cmd/go: check for another GCC error message

[official-gcc.git] / libgo / go / cmd / cgo / out.go

// Copyright 2009 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

package main

import (
        "bytes"
        "debug/elf"
        "debug/macho"
        "debug/pe"
        "debug/xcoff"
        "fmt"
        "go/ast"
        "go/printer"
        "go/token"
        "io"
        "os"
        "path/filepath"
        "sort"
        "strings"
)

var (
        conf         = printer.Config{Mode: printer.SourcePos, Tabwidth: 8}
        noSourceConf = printer.Config{Tabwidth: 8}
)

// writeDefs creates output files to be compiled by gc and gcc.
func (p *Package) writeDefs() {
        var fgo2, fc io.Writer
        f := creat(*objDir + "_cgo_gotypes.go")
        defer f.Close()
        fgo2 = f
        if *gccgo {
                f := creat(*objDir + "_cgo_defun.c")
                defer f.Close()
                fc = f
        }
        fm := creat(*objDir + "_cgo_main.c")

        var gccgoInit bytes.Buffer

        fflg := creat(*objDir + "_cgo_flags")
        var flags []string
        for k, v := range p.CgoFlags {
                flags = append(flags, fmt.Sprintf("_CGO_%s=%s", k, strings.Join(v, " ")))
                if k == "LDFLAGS" && !*gccgo {
                        for _, arg := range v {
                                fmt.Fprintf(fgo2, "//go:cgo_ldflag %q\n", arg)
                        }
                }
        }
        sort.Strings(flags)
        for _, flag := range flags {
                fmt.Fprintln(fflg, flag)
        }
        fflg.Close()

        // Write C main file for using gcc to resolve imports.
        fmt.Fprintf(fm, "int main() { return 0; }\n")
        if *importRuntimeCgo {
                fmt.Fprintf(fm, "void crosscall2(void(*fn)(void*, int, __SIZE_TYPE__), void *a, int c, __SIZE_TYPE__ ctxt) { }\n")
                fmt.Fprintf(fm, "__SIZE_TYPE__ _cgo_wait_runtime_init_done() { return 0; }\n")
                fmt.Fprintf(fm, "void _cgo_release_context(__SIZE_TYPE__ ctxt) { }\n")
                fmt.Fprintf(fm, "char* _cgo_topofstack(void) { return (char*)0; }\n")
        } else {
                // If we're not importing runtime/cgo, we *are* runtime/cgo,
                // which provides these functions. We just need a prototype.
                fmt.Fprintf(fm, "void crosscall2(void(*fn)(void*, int, __SIZE_TYPE__), void *a, int c, __SIZE_TYPE__ ctxt);\n")
                fmt.Fprintf(fm, "__SIZE_TYPE__ _cgo_wait_runtime_init_done();\n")
                fmt.Fprintf(fm, "void _cgo_release_context(__SIZE_TYPE__);\n")
        }
        fmt.Fprintf(fm, "void _cgo_allocate(void *a, int c) { }\n")
        fmt.Fprintf(fm, "void _cgo_panic(void *a, int c) { }\n")
        fmt.Fprintf(fm, "void _cgo_reginit(void) { }\n")

        // Write second Go output: definitions of _C_xxx.
        // In a separate file so that the import of "unsafe" does not
        // pollute the original file.
        fmt.Fprintf(fgo2, "// Created by cgo - DO NOT EDIT\n\n")
        fmt.Fprintf(fgo2, "package %s\n\n", p.PackageName)
        fmt.Fprintf(fgo2, "import \"unsafe\"\n\n")
        if !*gccgo && *importRuntimeCgo {
                fmt.Fprintf(fgo2, "import _ \"runtime/cgo\"\n\n")
        }
        if *importSyscall {
                fmt.Fprintf(fgo2, "import \"syscall\"\n\n")
                fmt.Fprintf(fgo2, "var _ syscall.Errno\n")
        }
        fmt.Fprintf(fgo2, "func _Cgo_ptr(ptr unsafe.Pointer) unsafe.Pointer { return ptr }\n\n")

        if !*gccgo {
                fmt.Fprintf(fgo2, "//go:linkname _Cgo_always_false runtime.cgoAlwaysFalse\n")
                fmt.Fprintf(fgo2, "var _Cgo_always_false bool\n")
                fmt.Fprintf(fgo2, "//go:linkname _Cgo_use runtime.cgoUse\n")
                fmt.Fprintf(fgo2, "func _Cgo_use(interface{})\n")
        }

        typedefNames := make([]string, 0, len(typedef))
        for name := range typedef {
                typedefNames = append(typedefNames, name)
        }
        sort.Strings(typedefNames)
        for _, name := range typedefNames {
                def := typedef[name]
                fmt.Fprintf(fgo2, "type %s ", name)
                // We don't have source info for these types, so write them out without source info.
                // Otherwise types would look like:
                //
                // type _Ctype_struct_cb struct {
                // //line :1
                //        on_test *[0]byte
                // //line :1
                // }
                //
                // Which is not useful. Moreover we never override source info,
                // so subsequent source code uses the same source info.
                // Moreover, empty file name makes compile emit no source debug info at all.
                var buf bytes.Buffer
                noSourceConf.Fprint(&buf, fset, def.Go)
                if bytes.HasPrefix(buf.Bytes(), []byte("_Ctype_")) {
                        // This typedef is of the form `typedef a b` and should be an alias.
                        fmt.Fprintf(fgo2, "= ")
                }
                fmt.Fprintf(fgo2, "%s", buf.Bytes())
                fmt.Fprintf(fgo2, "\n\n")
        }
        if *gccgo {
                fmt.Fprintf(fgo2, "type _Ctype_void byte\n")
        } else {
                fmt.Fprintf(fgo2, "type _Ctype_void [0]byte\n")
        }

        if *gccgo {
                fmt.Fprint(fgo2, gccgoGoProlog)
                fmt.Fprint(fc, p.cPrologGccgo())
        } else {
                fmt.Fprint(fgo2, goProlog)
        }

        if fc != nil {
                fmt.Fprintf(fc, "#line 1 \"cgo-generated-wrappers\"\n")
        }
        if fm != nil {
                fmt.Fprintf(fm, "#line 1 \"cgo-generated-wrappers\"\n")
        }

        gccgoSymbolPrefix := p.gccgoSymbolPrefix()

        cVars := make(map[string]bool)
        for _, key := range nameKeys(p.Name) {
                n := p.Name[key]
                if !n.IsVar() {
                        continue
                }

                if !cVars[n.C] {
                        if *gccgo {
                                fmt.Fprintf(fc, "extern byte *%s;\n", n.C)
                        } else {
                                fmt.Fprintf(fm, "extern char %s[];\n", n.C)
                                fmt.Fprintf(fm, "void *_cgohack_%s = %s;\n\n", n.C, n.C)
                                fmt.Fprintf(fgo2, "//go:linkname __cgo_%s %s\n", n.C, n.C)
                                fmt.Fprintf(fgo2, "//go:cgo_import_static %s\n", n.C)
                                fmt.Fprintf(fgo2, "var __cgo_%s byte\n", n.C)
                        }
                        cVars[n.C] = true
                }

                var node ast.Node
                if n.Kind == "var" {
                        node = &ast.StarExpr{X: n.Type.Go}
                } else if n.Kind == "fpvar" {
                        node = n.Type.Go
                } else {
                        panic(fmt.Errorf("invalid var kind %q", n.Kind))
                }
                if *gccgo {
                        fmt.Fprintf(fc, `extern void *%s __asm__("%s.%s");`, n.Mangle, gccgoSymbolPrefix, n.Mangle)
                        fmt.Fprintf(&gccgoInit, "\t%s = &%s;\n", n.Mangle, n.C)
                        fmt.Fprintf(fc, "\n")
                }

                fmt.Fprintf(fgo2, "var %s ", n.Mangle)
                conf.Fprint(fgo2, fset, node)
                if !*gccgo {
                        fmt.Fprintf(fgo2, " = (")
                        conf.Fprint(fgo2, fset, node)
                        fmt.Fprintf(fgo2, ")(unsafe.Pointer(&__cgo_%s))", n.C)
                }
                fmt.Fprintf(fgo2, "\n")
        }
        if *gccgo {
                fmt.Fprintf(fc, "\n")
        }

        for _, key := range nameKeys(p.Name) {
                n := p.Name[key]
                if n.Const != "" {
                        fmt.Fprintf(fgo2, "const %s = %s\n", n.Mangle, n.Const)
                }
        }
        fmt.Fprintf(fgo2, "\n")

        callsMalloc := false
        for _, key := range nameKeys(p.Name) {
                n := p.Name[key]
                if n.FuncType != nil {
                        p.writeDefsFunc(fgo2, n, &callsMalloc)
                }
        }

        fgcc := creat(*objDir + "_cgo_export.c")
        fgcch := creat(*objDir + "_cgo_export.h")
        if *gccgo {
                p.writeGccgoExports(fgo2, fm, fgcc, fgcch)
        } else {
                p.writeExports(fgo2, fm, fgcc, fgcch)
        }

        if callsMalloc && !*gccgo {
                fmt.Fprint(fgo2, strings.Replace(cMallocDefGo, "PREFIX", cPrefix, -1))
                fmt.Fprint(fgcc, strings.Replace(strings.Replace(cMallocDefC, "PREFIX", cPrefix, -1), "PACKED", p.packedAttribute(), -1))
        }

        if err := fgcc.Close(); err != nil {
                fatalf("%s", err)
        }
        if err := fgcch.Close(); err != nil {
                fatalf("%s", err)
        }

        if *exportHeader != "" && len(p.ExpFunc) > 0 {
                fexp := creat(*exportHeader)
                fgcch, err := os.Open(*objDir + "_cgo_export.h")
                if err != nil {
                        fatalf("%s", err)
                }
                _, err = io.Copy(fexp, fgcch)
                if err != nil {
                        fatalf("%s", err)
                }
                if err = fexp.Close(); err != nil {
                        fatalf("%s", err)
                }
        }

        init := gccgoInit.String()
        if init != "" {
                fmt.Fprintln(fc, "static void init(void) __attribute__ ((constructor));")
                fmt.Fprintln(fc, "static void init(void) {")
                fmt.Fprint(fc, init)
                fmt.Fprintln(fc, "}")
        }
}

func dynimport(obj string) {
        stdout := os.Stdout
        if *dynout != "" {
                f, err := os.Create(*dynout)
                if err != nil {
                        fatalf("%s", err)
                }
                stdout = f
        }

        fmt.Fprintf(stdout, "package %s\n", *dynpackage)

        if f, err := elf.Open(obj); err == nil {
                if *dynlinker {
                        // Emit the cgo_dynamic_linker line.
                        if sec := f.Section(".interp"); sec != nil {
                                if data, err := sec.Data(); err == nil && len(data) > 1 {
                                        // skip trailing \0 in data
                                        fmt.Fprintf(stdout, "//go:cgo_dynamic_linker %q\n", string(data[:len(data)-1]))
                                }
                        }
                }
                sym, err := f.ImportedSymbols()
                if err != nil {
                        fatalf("cannot load imported symbols from ELF file %s: %v", obj, err)
                }
                for _, s := range sym {
                        targ := s.Name
                        if s.Version != "" {
                                targ += "#" + s.Version
                        }
                        fmt.Fprintf(stdout, "//go:cgo_import_dynamic %s %s %q\n", s.Name, targ, s.Library)
                }
                lib, err := f.ImportedLibraries()
                if err != nil {
                        fatalf("cannot load imported libraries from ELF file %s: %v", obj, err)
                }
                for _, l := range lib {
                        fmt.Fprintf(stdout, "//go:cgo_import_dynamic _ _ %q\n", l)
                }
                return
        }

        if f, err := macho.Open(obj); err == nil {
                sym, err := f.ImportedSymbols()
                if err != nil {
                        fatalf("cannot load imported symbols from Mach-O file %s: %v", obj, err)
                }
                for _, s := range sym {
                        if len(s) > 0 && s[0] == '_' {
                                s = s[1:]
                        }
                        fmt.Fprintf(stdout, "//go:cgo_import_dynamic %s %s %q\n", s, s, "")
                }
                lib, err := f.ImportedLibraries()
                if err != nil {
                        fatalf("cannot load imported libraries from Mach-O file %s: %v", obj, err)
                }
                for _, l := range lib {
                        fmt.Fprintf(stdout, "//go:cgo_import_dynamic _ _ %q\n", l)
                }
                return
        }

        if f, err := pe.Open(obj); err == nil {
                sym, err := f.ImportedSymbols()
                if err != nil {
                        fatalf("cannot load imported symbols from PE file %s: %v", obj, err)
                }
                for _, s := range sym {
                        ss := strings.Split(s, ":")
                        name := strings.Split(ss[0], "@")[0]
                        fmt.Fprintf(stdout, "//go:cgo_import_dynamic %s %s %q\n", name, ss[0], strings.ToLower(ss[1]))
                }
                return
        }

        if f, err := xcoff.Open(obj); err == nil {
                sym, err := f.ImportedSymbols()
                if err != nil {
                        fatalf("cannot load imported symbols from XCOFF file %s: %v", obj, err)
                }
                for _, s := range sym {
                        fmt.Fprintf(stdout, "//go:cgo_import_dynamic %s %s %q\n", s.Name, s.Name, s.Library)
                }
                lib, err := f.ImportedLibraries()
                if err != nil {
                        fatalf("cannot load imported libraries from XCOFF file %s: %v", obj, err)
                }
                for _, l := range lib {
                        fmt.Fprintf(stdout, "//go:cgo_import_dynamic _ _ %q\n", l)
                }
                return
        }

        fatalf("cannot parse %s as ELF, Mach-O, PE or XCOFF", obj)
}

// Construct a gcc struct matching the gc argument frame.
// Assumes that in gcc, char is 1 byte, short 2 bytes, int 4 bytes, long long 8 bytes.
// These assumptions are checked by the gccProlog.
// Also assumes that gc convention is to word-align the
// input and output parameters.
func (p *Package) structType(n *Name) (string, int64) {
        var buf bytes.Buffer
        fmt.Fprint(&buf, "struct {\n")
        off := int64(0)
        for i, t := range n.FuncType.Params {
                if off%t.Align != 0 {
                        pad := t.Align - off%t.Align
                        fmt.Fprintf(&buf, "\t\tchar __pad%d[%d];\n", off, pad)
                        off += pad
                }
                c := t.Typedef
                if c == "" {
                        c = t.C.String()
                }
                fmt.Fprintf(&buf, "\t\t%s p%d;\n", c, i)
                off += t.Size
        }
        if off%p.PtrSize != 0 {
                pad := p.PtrSize - off%p.PtrSize
                fmt.Fprintf(&buf, "\t\tchar __pad%d[%d];\n", off, pad)
                off += pad
        }
        if t := n.FuncType.Result; t != nil {
                if off%t.Align != 0 {
                        pad := t.Align - off%t.Align
                        fmt.Fprintf(&buf, "\t\tchar __pad%d[%d];\n", off, pad)
                        off += pad
                }
                fmt.Fprintf(&buf, "\t\t%s r;\n", t.C)
                off += t.Size
        }
        if off%p.PtrSize != 0 {
                pad := p.PtrSize - off%p.PtrSize
                fmt.Fprintf(&buf, "\t\tchar __pad%d[%d];\n", off, pad)
                off += pad
        }
        if off == 0 {
                fmt.Fprintf(&buf, "\t\tchar unused;\n") // avoid empty struct
        }
        fmt.Fprintf(&buf, "\t}")
        return buf.String(), off
}

func (p *Package) writeDefsFunc(fgo2 io.Writer, n *Name, callsMalloc *bool) {
        name := n.Go
        gtype := n.FuncType.Go
        void := gtype.Results == nil || len(gtype.Results.List) == 0
        if n.AddError {
                // Add "error" to return type list.
                // Type list is known to be 0 or 1 element - it's a C function.
                err := &ast.Field{Type: ast.NewIdent("error")}
                l := gtype.Results.List
                if len(l) == 0 {
                        l = []*ast.Field{err}
                } else {
                        l = []*ast.Field{l[0], err}
                }
                t := new(ast.FuncType)
                *t = *gtype
                t.Results = &ast.FieldList{List: l}
                gtype = t
        }

        // Go func declaration.
        d := &ast.FuncDecl{
                Name: ast.NewIdent(n.Mangle),
                Type: gtype,
        }

        // Builtins defined in the C prolog.
        inProlog := builtinDefs[name] != ""
        cname := fmt.Sprintf("_cgo%s%s", cPrefix, n.Mangle)
        paramnames := []string(nil)
        if d.Type.Params != nil {
                for i, param := range d.Type.Params.List {
                        paramName := fmt.Sprintf("p%d", i)
                        param.Names = []*ast.Ident{ast.NewIdent(paramName)}
                        paramnames = append(paramnames, paramName)
                }
        }

        if *gccgo {
                // Gccgo style hooks.
                fmt.Fprint(fgo2, "\n")
                conf.Fprint(fgo2, fset, d)
                fmt.Fprint(fgo2, " {\n")
                if !inProlog {
                        fmt.Fprint(fgo2, "\tdefer syscall.CgocallDone()\n")
                        fmt.Fprint(fgo2, "\tsyscall.Cgocall()\n")
                }
                if n.AddError {
                        fmt.Fprint(fgo2, "\tsyscall.SetErrno(0)\n")
                }
                fmt.Fprint(fgo2, "\t")
                if !void {
                        fmt.Fprint(fgo2, "r := ")
                }
                fmt.Fprintf(fgo2, "%s(%s)\n", cname, strings.Join(paramnames, ", "))

                if n.AddError {
                        fmt.Fprint(fgo2, "\te := syscall.GetErrno()\n")
                        fmt.Fprint(fgo2, "\tif e != 0 {\n")
                        fmt.Fprint(fgo2, "\t\treturn ")
                        if !void {
                                fmt.Fprint(fgo2, "r, ")
                        }
                        fmt.Fprint(fgo2, "e\n")
                        fmt.Fprint(fgo2, "\t}\n")
                        fmt.Fprint(fgo2, "\treturn ")
                        if !void {
                                fmt.Fprint(fgo2, "r, ")
                        }
                        fmt.Fprint(fgo2, "nil\n")
                } else if !void {
                        fmt.Fprint(fgo2, "\treturn r\n")
                }

                fmt.Fprint(fgo2, "}\n")

                // declare the C function.
                fmt.Fprintf(fgo2, "//extern %s\n", cname)
                d.Name = ast.NewIdent(cname)
                if n.AddError {
                        l := d.Type.Results.List
                        d.Type.Results.List = l[:len(l)-1]
                }
                conf.Fprint(fgo2, fset, d)
                fmt.Fprint(fgo2, "\n")

                return
        }

        if inProlog {
                fmt.Fprint(fgo2, builtinDefs[name])
                if strings.Contains(builtinDefs[name], "_cgo_cmalloc") {
                        *callsMalloc = true
                }
                return
        }

        // Wrapper calls into gcc, passing a pointer to the argument frame.
        fmt.Fprintf(fgo2, "//go:cgo_import_static %s\n", cname)
        fmt.Fprintf(fgo2, "//go:linkname __cgofn_%s %s\n", cname, cname)
        fmt.Fprintf(fgo2, "var __cgofn_%s byte\n", cname)
        fmt.Fprintf(fgo2, "var %s = unsafe.Pointer(&__cgofn_%s)\n", cname, cname)

        nret := 0
        if !void {
                d.Type.Results.List[0].Names = []*ast.Ident{ast.NewIdent("r1")}
                nret = 1
        }
        if n.AddError {
                d.Type.Results.List[nret].Names = []*ast.Ident{ast.NewIdent("r2")}
        }

        fmt.Fprint(fgo2, "\n")
        fmt.Fprint(fgo2, "//go:cgo_unsafe_args\n")
        conf.Fprint(fgo2, fset, d)
        fmt.Fprint(fgo2, " {\n")

        // NOTE: Using uintptr to hide from escape analysis.
        arg := "0"
        if len(paramnames) > 0 {
                arg = "uintptr(unsafe.Pointer(&p0))"
        } else if !void {
                arg = "uintptr(unsafe.Pointer(&r1))"
        }

        prefix := ""
        if n.AddError {
                prefix = "errno := "
        }
        fmt.Fprintf(fgo2, "\t%s_cgo_runtime_cgocall(%s, %s)\n", prefix, cname, arg)
        if n.AddError {
                fmt.Fprintf(fgo2, "\tif errno != 0 { r2 = syscall.Errno(errno) }\n")
        }
        fmt.Fprintf(fgo2, "\tif _Cgo_always_false {\n")
        if d.Type.Params != nil {
                for i := range d.Type.Params.List {
                        fmt.Fprintf(fgo2, "\t\t_Cgo_use(p%d)\n", i)
                }
        }
        fmt.Fprintf(fgo2, "\t}\n")
        fmt.Fprintf(fgo2, "\treturn\n")
        fmt.Fprintf(fgo2, "}\n")
}

// writeOutput creates stubs for a specific source file to be compiled by gc
func (p *Package) writeOutput(f *File, srcfile string) {
        base := srcfile
        if strings.HasSuffix(base, ".go") {
                base = base[0 : len(base)-3]
        }
        base = filepath.Base(base)
        fgo1 := creat(*objDir + base + ".cgo1.go")
        fgcc := creat(*objDir + base + ".cgo2.c")

        p.GoFiles = append(p.GoFiles, base+".cgo1.go")
        p.GccFiles = append(p.GccFiles, base+".cgo2.c")

        // Write Go output: Go input with rewrites of C.xxx to _C_xxx.
        fmt.Fprintf(fgo1, "// Created by cgo - DO NOT EDIT\n\n")
        fmt.Fprintf(fgo1, "//line %s:1\n", srcfile)
        fgo1.Write(f.Edit.Bytes())

        // While we process the vars and funcs, also write gcc output.
        // Gcc output starts with the preamble.
        fmt.Fprintf(fgcc, "%s\n", builtinProlog)
        fmt.Fprintf(fgcc, "%s\n", f.Preamble)
        fmt.Fprintf(fgcc, "%s\n", gccProlog)
        fmt.Fprintf(fgcc, "%s\n", tsanProlog)

        for _, key := range nameKeys(f.Name) {
                n := f.Name[key]
                if n.FuncType != nil {
                        p.writeOutputFunc(fgcc, n)
                }
        }

        fgo1.Close()
        fgcc.Close()
}

// fixGo converts the internal Name.Go field into the name we should show
// to users in error messages. There's only one for now: on input we rewrite
// C.malloc into C._CMalloc, so change it back here.
func fixGo(name string) string {
        if name == "_CMalloc" {
                return "malloc"
        }
        return name
}

var isBuiltin = map[string]bool{
        "_Cfunc_CString":   true,
        "_Cfunc_CBytes":    true,
        "_Cfunc_GoString":  true,
        "_Cfunc_GoStringN": true,
        "_Cfunc_GoBytes":   true,
        "_Cfunc__CMalloc":  true,
}

func (p *Package) writeOutputFunc(fgcc *os.File, n *Name) {
        name := n.Mangle
        if isBuiltin[name] || p.Written[name] {
                // The builtins are already defined in the C prolog, and we don't
                // want to duplicate function definitions we've already done.
                return
        }
        p.Written[name] = true

        if *gccgo {
                p.writeGccgoOutputFunc(fgcc, n)
                return
        }

        ctype, _ := p.structType(n)

        // Gcc wrapper unpacks the C argument struct
        // and calls the actual C function.
        fmt.Fprintf(fgcc, "CGO_NO_SANITIZE_THREAD\n")
        if n.AddError {
                fmt.Fprintf(fgcc, "int\n")
        } else {
                fmt.Fprintf(fgcc, "void\n")
        }
        fmt.Fprintf(fgcc, "_cgo%s%s(void *v)\n", cPrefix, n.Mangle)
        fmt.Fprintf(fgcc, "{\n")
        if n.AddError {
                fmt.Fprintf(fgcc, "\tint _cgo_errno;\n")
        }
        // We're trying to write a gcc struct that matches gc's layout.
        // Use packed attribute to force no padding in this struct in case
        // gcc has different packing requirements.
        fmt.Fprintf(fgcc, "\t%s %v *a = v;\n", ctype, p.packedAttribute())
        if n.FuncType.Result != nil {
                // Save the stack top for use below.
                fmt.Fprintf(fgcc, "\tchar *stktop = _cgo_topofstack();\n")
        }
        tr := n.FuncType.Result
        if tr != nil {
                fmt.Fprintf(fgcc, "\t__typeof__(a->r) r;\n")
        }
        fmt.Fprintf(fgcc, "\t_cgo_tsan_acquire();\n")
        if n.AddError {
                fmt.Fprintf(fgcc, "\terrno = 0;\n")
        }
        fmt.Fprintf(fgcc, "\t")
        if tr != nil {
                fmt.Fprintf(fgcc, "r = ")
                if c := tr.C.String(); c[len(c)-1] == '*' {
                        fmt.Fprint(fgcc, "(__typeof__(a->r)) ")
                }
        }
        if n.Kind == "macro" {
                fmt.Fprintf(fgcc, "%s;\n", n.C)
        } else {
                fmt.Fprintf(fgcc, "%s(", n.C)
                for i := range n.FuncType.Params {
                        if i > 0 {
                                fmt.Fprintf(fgcc, ", ")
                        }
                        fmt.Fprintf(fgcc, "a->p%d", i)
                }
                fmt.Fprintf(fgcc, ");\n")
        }
        if n.AddError {
                fmt.Fprintf(fgcc, "\t_cgo_errno = errno;\n")
        }
        fmt.Fprintf(fgcc, "\t_cgo_tsan_release();\n")
        if n.FuncType.Result != nil {
                // The cgo call may have caused a stack copy (via a callback).
                // Adjust the return value pointer appropriately.
                fmt.Fprintf(fgcc, "\ta = (void*)((char*)a + (_cgo_topofstack() - stktop));\n")
                // Save the return value.
                fmt.Fprintf(fgcc, "\ta->r = r;\n")
        }
        if n.AddError {
                fmt.Fprintf(fgcc, "\treturn _cgo_errno;\n")
        }
        fmt.Fprintf(fgcc, "}\n")
        fmt.Fprintf(fgcc, "\n")
}

// Write out a wrapper for a function when using gccgo. This is a
// simple wrapper that just calls the real function. We only need a
// wrapper to support static functions in the prologue--without a
// wrapper, we can't refer to the function, since the reference is in
// a different file.
func (p *Package) writeGccgoOutputFunc(fgcc *os.File, n *Name) {
        fmt.Fprintf(fgcc, "CGO_NO_SANITIZE_THREAD\n")
        if t := n.FuncType.Result; t != nil {
                fmt.Fprintf(fgcc, "%s\n", t.C.String())
        } else {
                fmt.Fprintf(fgcc, "void\n")
        }
        fmt.Fprintf(fgcc, "_cgo%s%s(", cPrefix, n.Mangle)
        for i, t := range n.FuncType.Params {
                if i > 0 {
                        fmt.Fprintf(fgcc, ", ")
                }
                c := t.Typedef
                if c == "" {
                        c = t.C.String()
                }
                fmt.Fprintf(fgcc, "%s p%d", c, i)
        }
        fmt.Fprintf(fgcc, ")\n")
        fmt.Fprintf(fgcc, "{\n")
        if t := n.FuncType.Result; t != nil {
                fmt.Fprintf(fgcc, "\t%s r;\n", t.C.String())
        }
        fmt.Fprintf(fgcc, "\t_cgo_tsan_acquire();\n")
        fmt.Fprintf(fgcc, "\t")
        if t := n.FuncType.Result; t != nil {
                fmt.Fprintf(fgcc, "r = ")
                // Cast to void* to avoid warnings due to omitted qualifiers.
                if c := t.C.String(); c[len(c)-1] == '*' {
                        fmt.Fprintf(fgcc, "(void*)")
                }
        }
        if n.Kind == "macro" {
                fmt.Fprintf(fgcc, "%s;\n", n.C)
        } else {
                fmt.Fprintf(fgcc, "%s(", n.C)
                for i := range n.FuncType.Params {
                        if i > 0 {
                                fmt.Fprintf(fgcc, ", ")
                        }
                        fmt.Fprintf(fgcc, "p%d", i)
                }
                fmt.Fprintf(fgcc, ");\n")
        }
        fmt.Fprintf(fgcc, "\t_cgo_tsan_release();\n")
        if t := n.FuncType.Result; t != nil {
                fmt.Fprintf(fgcc, "\treturn ")
                // Cast to void* to avoid warnings due to omitted qualifiers
                // and explicit incompatible struct types.
                if c := t.C.String(); c[len(c)-1] == '*' {
                        fmt.Fprintf(fgcc, "(void*)")
                }
                fmt.Fprintf(fgcc, "r;\n")
        }
        fmt.Fprintf(fgcc, "}\n")
        fmt.Fprintf(fgcc, "\n")
}

// packedAttribute returns host compiler struct attribute that will be
// used to match gc's struct layout. For example, on 386 Windows,
// gcc wants to 8-align int64s, but gc does not.
// Use __gcc_struct__ to work around http://gcc.gnu.org/PR52991 on x86,
// and https://golang.org/issue/5603.
func (p *Package) packedAttribute() string {
        s := "__attribute__((__packed__"
        if !p.GccIsClang && (goarch == "amd64" || goarch == "386") {
                s += ", __gcc_struct__"
        }
        return s + "))"
}

// Write out the various stubs we need to support functions exported
// from Go so that they are callable from C.
func (p *Package) writeExports(fgo2, fm, fgcc, fgcch io.Writer) {
        p.writeExportHeader(fgcch)

        fmt.Fprintf(fgcc, "/* Created by cgo - DO NOT EDIT. */\n")
        fmt.Fprintf(fgcc, "#include <stdlib.h>\n")
        fmt.Fprintf(fgcc, "#include \"_cgo_export.h\"\n\n")

        fmt.Fprintf(fgcc, "extern void crosscall2(void (*fn)(void *, int, __SIZE_TYPE__), void *, int, __SIZE_TYPE__);\n")
        fmt.Fprintf(fgcc, "extern __SIZE_TYPE__ _cgo_wait_runtime_init_done();\n")
        fmt.Fprintf(fgcc, "extern void _cgo_release_context(__SIZE_TYPE__);\n\n")
        fmt.Fprintf(fgcc, "extern char* _cgo_topofstack(void);")
        fmt.Fprintf(fgcc, "%s\n", tsanProlog)

        for _, exp := range p.ExpFunc {
                fn := exp.Func

                // Construct a gcc struct matching the gc argument and
                // result frame. The gcc struct will be compiled with
                // __attribute__((packed)) so all padding must be accounted
                // for explicitly.
                ctype := "struct {\n"
                off := int64(0)
                npad := 0
                if fn.Recv != nil {
                        t := p.cgoType(fn.Recv.List[0].Type)
                        ctype += fmt.Sprintf("\t\t%s recv;\n", t.C)
                        off += t.Size
                }
                fntype := fn.Type
                forFieldList(fntype.Params,
                        func(i int, aname string, atype ast.Expr) {
                                t := p.cgoType(atype)
                                if off%t.Align != 0 {
                                        pad := t.Align - off%t.Align
                                        ctype += fmt.Sprintf("\t\tchar __pad%d[%d];\n", npad, pad)
                                        off += pad
                                        npad++
                                }
                                ctype += fmt.Sprintf("\t\t%s p%d;\n", t.C, i)
                                off += t.Size
                        })
                if off%p.PtrSize != 0 {
                        pad := p.PtrSize - off%p.PtrSize
                        ctype += fmt.Sprintf("\t\tchar __pad%d[%d];\n", npad, pad)
                        off += pad
                        npad++
                }
                forFieldList(fntype.Results,
                        func(i int, aname string, atype ast.Expr) {
                                t := p.cgoType(atype)
                                if off%t.Align != 0 {
                                        pad := t.Align - off%t.Align
                                        ctype += fmt.Sprintf("\t\tchar __pad%d[%d];\n", npad, pad)
                                        off += pad
                                        npad++
                                }
                                ctype += fmt.Sprintf("\t\t%s r%d;\n", t.C, i)
                                off += t.Size
                        })
                if off%p.PtrSize != 0 {
                        pad := p.PtrSize - off%p.PtrSize
                        ctype += fmt.Sprintf("\t\tchar __pad%d[%d];\n", npad, pad)
                        off += pad
                        npad++
                }
                if ctype == "struct {\n" {
                        ctype += "\t\tchar unused;\n" // avoid empty struct
                }
                ctype += "\t}"

                // Get the return type of the wrapper function
                // compiled by gcc.
                gccResult := ""
                if fntype.Results == nil || len(fntype.Results.List) == 0 {
                        gccResult = "void"
                } else if len(fntype.Results.List) == 1 && len(fntype.Results.List[0].Names) <= 1 {
                        gccResult = p.cgoType(fntype.Results.List[0].Type).C.String()
                } else {
                        fmt.Fprintf(fgcch, "\n/* Return type for %s */\n", exp.ExpName)
                        fmt.Fprintf(fgcch, "struct %s_return {\n", exp.ExpName)
                        forFieldList(fntype.Results,
                                func(i int, aname string, atype ast.Expr) {
                                        fmt.Fprintf(fgcch, "\t%s r%d;", p.cgoType(atype).C, i)
                                        if len(aname) > 0 {
                                                fmt.Fprintf(fgcch, " /* %s */", aname)
                                        }
                                        fmt.Fprint(fgcch, "\n")
                                })
                        fmt.Fprintf(fgcch, "};\n")
                        gccResult = "struct " + exp.ExpName + "_return"
                }

                // Build the wrapper function compiled by gcc.
                s := fmt.Sprintf("%s %s(", gccResult, exp.ExpName)
                if fn.Recv != nil {
                        s += p.cgoType(fn.Recv.List[0].Type).C.String()
                        s += " recv"
                }
                forFieldList(fntype.Params,
                        func(i int, aname string, atype ast.Expr) {
                                if i > 0 || fn.Recv != nil {
                                        s += ", "
                                }
                                s += fmt.Sprintf("%s p%d", p.cgoType(atype).C, i)
                        })
                s += ")"

                if len(exp.Doc) > 0 {
                        fmt.Fprintf(fgcch, "\n%s", exp.Doc)
                }
                fmt.Fprintf(fgcch, "\nextern %s;\n", s)

                fmt.Fprintf(fgcc, "extern void _cgoexp%s_%s(void *, int, __SIZE_TYPE__);\n", cPrefix, exp.ExpName)
                fmt.Fprintf(fgcc, "\nCGO_NO_SANITIZE_THREAD")
                fmt.Fprintf(fgcc, "\n%s\n", s)
                fmt.Fprintf(fgcc, "{\n")
                fmt.Fprintf(fgcc, "\t__SIZE_TYPE__ _cgo_ctxt = _cgo_wait_runtime_init_done();\n")
                fmt.Fprintf(fgcc, "\t%s %v a;\n", ctype, p.packedAttribute())
                if gccResult != "void" && (len(fntype.Results.List) > 1 || len(fntype.Results.List[0].Names) > 1) {
                        fmt.Fprintf(fgcc, "\t%s r;\n", gccResult)
                }
                if fn.Recv != nil {
                        fmt.Fprintf(fgcc, "\ta.recv = recv;\n")
                }
                forFieldList(fntype.Params,
                        func(i int, aname string, atype ast.Expr) {
                                fmt.Fprintf(fgcc, "\ta.p%d = p%d;\n", i, i)
                        })
                fmt.Fprintf(fgcc, "\t_cgo_tsan_release();\n")
                fmt.Fprintf(fgcc, "\tcrosscall2(_cgoexp%s_%s, &a, %d, _cgo_ctxt);\n", cPrefix, exp.ExpName, off)
                fmt.Fprintf(fgcc, "\t_cgo_tsan_acquire();\n")
                fmt.Fprintf(fgcc, "\t_cgo_release_context(_cgo_ctxt);\n")
                if gccResult != "void" {
                        if len(fntype.Results.List) == 1 && len(fntype.Results.List[0].Names) <= 1 {
                                fmt.Fprintf(fgcc, "\treturn a.r0;\n")
                        } else {
                                forFieldList(fntype.Results,
                                        func(i int, aname string, atype ast.Expr) {
                                                fmt.Fprintf(fgcc, "\tr.r%d = a.r%d;\n", i, i)
                                        })
                                fmt.Fprintf(fgcc, "\treturn r;\n")
                        }
                }
                fmt.Fprintf(fgcc, "}\n")

                // Build the wrapper function compiled by cmd/compile.
                goname := "_cgoexpwrap" + cPrefix + "_"
                if fn.Recv != nil {
                        goname += fn.Recv.List[0].Names[0].Name + "_"
                }
                goname += exp.Func.Name.Name
                fmt.Fprintf(fgo2, "//go:cgo_export_dynamic %s\n", exp.ExpName)
                fmt.Fprintf(fgo2, "//go:linkname _cgoexp%s_%s _cgoexp%s_%s\n", cPrefix, exp.ExpName, cPrefix, exp.ExpName)
                fmt.Fprintf(fgo2, "//go:cgo_export_static _cgoexp%s_%s\n", cPrefix, exp.ExpName)
                fmt.Fprintf(fgo2, "//go:nosplit\n") // no split stack, so no use of m or g
                fmt.Fprintf(fgo2, "//go:norace\n")  // must not have race detector calls inserted
                fmt.Fprintf(fgo2, "func _cgoexp%s_%s(a unsafe.Pointer, n int32, ctxt uintptr) {\n", cPrefix, exp.ExpName)
                fmt.Fprintf(fgo2, "\tfn := %s\n", goname)
                // The indirect here is converting from a Go function pointer to a C function pointer.
                fmt.Fprintf(fgo2, "\t_cgo_runtime_cgocallback(**(**unsafe.Pointer)(unsafe.Pointer(&fn)), a, uintptr(n), ctxt);\n")
                fmt.Fprintf(fgo2, "}\n")

                fmt.Fprintf(fm, "int _cgoexp%s_%s;\n", cPrefix, exp.ExpName)

                // This code uses printer.Fprint, not conf.Fprint,
                // because we don't want //line comments in the middle
                // of the function types.
                fmt.Fprintf(fgo2, "\n")
                fmt.Fprintf(fgo2, "func %s(", goname)
                comma := false
                if fn.Recv != nil {
                        fmt.Fprintf(fgo2, "recv ")
                        printer.Fprint(fgo2, fset, fn.Recv.List[0].Type)
                        comma = true
                }
                forFieldList(fntype.Params,
                        func(i int, aname string, atype ast.Expr) {
                                if comma {
                                        fmt.Fprintf(fgo2, ", ")
                                }
                                fmt.Fprintf(fgo2, "p%d ", i)
                                printer.Fprint(fgo2, fset, atype)
                                comma = true
                        })
                fmt.Fprintf(fgo2, ")")
                if gccResult != "void" {
                        fmt.Fprint(fgo2, " (")
                        forFieldList(fntype.Results,
                                func(i int, aname string, atype ast.Expr) {
                                        if i > 0 {
                                                fmt.Fprint(fgo2, ", ")
                                        }
                                        fmt.Fprintf(fgo2, "r%d ", i)
                                        printer.Fprint(fgo2, fset, atype)
                                })
                        fmt.Fprint(fgo2, ")")
                }
                fmt.Fprint(fgo2, " {\n")
                if gccResult == "void" {
                        fmt.Fprint(fgo2, "\t")
                } else {
                        // Verify that any results don't contain any
                        // Go pointers.
                        addedDefer := false
                        forFieldList(fntype.Results,
                                func(i int, aname string, atype ast.Expr) {
                                        if !p.hasPointer(nil, atype, false) {
                                                return
                                        }
                                        if !addedDefer {
                                                fmt.Fprint(fgo2, "\tdefer func() {\n")
                                                addedDefer = true
                                        }
                                        fmt.Fprintf(fgo2, "\t\t_cgoCheckResult(r%d)\n", i)
                                })
                        if addedDefer {
                                fmt.Fprint(fgo2, "\t}()\n")
                        }
                        fmt.Fprint(fgo2, "\treturn ")
                }
                if fn.Recv != nil {
                        fmt.Fprintf(fgo2, "recv.")
                }
                fmt.Fprintf(fgo2, "%s(", exp.Func.Name)
                forFieldList(fntype.Params,
                        func(i int, aname string, atype ast.Expr) {
                                if i > 0 {
                                        fmt.Fprint(fgo2, ", ")
                                }
                                fmt.Fprintf(fgo2, "p%d", i)
                        })
                fmt.Fprint(fgo2, ")\n")
                fmt.Fprint(fgo2, "}\n")
        }

        fmt.Fprintf(fgcch, "%s", gccExportHeaderEpilog)
}

// Write out the C header allowing C code to call exported gccgo functions.
func (p *Package) writeGccgoExports(fgo2, fm, fgcc, fgcch io.Writer) {
        gccgoSymbolPrefix := p.gccgoSymbolPrefix()

        p.writeExportHeader(fgcch)

        fmt.Fprintf(fgcc, "/* Created by cgo - DO NOT EDIT. */\n")
        fmt.Fprintf(fgcc, "#include \"_cgo_export.h\"\n")

        fmt.Fprintf(fgcc, "%s\n", gccgoExportFileProlog)
        fmt.Fprintf(fgcc, "%s\n", tsanProlog)

        for _, exp := range p.ExpFunc {
                fn := exp.Func
                fntype := fn.Type

                cdeclBuf := new(bytes.Buffer)
                resultCount := 0
                forFieldList(fntype.Results,
                        func(i int, aname string, atype ast.Expr) { resultCount++ })
                switch resultCount {
                case 0:
                        fmt.Fprintf(cdeclBuf, "void")
                case 1:
                        forFieldList(fntype.Results,
                                func(i int, aname string, atype ast.Expr) {
                                        t := p.cgoType(atype)
                                        fmt.Fprintf(cdeclBuf, "%s", t.C)
                                })
                default:
                        // Declare a result struct.
                        fmt.Fprintf(fgcch, "\n/* Return type for %s */\n", exp.ExpName)
                        fmt.Fprintf(fgcch, "struct %s_return {\n", exp.ExpName)
                        forFieldList(fntype.Results,
                                func(i int, aname string, atype ast.Expr) {
                                        t := p.cgoType(atype)
                                        fmt.Fprintf(fgcch, "\t%s r%d;", t.C, i)
                                        if len(aname) > 0 {
                                                fmt.Fprintf(fgcch, " /* %s */", aname)
                                        }
                                        fmt.Fprint(fgcch, "\n")
                                })
                        fmt.Fprintf(fgcch, "};\n")
                        fmt.Fprintf(cdeclBuf, "struct %s_return", exp.ExpName)
                }

                cRet := cdeclBuf.String()

                cdeclBuf = new(bytes.Buffer)
                fmt.Fprintf(cdeclBuf, "(")
                if fn.Recv != nil {
                        fmt.Fprintf(cdeclBuf, "%s recv", p.cgoType(fn.Recv.List[0].Type).C.String())
                }
                // Function parameters.
                forFieldList(fntype.Params,
                        func(i int, aname string, atype ast.Expr) {
                                if i > 0 || fn.Recv != nil {
                                        fmt.Fprintf(cdeclBuf, ", ")
                                }
                                t := p.cgoType(atype)
                                fmt.Fprintf(cdeclBuf, "%s p%d", t.C, i)
                        })
                fmt.Fprintf(cdeclBuf, ")")
                cParams := cdeclBuf.String()

                if len(exp.Doc) > 0 {
                        fmt.Fprintf(fgcch, "\n%s", exp.Doc)
                }

                fmt.Fprintf(fgcch, "extern %s %s%s;\n", cRet, exp.ExpName, cParams)

                // We need to use a name that will be exported by the
                // Go code; otherwise gccgo will make it static and we
                // will not be able to link against it from the C
                // code.
                goName := "Cgoexp_" + exp.ExpName
                fmt.Fprintf(fgcc, `extern %s %s %s __asm__("%s.%s");`, cRet, goName, cParams, gccgoSymbolPrefix, goName)
                fmt.Fprint(fgcc, "\n")

                fmt.Fprint(fgcc, "\nCGO_NO_SANITIZE_THREAD\n")
                fmt.Fprintf(fgcc, "%s %s %s {\n", cRet, exp.ExpName, cParams)
                if resultCount > 0 {
                        fmt.Fprintf(fgcc, "\t%s r;\n", cRet)
                }
                fmt.Fprintf(fgcc, "\tif(_cgo_wait_runtime_init_done)\n")
                fmt.Fprintf(fgcc, "\t\t_cgo_wait_runtime_init_done();\n")
                fmt.Fprintf(fgcc, "\t_cgo_tsan_release();\n")
                fmt.Fprint(fgcc, "\t")
                if resultCount > 0 {
                        fmt.Fprint(fgcc, "r = ")
                }
                fmt.Fprintf(fgcc, "%s(", goName)
                if fn.Recv != nil {
                        fmt.Fprint(fgcc, "recv")
                }
                forFieldList(fntype.Params,
                        func(i int, aname string, atype ast.Expr) {
                                if i > 0 || fn.Recv != nil {
                                        fmt.Fprintf(fgcc, ", ")
                                }
                                fmt.Fprintf(fgcc, "p%d", i)
                        })
                fmt.Fprint(fgcc, ");\n")
                fmt.Fprintf(fgcc, "\t_cgo_tsan_acquire();\n")
                if resultCount > 0 {
                        fmt.Fprint(fgcc, "\treturn r;\n")
                }
                fmt.Fprint(fgcc, "}\n")

                // Dummy declaration for _cgo_main.c
                fmt.Fprintf(fm, `char %s[1] __asm__("%s.%s");`, goName, gccgoSymbolPrefix, goName)
                fmt.Fprint(fm, "\n")

                // For gccgo we use a wrapper function in Go, in order
                // to call CgocallBack and CgocallBackDone.

                // This code uses printer.Fprint, not conf.Fprint,
                // because we don't want //line comments in the middle
                // of the function types.
                fmt.Fprint(fgo2, "\n")
                fmt.Fprintf(fgo2, "func %s(", goName)
                if fn.Recv != nil {
                        fmt.Fprint(fgo2, "recv ")
                        printer.Fprint(fgo2, fset, fn.Recv.List[0].Type)
                }
                forFieldList(fntype.Params,
                        func(i int, aname string, atype ast.Expr) {
                                if i > 0 || fn.Recv != nil {
                                        fmt.Fprintf(fgo2, ", ")
                                }
                                fmt.Fprintf(fgo2, "p%d ", i)
                                printer.Fprint(fgo2, fset, atype)
                        })
                fmt.Fprintf(fgo2, ")")
                if resultCount > 0 {
                        fmt.Fprintf(fgo2, " (")
                        forFieldList(fntype.Results,
                                func(i int, aname string, atype ast.Expr) {
                                        if i > 0 {
                                                fmt.Fprint(fgo2, ", ")
                                        }
                                        printer.Fprint(fgo2, fset, atype)
                                })
                        fmt.Fprint(fgo2, ")")
                }
                fmt.Fprint(fgo2, " {\n")
                fmt.Fprint(fgo2, "\tsyscall.CgocallBack()\n")
                fmt.Fprint(fgo2, "\tdefer syscall.CgocallBackDone()\n")
                fmt.Fprint(fgo2, "\t")
                if resultCount > 0 {
                        fmt.Fprint(fgo2, "return ")
                }
                if fn.Recv != nil {
                        fmt.Fprint(fgo2, "recv.")
                }
                fmt.Fprintf(fgo2, "%s(", exp.Func.Name)
                forFieldList(fntype.Params,
                        func(i int, aname string, atype ast.Expr) {
                                if i > 0 {
                                        fmt.Fprint(fgo2, ", ")
                                }
                                fmt.Fprintf(fgo2, "p%d", i)
                        })
                fmt.Fprint(fgo2, ")\n")
                fmt.Fprint(fgo2, "}\n")
        }

        fmt.Fprintf(fgcch, "%s", gccExportHeaderEpilog)
}

// writeExportHeader writes out the start of the _cgo_export.h file.
func (p *Package) writeExportHeader(fgcch io.Writer) {
        fmt.Fprintf(fgcch, "/* Created by \"go tool cgo\" - DO NOT EDIT. */\n\n")
        pkg := *importPath
        if pkg == "" {
                pkg = p.PackagePath
        }
        fmt.Fprintf(fgcch, "/* package %s */\n\n", pkg)
        fmt.Fprintf(fgcch, "%s\n", builtinExportProlog)

        fmt.Fprintf(fgcch, "/* Start of preamble from import \"C\" comments.  */\n\n")
        fmt.Fprintf(fgcch, "%s\n", p.Preamble)
        fmt.Fprintf(fgcch, "\n/* End of preamble from import \"C\" comments.  */\n\n")

        fmt.Fprintf(fgcch, "%s\n", p.gccExportHeaderProlog())
}

// Return the package prefix when using gccgo.
func (p *Package) gccgoSymbolPrefix() string {
        if !*gccgo {
                return ""
        }

        clean := func(r rune) rune {
                switch {
                case 'A' <= r && r <= 'Z', 'a' <= r && r <= 'z',
                        '0' <= r && r <= '9':
                        return r
                }
                return '_'
        }

        if *gccgopkgpath != "" {
                return strings.Map(clean, *gccgopkgpath)
        }
        if *gccgoprefix == "" && p.PackageName == "main" {
                return "main"
        }
        prefix := strings.Map(clean, *gccgoprefix)
        if prefix == "" {
                prefix = "go"
        }
        return prefix + "." + p.PackageName
}

// Call a function for each entry in an ast.FieldList, passing the
// index into the list, the name if any, and the type.
func forFieldList(fl *ast.FieldList, fn func(int, string, ast.Expr)) {
        if fl == nil {
                return
        }
        i := 0
        for _, r := range fl.List {
                if r.Names == nil {
                        fn(i, "", r.Type)
                        i++
                } else {
                        for _, n := range r.Names {
                                fn(i, n.Name, r.Type)
                                i++
                        }
                }
        }
}

func c(repr string, args ...interface{}) *TypeRepr {
        return &TypeRepr{repr, args}
}

// Map predeclared Go types to Type.
var goTypes = map[string]*Type{
        "bool":       {Size: 1, Align: 1, C: c("GoUint8")},
        "byte":       {Size: 1, Align: 1, C: c("GoUint8")},
        "int":        {Size: 0, Align: 0, C: c("GoInt")},
        "uint":       {Size: 0, Align: 0, C: c("GoUint")},
        "rune":       {Size: 4, Align: 4, C: c("GoInt32")},
        "int8":       {Size: 1, Align: 1, C: c("GoInt8")},
        "uint8":      {Size: 1, Align: 1, C: c("GoUint8")},
        "int16":      {Size: 2, Align: 2, C: c("GoInt16")},
        "uint16":     {Size: 2, Align: 2, C: c("GoUint16")},
        "int32":      {Size: 4, Align: 4, C: c("GoInt32")},
        "uint32":     {Size: 4, Align: 4, C: c("GoUint32")},
        "int64":      {Size: 8, Align: 8, C: c("GoInt64")},
        "uint64":     {Size: 8, Align: 8, C: c("GoUint64")},
        "float32":    {Size: 4, Align: 4, C: c("GoFloat32")},
        "float64":    {Size: 8, Align: 8, C: c("GoFloat64")},
        "complex64":  {Size: 8, Align: 4, C: c("GoComplex64")},
        "complex128": {Size: 16, Align: 8, C: c("GoComplex128")},
}

// Map an ast type to a Type.
func (p *Package) cgoType(e ast.Expr) *Type {
        switch t := e.(type) {
        case *ast.StarExpr:
                x := p.cgoType(t.X)
                return &Type{Size: p.PtrSize, Align: p.PtrSize, C: c("%s*", x.C)}
        case *ast.ArrayType:
                if t.Len == nil {
                        // Slice: pointer, len, cap.
                        return &Type{Size: p.PtrSize * 3, Align: p.PtrSize, C: c("GoSlice")}
                }
                // Non-slice array types are not supported.
        case *ast.StructType:
                // Not supported.
        case *ast.FuncType:
                return &Type{Size: p.PtrSize, Align: p.PtrSize, C: c("void*")}
        case *ast.InterfaceType:
                return &Type{Size: 2 * p.PtrSize, Align: p.PtrSize, C: c("GoInterface")}
        case *ast.MapType:
                return &Type{Size: p.PtrSize, Align: p.PtrSize, C: c("GoMap")}
        case *ast.ChanType:
                return &Type{Size: p.PtrSize, Align: p.PtrSize, C: c("GoChan")}
        case *ast.Ident:
                // Look up the type in the top level declarations.
                // TODO: Handle types defined within a 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.cgoType(ts.Type)
                                }
                        }
                }
                if def := typedef[t.Name]; def != nil {
                        return def
                }
                if t.Name == "uintptr" {
                        return &Type{Size: p.PtrSize, Align: p.PtrSize, C: c("GoUintptr")}
                }
                if t.Name == "string" {
                        // The string data is 1 pointer + 1 (pointer-sized) int.
                        return &Type{Size: 2 * p.PtrSize, Align: p.PtrSize, C: c("GoString")}
                }
                if t.Name == "error" {
                        return &Type{Size: 2 * p.PtrSize, Align: p.PtrSize, C: c("GoInterface")}
                }
                if r, ok := goTypes[t.Name]; ok {
                        if r.Size == 0 { // int or uint
                                rr := new(Type)
                                *rr = *r
                                rr.Size = p.IntSize
                                rr.Align = p.IntSize
                                r = rr
                        }
                        if r.Align > p.PtrSize {
                                r.Align = p.PtrSize
                        }
                        return r
                }
                error_(e.Pos(), "unrecognized Go type %s", t.Name)
                return &Type{Size: 4, Align: 4, C: c("int")}
        case *ast.SelectorExpr:
                id, ok := t.X.(*ast.Ident)
                if ok && id.Name == "unsafe" && t.Sel.Name == "Pointer" {
                        return &Type{Size: p.PtrSize, Align: p.PtrSize, C: c("void*")}
                }
        }
        error_(e.Pos(), "Go type not supported in export: %s", gofmt(e))
        return &Type{Size: 4, Align: 4, C: c("int")}
}

const gccProlog = `
#line 1 "cgo-gcc-prolog"
/*
  If x and y are not equal, the type will be invalid
  (have a negative array count) and an inscrutable error will come
  out of the compiler and hopefully mention "name".
*/
#define __cgo_compile_assert_eq(x, y, name) typedef char name[(x-y)*(x-y)*-2+1];

/* Check at compile time that the sizes we use match our expectations. */
#define __cgo_size_assert(t, n) __cgo_compile_assert_eq(sizeof(t), n, _cgo_sizeof_##t##_is_not_##n)

__cgo_size_assert(char, 1)
__cgo_size_assert(short, 2)
__cgo_size_assert(int, 4)
typedef long long __cgo_long_long;
__cgo_size_assert(__cgo_long_long, 8)
__cgo_size_assert(float, 4)
__cgo_size_assert(double, 8)

extern char* _cgo_topofstack(void);

#include <errno.h>
#include <string.h>
`

// Prologue defining TSAN functions in C.
const noTsanProlog = `
#define CGO_NO_SANITIZE_THREAD
#define _cgo_tsan_acquire()
#define _cgo_tsan_release()
`

// This must match the TSAN code in runtime/cgo/libcgo.h.
// This is used when the code is built with the C/C++ Thread SANitizer,
// which is not the same as the Go race detector.
// __tsan_acquire tells TSAN that we are acquiring a lock on a variable,
// in this case _cgo_sync. __tsan_release releases the lock.
// (There is no actual lock, we are just telling TSAN that there is.)
//
// When we call from Go to C we call _cgo_tsan_acquire.
// When the C function returns we call _cgo_tsan_release.
// Similarly, when C calls back into Go we call _cgo_tsan_release
// and then call _cgo_tsan_acquire when we return to C.
// These calls tell TSAN that there is a serialization point at the C call.
//
// This is necessary because TSAN, which is a C/C++ tool, can not see
// the synchronization in the Go code. Without these calls, when
// multiple goroutines call into C code, TSAN does not understand
// that the calls are properly synchronized on the Go side.
//
// To be clear, if the calls are not properly synchronized on the Go side,
// we will be hiding races. But when using TSAN on mixed Go C/C++ code
// it is more important to avoid false positives, which reduce confidence
// in the tool, than to avoid false negatives.
const yesTsanProlog = `
#line 1 "cgo-tsan-prolog"
#define CGO_NO_SANITIZE_THREAD __attribute__ ((no_sanitize_thread))

long long _cgo_sync __attribute__ ((common));

extern void __tsan_acquire(void*);
extern void __tsan_release(void*);

__attribute__ ((unused))
static void _cgo_tsan_acquire() {
        __tsan_acquire(&_cgo_sync);
}

__attribute__ ((unused))
static void _cgo_tsan_release() {
        __tsan_release(&_cgo_sync);
}
`

// Set to yesTsanProlog if we see -fsanitize=thread in the flags for gcc.
var tsanProlog = noTsanProlog

const builtinProlog = `
#line 1 "cgo-builtin-prolog"
#include <stddef.h> /* for ptrdiff_t and size_t below */

/* Define intgo when compiling with GCC.  */
typedef ptrdiff_t intgo;

typedef struct { const char *p; intgo n; } _GoString_;
typedef struct { char *p; intgo n; intgo c; } _GoBytes_;
_GoString_ GoString(char *p);
_GoString_ GoStringN(char *p, int l);
_GoBytes_ GoBytes(void *p, int n);
char *CString(_GoString_);
void *CBytes(_GoBytes_);
void *_CMalloc(size_t);

__attribute__ ((unused))
static size_t _GoStringLen(_GoString_ s) { return s.n; }

__attribute__ ((unused))
static const char *_GoStringPtr(_GoString_ s) { return s.p; }
`

const goProlog = `
//go:linkname _cgo_runtime_cgocall runtime.cgocall
func _cgo_runtime_cgocall(unsafe.Pointer, uintptr) int32

//go:linkname _cgo_runtime_cgocallback runtime.cgocallback
func _cgo_runtime_cgocallback(unsafe.Pointer, unsafe.Pointer, uintptr, uintptr)

//go:linkname _cgoCheckPointer runtime.cgoCheckPointer
func _cgoCheckPointer(interface{}, ...interface{})

//go:linkname _cgoCheckResult runtime.cgoCheckResult
func _cgoCheckResult(interface{})
`

const gccgoGoProlog = `
func _cgoCheckPointer(interface{}, ...interface{})

func _cgoCheckResult(interface{})
`

const goStringDef = `
//go:linkname _cgo_runtime_gostring runtime.gostring
func _cgo_runtime_gostring(*_Ctype_char) string

func _Cfunc_GoString(p *_Ctype_char) string {
        return _cgo_runtime_gostring(p)
}
`

const goStringNDef = `
//go:linkname _cgo_runtime_gostringn runtime.gostringn
func _cgo_runtime_gostringn(*_Ctype_char, int) string

func _Cfunc_GoStringN(p *_Ctype_char, l _Ctype_int) string {
        return _cgo_runtime_gostringn(p, int(l))
}
`

const goBytesDef = `
//go:linkname _cgo_runtime_gobytes runtime.gobytes
func _cgo_runtime_gobytes(unsafe.Pointer, int) []byte

func _Cfunc_GoBytes(p unsafe.Pointer, l _Ctype_int) []byte {
        return _cgo_runtime_gobytes(p, int(l))
}
`

const cStringDef = `
func _Cfunc_CString(s string) *_Ctype_char {
        p := _cgo_cmalloc(uint64(len(s)+1))
        pp := (*[1<<30]byte)(p)
        copy(pp[:], s)
        pp[len(s)] = 0
        return (*_Ctype_char)(p)
}
`

const cBytesDef = `
func _Cfunc_CBytes(b []byte) unsafe.Pointer {
        p := _cgo_cmalloc(uint64(len(b)))
        pp := (*[1<<30]byte)(p)
        copy(pp[:], b)
        return p
}
`

const cMallocDef = `
func _Cfunc__CMalloc(n _Ctype_size_t) unsafe.Pointer {
        return _cgo_cmalloc(uint64(n))
}
`

var builtinDefs = map[string]string{
        "GoString":  goStringDef,
        "GoStringN": goStringNDef,
        "GoBytes":   goBytesDef,
        "CString":   cStringDef,
        "CBytes":    cBytesDef,
        "_CMalloc":  cMallocDef,
}

// Definitions for C.malloc in Go and in C. We define it ourselves
// since we call it from functions we define, such as C.CString.
// Also, we have historically ensured that C.malloc does not return
// nil even for an allocation of 0.

const cMallocDefGo = `
//go:cgo_import_static _cgoPREFIX_Cfunc__Cmalloc
//go:linkname __cgofn__cgoPREFIX_Cfunc__Cmalloc _cgoPREFIX_Cfunc__Cmalloc
var __cgofn__cgoPREFIX_Cfunc__Cmalloc byte
var _cgoPREFIX_Cfunc__Cmalloc = unsafe.Pointer(&__cgofn__cgoPREFIX_Cfunc__Cmalloc)

//go:linkname runtime_throw runtime.throw
func runtime_throw(string)

//go:cgo_unsafe_args
func _cgo_cmalloc(p0 uint64) (r1 unsafe.Pointer) {
        _cgo_runtime_cgocall(_cgoPREFIX_Cfunc__Cmalloc, uintptr(unsafe.Pointer(&p0)))
        if r1 == nil {
                runtime_throw("runtime: C malloc failed")
        }
        return
}
`

// cMallocDefC defines the C version of C.malloc for the gc compiler.
// It is defined here because C.CString and friends need a definition.
// We define it by hand, rather than simply inventing a reference to
// C.malloc, because <stdlib.h> may not have been included.
// This is approximately what writeOutputFunc would generate, but
// skips the cgo_topofstack code (which is only needed if the C code
// calls back into Go). This also avoids returning nil for an
// allocation of 0 bytes.
const cMallocDefC = `
CGO_NO_SANITIZE_THREAD
void _cgoPREFIX_Cfunc__Cmalloc(void *v) {
        struct {
                unsigned long long p0;
                void *r1;
        } PACKED *a = v;
        void *ret;
        _cgo_tsan_acquire();
        ret = malloc(a->p0);
        if (ret == 0 && a->p0 == 0) {
                ret = malloc(1);
        }
        a->r1 = ret;
        _cgo_tsan_release();
}
`

func (p *Package) cPrologGccgo() string {
        return strings.Replace(strings.Replace(cPrologGccgo, "PREFIX", cPrefix, -1),
                "GCCGOSYMBOLPREF", p.gccgoSymbolPrefix(), -1)
}

const cPrologGccgo = `
#line 1 "cgo-c-prolog-gccgo"
#include <stdint.h>
#include <stdlib.h>
#include <string.h>

typedef unsigned char byte;
typedef intptr_t intgo;

struct __go_string {
        const unsigned char *__data;
        intgo __length;
};

typedef struct __go_open_array {
        void* __values;
        intgo __count;
        intgo __capacity;
} Slice;

struct __go_string __go_byte_array_to_string(const void* p, intgo len);
struct __go_open_array __go_string_to_byte_array (struct __go_string str);

const char *_cgoPREFIX_Cfunc_CString(struct __go_string s) {
        char *p = malloc(s.__length+1);
        memmove(p, s.__data, s.__length);
        p[s.__length] = 0;
        return p;
}

void *_cgoPREFIX_Cfunc_CBytes(struct __go_open_array b) {
        char *p = malloc(b.__count);
        memmove(p, b.__values, b.__count);
        return p;
}

struct __go_string _cgoPREFIX_Cfunc_GoString(char *p) {
        intgo len = (p != NULL) ? strlen(p) : 0;
        return __go_byte_array_to_string(p, len);
}

struct __go_string _cgoPREFIX_Cfunc_GoStringN(char *p, int32_t n) {
        return __go_byte_array_to_string(p, n);
}

Slice _cgoPREFIX_Cfunc_GoBytes(char *p, int32_t n) {
        struct __go_string s = { (const unsigned char *)p, n };
        return __go_string_to_byte_array(s);
}

extern void runtime_throw(const char *);
void *_cgoPREFIX_Cfunc__CMalloc(size_t n) {
        void *p = malloc(n);
        if(p == NULL && n == 0)
                p = malloc(1);
        if(p == NULL)
                runtime_throw("runtime: C malloc failed");
        return p;
}

struct __go_type_descriptor;
typedef struct __go_empty_interface {
        const struct __go_type_descriptor *__type_descriptor;
        void *__object;
} Eface;

extern void runtimeCgoCheckPointer(Eface, Slice)
        __asm__("runtime.cgoCheckPointer")
        __attribute__((weak));

extern void localCgoCheckPointer(Eface, Slice)
        __asm__("GCCGOSYMBOLPREF._cgoCheckPointer");

void localCgoCheckPointer(Eface ptr, Slice args) {
        if(runtimeCgoCheckPointer) {
                runtimeCgoCheckPointer(ptr, args);
        }
}

extern void runtimeCgoCheckResult(Eface)
        __asm__("runtime.cgoCheckResult")
        __attribute__((weak));

extern void localCgoCheckResult(Eface)
        __asm__("GCCGOSYMBOLPREF._cgoCheckResult");

void localCgoCheckResult(Eface val) {
        if(runtimeCgoCheckResult) {
                runtimeCgoCheckResult(val);
        }
}
`

// builtinExportProlog is a shorter version of builtinProlog,
// to be put into the _cgo_export.h file.
// For historical reasons we can't use builtinProlog in _cgo_export.h,
// because _cgo_export.h defines GoString as a struct while builtinProlog
// defines it as a function. We don't change this to avoid unnecessarily
// breaking existing code.
const builtinExportProlog = `
#line 1 "cgo-builtin-prolog"

#include <stddef.h> /* for ptrdiff_t below */

#ifndef GO_CGO_EXPORT_PROLOGUE_H
#define GO_CGO_EXPORT_PROLOGUE_H

typedef ptrdiff_t intgo;

typedef struct { const char *p; intgo n; } _GoString_;

#endif
`

func (p *Package) gccExportHeaderProlog() string {
        return strings.Replace(gccExportHeaderProlog, "GOINTBITS", fmt.Sprint(8*p.IntSize), -1)
}

const gccExportHeaderProlog = `
/* Start of boilerplate cgo prologue.  */
#line 1 "cgo-gcc-export-header-prolog"

#ifndef GO_CGO_PROLOGUE_H
#define GO_CGO_PROLOGUE_H

typedef signed char GoInt8;
typedef unsigned char GoUint8;
typedef short GoInt16;
typedef unsigned short GoUint16;
typedef int GoInt32;
typedef unsigned int GoUint32;
typedef long long GoInt64;
typedef unsigned long long GoUint64;
typedef GoIntGOINTBITS GoInt;
typedef GoUintGOINTBITS GoUint;
typedef __SIZE_TYPE__ GoUintptr;
typedef float GoFloat32;
typedef double GoFloat64;
typedef float _Complex GoComplex64;
typedef double _Complex GoComplex128;

/*
  static assertion to make sure the file is being used on architecture
  at least with matching size of GoInt.
*/
typedef char _check_for_GOINTBITS_bit_pointer_matching_GoInt[sizeof(void*)==GOINTBITS/8 ? 1:-1];

typedef _GoString_ GoString;
typedef void *GoMap;
typedef void *GoChan;
typedef struct { void *t; void *v; } GoInterface;
typedef struct { void *data; GoInt len; GoInt cap; } GoSlice;

#endif

/* End of boilerplate cgo prologue.  */

#ifdef __cplusplus
extern "C" {
#endif
`

// gccExportHeaderEpilog goes at the end of the generated header file.
const gccExportHeaderEpilog = `
#ifdef __cplusplus
}
#endif
`

// gccgoExportFileProlog is written to the _cgo_export.c file when
// using gccgo.
// We use weak declarations, and test the addresses, so that this code
// works with older versions of gccgo.
const gccgoExportFileProlog = `
#line 1 "cgo-gccgo-export-file-prolog"
extern _Bool runtime_iscgo __attribute__ ((weak));

static void GoInit(void) __attribute__ ((constructor));
static void GoInit(void) {
        if(&runtime_iscgo)
                runtime_iscgo = 1;
}

extern __SIZE_TYPE__ _cgo_wait_runtime_init_done() __attribute__ ((weak));
`