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From:   Sami Tolvanen <samitolvanen@google.com>
Date:   Fri, 21 May 2021 09:36:11 -0700
Message-ID: <CABCJKue8=HO+E596=LkMqFD2wN1=6vB_0+ZRSEnG8tqOz7s2Uw@mail.gmail.com>
Subject: Re: [PATCH] init: verify that function is initcall_t at compile-time
To:     Marco Elver <elver@google.com>
Cc:     LKML <linux-kernel@vger.kernel.org>,
        Kees Cook <keescook@chromium.org>, ojeda@kernel.org,
        johan@kernel.org, Andrew Morton <akpm@linux-foundation.org>,
        Masahiro Yamada <masahiroy@kernel.org>,
        Joe Perches <joe@perches.com>, Arnd Bergmann <arnd@arndb.de>,
        "Paul E. McKenney" <paulmck@kernel.org>,
        Nathan Chancellor <nathan@kernel.org>
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Hi Marco,

On Fri, May 21, 2021 at 12:26 AM Marco Elver <elver@google.com> wrote:
>
> In the spirit of making it hard to misuse an interface, add a
> compile-time assertion in the CONFIG_HAVE_ARCH_PREL32_RELOCATIONS case
> to verify the initcall function matches initcall_t, because the inline
> asm bypasses any type-checking the compiler would otherwise do. This
> will help developers catch incorrect API use in all configurations.
>
> A recent example of this is:
> https://lkml.kernel.org/r/20210514140015.2944744-1-arnd@kernel.org
>
> Signed-off-by: Marco Elver <elver@google.com>
> Reviewed-by: Miguel Ojeda <ojeda@kernel.org>
> Reviewed-by: Nathan Chancellor <nathan@kernel.org>
> Tested-by: Nathan Chancellor <nathan@kernel.org>
> ---
>  include/linux/init.h | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/include/linux/init.h b/include/linux/init.h
> index 045ad1650ed1..d82b4b2e1d25 100644
> --- a/include/linux/init.h
> +++ b/include/linux/init.h
> @@ -242,7 +242,8 @@ extern bool initcall_debug;
>         asm(".section   \"" __sec "\", \"a\"            \n"     \
>             __stringify(__name) ":                      \n"     \
>             ".long      " __stringify(__stub) " - .     \n"     \
> -           ".previous                                  \n");
> +           ".previous                                  \n");   \
> +       static_assert(__same_type(initcall_t, &fn));
>  #else
>  #define ____define_initcall(fn, __unused, __name, __sec)       \
>         static initcall_t __name __used                         \

This looks like a nice improvement, thank you for sending the patch!

Reviewed-by: Sami Tolvanen <samitolvanen@google.com>

Sami