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
218
219
220
221
222
223
224
225
226
|
#!/usr/bin/python3
# ELF editor for load align tests.
# Copyright (C) 2022-2025 Free Software Foundation, Inc.
# Copyright The GNU Toolchain Authors.
# 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
import os
import sys
import struct
EI_NIDENT=16
EI_MAG0=0
ELFMAG0=b'\x7f'
EI_MAG1=1
ELFMAG1=b'E'
EI_MAG2=2
ELFMAG2=b'L'
EI_MAG3=3
ELFMAG3=b'F'
EI_CLASS=4
ELFCLASSNONE=b'0'
ELFCLASS32=b'\x01'
ELFCLASS64=b'\x02'
EI_DATA=5
ELFDATA2LSB=b'\x01'
ELFDATA2MSB=b'\x02'
ET_EXEC=2
ET_DYN=3
PT_LOAD=1
PT_TLS=7
def elf_types_fmts(e_ident):
endian = '<' if e_ident[EI_DATA] == ELFDATA2LSB else '>'
addr = 'I' if e_ident[EI_CLASS] == ELFCLASS32 else 'Q'
off = 'I' if e_ident[EI_CLASS] == ELFCLASS32 else 'Q'
return (endian, addr, off)
class Elf_Ehdr:
def __init__(self, e_ident):
endian, addr, off = elf_types_fmts(e_ident)
self.fmt = '{0}HHI{1}{2}{2}IHHHHHH'.format(endian, addr, off)
self.len = struct.calcsize(self.fmt)
def read(self, f):
buf = f.read(self.len)
if not buf:
error('{}: header too small'.format(f.name))
data = struct.unpack(self.fmt, buf)
self.e_type = data[0]
self.e_machine = data[1]
self.e_version = data[2]
self.e_entry = data[3]
self.e_phoff = data[4]
self.e_shoff = data[5]
self.e_flags = data[6]
self.e_ehsize = data[7]
self.e_phentsize= data[8]
self.e_phnum = data[9]
self.e_shstrndx = data[10]
class Elf_Phdr:
def __init__(self, e_ident):
endian, addr, off = elf_types_fmts(e_ident)
self.ei_class = e_ident[EI_CLASS]
if self.ei_class == ELFCLASS32:
self.fmt = '{0}I{2}{1}{1}IIII'.format(endian, addr, off)
else:
self.fmt = '{0}II{2}{1}{1}QQQ'.format(endian, addr, off)
self.len = struct.calcsize(self.fmt)
def read(self, f):
buf = f.read(self.len)
if len(buf) < self.len:
error('{}: program header too small'.format(f.name))
data = struct.unpack(self.fmt, buf)
if self.ei_class == ELFCLASS32:
self.p_type = data[0]
self.p_offset = data[1]
self.p_vaddr = data[2]
self.p_paddr = data[3]
self.p_filesz = data[4]
self.p_memsz = data[5]
self.p_flags = data[6]
self.p_align = data[7]
else:
self.p_type = data[0]
self.p_flags = data[1]
self.p_offset = data[2]
self.p_vaddr = data[3]
self.p_paddr = data[4]
self.p_filesz = data[5]
self.p_memsz = data[6]
self.p_align = data[7]
def write(self, f):
if self.ei_class == ELFCLASS32:
data = struct.pack(self.fmt,
self.p_type,
self.p_offset,
self.p_vaddr,
self.p_paddr,
self.p_filesz,
self.p_memsz,
self.p_flags,
self.p_align)
else:
data = struct.pack(self.fmt,
self.p_type,
self.p_flags,
self.p_offset,
self.p_vaddr,
self.p_paddr,
self.p_filesz,
self.p_memsz,
self.p_align)
f.write(data)
def error(msg):
print(msg, file=sys.stderr)
sys.exit(1)
def elf_edit_align(phdr, align):
if align == 'half':
phdr.p_align = phdr.p_align >> 1
else:
phdr.p_align = int(align)
def elf_edit_maximize_tls_size(phdr, elfclass):
if elfclass == ELFCLASS32:
# It is possible that the kernel can allocate half of the
# address space, so use something larger.
phdr.p_memsz = 0xfff00000
else:
phdr.p_memsz = 1 << 63
def elf_edit(f, opts):
ei_nident_fmt = 'c' * EI_NIDENT
ei_nident_len = struct.calcsize(ei_nident_fmt)
data = f.read(ei_nident_len)
if len(data) < ei_nident_len:
error('{}: e_nident too small'.format(f.name))
e_ident = struct.unpack(ei_nident_fmt, data)
if e_ident[EI_MAG0] != ELFMAG0 \
or e_ident[EI_MAG1] != ELFMAG1 \
or e_ident[EI_MAG2] != ELFMAG2 \
or e_ident[EI_MAG3] != ELFMAG3:
error('{}: bad ELF header'.format(f.name))
if e_ident[EI_CLASS] != ELFCLASS32 \
and e_ident[EI_CLASS] != ELFCLASS64:
error('{}: unsupported ELF class: {}'.format(f.name, e_ident[EI_CLASS]))
if e_ident[EI_DATA] != ELFDATA2LSB \
and e_ident[EI_DATA] != ELFDATA2MSB: \
error('{}: unsupported ELF data: {}'.format(f.name, e_ident[EI_DATA]))
ehdr = Elf_Ehdr(e_ident)
ehdr.read(f)
if ehdr.e_type not in (ET_EXEC, ET_DYN):
error('{}: not an executable or shared library'.format(f.name))
phdr = Elf_Phdr(e_ident)
maximize_tls_size_done = False
for i in range(0, ehdr.e_phnum):
f.seek(ehdr.e_phoff + i * phdr.len)
phdr.read(f)
if phdr.p_type == PT_LOAD and opts.align is not None:
elf_edit_align(phdr, opts.align)
f.seek(ehdr.e_phoff + i * phdr.len)
phdr.write(f)
break
if phdr.p_type == PT_TLS and opts.maximize_tls_size:
elf_edit_maximize_tls_size(phdr, e_ident[EI_CLASS])
f.seek(ehdr.e_phoff + i * phdr.len)
phdr.write(f)
maximize_tls_size_done = True
break
if opts.maximize_tls_size and not maximize_tls_size_done:
error('{}: TLS maximum size was not updated'.format(f.name))
def get_parser():
parser = argparse.ArgumentParser(description=__doc__)
parser.add_argument('-a', dest='align',
help='How to set the LOAD alignment')
parser.add_argument('--maximize-tls-size', action='store_true',
help='Set maximum PT_TLS size')
parser.add_argument('output',
help='ELF file to edit')
return parser
def main(argv):
parser = get_parser()
opts = parser.parse_args(argv)
with open(opts.output, 'r+b') as fout:
elf_edit(fout, opts)
if __name__ == '__main__':
main(sys.argv[1:])
|
