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

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Message-ID: <60989b76-1ae6-6be3-0277-df9f0cc8dc3e@redhat.com>
Date:   Thu, 25 Feb 2021 14:47:28 +0100
From:   David Hildenbrand <david@...hat.com>
To:     Arnd Bergmann <arnd@...nel.org>, Mike Rapoport <rppt@...nel.org>,
        Nathan Chancellor <nathan@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Faiyaz Mohammed <faiyazm@...eaurora.org>
Cc:     Arnd Bergmann <arnd@...db.de>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Baoquan He <bhe@...hat.com>,
        Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
        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 25.02.21 14:38, 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.

Did I understand correctly, that with this change it will not get 
inlined with any version of clang? Maybe __always_inline is more 
appropriate then.

(I don't see why to not inline that function, but I am obviously not a 
compiler person :) )

-- 
Thanks,

David / dhildenb