linux-kernel - Re: [PATCH] memblock: fix section mismatch warning

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Date:   Thu, 25 Feb 2021 22:59:08 +0200
From:   Mike Rapoport <rppt@...nel.org>
To:     Arnd Bergmann <arnd@...nel.org>
Cc:     Nathan Chancellor <nathan@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Faiyaz Mohammed <faiyazm@...eaurora.org>,
        Arnd Bergmann <arnd@...db.de>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Baoquan He <bhe@...hat.com>,
        Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
        David Hildenbrand <david@...hat.com>,
        Aslan Bakirov <aslan@...com>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, clang-built-linux@...glegroups.com
Subject: Re: [PATCH] memblock: fix section mismatch warning

On Thu, Feb 25, 2021 at 02:38:00PM +0100, Arnd Bergmann wrote:
> From: Arnd Bergmann <arnd@...db.de>
> 
> The inlining logic in clang-13 is rewritten to often not inline
> some functions that were inlined by all earlier compilers.
> 
> In case of the memblock interfaces, this exposed a harmless bug
> of a missing __init annotation:
> 
> WARNING: modpost: vmlinux.o(.text+0x507c0a): Section mismatch in reference from the function memblock_bottom_up() to the variable .meminit.data:memblock
> The function memblock_bottom_up() references
> the variable __meminitdata memblock.
> This is often because memblock_bottom_up lacks a __meminitdata
> annotation or the annotation of memblock is wrong.
> 
> Interestingly, these annotations were present originally, but got removed
> with the explanation that the __init annotation prevents the function
> from getting inlined. I checked this again and found that while this
> is the case with clang, gcc (version 7 through 10, did not test others)
> does inline the functions regardless.
> 
> As the previous change was apparently intended to help the clang
> builds, reverting it to help the newer clang versions seems appropriate
> as well. gcc builds don't seem to care either way.
> 
> Fixes: 5bdba520c1b3 ("mm: memblock: drop __init from memblock functions to make it inline")
> Reference: 2cfb3665e864 ("include/linux/memblock.h: add __init to memblock_set_bottom_up()")
> Signed-off-by: Arnd Bergmann <arnd@...db.de>

I thought it'll go via memblock tree but since Andrew has already took it

Reviewed-by: Mike Rapoport <rppt@...ux.ibm.com>

> ---
>  include/linux/memblock.h | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/include/linux/memblock.h b/include/linux/memblock.h
> index c88bc24e31aa..d13e3cd938b4 100644
> --- a/include/linux/memblock.h
> +++ b/include/linux/memblock.h
> @@ -460,7 +460,7 @@ static inline void memblock_free_late(phys_addr_t base, phys_addr_t size)
>  /*
>   * Set the allocation direction to bottom-up or top-down.
>   */
> -static inline void memblock_set_bottom_up(bool enable)
> +static inline __init void memblock_set_bottom_up(bool enable)
>  {
>  	memblock.bottom_up = enable;
>  }
> @@ -470,7 +470,7 @@ static inline void memblock_set_bottom_up(bool enable)
>   * if this is true, that said, memblock will allocate memory
>   * in bottom-up direction.
>   */
> -static inline bool memblock_bottom_up(void)
> +static inline __init bool memblock_bottom_up(void)
>  {
>  	return memblock.bottom_up;
>  }
> -- 
> 2.29.2
> 

-- 
Sincerely yours,
Mike.