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// Copyright 2016 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 gccgoexportdata provides functions for reading export data
// files containing type information produced by the gccgo compiler.
// This package is a stop-gap until such time as gccgo uses the same
// export data format as gc; see Go issue 17573. Once that occurs, this
// package will be deprecated and eventually deleted.
package gccgoexportdata
// TODO(adonovan): add Find, Write, Importer to the API,
// for symmetry with gcexportdata.
import (
// CompilerInfo executes the specified gccgo compiler and returns
// information about it: its version (e.g. "4.8.0"), its target triple
// (e.g. "x86_64-unknown-linux-gnu"), and the list of directories it
// searches to find standard packages. The given arguments are passed
// directly to calls to the specified gccgo compiler.
func CompilerInfo(gccgo string, args ...string) (version, triple string, dirs []string, err error) {
var inst gccgoimporter.GccgoInstallation
err = inst.InitFromDriver(gccgo, args...)
if err == nil {
version = inst.GccVersion
triple = inst.TargetTriple
dirs = inst.SearchPaths()
// NewReader returns a reader for the export data section of an object
// (.o) or archive (.a) file read from r.
func NewReader(r io.Reader) (io.Reader, error) {
data, err := ioutil.ReadAll(r)
if err != nil {
return nil, err
// If the file is an archive, extract the first section.
const archiveMagic = "!<arch>\n"
if bytes.HasPrefix(data, []byte(archiveMagic)) {
section, err := firstSection(data[len(archiveMagic):])
if err != nil {
return nil, err
data = section
// Data contains an ELF file with a .go_export section.
// ELF magic number is "\x7fELF".
ef, err := elf.NewFile(bytes.NewReader(data))
if err != nil {
return nil, err
sec := ef.Section(".go_export")
if sec == nil {
return nil, fmt.Errorf("no .go_export section")
return sec.Open(), nil
// firstSection returns the contents of the first regular file in an ELF
// archive (, ยง7.2).
func firstSection(a []byte) ([]byte, error) {
for len(a) >= 60 {
var hdr []byte
hdr, a = a[:60], a[60:]
name := strings.TrimSpace(string(hdr[:16]))
sizeStr := string(hdr[48:58])
size, err := strconv.Atoi(strings.TrimSpace(sizeStr))
if err != nil {
return nil, fmt.Errorf("invalid size: %q", sizeStr)
if len(a) < size {
return nil, fmt.Errorf("invalid section size: %d", size)
// The payload is padded to an even number of bytes.
var payload []byte
payload, a = a[:size], a[size+size&1:]
// Skip special files:
// "/" archive symbol table
// "/SYM64/" archive symbol table on e.g. s390x
// "//" archive string table (if any filename is >15 bytes)
if name == "/" || name == "/SYM64/" || name == "//" {
return payload, nil
return nil, fmt.Errorf("archive has no regular sections")
// Read reads export data from in, decodes it, and returns type
// information for the package.
// The package name is specified by path.
// The FileSet parameter is currently unused but exists for symmetry
// with gcexportdata.
// Read may inspect and add to the imports map to ensure that references
// within the export data to other packages are consistent. The caller
// must ensure that imports[path] does not exist, or exists but is
// incomplete (see types.Package.Complete), and Read inserts the
// resulting package into this map entry.
// On return, the state of the reader is undefined.
func Read(in io.Reader, _ *token.FileSet, imports map[string]*types.Package, path string) (*types.Package, error) {
return gccgoimporter.Parse(in, imports, path)