cgo: add -gccgopkgpath option to match gccgo -fgo-pkgpath

R=golang-dev, r, iant
CC=golang-dev
https://golang.org/cl/6416056

src/cmd/cgo/main.go

@@ -144,7 +144,8 @@ var cdefs = flag.Bool("cdefs", false, "for bootstrap: write C definitions for C
 var objDir = flag.String("objdir", "", "object directory")
 
 var gccgo = flag.Bool("gccgo", false, "generate files for use with gccgo")
-var gccgoprefix = flag.String("gccgoprefix", "go", "prefix of symbols generated by gccgo")
+var gccgoprefix = flag.String("gccgoprefix", "", "-fgo-prefix option used with gccgo")
+var gccgopkgpath = flag.String("gccgopkgpath", "", "-fgo-pkgpath option used with gccgo")
 var importRuntimeCgo = flag.Bool("import_runtime_cgo", true, "import runtime/cgo in generated code")
 var goarch, goos string
 

src/cmd/cgo/out.go

@@ -669,7 +669,21 @@ func (p *Package) writeGccgoExports(fgo2, fc, fm *os.File) {
 		}
 		return '_'
 	}
-	gccgoSymbolPrefix := strings.Map(clean, *gccgoprefix)
+
+	var gccgoSymbolPrefix string
+	if *gccgopkgpath != "" {
+		gccgoSymbolPrefix = strings.Map(clean, *gccgopkgpath)
+	} else {
+		if *gccgoprefix == "" && p.PackageName == "main" {
+			gccgoSymbolPrefix = "main"
+		} else {
+			prefix := strings.Map(clean, *gccgoprefix)
+			if prefix == "" {
+				prefix = "go"
+			}
+			gccgoSymbolPrefix = prefix + "." + p.PackageName
+		}
+	}
 
 	for _, exp := range p.ExpFunc {
 		// TODO: support functions with receivers.
@@ -707,7 +721,7 @@ func (p *Package) writeGccgoExports(fgo2, fc, fm *os.File) {
 
 		// The function name.
 		fmt.Fprintf(cdeclBuf, " "+exp.ExpName)
-		gccgoSymbol := fmt.Sprintf("%s.%s.%s", gccgoSymbolPrefix, p.PackageName, exp.Func.Name)
+		gccgoSymbol := fmt.Sprintf("%s.%s", gccgoSymbolPrefix, exp.Func.Name)
 		fmt.Fprintf(cdeclBuf, " (")
 		// Function parameters.
 		forFieldList(fntype.Params,