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

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Message-ID: <CAMj1kXEQs67X_uqvrJQu0jSegFSBzHiteau+riX_VUZi6AMKmg@mail.gmail.com>
Date: Wed, 22 Jan 2025 12:56:55 +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>
Subject: Re: [PATCH 2/2] efi: libstub: 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 EFI libstub Makefile uses its
> own set of KBUILD_CFLAGS for x86 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 cflags to resolve the error and consistently
> use the same C standard version for the entire kernel. All other
> architectures reuse KBUILD_CFLAGS from the rest of the kernel, so this
> issue is not visible for them.
>
> 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>
> ---
>  drivers/firmware/efi/libstub/Makefile | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/firmware/efi/libstub/Makefile b/drivers/firmware/efi/libstub/Makefile
> index ed4e8ddbe76a..1141cd06011f 100644
> --- a/drivers/firmware/efi/libstub/Makefile
> +++ b/drivers/firmware/efi/libstub/Makefile
> @@ -11,7 +11,7 @@ cflags-y                      := $(KBUILD_CFLAGS)
>
>  cflags-$(CONFIG_X86_32)                := -march=i386
>  cflags-$(CONFIG_X86_64)                := -mcmodel=small
> -cflags-$(CONFIG_X86)           += -m$(BITS) -D__KERNEL__ \
> +cflags-$(CONFIG_X86)           += -m$(BITS) -D__KERNEL__ -std=gnu11 \
>                                    -fPIC -fno-strict-aliasing -mno-red-zone \
>                                    -mno-mmx -mno-sse -fshort-wchar \
>                                    -Wno-pointer-sign \
>


Thanks - I'll add this one to the EFI pile.