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// Copyright 2015 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 buildid
import (
"bytes"
"debug/elf"
"debug/macho"
"encoding/binary"
"fmt"
"io"
"io/fs"
"os"
)
func readAligned4(r io.Reader, sz int32) ([]byte, error) {
full := (sz + 3) &^ 3
data := make([]byte, full)
_, err := io.ReadFull(r, data)
if err != nil {
return nil, err
}
data = data[:sz]
return data, nil
}
func ReadELFNote(filename, name string, typ int32) ([]byte, error) {
f, err := elf.Open(filename)
if err != nil {
return nil, err
}
defer f.Close()
for _, sect := range f.Sections {
if sect.Type != elf.SHT_NOTE {
continue
}
r := sect.Open()
for {
var namesize, descsize, noteType int32
err = binary.Read(r, f.ByteOrder, &namesize)
if err != nil {
if err == io.EOF {
break
}
return nil, fmt.Errorf("read namesize failed: %v", err)
}
err = binary.Read(r, f.ByteOrder, &descsize)
if err != nil {
return nil, fmt.Errorf("read descsize failed: %v", err)
}
err = binary.Read(r, f.ByteOrder, ¬eType)
if err != nil {
return nil, fmt.Errorf("read type failed: %v", err)
}
noteName, err := readAligned4(r, namesize)
if err != nil {
return nil, fmt.Errorf("read name failed: %v", err)
}
desc, err := readAligned4(r, descsize)
if err != nil {
return nil, fmt.Errorf("read desc failed: %v", err)
}
if name == string(noteName) && typ == noteType {
return desc, nil
}
}
}
return nil, nil
}
var elfGoNote = []byte("Go\x00\x00")
var elfGNUNote = []byte("GNU\x00")
// The Go build ID is stored in a note described by an ELF PT_NOTE prog
// header. The caller has already opened filename, to get f, and read
// at least 4 kB out, in data.
func readELF(name string, f *os.File, data []byte) (buildid string, err error) {
// Assume the note content is in the data, already read.
// Rewrite the ELF header to set shnum to 0, so that we can pass
// the data to elf.NewFile and it will decode the Prog list but not
// try to read the section headers and the string table from disk.
// That's a waste of I/O when all we care about is the Prog list
// and the one ELF note.
switch elf.Class(data[elf.EI_CLASS]) {
case elf.ELFCLASS32:
data[48] = 0
data[49] = 0
case elf.ELFCLASS64:
data[60] = 0
data[61] = 0
}
const elfGoBuildIDTag = 4
const gnuBuildIDTag = 3
ef, err := elf.NewFile(bytes.NewReader(data))
if err != nil {
return "", &fs.PathError{Path: name, Op: "parse", Err: err}
}
var gnu string
for _, p := range ef.Progs {
if p.Type != elf.PT_NOTE || p.Filesz < 16 {
continue
}
var note []byte
if p.Off+p.Filesz < uint64(len(data)) {
note = data[p.Off : p.Off+p.Filesz]
} else {
// For some linkers, such as the Solaris linker,
// the buildid may not be found in data (which
// likely contains the first 16kB of the file)
// or even the first few megabytes of the file
// due to differences in note segment placement;
// in that case, extract the note data manually.
_, err = f.Seek(int64(p.Off), io.SeekStart)
if err != nil {
return "", err
}
note = make([]byte, p.Filesz)
_, err = io.ReadFull(f, note)
if err != nil {
return "", err
}
}
filesz := p.Filesz
off := p.Off
for filesz >= 16 {
nameSize := ef.ByteOrder.Uint32(note)
valSize := ef.ByteOrder.Uint32(note[4:])
tag := ef.ByteOrder.Uint32(note[8:])
nname := note[12:16]
if nameSize == 4 && 16+valSize <= uint32(len(note)) && tag == elfGoBuildIDTag && bytes.Equal(nname, elfGoNote) {
return string(note[16 : 16+valSize]), nil
}
if nameSize == 4 && 16+valSize <= uint32(len(note)) && tag == gnuBuildIDTag && bytes.Equal(nname, elfGNUNote) {
gnu = string(note[16 : 16+valSize])
}
nameSize = (nameSize + 3) &^ 3
valSize = (valSize + 3) &^ 3
notesz := uint64(12 + nameSize + valSize)
if filesz <= notesz {
break
}
off += notesz
align := p.Align
alignedOff := (off + align - 1) &^ (align - 1)
notesz += alignedOff - off
off = alignedOff
filesz -= notesz
note = note[notesz:]
}
}
// If we didn't find a Go note, use a GNU note if available.
// This is what gccgo uses.
if gnu != "" {
return gnu, nil
}
// No note. Treat as successful but build ID empty.
return "", nil
}
// The Go build ID is stored at the beginning of the Mach-O __text segment.
// The caller has already opened filename, to get f, and read a few kB out, in data.
// Sadly, that's not guaranteed to hold the note, because there is an arbitrary amount
// of other junk placed in the file ahead of the main text.
func readMacho(name string, f *os.File, data []byte) (buildid string, err error) {
// If the data we want has already been read, don't worry about Mach-O parsing.
// This is both an optimization and a hedge against the Mach-O parsing failing
// in the future due to, for example, the name of the __text section changing.
if b, err := readRaw(name, data); b != "" && err == nil {
return b, err
}
mf, err := macho.NewFile(f)
if err != nil {
return "", &fs.PathError{Path: name, Op: "parse", Err: err}
}
sect := mf.Section("__text")
if sect == nil {
// Every binary has a __text section. Something is wrong.
return "", &fs.PathError{Path: name, Op: "parse", Err: fmt.Errorf("cannot find __text section")}
}
// It should be in the first few bytes, but read a lot just in case,
// especially given our past problems on OS X with the build ID moving.
// There shouldn't be much difference between reading 4kB and 32kB:
// the hard part is getting to the data, not transferring it.
n := sect.Size
if n > uint64(readSize) {
n = uint64(readSize)
}
buf := make([]byte, n)
if _, err := f.ReadAt(buf, int64(sect.Offset)); err != nil {
return "", err
}
return readRaw(name, buf)
}
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