github.com/ethanhsieh/snapd@v0.0.0-20210615102523-3db9b8e4edc5/osutil/buildid.go (about)

     1  // -*- Mode: Go; indent-tabs-mode: t -*-
     2  
     3  /*
     4   * Copyright (C) 2017 Canonical Ltd
     5   *
     6   * This program is free software: you can redistribute it and/or modify
     7   * it under the terms of the GNU General Public License version 3 as
     8   * published by the Free Software Foundation.
     9   *
    10   * This program is distributed in the hope that it will be useful,
    11   * but WITHOUT ANY WARRANTY; without even the implied warranty of
    12   * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
    13   * GNU General Public License for more details.
    14   *
    15   * You should have received a copy of the GNU General Public License
    16   * along with this program.  If not, see <http://www.gnu.org/licenses/>.
    17   *
    18   */
    19  
    20  package osutil
    21  
    22  import (
    23  	"debug/elf"
    24  	"encoding/binary"
    25  	"encoding/hex"
    26  	"errors"
    27  	"os"
    28  )
    29  
    30  // ErrNoBuildID is returned when an executable does not contain a Build-ID
    31  var ErrNoBuildID = errors.New("executable does not contain a build ID")
    32  
    33  type elfNoteHeader struct {
    34  	Namesz uint32
    35  	Descsz uint32
    36  	Type   uint32
    37  }
    38  
    39  const (
    40  	gnuElfNote = "GNU\x00"
    41  	gnuHdrType = 3
    42  	goElfNote  = "Go\x00\x00"
    43  	goHdrType  = 4
    44  )
    45  
    46  // ReadBuildID returns the build ID of a given binary. GNU BuildID is is
    47  // preferred over Go BuildID. Returns an error when neither is found.
    48  func ReadBuildID(fname string) (string, error) {
    49  	if buildId, err := readGenericBuildID(fname, gnuElfNote, gnuHdrType); err == nil {
    50  		return buildId, nil
    51  	}
    52  	return readGenericBuildID(fname, goElfNote, goHdrType)
    53  }
    54  
    55  func readGenericBuildID(fname, elfNote string, hdrType uint32) (string, error) {
    56  	// Open the designated ELF file
    57  	f, err := elf.Open(fname)
    58  	if err != nil {
    59  		return "", err
    60  	}
    61  	defer f.Close()
    62  
    63  	for _, section := range f.Sections {
    64  
    65  		// We are looking for note sections
    66  		if section.Type != elf.SHT_NOTE {
    67  			continue
    68  		}
    69  
    70  		// NOTE: this is a ReadSeeker so no need to close it
    71  		sr := section.Open()
    72  		sr.Seek(0, os.SEEK_SET)
    73  
    74  		// Read the ELF Note header
    75  		nHdr := new(elfNoteHeader)
    76  		if err := binary.Read(sr, f.ByteOrder, nHdr); err != nil {
    77  			return "", err
    78  		}
    79  
    80  		// We are looking for a specific type of note
    81  		if nHdr.Type != hdrType {
    82  			continue
    83  		}
    84  
    85  		// Read note name
    86  		noteName := make([]byte, nHdr.Namesz)
    87  		if err := binary.Read(sr, f.ByteOrder, noteName); err != nil {
    88  			return "", err
    89  		}
    90  
    91  		// We are only interested in GNU build IDs
    92  		if string(noteName) != elfNote {
    93  			continue
    94  		}
    95  
    96  		// Read note data
    97  		noteData := make([]byte, nHdr.Descsz)
    98  		if err := binary.Read(sr, f.ByteOrder, noteData); err != nil {
    99  			return "", err
   100  		}
   101  
   102  		// Return the first build-id we manage to find
   103  		return hex.EncodeToString(noteData), nil
   104  	}
   105  	return "", ErrNoBuildID
   106  }
   107  
   108  // MyBuildID return the build-id of the currently running executable
   109  func MyBuildID() (string, error) {
   110  	exe, err := osReadlink("/proc/self/exe")
   111  	if err != nil {
   112  		return "", err
   113  	}
   114  
   115  	return ReadBuildID(exe)
   116  }