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Date: Mon, 20 Oct 2025 15:30:50 +0200
From: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To: "Matthieu Baerts (NGI0)" <matttbe@kernel.org>
Cc: stable@vger.kernel.org, Sasha Levin <sashal@kernel.org>,
	MPTCP Upstream <mptcp@lists.linux.dev>,
	Nathan Chancellor <nathan@kernel.org>,
	Ard Biesheuvel <ardb@kernel.org>,
	Alexey Dobriyan <adobriyan@gmail.com>,
	Arnd Bergmann <arnd@arndb.de>
Subject: Re: [PATCH 5.15.y 2/3] arch: back to -std=gnu89 in < v5.18
Message-ID: <2025102015-alongside-kiwi-6f75@gregkh>
References: <20251017-v5-15-gcc-15-v1-0-da6c065049d7@kernel.org>
 <20251017-v5-15-gcc-15-v1-2-da6c065049d7@kernel.org>
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In-Reply-To: <20251017-v5-15-gcc-15-v1-2-da6c065049d7@kernel.org>

On Fri, Oct 17, 2025 at 06:24:01PM +0200, Matthieu Baerts (NGI0) wrote:
> Recent fixes have been backported to < v5.18 to fix build issues with
> GCC 5.15. They all force -std=gnu11 in the CFLAGS, "because [the kernel]
> requests the gnu11 standard via '-std=' in the main Makefile".
> 
> This is true for >= 5.18 versions, but not before. This switch to
> -std=gnu11 has been done in commit e8c07082a810 ("Kbuild: move to
> -std=gnu11").
> 
> For a question of uniformity, force -std=gnu89, similar to what is done
> in the main Makefile.
> 
> Note: the fixes tags below refers to upstream commits, but this fix is
> only for kernels not having commit e8c07082a810 ("Kbuild: move to
> -std=gnu11").
> 
> Fixes: 7cbb015e2d3d ("parisc: fix building with gcc-15")
> Fixes: 3b8b80e99376 ("s390: Add '-std=gnu11' to decompressor and purgatory CFLAGS")
> Fixes: b3bee1e7c3f2 ("x86/boot: Compile boot code with -std=gnu11 too")
> Fixes: ee2ab467bddf ("x86/boot: Use '-std=gnu11' to fix build with GCC 15")
> Fixes: 8ba14d9f490a ("efi: libstub: Use '-std=gnu11' to fix build with GCC 15")
> Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
> ---
> Note:
>   An alternative is to backport commit e8c07082a810 ("Kbuild: move to
>   -std=gnu11"), but I guess we might not want to do that for stable, as
>   it might introduce new warnings.

I would rather do that, as that would allow us to make things align up
and be easier to support over the next two years that this kernel needs
to be alive for.  How much work would that entail?

thanks,

greg k-h