linux-kernel - Re: [PATCH] init: verify that function is initcall

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Date:   Fri, 21 May 2021 10:32:55 -0700
From:   "Paul E. McKenney" <paulmck@...nel.org>
To:     Marco Elver <elver@...gle.com>
Cc:     linux-kernel@...r.kernel.org, keescook@...omium.org,
        samitolvanen@...gle.com, ojeda@...nel.org, johan@...nel.org,
        akpm@...ux-foundation.org, masahiroy@...nel.org, joe@...ches.com,
        Arnd Bergmann <arnd@...db.de>,
        Nathan Chancellor <nathan@...nel.org>
Subject: Re: [PATCH] init: verify that function is initcall_t at compile-time

On Fri, May 21, 2021 at 09:26:10AM +0200, Marco Elver 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@...gle.com>
> Reviewed-by: Miguel Ojeda <ojeda@...nel.org>
> Reviewed-by: Nathan Chancellor <nathan@...nel.org>
> Tested-by: Nathan Chancellor <nathan@...nel.org>

Tested-by: Paul E. McKenney <paulmck@...nel.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 			\
> -- 
> 2.31.1.818.g46aad6cb9e-goog
>