runtime: recursively disallow write barriers in sighandler

sighandler may run during STW, so write barriers are not allowed.

Change-Id: Icdf46be10ea296fd87e73ab56ebb718c5d3c97ac
Reviewed-on: https://go-review.googlesource.com/17007Reviewed-by: Russ Cox <rsc@golang.org>

src/runtime/os3_plan9.go

@@ -10,7 +10,8 @@ import (
 )
 
 // May run during STW, so write barriers are not allowed.
-//go:nowritebarrier
+//
+//go:nowritebarrierrec
 func sighandler(_ureg *ureg, note *byte, gp *g) int {
 	_g_ := getg()
 	var t sigTabT

src/runtime/signal_386.go

@@ -30,7 +30,8 @@ func dumpregs(c *sigctxt) {
 var crashing int32
 
 // May run during STW, so write barriers are not allowed.
-//go:nowritebarrier
+//
+//go:nowritebarrierrec
 func sighandler(sig uint32, info *siginfo, ctxt unsafe.Pointer, gp *g) {
 	_g_ := getg()
 	c := &sigctxt{info, ctxt}

src/runtime/signal_amd64x.go

@@ -39,7 +39,8 @@ func dumpregs(c *sigctxt) {
 var crashing int32
 
 // May run during STW, so write barriers are not allowed.
-//go:nowritebarrier
+//
+//go:nowritebarrierrec
 func sighandler(sig uint32, info *siginfo, ctxt unsafe.Pointer, gp *g) {
 	_g_ := getg()
 	c := &sigctxt{info, ctxt}

src/runtime/signal_arm.go

@@ -35,7 +35,8 @@ func dumpregs(c *sigctxt) {
 var crashing int32
 
 // May run during STW, so write barriers are not allowed.
-//go:nowritebarrier
+//
+//go:nowritebarrierrec
 func sighandler(sig uint32, info *siginfo, ctxt unsafe.Pointer, gp *g) {
 	_g_ := getg()
 	c := &sigctxt{info, ctxt}

src/runtime/signal_arm64.go

@@ -51,7 +51,8 @@ func dumpregs(c *sigctxt) {
 var crashing int32
 
 // May run during STW, so write barriers are not allowed.
-//go:nowritebarrier
+//
+//go:nowritebarrierrec
 func sighandler(sig uint32, info *siginfo, ctxt unsafe.Pointer, gp *g) {
 	_g_ := getg()
 	c := &sigctxt{info, ctxt}

src/runtime/signal_mips64x.go

@@ -54,7 +54,8 @@ func dumpregs(c *sigctxt) {
 var crashing int32
 
 // May run during STW, so write barriers are not allowed.
-//go:nowritebarrier
+//
+//go:nowritebarrierrec
 func sighandler(sig uint32, info *siginfo, ctxt unsafe.Pointer, gp *g) {
 	_g_ := getg()
 	c := &sigctxt{info, ctxt}

src/runtime/signal_ppc64x.go

@@ -56,7 +56,8 @@ func dumpregs(c *sigctxt) {
 var crashing int32
 
 // May run during STW, so write barriers are not allowed.
-//go:nowritebarrier
+//
+//go:nowritebarrierrec
 func sighandler(sig uint32, info *siginfo, ctxt unsafe.Pointer, gp *g) {
 	_g_ := getg()
 	c := &sigctxt{info, ctxt}