runtime/cgo: make compatible with race detector

Some routines run without and m or g and cannot invoke the
race detector runtime. They must be opaque to the runtime.
That used to be true because they were written in C.
Now that they are written in Go, disable the race detector
annotations for those functions explicitly.

Add test.

Fixes #10874.

Change-Id: Ia8cc28d51e7051528f9f9594b75634e6bb66a785
Reviewed-on: https://go-review.googlesource.com/12534
Reviewed-by: Ian Lance Taylor <[email protected]>

Author: rsc

src/cmd/cgo/out.go

@@ -809,6 +809,7 @@ func (p *Package) writeExports(fgo2, fm, fgcc, fgcch io.Writer) {
 		fmt.Fprintf(fgo2, "//go:linkname _cgoexp%s_%s _cgoexp%s_%s\n", cPrefix, exp.ExpName, cPrefix, exp.ExpName)
 		fmt.Fprintf(fgo2, "//go:cgo_export_static _cgoexp%s_%s\n", cPrefix, exp.ExpName)
 		fmt.Fprintf(fgo2, "//go:nosplit\n") // no split stack, so no use of m or g
+		fmt.Fprintf(fgo2, "//go:norace\n")  // must not have race detector calls inserted
 		fmt.Fprintf(fgo2, "func _cgoexp%s_%s(a unsafe.Pointer, n int32) {", cPrefix, exp.ExpName)
 		fmt.Fprintf(fgo2, "\tfn := %s\n", goname)
 		// The indirect here is converting from a Go function pointer to a C function pointer.

src/cmd/compile/internal/gc/go.go

@@ -660,6 +660,7 @@ var (
 	nosplit        bool
 	nowritebarrier bool
 	systemstack    bool
+	norace         bool
 )
 
 var debuglive int

src/cmd/compile/internal/gc/go.y

@@ -1390,6 +1390,7 @@ xfndcl:
 		$$.Nbody = $3;
 		$$.Func.Endlineno = lineno;
 		$$.Noescape = noescape;
+		$$.Func.Norace = norace;
 		$$.Func.Nosplit = nosplit;
 		$$.Func.Nowritebarrier = nowritebarrier;
 		$$.Func.Systemstack = systemstack;
@@ -1579,6 +1580,7 @@ xdcl_list:
 		}
 		nointerface = false
 		noescape = false
+		norace = false
 		nosplit = false
 		nowritebarrier = false
 		systemstack = false

src/cmd/compile/internal/gc/lex.go

@@ -1612,6 +1612,11 @@ func getlinepragma() int {
 			return c
 		}
 
+		if verb == "go:norace" {
+			norace = true
+			return c
+		}
+
 		if verb == "go:nosplit" {
 			nosplit = true
 			return c

src/cmd/compile/internal/gc/racewalk.go

@@ -42,6 +42,7 @@ func ispkgin(pkgs []string) bool {
 	return false
 }
 
+// TODO(rsc): Remove. Put //go:norace on forkAndExecInChild instead.
 func isforkfunc(fn *Node) bool {
 	// Special case for syscall.forkAndExecInChild.
 	// In the child, this function must not acquire any locks, because
@@ -52,7 +53,7 @@ func isforkfunc(fn *Node) bool {
 }
 
 func racewalk(fn *Node) {
-	if ispkgin(omit_pkgs) || isforkfunc(fn) {
+	if ispkgin(omit_pkgs) || isforkfunc(fn) || fn.Func.Norace {
 		return
 	}
 

src/cmd/compile/internal/gc/syntax.go

@@ -169,6 +169,7 @@ type Func struct {
 
 	Endlineno int32
 
+	Norace         bool // func must not have race detector annotations
 	Nosplit        bool // func should not execute on separate stack
 	Nowritebarrier bool // emit compiler error instead of write barrier
 	Dupok          bool // duplicate definitions ok