A couple of build fixes for x86 when using GCC 15

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

Posted by Nathan Chancellor 1 year ago

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@vger.kernel.org
Reported-by: Kostadin Shishmanov <kostadinshishmanov@protonmail.com>
Closes: https://lore.kernel.org/4OAhbllK7x4QJGpZjkYjtBYNLd_2whHx9oFiuZcGwtVR4hIzvduultkgfAIRZI3vQpZylu7Gl929HaYFRGeMEalWCpeMzCIIhLxxRhq4U-Y=@protonmail.com/
Reported-by: Jakub Jelinek <jakub@redhat.com>
Closes: https://lore.kernel.org/Z4467umXR2PZ0M1H@tucnak/
Signed-off-by: Nathan Chancellor <nathan@kernel.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 \

-- 
2.48.1

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

Posted by Ard Biesheuvel 1 year ago

On Wed, 22 Jan 2025 at 02:12, Nathan Chancellor <nathan@kernel.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@vger.kernel.org
> Reported-by: Kostadin Shishmanov <kostadinshishmanov@protonmail.com>
> Closes: https://lore.kernel.org/4OAhbllK7x4QJGpZjkYjtBYNLd_2whHx9oFiuZcGwtVR4hIzvduultkgfAIRZI3vQpZylu7Gl929HaYFRGeMEalWCpeMzCIIhLxxRhq4U-Y=@protonmail.com/
> Reported-by: Jakub Jelinek <jakub@redhat.com>
> Closes: https://lore.kernel.org/Z4467umXR2PZ0M1H@tucnak/
> Signed-off-by: Nathan Chancellor <nathan@kernel.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.

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