libgo: Update to go1.6rc1.

Reviewed-on: https://go-review.googlesource.com/19200

From-SVN: r233110

libgo/go/runtime/signal2_unix.go

@@ -0,0 +1,69 @@
+// 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 darwin dragonfly freebsd linux netbsd openbsd
+
+package runtime
+
+import "unsafe"
+
+//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 := fwdSig[sig]
+
+	if !signalsOK {
+		// The only way we can get here is if we are in a
+		// library or archive, we installed a signal handler
+		// at program startup, but the Go runtime has not yet
+		// been initialized.
+		if fwdFn == _SIG_DFL {
+			dieFromSignal(int32(sig))
+		} else {
+			sigfwd(fwdFn, sig, info, ctx)
+		}
+		return true
+	}
+
+	flags := sigtable[sig].flags
+
+	// If there is no handler to forward to, no need to forward.
+	if fwdFn == _SIG_DFL {
+		return false
+	}
+
+	// If we aren't handling the signal, forward it.
+	if flags&_SigHandling == 0 {
+		sigfwd(fwdFn, sig, info, ctx)
+		return true
+	}
+
+	// Only forward synchronous signals.
+	c := &sigctxt{info, ctx}
+	if c.sigcode() == _SI_USER || flags&_SigPanic == 0 {
+		return false
+	}
+	// Determine if the signal occurred inside Go code.  We test that:
+	//   (1) we were in a goroutine (i.e., m.curg != nil), and
+	//   (2) we weren't in CGO (i.e., m.curg.syscallsp == 0).
+	g := getg()
+	if g != nil && g.m != nil && g.m.curg != nil && g.m.curg.syscallsp == 0 {
+		return false
+	}
+	// Signal not handled by Go, forward it.
+	if fwdFn != _SIG_IGN {
+		sigfwd(fwdFn, sig, info, ctx)
+	}
+	return true
+}