1 // Copyright 2015 The Go Authors. All rights reserved.
2 // Use of this source code is governed by a BSD-style
3 // license that can be found in the LICENSE file.
5 // Package cgocall defines an Analyzer that detects some violations of
6 // the cgo pointer passing rules.
20 "golang.org/x/tools/go/analysis"
21 "golang.org/x/tools/go/analysis/passes/internal/analysisutil"
26 const Doc = `detect some violations of the cgo pointer passing rules
28 Check for invalid cgo pointer passing.
29 This looks for code that uses cgo to call C code passing values
30 whose types are almost always invalid according to the cgo pointer
32 Specifically, it warns about attempts to pass a Go chan, map, func,
33 or slice to C, either directly, or via a pointer, array, or struct.`
35 var Analyzer = &analysis.Analyzer{
38 RunDespiteErrors: true,
42 func run(pass *analysis.Pass) (interface{}, error) {
43 if !analysisutil.Imports(pass.Pkg, "runtime/cgo") {
44 return nil, nil // doesn't use cgo
47 cgofiles, info, err := typeCheckCgoSourceFiles(pass.Fset, pass.Pkg, pass.Files, pass.TypesInfo, pass.TypesSizes)
51 for _, f := range cgofiles {
52 checkCgo(pass.Fset, f, info, pass.Reportf)
57 func checkCgo(fset *token.FileSet, f *ast.File, info *types.Info, reportf func(token.Pos, string, ...interface{})) {
58 ast.Inspect(f, func(n ast.Node) bool {
59 call, ok := n.(*ast.CallExpr)
64 // Is this a C.f() call?
66 if sel, ok := analysisutil.Unparen(call.Fun).(*ast.SelectorExpr); ok {
67 if id, ok := sel.X.(*ast.Ident); ok && id.Name == "C" {
72 return true // not a call we need to check
75 // A call to C.CBytes passes a pointer but is always safe.
81 log.Printf("%s: call to C.%s", fset.Position(call.Lparen), name)
84 for _, arg := range call.Args {
85 if !typeOKForCgoCall(cgoBaseType(info, arg), make(map[types.Type]bool)) {
86 reportf(arg.Pos(), "possibly passing Go type with embedded pointer to C")
90 // Check for passing the address of a bad type.
91 if conv, ok := arg.(*ast.CallExpr); ok && len(conv.Args) == 1 &&
92 isUnsafePointer(info, conv.Fun) {
95 if u, ok := arg.(*ast.UnaryExpr); ok && u.Op == token.AND {
96 if !typeOKForCgoCall(cgoBaseType(info, u.X), make(map[types.Type]bool)) {
97 reportf(arg.Pos(), "possibly passing Go type with embedded pointer to C")
106 // typeCheckCgoSourceFiles returns type-checked syntax trees for the raw
107 // cgo files of a package (those that import "C"). Such files are not
108 // Go, so there may be gaps in type information around C.f references.
110 // This checker was initially written in vet to inspect raw cgo source
111 // files using partial type information. However, Analyzers in the new
112 // analysis API are presented with the type-checked, "cooked" Go ASTs
113 // resulting from cgo-processing files, so we must choose between
114 // working with the cooked file generated by cgo (which was tried but
115 // proved fragile) or locating the raw cgo file (e.g. from //line
116 // directives) and working with that, as we now do.
118 // Specifically, we must type-check the raw cgo source files (or at
119 // least the subtrees needed for this analyzer) in an environment that
120 // simulates the rest of the already type-checked package.
122 // For example, for each raw cgo source file in the original package,
130 // var x, y = fmt.Println()
132 // func g() { ... C.malloc(k) ... }
133 // func (T) f(int) string { ... }
135 // we synthesize a new ast.File, shown below, that dot-imports the
136 // original "cooked" package using a special name ("·this·"), so that all
137 // references to package members resolve correctly. (References to
138 // unexported names cause an "unexported" error, which we ignore.)
140 // To avoid shadowing names imported from the cooked package,
141 // package-level declarations in the new source file are modified so
142 // that they do not declare any names.
143 // (The cgocall analysis is concerned with uses, not declarations.)
144 // Specifically, type declarations are discarded;
145 // all names in each var and const declaration are blanked out;
146 // each method is turned into a regular function by turning
147 // the receiver into the first parameter;
148 // and all functions are renamed to "_".
151 // import . "·this·" // declares T, k, x, y, f, g, T.f
155 // var _, _ = fmt.Println()
157 // func _() { ... C.malloc(k) ... }
158 // func _(T, int) string { ... }
160 // In this way, the raw function bodies and const/var initializer
161 // expressions are preserved but refer to the "cooked" objects imported
162 // from "·this·", and none of the transformed package-level declarations
163 // actually declares anything. In the example above, the reference to k
164 // in the argument of the call to C.malloc resolves to "·this·".k, which
165 // has an accurate type.
167 // This approach could in principle be generalized to more complex
168 // analyses on raw cgo files. One could synthesize a "C" package so that
169 // C.f would resolve to "·this·"._C_func_f, for example. But we have
170 // limited ourselves here to preserving function bodies and initializer
171 // expressions since that is all that the cgocall analyzer needs.
173 func typeCheckCgoSourceFiles(fset *token.FileSet, pkg *types.Package, files []*ast.File, info *types.Info, sizes types.Sizes) ([]*ast.File, *types.Info, error) {
174 const thispkg = "·this·"
176 // Which files are cgo files?
177 var cgoFiles []*ast.File
178 importMap := map[string]*types.Package{thispkg: pkg}
179 for _, raw := range files {
180 // If f is a cgo-generated file, Position reports
181 // the original file, honoring //line directives.
182 filename := fset.Position(raw.Pos()).Filename
183 f, err := parser.ParseFile(fset, filename, nil, parser.Mode(0))
185 return nil, nil, fmt.Errorf("can't parse raw cgo file: %v", err)
188 for _, spec := range f.Imports {
189 if spec.Path.Value == `"C"` {
195 continue // not a cgo file
198 // Record the original import map.
199 for _, spec := range raw.Imports {
200 path, _ := strconv.Unquote(spec.Path.Value)
201 importMap[path] = imported(info, spec)
204 // Add special dot-import declaration:
207 decls = append(decls, &ast.GenDecl{
211 Name: &ast.Ident{Name: "."},
214 Value: strconv.Quote(thispkg),
220 // Transform declarations from the raw cgo file.
221 for _, decl := range f.Decls {
222 switch decl := decl.(type) {
226 // Discard type declarations.
230 case token.VAR, token.CONST:
231 // Blank the declared var/const names.
232 for _, spec := range decl.Specs {
233 spec := spec.(*ast.ValueSpec)
234 for i := range spec.Names {
235 spec.Names[i].Name = "_"
240 // Blank the declared func name.
243 // Turn a method receiver: func (T) f(P) R {...}
244 // into regular parameter: func _(T, P) R {...}
245 if decl.Recv != nil {
246 var params []*ast.Field
247 params = append(params, decl.Recv.List...)
248 params = append(params, decl.Type.Params.List...)
249 decl.Type.Params.List = params
253 decls = append(decls, decl)
257 format.Node(os.Stderr, fset, f) // debugging
259 cgoFiles = append(cgoFiles, f)
262 return nil, nil, nil // nothing to do (can't happen?)
265 // Type-check the synthetic files.
268 Importer: importerFunc(func(path string) (*types.Package, error) {
269 return importMap[path], nil
272 Error: func(error) {}, // ignore errors (e.g. unused import)
275 // It's tempting to record the new types in the
276 // existing pass.TypesInfo, but we don't own it.
277 altInfo := &types.Info{
278 Types: make(map[ast.Expr]types.TypeAndValue),
280 tc.Check(pkg.Path(), fset, cgoFiles, altInfo)
282 return cgoFiles, altInfo, nil
285 // cgoBaseType tries to look through type conversions involving
286 // unsafe.Pointer to find the real type. It converts:
287 // unsafe.Pointer(x) => x
288 // *(*unsafe.Pointer)(unsafe.Pointer(&x)) => x
289 func cgoBaseType(info *types.Info, arg ast.Expr) types.Type {
290 switch arg := arg.(type) {
292 if len(arg.Args) == 1 && isUnsafePointer(info, arg.Fun) {
293 return cgoBaseType(info, arg.Args[0])
296 call, ok := arg.X.(*ast.CallExpr)
297 if !ok || len(call.Args) != 1 {
300 // Here arg is *f(v).
301 t := info.Types[call.Fun].Type
305 ptr, ok := t.Underlying().(*types.Pointer)
309 // Here arg is *(*p)(v)
310 elem, ok := ptr.Elem().Underlying().(*types.Basic)
311 if !ok || elem.Kind() != types.UnsafePointer {
314 // Here arg is *(*unsafe.Pointer)(v)
315 call, ok = call.Args[0].(*ast.CallExpr)
316 if !ok || len(call.Args) != 1 {
319 // Here arg is *(*unsafe.Pointer)(f(v))
320 if !isUnsafePointer(info, call.Fun) {
323 // Here arg is *(*unsafe.Pointer)(unsafe.Pointer(v))
324 u, ok := call.Args[0].(*ast.UnaryExpr)
325 if !ok || u.Op != token.AND {
328 // Here arg is *(*unsafe.Pointer)(unsafe.Pointer(&v))
329 return cgoBaseType(info, u.X)
332 return info.Types[arg].Type
335 // typeOKForCgoCall reports whether the type of arg is OK to pass to a
336 // C function using cgo. This is not true for Go types with embedded
337 // pointers. m is used to avoid infinite recursion on recursive types.
338 func typeOKForCgoCall(t types.Type, m map[types.Type]bool) bool {
339 if t == nil || m[t] {
343 switch t := t.Underlying().(type) {
344 case *types.Chan, *types.Map, *types.Signature, *types.Slice:
347 return typeOKForCgoCall(t.Elem(), m)
349 return typeOKForCgoCall(t.Elem(), m)
351 for i := 0; i < t.NumFields(); i++ {
352 if !typeOKForCgoCall(t.Field(i).Type(), m) {
360 func isUnsafePointer(info *types.Info, e ast.Expr) bool {
361 t := info.Types[e].Type
362 return t != nil && t.Underlying() == types.Typ[types.UnsafePointer]
365 type importerFunc func(path string) (*types.Package, error)
367 func (f importerFunc) Import(path string) (*types.Package, error) { return f(path) }
369 // TODO(adonovan): make this a library function or method of Info.
370 func imported(info *types.Info, spec *ast.ImportSpec) *types.Package {
371 obj, ok := info.Implicits[spec]
373 obj = info.Defs[spec.Name] // renaming import
375 return obj.(*types.PkgName).Imported()