dwarf-assembly/generate_eh_elf.py

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Python
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2018-04-25 17:33:59 +02:00
#!/usr/bin/env python3
"""
Generates the `.eh_frame` equivalent in C code of the given ELF file, and
all the shared objects it depends upon.
"""
import os
import sys
import subprocess
import re
import tempfile
import argparse
DWARF_ASSEMBLY_BIN = os.path.join(
os.path.dirname(os.path.abspath(sys.argv[0])),
'dwarf-assembly')
C_BIN = (
'gcc' if 'C' not in os.environ
else os.environ['C'])
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def elf_so_deps(path):
''' Get the list of shared objects dependencies of the given ELF object.
This is obtained by running `ldd`. '''
deps_list = []
try:
ldd_output = subprocess.check_output(['/usr/bin/ldd', path]) \
.decode('utf-8')
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ldd_re = re.compile(r'^.* => (.*) \(0x[0-9a-fA-F]*\)$')
ldd_lines = ldd_output.strip().split('\n')
for line in ldd_lines:
line = line.strip()
match = ldd_re.match(line)
if match is None:
continue # Just ignore that line — it might be eg. linux-vdso
deps_list.append(match.group(1))
return deps_list
except subprocess.CalledProcessError as e:
raise Exception(
("Cannot get dependencies for {}: ldd terminated with exit code "
"{}.").format(path, e.returncode))
def gen_dw_asm_c(obj_path, out_path):
''' Generate the C code produced by dwarf-assembly from `obj_path`, saving
it as `out_path` '''
try:
with open(out_path, 'w') as out_handle:
# TODO enhance error handling
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dw_asm_output = subprocess.check_output(
[DWARF_ASSEMBLY_BIN, obj_path]) \
.decode('utf-8')
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out_handle.write(dw_asm_output)
except subprocess.CalledProcessError as e:
raise Exception(
("Cannot generate C code from object file {} using {}: process "
"terminated with exit code {}.").format(
obj_path,
DWARF_ASSEMBLY_BIN,
e.returncode))
def gen_eh_elf(obj_path, out_dir=None):
''' Generate the eh_elf corresponding to `obj_path`, saving it as
`out_dir/$(basename obj_path).eh_elf.so` (or in the current working
directory if out_dir is None) '''
if out_dir is None:
out_dir = '.'
print("> {}...".format(os.path.basename(obj_path)))
out_base_name = os.path.basename(obj_path) + '.eh_elf'
out_so_path = os.path.join(out_dir, (out_base_name + '.so'))
try:
so_mtime = os.path.getmtime(out_so_path)
obj_mtime = os.path.getmtime(obj_path)
if obj_mtime < so_mtime:
return # The object is recent enough, no need to recreate it
except OSError:
pass
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with tempfile.TemporaryDirectory() as compile_dir:
# Generate the C source file
print("\tGenerating C…")
c_path = os.path.join(compile_dir, (out_base_name + '.c'))
gen_dw_asm_c(obj_path, c_path)
# Compile it into a .o
print("\tCompiling into .o…")
o_path = os.path.join(compile_dir, (out_base_name + '.o'))
call_rc = subprocess.call(
[C_BIN, '-o', o_path, '-c', c_path, '-O3', '-fPIC'])
if call_rc != 0:
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raise Exception("Failed to compile to a .o file")
# Compile it into a .so
print("\tCompiling into .so…")
call_rc = subprocess.call(
[C_BIN, '-o', out_so_path, '-shared', o_path])
if call_rc != 0:
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raise Exception("Failed to compile to a .so file")
def gen_all_eh_elf(obj_path, out_dir=None):
''' Call `gen_eh_elf` on obj_path and all its dependencies '''
if out_dir is None:
out_dir = '.'
deps = elf_so_deps(obj_path)
deps.append(obj_path)
for dep in deps:
gen_eh_elf(dep, out_dir)
def process_args():
''' Process `sys.argv` arguments '''
parser = argparse.ArgumentParser(
description="Compile ELFs into their related eh_elfs",
)
parser.add_argument('--deps', action='store_const',
const=gen_all_eh_elf, default=gen_eh_elf,
dest='gen_func',
help=("Also generate eh_elfs for the shared objects "
"this object depends on"))
parser.add_argument('-o', '--output', metavar="path",
help=("Save the generated objects at the given path "
"instead of the current working directory"))
parser.add_argument('object', nargs='+',
help="The ELF object(s) to process")
return parser.parse_args()
def main():
args = process_args()
for obj in args.object:
args.gen_func(obj, args.output)
if __name__ == "__main__":
main()