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- // Copyright 2022 Google Inc. All rights reserved.
- //
- // Licensed under the Apache License, Version 2.0 (the "License");
- // you may not use this file except in compliance with the License.
- // You may obtain a copy of the License at
- //
- // http://www.apache.org/licenses/LICENSE-2.0
- //
- // Unless required by applicable law or agreed to in writing, software
- // distributed under the License is distributed on an "AS IS" BASIS,
- // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
- // See the License for the specific language governing permissions and
- // limitations under the License.
- package main
- import (
- "debug/elf"
- "encoding/binary"
- "encoding/hex"
- "errors"
- "fmt"
- "io"
- "os"
- )
- const gnuBuildID = "GNU\x00"
- // elfIdentifier extracts the elf build ID from an elf file. If allowMissing is true it returns
- // an empty identifier if the file exists but the build ID note does not.
- func elfIdentifier(filename string, allowMissing bool) (string, error) {
- f, err := os.Open(filename)
- if err != nil {
- return "", fmt.Errorf("failed to open %s: %w", filename, err)
- }
- defer f.Close()
- return elfIdentifierFromReaderAt(f, filename, allowMissing)
- }
- // elfIdentifierFromReaderAt extracts the elf build ID from a ReaderAt. If allowMissing is true it
- // returns an empty identifier if the file exists but the build ID note does not.
- func elfIdentifierFromReaderAt(r io.ReaderAt, filename string, allowMissing bool) (string, error) {
- f, err := elf.NewFile(r)
- if err != nil {
- if allowMissing {
- if errors.Is(err, io.EOF) || errors.Is(err, io.ErrUnexpectedEOF) {
- return "", nil
- }
- if _, ok := err.(*elf.FormatError); ok {
- // The file was not an elf file.
- return "", nil
- }
- }
- return "", fmt.Errorf("failed to parse elf file %s: %w", filename, err)
- }
- defer f.Close()
- buildIDNote := f.Section(".note.gnu.build-id")
- if buildIDNote == nil {
- if allowMissing {
- return "", nil
- }
- return "", fmt.Errorf("failed to find .note.gnu.build-id in %s", filename)
- }
- buildIDs, err := readNote(buildIDNote.Open(), f.ByteOrder)
- if err != nil {
- return "", fmt.Errorf("failed to read .note.gnu.build-id: %w", err)
- }
- for name, desc := range buildIDs {
- if name == gnuBuildID {
- return hex.EncodeToString(desc), nil
- }
- }
- return "", nil
- }
- // readNote reads the contents of a note section, returning it as a map from name to descriptor.
- func readNote(note io.Reader, byteOrder binary.ByteOrder) (map[string][]byte, error) {
- var noteHeader struct {
- Namesz uint32
- Descsz uint32
- Type uint32
- }
- notes := make(map[string][]byte)
- for {
- err := binary.Read(note, byteOrder, ¬eHeader)
- if err != nil {
- if err == io.EOF {
- return notes, nil
- }
- return nil, fmt.Errorf("failed to read note header: %w", err)
- }
- nameBuf := make([]byte, align4(noteHeader.Namesz))
- err = binary.Read(note, byteOrder, &nameBuf)
- if err != nil {
- return nil, fmt.Errorf("failed to read note name: %w", err)
- }
- name := string(nameBuf[:noteHeader.Namesz])
- descBuf := make([]byte, align4(noteHeader.Descsz))
- err = binary.Read(note, byteOrder, &descBuf)
- if err != nil {
- return nil, fmt.Errorf("failed to read note desc: %w", err)
- }
- notes[name] = descBuf[:noteHeader.Descsz]
- }
- }
- // align4 rounds the input up to the next multiple of 4.
- func align4(i uint32) uint32 {
- return (i + 3) &^ 3
- }
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