linux-kernel - Re: [PATCH 04/27] modpost: add a separate error for exported symbols without definition

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Date:   Mon, 25 Apr 2022 11:21:39 -0700
From:   Nick Desaulniers <ndesaulniers@...gle.com>
To:     Masahiro Yamada <masahiroy@...nel.org>
Cc:     linux-kbuild@...r.kernel.org, linux-kernel@...r.kernel.org,
        Michal Marek <michal.lkml@...kovi.net>
Subject: Re: [PATCH 04/27] modpost: add a separate error for exported symbols
 without definition

On Sun, Apr 24, 2022 at 12:09 PM Masahiro Yamada <masahiroy@...nel.org> wrote:
>
> It took me a while to understand the intent of "exp->module == mod".
>
> This code goes back to 2003 (pre-git era).
>
> The commit is not in this git repository, and might be worth a little
> explanation.
>
> You can add EXPORT_SYMBOL() with no definition in the same file (but you
> need to put a declaration).
>
>   int foo(void);
>   EXPORT_SYMBOL(foo);
>
> This is typical when EXPORT_SYMBOL() is defined in a C file, but the
> actual implementation is in a separate assembly file. In old days,
> EXPORT_SYMBOL() were only available in C files (but this limitation
> does not exist any more).
>
> Add a separate, clearer message if an exported symbol has no definition.
> It should be an error even if KBUILD_MODPOST_WARN is given.
>
> [1]: https://git.kernel.org/pub/scm/linux/kernel/git/history/history.git/commit/?id=2763b6bcb96e6a38a2fe31108fe5759ec5bcc80a

Differentiating between the two (and your explanation of how to reach
such a situation) is a nice touch.
Reviewed-by: Nick Desaulniers <ndesaulniers@...gle.com>

>
> Signed-off-by: Masahiro Yamada <masahiroy@...nel.org>
> ---
>
>  scripts/mod/modpost.c | 7 ++++++-
>  1 file changed, 6 insertions(+), 1 deletion(-)
>
> diff --git a/scripts/mod/modpost.c b/scripts/mod/modpost.c
> index c7cfeeb088f7..969a081dba62 100644
> --- a/scripts/mod/modpost.c
> +++ b/scripts/mod/modpost.c
> @@ -2147,13 +2147,18 @@ static void check_exports(struct module *mod)
>         for (s = mod->unres; s; s = s->next) {
>                 const char *basename;
>                 exp = find_symbol(s->name);
> -               if (!exp || exp->module == mod) {
> +               if (!exp) {
>                         if (!s->weak && nr_unresolved++ < MAX_UNRESOLVED_REPORTS)
>                                 modpost_log(warn_unresolved ? LOG_WARN : LOG_ERROR,
>                                             "\"%s\" [%s.ko] undefined!\n",
>                                             s->name, mod->name);
>                         continue;
>                 }
> +               if (exp->module == mod) {
> +                       error("\"%s\" [%s.ko] was exported without definition\n",
> +                             s->name, mod->name);
> +                       continue;
> +               }
>                 basename = strrchr(mod->name, '/');
>                 if (basename)
>                         basename++;
> --
> 2.32.0
>


-- 
Thanks,
~Nick Desaulniers