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#!/usr/bin/python3
# ELF editor for load align tests.
# Copyright (C) 2022-2024 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:])
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