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// The `replace-buildid` tool is used to replace a build ID in an ELF binary with a new build ID.
// Note that this tool is extremely naive: it simply takes the old input ID as string, verifies
// that this ID is contained in the binary exactly once, and then replaces it. It has no knowledge
// about ELF binaries whatsoever.
//
// This tool is mainly used to replace our static GNU build ID we set in our Makefile with a
// derived build ID without having to build binaries twice.
package main
import (
"bytes"
"encoding/hex"
"flag"
"fmt"
"io"
"os"
"path/filepath"
"gitlab.com/gitlab-org/gitaly/v16/internal/helper/perm"
)
func main() {
var inputPath, outputPath, inputBuildID, outputBuildID string
flag.StringVar(&inputPath, "input", "", "path to the binary whose GNU build ID should be replaced")
flag.StringVar(&outputPath, "output", "", "path whether the resulting binary should be placed")
flag.StringVar(&inputBuildID, "input-build-id", "", "static build ID to replace")
flag.StringVar(&outputBuildID, "output-build-id", "", "new build ID to replace old value with")
flag.Parse()
if err := replaceBuildID(inputPath, outputPath, inputBuildID, outputBuildID); err != nil {
fmt.Fprintf(os.Stderr, "%s\n", err)
os.Exit(1)
}
}
func replaceBuildID(inputPath, outputPath, inputBuildID, outputBuildID string) error {
if inputPath == "" {
return fmt.Errorf("missing input path")
}
if outputPath == "" {
return fmt.Errorf("missing output path")
}
if inputBuildID == "" {
return fmt.Errorf("missing output path")
}
if outputBuildID == "" {
return fmt.Errorf("missing output path")
}
if flag.NArg() > 0 {
return fmt.Errorf("extra arguments")
}
inputBuildIDDecoded, err := hex.DecodeString(inputBuildID)
if err != nil {
return fmt.Errorf("decoding input build ID: %w", err)
}
outputBuildIDDecoded, err := hex.DecodeString(outputBuildID)
if err != nil {
return fmt.Errorf("decoding output build ID: %w", err)
}
if len(inputBuildIDDecoded) != len(outputBuildIDDecoded) {
return fmt.Errorf("input and output build IDs do not have the same length")
}
data, err := readAndReplace(inputPath, inputBuildIDDecoded, outputBuildIDDecoded)
if err != nil {
return fmt.Errorf("could not replace build ID: %w", err)
}
if err := writeBinary(outputPath, data); err != nil {
return fmt.Errorf("writing binary: %w", err)
}
return nil
}
func readAndReplace(binaryPath string, inputBuildID, outputBuildID []byte) ([]byte, error) {
inputFile, err := os.Open(binaryPath)
if err != nil {
return nil, fmt.Errorf("opening input file: %w", err)
}
defer inputFile.Close()
data, err := io.ReadAll(inputFile)
if err != nil {
return nil, fmt.Errorf("reading input file: %w", err)
}
if occurrences := bytes.Count(data, inputBuildID); occurrences != 1 {
return nil, fmt.Errorf("exactly one match for old build ID expected, got %d", occurrences)
}
return bytes.ReplaceAll(data, inputBuildID, outputBuildID), nil
}
func writeBinary(binaryPath string, contents []byte) error {
f, err := os.CreateTemp(filepath.Dir(binaryPath), filepath.Base(binaryPath))
if err != nil {
return fmt.Errorf("could not create binary: %w", err)
}
defer func() {
_ = os.RemoveAll(f.Name())
f.Close()
}()
if err := f.Chmod(perm.SharedExecutable); err != nil {
return fmt.Errorf("could not change permissions: %w", err)
}
if _, err := io.Copy(f, bytes.NewReader(contents)); err != nil {
return fmt.Errorf("could not write binary: %w", err)
}
if err := f.Close(); err != nil {
return fmt.Errorf("could not close binary: %w", err)
}
if err := os.Rename(f.Name(), binaryPath); err != nil {
return fmt.Errorf("could not move binary into place: %w", err)
}
return nil
}
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