#!/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') CXX_BIN = ( 'g++' if 'CXX' not in os.environ else os.environ['CXX']) 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], encoding='utf8') ldd_re = re.compile(r'^.* => (.*) \(0x[0-9a-fA-F]*\)$') ldd_lines = ldd_output.strip().split('\n') for line in ldd_lines: line = line.strip() match = ldd_re.match(line) if match is None: continue # Just ignore that line — it might be eg. linux-vdso deps_list.append(match.group(1)) return deps_list except subprocess.CalledProcessError as e: raise Exception( ("Cannot get dependencies for {}: ldd terminated with exit code " "{}.").format(path, e.returncode)) def gen_dw_asm_c(obj_path, out_path): ''' Generate the C code produced by dwarf-assembly from `obj_path`, saving it as `out_path` ''' try: with open(out_path, 'w') as out_handle: dw_asm_output = subprocess.check_output( [DWARF_ASSEMBLY_BIN, obj_path], encoding='utf8') # TODO enhance error handling out_handle.write(dw_asm_output) except subprocess.CalledProcessError as e: raise Exception( ("Cannot generate C code from object file {} using {}: process " "terminated with exit code {}.").format( obj_path, DWARF_ASSEMBLY_BIN, e.returncode)) def gen_eh_elf(obj_path, out_dir=None): ''' Generate the eh_elf corresponding to `obj_path`, saving it as `out_dir/$(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' 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')) if subprocess.call([CXX_BIN, '-o', o_path, '-c', c_path, '-O3', '-fPIC']) != 0: raise Exception("Failed to compile to a .o file") # Compile it into a .so print("\tCompiling into .so…") so_path = os.path.join(out_dir, (out_base_name + '.so')) if subprocess.call([CXX_BIN, '-o', so_path, '-shared', o_path]) != 0: 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()