--- /dev/null
+// Copyright 2017 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 loader
+
+import (
+ "bytes"
+ "debug/elf"
+ "errors"
+ "fmt"
+ "io"
+ "os"
+ "strconv"
+ "strings"
+)
+
+var errBuildIDMalformed = fmt.Errorf("malformed object file")
+
+var (
+ bangArch = []byte("!<arch>")
+ pkgdef = []byte("__.PKGDEF")
+ goobject = []byte("go object ")
+ buildid = []byte("build id ")
+)
+
+// ReadFile reads the build ID from an archive or executable file.
+func ReadFile(name string) (id string, err error) {
+ f, err := os.Open(name)
+ if err != nil {
+ return "", err
+ }
+ defer f.Close()
+
+ buf := make([]byte, 8)
+ if _, err := f.ReadAt(buf, 0); err != nil {
+ return "", err
+ }
+ if string(buf) != "!<arch>\n" {
+ if string(buf) == "<bigaf>\n" {
+ return "", errors.New("unsupported")
+ }
+ return readBinary(name, f)
+ }
+
+ // Read just enough of the target to fetch the build ID.
+ // The archive is expected to look like:
+ //
+ // !<arch>
+ // __.PKGDEF 0 0 0 644 7955 `
+ // go object darwin amd64 devel X:none
+ // build id "b41e5c45250e25c9fd5e9f9a1de7857ea0d41224"
+ //
+ // The variable-sized strings are GOOS, GOARCH, and the experiment list (X:none).
+ // Reading the first 1024 bytes should be plenty.
+ data := make([]byte, 1024)
+ n, err := io.ReadFull(f, data)
+ if err != nil && n == 0 {
+ return "", err
+ }
+
+ tryGccgo := func() (string, error) {
+ return readGccgoArchive(name, f)
+ }
+
+ // Archive header.
+ for i := 0; ; i++ { // returns during i==3
+ j := bytes.IndexByte(data, '\n')
+ if j < 0 {
+ return tryGccgo()
+ }
+ line := data[:j]
+ data = data[j+1:]
+ switch i {
+ case 0:
+ if !bytes.Equal(line, bangArch) {
+ return tryGccgo()
+ }
+ case 1:
+ if !bytes.HasPrefix(line, pkgdef) {
+ return tryGccgo()
+ }
+ case 2:
+ if !bytes.HasPrefix(line, goobject) {
+ return tryGccgo()
+ }
+ case 3:
+ if !bytes.HasPrefix(line, buildid) {
+ // Found the object header, just doesn't have a build id line.
+ // Treat as successful, with empty build id.
+ return "", nil
+ }
+ id, err := strconv.Unquote(string(line[len(buildid):]))
+ if err != nil {
+ return tryGccgo()
+ }
+ return id, nil
+ }
+ }
+}
+
+// readGccgoArchive tries to parse the archive as a standard Unix
+// archive file, and fetch the build ID from the _buildid.o entry.
+// The _buildid.o entry is written by (*Builder).gccgoBuildIDELFFile
+// in cmd/go/internal/work/exec.go.
+func readGccgoArchive(name string, f *os.File) (string, error) {
+ bad := func() (string, error) {
+ return "", &os.PathError{Op: "parse", Path: name, Err: errBuildIDMalformed}
+ }
+
+ off := int64(8)
+ for {
+ if _, err := f.Seek(off, io.SeekStart); err != nil {
+ return "", err
+ }
+
+ // TODO(iant): Make a debug/ar package, and use it
+ // here and in cmd/link.
+ var hdr [60]byte
+ if _, err := io.ReadFull(f, hdr[:]); err != nil {
+ if err == io.EOF {
+ // No more entries, no build ID.
+ return "", nil
+ }
+ return "", err
+ }
+ off += 60
+
+ sizeStr := strings.TrimSpace(string(hdr[48:58]))
+ size, err := strconv.ParseInt(sizeStr, 0, 64)
+ if err != nil {
+ return bad()
+ }
+
+ name := strings.TrimSpace(string(hdr[:16]))
+ if name == "_buildid.o/" {
+ sr := io.NewSectionReader(f, off, size)
+ e, err := elf.NewFile(sr)
+ if err != nil {
+ return bad()
+ }
+ s := e.Section(".go.buildid")
+ if s == nil {
+ return bad()
+ }
+ data, err := s.Data()
+ if err != nil {
+ return bad()
+ }
+ return string(data), nil
+ }
+
+ off += size
+ if off&1 != 0 {
+ off++
+ }
+ }
+}
+
+var (
+ goBuildPrefix = []byte("\xff Go build ID: \"")
+ goBuildEnd = []byte("\"\n \xff")
+
+ elfPrefix = []byte("\x7fELF")
+
+ machoPrefixes = [][]byte{
+ {0xfe, 0xed, 0xfa, 0xce},
+ {0xfe, 0xed, 0xfa, 0xcf},
+ {0xce, 0xfa, 0xed, 0xfe},
+ {0xcf, 0xfa, 0xed, 0xfe},
+ }
+)
+
+var readSize = 32 * 1024 // changed for testing
+
+// readBinary reads the build ID from a binary.
+//
+// ELF binaries store the build ID in a proper PT_NOTE section.
+//
+// Other binary formats are not so flexible. For those, the linker
+// stores the build ID as non-instruction bytes at the very beginning
+// of the text segment, which should appear near the beginning
+// of the file. This is clumsy but fairly portable. Custom locations
+// can be added for other binary types as needed, like we did for ELF.
+func readBinary(name string, f *os.File) (id string, err error) {
+ // Read the first 32 kB of the binary file.
+ // That should be enough to find the build ID.
+ // In ELF files, the build ID is in the leading headers,
+ // which are typically less than 4 kB, not to mention 32 kB.
+ // In Mach-O files, there's no limit, so we have to parse the file.
+ // On other systems, we're trying to read enough that
+ // we get the beginning of the text segment in the read.
+ // The offset where the text segment begins in a hello
+ // world compiled for each different object format today:
+ //
+ // Plan 9: 0x20
+ // Windows: 0x600
+ //
+ data := make([]byte, readSize)
+ _, err = io.ReadFull(f, data)
+ if err == io.ErrUnexpectedEOF {
+ err = nil
+ }
+ if err != nil {
+ return "", err
+ }
+
+ if bytes.HasPrefix(data, elfPrefix) {
+ return readELF(name, f, data)
+ }
+ for _, m := range machoPrefixes {
+ if bytes.HasPrefix(data, m) {
+ return readMacho(name, f, data)
+ }
+ }
+ return readRaw(name, data)
+}
+
+// readRaw finds the raw build ID stored in text segment data.
+func readRaw(name string, data []byte) (id string, err error) {
+ i := bytes.Index(data, goBuildPrefix)
+ if i < 0 {
+ // Missing. Treat as successful but build ID empty.
+ return "", nil
+ }
+
+ j := bytes.Index(data[i+len(goBuildPrefix):], goBuildEnd)
+ if j < 0 {
+ return "", &os.PathError{Op: "parse", Path: name, Err: errBuildIDMalformed}
+ }
+
+ quoted := data[i+len(goBuildPrefix)-1 : i+len(goBuildPrefix)+j+1]
+ id, err = strconv.Unquote(string(quoted))
+ if err != nil {
+ return "", &os.PathError{Op: "parse", Path: name, Err: errBuildIDMalformed}
+ }
+ return id, nil
+}
projects / dotfiles / .git / blobdiff