Issue 41976 added ctypes.util._is_elf() to filter out linker scripts such as "libc.so". The PR was backported to 3.7. _is_elf() assumes the trace result has absolute paths that can be opened, but Matthias is getting the relative filename "liblibc.a" in the result. Whatever the reason, I think if the file can't be opened for reading, then _is_elf() should just return False. For example:

    def _is_elf(filename):
        "Return True if the given file is an ELF file"
        elf_header = b'\x7fELF'
        try:
            with open(filename, 'br') as thefile:
                return thefile.read(4) == elf_header
        except OSError:
            return False