// 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":
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
}
 |
The pages are generated with Golds v0.3.2. (GOOS=linux GOARCH=amd64)
Golds is a Go 101 project developed by Tapir Liu.
PR and bug reports are welcome and can be submitted to the issue list.
Please follow @Go100and1 (reachable from the left QR code) to get the latest news of Golds. |