dynamically calling an ffi function in python?

Question

I'm writing a simple program that needs to reach out to libc for some functions. My problem is that I don't know what these functions are when writing the program ie. the functions that will be called are imported dynamically, based on some user input.

How can I do this? Ideally I'd like to have a python dictionary of all the functions from the imported library.

Thanks!

Answer 1

You could use the ctypes library, it allow you to call functions in shared libraries written in C.

Here is an example:

import ctypes

def load_library(lib_name):
    try:
        return ctypes.CDLL(lib_name)
    except OSError:
        print(f"Failed to load library: {lib_name}")
        return None

def load_functions(library, function_names):
    functions = {}
    for name in function_names:
        try:
            functions[name] = getattr(library, name)
        except AttributeError:
            print(f"Failed to load function: {name}")
    return functions

libc = load_library("libc.so.6")
if libc is not None:
    function_names = ["strlen", "strcpy", "strcmp"]
    libc_functions = load_functions(libc, function_names)

    strlen = libc_functions["strlen"]
    strlen.argtypes = [ctypes.c_char_p]
    strlen.restype = ctypes.c_size_t

    s = b"hello world"
    print(strlen(s))