1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
|
#!/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) 2014-2022 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()
|
