5.15-stable review patch. If anyone has any objections, please let me know.
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From: Nathan Chancellor nathan@kernel.org
commit ee2ab467bddfb2d7f68d996dbab94d7b88f8eaf7 upstream.
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.
Closes: https://lore.kernel.org/4OAhbllK7x4QJGpZjkYjtBYNLd_2whHx9oFiuZcGwtVR4hIzvduu... Closes: https://lore.kernel.org/Z4467umXR2PZ0M1H@tucnak/ Reported-by: Kostadin Shishmanov kostadinshishmanov@protonmail.com Reported-by: Jakub Jelinek jakub@redhat.com Signed-off-by: Nathan Chancellor nathan@kernel.org Signed-off-by: Dave Hansen dave.hansen@linux.intel.com Reviewed-by: Ard Biesheuvel ardb@kernel.org Cc:stable@vger.kernel.org Link: https://lore.kernel.org/all/20250121-x86-use-std-consistently-gcc-15-v1-1-8a... Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- arch/x86/boot/compressed/Makefile | 1 + 1 file changed, 1 insertion(+)
--- a/arch/x86/boot/compressed/Makefile +++ b/arch/x86/boot/compressed/Makefile @@ -33,6 +33,7 @@ targets := vmlinux vmlinux.bin vmlinux.b # 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