Commit 5ff8ad39 authored Oct 30, 2025 by Nathan Chancellor

kbuild: Add '-fms-extensions' to areas with dedicated CFLAGS



This is a follow up to commit c4781dc3 ("Kbuild: enable
-fms-extensions") but in a separate change due to being substantially
different from the initial submission.

There are many places within the kernel that use their own CFLAGS
instead of the main KBUILD_CFLAGS, meaning code written with the main
kernel's use of '-fms-extensions' in mind that may be tangentially
included in these areas will result in "error: declaration does not
declare anything" messages from the compiler.

Add '-fms-extensions' to all these areas to ensure consistency, along
with -Wno-microsoft-anon-tag to silence clang's warning about use of the
extension that the kernel cares about using. parisc does not build with
clang so it does not need this warning flag. LoongArch does not need it
either because -W flags from KBUILD_FLAGS are pulled into cflags-vdso.

Reported-by: Christian Brauner <brauner@kernel.org>
Closes: https://lore.kernel.org/20251030-meerjungfrau-getrocknet-7b46eacc215d@brauner/


Reviewed-by: Christian Brauner <brauner@kernel.org>
Acked-by: Ard Biesheuvel <ardb@kernel.org>
Signed-off-by: Nathan Chancellor <nathan@kernel.org>

parent c4781dc3

arch/arm64/kernel/vdso32/Makefile

+2 −1

Original line number	Diff line number	Diff line
		@@ -63,7 +63,7 @@ VDSO_CFLAGS += -Wall -Wundef -Wstrict-prototypes -Wno-trigraphs \
		$(filter -Werror,$(KBUILD_CPPFLAGS)) \
		-Werror-implicit-function-declaration \
		-Wno-format-security \
		-std=gnu11
		-std=gnu11 -fms-extensions
		VDSO_CFLAGS += -O2
		# Some useful compiler-dependent flags from top-level Makefile
		VDSO_CFLAGS += $(call cc32-option,-Wno-pointer-sign)
		@@ -71,6 +71,7 @@ VDSO_CFLAGS += -fno-strict-overflow
		VDSO_CFLAGS += $(call cc32-option,-Werror=strict-prototypes)
		VDSO_CFLAGS += -Werror=date-time
		VDSO_CFLAGS += $(call cc32-option,-Werror=incompatible-pointer-types)
		VDSO_CFLAGS += $(if $(CONFIG_CC_IS_CLANG),-Wno-microsoft-anon-tag)

		# Compile as THUMB2 or ARM. Unwinding via frame-pointers in THUMB2 is
		# unreliable.

arch/loongarch/vdso/Makefile

+1 −1

Original line number	Diff line number	Diff line
		@@ -19,7 +19,7 @@ ccflags-vdso := \
		cflags-vdso := $(ccflags-vdso) \
		-isystem $(shell $(CC) -print-file-name=include) \
		$(filter -W%,$(filter-out -Wa$(comma)%,$(KBUILD_CFLAGS))) \
		-std=gnu11 -O2 -g -fno-strict-aliasing -fno-common -fno-builtin \
		-std=gnu11 -fms-extensions -O2 -g -fno-strict-aliasing -fno-common -fno-builtin \
		-fno-stack-protector -fno-jump-tables -DDISABLE_BRANCH_PROFILING \
		$(call cc-option, -fno-asynchronous-unwind-tables) \
		$(call cc-option, -fno-stack-protector)

arch/parisc/boot/compressed/Makefile

+1 −1

Original line number	Diff line number	Diff line
		@@ -18,7 +18,7 @@ KBUILD_CFLAGS += -fno-PIE -mno-space-regs -mdisable-fpregs -Os
		ifndef CONFIG_64BIT
		KBUILD_CFLAGS += -mfast-indirect-calls
		endif
		KBUILD_CFLAGS += -std=gnu11
		KBUILD_CFLAGS += -std=gnu11 -fms-extensions

		LDFLAGS_vmlinux := -X -e startup --as-needed -T
		$(obj)/vmlinux: $(obj)/vmlinux.lds $(addprefix $(obj)/, $(OBJECTS)) $(LIBGCC) FORCE

arch/powerpc/boot/Makefile

+2 −1

Original line number	Diff line number	Diff line
		@@ -70,7 +70,7 @@ BOOTCPPFLAGS := -nostdinc $(LINUXINCLUDE)
		BOOTCPPFLAGS += -isystem $(shell $(BOOTCC) -print-file-name=include)

		BOOTCFLAGS := $(BOOTTARGETFLAGS) \
		-std=gnu11 \
		-std=gnu11 -fms-extensions \
		-Wall -Wundef -Wstrict-prototypes -Wno-trigraphs \
		-fno-strict-aliasing -O2 \
		-msoft-float -mno-altivec -mno-vsx \
		@@ -86,6 +86,7 @@ BOOTARFLAGS := -crD

		ifdef CONFIG_CC_IS_CLANG
		BOOTCFLAGS += $(CLANG_FLAGS)
		BOOTCFLAGS += -Wno-microsoft-anon-tag
		BOOTAFLAGS += $(CLANG_FLAGS)
		endif

arch/s390/Makefile

+2 −1

Original line number	Diff line number	Diff line
		@@ -22,7 +22,7 @@ KBUILD_AFLAGS_DECOMPRESSOR := $(CLANG_FLAGS) -m64 -D__ASSEMBLY__
		ifndef CONFIG_AS_IS_LLVM
		KBUILD_AFLAGS_DECOMPRESSOR += $(if $(CONFIG_DEBUG_INFO),$(aflags_dwarf))
		endif
		KBUILD_CFLAGS_DECOMPRESSOR := $(CLANG_FLAGS) -m64 -O2 -mpacked-stack -std=gnu11
		KBUILD_CFLAGS_DECOMPRESSOR := $(CLANG_FLAGS) -m64 -O2 -mpacked-stack -std=gnu11 -fms-extensions
		KBUILD_CFLAGS_DECOMPRESSOR += -DDISABLE_BRANCH_PROFILING -D__NO_FORTIFY
		KBUILD_CFLAGS_DECOMPRESSOR += -D__DECOMPRESSOR
		KBUILD_CFLAGS_DECOMPRESSOR += -Wno-pointer-sign
		@@ -35,6 +35,7 @@ KBUILD_CFLAGS_DECOMPRESSOR += $(call cc-disable-warning, address-of-packed-membe
		KBUILD_CFLAGS_DECOMPRESSOR += $(if $(CONFIG_DEBUG_INFO),-g)
		KBUILD_CFLAGS_DECOMPRESSOR += $(if $(CONFIG_DEBUG_INFO_DWARF4), $(call cc-option, -gdwarf-4,))
		KBUILD_CFLAGS_DECOMPRESSOR += $(if $(CONFIG_CC_NO_ARRAY_BOUNDS),-Wno-array-bounds)
		KBUILD_CFLAGS_DECOMPRESSOR += $(if $(CONFIG_CC_IS_CLANG),-Wno-microsoft-anon-tag)

		UTS_MACHINE := s390x
		STACK_SIZE := $(if $(CONFIG_KASAN),65536,$(if $(CONFIG_KMSAN),65536,16384))