linux-kernel - Re: [PATCH v2] include/linux/module.h: mark init/cleanup_module aliases as _

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Date:   Wed, 6 Feb 2019 22:19:37 +0100
From:   Miguel Ojeda <miguel.ojeda.sandonis@...il.com>
To:     Jessica Yu <jeyu@...nel.org>
Cc:     Laura Abbott <labbott@...hat.com>,
        Martin Sebor <msebor@....gnu.org>,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] include/linux/module.h: mark init/cleanup_module
 aliases as __init/exit

On Wed, Feb 6, 2019 at 6:56 PM Miguel Ojeda
<miguel.ojeda.sandonis@...il.com> wrote:
>
> diff --git a/include/linux/module.h b/include/linux/module.h
> index 8fa38d3e7538..1b5e370f1bc0 100644
> --- a/include/linux/module.h
> +++ b/include/linux/module.h
> @@ -129,13 +129,13 @@ extern void cleanup_module(void);
>  #define module_init(initfn)                                    \
>         static inline initcall_t __maybe_unused __inittest(void)                \
>         { return initfn; }                                      \
> -       int init_module(void) __attribute__((alias(#initfn)));
> +       int init_module(void) __init __attribute__((alias(#initfn)));
>
>  /* This is only required if you want to be unloadable. */
>  #define module_exit(exitfn)                                    \
>         static inline exitcall_t __maybe_unused __exittest(void)                \
>         { return exitfn; }                                      \
> -       void cleanup_module(void) __attribute__((alias(#exitfn)));
> +       void cleanup_module(void) __exit __attribute__((alias(#exitfn)));

It turns out that there are some modules without __init/__exit marked
functions, which GCC complains about, since now the alias is in a
different section than the target:

  * In some cases, this is due to a missing __init/__exit marking
(e.g. drivers/connector/connector.c). These should be fixed in any
case.
  * In other cases, the cleanup function is not marked as such because
it is called from another place in the TU, like the init function
(e.g. arch/x86/kvm/vmx.c). We would need to create an actual cleanup
function (marked as __exit) that simply calls the current exit static
function.

So we have a few alternatives:

  1) Going only with __cold.
  2) Using the new __copy attribute (because then they are copied only
in the cases they are actually used).
  3) Fix and go for __init/__exit. While this requires some tweaking
as explained above, it would be good if we can achieve it since then
we are enforcing proper __init/__exit markings for all modules
(whereas __copy wouldn't spot).

I think it is worth achieving 3), but that will take a bit more of
time. In that case, I suggest we push 1) or 2) for the moment (so that
the warning is fixed) and then work on fixing all instances. As soon
as that is done, we can push 3).

What do you think?

Cheers,
Miguel