1// Copyright 2017 The Go Authors. All rights reserved.
2// Use of this source code is governed by a BSD-style
3// license that can be found in the LICENSE file.
4
5package pprof
6
7import (
8	"encoding/binary"
9	"errors"
10	"fmt"
11	"os"
12)
13
14var (
15	errBadELF    = errors.New("malformed ELF binary")
16	errNoBuildID = errors.New("no NT_GNU_BUILD_ID found in ELF binary")
17)
18
19// elfBuildID returns the GNU build ID of the named ELF binary,
20// without introducing a dependency on debug/elf and its dependencies.
21func elfBuildID(file string) (string, error) {
22	buf := make([]byte, 256)
23	f, err := os.Open(file)
24	if err != nil {
25		return "", err
26	}
27	defer f.Close()
28
29	if _, err := f.ReadAt(buf[:64], 0); err != nil {
30		return "", err
31	}
32
33	// ELF file begins with \x7F E L F.
34	if buf[0] != 0x7F || buf[1] != 'E' || buf[2] != 'L' || buf[3] != 'F' {
35		return "", errBadELF
36	}
37
38	var byteOrder binary.ByteOrder
39	switch buf[5] {
40	default:
41		return "", errBadELF
42	case 1: // little-endian
43		byteOrder = binary.LittleEndian
44	case 2: // big-endian
45		byteOrder = binary.BigEndian
46	}
47
48	var shnum int
49	var shoff, shentsize int64
50	switch buf[4] {
51	default:
52		return "", errBadELF
53	case 1: // 32-bit file header
54		shoff = int64(byteOrder.Uint32(buf[32:]))
55		shentsize = int64(byteOrder.Uint16(buf[46:]))
56		if shentsize != 40 {
57			return "", errBadELF
58		}
59		shnum = int(byteOrder.Uint16(buf[48:]))
60	case 2: // 64-bit file header
61		shoff = int64(byteOrder.Uint64(buf[40:]))
62		shentsize = int64(byteOrder.Uint16(buf[58:]))
63		if shentsize != 64 {
64			return "", errBadELF
65		}
66		shnum = int(byteOrder.Uint16(buf[60:]))
67	}
68
69	for i := 0; i < shnum; i++ {
70		if _, err := f.ReadAt(buf[:shentsize], shoff+int64(i)*shentsize); err != nil {
71			return "", err
72		}
73		if typ := byteOrder.Uint32(buf[4:]); typ != 7 { // SHT_NOTE
74			continue
75		}
76		var off, size int64
77		if shentsize == 40 {
78			// 32-bit section header
79			off = int64(byteOrder.Uint32(buf[16:]))
80			size = int64(byteOrder.Uint32(buf[20:]))
81		} else {
82			// 64-bit section header
83			off = int64(byteOrder.Uint64(buf[24:]))
84			size = int64(byteOrder.Uint64(buf[32:]))
85		}
86		size += off
87		for off < size {
88			if _, err := f.ReadAt(buf[:16], off); err != nil { // room for header + name GNU\x00
89				return "", err
90			}
91			nameSize := int(byteOrder.Uint32(buf[0:]))
92			descSize := int(byteOrder.Uint32(buf[4:]))
93			noteType := int(byteOrder.Uint32(buf[8:]))
94			descOff := off + int64(12+(nameSize+3)&^3)
95			off = descOff + int64((descSize+3)&^3)
96			if nameSize != 4 || noteType != 3 || buf[12] != 'G' || buf[13] != 'N' || buf[14] != 'U' || buf[15] != '\x00' { // want name GNU\x00 type 3 (NT_GNU_BUILD_ID)
97				continue
98			}
99			if descSize > len(buf) {
100				return "", errBadELF
101			}
102			if _, err := f.ReadAt(buf[:descSize], descOff); err != nil {
103				return "", err
104			}
105			return fmt.Sprintf("%x", buf[:descSize]), nil
106		}
107	}
108	return "", errNoBuildID
109}
110