linux-kernel - Re: [PATCH 1/2] x86/boot: Use '-std=gnu11' to fix build with GCC 15

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Message-ID: <CAMj1kXHG-dyF=6CezF1exgnfodjQyuWY9ha8s6+TXBRVKbsO=A@mail.gmail.com>
Date: Wed, 29 Jan 2025 09:43:56 +0100
From: Ard Biesheuvel <ardb@...nel.org>
To: Nathan Chancellor <nathan@...nel.org>
Cc: Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>, 
	Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org, Kees Cook <kees@...nel.org>, 
	Sam James <sam@...too.org>, Masahiro Yamada <masahiroy@...nel.org>, Arnd Bergmann <arnd@...db.de>, 
	linux-kernel@...r.kernel.org, linux-efi@...r.kernel.org, 
	stable@...r.kernel.org, 
	Kostadin Shishmanov <kostadinshishmanov@...tonmail.com>, Jakub Jelinek <jakub@...hat.com>, 
	Daan De Meyer <daandemeyer@...com>
Subject: Re: [PATCH 1/2] x86/boot: Use '-std=gnu11' to fix build with GCC 15

On Wed, 22 Jan 2025 at 02:12, Nathan Chancellor <nathan@...nel.org> wrote:
>
> GCC 15 changed the default C standard version to C23, which should not
> have impacted the kernel because it requests the gnu11 standard via
> '-std=' in the main Makefile. However, the x86 compressed boot Makefile
> uses its own set of KBUILD_CFLAGS without a '-std=' value (i.e., using
> the default), resulting in errors from the kernel's definitions of bool,
> true, and false in stddef.h, which are reserved keywords under C23.
>
>   ./include/linux/stddef.h:11:9: error: expected identifier before ‘false’
>      11 |         false   = 0,
>   ./include/linux/types.h:35:33: error: two or more data types in declaration specifiers
>      35 | typedef _Bool                   bool;
>
> Set '-std=gnu11' in the x86 compressed boot Makefile to resolve the
> error and consistently use the same C standard version for the entire
> kernel.
>
> Cc: stable@...r.kernel.org
> Reported-by: Kostadin Shishmanov <kostadinshishmanov@...tonmail.com>
> Closes: https://lore.kernel.org/4OAhbllK7x4QJGpZjkYjtBYNLd_2whHx9oFiuZcGwtVR4hIzvduultkgfAIRZI3vQpZylu7Gl929HaYFRGeMEalWCpeMzCIIhLxxRhq4U-Y=@protonmail.com/
> Reported-by: Jakub Jelinek <jakub@...hat.com>
> Closes: https://lore.kernel.org/Z4467umXR2PZ0M1H@tucnak/
> Signed-off-by: Nathan Chancellor <nathan@...nel.org>
> ---
>  arch/x86/boot/compressed/Makefile | 1 +
>  1 file changed, 1 insertion(+)
>
> diff --git a/arch/x86/boot/compressed/Makefile b/arch/x86/boot/compressed/Makefile
> index f2051644de94..606c74f27459 100644
> --- a/arch/x86/boot/compressed/Makefile
> +++ b/arch/x86/boot/compressed/Makefile
> @@ -25,6 +25,7 @@ targets := vmlinux vmlinux.bin vmlinux.bin.gz vmlinux.bin.bz2 vmlinux.bin.lzma \
>  # avoid errors with '-march=i386', and future flags may depend on the target to
>  # be valid.
>  KBUILD_CFLAGS := -m$(BITS) -O2 $(CLANG_FLAGS)
> +KBUILD_CFLAGS += -std=gnu11
>  KBUILD_CFLAGS += -fno-strict-aliasing -fPIE
>  KBUILD_CFLAGS += -Wundef
>  KBUILD_CFLAGS += -DDISABLE_BRANCH_PROFILING
>

Reviewed-by: Ard Biesheuvel <ardb@...nel.org>