android的 NOTE Section：.note.android.ident
.note.android.ident section 是由这个 ndk/sources/crt/crtbrand.S 汇编代码文件引入的，其中放了包括 android_api、ndk_version和 ndk_build_number 三段信息。
1.readelf 的 string-dump功能将其dump出来：
readelf --string-dump=.note.android.ident $ANDROID_NDK_HOME/toolchains/llvm/prebuilt/darwin-x86_64/sysroot/usr/lib/aarch64-linux-android/libc++_shared.so
String dump of section '.note.android.ident':
[ c] Android
[ 18] r21e
[ 58] 7075529
readelf --hex-dump=.note.android.ident $ANDROID_NDK_HOME/toolchains/llvm/prebuilt/darwin-x86_64/sysroot/usr/lib/aarch64-linux-android/libc++_shared.so
Hex dump of section '.note.android.ident':
0x000d59fc 08000000 84000000 01000000 416e6472 ............Andr
0x000d5a0c 6f696400 15000000 72323165 00000000 oid.....r21e....
0x000d5a1c 00000000 00000000 00000000 00000000 ................
0x000d5a2c 00000000 00000000 00000000 00000000 ................
0x000d5a3c 00000000 00000000 00000000 00000000 ................
0x000d5a4c 00000000 00000000 37303735 35323900 ........7075529.
0x000d5a5c 00000000 00000000 00000000 00000000 ................
0x000d5a6c 00000000 00000000 00000000 00000000 ................
0x000d5a7c 00000000 00000000 00000000 00000000 ................
0x000d5a8c 00000000 00000000
printf "%d\n" 0x15
21
2. objcopy将.note.android.ident整个copy到一个文件中，后续再写一个简单的脚本按NOTE Section数据结构解析处理即可。
$ANDROID_NDK_HOME/ndk-which --abi arm64-v8a objcopy
/Users/xxx/Library/Android/sdk/ndk/21.4.7075529/prebuilt/darwin-x86_64/bin/../../../toolchains/llvm/prebuilt/darwin-x86_64/bin/aarch64-linux-android-objcopy
alias objcopy=$ANDROID_NDK_HOME/toolchains/llvm/prebuilt/darwin-x86_64/bin/llvm-objcopy
objcopy --dump-section=.note.android.ident=libc++_shared.so.android.note $ANDROID_NDK_HOME/toolchains/llvm/prebuilt/darwin-x86_64/sysroot/usr/lib/aarch64-linux-android/libc++_shared.so
ls -la
total 14616
drwxr-xr-x@ 5 forevermeng staff 160 8 16 13:54 .
drwxr-xr-x@ 4 forevermeng staff 128 8 14 21:26 ..
-rw-r--r-- 1 forevermeng staff 152 8 16 13:54 libc++_shared.so.android.note
-rw-r--r--@ 1 forevermeng staff 5500080 8 14 20:58 libcallbackhandler.so
-rw-r--r--@ 1 forevermeng staff 1977680 8 14 20:58 libchromium_android_linker.so
3.xxd解析note
xxd libc++_shared.so.android.note
00000000: 0800 0000 8400 0000 0100 0000 416e 6472 ............Andr
00000010: 6f69 6400 1500 0000 7232 3165 0000 0000 oid.....r21e....
00000020: 0000 0000 0000 0000 0000 0000 0000 0000 ................
00000030: 0000 0000 0000 0000 0000 0000 0000 0000 ................
00000040: 0000 0000 0000 0000 0000 0000 0000 0000 ................
00000050: 0000 0000 0000 0000 3730 3735 3532 3900 ........7075529.
00000060: 0000 0000 0000 0000 0000 0000 0000 0000 ................
00000070: 0000 0000 0000 0000 0000 0000 0000 0000 ................
00000080: 0000 0000 0000 0000 0000 0000 0000 0000 ................
00000090: 0000 0000 0000 0000
4. ndk/parse_elfnote.py， 可以直接用来解析 .note.android.ident
https://android.googlesource.com/platform/ndk/+/refs/heads/main/ndk/
#
# Dump the contents of the .note.android.ident section, a NOTE section
# embedded into Android binaries. See here:
# - master: ndk/sources/crt/crtbrand.S
# - master: bionic/libc/arch-common/bionic/crtbrand.S
# - NDK before r14: development/ndk/platforms/common/src/crtbrand.c
#
# Note sections can also be dumped with `readelf -n`.
#
https://android.googlesource.com/platform/ndk/+/refs/heads/main/parse_elfnote.py
4.1 parse_elfnote.py
#!/usr/bin/env python3
#
# Copyright (C) 2016 The Android Open Source Project
#
# 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.
#
#
# Dump the contents of the .note.android.ident section, a NOTE section
# embedded into Android binaries. See here:
# - master: ndk/sources/crt/crtbrand.S
# - master: bionic/libc/arch-common/bionic/crtbrand.S
# - NDK before r14: development/ndk/platforms/common/src/crtbrand.c
#
# Note sections can also be dumped with `readelf -n`.
#
from __future__ import division, print_function
import argparse
import logging
import shutil
import struct
import subprocess
import sys
import os
from typing import Optional
from pathlib import Path
SEC_NAME = ".note.android.ident"
NDK_RESERVED_SIZE = 64
def logger():
"""Returns the module logger."""
return logging.getLogger(__name__)
def round_up_to_nearest(val, step):
"""Round an integer, val, to the next multiple of a positive integer,
step."""
return (val + (step - 1)) // step * step
class StructParser:
def __init__(self, buf):
self.buf = buf
self.pos = 0
@property
def remaining(self):
return len(self.buf) - self.pos
@property
def empty(self):
return self.remaining == 0
def read(self, read_len):
buf = self.buf[self.pos: read_len + self.pos]
self.pos += read_len
return buf
def read_struct(self, fmt, kind):
fmt = struct.Struct(fmt)
if self.remaining < fmt.size:
sys.exit("error: {} was truncated".format(kind))
return fmt.unpack(self.read(fmt.size))
def iterate_notes(sec_data):
sec_data = StructParser(sec_data)
while not sec_data.empty:
(namesz, descsz, kind) = sec_data.read_struct("<III", "note header")
(name, desc) = sec_data.read_struct(
"{}s{}s".format(
round_up_to_nearest(namesz, 4), round_up_to_nearest(descsz, 4)
),
"note body",
)
name = name[:namesz]
if len(name) > 0:
if name[-1:] == b"\0":
name = name[:-1]
else:
logger().warning("note name %s isn't NUL-terminated", name)
yield name, kind, desc[:descsz]
def dump_android_ident_note(note):
note = StructParser(note)
(android_api,) = note.read_struct("<I", "note descriptor")
print("ABI_ANDROID_API: {}".format(android_api))
if note.empty:
return
# Binaries generated by NDK r14 and later have these extra fields. Platform
# binaries and binaries generated by older NDKs don't.
ndk_version, ndk_build_number = note.read_struct(
"{sz}s{sz}s".format(sz=NDK_RESERVED_SIZE), "note descriptor"
)
ndk_version = ndk_version.decode("utf-8")
ndk_build_number = ndk_build_number.decode("utf-8")
print("ABI_NDK_VERSION: {}".format(ndk_version.rstrip("\0")))
print("ABI_NDK_BUILD_NUMBER: {}".format(ndk_build_number.rstrip("\0")))
if not note.empty:
logger().warning("excess data at end of descriptor")
# Get the offset to a section from the output of readelf
def get_section_pos(readelf: Path, sec_name: str, file_path: str) -> tuple[int, int]:
cmd = [readelf, "--sections", "-W", file_path]
output = subprocess.check_output(cmd)
lines = output.decode("utf-8").splitlines()
for line in lines:
logger().debug('Checking line for "%s": %s', sec_name, line)
# Looking for a line like the following (all whitespace of unknown
# width).
#
# [ 8] .note.android.ident NOTE 00000000 0000ec 000098 00 A 0 0 4
#
# The only column that might have internal whitespace is the first one.
# Since we don't care about it, remove the head of the string until the
# closing bracket, then split.
if "]" not in line:
continue
line = line[line.index("]") + 1:]
sections = line.split()
if len(sections) < 5 or sec_name != sections[0]:
continue
off = int(sections[3], 16)
size = int(sections[4], 16)
return (off, size)
sys.exit("error: failed to find section: {}".format(sec_name))
def get_ndk_install_path() -> Optional[Path]:
ndk = os.getenv("ANDROID_NDK_HOME")
if ndk is not None:
return Path(ndk)
ndk = os.getenv("ANDROID_NDK")
if ndk is not None:
return Path(ndk)
android_sdk = os.getenv("ANDROID_HOME")
ndk_versioin = os.getenv("ANDROID_NDK_VERSION")
if android_sdk is not None and ndk_versioin is not None:
return Path(android_sdk) / "ndk" / ndk_versioin
return None
def readelf_from_ndk(ndk: Path) -> Path:
if not ndk.exists():
raise ValueError(f"--ndk is {ndk} but that path does not exist")
prebuilt_dir = ndk / "toolchains/llvm/prebuilt"
bins = list(prebuilt_dir.glob("*/bin"))
if not bins:
raise RuntimeError(f"{prebuilt_dir} contains no */bin")
if len(bins) != 1:
raise RuntimeError(f"{prebuilt_dir} contains more than one */bin")
bin_dir = bins[0]
readelf = (bin_dir / "llvm-readelf").with_suffix(
".exe" if sys.platform == "win32" else ""
)
if not readelf.exists():
raise RuntimeError(f"{readelf} does not exist")
return readelf
def find_readelf(ndk: Optional[Path]) -> Path:
if ndk is not None:
return readelf_from_ndk(ndk)
if (install_path := get_ndk_install_path()) is not None:
return readelf_from_ndk(install_path)
if (readelf := shutil.which("llvm-readelf")) is not None:
return Path(readelf)
if (readelf := shutil.which("readelf")) is not None:
return Path(readelf)
raise RuntimeError(
"Could not find llvm-readelf or readelf in PATH and could find find any NDK"
)
def parse_args():
"""Parses command line arguments."""
parser = argparse.ArgumentParser()
parser.add_argument("file_path", help="path of the ELF file with embedded ABI tags")
parser.add_argument(
"-v",
"--verbose",
dest="verbosity",
action="count",
default=0,
help="Increase logging verbosity.",
)
parser.add_argument(
"--ndk",
type=Path,
help="Path to the NDK. If given, the NDK's llvm-readelf will be used.",
)
return parser.parse_args()
def main():
args = parse_args()
if args.verbosity == 1:
logging.basicConfig(level=logging.INFO)
elif args.verbosity >= 2:
logging.basicConfig(level=logging.DEBUG)
else:
logging.basicConfig()
file_path = args.file_path
readelf = find_readelf(args.ndk)
with open(file_path, "rb") as obj_file:
(sec_off, sec_size) = get_section_pos(readelf, SEC_NAME, file_path)
obj_file.seek(sec_off)
sec_data = obj_file.read(sec_size)
if len(sec_data) != sec_size:
sys.exit("error: could not read {} section".format(SEC_NAME))
print("----------ABI INFO----------")
if len(sec_data) == 0:
logger().warning("%s section is empty", SEC_NAME)
for name, kind, desc in iterate_notes(sec_data):
if (name, kind) == (b"Android", 1):
dump_android_ident_note(desc)
else:
logger().warning(
"unrecognized note (name %s, type %d)", repr(name), kind
)
#############################
(sec_off, sec_size) = get_section_pos(readelf, ".note.gnu.build-id", file_path)
obj_file.seek(sec_off)
sec_data = obj_file.read(sec_size)
print("----------BUILD ID----------")
if len(sec_data) == 0:
logger().warning(".note.gnu.build-id section is empty")
for name, kind, desc in iterate_notes(sec_data):
if (name, kind) == (b"GNU", 3):
print("".join(format(x, "02x") for x in desc))
else:
logger().warning(
"unrecognized note (name %s, type %d)", repr(name), kind
)
if __name__ == "__main__":
main()
python3 parse_elfnote.py core-1.38.0/jni/arm64-v8a/libarcore_sdk_c.so
----------ABI INFO----------
ABI_ANDROID_API: 21
ABI_NDK_VERSION: r25
ABI_NDK_BUILD_NUMBER: 8775105
----------BUILD ID----------
50263bfe58995b3bef5fa5e659315d0f
4.2例子：静态连接libc++_shared.so查看 ndkversion
python3 parse_elfnote.py output/Android/arm64-v8a/libxxx.so
----------ABI INFO----------
ABI_ANDROID_API: 21
ABI_NDK_VERSION: r25b
ABI_NDK_BUILD_NUMBER: 8937393
----------BUILD ID----------
5fbce0048d153596f17e8154bccf17155e5e8f67