#!/usr/bin/env python3
# Copyright 2018 The Chromium Authors
# Use of this source code is governed by a BSD-style license that can be
# found in the LICENSE file.
"""Logic for reading .a files."""
import argparse
import logging
import os
def IsThinArchive(path):
"""Returns whether the given .a is a thin archive."""
with open(path, 'rb') as f:
return f.read(8) == b'!<thin>\n'
def CreateThinObjectPath(archive_path, subpath):
"""Given the .a path and .o subpath, returns the .o path."""
# |subpath| is path complete under Gold, and incomplete under LLD. Check its
# prefix to test completeness, and if not, use |archive_path| to supply the
# required prefix.
if subpath.startswith('obj/'):
return subpath
# .o subpaths in thin archives are relative to the directory of the .a.
parent_path = os.path.dirname(archive_path)
return os.path.normpath(os.path.join(parent_path, subpath))
def IterArchiveChunks(path):
"""For each .o embedded in the given .a file, yields (foo.o, foo_contents).
Args:
path: Path to .a file.
Returns:
A (str, bytes) tuple, specifying (.o file entry, None or payload data).
"""
# File format reference:
# https://github.com/pathscale/binutils/blob/master/gold/archive.cc
with open(path, 'rb') as f:
header = f.read(8)
is_thin = header == b'!<thin>\n'
if not is_thin and header != b'!<arch>\n':
raise Exception('Invalid .a: ' + path)
def read_payload(size):
ret = f.read(size)
# Entries are 2-byte aligned.
if size & 1 != 0:
f.read(1)
return ret
while True:
entry = f.read(60)
if not entry:
return
entry_name = entry[:16].rstrip()
entry_size = int(entry[48:58].rstrip())
if entry_name in (b'', b'/', b'//', b'/SYM64/'):
payload = read_payload(entry_size)
# Metadata sections we don't care about.
if entry_name == b'//':
name_list = payload
continue
if entry_name[0:1] == b'/':
# Name is specified as location in name table.
# E.g.: /123
name_offset = int(entry_name[1:])
# String table enties are delimited by \n (e.g. "browser.o/\n").
end_idx = name_list.index(b'\n', name_offset)
entry_name = name_list[name_offset:end_idx]
else:
# Name specified inline with spaces for padding (e.g. "browser.o/ ").
entry_name = entry_name.rstrip()
# Although entry_size exists for thin archives, no data exists in the .a.
entry_data = None if is_thin else read_payload(entry_size)
yield entry_name.rstrip(b'/').decode('ascii'), entry_data
def ExpandThinArchives(paths, output_directory):
"""Expands all thin archives found in |paths| into .o paths.
Args:
paths: List of paths relative to |output_directory|.
output_directory: Output directory.
Returns:
* A new list of paths with all thin archives replaced by .o paths.
* A set of all .a paths that were thin archives.
"""
expanded_paths = []
thin_paths = set()
num_archives = 0
for path in paths:
if not path.endswith('.a'):
expanded_paths.append(path)
continue
num_archives += 1
abs_path = os.path.join(output_directory, path)
if not os.path.exists(abs_path):
logging.warning('Linker input not found: %s', path)
continue
if not IsThinArchive(abs_path):
expanded_paths.append(path)
continue
thin_paths.add(path)
# Thin archive.
for subpath, _ in IterArchiveChunks(abs_path):
expanded_paths.append(CreateThinObjectPath(path, subpath))
logging.info('%d of %d .a files were thin archives',
len(thin_paths), num_archives)
return expanded_paths, thin_paths
def main():
parser = argparse.ArgumentParser()
parser.add_argument('ar_path')
parser.add_argument('--expand-thin', action='store_true')
parser.add_argument('--output-directory', default='.')
args = parser.parse_args()
if args.expand_thin:
expanded = ExpandThinArchives([args.ar_path], args.output_directory)[0]
print('\n'.join(expanded))
else:
for name, payload in IterArchiveChunks(args.ar_path):
print('{}: size={}'.format(name, len(payload) if payload else '<thin>'))
if __name__ == '__main__':
main()
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