initial support for cgo

I'm sure that the added test case doesn't cover many edge cases, but
it's a start.

Fixes #12.

main.go

@@ -287,8 +287,18 @@ func transformCompile(args []string) ([]string, error) {
 	args = flags
 	// TODO: randomize the order and names of the files
 	for i, file := range files {
-		file := transformGo(file, info)
-		tempFile := filepath.Join(tempDir, fmt.Sprintf("z%d.go", i))
+		origName := filepath.Base(filepath.Clean(paths[i]))
+		name := fmt.Sprintf("z%d.go", i)
+		switch {
+		case strings.HasPrefix(origName, "_cgo_"):
+			// Cgo generated code requires a prefix. Also, don't
+			// garble it, since it's just generated code and it gets
+			// messy.
+			name = "_cgo_" + name
+		default:
+			file = transformGo(file, info)
+		}
+		tempFile := filepath.Join(tempDir, name)
 		f, err := os.Create(tempFile)
 		if err != nil {
 			return nil, err
@@ -384,7 +394,7 @@ func hashWith(salt, value string) string {
 }
 
 // transformGo garbles the provided Go syntax node.
-func transformGo(file *ast.File, info *types.Info) ast.Node {
+func transformGo(file *ast.File, info *types.Info) *ast.File {
 	// Remove all comments, minus the "//go:" compiler directives.
 	// The final binary should still not contain comment text, but removing
 	// it helps ensure that (and makes position info less predictable).
@@ -406,6 +416,9 @@ func transformGo(file *ast.File, info *types.Info) ast.Node {
 			if node.Name == "_" {
 				return true // unnamed remains unnamed
 			}
+			if strings.HasPrefix(node.Name, "_C") || strings.Contains(node.Name, "_cgo") {
+				return true // don't mess with cgo-generated code
+			}
 			obj := info.ObjectOf(node)
 			// log.Printf("%#v %T", node, obj)
 			switch x := obj.(type) {
@@ -473,7 +486,7 @@ func transformGo(file *ast.File, info *types.Info) ast.Node {
 		}
 		return true
 	}
-	return astutil.Apply(file, pre, nil)
+	return astutil.Apply(file, pre, nil).(*ast.File)
 }
 
 func isStandardLibrary(path string) bool {

testdata/scripts/cgo.txt

@@ -0,0 +1,30 @@
+garble build
+exec ./main
+cmp stdout main.stdout
+binsubstr main$exe 'privateAdd'
+
+[short] stop # no need to verify this with -short
+
+go build
+exec ./main
+cmp stdout main.stdout
+
+-- go.mod --
+module foo.com/main
+-- main.go --
+package main
+
+/*
+static int privateAdd(int a, int b) {
+	return a + b;
+}
+*/
+import "C"
+
+import "fmt"
+
+func main() {
+	fmt.Println(C.privateAdd(C.int(1), C.int(2)))
+}
+-- main.stdout --
+3