runtime: drop sigfwd from signal forwarding unsupported platforms

This change splits signal_unix.go into signal_unix.go and
signal2_unix.go and removes the fake symbol sigfwd from signal
forwarding unsupported platforms for clarification purpose.

Change-Id: I205eab5cf1930fda8a68659b35cfa9f3a0e67ca6
Reviewed-on: https://go-review.googlesource.com/12062
Reviewed-by: Ian Lance Taylor <iant@golang.org>

src/runtime/os_dragonfly.go

@@ -12,9 +12,6 @@ func lwp_create(param *lwpparams) int32
 //go:noescape
 func sigaltstack(new, old *sigaltstackt)
 
-//go:noescape
-func sigfwd(fn uintptr, sig uint32, info *siginfo, ctx unsafe.Pointer)
-
 //go:noescape
 func sigaction(sig int32, new, old *sigactiont)
 

src/runtime/os_freebsd.go

@@ -12,9 +12,6 @@ func thr_new(param *thrparam, size int32)
 //go:noescape
 func sigaltstack(new, old *stackt)
 
-//go:noescape
-func sigfwd(fn uintptr, sig uint32, info *siginfo, ctx unsafe.Pointer)
-
 //go:noescape
 func sigaction(sig int32, new, old *sigactiont)
 

src/runtime/os_linux.go

@@ -18,9 +18,6 @@ func rt_sigaction(sig uintptr, new, old *sigactiont, size uintptr) int32
 //go:noescape
 func sigaltstack(new, old *sigaltstackt)
 
-//go:noescape
-func sigfwd(fn uintptr, sig uint32, info *siginfo, ctx unsafe.Pointer)
-
 //go:noescape
 func setitimer(mode int32, new, old *itimerval)
 

src/runtime/os_nacl.go

@@ -50,10 +50,6 @@ func sigpanic() {
 	panicmem()
 }
 
-func sigfwd(fn uintptr, sig uint32, info *siginfo, ctx unsafe.Pointer) {
-	throw("sigfwd not implemented")
-}
-
 func raiseproc(sig int32) {
 }
 

src/runtime/os_netbsd.go

@@ -15,10 +15,6 @@ func sigaction(sig int32, new, old *sigactiont)
 //go:noescape
 func sigaltstack(new, old *sigaltstackt)
 
-func sigfwd(fn uintptr, sig uint32, info *siginfo, ctx unsafe.Pointer) {
-	throw("sigfwd not implemented")
-}
-
 //go:noescape
 func sigprocmask(mode int32, new, old *sigset)
 

src/runtime/os_openbsd.go

@@ -4,8 +4,6 @@
 
 package runtime
 
-import "unsafe"
-
 //go:noescape
 func setitimer(mode int32, new, old *itimerval)
 
@@ -15,9 +13,6 @@ func sigaction(sig int32, new, old *sigactiont)
 //go:noescape
 func sigaltstack(new, old *stackt)
 
-//go:noescape
-func sigfwd(fn uintptr, sig uint32, info *siginfo, ctx unsafe.Pointer)
-
 //go:noescape
 func sigprocmask(mode int32, new uint32) uint32
 

src/runtime/os_solaris.go

@@ -10,9 +10,6 @@ type libcFunc uintptr
 
 var asmsysvicall6 libcFunc
 
-//go:noescape
-func sigfwd(fn uintptr, sig uint32, info *siginfo, ctx unsafe.Pointer)
-
 //go:nosplit
 func sysvicall0(fn *libcFunc) uintptr {
 	libcall := &getg().m.libcall

src/runtime/signal1_unix.go

@@ -16,7 +16,7 @@ const (
 // handle a particular signal (e.g., signal occurred on a non-Go thread).
 // See sigfwdgo() for more information on when the signals are forwarded.
 //
-// Signal forwarding is currently available only on Linux.
+// Signal forwarding is currently available only on Darwin and Linux.
 var fwdSig [_NSIG]uintptr
 
 // sigmask represents a general signal mask compatible with the GOOS

src/runtime/signal2_unix.go

@@ -0,0 +1,46 @@
+// 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 linux
+
+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.
+//go:nosplit
+func sigfwdgo(sig uint32, info *siginfo, ctx unsafe.Pointer) bool {
+	g := getg()
+	c := &sigctxt{info, ctx}
+	if sig >= uint32(len(sigtable)) {
+		return false
+	}
+	fwdFn := fwdSig[sig]
+	flags := sigtable[sig].flags
+
+	// If there is no handler to forward to, no need to forward.
+	if fwdFn == _SIG_DFL {
+		return false
+	}
+	// Only forward synchronous signals.
+	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).
+	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
+}

src/runtime/signal_darwin.go

@@ -46,9 +46,6 @@ var sigtable = [...]sigTabT{
 	/* 31 */ {_SigNotify, "SIGUSR2: user-defined signal 2"},
 }
 
-//go:noescape
-func sigfwd(fn uintptr, sig uint32, info *siginfo, ctx unsafe.Pointer)
-
 //go:noescape
 func sigreturn(ctx unsafe.Pointer, infostyle uint32)
 

src/runtime/signal_unix.go

@@ -6,43 +6,9 @@
 
 package runtime
 
-import "unsafe"
+import _ "unsafe" // for go:linkname
 
 //go:linkname os_sigpipe os.sigpipe
 func os_sigpipe() {
 	systemstack(sigpipe)
 }
-
-// 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.
-//go:nosplit
-func sigfwdgo(sig uint32, info *siginfo, ctx unsafe.Pointer) bool {
-	g := getg()
-	c := &sigctxt{info, ctx}
-	if sig >= uint32(len(sigtable)) {
-		return false
-	}
-	fwdFn := fwdSig[sig]
-	flags := sigtable[sig].flags
-
-	// If there is no handler to forward to, no need to forward.
-	if fwdFn == _SIG_DFL {
-		return false
-	}
-	// Only forward synchronous signals.
-	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).
-	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
-}