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// Copyright 2024 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 elf
import (
"io/fs"
"os"
"path/filepath"
"strings"
"sync"
"time"
)
func UpdateBuildIdDir(path string) error {
path = filepath.Clean(path)
buildIdPath := path + "/.build-id"
// Collect the list of files and build-id symlinks. If the symlinks are
// up to date (newer than the symbol files), there is nothing to do.
var buildIdFiles, symbolFiles []string
var buildIdMtime, symbolsMtime time.Time
filepath.WalkDir(path, func(path string, entry fs.DirEntry, err error) error {
if entry == nil || entry.IsDir() {
return nil
}
info, err := entry.Info()
if err != nil {
return err
}
mtime := info.ModTime()
if strings.HasPrefix(path, buildIdPath) {
if buildIdMtime.Compare(mtime) < 0 {
buildIdMtime = mtime
}
buildIdFiles = append(buildIdFiles, path)
} else {
if symbolsMtime.Compare(mtime) < 0 {
symbolsMtime = mtime
}
symbolFiles = append(symbolFiles, path)
}
return nil
})
if symbolsMtime.Compare(buildIdMtime) < 0 {
return nil
}
// Collect build-id -> file mapping from ELF files in the symbols directory.
concurrency := 8
done := make(chan error)
buildIdToFile := make(map[string]string)
var mu sync.Mutex
for i := 0; i != concurrency; i++ {
go func(paths []string) {
for _, path := range paths {
id, err := Identifier(path, true)
if err != nil {
done <- err
return
}
if id == "" {
continue
}
mu.Lock()
oldPath := buildIdToFile[id]
if oldPath == "" || oldPath > path {
buildIdToFile[id] = path
}
mu.Unlock()
}
done <- nil
}(symbolFiles[len(symbolFiles)*i/concurrency : len(symbolFiles)*(i+1)/concurrency])
}
// Collect previously generated build-id -> file mapping from the .build-id directory.
// We will use this for incremental updates. If we see anything in the .build-id
// directory that we did not expect, we'll delete it and start over.
prevBuildIdToFile := make(map[string]string)
out:
for _, buildIdFile := range buildIdFiles {
if !strings.HasSuffix(buildIdFile, ".debug") {
prevBuildIdToFile = nil
break
}
buildId := buildIdFile[len(buildIdPath)+1 : len(buildIdFile)-6]
for i, ch := range buildId {
if i == 2 {
if ch != '/' {
prevBuildIdToFile = nil
break out
}
} else {
if (ch < '0' || ch > '9') && (ch < 'a' || ch > 'f') {
prevBuildIdToFile = nil
break out
}
}
}
target, err := os.Readlink(buildIdFile)
if err != nil || !strings.HasPrefix(target, "../../") {
prevBuildIdToFile = nil
break
}
prevBuildIdToFile[buildId[0:2]+buildId[3:]] = path + target[5:]
}
if prevBuildIdToFile == nil {
err := os.RemoveAll(buildIdPath)
if err != nil {
return err
}
prevBuildIdToFile = make(map[string]string)
}
// Wait for build-id collection from ELF files to finish.
for i := 0; i != concurrency; i++ {
err := <-done
if err != nil {
return err
}
}
// Delete old symlinks.
for id, _ := range prevBuildIdToFile {
if buildIdToFile[id] == "" {
symlinkDir := buildIdPath + "/" + id[:2]
symlinkPath := symlinkDir + "/" + id[2:] + ".debug"
if err := os.Remove(symlinkPath); err != nil {
return err
}
}
}
// Add new symlinks and update changed symlinks.
for id, path := range buildIdToFile {
prevPath := prevBuildIdToFile[id]
if prevPath == path {
continue
}
symlinkDir := buildIdPath + "/" + id[:2]
symlinkPath := symlinkDir + "/" + id[2:] + ".debug"
if prevPath == "" {
if err := os.MkdirAll(symlinkDir, 0755); err != nil {
return err
}
} else {
if err := os.Remove(symlinkPath); err != nil {
return err
}
}
target, err := filepath.Rel(symlinkDir, path)
if err != nil {
return err
}
if err := os.Symlink(target, symlinkPath); err != nil {
return err
}
}
return nil
}
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