obfuscate local names in linkname directives

Previously, the local name part of linkname directives were never
obfuscated. Now that we can obfuscate function names in Go assembly,
that limitation is required no longer.

Fixes #309

main.go

@@ -643,14 +643,9 @@ func transformCompile(args []string) ([]string, error) {
 
 	newPaths := make([]string, 0, len(files))
 
-	for _, file := range files {
-		// Process directives before obfuscating any names of the package,
-		// this is needed for functions which are linknamed to another package,
-		// but also used in the package declaring them.
+	for i, file := range files {
 		tf.handleDirectives(file.Comments)
-	}
 
-	for i, file := range files {
 		origName := filepath.Base(paths[i])
 		name := origName
 		switch {
@@ -735,13 +730,9 @@ func (tf *transformer) handleDirectives(comments []*ast.CommentGroup) {
 				continue
 			}
 			// This directive has two arguments: "go:linkname localName newName"
-			localName := fields[1]
 
-			// The local name must not be obfuscated.
-			obj := tf.pkg.Scope().Lookup(localName)
-			if obj != nil {
-				tf.ignoreObjects[obj] = true
-			}
+			// obfuscate the local name.
+			fields[1] = hashWith(curPkg.GarbleActionID, fields[1])
 
 			// If the new name is of the form "pkgpath.Name", and
 			// we've obfuscated "Name" in that package, rewrite the
@@ -756,20 +747,22 @@ func (tf *transformer) handleDirectives(comments []*ast.CommentGroup) {
 			}
 			lpkg, err := listPackage(pkgPath)
 			if err != nil {
-				continue // probably a made up symbol name
+				// probably a made up symbol name, replace the comment
+				// in case the local name was obfuscated.
+				comment.Text = strings.Join(fields, " ")
+				continue
 			}
-			if !lpkg.Private {
-				continue // ignore non-private symbols
+			if lpkg.Private {
+				// The name exists and was obfuscated; obfuscate
+				// the new name.
+				newName := hashWith(lpkg.GarbleActionID, name)
+				newPkgPath := pkgPath
+				if pkgPath != "main" {
+					newPkgPath = lpkg.obfuscatedImportPath()
+				}
+				fields[2] = newPkgPath + "." + newName
 			}
 
-			// The name exists and was obfuscated; replace the
-			// comment with the obfuscated name.
-			newName := hashWith(lpkg.GarbleActionID, name)
-			newPkgPath := pkgPath
-			if pkgPath != "main" {
-				newPkgPath = lpkg.obfuscatedImportPath()
-			}
-			fields[2] = newPkgPath + "." + newName
 			comment.Text = strings.Join(fields, " ")
 		}
 	}