Add a symbols_map tool for extracting identifiers from elf and r8 files
Add a symbols_map tool that can extract an identifiying hash from
and elf file or an r8 dictionary. The tool writes the hash to a
textproto, and also supports a merge mode to combine textprotos into
a output file for inclusion in the build artifacts.
Bug: 218888599
Test: m dist
Test: symbols_map_test.go
Change-Id: Icd3ed6e5510e058c92d97c78759e7a4cfcdbb6ca
diff --git a/cmd/symbols_map/elf.go b/cmd/symbols_map/elf.go
new file mode 100644
index 0000000..b38896a
--- /dev/null
+++ b/cmd/symbols_map/elf.go
@@ -0,0 +1,95 @@
+// 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"
+ "fmt"
+ "io"
+)
+
+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 := elf.Open(filename)
+ if err != nil {
+ return "", fmt.Errorf("failed to open %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
+}