linux-kernel - Re: [PATCH] powerpc: fix function annotations to avoid section mismatch warnings with gcc-10

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Date:   Thu, 30 Jul 2020 22:04:27 +1000
From:   Michael Ellerman <mpe@...erman.id.au>
To:     Segher Boessenkool <segher@...nel.crashing.org>,
        Vladis Dronov <vdronov@...hat.com>
Cc:     linuxppc-dev@...ts.ozlabs.org,
        "Aneesh Kumar K . V" <aneesh.kumar@...ux.ibm.com>,
        linux-kernel@...r.kernel.org, Paul Mackerras <paulus@...ba.org>
Subject: Re: [PATCH] powerpc: fix function annotations to avoid section mismatch warnings with gcc-10

Segher Boessenkool <segher@...nel.crashing.org> writes:
> On Wed, Jul 29, 2020 at 03:44:56PM -0400, Vladis Dronov wrote:
>> > > Certain warnings are emitted for powerpc code when building with a gcc-10
>> > > toolset:
>> > > 
>> > >     WARNING: modpost: vmlinux.o(.text.unlikely+0x377c): Section mismatch in
>> > >     reference from the function remove_pmd_table() to the function
>> > >     .meminit.text:split_kernel_mapping()
>> > >     The function remove_pmd_table() references
>> > >     the function __meminit split_kernel_mapping().
>> > >     This is often because remove_pmd_table lacks a __meminit
>> > >     annotation or the annotation of split_kernel_mapping is wrong.
>> > > 
>> > > Add the appropriate __init and __meminit annotations to make modpost not
>> > > complain. In all the cases there are just a single callsite from another
>> > > __init or __meminit function:
>> > > 
>> > > __meminit remove_pagetable() -> remove_pud_table() -> remove_pmd_table()
>> > > __init prom_init() -> setup_secure_guest()
>> > > __init xive_spapr_init() -> xive_spapr_disabled()
>> > 
>> > So what changed?  These functions were inlined with older compilers, but
>> > not anymore?
>> 
>> Yes, exactly. Gcc-10 does not inline them anymore. If this is because of my
>> build system, this can happen to others also.
>> 
>> The same thing was fixed by Linus in e99332e7b4cd ("gcc-10: mark more functions
>> __init to avoid section mismatch warnings").
>
> It sounds like this is part of "-finline-functions was retuned" on
> <https://gcc.gnu.org/gcc-10/changes.html>?  So everyone should see it
> (no matter what config or build system), and it is a good thing too :-)

I haven't seen it in my GCC 10 builds, so there must be some other
subtlety. Probably it depends on details of the .config.

cheers