[PATCH 0/2] A couple of build fixes for x86 when using GCC 15

[PATCH 0/2] A couple of build fixes for x86 when using GCC 15

[Nathan Chancellor]

Hi all,

GCC 15 changed the default C standard version from gnu17 to gnu23, which
reveals a few places in the kernel where a C standard version was not
set, resulting in build failures because bool, true, and false are
reserved keywords in C23 [1][2]. Update these places to use the same C
standard version as the rest of the kernel, gnu11.

[1]: https://lore.kernel.org/4OAhbllK7x4QJGpZjkYjtBYNLd_2whHx9oFiuZcGwtVR4hIzvduultkgfAIRZI3vQpZylu7Gl929HaYFRGeMEalWCpeMzCIIhLxxRhq4U-Y=@protonmail.com/
[2]: https://lore.kernel.org/Z4467umXR2PZ0M1H@tucnak/

---
Nathan Chancellor (2):
      x86/boot: Use '-std=gnu11' to fix build with GCC 15
      efi: libstub: Use '-std=gnu11' to fix build with GCC 15

 arch/x86/boot/compressed/Makefile     | 1 +
 drivers/firmware/efi/libstub/Makefile | 2 +-
 2 files changed, 2 insertions(+), 1 deletion(-)
---
base-commit: ffd294d346d185b70e28b1a28abe367bbfe53c04
change-id: 20250121-x86-use-std-consistently-gcc-15-f95146e0050f

Best regards,
-- 
Nathan Chancellor <nathan@kernel.org>

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

[Nathan Chancellor]

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@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>
---
 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

-- 
2.48.1

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

[Nathan Chancellor]

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

[Ard Biesheuvel]

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.

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

[Ard Biesheuvel]

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 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@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>
> ---
>  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@kernel.org>

Re: [PATCH 0/2] A couple of build fixes for x86 when using GCC 15

[Kees Cook]

On Tue, Jan 21, 2025 at 06:11:32PM -0700, Nathan Chancellor wrote:
> GCC 15 changed the default C standard version from gnu17 to gnu23, which
> reveals a few places in the kernel where a C standard version was not
> set, resulting in build failures because bool, true, and false are
> reserved keywords in C23 [1][2]. Update these places to use the same C
> standard version as the rest of the kernel, gnu11.

Hello x86 maintainers!

I think this would be valuable to get into -rc1 since we're getting very
close to a GCC 15 release. Can someone get this into -tip urgent,
please? If everyone is busy I can take it via the hardening tree, as we
appear to be the ones tripping over it the most currently. :)

-Kees

> [1]: https://lore.kernel.org/4OAhbllK7x4QJGpZjkYjtBYNLd_2whHx9oFiuZcGwtVR4hIzvduultkgfAIRZI3vQpZylu7Gl929HaYFRGeMEalWCpeMzCIIhLxxRhq4U-Y=@protonmail.com/
> [2]: https://lore.kernel.org/Z4467umXR2PZ0M1H@tucnak/
> 
> ---
> Nathan Chancellor (2):
>       x86/boot: Use '-std=gnu11' to fix build with GCC 15
>       efi: libstub: Use '-std=gnu11' to fix build with GCC 15
> 
>  arch/x86/boot/compressed/Makefile     | 1 +
>  drivers/firmware/efi/libstub/Makefile | 2 +-
>  2 files changed, 2 insertions(+), 1 deletion(-)
> ---
> base-commit: ffd294d346d185b70e28b1a28abe367bbfe53c04
> change-id: 20250121-x86-use-std-consistently-gcc-15-f95146e0050f
> 
> Best regards,
> -- 
> Nathan Chancellor <nathan@kernel.org>
> 

-- 
Kees Cook

Re: [PATCH 0/2] A couple of build fixes for x86 when using GCC 15

[Ard Biesheuvel]

On Thu, 30 Jan 2025 at 17:07, Kees Cook <kees@kernel.org> wrote:
>
> On Tue, Jan 21, 2025 at 06:11:32PM -0700, Nathan Chancellor wrote:
> > GCC 15 changed the default C standard version from gnu17 to gnu23, which
> > reveals a few places in the kernel where a C standard version was not
> > set, resulting in build failures because bool, true, and false are
> > reserved keywords in C23 [1][2]. Update these places to use the same C
> > standard version as the rest of the kernel, gnu11.
>
> Hello x86 maintainers!
>
> I think this would be valuable to get into -rc1 since we're getting very
> close to a GCC 15 release. Can someone get this into -tip urgent,
> please? If everyone is busy I can take it via the hardening tree, as we
> appear to be the ones tripping over it the most currently. :)
>

+1

Note that I already took the EFI one.

Re: [PATCH 0/2] A couple of build fixes for x86 when using GCC 15

[Dave Hansen]

On 1/30/25 08:07, Kees Cook wrote:
> On Tue, Jan 21, 2025 at 06:11:32PM -0700, Nathan Chancellor wrote:
>> GCC 15 changed the default C standard version from gnu17 to gnu23, which
>> reveals a few places in the kernel where a C standard version was not
>> set, resulting in build failures because bool, true, and false are
>> reserved keywords in C23 [1][2]. Update these places to use the same C
>> standard version as the rest of the kernel, gnu11.
> Hello x86 maintainers!
> 
> I think this would be valuable to get into -rc1 since we're getting very
> close to a GCC 15 release. Can someone get this into -tip urgent,
> please? If everyone is busy I can take it via the hardening tree, as we
> appear to be the ones tripping over it the most currently. 🙂

Thanks for the heads up.  It's in here now:

> https://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git/log/?h=x86/urgent

Re: [PATCH 0/2] A couple of build fixes for x86 when using GCC 15

[Ingo Molnar]

* Kees Cook <kees@kernel.org> wrote:

> On Tue, Jan 21, 2025 at 06:11:32PM -0700, Nathan Chancellor wrote:
> > GCC 15 changed the default C standard version from gnu17 to gnu23, which
> > reveals a few places in the kernel where a C standard version was not
> > set, resulting in build failures because bool, true, and false are
> > reserved keywords in C23 [1][2]. Update these places to use the same C
> > standard version as the rest of the kernel, gnu11.
> 
> Hello x86 maintainers!
> 
> I think this would be valuable to get into -rc1 since we're getting very
> close to a GCC 15 release. Can someone get this into -tip urgent,
> please? If everyone is busy I can take it via the hardening tree, as we
> appear to be the ones tripping over it the most currently. :)

Just an update, the x86 fix is now upstream via:

  ee2ab467bddf ("x86/boot: Use '-std=gnu11' to fix build with GCC 15")

Thanks,

	Ingo