// Copyright 2017 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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package pprof
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import (
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"encoding/binary"
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"errors"
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"fmt"
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"os"
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)
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var (
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errBadELF = errors.New("malformed ELF binary")
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errNoBuildID = errors.New("no NT_GNU_BUILD_ID found in ELF binary")
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)
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// elfBuildID returns the GNU build ID of the named ELF binary,
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// without introducing a dependency on debug/elf and its dependencies.
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func elfBuildID(file string) (string, error) {
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buf := make([]byte, 256)
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f, err := os.Open(file)
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if err != nil {
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return "", err
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}
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defer f.Close()
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if _, err := f.ReadAt(buf[:64], 0); err != nil {
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return "", err
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}
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// ELF file begins with \x7F E L F.
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if buf[0] != 0x7F || buf[1] != 'E' || buf[2] != 'L' || buf[3] != 'F' {
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return "", errBadELF
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}
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var byteOrder binary.ByteOrder
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switch buf[5] {
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default:
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return "", errBadELF
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case 1: // little-endian
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byteOrder = binary.LittleEndian
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case 2: // big-endian
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byteOrder = binary.BigEndian
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}
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var shnum int
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var shoff, shentsize int64
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switch buf[4] {
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default:
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return "", errBadELF
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case 1: // 32-bit file header
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shoff = int64(byteOrder.Uint32(buf[32:]))
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shentsize = int64(byteOrder.Uint16(buf[46:]))
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if shentsize != 40 {
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return "", errBadELF
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}
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shnum = int(byteOrder.Uint16(buf[48:]))
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case 2: // 64-bit file header
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shoff = int64(byteOrder.Uint64(buf[40:]))
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shentsize = int64(byteOrder.Uint16(buf[58:]))
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if shentsize != 64 {
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return "", errBadELF
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}
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shnum = int(byteOrder.Uint16(buf[60:]))
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}
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for i := 0; i < shnum; i++ {
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if _, err := f.ReadAt(buf[:shentsize], shoff+int64(i)*shentsize); err != nil {
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return "", err
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}
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if typ := byteOrder.Uint32(buf[4:]); typ != 7 { // SHT_NOTE
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continue
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}
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var off, size int64
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if shentsize == 40 {
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// 32-bit section header
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off = int64(byteOrder.Uint32(buf[16:]))
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size = int64(byteOrder.Uint32(buf[20:]))
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} else {
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// 64-bit section header
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off = int64(byteOrder.Uint64(buf[24:]))
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size = int64(byteOrder.Uint64(buf[32:]))
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}
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size += off
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for off < size {
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if _, err := f.ReadAt(buf[:16], off); err != nil { // room for header + name GNU\x00
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return "", err
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}
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nameSize := int(byteOrder.Uint32(buf[0:]))
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descSize := int(byteOrder.Uint32(buf[4:]))
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noteType := int(byteOrder.Uint32(buf[8:]))
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descOff := off + int64(12+(nameSize+3)&^3)
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off = descOff + int64((descSize+3)&^3)
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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)
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continue
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}
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if descSize > len(buf) {
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return "", errBadELF
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}
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if _, err := f.ReadAt(buf[:descSize], descOff); err != nil {
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return "", err
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}
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return fmt.Sprintf("%x", buf[:descSize]), nil
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}
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}
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return "", errNoBuildID
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}
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