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fix(crashlytics,android): fix an issue with deobfuscating flavored builds #18085

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fix(crashlytics,android): fix an issue with deobfuscating flavored bu…
Lyokone Mar 6, 2026
1d27409
format
Lyokone Mar 6, 2026
c2de355
improve ELFBuildIdReader so it handles AAB as well
Lyokone Mar 6, 2026
3b73e5f
format
Lyokone Mar 6, 2026
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398 changes: 398 additions & 0 deletions ...ytics/android/src/main/java/io/flutter/plugins/firebase/crashlytics/ElfBuildIdReader.java
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// Copyright 2024 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

package io.flutter.plugins.firebase.crashlytics;

import android.content.Context;
import android.util.Log;
import java.io.File;
import java.io.InputStream;
import java.io.RandomAccessFile;
import java.nio.ByteBuffer;
import java.nio.ByteOrder;
import java.util.Enumeration;
import java.util.zip.ZipEntry;
import java.util.zip.ZipFile;

/**
* Reads the ELF build ID from libapp.so at runtime.
*
* <p>The Firebase CLI's {@code crashlytics:symbols:upload} command uses the ELF build ID (from the
* {@code .note.gnu.build-id} section) when uploading symbols. To ensure Crashlytics can match crash
* reports to uploaded symbols, the plugin must report the same ELF build ID rather than the Dart
* VM's internal snapshot build ID (which may differ, especially for AAB + flavor builds).
*/
final class ElfBuildIdReader {

private static final String TAG = "FLTFirebaseCrashlytics";

private static final byte[] ELF_MAGIC = {0x7f, 'E', 'L', 'F'};
private static final int ELFCLASS64 = 2;
private static final int PT_NOTE = 4;
private static final int NT_GNU_BUILD_ID = 3;
private static final String GNU_NOTE_NAME = "GNU";

private ElfBuildIdReader() {}

/**
* Reads the ELF build ID from libapp.so.
*
* <p>First checks the native library directory (for devices that extract native libs). If not
* found there, reads libapp.so from inside the APK (for devices with extractNativeLibs=false).
*
* @return the build ID as a lowercase hex string, or {@code null} if it cannot be read.
*/
static String readBuildId(Context context) {
try {
// Try extracted native library first.
String nativeLibDir = context.getApplicationInfo().nativeLibraryDir;
File libApp = new File(nativeLibDir, "libapp.so");
if (libApp.exists()) {
return readBuildIdFromElf(libApp);
}

// Fall back to reading from inside the APK (or split APKs for AAB installs).
return readBuildIdFromApk(context);
} catch (Exception e) {
Log.d(TAG, "Could not read ELF build ID from libapp.so", e);
return null;
}
}

/**
* Reads the ELF build ID from libapp.so stored inside the APK. On newer Android versions, native
* libraries may not be extracted to the filesystem.
*/
private static String readBuildIdFromApk(Context context) throws Exception {
// Check the base APK first.
String result = readBuildIdFromZip(context.getApplicationInfo().sourceDir);
if (result != null) {
return result;
}

// For AAB installs, libapp.so is in a split APK (e.g., split_config.arm64_v8a.apk).
String[] splitDirs = context.getApplicationInfo().splitSourceDirs;
if (splitDirs != null) {
for (String splitDir : splitDirs) {
result = readBuildIdFromZip(splitDir);
if (result != null) {
return result;
}
}
}
return null;
}

private static String readBuildIdFromZip(String apkPath) throws Exception {
try (ZipFile zipFile = new ZipFile(apkPath)) {
Enumeration<? extends ZipEntry> entries = zipFile.entries();
while (entries.hasMoreElements()) {
ZipEntry entry = entries.nextElement();
if (entry.getName().endsWith("/libapp.so")) {
try (InputStream is = zipFile.getInputStream(entry)) {
byte[] elfData = new byte[(int) entry.getSize()];
int offset = 0;
while (offset < elfData.length) {
int read = is.read(elfData, offset, elfData.length - offset);
if (read < 0) break;
offset += read;
}
return readBuildIdFromBytes(elfData);
}
}
}
}
return null;
}

private static String readBuildIdFromElf(File elfFile) throws Exception {
try (RandomAccessFile raf = new RandomAccessFile(elfFile, "r")) {
return readBuildIdFromRaf(raf);
}
}

private static String readBuildIdFromBytes(byte[] data) {
try {
ByteBuffer buf = ByteBuffer.wrap(data);

// Verify ELF magic bytes.
for (int i = 0; i < 4; i++) {
if (buf.get() != ELF_MAGIC[i]) {
return null;
}
}

int elfClass = buf.get() & 0xFF; // 1 = 32-bit, 2 = 64-bit
boolean is64 = elfClass == ELFCLASS64;

int dataEncoding = buf.get() & 0xFF; // 1 = little-endian, 2 = big-endian
ByteOrder order = dataEncoding == 1 ? ByteOrder.LITTLE_ENDIAN : ByteOrder.BIG_ENDIAN;
buf.order(order);

if (is64) {
return readBuildIdFromBuffer64(buf);
} else {
return readBuildIdFromBuffer32(buf);
}
} catch (Exception e) {
Log.d(TAG, "Could not parse ELF from APK", e);
return null;
}
}

private static String readBuildIdFromBuffer64(ByteBuffer buf) {
// e_phoff is at offset 32 in the 64-bit ELF header.
buf.position(32);
long phoff = buf.getLong();

// e_phentsize is at offset 54, e_phnum at offset 56.
buf.position(54);
int phentsize = buf.getShort() & 0xFFFF;
int phnum = buf.getShort() & 0xFFFF;

for (int i = 0; i < phnum; i++) {
int phdr = (int) (phoff + (long) i * phentsize);
buf.position(phdr);
int type = buf.getInt();
if (type == PT_NOTE) {
// p_offset is at phdr + 8, p_filesz at phdr + 32 for 64-bit.
buf.position(phdr + 8);
long noteOffset = buf.getLong();
buf.position(phdr + 32);
long noteSize = buf.getLong();

String buildId = findGnuBuildIdInBuffer(buf, noteOffset, noteSize);
if (buildId != null) {
return buildId;
}
}
}
return null;
}

private static String readBuildIdFromBuffer32(ByteBuffer buf) {
// e_phoff is at offset 28 in the 32-bit ELF header.
buf.position(28);
long phoff = buf.getInt() & 0xFFFFFFFFL;

// e_phentsize is at offset 42, e_phnum at offset 44.
buf.position(42);
int phentsize = buf.getShort() & 0xFFFF;
int phnum = buf.getShort() & 0xFFFF;

for (int i = 0; i < phnum; i++) {
int phdr = (int) (phoff + (long) i * phentsize);
buf.position(phdr);
int type = buf.getInt();
if (type == PT_NOTE) {
// p_offset is at phdr + 4, p_filesz at phdr + 16 for 32-bit.
buf.position(phdr + 4);
long noteOffset = buf.getInt() & 0xFFFFFFFFL;
buf.position(phdr + 16);
long noteSize = buf.getInt() & 0xFFFFFFFFL;

String buildId = findGnuBuildIdInBuffer(buf, noteOffset, noteSize);
if (buildId != null) {
return buildId;
}
}
}
return null;
}

private static String findGnuBuildIdInBuffer(ByteBuffer buf, long offset, long size) {
long end = offset + size;
long pos = offset;

while (pos + 12 <= end) {
buf.position((int) pos);
int namesz = buf.getInt();
int descsz = buf.getInt();
int type = buf.getInt();

if (namesz < 0 || descsz < 0 || namesz > 256) {
break;
}

int nameAligned = align4(namesz);
long descPos = pos + 12 + nameAligned;

if (namesz > 0 && type == NT_GNU_BUILD_ID && descPos + descsz <= end) {
byte[] nameBytes = new byte[namesz];
buf.get(nameBytes);
String name =
new String(
nameBytes, 0, Math.max(0, namesz - 1), java.nio.charset.StandardCharsets.US_ASCII);

if (GNU_NOTE_NAME.equals(name) && descsz > 0) {
buf.position((int) descPos);
byte[] desc = new byte[descsz];
buf.get(desc);
return bytesToHex(desc);
}
}

pos = descPos + align4(descsz);
}
return null;
}

private static String readBuildIdFromRaf(RandomAccessFile raf) throws Exception {
// Verify ELF magic bytes.
byte[] magic = new byte[4];
raf.readFully(magic);
for (int i = 0; i < 4; i++) {
if (magic[i] != ELF_MAGIC[i]) {
return null;
}
}

int elfClass = raf.read(); // 1 = 32-bit, 2 = 64-bit
boolean is64 = elfClass == ELFCLASS64;

int dataEncoding = raf.read(); // 1 = little-endian, 2 = big-endian
ByteOrder order = dataEncoding == 1 ? ByteOrder.LITTLE_ENDIAN : ByteOrder.BIG_ENDIAN;

if (is64) {
return readBuildIdFromElf64(raf, order);
} else {
return readBuildIdFromElf32(raf, order);
}
}

private static String readBuildIdFromElf64(RandomAccessFile raf, ByteOrder order)
throws Exception {
// e_phoff is at offset 32 in the 64-bit ELF header.
raf.seek(32);
long phoff = readLong(raf, order);

// e_phentsize is at offset 54, e_phnum at offset 56.
raf.seek(54);
int phentsize = readUnsignedShort(raf, order);
int phnum = readUnsignedShort(raf, order);

for (int i = 0; i < phnum; i++) {
long phdr = phoff + (long) i * phentsize;
raf.seek(phdr);
int type = readInt(raf, order);
if (type == PT_NOTE) {
// p_offset is at phdr + 8, p_filesz at phdr + 32 for 64-bit.
raf.seek(phdr + 8);
long noteOffset = readLong(raf, order);
raf.seek(phdr + 32);
long noteSize = readLong(raf, order);

String buildId = findGnuBuildId(raf, noteOffset, noteSize, order);
if (buildId != null) {
return buildId;
}
}
}
return null;
}

private static String readBuildIdFromElf32(RandomAccessFile raf, ByteOrder order)
throws Exception {
// e_phoff is at offset 28 in the 32-bit ELF header.
raf.seek(28);
long phoff = readInt(raf, order) & 0xFFFFFFFFL;

// e_phentsize is at offset 42, e_phnum at offset 44.
raf.seek(42);
int phentsize = readUnsignedShort(raf, order);
int phnum = readUnsignedShort(raf, order);

for (int i = 0; i < phnum; i++) {
long phdr = phoff + (long) i * phentsize;
raf.seek(phdr);
int type = readInt(raf, order);
if (type == PT_NOTE) {
// p_offset is at phdr + 4, p_filesz at phdr + 16 for 32-bit.
raf.seek(phdr + 4);
long noteOffset = readInt(raf, order) & 0xFFFFFFFFL;
raf.seek(phdr + 16);
long noteSize = readInt(raf, order) & 0xFFFFFFFFL;

String buildId = findGnuBuildId(raf, noteOffset, noteSize, order);
if (buildId != null) {
return buildId;
}
}
}
return null;
}

/**
* Searches a PT_NOTE segment for the GNU build ID note.
*
* <p>Note format: namesz (4) | descsz (4) | type (4) | name (aligned to 4) | desc (aligned to 4)
*/
private static String findGnuBuildId(
RandomAccessFile raf, long offset, long size, ByteOrder order) throws Exception {
long end = offset + size;
long pos = offset;

while (pos + 12 <= end) {
raf.seek(pos);
int namesz = readInt(raf, order);
int descsz = readInt(raf, order);
int type = readInt(raf, order);

if (namesz < 0 || descsz < 0 || namesz > 256) {
break;
}

int nameAligned = align4(namesz);
long descPos = pos + 12 + nameAligned;

if (namesz > 0 && type == NT_GNU_BUILD_ID && descPos + descsz <= end) {
byte[] nameBytes = new byte[namesz];
raf.readFully(nameBytes);
// Name is null-terminated.
String name =
namesz > 0 ? new String(nameBytes, 0, Math.max(0, namesz - 1), "US-ASCII") : "";

if (GNU_NOTE_NAME.equals(name) && descsz > 0) {
raf.seek(descPos);
byte[] desc = new byte[descsz];
raf.readFully(desc);
return bytesToHex(desc);
}
}

pos = descPos + align4(descsz);
}
return null;
}

private static int align4(int value) {
return (value + 3) & ~3;
}

private static int readInt(RandomAccessFile raf, ByteOrder order) throws Exception {
byte[] buf = new byte[4];
raf.readFully(buf);
return ByteBuffer.wrap(buf).order(order).getInt();
}

private static long readLong(RandomAccessFile raf, ByteOrder order) throws Exception {
byte[] buf = new byte[8];
raf.readFully(buf);
return ByteBuffer.wrap(buf).order(order).getLong();
}

private static int readUnsignedShort(RandomAccessFile raf, ByteOrder order) throws Exception {
byte[] buf = new byte[2];
raf.readFully(buf);
return ByteBuffer.wrap(buf).order(order).getShort() & 0xFFFF;
}

private static String bytesToHex(byte[] bytes) {
StringBuilder sb = new StringBuilder(bytes.length * 2);
for (byte b : bytes) {
sb.append(String.format("%02x", b & 0xff));
}
return sb.toString();
}
}
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