libgo: update to Go1.14beta1

[thirdparty/gcc.git] / libgo / go / cmd / cgo / gcc.go

// Copyright 2009 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.

// Annotate Ref in Prog with C types by parsing gcc debug output.
// Conversion of debug output to Go types.

package main

import (
        "bytes"
        "debug/dwarf"
        "debug/elf"
        "debug/macho"
        "debug/pe"
        "encoding/binary"
        "errors"
        "flag"
        "fmt"
        "go/ast"
        "go/parser"
        "go/token"
        "internal/xcoff"
        "math"
        "os"
        "strconv"
        "strings"
        "unicode"
        "unicode/utf8"
)

var debugDefine = flag.Bool("debug-define", false, "print relevant #defines")
var debugGcc = flag.Bool("debug-gcc", false, "print gcc invocations")

var nameToC = map[string]string{
        "schar":         "signed char",
        "uchar":         "unsigned char",
        "ushort":        "unsigned short",
        "uint":          "unsigned int",
        "ulong":         "unsigned long",
        "longlong":      "long long",
        "ulonglong":     "unsigned long long",
        "complexfloat":  "float _Complex",
        "complexdouble": "double _Complex",
}

// cname returns the C name to use for C.s.
// The expansions are listed in nameToC and also
// struct_foo becomes "struct foo", and similarly for
// union and enum.
func cname(s string) string {
        if t, ok := nameToC[s]; ok {
                return t
        }

        if strings.HasPrefix(s, "struct_") {
                return "struct " + s[len("struct_"):]
        }
        if strings.HasPrefix(s, "union_") {
                return "union " + s[len("union_"):]
        }
        if strings.HasPrefix(s, "enum_") {
                return "enum " + s[len("enum_"):]
        }
        if strings.HasPrefix(s, "sizeof_") {
                return "sizeof(" + cname(s[len("sizeof_"):]) + ")"
        }
        return s
}

// DiscardCgoDirectives processes the import C preamble, and discards
// all #cgo CFLAGS and LDFLAGS directives, so they don't make their
// way into _cgo_export.h.
func (f *File) DiscardCgoDirectives() {
        linesIn := strings.Split(f.Preamble, "\n")
        linesOut := make([]string, 0, len(linesIn))
        for _, line := range linesIn {
                l := strings.TrimSpace(line)
                if len(l) < 5 || l[:4] != "#cgo" || !unicode.IsSpace(rune(l[4])) {
                        linesOut = append(linesOut, line)
                } else {
                        linesOut = append(linesOut, "")
                }
        }
        f.Preamble = strings.Join(linesOut, "\n")
}

// addToFlag appends args to flag. All flags are later written out onto the
// _cgo_flags file for the build system to use.
func (p *Package) addToFlag(flag string, args []string) {
        if flag == "CFLAGS" {
                // We'll also need these when preprocessing for dwarf information.
                // However, discard any -g options: we need to be able
                // to parse the debug info, so stick to what we expect.
                for _, arg := range args {
                        if !strings.HasPrefix(arg, "-g") {
                                p.GccOptions = append(p.GccOptions, arg)
                        }
                }
        }

        skip := false
        for i, arg := range args {
                // The go tool will pass us a -I option pointing to objdir;
                // we don't need to record that for later, as the objdir
                // will disappear anyhow.
                if skip {
                        // Discard argument in "-I objdir" case.
                        skip = false
                } else if strings.HasPrefix(arg, "-I") && strings.HasPrefix(arg[2:], *objDir) {
                        // This is -Iobjdir. Don't save this argument.
                } else if arg == "-I" && i+1 < len(args) && strings.HasPrefix(args[i+1], *objDir) {
                        // This is -I objdir. Don't save this argument
                        // or the next one.
                        skip = true
                } else {
                        p.CgoFlags[flag] = append(p.CgoFlags[flag], arg)
                }
        }
}

// splitQuoted splits the string s around each instance of one or more consecutive
// white space characters while taking into account quotes and escaping, and
// returns an array of substrings of s or an empty list if s contains only white space.
// Single quotes and double quotes are recognized to prevent splitting within the
// quoted region, and are removed from the resulting substrings. If a quote in s
// isn't closed err will be set and r will have the unclosed argument as the
// last element. The backslash is used for escaping.
//
// For example, the following string:
//
//     `a b:"c d" 'e''f'  "g\""`
//
// Would be parsed as:
//
//     []string{"a", "b:c d", "ef", `g"`}
//
func splitQuoted(s string) (r []string, err error) {
        var args []string
        arg := make([]rune, len(s))
        escaped := false
        quoted := false
        quote := '\x00'
        i := 0
        for _, r := range s {
                switch {
                case escaped:
                        escaped = false
                case r == '\\':
                        escaped = true
                        continue
                case quote != 0:
                        if r == quote {
                                quote = 0
                                continue
                        }
                case r == '"' || r == '\'':
                        quoted = true
                        quote = r
                        continue
                case unicode.IsSpace(r):
                        if quoted || i > 0 {
                                quoted = false
                                args = append(args, string(arg[:i]))
                                i = 0
                        }
                        continue
                }
                arg[i] = r
                i++
        }
        if quoted || i > 0 {
                args = append(args, string(arg[:i]))
        }
        if quote != 0 {
                err = errors.New("unclosed quote")
        } else if escaped {
                err = errors.New("unfinished escaping")
        }
        return args, err
}

// Translate rewrites f.AST, the original Go input, to remove
// references to the imported package C, replacing them with
// references to the equivalent Go types, functions, and variables.
func (p *Package) Translate(f *File) {
        for _, cref := range f.Ref {
                // Convert C.ulong to C.unsigned long, etc.
                cref.Name.C = cname(cref.Name.Go)
        }

        var conv typeConv
        conv.Init(p.PtrSize, p.IntSize)

        p.loadDefines(f)
        p.typedefs = map[string]bool{}
        p.typedefList = nil
        numTypedefs := -1
        for len(p.typedefs) > numTypedefs {
                numTypedefs = len(p.typedefs)
                // Also ask about any typedefs we've seen so far.
                for _, info := range p.typedefList {
                        n := &Name{
                                Go: info.typedef,
                                C:  info.typedef,
                        }
                        f.Name[info.typedef] = n
                        f.NamePos[n] = info.pos
                }
                needType := p.guessKinds(f)
                if len(needType) > 0 {
                        p.loadDWARF(f, &conv, needType)
                }

                // In godefs mode we're OK with the typedefs, which
                // will presumably also be defined in the file, we
                // don't want to resolve them to their base types.
                if *godefs {
                        break
                }
        }
        p.prepareNames(f)
        if p.rewriteCalls(f) {
                // Add `import _cgo_unsafe "unsafe"` after the package statement.
                f.Edit.Insert(f.offset(f.AST.Name.End()), "; import _cgo_unsafe \"unsafe\"")
        }
        p.rewriteRef(f)
}

// loadDefines coerces gcc into spitting out the #defines in use
// in the file f and saves relevant renamings in f.Name[name].Define.
func (p *Package) loadDefines(f *File) {
        var b bytes.Buffer
        b.WriteString(builtinProlog)
        b.WriteString(f.Preamble)
        stdout := p.gccDefines(b.Bytes())

        for _, line := range strings.Split(stdout, "\n") {
                if len(line) < 9 || line[0:7] != "#define" {
                        continue
                }

                line = strings.TrimSpace(line[8:])

                var key, val string
                spaceIndex := strings.Index(line, " ")
                tabIndex := strings.Index(line, "\t")

                if spaceIndex == -1 && tabIndex == -1 {
                        continue
                } else if tabIndex == -1 || (spaceIndex != -1 && spaceIndex < tabIndex) {
                        key = line[0:spaceIndex]
                        val = strings.TrimSpace(line[spaceIndex:])
                } else {
                        key = line[0:tabIndex]
                        val = strings.TrimSpace(line[tabIndex:])
                }

                if key == "__clang__" {
                        p.GccIsClang = true
                }

                if n := f.Name[key]; n != nil {
                        if *debugDefine {
                                fmt.Fprintf(os.Stderr, "#define %s %s\n", key, val)
                        }
                        n.Define = val
                }
        }
}

// guessKinds tricks gcc into revealing the kind of each
// name xxx for the references C.xxx in the Go input.
// The kind is either a constant, type, or variable.
func (p *Package) guessKinds(f *File) []*Name {
        // Determine kinds for names we already know about,
        // like #defines or 'struct foo', before bothering with gcc.
        var names, needType []*Name
        optional := map[*Name]bool{}
        for _, key := range nameKeys(f.Name) {
                n := f.Name[key]
                // If we've already found this name as a #define
                // and we can translate it as a constant value, do so.
                if n.Define != "" {
                        if i, err := strconv.ParseInt(n.Define, 0, 64); err == nil {
                                n.Kind = "iconst"
                                // Turn decimal into hex, just for consistency
                                // with enum-derived constants. Otherwise
                                // in the cgo -godefs output half the constants
                                // are in hex and half are in whatever the #define used.
                                n.Const = fmt.Sprintf("%#x", i)
                        } else if n.Define[0] == '\'' {
                                if _, err := parser.ParseExpr(n.Define); err == nil {
                                        n.Kind = "iconst"
                                        n.Const = n.Define
                                }
                        } else if n.Define[0] == '"' {
                                if _, err := parser.ParseExpr(n.Define); err == nil {
                                        n.Kind = "sconst"
                                        n.Const = n.Define
                                }
                        }

                        if n.IsConst() {
                                continue
                        }
                }

                // If this is a struct, union, or enum type name, no need to guess the kind.
                if strings.HasPrefix(n.C, "struct ") || strings.HasPrefix(n.C, "union ") || strings.HasPrefix(n.C, "enum ") {
                        n.Kind = "type"
                        needType = append(needType, n)
                        continue
                }

                if goos == "darwin" && strings.HasSuffix(n.C, "Ref") {
                        // For FooRef, find out if FooGetTypeID exists.
                        s := n.C[:len(n.C)-3] + "GetTypeID"
                        n := &Name{Go: s, C: s}
                        names = append(names, n)
                        optional[n] = true
                }

                // Otherwise, we'll need to find out from gcc.
                names = append(names, n)
        }

        // Bypass gcc if there's nothing left to find out.
        if len(names) == 0 {
                return needType
        }

        // Coerce gcc into telling us whether each name is a type, a value, or undeclared.
        // For names, find out whether they are integer constants.
        // We used to look at specific warning or error messages here, but that tied the
        // behavior too closely to specific versions of the compilers.
        // Instead, arrange that we can infer what we need from only the presence or absence
        // of an error on a specific line.
        //
        // For each name, we generate these lines, where xxx is the index in toSniff plus one.
        //
        //      #line xxx "not-declared"
        //      void __cgo_f_xxx_1(void) { __typeof__(name) *__cgo_undefined__1; }
        //      #line xxx "not-type"
        //      void __cgo_f_xxx_2(void) { name *__cgo_undefined__2; }
        //      #line xxx "not-int-const"
        //      void __cgo_f_xxx_3(void) { enum { __cgo_undefined__3 = (name)*1 }; }
        //      #line xxx "not-num-const"
        //      void __cgo_f_xxx_4(void) { static const double __cgo_undefined__4 = (name); }
        //      #line xxx "not-str-lit"
        //      void __cgo_f_xxx_5(void) { static const char __cgo_undefined__5[] = (name); }
        //
        // If we see an error at not-declared:xxx, the corresponding name is not declared.
        // If we see an error at not-type:xxx, the corresponding name is a type.
        // If we see an error at not-int-const:xxx, the corresponding name is not an integer constant.
        // If we see an error at not-num-const:xxx, the corresponding name is not a number constant.
        // If we see an error at not-str-lit:xxx, the corresponding name is not a string literal.
        //
        // The specific input forms are chosen so that they are valid C syntax regardless of
        // whether name denotes a type or an expression.

        var b bytes.Buffer
        b.WriteString(builtinProlog)
        b.WriteString(f.Preamble)

        for i, n := range names {
                fmt.Fprintf(&b, "#line %d \"not-declared\"\n"+
                        "void __cgo_f_%d_1(void) { __typeof__(%s) *__cgo_undefined__1; }\n"+
                        "#line %d \"not-type\"\n"+
                        "void __cgo_f_%d_2(void) { %s *__cgo_undefined__2; }\n"+
                        "#line %d \"not-int-const\"\n"+
                        "void __cgo_f_%d_3(void) { enum { __cgo_undefined__3 = (%s)*1 }; }\n"+
                        "#line %d \"not-num-const\"\n"+
                        "void __cgo_f_%d_4(void) { static const double __cgo_undefined__4 = (%s); }\n"+
                        "#line %d \"not-str-lit\"\n"+
                        "void __cgo_f_%d_5(void) { static const char __cgo_undefined__5[] = (%s); }\n",
                        i+1, i+1, n.C,
                        i+1, i+1, n.C,
                        i+1, i+1, n.C,
                        i+1, i+1, n.C,
                        i+1, i+1, n.C,
                )
        }
        fmt.Fprintf(&b, "#line 1 \"completed\"\n"+
                "int __cgo__1 = __cgo__2;\n")

        stderr := p.gccErrors(b.Bytes())
        if stderr == "" {
                fatalf("%s produced no output\non input:\n%s", p.gccBaseCmd()[0], b.Bytes())
        }

        completed := false
        sniff := make([]int, len(names))
        const (
                notType = 1 << iota
                notIntConst
                notNumConst
                notStrLiteral
                notDeclared
        )
        sawUnmatchedErrors := false
        for _, line := range strings.Split(stderr, "\n") {
                // Ignore warnings and random comments, with one
                // exception: newer GCC versions will sometimes emit
                // an error on a macro #define with a note referring
                // to where the expansion occurs. We care about where
                // the expansion occurs, so in that case treat the note
                // as an error.
                isError := strings.Contains(line, ": error:")
                isErrorNote := strings.Contains(line, ": note:") && sawUnmatchedErrors
                if !isError && !isErrorNote {
                        continue
                }

                c1 := strings.Index(line, ":")
                if c1 < 0 {
                        continue
                }
                c2 := strings.Index(line[c1+1:], ":")
                if c2 < 0 {
                        continue
                }
                c2 += c1 + 1

                filename := line[:c1]
                i, _ := strconv.Atoi(line[c1+1 : c2])
                i--
                if i < 0 || i >= len(names) {
                        if isError {
                                sawUnmatchedErrors = true
                        }
                        continue
                }

                switch filename {
                case "completed":
                        // Strictly speaking, there is no guarantee that seeing the error at completed:1
                        // (at the end of the file) means we've seen all the errors from earlier in the file,
                        // but usually it does. Certainly if we don't see the completed:1 error, we did
                        // not get all the errors we expected.
                        completed = true

                case "not-declared":
                        sniff[i] |= notDeclared
                case "not-type":
                        sniff[i] |= notType
                case "not-int-const":
                        sniff[i] |= notIntConst
                case "not-num-const":
                        sniff[i] |= notNumConst
                case "not-str-lit":
                        sniff[i] |= notStrLiteral
                default:
                        if isError {
                                sawUnmatchedErrors = true
                        }
                        continue
                }

                sawUnmatchedErrors = false
        }

        if !completed {
                fatalf("%s did not produce error at completed:1\non input:\n%s\nfull error output:\n%s", p.gccBaseCmd()[0], b.Bytes(), stderr)
        }

        for i, n := range names {
                switch sniff[i] {
                default:
                        if sniff[i]&notDeclared != 0 && optional[n] {
                                // Ignore optional undeclared identifiers.
                                // Don't report an error, and skip adding n to the needType array.
                                continue
                        }
                        error_(f.NamePos[n], "could not determine kind of name for C.%s", fixGo(n.Go))
                case notStrLiteral | notType:
                        n.Kind = "iconst"
                case notIntConst | notStrLiteral | notType:
                        n.Kind = "fconst"
                case notIntConst | notNumConst | notType:
                        n.Kind = "sconst"
                case notIntConst | notNumConst | notStrLiteral:
                        n.Kind = "type"
                case notIntConst | notNumConst | notStrLiteral | notType:
                        n.Kind = "not-type"
                }
                needType = append(needType, n)
        }
        if nerrors > 0 {
                // Check if compiling the preamble by itself causes any errors,
                // because the messages we've printed out so far aren't helpful
                // to users debugging preamble mistakes. See issue 8442.
                preambleErrors := p.gccErrors([]byte(f.Preamble))
                if len(preambleErrors) > 0 {
                        error_(token.NoPos, "\n%s errors for preamble:\n%s", p.gccBaseCmd()[0], preambleErrors)
                }

                fatalf("unresolved names")
        }

        return needType
}

// loadDWARF parses the DWARF debug information generated
// by gcc to learn the details of the constants, variables, and types
// being referred to as C.xxx.
func (p *Package) loadDWARF(f *File, conv *typeConv, names []*Name) {
        // Extract the types from the DWARF section of an object
        // from a well-formed C program. Gcc only generates DWARF info
        // for symbols in the object file, so it is not enough to print the
        // preamble and hope the symbols we care about will be there.
        // Instead, emit
        //      __typeof__(names[i]) *__cgo__i;
        // for each entry in names and then dereference the type we
        // learn for __cgo__i.
        var b bytes.Buffer
        b.WriteString(builtinProlog)
        b.WriteString(f.Preamble)
        b.WriteString("#line 1 \"cgo-dwarf-inference\"\n")
        for i, n := range names {
                fmt.Fprintf(&b, "__typeof__(%s) *__cgo__%d;\n", n.C, i)
                if n.Kind == "iconst" {
                        fmt.Fprintf(&b, "enum { __cgo_enum__%d = %s };\n", i, n.C)
                }
        }

        // We create a data block initialized with the values,
        // so we can read them out of the object file.
        fmt.Fprintf(&b, "long long __cgodebug_ints[] = {\n")
        for _, n := range names {
                if n.Kind == "iconst" {
                        fmt.Fprintf(&b, "\t%s,\n", n.C)
                } else {
                        fmt.Fprintf(&b, "\t0,\n")
                }
        }
        // for the last entry, we cannot use 0, otherwise
        // in case all __cgodebug_data is zero initialized,
        // LLVM-based gcc will place the it in the __DATA.__common
        // zero-filled section (our debug/macho doesn't support
        // this)
        fmt.Fprintf(&b, "\t1\n")
        fmt.Fprintf(&b, "};\n")

        // do the same work for floats.
        fmt.Fprintf(&b, "double __cgodebug_floats[] = {\n")
        for _, n := range names {
                if n.Kind == "fconst" {
                        fmt.Fprintf(&b, "\t%s,\n", n.C)
                } else {
                        fmt.Fprintf(&b, "\t0,\n")
                }
        }
        fmt.Fprintf(&b, "\t1\n")
        fmt.Fprintf(&b, "};\n")

        // do the same work for strings.
        for i, n := range names {
                if n.Kind == "sconst" {
                        fmt.Fprintf(&b, "const char __cgodebug_str__%d[] = %s;\n", i, n.C)
                        fmt.Fprintf(&b, "const unsigned long long __cgodebug_strlen__%d = sizeof(%s)-1;\n", i, n.C)
                }
        }

        d, ints, floats, strs := p.gccDebug(b.Bytes(), len(names))

        // Scan DWARF info for top-level TagVariable entries with AttrName __cgo__i.
        types := make([]dwarf.Type, len(names))
        r := d.Reader()
        for {
                e, err := r.Next()
                if err != nil {
                        fatalf("reading DWARF entry: %s", err)
                }
                if e == nil {
                        break
                }
                switch e.Tag {
                case dwarf.TagVariable:
                        name, _ := e.Val(dwarf.AttrName).(string)
                        typOff, _ := e.Val(dwarf.AttrType).(dwarf.Offset)
                        if name == "" || typOff == 0 {
                                if e.Val(dwarf.AttrSpecification) != nil {
                                        // Since we are reading all the DWARF,
                                        // assume we will see the variable elsewhere.
                                        break
                                }
                                fatalf("malformed DWARF TagVariable entry")
                        }
                        if !strings.HasPrefix(name, "__cgo__") {
                                break
                        }
                        typ, err := d.Type(typOff)
                        if err != nil {
                                fatalf("loading DWARF type: %s", err)
                        }
                        t, ok := typ.(*dwarf.PtrType)
                        if !ok || t == nil {
                                fatalf("internal error: %s has non-pointer type", name)
                        }
                        i, err := strconv.Atoi(name[7:])
                        if err != nil {
                                fatalf("malformed __cgo__ name: %s", name)
                        }
                        types[i] = t.Type
                        p.recordTypedefs(t.Type, f.NamePos[names[i]])
                }
                if e.Tag != dwarf.TagCompileUnit {
                        r.SkipChildren()
                }
        }

        // Record types and typedef information.
        for i, n := range names {
                if strings.HasSuffix(n.Go, "GetTypeID") && types[i].String() == "func() CFTypeID" {
                        conv.getTypeIDs[n.Go[:len(n.Go)-9]] = true
                }
        }
        for i, n := range names {
                if types[i] == nil {
                        continue
                }
                pos := f.NamePos[n]
                f, fok := types[i].(*dwarf.FuncType)
                if n.Kind != "type" && fok {
                        n.Kind = "func"
                        n.FuncType = conv.FuncType(f, pos)
                } else {
                        n.Type = conv.Type(types[i], pos)
                        switch n.Kind {
                        case "iconst":
                                if i < len(ints) {
                                        if _, ok := types[i].(*dwarf.UintType); ok {
                                                n.Const = fmt.Sprintf("%#x", uint64(ints[i]))
                                        } else {
                                                n.Const = fmt.Sprintf("%#x", ints[i])
                                        }
                                }
                        case "fconst":
                                if i >= len(floats) {
                                        break
                                }
                                switch base(types[i]).(type) {
                                case *dwarf.IntType, *dwarf.UintType:
                                        // This has an integer type so it's
                                        // not really a floating point
                                        // constant. This can happen when the
                                        // C compiler complains about using
                                        // the value as an integer constant,
                                        // but not as a general constant.
                                        // Treat this as a variable of the
                                        // appropriate type, not a constant,
                                        // to get C-style type handling,
                                        // avoiding the problem that C permits
                                        // uint64(-1) but Go does not.
                                        // See issue 26066.
                                        n.Kind = "var"
                                default:
                                        n.Const = fmt.Sprintf("%f", floats[i])
                                }
                        case "sconst":
                                if i < len(strs) {
                                        n.Const = fmt.Sprintf("%q", strs[i])
                                }
                        }
                }
                conv.FinishType(pos)
        }
}

// recordTypedefs remembers in p.typedefs all the typedefs used in dtypes and its children.
func (p *Package) recordTypedefs(dtype dwarf.Type, pos token.Pos) {
        p.recordTypedefs1(dtype, pos, map[dwarf.Type]bool{})
}

func (p *Package) recordTypedefs1(dtype dwarf.Type, pos token.Pos, visited map[dwarf.Type]bool) {
        if dtype == nil {
                return
        }
        if visited[dtype] {
                return
        }
        visited[dtype] = true
        switch dt := dtype.(type) {
        case *dwarf.TypedefType:
                if strings.HasPrefix(dt.Name, "__builtin") {
                        // Don't look inside builtin types. There be dragons.
                        return
                }
                if !p.typedefs[dt.Name] {
                        p.typedefs[dt.Name] = true
                        p.typedefList = append(p.typedefList, typedefInfo{dt.Name, pos})
                        p.recordTypedefs1(dt.Type, pos, visited)
                }
        case *dwarf.PtrType:
                p.recordTypedefs1(dt.Type, pos, visited)
        case *dwarf.ArrayType:
                p.recordTypedefs1(dt.Type, pos, visited)
        case *dwarf.QualType:
                p.recordTypedefs1(dt.Type, pos, visited)
        case *dwarf.FuncType:
                p.recordTypedefs1(dt.ReturnType, pos, visited)
                for _, a := range dt.ParamType {
                        p.recordTypedefs1(a, pos, visited)
                }
        case *dwarf.StructType:
                for _, f := range dt.Field {
                        p.recordTypedefs1(f.Type, pos, visited)
                }
        }
}

// prepareNames finalizes the Kind field of not-type names and sets
// the mangled name of all names.
func (p *Package) prepareNames(f *File) {
        for _, n := range f.Name {
                if n.Kind == "not-type" {
                        if n.Define == "" {
                                n.Kind = "var"
                        } else {
                                n.Kind = "macro"
                                n.FuncType = &FuncType{
                                        Result: n.Type,
                                        Go: &ast.FuncType{
                                                Results: &ast.FieldList{List: []*ast.Field{{Type: n.Type.Go}}},
                                        },
                                }
                        }
                }
                p.mangleName(n)
        }
}

// mangleName does name mangling to translate names
// from the original Go source files to the names
// used in the final Go files generated by cgo.
func (p *Package) mangleName(n *Name) {
        // When using gccgo variables have to be
        // exported so that they become global symbols
        // that the C code can refer to.
        prefix := "_C"
        if *gccgo && n.IsVar() {
                prefix = "C"
        }
        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.
func (p *Package) rewriteCalls(f *File) bool {
        needsUnsafe := false
        // Walk backward so that in C.f1(C.f2()) we rewrite C.f2 first.
        for _, call := range f.Calls {
                if call.Done {
                        continue
                }
                start := f.offset(call.Call.Pos())
                end := f.offset(call.Call.End())
                str, nu := p.rewriteCall(f, call)
                if str != "" {
                        f.Edit.Replace(start, end, str)
                        if nu {
                                needsUnsafe = true
                        }
                }
        }
        return needsUnsafe
}

// rewriteCall rewrites one call to add pointer checks.
// If any pointer checks are required, we rewrite the call into a
// function literal that calls _cgoCheckPointer for each pointer
// argument and then calls the original function.
// This returns the rewritten call and whether the package needs to
// import unsafe as _cgo_unsafe.
// If it returns the empty string, the call did not need to be rewritten.
func (p *Package) rewriteCall(f *File, call *Call) (string, bool) {
        // This is a call to C.xxx; set goname to "xxx".
        // It may have already been mangled by rewriteName.
        var goname string
        switch fun := call.Call.Fun.(type) {
        case *ast.SelectorExpr:
                goname = fun.Sel.Name
        case *ast.Ident:
                goname = strings.TrimPrefix(fun.Name, "_C2func_")
                goname = strings.TrimPrefix(goname, "_Cfunc_")
        }
        if goname == "" || goname == "malloc" {
                return "", false
        }
        name := f.Name[goname]
        if name == nil || name.Kind != "func" {
                // Probably a type conversion.
                return "", false
        }

        params := name.FuncType.Params
        args := call.Call.Args

        // Avoid a crash if the number of arguments doesn't match
        // the number of parameters.
        // This will be caught when the generated file is compiled.
        if len(args) != len(params) {
                return "", false
        }

        any := false
        for i, param := range params {
                if p.needsPointerCheck(f, param.Go, args[i]) {
                        any = true
                        break
                }
        }
        if !any {
                return "", false
        }

        // We need to rewrite this call.
        //
        // Rewrite C.f(p) to
        //    func() {
        //            _cgo0 := p
        //            _cgoCheckPointer(_cgo0, nil)
        //            C.f(_cgo0)
        //    }()
        // Using a function literal like this lets us evaluate the
        // function arguments only once while doing pointer checks.
        // This is particularly useful when passing additional arguments
        // to _cgoCheckPointer, as done in checkIndex and checkAddr.
        //
        // When the function argument is a conversion to unsafe.Pointer,
        // we unwrap the conversion before checking the pointer,
        // and then wrap again when calling C.f. This lets us check
        // the real type of the pointer in some cases. See issue #25941.
        //
        // When the call to C.f is deferred, we use an additional function
        // literal to evaluate the arguments at the right time.
        //    defer func() func() {
        //            _cgo0 := p
        //            return func() {
        //                    _cgoCheckPointer(_cgo0, nil)
        //                    C.f(_cgo0)
        //            }
        //    }()()
        // This works because the defer statement evaluates the first
        // function literal in order to get the function to call.

        var sb bytes.Buffer
        sb.WriteString("func() ")
        if call.Deferred {
                sb.WriteString("func() ")
        }

        needsUnsafe := false
        result := false
        twoResults := false
        if !call.Deferred {
                // Check whether this call expects two results.
                for _, ref := range f.Ref {
                        if ref.Expr != &call.Call.Fun {
                                continue
                        }
                        if ref.Context == ctxCall2 {
                                sb.WriteString("(")
                                result = true
                                twoResults = true
                        }
                        break
                }

                // Add the result type, if any.
                if name.FuncType.Result != nil {
                        rtype := p.rewriteUnsafe(name.FuncType.Result.Go)
                        if rtype != name.FuncType.Result.Go {
                                needsUnsafe = true
                        }
                        sb.WriteString(gofmtLine(rtype))
                        result = true
                }

                // Add the second result type, if any.
                if twoResults {
                        if name.FuncType.Result == nil {
                                // An explicit void result looks odd but it
                                // seems to be how cgo has worked historically.
                                sb.WriteString("_Ctype_void")
                        }
                        sb.WriteString(", error)")
                }
        }

        sb.WriteString("{ ")

        // Define _cgoN for each argument value.
        // Write _cgoCheckPointer calls to sbCheck.
        var sbCheck bytes.Buffer
        for i, param := range params {
                origArg := args[i]
                arg, nu := p.mangle(f, &args[i])
                if nu {
                        needsUnsafe = true
                }

                // Use "var x T = ..." syntax to explicitly convert untyped
                // constants to the parameter type, to avoid a type mismatch.
                ptype := p.rewriteUnsafe(param.Go)

                if !p.needsPointerCheck(f, param.Go, args[i]) || param.BadPointer {
                        if ptype != param.Go {
                                needsUnsafe = true
                        }
                        fmt.Fprintf(&sb, "var _cgo%d %s = %s; ", i,
                                gofmtLine(ptype), gofmtPos(arg, origArg.Pos()))
                        continue
                }

                // Check for &a[i].
                if p.checkIndex(&sb, &sbCheck, arg, i) {
                        continue
                }

                // Check for &x.
                if p.checkAddr(&sb, &sbCheck, arg, i) {
                        continue
                }

                fmt.Fprintf(&sb, "_cgo%d := %s; ", i, gofmtPos(arg, origArg.Pos()))
                fmt.Fprintf(&sbCheck, "_cgoCheckPointer(_cgo%d, nil); ", i)
        }

        if call.Deferred {
                sb.WriteString("return func() { ")
        }

        // Write out the calls to _cgoCheckPointer.
        sb.WriteString(sbCheck.String())

        if result {
                sb.WriteString("return ")
        }

        m, nu := p.mangle(f, &call.Call.Fun)
        if nu {
                needsUnsafe = true
        }
        sb.WriteString(gofmtLine(m))

        sb.WriteString("(")
        for i := range params {
                if i > 0 {
                        sb.WriteString(", ")
                }
                fmt.Fprintf(&sb, "_cgo%d", i)
        }
        sb.WriteString("); ")
        if call.Deferred {
                sb.WriteString("}")
        }
        sb.WriteString("}")
        if call.Deferred {
                sb.WriteString("()")
        }
        sb.WriteString("()")

        return sb.String(), needsUnsafe
}

// needsPointerCheck reports whether the type t needs a pointer check.
// This is true if t is a pointer and if the value to which it points
// might contain a pointer.
func (p *Package) needsPointerCheck(f *File, t ast.Expr, arg ast.Expr) bool {
        // An untyped nil does not need a pointer check, and when
        // _cgoCheckPointer returns the untyped nil the type assertion we
        // are going to insert will fail.  Easier to just skip nil arguments.
        // TODO: Note that this fails if nil is shadowed.
        if id, ok := arg.(*ast.Ident); ok && id.Name == "nil" {
                return false
        }

        return p.hasPointer(f, t, true)
}

// hasPointer is used by needsPointerCheck. If top is true it returns
// whether t is or contains a pointer that might point to a pointer.
// If top is false it reports whether t is or contains a pointer.
// f may be nil.
func (p *Package) hasPointer(f *File, t ast.Expr, top bool) bool {
        switch t := t.(type) {
        case *ast.ArrayType:
                if t.Len == nil {
                        if !top {
                                return true
                        }
                        return p.hasPointer(f, t.Elt, false)
                }
                return p.hasPointer(f, t.Elt, top)
        case *ast.StructType:
                for _, field := range t.Fields.List {
                        if p.hasPointer(f, field.Type, top) {
                                return true
                        }
                }
                return false
        case *ast.StarExpr: // Pointer type.
                if !top {
                        return true
                }
                // Check whether this is a pointer to a C union (or class)
                // type that contains a pointer.
                if unionWithPointer[t.X] {
                        return true
                }
                return p.hasPointer(f, t.X, false)
        case *ast.FuncType, *ast.InterfaceType, *ast.MapType, *ast.ChanType:
                return true
        case *ast.Ident:
                // TODO: Handle types defined within function.
                for _, d := range p.Decl {
                        gd, ok := d.(*ast.GenDecl)
                        if !ok || gd.Tok != token.TYPE {
                                continue
                        }
                        for _, spec := range gd.Specs {
                                ts, ok := spec.(*ast.TypeSpec)
                                if !ok {
                                        continue
                                }
                                if ts.Name.Name == t.Name {
                                        return p.hasPointer(f, ts.Type, top)
                                }
                        }
                }
                if def := typedef[t.Name]; def != nil {
                        return p.hasPointer(f, def.Go, top)
                }
                if t.Name == "string" {
                        return !top
                }
                if t.Name == "error" {
                        return true
                }
                if goTypes[t.Name] != nil {
                        return false
                }
                // We can't figure out the type. Conservative
                // approach is to assume it has a pointer.
                return true
        case *ast.SelectorExpr:
                if l, ok := t.X.(*ast.Ident); !ok || l.Name != "C" {
                        // Type defined in a different package.
                        // Conservative approach is to assume it has a
                        // pointer.
                        return true
                }
                if f == nil {
                        // Conservative approach: assume pointer.
                        return true
                }
                name := f.Name[t.Sel.Name]
                if name != nil && name.Kind == "type" && name.Type != nil && name.Type.Go != nil {
                        return p.hasPointer(f, name.Type.Go, top)
                }
                // We can't figure out the type. Conservative
                // approach is to assume it has a pointer.
                return true
        default:
                error_(t.Pos(), "could not understand type %s", gofmt(t))
                return true
        }
}

// mangle replaces references to C names in arg with the mangled names,
// rewriting calls when it finds them.
// It removes the corresponding references in f.Ref and f.Calls, so that we
// don't try to do the replacement again in rewriteRef or rewriteCall.
func (p *Package) mangle(f *File, arg *ast.Expr) (ast.Expr, bool) {
        needsUnsafe := false
        f.walk(arg, ctxExpr, func(f *File, arg interface{}, context astContext) {
                px, ok := arg.(*ast.Expr)
                if !ok {
                        return
                }
                sel, ok := (*px).(*ast.SelectorExpr)
                if ok {
                        if l, ok := sel.X.(*ast.Ident); !ok || l.Name != "C" {
                                return
                        }

                        for _, r := range f.Ref {
                                if r.Expr == px {
                                        *px = p.rewriteName(f, r)
                                        r.Done = true
                                        break
                                }
                        }

                        return
                }

                call, ok := (*px).(*ast.CallExpr)
                if !ok {
                        return
                }

                for _, c := range f.Calls {
                        if !c.Done && c.Call.Lparen == call.Lparen {
                                cstr, nu := p.rewriteCall(f, c)
                                if cstr != "" {
                                        // Smuggle the rewritten call through an ident.
                                        *px = ast.NewIdent(cstr)
                                        if nu {
                                                needsUnsafe = true
                                        }
                                        c.Done = true
                                }
                        }
                }
        })
        return *arg, needsUnsafe
}

// checkIndex checks whether arg has the form &a[i], possibly inside
// type conversions. If so, then in the general case it writes
//    _cgoIndexNN := a
//    _cgoNN := &cgoIndexNN[i] // with type conversions, if any
// to sb, and writes
//    _cgoCheckPointer(_cgoNN, _cgoIndexNN)
// to sbCheck, and returns true. If a is a simple variable or field reference,
// it writes
//    _cgoIndexNN := &a
// and dereferences the uses of _cgoIndexNN. Taking the address avoids
// making a copy of an array.
//
// This tells _cgoCheckPointer to check the complete contents of the
// slice or array being indexed, but no other part of the memory allocation.
func (p *Package) checkIndex(sb, sbCheck *bytes.Buffer, arg ast.Expr, i int) bool {
        // Strip type conversions.
        x := arg
        for {
                c, ok := x.(*ast.CallExpr)
                if !ok || len(c.Args) != 1 || !p.isType(c.Fun) {
                        break
                }
                x = c.Args[0]
        }
        u, ok := x.(*ast.UnaryExpr)
        if !ok || u.Op != token.AND {
                return false
        }
        index, ok := u.X.(*ast.IndexExpr)
        if !ok {
                return false
        }

        addr := ""
        deref := ""
        if p.isVariable(index.X) {
                addr = "&"
                deref = "*"
        }

        fmt.Fprintf(sb, "_cgoIndex%d := %s%s; ", i, addr, gofmtPos(index.X, index.X.Pos()))
        origX := index.X
        index.X = ast.NewIdent(fmt.Sprintf("_cgoIndex%d", i))
        if deref == "*" {
                index.X = &ast.StarExpr{X: index.X}
        }
        fmt.Fprintf(sb, "_cgo%d := %s; ", i, gofmtPos(arg, arg.Pos()))
        index.X = origX

        fmt.Fprintf(sbCheck, "_cgoCheckPointer(_cgo%d, %s_cgoIndex%d); ", i, deref, i)

        return true
}

// checkAddr checks whether arg has the form &x, possibly inside type
// conversions. If so, it writes
//    _cgoBaseNN := &x
//    _cgoNN := _cgoBaseNN // with type conversions, if any
// to sb, and writes
//    _cgoCheckPointer(_cgoBaseNN, true)
// to sbCheck, and returns true. This tells _cgoCheckPointer to check
// just the contents of the pointer being passed, not any other part
// of the memory allocation. This is run after checkIndex, which looks
// for the special case of &a[i], which requires different checks.
func (p *Package) checkAddr(sb, sbCheck *bytes.Buffer, arg ast.Expr, i int) bool {
        // Strip type conversions.
        px := &arg
        for {
                c, ok := (*px).(*ast.CallExpr)
                if !ok || len(c.Args) != 1 || !p.isType(c.Fun) {
                        break
                }
                px = &c.Args[0]
        }
        if u, ok := (*px).(*ast.UnaryExpr); !ok || u.Op != token.AND {
                return false
        }

        fmt.Fprintf(sb, "_cgoBase%d := %s; ", i, gofmtPos(*px, (*px).Pos()))

        origX := *px
        *px = ast.NewIdent(fmt.Sprintf("_cgoBase%d", i))
        fmt.Fprintf(sb, "_cgo%d := %s; ", i, gofmtPos(arg, arg.Pos()))
        *px = origX

        // Use "0 == 0" to do the right thing in the unlikely event
        // that "true" is shadowed.
        fmt.Fprintf(sbCheck, "_cgoCheckPointer(_cgoBase%d, 0 == 0); ", i)

        return true
}

// isType reports whether the expression is definitely a type.
// This is conservative--it returns false for an unknown identifier.
func (p *Package) isType(t ast.Expr) bool {
        switch t := t.(type) {
        case *ast.SelectorExpr:
                id, ok := t.X.(*ast.Ident)
                if !ok {
                        return false
                }
                if id.Name == "unsafe" && t.Sel.Name == "Pointer" {
                        return true
                }
                if id.Name == "C" && typedef["_Ctype_"+t.Sel.Name] != nil {
                        return true
                }
                return false
        case *ast.Ident:
                // TODO: This ignores shadowing.
                switch t.Name {
                case "unsafe.Pointer", "bool", "byte",
                        "complex64", "complex128",
                        "error",
                        "float32", "float64",
                        "int", "int8", "int16", "int32", "int64",
                        "rune", "string",
                        "uint", "uint8", "uint16", "uint32", "uint64", "uintptr":

                        return true
                }
                if strings.HasPrefix(t.Name, "_Ctype_") {
                        return true
                }
        case *ast.ParenExpr:
                return p.isType(t.X)
        case *ast.StarExpr:
                return p.isType(t.X)
        case *ast.ArrayType, *ast.StructType, *ast.FuncType, *ast.InterfaceType,
                *ast.MapType, *ast.ChanType:

                return true
        }
        return false
}

// isVariable reports whether x is a variable, possibly with field references.
func (p *Package) isVariable(x ast.Expr) bool {
        switch x := x.(type) {
        case *ast.Ident:
                return true
        case *ast.SelectorExpr:
                return p.isVariable(x.X)
        case *ast.IndexExpr:
                return true
        }
        return false
}

// rewriteUnsafe returns a version of t with references to unsafe.Pointer
// rewritten to use _cgo_unsafe.Pointer instead.
func (p *Package) rewriteUnsafe(t ast.Expr) ast.Expr {
        switch t := t.(type) {
        case *ast.Ident:
                // We don't see a SelectorExpr for unsafe.Pointer;
                // this is created by code in this file.
                if t.Name == "unsafe.Pointer" {
                        return ast.NewIdent("_cgo_unsafe.Pointer")
                }
        case *ast.ArrayType:
                t1 := p.rewriteUnsafe(t.Elt)
                if t1 != t.Elt {
                        r := *t
                        r.Elt = t1
                        return &r
                }
        case *ast.StructType:
                changed := false
                fields := *t.Fields
                fields.List = nil
                for _, f := range t.Fields.List {
                        ft := p.rewriteUnsafe(f.Type)
                        if ft == f.Type {
                                fields.List = append(fields.List, f)
                        } else {
                                fn := *f
                                fn.Type = ft
                                fields.List = append(fields.List, &fn)
                                changed = true
                        }
                }
                if changed {
                        r := *t
                        r.Fields = &fields
                        return &r
                }
        case *ast.StarExpr: // Pointer type.
                x1 := p.rewriteUnsafe(t.X)
                if x1 != t.X {
                        r := *t
                        r.X = x1
                        return &r
                }
        }
        return t
}

// rewriteRef rewrites all the C.xxx references in f.AST to refer to the
// Go equivalents, now that we have figured out the meaning of all
// the xxx. In *godefs mode, rewriteRef replaces the names
// with full definitions instead of mangled names.
func (p *Package) rewriteRef(f *File) {
        // Keep a list of all the functions, to remove the ones
        // only used as expressions and avoid generating bridge
        // code for them.
        functions := make(map[string]bool)

        for _, n := range f.Name {
                if n.Kind == "func" {
                        functions[n.Go] = false
                }
        }

        // Now that we have all the name types filled in,
        // scan through the Refs to identify the ones that
        // are trying to do a ,err call. Also check that
        // functions are only used in calls.
        for _, r := range f.Ref {
                if r.Name.IsConst() && r.Name.Const == "" {
                        error_(r.Pos(), "unable to find value of constant C.%s", fixGo(r.Name.Go))
                }

                if r.Name.Kind == "func" {
                        switch r.Context {
                        case ctxCall, ctxCall2:
                                functions[r.Name.Go] = true
                        }
                }

                expr := p.rewriteName(f, r)

                if *godefs {
                        // Substitute definition for mangled type name.
                        if id, ok := expr.(*ast.Ident); ok {
                                if t := typedef[id.Name]; t != nil {
                                        expr = t.Go
                                }
                                if id.Name == r.Name.Mangle && r.Name.Const != "" {
                                        expr = ast.NewIdent(r.Name.Const)
                                }
                        }
                }

                // Copy position information from old expr into new expr,
                // in case expression being replaced is first on line.
                // See golang.org/issue/6563.
                pos := (*r.Expr).Pos()
                if x, ok := expr.(*ast.Ident); ok {
                        expr = &ast.Ident{NamePos: pos, Name: x.Name}
                }

                // Change AST, because some later processing depends on it,
                // and also because -godefs mode still prints the AST.
                old := *r.Expr
                *r.Expr = expr

                // Record source-level edit for cgo output.
                if !r.Done {
                        // Prepend a space in case the earlier code ends
                        // with '/', which would give us a "//" comment.
                        repl := " " + gofmtPos(expr, old.Pos())
                        end := fset.Position(old.End())
                        // Subtract 1 from the column if we are going to
                        // append a close parenthesis. That will set the
                        // correct column for the following characters.
                        sub := 0
                        if r.Name.Kind != "type" {
                                sub = 1
                        }
                        if end.Column > sub {
                                repl = fmt.Sprintf("%s /*line :%d:%d*/", repl, end.Line, end.Column-sub)
                        }
                        if r.Name.Kind != "type" {
                                repl = "(" + repl + ")"
                        }
                        f.Edit.Replace(f.offset(old.Pos()), f.offset(old.End()), repl)
                }
        }

        // Remove functions only used as expressions, so their respective
        // bridge functions are not generated.
        for name, used := range functions {
                if !used {
                        delete(f.Name, name)
                }
        }
}

// rewriteName returns the expression used to rewrite a reference.
func (p *Package) rewriteName(f *File, r *Ref) ast.Expr {
        var expr ast.Expr = ast.NewIdent(r.Name.Mangle) // default
        switch r.Context {
        case ctxCall, ctxCall2:
                if r.Name.Kind != "func" {
                        if r.Name.Kind == "type" {
                                r.Context = ctxType
                                if r.Name.Type == nil {
                                        error_(r.Pos(), "invalid conversion to C.%s: undefined C type '%s'", fixGo(r.Name.Go), r.Name.C)
                                        break
                                }
                                expr = r.Name.Type.Go
                                break
                        }
                        error_(r.Pos(), "call of non-function C.%s", fixGo(r.Name.Go))
                        break
                }
                if r.Context == ctxCall2 {
                        if r.Name.Go == "_CMalloc" {
                                error_(r.Pos(), "no two-result form for C.malloc")
                                break
                        }
                        // Invent new Name for the two-result function.
                        n := f.Name["2"+r.Name.Go]
                        if n == nil {
                                n = new(Name)
                                *n = *r.Name
                                n.AddError = true
                                n.Mangle = "_C2func_" + n.Go
                                f.Name["2"+r.Name.Go] = n
                        }
                        expr = ast.NewIdent(n.Mangle)
                        r.Name = n
                        break
                }
        case ctxExpr:
                switch r.Name.Kind {
                case "func":
                        if builtinDefs[r.Name.C] != "" {
                                error_(r.Pos(), "use of builtin '%s' not in function call", fixGo(r.Name.C))
                        }

                        // Function is being used in an expression, to e.g. pass around a C function pointer.
                        // Create a new Name for this Ref which causes the variable to be declared in Go land.
                        fpName := "fp_" + r.Name.Go
                        name := f.Name[fpName]
                        if name == nil {
                                name = &Name{
                                        Go:   fpName,
                                        C:    r.Name.C,
                                        Kind: "fpvar",
                                        Type: &Type{Size: p.PtrSize, Align: p.PtrSize, C: c("void*"), Go: ast.NewIdent("unsafe.Pointer")},
                                }
                                p.mangleName(name)
                                f.Name[fpName] = name
                        }
                        r.Name = name
                        // Rewrite into call to _Cgo_ptr to prevent assignments. The _Cgo_ptr
                        // function is defined in out.go and simply returns its argument. See
                        // issue 7757.
                        expr = &ast.CallExpr{
                                Fun:  &ast.Ident{NamePos: (*r.Expr).Pos(), Name: "_Cgo_ptr"},
                                Args: []ast.Expr{ast.NewIdent(name.Mangle)},
                        }
                case "type":
                        // Okay - might be new(T)
                        if r.Name.Type == nil {
                                error_(r.Pos(), "expression C.%s: undefined C type '%s'", fixGo(r.Name.Go), r.Name.C)
                                break
                        }
                        expr = r.Name.Type.Go
                case "var":
                        expr = &ast.StarExpr{Star: (*r.Expr).Pos(), X: expr}
                case "macro":
                        expr = &ast.CallExpr{Fun: expr}
                }
        case ctxSelector:
                if r.Name.Kind == "var" {
                        expr = &ast.StarExpr{Star: (*r.Expr).Pos(), X: expr}
                } else {
                        error_(r.Pos(), "only C variables allowed in selector expression %s", fixGo(r.Name.Go))
                }
        case ctxType:
                if r.Name.Kind != "type" {
                        error_(r.Pos(), "expression C.%s used as type", fixGo(r.Name.Go))
                } else if r.Name.Type == nil {
                        // Use of C.enum_x, C.struct_x or C.union_x without C definition.
                        // GCC won't raise an error when using pointers to such unknown types.
                        error_(r.Pos(), "type C.%s: undefined C type '%s'", fixGo(r.Name.Go), r.Name.C)
                } else {
                        expr = r.Name.Type.Go
                }
        default:
                if r.Name.Kind == "func" {
                        error_(r.Pos(), "must call C.%s", fixGo(r.Name.Go))
                }
        }
        return expr
}

// gofmtPos returns the gofmt-formatted string for an AST node,
// with a comment setting the position before the node.
func gofmtPos(n ast.Expr, pos token.Pos) string {
        s := gofmtLine(n)
        p := fset.Position(pos)
        if p.Column == 0 {
                return s
        }
        return fmt.Sprintf("/*line :%d:%d*/%s", p.Line, p.Column, s)
}

// gccBaseCmd returns the start of the compiler command line.
// It uses $CC if set, or else $GCC, or else the compiler recorded
// during the initial build as defaultCC.
// defaultCC is defined in zdefaultcc.go, written by cmd/dist.
func (p *Package) gccBaseCmd() []string {
        // Use $CC if set, since that's what the build uses.
        if ret := strings.Fields(os.Getenv("CC")); len(ret) > 0 {
                return ret
        }
        // Try $GCC if set, since that's what we used to use.
        if ret := strings.Fields(os.Getenv("GCC")); len(ret) > 0 {
                return ret
        }
        return strings.Fields(defaultCC(goos, goarch))
}

// gccMachine returns the gcc -m flag to use, either "-m32", "-m64" or "-marm".
func (p *Package) gccMachine() []string {
        switch goarch {
        case "amd64":
                return []string{"-m64"}
        case "386":
                return []string{"-m32"}
        case "arm":
                return []string{"-marm"} // not thumb
        case "s390":
                return []string{"-m31"}
        case "s390x":
                return []string{"-m64"}
        case "mips64", "mips64le":
                return []string{"-mabi=64"}
        case "mips", "mipsle":
                return []string{"-mabi=32"}
        case "ppc64":
                if goos == "aix" {
                        return []string{"-maix64"}
                }
        }
        return nil
}

func gccTmp() string {
        return *objDir + "_cgo_.o"
}

// gccCmd returns the gcc command line to use for compiling
// the input.
func (p *Package) gccCmd() []string {
        c := append(p.gccBaseCmd(),
                "-w",          // no warnings
                "-Wno-error",  // warnings are not errors
                "-o"+gccTmp(), // write object to tmp
                "-gdwarf-2",   // generate DWARF v2 debugging symbols
                "-c",          // do not link
                "-xc",         // input language is C
        )
        if p.GccIsClang {
                c = append(c,
                        "-ferror-limit=0",
                        // Apple clang version 1.7 (tags/Apple/clang-77) (based on LLVM 2.9svn)
                        // doesn't have -Wno-unneeded-internal-declaration, so we need yet another
                        // flag to disable the warning. Yes, really good diagnostics, clang.
                        "-Wno-unknown-warning-option",
                        "-Wno-unneeded-internal-declaration",
                        "-Wno-unused-function",
                        "-Qunused-arguments",
                        // Clang embeds prototypes for some builtin functions,
                        // like malloc and calloc, but all size_t parameters are
                        // incorrectly typed unsigned long. We work around that
                        // by disabling the builtin functions (this is safe as
                        // it won't affect the actual compilation of the C code).
                        // See: https://golang.org/issue/6506.
                        "-fno-builtin",
                )
        }

        c = append(c, p.GccOptions...)
        c = append(c, p.gccMachine()...)
        if goos == "aix" {
                c = append(c, "-maix64")
                c = append(c, "-mcmodel=large")
        }
        c = append(c, "-") //read input from standard input
        return c
}

// gccDebug runs gcc -gdwarf-2 over the C program stdin and
// returns the corresponding DWARF data and, if present, debug data block.
func (p *Package) gccDebug(stdin []byte, nnames int) (d *dwarf.Data, ints []int64, floats []float64, strs []string) {
        runGcc(stdin, p.gccCmd())

        isDebugInts := func(s string) bool {
                // Some systems use leading _ to denote non-assembly symbols.
                return s == "__cgodebug_ints" || s == "___cgodebug_ints"
        }
        isDebugFloats := func(s string) bool {
                // Some systems use leading _ to denote non-assembly symbols.
                return s == "__cgodebug_floats" || s == "___cgodebug_floats"
        }
        indexOfDebugStr := func(s string) int {
                // Some systems use leading _ to denote non-assembly symbols.
                if strings.HasPrefix(s, "___") {
                        s = s[1:]
                }
                if strings.HasPrefix(s, "__cgodebug_str__") {
                        if n, err := strconv.Atoi(s[len("__cgodebug_str__"):]); err == nil {
                                return n
                        }
                }
                return -1
        }
        indexOfDebugStrlen := func(s string) int {
                // Some systems use leading _ to denote non-assembly symbols.
                if strings.HasPrefix(s, "___") {
                        s = s[1:]
                }
                if strings.HasPrefix(s, "__cgodebug_strlen__") {
                        if n, err := strconv.Atoi(s[len("__cgodebug_strlen__"):]); err == nil {
                                return n
                        }
                }
                return -1
        }

        strs = make([]string, nnames)

        strdata := make(map[int]string, nnames)
        strlens := make(map[int]int, nnames)

        buildStrings := func() {
                for n, strlen := range strlens {
                        data := strdata[n]
                        if len(data) <= strlen {
                                fatalf("invalid string literal")
                        }
                        strs[n] = data[:strlen]
                }
        }

        if f, err := macho.Open(gccTmp()); err == nil {
                defer f.Close()
                d, err := f.DWARF()
                if err != nil {
                        fatalf("cannot load DWARF output from %s: %v", gccTmp(), err)
                }
                bo := f.ByteOrder
                if f.Symtab != nil {
                        for i := range f.Symtab.Syms {
                                s := &f.Symtab.Syms[i]
                                switch {
                                case isDebugInts(s.Name):
                                        // Found it. Now find data section.
                                        if i := int(s.Sect) - 1; 0 <= i && i < len(f.Sections) {
                                                sect := f.Sections[i]
                                                if sect.Addr <= s.Value && s.Value < sect.Addr+sect.Size {
                                                        if sdat, err := sect.Data(); err == nil {
                                                                data := sdat[s.Value-sect.Addr:]
                                                                ints = make([]int64, len(data)/8)
                                                                for i := range ints {
                                                                        ints[i] = int64(bo.Uint64(data[i*8:]))
                                                                }
                                                        }
                                                }
                                        }
                                case isDebugFloats(s.Name):
                                        // Found it. Now find data section.
                                        if i := int(s.Sect) - 1; 0 <= i && i < len(f.Sections) {
                                                sect := f.Sections[i]
                                                if sect.Addr <= s.Value && s.Value < sect.Addr+sect.Size {
                                                        if sdat, err := sect.Data(); err == nil {
                                                                data := sdat[s.Value-sect.Addr:]
                                                                floats = make([]float64, len(data)/8)
                                                                for i := range floats {
                                                                        floats[i] = math.Float64frombits(bo.Uint64(data[i*8:]))
                                                                }
                                                        }
                                                }
                                        }
                                default:
                                        if n := indexOfDebugStr(s.Name); n != -1 {
                                                // Found it. Now find data section.
                                                if i := int(s.Sect) - 1; 0 <= i && i < len(f.Sections) {
                                                        sect := f.Sections[i]
                                                        if sect.Addr <= s.Value && s.Value < sect.Addr+sect.Size {
                                                                if sdat, err := sect.Data(); err == nil {
                                                                        data := sdat[s.Value-sect.Addr:]
                                                                        strdata[n] = string(data)
                                                                }
                                                        }
                                                }
                                                break
                                        }
                                        if n := indexOfDebugStrlen(s.Name); n != -1 {
                                                // Found it. Now find data section.
                                                if i := int(s.Sect) - 1; 0 <= i && i < len(f.Sections) {
                                                        sect := f.Sections[i]
                                                        if sect.Addr <= s.Value && s.Value < sect.Addr+sect.Size {
                                                                if sdat, err := sect.Data(); err == nil {
                                                                        data := sdat[s.Value-sect.Addr:]
                                                                        strlen := bo.Uint64(data[:8])
                                                                        if strlen > (1<<(uint(p.IntSize*8)-1) - 1) { // greater than MaxInt?
                                                                                fatalf("string literal too big")
                                                                        }
                                                                        strlens[n] = int(strlen)
                                                                }
                                                        }
                                                }
                                                break
                                        }
                                }
                        }

                        buildStrings()
                }
                return d, ints, floats, strs
        }

        if f, err := elf.Open(gccTmp()); err == nil {
                defer f.Close()
                d, err := f.DWARF()
                if err != nil {
                        fatalf("cannot load DWARF output from %s: %v", gccTmp(), err)
                }
                bo := f.ByteOrder
                symtab, err := f.Symbols()
                if err == nil {
                        for i := range symtab {
                                s := &symtab[i]
                                switch {
                                case isDebugInts(s.Name):
                                        // Found it. Now find data section.
                                        if i := int(s.Section); 0 <= i && i < len(f.Sections) {
                                                sect := f.Sections[i]
                                                if sect.Addr <= s.Value && s.Value < sect.Addr+sect.Size {
                                                        if sdat, err := sect.Data(); err == nil {
                                                                data := sdat[s.Value-sect.Addr:]
                                                                ints = make([]int64, len(data)/8)
                                                                for i := range ints {
                                                                        ints[i] = int64(bo.Uint64(data[i*8:]))
                                                                }
                                                        }
                                                }
                                        }
                                case isDebugFloats(s.Name):
                                        // Found it. Now find data section.
                                        if i := int(s.Section); 0 <= i && i < len(f.Sections) {
                                                sect := f.Sections[i]
                                                if sect.Addr <= s.Value && s.Value < sect.Addr+sect.Size {
                                                        if sdat, err := sect.Data(); err == nil {
                                                                data := sdat[s.Value-sect.Addr:]
                                                                floats = make([]float64, len(data)/8)
                                                                for i := range floats {
                                                                        floats[i] = math.Float64frombits(bo.Uint64(data[i*8:]))
                                                                }
                                                        }
                                                }
                                        }
                                default:
                                        if n := indexOfDebugStr(s.Name); n != -1 {
                                                // Found it. Now find data section.
                                                if i := int(s.Section); 0 <= i && i < len(f.Sections) {
                                                        sect := f.Sections[i]
                                                        if sect.Addr <= s.Value && s.Value < sect.Addr+sect.Size {
                                                                if sdat, err := sect.Data(); err == nil {
                                                                        data := sdat[s.Value-sect.Addr:]
                                                                        strdata[n] = string(data)
                                                                }
                                                        }
                                                }
                                                break
                                        }
                                        if n := indexOfDebugStrlen(s.Name); n != -1 {
                                                // Found it. Now find data section.
                                                if i := int(s.Section); 0 <= i && i < len(f.Sections) {
                                                        sect := f.Sections[i]
                                                        if sect.Addr <= s.Value && s.Value < sect.Addr+sect.Size {
                                                                if sdat, err := sect.Data(); err == nil {
                                                                        data := sdat[s.Value-sect.Addr:]
                                                                        strlen := bo.Uint64(data[:8])
                                                                        if strlen > (1<<(uint(p.IntSize*8)-1) - 1) { // greater than MaxInt?
                                                                                fatalf("string literal too big")
                                                                        }
                                                                        strlens[n] = int(strlen)
                                                                }
                                                        }
                                                }
                                                break
                                        }
                                }
                        }

                        buildStrings()
                }
                return d, ints, floats, strs
        }

        if f, err := pe.Open(gccTmp()); err == nil {
                defer f.Close()
                d, err := f.DWARF()
                if err != nil {
                        fatalf("cannot load DWARF output from %s: %v", gccTmp(), err)
                }
                bo := binary.LittleEndian
                for _, s := range f.Symbols {
                        switch {
                        case isDebugInts(s.Name):
                                if i := int(s.SectionNumber) - 1; 0 <= i && i < len(f.Sections) {
                                        sect := f.Sections[i]
                                        if s.Value < sect.Size {
                                                if sdat, err := sect.Data(); err == nil {
                                                        data := sdat[s.Value:]
                                                        ints = make([]int64, len(data)/8)
                                                        for i := range ints {
                                                                ints[i] = int64(bo.Uint64(data[i*8:]))
                                                        }
                                                }
                                        }
                                }
                        case isDebugFloats(s.Name):
                                if i := int(s.SectionNumber) - 1; 0 <= i && i < len(f.Sections) {
                                        sect := f.Sections[i]
                                        if s.Value < sect.Size {
                                                if sdat, err := sect.Data(); err == nil {
                                                        data := sdat[s.Value:]
                                                        floats = make([]float64, len(data)/8)
                                                        for i := range floats {
                                                                floats[i] = math.Float64frombits(bo.Uint64(data[i*8:]))
                                                        }
                                                }
                                        }
                                }
                        default:
                                if n := indexOfDebugStr(s.Name); n != -1 {
                                        if i := int(s.SectionNumber) - 1; 0 <= i && i < len(f.Sections) {
                                                sect := f.Sections[i]
                                                if s.Value < sect.Size {
                                                        if sdat, err := sect.Data(); err == nil {
                                                                data := sdat[s.Value:]
                                                                strdata[n] = string(data)
                                                        }
                                                }
                                        }
                                        break
                                }
                                if n := indexOfDebugStrlen(s.Name); n != -1 {
                                        if i := int(s.SectionNumber) - 1; 0 <= i && i < len(f.Sections) {
                                                sect := f.Sections[i]
                                                if s.Value < sect.Size {
                                                        if sdat, err := sect.Data(); err == nil {
                                                                data := sdat[s.Value:]
                                                                strlen := bo.Uint64(data[:8])
                                                                if strlen > (1<<(uint(p.IntSize*8)-1) - 1) { // greater than MaxInt?
                                                                        fatalf("string literal too big")
                                                                }
                                                                strlens[n] = int(strlen)
                                                        }
                                                }
                                        }
                                        break
                                }
                        }
                }

                buildStrings()

                return d, ints, floats, strs
        }

        if f, err := xcoff.Open(gccTmp()); err == nil {
                defer f.Close()
                d, err := f.DWARF()
                if err != nil {
                        fatalf("cannot load DWARF output from %s: %v", gccTmp(), err)
                }
                bo := binary.BigEndian
                for _, s := range f.Symbols {
                        switch {
                        case isDebugInts(s.Name):
                                if i := int(s.SectionNumber) - 1; 0 <= i && i < len(f.Sections) {
                                        sect := f.Sections[i]
                                        if s.Value < sect.Size {
                                                if sdat, err := sect.Data(); err == nil {
                                                        data := sdat[s.Value:]
                                                        ints = make([]int64, len(data)/8)
                                                        for i := range ints {
                                                                ints[i] = int64(bo.Uint64(data[i*8:]))
                                                        }
                                                }
                                        }
                                }
                        case isDebugFloats(s.Name):
                                if i := int(s.SectionNumber) - 1; 0 <= i && i < len(f.Sections) {
                                        sect := f.Sections[i]
                                        if s.Value < sect.Size {
                                                if sdat, err := sect.Data(); err == nil {
                                                        data := sdat[s.Value:]
                                                        floats = make([]float64, len(data)/8)
                                                        for i := range floats {
                                                                floats[i] = math.Float64frombits(bo.Uint64(data[i*8:]))
                                                        }
                                                }
                                        }
                                }
                        default:
                                if n := indexOfDebugStr(s.Name); n != -1 {
                                        if i := int(s.SectionNumber) - 1; 0 <= i && i < len(f.Sections) {
                                                sect := f.Sections[i]
                                                if s.Value < sect.Size {
                                                        if sdat, err := sect.Data(); err == nil {
                                                                data := sdat[s.Value:]
                                                                strdata[n] = string(data)
                                                        }
                                                }
                                        }
                                        break
                                }
                                if n := indexOfDebugStrlen(s.Name); n != -1 {
                                        if i := int(s.SectionNumber) - 1; 0 <= i && i < len(f.Sections) {
                                                sect := f.Sections[i]
                                                if s.Value < sect.Size {
                                                        if sdat, err := sect.Data(); err == nil {
                                                                data := sdat[s.Value:]
                                                                strlen := bo.Uint64(data[:8])
                                                                if strlen > (1<<(uint(p.IntSize*8)-1) - 1) { // greater than MaxInt?
                                                                        fatalf("string literal too big")
                                                                }
                                                                strlens[n] = int(strlen)
                                                        }
                                                }
                                        }
                                        break
                                }
                        }
                }

                buildStrings()
                return d, ints, floats, strs
        }
        fatalf("cannot parse gcc output %s as ELF, Mach-O, PE, XCOFF object", gccTmp())
        panic("not reached")
}

// gccDefines runs gcc -E -dM -xc - over the C program stdin
// and returns the corresponding standard output, which is the
// #defines that gcc encountered while processing the input
// and its included files.
func (p *Package) gccDefines(stdin []byte) string {
        base := append(p.gccBaseCmd(), "-E", "-dM", "-xc")
        base = append(base, p.gccMachine()...)
        stdout, _ := runGcc(stdin, append(append(base, p.GccOptions...), "-"))
        return stdout
}

// gccErrors runs gcc over the C program stdin and returns
// the errors that gcc prints. That is, this function expects
// gcc to fail.
func (p *Package) gccErrors(stdin []byte) string {
        // TODO(rsc): require failure
        args := p.gccCmd()

        // Optimization options can confuse the error messages; remove them.
        nargs := make([]string, 0, len(args))
        for _, arg := range args {
                if !strings.HasPrefix(arg, "-O") {
                        nargs = append(nargs, arg)
                }
        }

        // Force -O0 optimization but keep the trailing "-" at the end.
        nargs = append(nargs, "-O0")
        nl := len(nargs)
        nargs[nl-2], nargs[nl-1] = nargs[nl-1], nargs[nl-2]

        if *debugGcc {
                fmt.Fprintf(os.Stderr, "$ %s <<EOF\n", strings.Join(nargs, " "))
                os.Stderr.Write(stdin)
                fmt.Fprint(os.Stderr, "EOF\n")
        }
        stdout, stderr, _ := run(stdin, nargs)
        if *debugGcc {
                os.Stderr.Write(stdout)
                os.Stderr.Write(stderr)
        }
        return string(stderr)
}

// runGcc runs the gcc command line args with stdin on standard input.
// If the command exits with a non-zero exit status, runGcc prints
// details about what was run and exits.
// Otherwise runGcc returns the data written to standard output and standard error.
// Note that for some of the uses we expect useful data back
// on standard error, but for those uses gcc must still exit 0.
func runGcc(stdin []byte, args []string) (string, string) {
        if *debugGcc {
                fmt.Fprintf(os.Stderr, "$ %s <<EOF\n", strings.Join(args, " "))
                os.Stderr.Write(stdin)
                fmt.Fprint(os.Stderr, "EOF\n")
        }
        stdout, stderr, ok := run(stdin, args)
        if *debugGcc {
                os.Stderr.Write(stdout)
                os.Stderr.Write(stderr)
        }
        if !ok {
                os.Stderr.Write(stderr)
                os.Exit(2)
        }
        return string(stdout), string(stderr)
}

// A typeConv is a translator from dwarf types to Go types
// with equivalent memory layout.
type typeConv struct {
        // Cache of already-translated or in-progress types.
        m map[string]*Type

        // Map from types to incomplete pointers to those types.
        ptrs map[string][]*Type
        // Keys of ptrs in insertion order (deterministic worklist)
        // ptrKeys contains exactly the keys in ptrs.
        ptrKeys []dwarf.Type

        // Type names X for which there exists an XGetTypeID function with type func() CFTypeID.
        getTypeIDs map[string]bool

        // Predeclared types.
        bool                                   ast.Expr
        byte                                   ast.Expr // denotes padding
        int8, int16, int32, int64              ast.Expr
        uint8, uint16, uint32, uint64, uintptr ast.Expr
        float32, float64                       ast.Expr
        complex64, complex128                  ast.Expr
        void                                   ast.Expr
        string                                 ast.Expr
        goVoid                                 ast.Expr // _Ctype_void, denotes C's void
        goVoidPtr                              ast.Expr // unsafe.Pointer or *byte

        ptrSize int64
        intSize int64
}

var tagGen int
var typedef = make(map[string]*Type)
var goIdent = make(map[string]*ast.Ident)

// unionWithPointer is true for a Go type that represents a C union (or class)
// that may contain a pointer. This is used for cgo pointer checking.
var unionWithPointer = make(map[ast.Expr]bool)

func (c *typeConv) Init(ptrSize, intSize int64) {
        c.ptrSize = ptrSize
        c.intSize = intSize
        c.m = make(map[string]*Type)
        c.ptrs = make(map[string][]*Type)
        c.getTypeIDs = make(map[string]bool)
        c.bool = c.Ident("bool")
        c.byte = c.Ident("byte")
        c.int8 = c.Ident("int8")
        c.int16 = c.Ident("int16")
        c.int32 = c.Ident("int32")
        c.int64 = c.Ident("int64")
        c.uint8 = c.Ident("uint8")
        c.uint16 = c.Ident("uint16")
        c.uint32 = c.Ident("uint32")
        c.uint64 = c.Ident("uint64")
        c.uintptr = c.Ident("uintptr")
        c.float32 = c.Ident("float32")
        c.float64 = c.Ident("float64")
        c.complex64 = c.Ident("complex64")
        c.complex128 = c.Ident("complex128")
        c.void = c.Ident("void")
        c.string = c.Ident("string")
        c.goVoid = c.Ident("_Ctype_void")

        // Normally cgo translates void* to unsafe.Pointer,
        // but for historical reasons -godefs uses *byte instead.
        if *godefs {
                c.goVoidPtr = &ast.StarExpr{X: c.byte}
        } else {
                c.goVoidPtr = c.Ident("unsafe.Pointer")
        }
}

// base strips away qualifiers and typedefs to get the underlying type
func base(dt dwarf.Type) dwarf.Type {
        for {
                if d, ok := dt.(*dwarf.QualType); ok {
                        dt = d.Type
                        continue
                }
                if d, ok := dt.(*dwarf.TypedefType); ok {
                        dt = d.Type
                        continue
                }
                break
        }
        return dt
}

// unqual strips away qualifiers from a DWARF type.
// In general we don't care about top-level qualifiers.
func unqual(dt dwarf.Type) dwarf.Type {
        for {
                if d, ok := dt.(*dwarf.QualType); ok {
                        dt = d.Type
                } else {
                        break
                }
        }
        return dt
}

// Map from dwarf text names to aliases we use in package "C".
var dwarfToName = map[string]string{
        "long int":               "long",
        "long unsigned int":      "ulong",
        "unsigned int":           "uint",
        "short unsigned int":     "ushort",
        "unsigned short":         "ushort", // Used by Clang; issue 13129.
        "short int":              "short",
        "long long int":          "longlong",
        "long long unsigned int": "ulonglong",
        "signed char":            "schar",
        "unsigned char":          "uchar",
}

const signedDelta = 64

// String returns the current type representation. Format arguments
// are assembled within this method so that any changes in mutable
// values are taken into account.
func (tr *TypeRepr) String() string {
        if len(tr.Repr) == 0 {
                return ""
        }
        if len(tr.FormatArgs) == 0 {
                return tr.Repr
        }
        return fmt.Sprintf(tr.Repr, tr.FormatArgs...)
}

// Empty reports whether the result of String would be "".
func (tr *TypeRepr) Empty() bool {
        return len(tr.Repr) == 0
}

// Set modifies the type representation.
// If fargs are provided, repr is used as a format for fmt.Sprintf.
// Otherwise, repr is used unprocessed as the type representation.
func (tr *TypeRepr) Set(repr string, fargs ...interface{}) {
        tr.Repr = repr
        tr.FormatArgs = fargs
}

// FinishType completes any outstanding type mapping work.
// In particular, it resolves incomplete pointer types.
func (c *typeConv) FinishType(pos token.Pos) {
        // Completing one pointer type might produce more to complete.
        // Keep looping until they're all done.
        for len(c.ptrKeys) > 0 {
                dtype := c.ptrKeys[0]
                dtypeKey := dtype.String()
                c.ptrKeys = c.ptrKeys[1:]
                ptrs := c.ptrs[dtypeKey]
                delete(c.ptrs, dtypeKey)

                // Note Type might invalidate c.ptrs[dtypeKey].
                t := c.Type(dtype, pos)
                for _, ptr := range ptrs {
                        ptr.Go.(*ast.StarExpr).X = t.Go
                        ptr.C.Set("%s*", t.C)
                }
        }
}

// Type returns a *Type with the same memory layout as
// dtype when used as the type of a variable or a struct field.
func (c *typeConv) Type(dtype dwarf.Type, pos token.Pos) *Type {
        return c.loadType(dtype, pos, "")
}

// loadType recursively loads the requested dtype and its dependency graph.
func (c *typeConv) loadType(dtype dwarf.Type, pos token.Pos, parent string) *Type {
        // Always recompute bad pointer typedefs, as the set of such
        // typedefs changes as we see more types.
        checkCache := true
        if dtt, ok := dtype.(*dwarf.TypedefType); ok && c.badPointerTypedef(dtt) {
                checkCache = false
        }

        // The cache key should be relative to its parent.
        // See issue https://golang.org/issue/31891
        key := parent + " > " + dtype.String()

        if checkCache {
                if t, ok := c.m[key]; ok {
                        if t.Go == nil {
                                fatalf("%s: type conversion loop at %s", lineno(pos), dtype)
                        }
                        return t
                }
        }

        t := new(Type)
        t.Size = dtype.Size() // note: wrong for array of pointers, corrected below
        t.Align = -1
        t.C = &TypeRepr{Repr: dtype.Common().Name}
        c.m[key] = t

        switch dt := dtype.(type) {
        default:
                fatalf("%s: unexpected type: %s", lineno(pos), dtype)

        case *dwarf.AddrType:
                if t.Size != c.ptrSize {
                        fatalf("%s: unexpected: %d-byte address type - %s", lineno(pos), t.Size, dtype)
                }
                t.Go = c.uintptr
                t.Align = t.Size

        case *dwarf.ArrayType:
                if dt.StrideBitSize > 0 {
                        // Cannot represent bit-sized elements in Go.
                        t.Go = c.Opaque(t.Size)
                        break
                }
                count := dt.Count
                if count == -1 {
                        // Indicates flexible array member, which Go doesn't support.
                        // Translate to zero-length array instead.
                        count = 0
                }
                sub := c.loadType(dt.Type, pos, key)
                t.Align = sub.Align
                t.Go = &ast.ArrayType{
                        Len: c.intExpr(count),
                        Elt: sub.Go,
                }
                // Recalculate t.Size now that we know sub.Size.
                t.Size = count * sub.Size
                t.C.Set("__typeof__(%s[%d])", sub.C, dt.Count)

        case *dwarf.BoolType:
                t.Go = c.bool
                t.Align = 1

        case *dwarf.CharType:
                if t.Size != 1 {
                        fatalf("%s: unexpected: %d-byte char type - %s", lineno(pos), t.Size, dtype)
                }
                t.Go = c.int8
                t.Align = 1

        case *dwarf.EnumType:
                if t.Align = t.Size; t.Align >= c.ptrSize {
                        t.Align = c.ptrSize
                }
                t.C.Set("enum " + dt.EnumName)
                signed := 0
                t.EnumValues = make(map[string]int64)
                for _, ev := range dt.Val {
                        t.EnumValues[ev.Name] = ev.Val
                        if ev.Val < 0 {
                                signed = signedDelta
                        }
                }
                switch t.Size + int64(signed) {
                default:
                        fatalf("%s: unexpected: %d-byte enum type - %s", lineno(pos), t.Size, dtype)
                case 1:
                        t.Go = c.uint8
                case 2:
                        t.Go = c.uint16
                case 4:
                        t.Go = c.uint32
                case 8:
                        t.Go = c.uint64
                case 1 + signedDelta:
                        t.Go = c.int8
                case 2 + signedDelta:
                        t.Go = c.int16
                case 4 + signedDelta:
                        t.Go = c.int32
                case 8 + signedDelta:
                        t.Go = c.int64
                }

        case *dwarf.FloatType:
                switch t.Size {
                default:
                        fatalf("%s: unexpected: %d-byte float type - %s", lineno(pos), t.Size, dtype)
                case 4:
                        t.Go = c.float32
                case 8:
                        t.Go = c.float64
                }
                if t.Align = t.Size; t.Align >= c.ptrSize {
                        t.Align = c.ptrSize
                }

        case *dwarf.ComplexType:
                switch t.Size {
                default:
                        fatalf("%s: unexpected: %d-byte complex type - %s", lineno(pos), t.Size, dtype)
                case 8:
                        t.Go = c.complex64
                case 16:
                        t.Go = c.complex128
                }
                if t.Align = t.Size / 2; t.Align >= c.ptrSize {
                        t.Align = c.ptrSize
                }

        case *dwarf.FuncType:
                // No attempt at translation: would enable calls
                // directly between worlds, but we need to moderate those.
                t.Go = c.uintptr
                t.Align = c.ptrSize

        case *dwarf.IntType:
                if dt.BitSize > 0 {
                        fatalf("%s: unexpected: %d-bit int type - %s", lineno(pos), dt.BitSize, dtype)
                }
                switch t.Size {
                default:
                        fatalf("%s: unexpected: %d-byte int type - %s", lineno(pos), t.Size, dtype)
                case 1:
                        t.Go = c.int8
                case 2:
                        t.Go = c.int16
                case 4:
                        t.Go = c.int32
                case 8:
                        t.Go = c.int64
                case 16:
                        t.Go = &ast.ArrayType{
                                Len: c.intExpr(t.Size),
                                Elt: c.uint8,
                        }
                }
                if t.Align = t.Size; t.Align >= c.ptrSize {
                        t.Align = c.ptrSize
                }

        case *dwarf.PtrType:
                // Clang doesn't emit DW_AT_byte_size for pointer types.
                if t.Size != c.ptrSize && t.Size != -1 {
                        fatalf("%s: unexpected: %d-byte pointer type - %s", lineno(pos), t.Size, dtype)
                }
                t.Size = c.ptrSize
                t.Align = c.ptrSize

                if _, ok := base(dt.Type).(*dwarf.VoidType); ok {
                        t.Go = c.goVoidPtr
                        t.C.Set("void*")
                        dq := dt.Type
                        for {
                                if d, ok := dq.(*dwarf.QualType); ok {
                                        t.C.Set(d.Qual + " " + t.C.String())
                                        dq = d.Type
                                } else {
                                        break
                                }
                        }
                        break
                }

                // Placeholder initialization; completed in FinishType.
                t.Go = &ast.StarExpr{}
                t.C.Set("<incomplete>*")
                key := dt.Type.String()
                if _, ok := c.ptrs[key]; !ok {
                        c.ptrKeys = append(c.ptrKeys, dt.Type)
                }
                c.ptrs[key] = append(c.ptrs[key], t)

        case *dwarf.QualType:
                t1 := c.loadType(dt.Type, pos, key)
                t.Size = t1.Size
                t.Align = t1.Align
                t.Go = t1.Go
                if unionWithPointer[t1.Go] {
                        unionWithPointer[t.Go] = true
                }
                t.EnumValues = nil
                t.Typedef = ""
                t.C.Set("%s "+dt.Qual, t1.C)
                return t

        case *dwarf.StructType:
                // Convert to Go struct, being careful about alignment.
                // Have to give it a name to simulate C "struct foo" references.
                tag := dt.StructName
                if dt.ByteSize < 0 && tag == "" { // opaque unnamed struct - should not be possible
                        break
                }
                if tag == "" {
                        tag = "__" + strconv.Itoa(tagGen)
                        tagGen++
                } else if t.C.Empty() {
                        t.C.Set(dt.Kind + " " + tag)
                }
                name := c.Ident("_Ctype_" + dt.Kind + "_" + tag)
                t.Go = name // publish before recursive calls
                goIdent[name.Name] = name
                if dt.ByteSize < 0 {
                        // Size calculation in c.Struct/c.Opaque will die with size=-1 (unknown),
                        // so execute the basic things that the struct case would do
                        // other than try to determine a Go representation.
                        tt := *t
                        tt.C = &TypeRepr{"%s %s", []interface{}{dt.Kind, tag}}
                        tt.Go = c.Ident("struct{}")
                        typedef[name.Name] = &tt
                        break
                }
                switch dt.Kind {
                case "class", "union":
                        t.Go = c.Opaque(t.Size)
                        if c.dwarfHasPointer(dt, pos) {
                                unionWithPointer[t.Go] = true
                        }
                        if t.C.Empty() {
                                t.C.Set("__typeof__(unsigned char[%d])", t.Size)
                        }
                        t.Align = 1 // TODO: should probably base this on field alignment.
                        typedef[name.Name] = t
                case "struct":
                        g, csyntax, align := c.Struct(dt, pos)
                        if t.C.Empty() {
                                t.C.Set(csyntax)
                        }
                        t.Align = align
                        tt := *t
                        if tag != "" {
                                tt.C = &TypeRepr{"struct %s", []interface{}{tag}}
                        }
                        tt.Go = g
                        typedef[name.Name] = &tt
                }

        case *dwarf.TypedefType:
                // Record typedef for printing.
                if dt.Name == "_GoString_" {
                        // Special C name for Go string type.
                        // Knows string layout used by compilers: pointer plus length,
                        // which rounds up to 2 pointers after alignment.
                        t.Go = c.string
                        t.Size = c.ptrSize * 2
                        t.Align = c.ptrSize
                        break
                }
                if dt.Name == "_GoBytes_" {
                        // Special C name for Go []byte type.
                        // Knows slice layout used by compilers: pointer, length, cap.
                        t.Go = c.Ident("[]byte")
                        t.Size = c.ptrSize + 4 + 4
                        t.Align = c.ptrSize
                        break
                }
                name := c.Ident("_Ctype_" + dt.Name)
                goIdent[name.Name] = name
                sub := c.loadType(dt.Type, pos, key)
                if c.badPointerTypedef(dt) {
                        // Treat this typedef as a uintptr.
                        s := *sub
                        s.Go = c.uintptr
                        s.BadPointer = true
                        sub = &s
                        // Make sure we update any previously computed type.
                        if oldType := typedef[name.Name]; oldType != nil {
                                oldType.Go = sub.Go
                                oldType.BadPointer = true
                        }
                }
                t.Go = name
                t.BadPointer = sub.BadPointer
                if unionWithPointer[sub.Go] {
                        unionWithPointer[t.Go] = true
                }
                t.Size = sub.Size
                t.Align = sub.Align
                oldType := typedef[name.Name]
                if oldType == nil {
                        tt := *t
                        tt.Go = sub.Go
                        tt.BadPointer = sub.BadPointer
                        typedef[name.Name] = &tt
                }

                // If sub.Go.Name is "_Ctype_struct_foo" or "_Ctype_union_foo" or "_Ctype_class_foo",
                // use that as the Go form for this typedef too, so that the typedef will be interchangeable
                // with the base type.
                // In -godefs mode, do this for all typedefs.
                if isStructUnionClass(sub.Go) || *godefs {
                        t.Go = sub.Go

                        if isStructUnionClass(sub.Go) {
                                // Use the typedef name for C code.
                                typedef[sub.Go.(*ast.Ident).Name].C = t.C
                        }

                        // If we've seen this typedef before, and it
                        // was an anonymous struct/union/class before
                        // too, use the old definition.
                        // TODO: it would be safer to only do this if
                        // we verify that the types are the same.
                        if oldType != nil && isStructUnionClass(oldType.Go) {
                                t.Go = oldType.Go
                        }
                }

        case *dwarf.UcharType:
                if t.Size != 1 {
                        fatalf("%s: unexpected: %d-byte uchar type - %s", lineno(pos), t.Size, dtype)
                }
                t.Go = c.uint8
                t.Align = 1

        case *dwarf.UintType:
                if dt.BitSize > 0 {
                        fatalf("%s: unexpected: %d-bit uint type - %s", lineno(pos), dt.BitSize, dtype)
                }
                switch t.Size {
                default:
                        fatalf("%s: unexpected: %d-byte uint type - %s", lineno(pos), t.Size, dtype)
                case 1:
                        t.Go = c.uint8
                case 2:
                        t.Go = c.uint16
                case 4:
                        t.Go = c.uint32
                case 8:
                        t.Go = c.uint64
                case 16:
                        t.Go = &ast.ArrayType{
                                Len: c.intExpr(t.Size),
                                Elt: c.uint8,
                        }
                }
                if t.Align = t.Size; t.Align >= c.ptrSize {
                        t.Align = c.ptrSize
                }

        case *dwarf.VoidType:
                t.Go = c.goVoid
                t.C.Set("void")
                t.Align = 1
        }

        switch dtype.(type) {
        case *dwarf.AddrType, *dwarf.BoolType, *dwarf.CharType, *dwarf.ComplexType, *dwarf.IntType, *dwarf.FloatType, *dwarf.UcharType, *dwarf.UintType:
                s := dtype.Common().Name
                if s != "" {
                        if ss, ok := dwarfToName[s]; ok {
                                s = ss
                        }
                        s = strings.Replace(s, " ", "", -1)
                        name := c.Ident("_Ctype_" + s)
                        tt := *t
                        typedef[name.Name] = &tt
                        if !*godefs {
                                t.Go = name
                        }
                }
        }

        if t.Size < 0 {
                // Unsized types are [0]byte, unless they're typedefs of other types
                // or structs with tags.
                // if so, use the name we've already defined.
                t.Size = 0
                switch dt := dtype.(type) {
                case *dwarf.TypedefType:
                        // ok
                case *dwarf.StructType:
                        if dt.StructName != "" {
                                break
                        }
                        t.Go = c.Opaque(0)
                default:
                        t.Go = c.Opaque(0)
                }
                if t.C.Empty() {
                        t.C.Set("void")
                }
        }

        if t.C.Empty() {
                fatalf("%s: internal error: did not create C name for %s", lineno(pos), dtype)
        }

        return t
}

// isStructUnionClass reports whether the type described by the Go syntax x
// is a struct, union, or class with a tag.
func isStructUnionClass(x ast.Expr) bool {
        id, ok := x.(*ast.Ident)
        if !ok {
                return false
        }
        name := id.Name
        return strings.HasPrefix(name, "_Ctype_struct_") ||
                strings.HasPrefix(name, "_Ctype_union_") ||
                strings.HasPrefix(name, "_Ctype_class_")
}

// FuncArg returns a Go type with the same memory layout as
// dtype when used as the type of a C function argument.
func (c *typeConv) FuncArg(dtype dwarf.Type, pos token.Pos) *Type {
        t := c.Type(unqual(dtype), pos)
        switch dt := dtype.(type) {
        case *dwarf.ArrayType:
                // Arrays are passed implicitly as pointers in C.
                // In Go, we must be explicit.
                tr := &TypeRepr{}
                tr.Set("%s*", t.C)
                return &Type{
                        Size:  c.ptrSize,
                        Align: c.ptrSize,
                        Go:    &ast.StarExpr{X: t.Go},
                        C:     tr,
                }
        case *dwarf.TypedefType:
                // C has much more relaxed rules than Go for
                // implicit type conversions. When the parameter
                // is type T defined as *X, simulate a little of the
                // laxness of C by making the argument *X instead of T.
                if ptr, ok := base(dt.Type).(*dwarf.PtrType); ok {
                        // Unless the typedef happens to point to void* since
                        // Go has special rules around using unsafe.Pointer.
                        if _, void := base(ptr.Type).(*dwarf.VoidType); void {
                                break
                        }
                        // ...or the typedef is one in which we expect bad pointers.
                        // It will be a uintptr instead of *X.
                        if c.baseBadPointerTypedef(dt) {
                                break
                        }

                        t = c.Type(ptr, pos)
                        if t == nil {
                                return nil
                        }

                        // For a struct/union/class, remember the C spelling,
                        // in case it has __attribute__((unavailable)).
                        // See issue 2888.
                        if isStructUnionClass(t.Go) {
                                t.Typedef = dt.Name
                        }
                }
        }
        return t
}

// FuncType returns the Go type analogous to dtype.
// There is no guarantee about matching memory layout.
func (c *typeConv) FuncType(dtype *dwarf.FuncType, pos token.Pos) *FuncType {
        p := make([]*Type, len(dtype.ParamType))
        gp := make([]*ast.Field, len(dtype.ParamType))
        for i, f := range dtype.ParamType {
                // gcc's DWARF generator outputs a single DotDotDotType parameter for
                // function pointers that specify no parameters (e.g. void
                // (*__cgo_0)()).  Treat this special case as void. This case is
                // invalid according to ISO C anyway (i.e. void (*__cgo_1)(...) is not
                // legal).
                if _, ok := f.(*dwarf.DotDotDotType); ok && i == 0 {
                        p, gp = nil, nil
                        break
                }
                p[i] = c.FuncArg(f, pos)
                gp[i] = &ast.Field{Type: p[i].Go}
        }
        var r *Type
        var gr []*ast.Field
        if _, ok := base(dtype.ReturnType).(*dwarf.VoidType); ok {
                gr = []*ast.Field{{Type: c.goVoid}}
        } else if dtype.ReturnType != nil {
                r = c.Type(unqual(dtype.ReturnType), pos)
                gr = []*ast.Field{{Type: r.Go}}
        }
        return &FuncType{
                Params: p,
                Result: r,
                Go: &ast.FuncType{
                        Params:  &ast.FieldList{List: gp},
                        Results: &ast.FieldList{List: gr},
                },
        }
}

// Identifier
func (c *typeConv) Ident(s string) *ast.Ident {
        return ast.NewIdent(s)
}

// Opaque type of n bytes.
func (c *typeConv) Opaque(n int64) ast.Expr {
        return &ast.ArrayType{
                Len: c.intExpr(n),
                Elt: c.byte,
        }
}

// Expr for integer n.
func (c *typeConv) intExpr(n int64) ast.Expr {
        return &ast.BasicLit{
                Kind:  token.INT,
                Value: strconv.FormatInt(n, 10),
        }
}

// Add padding of given size to fld.
func (c *typeConv) pad(fld []*ast.Field, sizes []int64, size int64) ([]*ast.Field, []int64) {
        n := len(fld)
        fld = fld[0 : n+1]
        fld[n] = &ast.Field{Names: []*ast.Ident{c.Ident("_")}, Type: c.Opaque(size)}
        sizes = sizes[0 : n+1]
        sizes[n] = size
        return fld, sizes
}

// Struct conversion: return Go and (gc) C syntax for type.
func (c *typeConv) Struct(dt *dwarf.StructType, pos token.Pos) (expr *ast.StructType, csyntax string, align int64) {
        // Minimum alignment for a struct is 1 byte.
        align = 1

        var buf bytes.Buffer
        buf.WriteString("struct {")
        fld := make([]*ast.Field, 0, 2*len(dt.Field)+1) // enough for padding around every field
        sizes := make([]int64, 0, 2*len(dt.Field)+1)
        off := int64(0)

        // Rename struct fields that happen to be named Go keywords into
        // _{keyword}.  Create a map from C ident -> Go ident. The Go ident will
        // be mangled. Any existing identifier that already has the same name on
        // the C-side will cause the Go-mangled version to be prefixed with _.
        // (e.g. in a struct with fields '_type' and 'type', the latter would be
        // rendered as '__type' in Go).
        ident := make(map[string]string)
        used := make(map[string]bool)
        for _, f := range dt.Field {
                ident[f.Name] = f.Name
                used[f.Name] = true
        }

        if !*godefs {
                for cid, goid := range ident {
                        if token.Lookup(goid).IsKeyword() {
                                // Avoid keyword
                                goid = "_" + goid

                                // Also avoid existing fields
                                for _, exist := used[goid]; exist; _, exist = used[goid] {
                                        goid = "_" + goid
                                }

                                used[goid] = true
                                ident[cid] = goid
                        }
                }
        }

        anon := 0
        for _, f := range dt.Field {
                name := f.Name
                ft := f.Type

                // In godefs mode, if this field is a C11
                // anonymous union then treat the first field in the
                // union as the field in the struct. This handles
                // cases like the glibc <sys/resource.h> file; see
                // issue 6677.
                if *godefs {
                        if st, ok := f.Type.(*dwarf.StructType); ok && name == "" && st.Kind == "union" && len(st.Field) > 0 && !used[st.Field[0].Name] {
                                name = st.Field[0].Name
                                ident[name] = name
                                ft = st.Field[0].Type
                        }
                }

                // TODO: Handle fields that are anonymous structs by
                // promoting the fields of the inner struct.

                t := c.Type(ft, pos)
                tgo := t.Go
                size := t.Size
                talign := t.Align
                if f.BitSize > 0 {
                        switch f.BitSize {
                        case 8, 16, 32, 64:
                        default:
                                continue
                        }
                        size = f.BitSize / 8
                        name := tgo.(*ast.Ident).String()
                        if strings.HasPrefix(name, "int") {
                                name = "int"
                        } else {
                                name = "uint"
                        }
                        tgo = ast.NewIdent(name + fmt.Sprint(f.BitSize))
                        talign = size
                }

                if talign > 0 && f.ByteOffset%talign != 0 {
                        // Drop misaligned fields, the same way we drop integer bit fields.
                        // The goal is to make available what can be made available.
                        // Otherwise one bad and unneeded field in an otherwise okay struct
                        // makes the whole program not compile. Much of the time these
                        // structs are in system headers that cannot be corrected.
                        continue
                }

                // Round off up to talign, assumed to be a power of 2.
                off = (off + talign - 1) &^ (talign - 1)

                if f.ByteOffset > off {
                        fld, sizes = c.pad(fld, sizes, f.ByteOffset-off)
                        off = f.ByteOffset
                }
                if f.ByteOffset < off {
                        // Drop a packed field that we can't represent.
                        continue
                }

                n := len(fld)
                fld = fld[0 : n+1]
                if name == "" {
                        name = fmt.Sprintf("anon%d", anon)
                        anon++
                        ident[name] = name
                }
                fld[n] = &ast.Field{Names: []*ast.Ident{c.Ident(ident[name])}, Type: tgo}
                sizes = sizes[0 : n+1]
                sizes[n] = size
                off += size
                buf.WriteString(t.C.String())
                buf.WriteString(" ")
                buf.WriteString(name)
                buf.WriteString("; ")
                if talign > align {
                        align = talign
                }
        }
        if off < dt.ByteSize {
                fld, sizes = c.pad(fld, sizes, dt.ByteSize-off)
                off = dt.ByteSize
        }

        // If the last field in a non-zero-sized struct is zero-sized
        // the compiler is going to pad it by one (see issue 9401).
        // We can't permit that, because then the size of the Go
        // struct will not be the same as the size of the C struct.
        // Our only option in such a case is to remove the field,
        // which means that it cannot be referenced from Go.
        for off > 0 && sizes[len(sizes)-1] == 0 {
                n := len(sizes)
                fld = fld[0 : n-1]
                sizes = sizes[0 : n-1]
        }

        if off != dt.ByteSize {
                fatalf("%s: struct size calculation error off=%d bytesize=%d", lineno(pos), off, dt.ByteSize)
        }
        buf.WriteString("}")
        csyntax = buf.String()

        if *godefs {
                godefsFields(fld)
        }
        expr = &ast.StructType{Fields: &ast.FieldList{List: fld}}
        return
}

// dwarfHasPointer reports whether the DWARF type dt contains a pointer.
func (c *typeConv) dwarfHasPointer(dt dwarf.Type, pos token.Pos) bool {
        switch dt := dt.(type) {
        default:
                fatalf("%s: unexpected type: %s", lineno(pos), dt)
                return false

        case *dwarf.AddrType, *dwarf.BoolType, *dwarf.CharType, *dwarf.EnumType,
                *dwarf.FloatType, *dwarf.ComplexType, *dwarf.FuncType,
                *dwarf.IntType, *dwarf.UcharType, *dwarf.UintType, *dwarf.VoidType:

                return false

        case *dwarf.ArrayType:
                return c.dwarfHasPointer(dt.Type, pos)

        case *dwarf.PtrType:
                return true

        case *dwarf.QualType:
                return c.dwarfHasPointer(dt.Type, pos)

        case *dwarf.StructType:
                for _, f := range dt.Field {
                        if c.dwarfHasPointer(f.Type, pos) {
                                return true
                        }
                }
                return false

        case *dwarf.TypedefType:
                if dt.Name == "_GoString_" || dt.Name == "_GoBytes_" {
                        return true
                }
                return c.dwarfHasPointer(dt.Type, pos)
        }
}

func upper(s string) string {
        if s == "" {
                return ""
        }
        r, size := utf8.DecodeRuneInString(s)
        if r == '_' {
                return "X" + s
        }
        return string(unicode.ToUpper(r)) + s[size:]
}

// godefsFields rewrites field names for use in Go or C definitions.
// It strips leading common prefixes (like tv_ in tv_sec, tv_usec)
// converts names to upper case, and rewrites _ into Pad_godefs_n,
// so that all fields are exported.
func godefsFields(fld []*ast.Field) {
        prefix := fieldPrefix(fld)
        npad := 0
        for _, f := range fld {
                for _, n := range f.Names {
                        if n.Name != prefix {
                                n.Name = strings.TrimPrefix(n.Name, prefix)
                        }
                        if n.Name == "_" {
                                // Use exported name instead.
                                n.Name = "Pad_cgo_" + strconv.Itoa(npad)
                                npad++
                        }
                        n.Name = upper(n.Name)
                }
        }
}

// fieldPrefix returns the prefix that should be removed from all the
// field names when generating the C or Go code. For generated
// C, we leave the names as is (tv_sec, tv_usec), since that's what
// people are used to seeing in C.  For generated Go code, such as
// package syscall's data structures, we drop a common prefix
// (so sec, usec, which will get turned into Sec, Usec for exporting).
func fieldPrefix(fld []*ast.Field) string {
        prefix := ""
        for _, f := range fld {
                for _, n := range f.Names {
                        // Ignore field names that don't have the prefix we're
                        // looking for. It is common in C headers to have fields
                        // named, say, _pad in an otherwise prefixed header.
                        // If the struct has 3 fields tv_sec, tv_usec, _pad1, then we
                        // still want to remove the tv_ prefix.
                        // The check for "orig_" here handles orig_eax in the
                        // x86 ptrace register sets, which otherwise have all fields
                        // with reg_ prefixes.
                        if strings.HasPrefix(n.Name, "orig_") || strings.HasPrefix(n.Name, "_") {
                                continue
                        }
                        i := strings.Index(n.Name, "_")
                        if i < 0 {
                                continue
                        }
                        if prefix == "" {
                                prefix = n.Name[:i+1]
                        } else if prefix != n.Name[:i+1] {
                                return ""
                        }
                }
        }
        return prefix
}

// badPointerTypedef reports whether t is a C typedef that should not be considered a pointer in Go.
// A typedef is bad if C code sometimes stores non-pointers in this type.
// TODO: Currently our best solution is to find these manually and list them as
// they come up. A better solution is desired.
func (c *typeConv) badPointerTypedef(dt *dwarf.TypedefType) bool {
        if c.badCFType(dt) {
                return true
        }
        if c.badJNI(dt) {
                return true
        }
        if c.badEGLDisplay(dt) {
                return true
        }
        return false
}

// baseBadPointerTypedef reports whether the base of a chain of typedefs is a bad typedef
// as badPointerTypedef reports.
func (c *typeConv) baseBadPointerTypedef(dt *dwarf.TypedefType) bool {
        for {
                if t, ok := dt.Type.(*dwarf.TypedefType); ok {
                        dt = t
                        continue
                }
                break
        }
        return c.badPointerTypedef(dt)
}

func (c *typeConv) badCFType(dt *dwarf.TypedefType) bool {
        // The real bad types are CFNumberRef and CFDateRef.
        // Sometimes non-pointers are stored in these types.
        // CFTypeRef is a supertype of those, so it can have bad pointers in it as well.
        // We return true for the other *Ref types just so casting between them is easier.
        // We identify the correct set of types as those ending in Ref and for which
        // there exists a corresponding GetTypeID function.
        // See comment below for details about the bad pointers.
        if goos != "darwin" {
                return false
        }
        s := dt.Name
        if !strings.HasSuffix(s, "Ref") {
                return false
        }
        s = s[:len(s)-3]
        if s == "CFType" {
                return true
        }
        if c.getTypeIDs[s] {
                return true
        }
        if i := strings.Index(s, "Mutable"); i >= 0 && c.getTypeIDs[s[:i]+s[i+7:]] {
                // Mutable and immutable variants share a type ID.
                return true
        }
        return false
}

// Comment from Darwin's CFInternal.h
/*
// Tagged pointer support
// Low-bit set means tagged object, next 3 bits (currently)
// define the tagged object class, next 4 bits are for type
// information for the specific tagged object class.  Thus,
// the low byte is for type info, and the rest of a pointer
// (32 or 64-bit) is for payload, whatever the tagged class.
//
// Note that the specific integers used to identify the
// specific tagged classes can and will change from release
// to release (that's why this stuff is in CF*Internal*.h),
// as can the definition of type info vs payload above.
//
#if __LP64__
#define CF_IS_TAGGED_OBJ(PTR)   ((uintptr_t)(PTR) & 0x1)
#define CF_TAGGED_OBJ_TYPE(PTR) ((uintptr_t)(PTR) & 0xF)
#else
#define CF_IS_TAGGED_OBJ(PTR)   0
#define CF_TAGGED_OBJ_TYPE(PTR) 0
#endif

enum {
    kCFTaggedObjectID_Invalid = 0,
    kCFTaggedObjectID_Atom = (0 << 1) + 1,
    kCFTaggedObjectID_Undefined3 = (1 << 1) + 1,
    kCFTaggedObjectID_Undefined2 = (2 << 1) + 1,
    kCFTaggedObjectID_Integer = (3 << 1) + 1,
    kCFTaggedObjectID_DateTS = (4 << 1) + 1,
    kCFTaggedObjectID_ManagedObjectID = (5 << 1) + 1, // Core Data
    kCFTaggedObjectID_Date = (6 << 1) + 1,
    kCFTaggedObjectID_Undefined7 = (7 << 1) + 1,
};
*/

func (c *typeConv) badJNI(dt *dwarf.TypedefType) bool {
        // In Dalvik and ART, the jobject type in the JNI interface of the JVM has the
        // property that it is sometimes (always?) a small integer instead of a real pointer.
        // Note: although only the android JVMs are bad in this respect, we declare the JNI types
        // bad regardless of platform, so the same Go code compiles on both android and non-android.
        if parent, ok := jniTypes[dt.Name]; ok {
                // Try to make sure we're talking about a JNI type, not just some random user's
                // type that happens to use the same name.
                // C doesn't have the notion of a package, so it's hard to be certain.

                // Walk up to jobject, checking each typedef on the way.
                w := dt
                for parent != "" {
                        t, ok := w.Type.(*dwarf.TypedefType)
                        if !ok || t.Name != parent {
                                return false
                        }
                        w = t
                        parent, ok = jniTypes[w.Name]
                        if !ok {
                                return false
                        }
                }

                // Check that the typedef is either:
                // 1:
                //      struct _jobject;
                //      typedef struct _jobject *jobject;
                // 2: (in NDK16 in C++)
                //      class _jobject {};
                //      typedef _jobject* jobject;
                // 3: (in NDK16 in C)
                //      typedef void* jobject;
                if ptr, ok := w.Type.(*dwarf.PtrType); ok {
                        switch v := ptr.Type.(type) {
                        case *dwarf.VoidType:
                                return true
                        case *dwarf.StructType:
                                if v.StructName == "_jobject" && len(v.Field) == 0 {
                                        switch v.Kind {
                                        case "struct":
                                                if v.Incomplete {
                                                        return true
                                                }
                                        case "class":
                                                if !v.Incomplete {
                                                        return true
                                                }
                                        }
                                }
                        }
                }
        }
        return false
}

func (c *typeConv) badEGLDisplay(dt *dwarf.TypedefType) bool {
        if dt.Name != "EGLDisplay" {
                return false
        }
        // Check that the typedef is "typedef void *EGLDisplay".
        if ptr, ok := dt.Type.(*dwarf.PtrType); ok {
                if _, ok := ptr.Type.(*dwarf.VoidType); ok {
                        return true
                }
        }
        return false
}

// jniTypes maps from JNI types that we want to be uintptrs, to the underlying type to which
// they are mapped. The base "jobject" maps to the empty string.
var jniTypes = map[string]string{
        "jobject":       "",
        "jclass":        "jobject",
        "jthrowable":    "jobject",
        "jstring":       "jobject",
        "jarray":        "jobject",
        "jbooleanArray": "jarray",
        "jbyteArray":    "jarray",
        "jcharArray":    "jarray",
        "jshortArray":   "jarray",
        "jintArray":     "jarray",
        "jlongArray":    "jarray",
        "jfloatArray":   "jarray",
        "jdoubleArray":  "jarray",
        "jobjectArray":  "jarray",
        "jweak":         "jobject",
}