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// Copyright 2014 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.
// Package unsafeptr defines an Analyzer that checks for invalid
// conversions of uintptr to unsafe.Pointer.
package unsafeptr
import (
const Doc = `check for invalid conversions of uintptr to unsafe.Pointer
The unsafeptr analyzer reports likely incorrect uses of unsafe.Pointer
to convert integers to pointers. A conversion from uintptr to
unsafe.Pointer is invalid if it implies that there is a uintptr-typed
word in memory that holds a pointer value, because that word will be
invisible to stack copying and to the garbage collector.`
var Analyzer = &analysis.Analyzer{
Name: "unsafeptr",
Doc: Doc,
Requires: []*analysis.Analyzer{inspect.Analyzer},
Run: run,
func run(pass *analysis.Pass) (interface{}, error) {
inspect := pass.ResultOf[inspect.Analyzer].(*inspector.Inspector)
nodeFilter := []ast.Node{
inspect.Preorder(nodeFilter, func(n ast.Node) {
x := n.(*ast.CallExpr)
if len(x.Args) != 1 {
if hasBasicType(pass.TypesInfo, x.Fun, types.UnsafePointer) &&
hasBasicType(pass.TypesInfo, x.Args[0], types.Uintptr) &&
!isSafeUintptr(pass.TypesInfo, x.Args[0]) {
pass.ReportRangef(x, "possible misuse of unsafe.Pointer")
return nil, nil
// isSafeUintptr reports whether x - already known to be a uintptr -
// is safe to convert to unsafe.Pointer. It is safe if x is itself derived
// directly from an unsafe.Pointer via conversion and pointer arithmetic
// or if x is the result of reflect.Value.Pointer or reflect.Value.UnsafeAddr
// or obtained from the Data field of a *reflect.SliceHeader or *reflect.StringHeader.
func isSafeUintptr(info *types.Info, x ast.Expr) bool {
switch x := x.(type) {
case *ast.ParenExpr:
return isSafeUintptr(info, x.X)
case *ast.SelectorExpr:
if x.Sel.Name != "Data" {
// reflect.SliceHeader and reflect.StringHeader are okay,
// but only if they are pointing at a real slice or string.
// It's not okay to do:
// var x SliceHeader
// x.Data = uintptr(unsafe.Pointer(...))
// ... use x ...
// p := unsafe.Pointer(x.Data)
// because in the middle the garbage collector doesn't
// see x.Data as a pointer and so x.Data may be dangling
// by the time we get to the conversion at the end.
// For now approximate by saying that *Header is okay
// but Header is not.
pt, ok := info.Types[x.X].Type.(*types.Pointer)
if ok {
t, ok := pt.Elem().(*types.Named)
if ok && t.Obj().Pkg().Path() == "reflect" {
switch t.Obj().Name() {
case "StringHeader", "SliceHeader":
return true
case *ast.CallExpr:
switch len(x.Args) {
case 0:
// maybe call to reflect.Value.Pointer or reflect.Value.UnsafeAddr.
sel, ok := x.Fun.(*ast.SelectorExpr)
if !ok {
switch sel.Sel.Name {
case "Pointer", "UnsafeAddr":
t, ok := info.Types[sel.X].Type.(*types.Named)
if ok && t.Obj().Pkg().Path() == "reflect" && t.Obj().Name() == "Value" {
return true
case 1:
// maybe conversion of uintptr to unsafe.Pointer
return hasBasicType(info, x.Fun, types.Uintptr) &&
hasBasicType(info, x.Args[0], types.UnsafePointer)
case *ast.BinaryExpr:
switch x.Op {
case token.ADD, token.SUB, token.AND_NOT:
return isSafeUintptr(info, x.X) && !isSafeUintptr(info, x.Y)
return false
// hasBasicType reports whether x's type is a types.Basic with the given kind.
func hasBasicType(info *types.Info, x ast.Expr, kind types.BasicKind) bool {
t := info.Types[x].Type
if t != nil {
t = t.Underlying()
b, ok := t.(*types.Basic)
return ok && b.Kind() == kind