runtime: add nowritebarrierrec to funcs called at signal time

Also nosplit where needed.

Change-Id: I1e3f6f8f76df9ee7e87ed1b8560cef145928314c
Reviewed-on: https://go-review.googlesource.com/18395
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

src/runtime/os3_solaris.go

@@ -520,6 +520,8 @@ func sigaction(sig int32, act *sigactiont, oact *sigactiont) /* int32 */ {
 	sysvicall3(&libc_sigaction, uintptr(sig), uintptr(unsafe.Pointer(act)), uintptr(unsafe.Pointer(oact)))
 }
 
+//go:nosplit
+//go:nowritebarrierrec
 func sigaltstack(ss *sigaltstackt, oss *sigaltstackt) /* int32 */ {
 	sysvicall2(&libc_sigaltstack, uintptr(unsafe.Pointer(ss)), uintptr(unsafe.Pointer(oss)))
 }

src/runtime/signal2_unix.go

@@ -14,7 +14,9 @@ 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

src/runtime/signal_darwin.go

@@ -50,6 +50,7 @@ var sigtable = [...]sigTabT{
 func sigreturn(ctx unsafe.Pointer, infostyle uint32)
 
 //go:nosplit
+//go:nowritebarrierrec
 func sigtrampgo(fn uintptr, infostyle, sig uint32, info *siginfo, ctx unsafe.Pointer) {
 	if sigfwdgo(sig, info, ctx) {
 		sigreturn(ctx, infostyle)

src/runtime/signal_freebsd.go

@@ -48,6 +48,7 @@ var sigtable = [...]sigTabT{
 }
 
 //go:nosplit
+//go:nowritebarrierrec
 func sigtrampgo(sig uint32, info *siginfo, ctx unsafe.Pointer) {
 	if sigfwdgo(sig, info, ctx) {
 		return

src/runtime/signal_openbsd.go

@@ -48,6 +48,7 @@ var sigtable = [...]sigTabT{
 }
 
 //go:nosplit
+//go:nowritebarrierrec
 func sigtrampgo(sig uint32, info *siginfo, ctx unsafe.Pointer) {
 	if sigfwdgo(sig, info, ctx) {
 		return

src/runtime/signal_sigtramp.go

@@ -9,7 +9,9 @@ package runtime
 import "unsafe"
 
 // Continuation of the (assembly) sigtramp() logic.
+// This may be called with the world stopped.
 //go:nosplit
+//go:nowritebarrierrec
 func sigtrampgo(sig uint32, info *siginfo, ctx unsafe.Pointer) {
 	if sigfwdgo(sig, info, ctx) {
 		return

src/runtime/sigqueue.go

@@ -180,6 +180,7 @@ func signal_ignored(s uint32) bool {
 // 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) {
 	cgocallback(unsafe.Pointer(funcPC(badsignalgo)), noescape(unsafe.Pointer(&sig)), unsafe.Sizeof(sig))
 }