cmd/cgo: reject names that are likely to be mangled C name

Fixes #28721

Change-Id: I00356f3a9b0c2fb21dc9c2237dd5296fcb3b319b
Reviewed-on: https://go-review.googlesource.com/c/152657
Run-TryBot: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

misc/cgo/errors/errors_test.go

@@ -121,6 +121,7 @@ func TestReportsTypeErrors(t *testing.T) {
 		"issue16591.go",
 		"issue18452.go",
 		"issue18889.go",
+		"issue28721.go",
 	} {
 		check(t, file)
 	}

misc/cgo/errors/src/issue28721.go

@@ -0,0 +1,29 @@
+// Copyright 2018 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// cgo should reject the use of mangled C names.
+
+package main
+
+/*
+typedef struct a {
+	int i;
+} a;
+void fn(void) {}
+*/
+import "C"
+
+type B _Ctype_struct_a // ERROR HERE
+
+var a _Ctype_struct_a // ERROR HERE
+
+type A struct {
+	a *_Ctype_struct_a // ERROR HERE
+}
+
+var notExist _Ctype_NotExist // ERROR HERE
+
+func main() {
+	_Cfunc_fn() // ERROR HERE
+}

src/cmd/cgo/ast.go

@@ -145,6 +145,7 @@ func (f *File) ParseGo(name string, src []byte) {
 	if f.Ref == nil {
 		f.Ref = make([]*Ref, 0, 8)
 	}
+	f.walk(ast2, ctxProg, (*File).validateIdents)
 	f.walk(ast2, ctxProg, (*File).saveExprs)
 
 	// Accumulate exported functions.
@@ -181,6 +182,14 @@ func commentText(g *ast.CommentGroup) string {
 	return strings.Join(pieces, "")
 }
 
+func (f *File) validateIdents(x interface{}, context astContext) {
+	if x, ok := x.(*ast.Ident); ok {
+		if f.isMangledName(x.Name) {
+			error_(x.Pos(), "identifier %q may conflict with identifiers generated by cgo", x.Name)
+		}
+	}
+}
+
 // Save various references we are going to need later.
 func (f *File) saveExprs(x interface{}, context astContext) {
 	switch x := x.(type) {

src/cmd/cgo/gcc.go

@@ -719,6 +719,19 @@ func (p *Package) mangleName(n *Name) {
 	n.Mangle = prefix + n.Kind + "_" + n.Go
 }
 
+func (f *File) isMangledName(s string) bool {
+	prefix := "_C"
+	if strings.HasPrefix(s, prefix) {
+		t := s[len(prefix):]
+		for _, k := range nameKinds {
+			if strings.HasPrefix(t, k+"_") {
+				return true
+			}
+		}
+	}
+	return false
+}
+
 // rewriteCalls rewrites all calls that pass pointers to check that
 // they follow the rules for passing pointers between Go and C.
 // This reports whether the package needs to import unsafe as _cgo_unsafe.

src/cmd/cgo/main.go

@@ -106,13 +106,15 @@ func (r *Ref) Pos() token.Pos {
 	return (*r.Expr).Pos()
 }
 
+var nameKinds = []string{"iconst", "fconst", "sconst", "type", "var", "fpvar", "func", "macro", "not-type"}
+
 // A Name collects information about C.xxx.
 type Name struct {
 	Go       string // name used in Go referring to package C
 	Mangle   string // name used in generated Go
 	C        string // name used in C
 	Define   string // #define expansion
-	Kind     string // "iconst", "fconst", "sconst", "type", "var", "fpvar", "func", "macro", "not-type"
+	Kind     string // one of the nameKinds
 	Type     *Type  // the type of xxx
 	FuncType *FuncType
 	AddError bool