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glibc/conform/linknamespace.py

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#!/usr/bin/python3
# Check that use of symbols declared in a given header does not result
# in any symbols being brought in that are not reserved with external
# linkage for the given standard.
# Copyright (C) 2014-2024 Free Software Foundation, Inc.
# This file is part of the GNU C Library.
#
# The GNU C Library is free software; you can redistribute it and/or
# modify it under the terms of the GNU Lesser General Public
# License as published by the Free Software Foundation; either
# version 2.1 of the License, or (at your option) any later version.
#
# The GNU C Library is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
# Lesser General Public License for more details.
#
# You should have received a copy of the GNU Lesser General Public
# License along with the GNU C Library; if not, see
# <https://www.gnu.org/licenses/>.
import argparse
from collections import defaultdict
import os.path
import re
import subprocess
import sys
import tempfile
import glibcconform
# The following whitelisted symbols are also allowed for now.
#
# * Bug 17576: stdin, stdout, stderr only reserved with external
# linkage when stdio.h included (and possibly not then), not
# generally.
#
# * Bug 18442: re_syntax_options wrongly brought in by regcomp and
# used by re_comp.
#
WHITELIST = {'stdin', 'stdout', 'stderr', 're_syntax_options'}
def list_syms(filename):
"""Return information about GLOBAL and WEAK symbols listed in readelf
-s output."""
ret = []
cur_file = filename
with open(filename, 'r') as syms_file:
for line in syms_file:
line = line.rstrip()
if line.startswith('File: '):
cur_file = line[len('File: '):]
cur_file = cur_file.split('/')[-1]
continue
# Architecture-specific st_other bits appear inside [] and
# disrupt the format of readelf output.
line = re.sub(r'\[.*?\]', '', line)
fields = line.split()
if len(fields) < 8:
continue
bind = fields[4]
ndx = fields[6]
sym = fields[7]
if bind not in ('GLOBAL', 'WEAK'):
continue
if not re.fullmatch('[A-Za-z0-9_]+', sym):
continue
ret.append((cur_file, sym, bind, ndx != 'UND'))
return ret
def main():
"""The main entry point."""
parser = argparse.ArgumentParser(description='Check link-time namespace.')
parser.add_argument('--header', metavar='HEADER',
help='name of header')
parser.add_argument('--standard', metavar='STD',
help='standard to use when processing header')
parser.add_argument('--cc', metavar='CC',
help='C compiler to use')
parser.add_argument('--flags', metavar='CFLAGS',
help='Compiler flags to use with CC')
parser.add_argument('--stdsyms', metavar='FILE',
help='File with list of standard symbols')
parser.add_argument('--libsyms', metavar='FILE',
help='File with symbol information from libraries')
parser.add_argument('--readelf', metavar='READELF',
help='readelf program to use')
args = parser.parse_args()
# Load the list of symbols that are OK.
stdsyms = set()
with open(args.stdsyms, 'r') as stdsyms_file:
for line in stdsyms_file:
stdsyms.add(line.rstrip())
stdsyms |= WHITELIST
# Load information about GLOBAL and WEAK symbols defined or used
# in the standard libraries.
# Symbols from a given object, except for weak defined symbols.
seen_syms = defaultdict(list)
# Strong undefined symbols from a given object.
strong_undef_syms = defaultdict(list)
# Objects defining a given symbol (strongly or weakly).
sym_objs = defaultdict(list)
for file, name, bind, defined in list_syms(args.libsyms):
if defined:
sym_objs[name].append(file)
if bind == 'GLOBAL' or not defined:
seen_syms[file].append(name)
if bind == 'GLOBAL' and not defined:
strong_undef_syms[file].append(name)
# Determine what ELF-level symbols are brought in by use of C-level
# symbols declared in the given header.
#
# The rules followed are heuristic and so may produce false
# positives and false negatives.
#
# * All undefined symbols are considered of signficance, but it is
# possible that (a) any standard library definition is weak, so
# can be overridden by the user's definition, and (b) the symbol
# is only used conditionally and not if the program is limited to
# standard functionality.
#
# * If a symbol reference is only brought in by the user using a
# data symbol rather than a function from the standard library,
# this will not be detected.
#
# * If a symbol reference is only brought in by crt*.o or libgcc,
# this will not be detected.
#
# * If a symbol reference is only brought in through __builtin_foo
# in a standard macro being compiled to call foo, this will not be
# detected.
#
# * Header inclusions should be compiled several times with
# different options such as -O2, -D_FORTIFY_SOURCE and
# -D_FILE_OFFSET_BITS=64 to find out what symbols are undefined
# from such a compilation; this is not yet implemented.
#
# * This script finds symbols referenced through use of macros on
# the basis that if a macro calls an internal function, that
# function must also be declared in the header. However, the
# header might also declare implementation-namespace functions
# that are not called by any standard macro in the header,
# resulting in false positives for any symbols brought in only
# through use of those implementation-namespace functions.
#
# * Namespace issues can apply for dynamic linking as well as
# static linking, when a call is from one shared library to
# another or uses a PLT entry for a call within a shared library;
# such issues are only detected by this script if the same
# namespace issue applies for static linking.
seen_where = {}
files_seen = set()
all_undef = {}
current_undef = {}
compiler = '%s %s' % (args.cc, args.flags)
c_syms = glibcconform.list_exported_functions(compiler, args.standard,
args.header)
with tempfile.TemporaryDirectory() as temp_dir:
cincfile_name = os.path.join(temp_dir, 'undef.c')
cincfile_o_name = os.path.join(temp_dir, 'undef.o')
cincfile_sym_name = os.path.join(temp_dir, 'undef.sym')
cincfile_text = ('#include <%s>\n%s\n'
% (args.header,
'\n'.join('void *__glibc_test_%s = (void *) &%s;'
% (sym, sym) for sym in sorted(c_syms))))
with open(cincfile_name, 'w') as cincfile:
cincfile.write(cincfile_text)
cmd = ('%s %s -D_ISOMAC %s -c %s -o %s'
% (args.cc, args.flags, glibcconform.CFLAGS[args.standard],
cincfile_name, cincfile_o_name))
subprocess.check_call(cmd, shell=True)
cmd = ('LC_ALL=C %s -W -s %s > %s'
% (args.readelf, cincfile_o_name, cincfile_sym_name))
subprocess.check_call(cmd, shell=True)
for file, name, bind, defined in list_syms(cincfile_sym_name):
if bind == 'GLOBAL' and not defined:
sym_text = '[initial] %s' % name
seen_where[name] = sym_text
all_undef[name] = sym_text
current_undef[name] = sym_text
while current_undef:
new_undef = {}
for sym, cu_sym in sorted(current_undef.items()):
for file in sym_objs[sym]:
if file in files_seen:
continue
files_seen.add(file)
for ssym in seen_syms[file]:
if ssym not in seen_where:
seen_where[ssym] = ('%s -> [%s] %s'
% (cu_sym, file, ssym))
for usym in strong_undef_syms[file]:
if usym not in all_undef:
usym_text = '%s -> [%s] %s' % (cu_sym, file, usym)
all_undef[usym] = usym_text
new_undef[usym] = usym_text
current_undef = new_undef
ret = 0
for sym in sorted(seen_where):
if sym.startswith('_'):
continue
if sym in stdsyms:
continue
print(seen_where[sym])
ret = 1
sys.exit(ret)
if __name__ == '__main__':
main()
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