// 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"
	"os/exec"
	"strconv"
	"strings"
	"unicode"
	"unicode/utf8"

	"cmd/internal/quoted"
)

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) {
	p.CgoFlags[flag] = append(p.CgoFlags[flag], args...)
	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)
			}
		}
	}
}

// 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 {
			if f.Name[info.typedef] != nil {
				continue
			}
			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" || goos == "ios") && 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 not 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")

	// We need to parse the output from this gcc command, so ensure that it
	// doesn't have any ANSI escape sequences in it. (TERM=dumb is
	// insufficient; if the user specifies CGO_CFLAGS=-fdiagnostics-color,
	// GCC will ignore TERM, and GCC can also be configured at compile-time
	// to ignore TERM.)
	stderr := p.gccErrors(b.Bytes(), "-fdiagnostics-color=never")
	if strings.Contains(stderr, "unrecognized command line option") {
		// We're using an old version of GCC that doesn't understand
		// -fdiagnostics-color. Those versions can't print color anyway,
		// so just rerun without that option.
		stderr = p.gccErrors(b.Bytes())
	}
	if stderr == "" {
		fatalf("%s produced no output\non input:\n%s", 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", 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", 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)
		if n.Kind == "type" && typedef[n.Mangle] == nil {
			typedef[n.Mangle] = n.Type
		}
	}
}

// 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], true)
		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, false)
	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.
// If addPosition is true, add position info to the idents of C names in arg.
func (p *Package) mangle(f *File, arg *ast.Expr, addPosition bool) (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, addPosition)
					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, false)

		if *godefs {
			// Substitute definition for mangled type name.
			if r.Name.Type != nil && r.Name.Kind == "type" {
				expr = r.Name.Type.Go
			}
			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.
// If addPosition is true, add position info in the ident name.
func (p *Package) rewriteName(f *File, r *Ref, addPosition bool) ast.Expr {
	getNewIdent := ast.NewIdent
	if addPosition {
		getNewIdent = func(newName string) *ast.Ident {
			mangledIdent := ast.NewIdent(newName)
			if len(newName) == len(r.Name.Go) {
				return mangledIdent
			}
			p := fset.Position((*r.Expr).End())
			if p.Column == 0 {
				return mangledIdent
			}
			return ast.NewIdent(fmt.Sprintf("%s /*line :%d:%d*/", newName, p.Line, p.Column))
		}
	}
	var expr ast.Expr = getNewIdent(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
			}
			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 = getNewIdent(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{getNewIdent(name.Mangle)},
			}
		case "type":
			// Okay - might be new(T), T(x), Generic[T], etc.
			if r.Name.Type == nil {
				error_(r.Pos(), "expression C.%s: undefined C type '%s'", fixGo(r.Name.Go), r.Name.C)
			}
		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)
		}
	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)
}

// checkGCCBaseCmd 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.
//
// The compiler command line is split into arguments on whitespace. Quotes
// are understood, so arguments may contain whitespace.
//
// checkGCCBaseCmd confirms that the compiler exists in PATH, returning
// an error if it does not.
func checkGCCBaseCmd() ([]string, error) {
	// Use $CC if set, since that's what the build uses.
	value := os.Getenv("CC")
	if value == "" {
		// Try $GCC if set, since that's what we used to use.
		value = os.Getenv("GCC")
	}
	if value == "" {
		value = defaultCC(goos, goarch)
	}
	args, err := quoted.Split(value)
	if err != nil {
		return nil, err
	}
	if len(args) == 0 {
		return nil, errors.New("CC not set and no default found")
	}
	if _, err := exec.LookPath(args[0]); err != nil {
		return nil, fmt.Errorf("C compiler %q not found: %v", args[0], err)
	}
	return args[:len(args):len(args)], nil
}

// gccMachine returns the gcc -m flag to use, either "-m32", "-m64" or "-marm".
func (p *Package) gccMachine() []string {
	switch goarch {
	case "amd64":
		if goos == "darwin" {
			return []string{"-arch", "x86_64", "-m64"}
		}
		return []string{"-m64"}
	case "arm64":
		if goos == "darwin" {
			return []string{"-arch", "arm64"}
		}
	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":
		if gomips64 == "hardfloat" {
			return []string{"-mabi=64", "-mhard-float"}
		} else if gomips64 == "softfloat" {
			return []string{"-mabi=64", "-msoft-float"}
		}
	case "mips", "mipsle":
		if gomips == "hardfloat" {
			return []string{"-mabi=32", "-mfp32", "-mhard-float", "-mno-odd-spreg"}
		} else if gomips == "softfloat" {
			return []string{"-mabi=32", "-msoft-float"}
		}
	}
	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(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")
	}
	// disable LTO so we get an object whose symbols we can read
	c = append(c, "-fno-lto")
	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(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, extraArgs ...string) string {
	// TODO(rsc): require failure
	args := p.gccCmd()

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

	// Force -O0 optimization and append extra arguments, but keep the
	// trailing "-" at the end.
	li := len(nargs) - 1
	last := nargs[li]
	nargs[li] = "-O0"
	nargs = append(nargs, extraArgs...)
	nargs = append(nargs, last)

	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

	// badStructs contains C structs that should be marked NotInHeap.
	notInHeapStructs 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
	goVoidPtrNoHeap                        ast.Expr // *_Ctype_void_notinheap, like goVoidPtr but marked NotInHeap

	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)

// anonymousStructTag provides a consistent tag for an anonymous struct.
// The same dwarf.StructType pointer will always get the same tag.
var anonymousStructTag = make(map[*dwarf.StructType]string)

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.notInHeapStructs = 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")
	c.goVoidPtrNoHeap = c.Ident("*_Ctype_void_notinheap")

	// 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.Type(dt.Type, pos)
		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.Type(dt.Type, pos)
		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 = anonymousStructTag[dt]
			if tag == "" {
				tag = "__" + strconv.Itoa(tagGen)
				tagGen++
				anonymousStructTag[dt] = tag
			}
		} 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{}")
			if dt.Kind == "struct" {
				// We don't know what the representation of this struct is, so don't let
				// anyone allocate one on the Go side. As a side effect of this annotation,
				// pointers to this type will not be considered pointers in Go. They won't
				// get writebarrier-ed or adjusted during a stack copy. This should handle
				// all the cases badPointerTypedef used to handle, but hopefully will
				// continue to work going forward without any more need for cgo changes.
				tt.NotInHeap = true
				// TODO: we should probably do the same for unions. Unions can't live
				// on the Go heap, right? It currently doesn't work for unions because
				// they are defined as a type alias for struct{}, not a defined type.
			}
			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
			tt.NotInHeap = c.notInHeapStructs[tag]
			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
		akey := ""
		if c.anonymousStructTypedef(dt) {
			// only load type recursively for typedefs of anonymous
			// structs, see issues 37479 and 37621.
			akey = key
		}
		sub := c.loadType(dt.Type, pos, akey)
		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
			}
		}
		if c.badVoidPointerTypedef(dt) {
			// Treat this typedef as a pointer to a NotInHeap void.
			s := *sub
			s.Go = c.goVoidPtrNoHeap
			sub = &s
			// Make sure we update any previously computed type.
			if oldType := typedef[name.Name]; oldType != nil {
				oldType.Go = sub.Go
			}
		}
		// Check for non-pointer "struct <tag>{...}; typedef struct <tag> *<name>"
		// typedefs that should be marked NotInHeap.
		if ptr, ok := dt.Type.(*dwarf.PtrType); ok {
			if strct, ok := ptr.Type.(*dwarf.StructType); ok {
				if c.badStructPointerTypedef(dt.Name, strct) {
					c.notInHeapStructs[strct.StructName] = true
					// Make sure we update any previously computed type.
					name := "_Ctype_struct_" + strct.StructName
					if oldType := typedef[name]; oldType != nil {
						oldType.NotInHeap = true
					}
				}
			}
		}
		t.Go = name
		t.BadPointer = sub.BadPointer
		t.NotInHeap = sub.NotInHeap
		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
			tt.NotInHeap = sub.NotInHeap
			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.BitOffset > 0 || f.BitSize > 0 {
			// The layout of bitfields is implementation defined,
			// so we don't know how they correspond to Go fields
			// even if they are aligned at byte boundaries.
			continue
		}

		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)

	// Issue 48396: check for duplicate field names.
	if prefix != "" {
		names := make(map[string]bool)
	fldLoop:
		for _, f := range fld {
			for _, n := range f.Names {
				name := n.Name
				if name == "_" {
					continue
				}
				if name != prefix {
					name = strings.TrimPrefix(n.Name, prefix)
				}
				name = upper(name)
				if names[name] {
					// Field name conflict: don't remove prefix.
					prefix = ""
					break fldLoop
				}
				names[name] = true
			}
		}
	}

	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
}

// anonymousStructTypedef reports whether dt is a C typedef for an anonymous
// struct.
func (c *typeConv) anonymousStructTypedef(dt *dwarf.TypedefType) bool {
	st, ok := dt.Type.(*dwarf.StructType)
	return ok && st.StructName == ""
}

// badPointerTypedef reports whether dt 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.
// Note: DEPRECATED. There is now a better solution. Search for NotInHeap in this file.
func (c *typeConv) badPointerTypedef(dt *dwarf.TypedefType) bool {
	if c.badCFType(dt) {
		return true
	}
	if c.badJNI(dt) {
		return true
	}
	if c.badEGLType(dt) {
		return true
	}
	return false
}

// badVoidPointerTypedef is like badPointerTypeDef, but for "void *" typedefs that should be NotInHeap.
func (c *typeConv) badVoidPointerTypedef(dt *dwarf.TypedefType) bool {
	// Match the Windows HANDLE type (#42018).
	if goos != "windows" || dt.Name != "HANDLE" {
		return false
	}
	// Check that the typedef is "typedef void *<name>".
	if ptr, ok := dt.Type.(*dwarf.PtrType); ok {
		if _, ok := ptr.Type.(*dwarf.VoidType); ok {
			return true
		}
	}
	return false
}

// badStructPointerTypedef is like badVoidPointerTypedefs but for structs.
func (c *typeConv) badStructPointerTypedef(name string, dt *dwarf.StructType) bool {
	// Windows handle types can all potentially contain non-pointers.
	// badVoidPointerTypedef handles the "void *" HANDLE type, but other
	// handles are defined as
	//
	// struct <name>__{int unused;}; typedef struct <name>__ *name;
	//
	// by the DECLARE_HANDLE macro in STRICT mode. The macro is declared in
	// the Windows ntdef.h header,
	//
	// https://github.com/tpn/winsdk-10/blob/master/Include/10.0.16299.0/shared/ntdef.h#L779
	if goos != "windows" {
		return false
	}
	if len(dt.Field) != 1 {
		return false
	}
	if dt.StructName != name+"__" {
		return false
	}
	if f := dt.Field[0]; f.Name != "unused" || f.Type.Common().Name != "int" {
		return false
	}
	return true
}

// 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" && goos != "ios" {
		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) badEGLType(dt *dwarf.TypedefType) bool {
	if dt.Name != "EGLDisplay" && dt.Name != "EGLConfig" {
		return false
	}
	// Check that the typedef is "typedef void *<name>".
	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",
}