diff options
Diffstat (limited to 'third_party/libwebrtc/build/extract_partition.py')
| -rwxr-xr-x | third_party/libwebrtc/build/extract_partition.py | 174 |
1 files changed, 174 insertions, 0 deletions
diff --git a/third_party/libwebrtc/build/extract_partition.py b/third_party/libwebrtc/build/extract_partition.py new file mode 100755 index 0000000000..8b79a065d7 --- /dev/null +++ b/third_party/libwebrtc/build/extract_partition.py @@ -0,0 +1,174 @@ +#!/usr/bin/env python +# Copyright 2019 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. +"""Extracts an LLD partition from an ELF file.""" + +import argparse +import hashlib +import math +import os +import struct +import subprocess +import sys +import tempfile + + +def _ComputeNewBuildId(old_build_id, file_path): + """ + Computes the new build-id from old build-id and file_path. + + Args: + old_build_id: Original build-id in bytearray. + file_path: Path to output ELF file. + + Returns: + New build id with the same length as |old_build_id|. + """ + m = hashlib.sha256() + m.update(old_build_id) + m.update(os.path.basename(file_path).encode('utf-8')) + hash_bytes = m.digest() + # In case build_id is longer than hash computed, repeat the hash + # to the desired length first. + id_size = len(old_build_id) + hash_size = len(hash_bytes) + return (hash_bytes * (id_size // hash_size + 1))[:id_size] + + +def _ExtractPartition(objcopy, input_elf, output_elf, partition): + """ + Extracts a partition from an ELF file. + + For partitions other than main partition, we need to rewrite + the .note.gnu.build-id section so that the build-id remains + unique. + + Note: + - `objcopy` does not modify build-id when partitioning the + combined ELF file by default. + - The new build-id is calculated as hash of original build-id + and partitioned ELF file name. + + Args: + objcopy: Path to objcopy binary. + input_elf: Path to input ELF file. + output_elf: Path to output ELF file. + partition: Partition to extract from combined ELF file. None when + extracting main partition. + """ + if not partition: # main partition + # We do not overwrite build-id on main partition to allow the expected + # partition build ids to be synthesized given a libchrome.so binary, + # if necessary. + subprocess.check_call( + [objcopy, '--extract-main-partition', input_elf, output_elf]) + return + + # partitioned libs + build_id_section = '.note.gnu.build-id' + + with tempfile.TemporaryDirectory() as tempdir: + temp_elf = os.path.join(tempdir, 'obj_without_id.so') + old_build_id_file = os.path.join(tempdir, 'old_build_id') + new_build_id_file = os.path.join(tempdir, 'new_build_id') + + # Dump out build-id section and remove original build-id section from + # ELF file. + subprocess.check_call([ + objcopy, + '--extract-partition', + partition, + # Note: Not using '--update-section' here as it is not supported + # by llvm-objcopy. + '--remove-section', + build_id_section, + '--dump-section', + '{}={}'.format(build_id_section, old_build_id_file), + input_elf, + temp_elf, + ]) + + with open(old_build_id_file, 'rb') as f: + note_content = f.read() + + # .note section has following format according to <elf/external.h> + # typedef struct { + # unsigned char namesz[4]; /* Size of entry's owner string */ + # unsigned char descsz[4]; /* Size of the note descriptor */ + # unsigned char type[4]; /* Interpretation of the descriptor */ + # char name[1]; /* Start of the name+desc data */ + # } Elf_External_Note; + # `build-id` rewrite is only required on Android platform, + # where we have partitioned lib. + # Android platform uses little-endian. + # <: little-endian + # 4x: Skip 4 bytes + # L: unsigned long, 4 bytes + descsz, = struct.Struct('<4xL').unpack_from(note_content) + prefix = note_content[:-descsz] + build_id = note_content[-descsz:] + + with open(new_build_id_file, 'wb') as f: + f.write(prefix + _ComputeNewBuildId(build_id, output_elf)) + + # Write back the new build-id section. + subprocess.check_call([ + objcopy, + '--add-section', + '{}={}'.format(build_id_section, new_build_id_file), + # Add alloc section flag, or else the section will be removed by + # objcopy --strip-all when generating unstripped lib file. + '--set-section-flags', + '{}={}'.format(build_id_section, 'alloc'), + temp_elf, + output_elf, + ]) + + +def main(): + parser = argparse.ArgumentParser(description=__doc__) + parser.add_argument( + '--partition', + help='Name of partition if not the main partition', + metavar='PART') + parser.add_argument( + '--objcopy', + required=True, + help='Path to llvm-objcopy binary', + metavar='FILE') + parser.add_argument( + '--unstripped-output', + required=True, + help='Unstripped output file', + metavar='FILE') + parser.add_argument( + '--stripped-output', + required=True, + help='Stripped output file', + metavar='FILE') + parser.add_argument('--dwp', help='Path to dwp binary', metavar='FILE') + parser.add_argument('input', help='Input file') + args = parser.parse_args() + + _ExtractPartition(args.objcopy, args.input, args.unstripped_output, + args.partition) + subprocess.check_call([ + args.objcopy, + '--strip-all', + args.unstripped_output, + args.stripped_output, + ]) + + if args.dwp: + dwp_args = [ + args.dwp, '-e', args.unstripped_output, '-o', + args.unstripped_output + '.dwp' + ] + # Suppress output here because it doesn't seem to be useful. The most + # common error is a segfault, which will happen if files are missing. + subprocess.check_output(dwp_args, stderr=subprocess.STDOUT) + + +if __name__ == '__main__': + sys.exit(main()) |