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Diffstat (limited to 'src/runtime/signal_unix.go')
| -rw-r--r-- | src/runtime/signal_unix.go | 1232 |
1 files changed, 1232 insertions, 0 deletions
diff --git a/src/runtime/signal_unix.go b/src/runtime/signal_unix.go new file mode 100644 index 0000000..89f936e --- /dev/null +++ b/src/runtime/signal_unix.go @@ -0,0 +1,1232 @@ +// 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" +) + +// 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 +) + +// sigPreempt is the signal used for non-cooperative preemption. +// +// There's no good way to choose this signal, but there are some +// heuristics: +// +// 1. It should be a signal that's passed-through by debuggers by +// default. On Linux, this is SIGALRM, SIGURG, SIGCHLD, SIGIO, +// SIGVTALRM, SIGPROF, and SIGWINCH, plus some glibc-internal signals. +// +// 2. It shouldn't be used internally by libc in mixed Go/C binaries +// because libc may assume it's the only thing that can handle these +// signals. For example SIGCANCEL or SIGSETXID. +// +// 3. It should be a signal that can happen spuriously without +// consequences. For example, SIGALRM is a bad choice because the +// signal handler can't tell if it was caused by the real process +// alarm or not (arguably this means the signal is broken, but I +// digress). SIGUSR1 and SIGUSR2 are also bad because those are often +// used in meaningful ways by applications. +// +// 4. We need to deal with platforms without real-time signals (like +// macOS), so those are out. +// +// We use SIGURG because it meets all of these criteria, is extremely +// unlikely to be used by an application for its "real" meaning (both +// because out-of-band data is basically unused and because SIGURG +// doesn't report which socket has the condition, making it pretty +// useless), and even if it is, the application has to be ready for +// spurious SIGURG. SIGIO wouldn't be a bad choice either, but is more +// likely to be used for real. +const sigPreempt = _SIGURG + +// 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 { + // 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) + } else if fwdSig[i] == _SIG_IGN { + sigInitIgnored(i) + } + continue + } + + handlingSig[i] = 1 + setsig(i, funcPC(sighandler)) + } +} + +//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, funcPC(sighandler)) + } + } +} + +// 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)) + } + + var it itimerval + it.it_interval.tv_sec = 0 + it.it_interval.set_usec(1000000 / hz) + it.it_value = it.it_interval + setitimer(_ITIMER_PROF, &it, nil) + } else { + // If the Go signal handler should be disabled by default, + // switch back to the signal handler that was installed + // when we enabled profiling. We don't try to handle the case + // of a program that changes the SIGPROF handler while Go + // profiling is enabled. + // + // If no signal handler was installed before, then start + // ignoring SIGPROF signals. We do this, rather than change + // to SIG_DFL, because there may be a pending SIGPROF + // signal that has not yet been delivered to some other thread. + // If we change to SIG_DFL here, the program will crash + // when that SIGPROF is delivered. We assume that programs + // that use profiling don't want to crash on a stray SIGPROF. + // See issue 19320. + if !sigInstallGoHandler(_SIGPROF) { + if atomic.Cas(&handlingSig[_SIGPROF], 1, 0) { + h := atomic.Loaduintptr(&fwdSig[_SIGPROF]) + if h == _SIG_DFL { + h = _SIG_IGN + } + setsig(_SIGPROF, h) + } + } + + setitimer(_ITIMER_PROF, &itimerval{}, nil) + } +} + +// setThreadCPUProfiler makes any thread-specific changes required to +// implement profiling at a rate of hz. +// No changes required on Unix systems. +func setThreadCPUProfiler(hz int32) { + getg().m.profilehz = hz +} + +func sigpipe() { + if signal_ignored(_SIGPIPE) || sigsend(_SIGPIPE) { + return + } + dieFromSignal(_SIGPIPE) +} + +// doSigPreempt handles a preemption signal on gp. +func doSigPreempt(gp *g, ctxt *sigctxt) { + // Check if this G wants to be preempted and is safe to + // preempt. + if wantAsyncPreempt(gp) { + if ok, newpc := isAsyncSafePoint(gp, ctxt.sigpc(), ctxt.sigsp(), ctxt.siglr()); ok { + // Adjust the PC and inject a call to asyncPreempt. + ctxt.pushCall(funcPC(asyncPreempt), newpc) + } + } + + // Acknowledge the preemption. + atomic.Xadd(&gp.m.preemptGen, 1) + atomic.Store(&gp.m.signalPending, 0) + + if GOOS == "darwin" || GOOS == "ios" { + atomic.Xadd(&pendingPreemptSignals, -1) + } +} + +const preemptMSupported = true + +// preemptM sends a preemption request to mp. This request may be +// handled asynchronously and may be coalesced with other requests to +// the M. When the request is received, if the running G or P are +// marked for preemption and the goroutine is at an asynchronous +// safe-point, it will preempt the goroutine. It always atomically +// increments mp.preemptGen after handling a preemption request. +func preemptM(mp *m) { + // On Darwin, don't try to preempt threads during exec. + // Issue #41702. + if GOOS == "darwin" || GOOS == "ios" { + execLock.rlock() + } + + if atomic.Cas(&mp.signalPending, 0, 1) { + if GOOS == "darwin" || GOOS == "ios" { + atomic.Xadd(&pendingPreemptSignals, 1) + } + + // If multiple threads are preempting the same M, it may send many + // signals to the same M such that it hardly make progress, causing + // live-lock problem. Apparently this could happen on darwin. See + // issue #37741. + // Only send a signal if there isn't already one pending. + signalM(mp, sigPreempt) + } + + if GOOS == "darwin" || GOOS == "ios" { + execLock.runlock() + } +} + +// sigFetchG fetches the value of G safely when running in a signal handler. +// On some architectures, the g value may be clobbered when running in a VDSO. +// See issue #32912. +// +//go:nosplit +func sigFetchG(c *sigctxt) *g { + switch GOARCH { + case "arm", "arm64", "ppc64", "ppc64le": + if !iscgo && inVDSOPage(c.sigpc()) { + // When using cgo, we save the g on TLS and load it from there + // in sigtramp. Just use that. + // Otherwise, before making a VDSO call we save the g to the + // bottom of the signal stack. Fetch from there. + // TODO: in efence mode, stack is sysAlloc'd, so this wouldn't + // work. + sp := getcallersp() + s := spanOf(sp) + if s != nil && s.state.get() == mSpanManual && s.base() < sp && sp < s.limit { + gp := *(**g)(unsafe.Pointer(s.base())) + return gp + } + return nil + } + } + return getg() +} + +// 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, ctx unsafe.Pointer) { + if sigfwdgo(sig, info, ctx) { + return + } + c := &sigctxt{info, ctx} + g := sigFetchG(c) + setg(g) + if g == nil { + if sig == _SIGPROF { + sigprofNonGoPC(c.sigpc()) + return + } + if sig == sigPreempt && preemptMSupported && debug.asyncpreemptoff == 0 { + // This is probably a signal from preemptM sent + // while executing Go code but received while + // executing non-Go code. + // We got past sigfwdgo, so we know that there is + // no non-Go signal handler for sigPreempt. + // The default behavior for sigPreempt is to ignore + // the signal, so badsignal will be a no-op anyway. + if GOOS == "darwin" || GOOS == "ios" { + atomic.Xadd(&pendingPreemptSignals, -1) + } + return + } + c.fixsigcode(sig) + badsignal(uintptr(sig), c) + return + } + + setg(g.m.gsignal) + + // If some non-Go code called sigaltstack, adjust. + var gsignalStack gsignalStack + setStack := adjustSignalStack(sig, g.m, &gsignalStack) + if setStack { + g.m.gsignal.stktopsp = getcallersp() + } + + if g.stackguard0 == stackFork { + signalDuringFork(sig) + } + + c.fixsigcode(sig) + sighandler(sig, info, ctx, g) + setg(g) + if setStack { + restoreGsignalStack(&gsignalStack) + } +} + +// adjustSignalStack adjusts the current stack guard based on the +// stack pointer that is actually in use while handling a signal. +// We do this in case some non-Go code called sigaltstack. +// This reports whether the stack was adjusted, and if so stores the old +// signal stack in *gsigstack. +//go:nosplit +func adjustSignalStack(sig uint32, mp *m, gsigStack *gsignalStack) bool { + sp := uintptr(unsafe.Pointer(&sig)) + if sp >= mp.gsignal.stack.lo && sp < mp.gsignal.stack.hi { + return false + } + + var st stackt + sigaltstack(nil, &st) + stsp := uintptr(unsafe.Pointer(st.ss_sp)) + if st.ss_flags&_SS_DISABLE == 0 && sp >= stsp && sp < stsp+st.ss_size { + setGsignalStack(&st, gsigStack) + return true + } + + if sp >= mp.g0.stack.lo && sp < mp.g0.stack.hi { + // The signal was delivered on the g0 stack. + // This can happen when linked with C code + // using the thread sanitizer, which collects + // signals then delivers them itself by calling + // the signal handler directly when C code, + // including C code called via cgo, calls a + // TSAN-intercepted function such as malloc. + // + // We check this condition last as g0.stack.lo + // may be not very accurate (see mstart). + st := stackt{ss_size: mp.g0.stack.hi - mp.g0.stack.lo} + setSignalstackSP(&st, mp.g0.stack.lo) + setGsignalStack(&st, gsigStack) + return true + } + + // sp is not within gsignal stack, g0 stack, or sigaltstack. Bad. + setg(nil) + needm() + if st.ss_flags&_SS_DISABLE != 0 { + noSignalStack(sig) + } else { + sigNotOnStack(sig) + } + dropm() + return false +} + +// crashing is the number of m's we have waited for when implementing +// GOTRACEBACK=crash when a signal is received. +var crashing int32 + +// testSigtrap and testSigusr1 are used by the runtime tests. If +// non-nil, it is called on SIGTRAP/SIGUSR1. If it returns true, the +// normal behavior on this signal is suppressed. +var testSigtrap func(info *siginfo, ctxt *sigctxt, gp *g) bool +var testSigusr1 func(gp *g) bool + +// sighandler is invoked when a signal occurs. The global g will be +// set to a gsignal goroutine and we will be running on the alternate +// signal stack. The parameter g will be the value of the global g +// when the signal occurred. The sig, info, and ctxt parameters are +// from the system signal handler: they are the parameters passed when +// the SA is passed to the sigaction system call. +// +// The garbage collector may have stopped the world, so write barriers +// are not allowed. +// +//go:nowritebarrierrec +func sighandler(sig uint32, info *siginfo, ctxt unsafe.Pointer, gp *g) { + _g_ := getg() + c := &sigctxt{info, ctxt} + + if sig == _SIGPROF { + sigprof(c.sigpc(), c.sigsp(), c.siglr(), gp, _g_.m) + return + } + + if sig == _SIGTRAP && testSigtrap != nil && testSigtrap(info, (*sigctxt)(noescape(unsafe.Pointer(c))), gp) { + return + } + + if sig == _SIGUSR1 && testSigusr1 != nil && testSigusr1(gp) { + return + } + + if sig == sigPreempt && debug.asyncpreemptoff == 0 { + // Might be a preemption signal. + doSigPreempt(gp, c) + // Even if this was definitely a preemption signal, it + // may have been coalesced with another signal, so we + // still let it through to the application. + } + + flags := int32(_SigThrow) + if sig < uint32(len(sigtable)) { + flags = sigtable[sig].flags + } + if c.sigcode() != _SI_USER && flags&_SigPanic != 0 && gp.throwsplit { + // We can't safely sigpanic because it may grow the + // stack. Abort in the signal handler instead. + flags = _SigThrow + } + if isAbortPC(c.sigpc()) { + // On many architectures, the abort function just + // causes a memory fault. Don't turn that into a panic. + flags = _SigThrow + } + if c.sigcode() != _SI_USER && flags&_SigPanic != 0 { + // The signal is going to cause a panic. + // Arrange the stack so that it looks like the point + // where the signal occurred made a call to the + // function sigpanic. Then set the PC to sigpanic. + + // Have to pass arguments out of band since + // augmenting the stack frame would break + // the unwinding code. + gp.sig = sig + gp.sigcode0 = uintptr(c.sigcode()) + gp.sigcode1 = uintptr(c.fault()) + gp.sigpc = c.sigpc() + + c.preparePanic(sig, gp) + return + } + + if c.sigcode() == _SI_USER || flags&_SigNotify != 0 { + if sigsend(sig) { + return + } + } + + if c.sigcode() == _SI_USER && signal_ignored(sig) { + return + } + + if flags&_SigKill != 0 { + dieFromSignal(sig) + } + + // _SigThrow means that we should exit now. + // If we get here with _SigPanic, it means that the signal + // was sent to us by a program (c.sigcode() == _SI_USER); + // in that case, if we didn't handle it in sigsend, we exit now. + if flags&(_SigThrow|_SigPanic) == 0 { + return + } + + _g_.m.throwing = 1 + _g_.m.caughtsig.set(gp) + + if crashing == 0 { + startpanic_m() + } + + if sig < uint32(len(sigtable)) { + print(sigtable[sig].name, "\n") + } else { + print("Signal ", sig, "\n") + } + + print("PC=", hex(c.sigpc()), " m=", _g_.m.id, " sigcode=", c.sigcode(), "\n") + if _g_.m.lockedg != 0 && _g_.m.ncgo > 0 && gp == _g_.m.g0 { + print("signal arrived during cgo execution\n") + gp = _g_.m.lockedg.ptr() + } + if sig == _SIGILL || sig == _SIGFPE { + // It would be nice to know how long the instruction is. + // Unfortunately, that's complicated to do in general (mostly for x86 + // and s930x, but other archs have non-standard instruction lengths also). + // Opt to print 16 bytes, which covers most instructions. + const maxN = 16 + n := uintptr(maxN) + // We have to be careful, though. If we're near the end of + // a page and the following page isn't mapped, we could + // segfault. So make sure we don't straddle a page (even though + // that could lead to printing an incomplete instruction). + // We're assuming here we can read at least the page containing the PC. + // I suppose it is possible that the page is mapped executable but not readable? + pc := c.sigpc() + if n > physPageSize-pc%physPageSize { + n = physPageSize - pc%physPageSize + } + print("instruction bytes:") + b := (*[maxN]byte)(unsafe.Pointer(pc)) + for i := uintptr(0); i < n; i++ { + print(" ", hex(b[i])) + } + println() + } + print("\n") + + level, _, docrash := gotraceback() + if level > 0 { + goroutineheader(gp) + tracebacktrap(c.sigpc(), c.sigsp(), c.siglr(), gp) + if crashing > 0 && gp != _g_.m.curg && _g_.m.curg != nil && readgstatus(_g_.m.curg)&^_Gscan == _Grunning { + // tracebackothers on original m skipped this one; trace it now. + goroutineheader(_g_.m.curg) + traceback(^uintptr(0), ^uintptr(0), 0, _g_.m.curg) + } else if crashing == 0 { + tracebackothers(gp) + print("\n") + } + dumpregs(c) + } + + if docrash { + crashing++ + if crashing < mcount()-int32(extraMCount) { + // There are other m's that need to dump their stacks. + // Relay SIGQUIT to the next m by sending it to the current process. + // All m's that have already received SIGQUIT have signal masks blocking + // receipt of any signals, so the SIGQUIT will go to an m that hasn't seen it yet. + // When the last m receives the SIGQUIT, it will fall through to the call to + // crash below. Just in case the relaying gets botched, each m involved in + // the relay sleeps for 5 seconds and then does the crash/exit itself. + // In expected operation, the last m has received the SIGQUIT and run + // crash/exit and the process is gone, all long before any of the + // 5-second sleeps have finished. + print("\n-----\n\n") + raiseproc(_SIGQUIT) + usleep(5 * 1000 * 1000) + } + crash() + } + + printDebugLog() + + exit(2) +} + +// 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. +// +// This must NOT be nosplit because the linker doesn't know where +// sigpanic calls can be injected. +// +// The signal handler must not inject a call to sigpanic if +// getg().throwsplit, since sigpanic may need to grow the stack. +// +// This is exported via linkname to assembly in runtime/cgo. +//go:linkname sigpanic +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 { + panicmemAddr(g.sigcode1) + } + 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 { + panicmemAddr(g.sigcode1) + } + 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() + + // 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. + // + // On FreeBSD, the libthr sigaction code prevents + // this from working so we fall through to raise. + if GOOS != "freebsd" && (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, funcPC(sighandler)) +} + +//go:nosplit +func crash() { + // 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 GOOS == "darwin" && 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. + sigBlocked := sigset_all + 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") +} + +var badginsignalMsg = "fatal: bad g in signal handler\n" + +// 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) { + if !iscgo && !cgoHasExtraM { + // There is no extra M. needm will not be able to grab + // an M. Instead of hanging, just crash. + // Cannot call split-stack function as there is no G. + s := stringStructOf(&badginsignalMsg) + write(2, s.str, int32(s.len)) + exit(2) + *(*uintptr)(unsafe.Pointer(uintptr(123))) = 2 + } + needm() + 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() +} + +//go:noescape +func sigfwd(fn uintptr, sig uint32, info *siginfo, ctx unsafe.Pointer) + +// 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, 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 + } + + // This function and its caller sigtrampgo assumes SIGPIPE is delivered on the + // originating thread. This property does not hold on macOS (golang.org/issue/33384), + // so we have no choice but to ignore SIGPIPE. + if (GOOS == "darwin" || GOOS == "ios") && sig == _SIGPIPE { + 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 weren't in VDSO page, + // (2) we were in a goroutine (i.e., m.curg != nil), and + // (3) we weren't in CGO. + g := sigFetchG(c) + 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 +} + +// sigsave saves the current thread's signal mask into *p. +// 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 sigsave(p *sigset) { + sigprocmask(_SIG_SETMASK, nil, p) +} + +// 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) +} + +// sigsetAllExiting is used by sigblock(true) when a thread is +// exiting. sigset_all is defined in OS specific code, and per GOOS +// behavior may override this default for sigsetAllExiting: see +// osinit(). +var sigsetAllExiting = sigset_all + +// sigblock blocks 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. When a thread is exiting +// we use the sigsetAllExiting value, otherwise the OS specific +// definition of sigset_all is used. +// 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(exiting bool) { + if exiting { + sigprocmask(_SIG_SETMASK, &sigsetAllExiting, nil) + return + } + sigprocmask(_SIG_SETMASK, &sigset_all, 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 + 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. We also set the alternate +// signal stack to the gsignal stack if cgo is not used (regardless +// of whether it is already set). Record which choice was made in +// newSigstack, so that it can be undone in unminit. +func minitSignalStack() { + _g_ := getg() + var st stackt + sigaltstack(nil, &st) + if st.ss_flags&_SS_DISABLE != 0 || !iscgo { + signalstack(&_g_.m.gsignal.stack) + _g_.m.newSigstack = true + } else { + setGsignalStack(&st, &_g_.m.goSigStack) + _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 +// sigsave 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 +func unminitSignals() { + if getg().m.newSigstack { + st := stackt{ss_flags: _SS_DISABLE} + sigaltstack(&st, nil) + } else { + // We got the signal stack from someone else. Restore + // the Go-allocated stack in case this M gets reused + // for another thread (e.g., it's an extram). Also, on + // Android, libc allocates a signal stack for all + // threads, so it's important to restore the Go stack + // even on Go-created threads so we can free it. + restoreGsignalStack(&getg().m.goSigStack) + } +} + +// blockableSig reports 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 +} + +// gsignalStack saves the fields of the gsignal stack changed by +// setGsignalStack. +type gsignalStack struct { + stack stack + stackguard0 uintptr + stackguard1 uintptr + stktopsp uintptr +} + +// setGsignalStack sets the gsignal stack of the current m to an +// alternate signal stack returned from the sigaltstack system call. +// It saves the old values in *old for use by restoreGsignalStack. +// This is used when handling a signal if non-Go code has set the +// alternate signal stack. +//go:nosplit +//go:nowritebarrierrec +func setGsignalStack(st *stackt, old *gsignalStack) { + g := getg() + if old != nil { + old.stack = g.m.gsignal.stack + old.stackguard0 = g.m.gsignal.stackguard0 + old.stackguard1 = g.m.gsignal.stackguard1 + old.stktopsp = g.m.gsignal.stktopsp + } + stsp := uintptr(unsafe.Pointer(st.ss_sp)) + g.m.gsignal.stack.lo = stsp + g.m.gsignal.stack.hi = stsp + st.ss_size + g.m.gsignal.stackguard0 = stsp + _StackGuard + g.m.gsignal.stackguard1 = stsp + _StackGuard +} + +// restoreGsignalStack restores the gsignal stack to the value it had +// before entering the signal handler. +//go:nosplit +//go:nowritebarrierrec +func restoreGsignalStack(st *gsignalStack) { + gp := getg().m.gsignal + gp.stack = st.stack + gp.stackguard0 = st.stackguard0 + gp.stackguard1 = st.stackguard1 + gp.stktopsp = st.stktopsp +} + +// signalstack sets the current thread's alternate signal stack to s. +//go:nosplit +func signalstack(s *stack) { + st := stackt{ss_size: s.hi - s.lo} + setSignalstackSP(&st, s.lo) + sigaltstack(&st, nil) +} + +// setsigsegv is used on darwin/arm64 to fake a segmentation fault. +// +// This is exported via linkname to assembly in runtime/cgo. +// +//go:nosplit +//go:linkname setsigsegv +func setsigsegv(pc uintptr) { + g := getg() + g.sig = _SIGSEGV + g.sigpc = pc + g.sigcode0 = _SEGV_MAPERR + g.sigcode1 = 0 // TODO: emulate si_addr +} |