Dump the contents of the NOTE sections of Android native libraries: .note.android.ident and .note.gnu.build-id.

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 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() -> Path | None:
    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: Path | None) -> 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  /path/to/libxyz.so

Output:

----------ABI INFO----------
ABI_ANDROID_API: 21
ABI_NDK_VERSION: r25
ABI_NDK_BUILD_NUMBER: 8775105
----------BUILD ID----------
c6cb00844756c8d0504c8c15dd4340bc

The original file can be found in NDK source repo of AOSP: https://cs.android.com/android/platform/superproject/+/master-ndk:ndk/parse_elfnote.py