Userland host native setup broken with `KeyError: 'gem5_arch'`

[cirosantilli]

On fb39ab4 Ubuntu 25.10, running:

cd userlane
./build c/hello

as per https://cirosantilli.com/linux-kernel-module-cheat/#userland-setup-getting-started-natively blows up:

Traceback (most recent call last):
  File "/home/ciro/bak/git/linux-kernel-module-cheat/userland/./build", line 29, in <module>
    Main().cli()
    ~~~~~~~~~~^^
  File "/home/ciro/bak/git/linux-kernel-module-cheat/cli_function.py", line 267, in cli
    exit_status = self.cli_noexit(*args, **kwargs)
  File "/home/ciro/bak/git/linux-kernel-module-cheat/cli_function.py", line 258, in cli_noexit
    return self._do_main(vars(args))
           ~~~~~~~~~~~~~^^^^^^^^^^^^
  File "/home/ciro/bak/git/linux-kernel-module-cheat/cli_function.py", line 152, in _do_main
    return self.main(**self._get_args(kwargs))
           ~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/ciro/bak/git/linux-kernel-module-cheat/common.py", line 1556, in main
    self._init_env(self.env)
    ~~~~~~~~~~~~~~^^^^^^^^^^
  File "/home/ciro/bak/git/linux-kernel-module-cheat/common.py", line 926, in _init_env
    env['gem5_executable_dir'] = join(env['gem5_build_build_dir'], env['gem5_arch'])
                                                                   ~~~^^^^^^^^^^^^^
KeyError: 'gem5_arch'

Possible root cause might be:

import platform
consts['host_arch'] = platform.processor()

being empty on Ubuntu 25.10. uname -p is unknown. Related:

• https://stackoverflow.com/questions/63755511/why-python3-platform-processor-on-import-platform-give-an-empty-output
• https://unix.stackexchange.com/questions/307955/uname-p-i-are-unknown