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_2whHx9oFiuZcGwtVR4hIzvduu... [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,
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_2whHx9oFiuZcGwtVR4hIzvduu... 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
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_2whHx9oFiuZcGwtVR4hIzvduu... 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 \
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_2whHx9oFiuZcGwtVR4hIzvduu... 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.
linux-stable-mirror@lists.linaro.org
-
Ard Biesheuvel -
Nathan Chancellor