On Tue, Nov 19, 2024 at 02:57:28AM +0000, Sam James wrote: > Nathan Chancellor <nathan@xxxxxxxxxx> writes: > > > Hi Kostadin, > > > > Just a quick FYI off the bat, you only directed this to LKML, which is > > basically like sending it into the void because very few people actually > > read every message on LKML. I only caught it because I have a filter set > > up for mentions of Clang and LLVM. I'd suggest adding at least the > > Kbuild mailing list, which I have done now. I have also added Arnd > > because I seem to recall him looking into how hard it would be to build > > the kernel with C23. > > FWIW, scripts/get_maintainers.pl for stddef.h and types.h doesn't > include kbuild -- maybe we should add that in. Yeah, it would be good to have someone own these files. Not sure it makes sense for Kbuild to be it though, I merely suggested that since the actual root cause of the error is more in Kbuild's realm. > I can reproduce it with `make defconfig` at > 158f238aa69d91ad74e535c73f552bd4b025109c in Linus' tree with just `make > V=1 -j$(nproc) -l$(nproc)` (i.e. no CFLAGS manipulation at all). > > ``` > # CC drivers/firmware/efi/libstub/x86-5lvl.o > gcc -Wp,-MMD,drivers/firmware/efi/libstub/.x86-5lvl.o.d -nostdinc -I./arch/x86/include -I./arch/x86/include/generated -I./include -I./arch/x86/include/uapi -I./arch/x86/include/genera > ted/uapi -I./include/uapi -I./include/generated/uapi -include ./include/linux/compiler-version.h -include ./include/linux/kconfig.h -include ./include/linux/compiler_types.h -D__KERNEL__ > -fmacro-prefix-map=./= -mcmodel=small -m64 -D__KERNEL__ -fPIC -fno-strict-aliasing -mno-red-zone -mno-mmx -mno-sse -fshort-wchar -Wno-pointer-sign -Wno-address-of-packed-member -fno-asy > nchronous-unwind-tables -Os -DDISABLE_BRANCH_PROFILING -include ./include/linux/hidden.h -D__NO_FORTIFY -ffreestanding -fno-stack-protector -D__DISABLE_EXPORTS -DKBUILD_MODFILE='"driv > ers/firmware/efi/libstub/x86-5lvl"' -DKBUILD_BASENAME='"x86_5lvl"' -DKBUILD_MODNAME='"x86_5lvl"' -D__KBUILD_MODNAME=kmod_x86_5lvl -c -o drivers/firmware/efi/libstub/x86-5lvl.o drivers/fi > rmware/efi/libstub/x86-5lvl.c > In file included from ./include/uapi/linux/posix_types.h:5, > from ./include/uapi/linux/types.h:14, > from ./include/linux/types.h:6, > from ./include/linux/kasan-checks.h:5, > from ./include/asm-generic/rwonce.h:26, > from ./arch/x86/include/generated/asm/rwonce.h:1, > from ./include/linux/compiler.h:317, > from ./include/linux/build_bug.h:5, > from ./include/linux/init.h:5, > from ./include/linux/efi.h:15, > from drivers/firmware/efi/libstub/file.c:10: > ./include/linux/stddef.h:11:9: error: expected identifier before ‘false’ > 11 | false = 0, > | ^~~~~ > ``` > > -std=gnu11 certainly isn't there. Ugh, this is because drivers/firmware/efi/libstub does not use KBUILD_CFLAGS from the rest of the kernel when targeting x86: $ sed -n '9,21p' drivers/firmware/efi/libstub/Makefile # non-x86 reuses KBUILD_CFLAGS, x86 does not cflags-y := $(KBUILD_CFLAGS) cflags-$(CONFIG_X86_32) := -march=i386 cflags-$(CONFIG_X86_64) := -mcmodel=small cflags-$(CONFIG_X86) += -m$(BITS) -D__KERNEL__ \ -fPIC -fno-strict-aliasing -mno-red-zone \ -mno-mmx -mno-sse -fshort-wchar \ -Wno-pointer-sign \ $(call cc-disable-warning, address-of-packed-member) \ $(call cc-disable-warning, gnu) \ -fno-asynchronous-unwind-tables \ $(CLANG_FLAGS) This isn't the first time this peculiarity has bitten us :/ sticking '-std=gnu11' in there should resolve that issue. arch/x86/boot/compressed/Makefile might need the same treatment. It might make sense to introduce something like 'CSTD_FLAG := -std=gnu11' then use that in the various places within the kernel that need it so it can be consistently updated in the future whenever needed. I see that flag in Makefile, arch/arm64/kernel/vdso32/Makefile, and arch/x86/Makefile. Cheers, Nathan