90 lines
3.2 KiB
Python
90 lines
3.2 KiB
Python
#!/usr/bin/python3
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# Compute the hash-based name of the __libc_early_init function.
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# Copyright (C) 2022 Free Software Foundation, Inc.
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# This file is part of the GNU C Library.
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#
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# The GNU C Library is free software; you can redistribute it and/or
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# modify it under the terms of the GNU Lesser General Public
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# License as published by the Free Software Foundation; either
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# version 2.1 of the License, or (at your option) any later version.
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#
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# The GNU C Library is distributed in the hope that it will be useful,
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# but WITHOUT ANY WARRANTY; without even the implied warranty of
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# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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# Lesser General Public License for more details.
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#
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# You should have received a copy of the GNU Lesser General Public
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# License along with the GNU C Library; if not, see
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# <https://www.gnu.org/licenses/>.
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"""Compute the name of the __libc_early_init function, which is used
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as a protocol version marker between ld.so and libc.so.
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The name contains a hash suffix, and the hash changes if certain key
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files in the source tree change. Distributions can also configure
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with --with-extra-version-id, to make the computed hash dependent on
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the package version.
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"""
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import argparse
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import hashlib
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import os
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import string
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import sys
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def gnu_hash(s):
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"""Computes the GNU hash of the string."""
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h = 5381
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for ch in s:
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if type(ch) is not int:
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ch = ord(ch)
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h = (h * 33 + ch) & 0xffffffff
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return h
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# Parse the command line.
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parser = argparse.ArgumentParser(description=__doc__)
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parser.add_argument('--output', metavar='PATH',
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help='path to header file this tool generates')
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parser.add_argument('--extra-version-id', metavar='ID',
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help='extra string to influence hash computation')
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parser.add_argument('inputs', metavar='PATH', nargs='*',
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help='files whose contents influences the generated hash')
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opts = parser.parse_args()
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# Obtain the blobs that affect the generated hash.
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blobs = [(opts.extra_version_id or '').encode('UTF-8')]
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for path in opts.inputs:
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with open(path, 'rb') as inp:
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blobs.append(inp.read())
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# Hash the file boundaries.
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md = hashlib.sha256()
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md.update(repr([len(blob) for blob in blobs]).encode('UTF-8'))
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# And then hash the file contents. Do not hash the paths, to avoid
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# impacting reproducibility.
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for blob in blobs:
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md.update(blob)
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# These are the bits used to compute the suffix.
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derived_bits = int.from_bytes(md.digest(), byteorder='big', signed=False)
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# These digits are used in the suffix (should result in base-62 encoding).
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# They must be valid in C identifiers.
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digits = string.digits + string.ascii_letters
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# Generate eight digits as a suffix. They should provide enough
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# uniqueness (47.6 bits).
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name = '__libc_early_init_'
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for n in range(8):
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name += digits[derived_bits % len(digits)]
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derived_bits //= len(digits)
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# Write the output file.
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with open(opts.output, 'w') if opts.output else sys.stdout as out:
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out.write('#define LIBC_EARLY_INIT_NAME {}\n'.format(name))
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out.write('#define LIBC_EARLY_INIT_NAME_STRING "{}"\n'.format(name))
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out.write('#define LIBC_EARLY_INIT_GNU_HASH {}\n'.format(
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gnu_hash(name)))
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