                return
        }

        // SIGPROF is handled specially for profiling.
        if sig == _SIGPROF {
                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) {
                        atomic.Store(&handlingSig[sig], 0)
                        setsig(sig, atomic.Loaduintptr(&fwdSig[sig]))
                }
        }
}

// sigignore ignores the signal sig.
// It is only called while holding the os/signal.handlers lock,
// via os/signal.ignoreSignal and signal_ignore.
func sigignore(sig uint32) {
        if sig >= uint32(len(sigtable)) {
                return
        }

        // SIGPROF is handled specially for profiling.
        if sig == _SIGPROF {
                return
        }

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

// clearSignalHandlers clears all signal handlers that are not ignored
// back to the default. This is called by the child after a fork, so that
// we can enable the signal mask for the exec without worrying about
// running a signal handler in the child.
//go:nosplit
//go:nowritebarrierrec
func clearSignalHandlers() {
        for i := uint32(0); i < _NSIG; i++ {
                if atomic.Load(&handlingSig[i]) != 0 {
                        setsig(i, _SIG_DFL)
                }
        }
}

// setProcessCPUProfiler is called when the profiling timer changes.
// It is called with prof.lock held. hz is the new timer, and is 0 if
// profiling is being disabled. Enable or disable the signal as
// required for -buildmode=c-archive.
func setProcessCPUProfiler(hz int32) {
        if hz != 0 {
                // Enable the Go signal handler if not enabled.
                if atomic.Cas(&handlingSig[_SIGPROF], 0, 1) {
                        atomic.Storeuintptr(&fwdSig[_SIGPROF], getsig(_SIGPROF))
                        setsig(_SIGPROF, funcPC(sighandler))
                }
        } else {
                // If the Go signal handler should be disabled by default,
                // disable it if it is enabled.
                if !sigInstallGoHandler(_SIGPROF) {
                        if atomic.Cas(&handlingSig[_SIGPROF], 1, 0) {
                                setsig(_SIGPROF, atomic.Loaduintptr(&fwdSig[_SIGPROF]))
                        }
                }
        }
}

// setThreadCPUProfiler makes any thread-specific changes required to
// implement profiling at a rate of hz.
func setThreadCPUProfiler(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.
//
// It must be nosplit because getg() is still the G that was running
// (if any) when the signal was delivered, but it's (usually) called
// on the gsignal stack. Until this switches the G to gsignal, the
// stack bounds check won't work.
//
//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) {
        unblocksig(sig)
        // Mark the signal as unhandled to ensure it is forwarded.
        atomic.Store(&handlingSig[sig], 0)
        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 that didn't work, try _SIG_DFL.
        setsig(sig, _SIG_DFL)
        raise(sig)

        osyield()
        osyield()
        osyield()

        // On Darwin we may still fail to die, because raise sends the
        // signal to the whole process rather than just the current thread,
        // and osyield just sleeps briefly rather than letting all other
        // threads run. See issue 20315. Sleep longer.
        if GOOS == "darwin" {
                usleep(100)
        }

        // 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 = atomic.Loaduintptr(&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 GOARCH == "amd64" {
                        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 !blockableSig(uint32(i)) {
                                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 && blockableSig(sig) {
                                        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")
}

// signalDuringFork is called if we receive a signal while doing a fork.
// We do not want signals at that time, as a signal sent to the process
// group may be delivered to the child process, causing confusion.
// This should never be called, because we block signals across the fork;
// this function is just a safety check. See issue 18600 for background.
func signalDuringFork(sig uint32) {
        println("signal", sig, "received during fork")
        throw("signal received during fork")
}

// 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 := atomic.Loaduintptr(&fwdSig[sig])
        flags := sigtable[sig].flags

        // If we aren't handling the signal, forward it.
        if atomic.Load(&handlingSig[sig]) == 0 || !signalsOK {
                // If the signal is ignored, doing nothing is the same as forwarding.
                if fwdFn == _SIG_IGN || (fwdFn == _SIG_DFL && flags&_SigIgn != 0) {
                        return true
                }
                // We are not handling the signal and there is no other handler to forward to.
                // Crash with the default behavior.
                if fwdFn == _SIG_DFL {
                        setsig(sig, _SIG_DFL)
                        dieFromSignal(sig)
                        return false
                }

                sigfwd(fwdFn, sig, info, ctx)
                return true
        }

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

        c := sigctxt{info, ctx}
        // Only forward synchronous signals and SIGPIPE.
        // Unfortunately, user generated SIGPIPEs will also be forwarded, because si_code
        // is set to _SI_USER even for a SIGPIPE raised from a write to a closed socket
        // or pipe.
        if (c.sigcode() == _SI_USER || flags&_SigPanic == 0) && sig != _SIGPIPE {
                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.
        g := getg()
        if g != nil && g.m != nil && g.m.curg != nil && !g.m.incgo {
                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 !blockableSig(uint32(i)) {
                        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)
        }
}

// blockableSig returns whether sig may be blocked by the signal mask.
// We never want to block the signals marked _SigUnblock;
// these are the synchronous signals that turn into a Go panic.
// In a Go program--not a c-archive/c-shared--we never want to block
// the signals marked _SigKill or _SigThrow, as otherwise it's possible
// for all running threads to block them and delay their delivery until
// we start a new thread. When linked into a C program we let the C code
// decide on the disposition of those signals.
func blockableSig(sig uint32) bool {
        flags := sigtable[sig].flags
        if flags&_SigUnblock != 0 {
                return false
        }
        if isarchive || islibrary {
                return true
        }
        return flags&(_SigKill|_SigThrow) == 0
}