From a6773e6932cbfbc0e123bc0529ea27f2a8abb833 Mon Sep 17 00:00:00 2001 From: Nathan Chancellor Date: Thu, 23 Oct 2025 10:38:50 -0700 Subject: [PATCH 1/3] jfs: Rename _inline to avoid conflict with clang's '-fms-extensions' Building fs/jfs with clang and '-fms-extensions' errors with: In file included from fs/jfs/jfs_unicode.c:8: fs/jfs/jfs_incore.h:86:13: error: type name does not allow function specifier to be specified 86 | unchar _inline[128]; | ^ fs/jfs/jfs_incore.h:86:20: error: expected member name or ';' after declaration specifiers 86 | unchar _inline[128]; | ~~~~~~~~~~~~~~^ '-fms-extensions' in clang enables several other Microsoft specific keywords such as _inline [1], presumably for compatibility with MSVC, as Microsoft's documentation [2] mentions: For compatibility with previous versions, _inline and _forceinline are synonyms for __inline and __forceinline, respectively Rename the _inline array in 'struct jfs_inode_info' to _inline_sym to avoid this conflict, which is not a large workaround as this member is only ever referred to via the i_inline macro. Link: https://github.com/llvm/llvm-project/blob/249883d0c5883996bed038cd82a8999f342994c9/clang/include/clang/Basic/TokenKinds.def#L744-L79 [1] Link: https://learn.microsoft.com/en-us/cpp/c-language/inline-functions [2] Acked-by: Dave Kleikamp Link: https://patch.msgid.link/20251023-jfs-fix-conflict-with-clang-ms-ext-v1-1-e219d59a1e68@kernel.org Signed-off-by: Nathan Chancellor --- fs/jfs/jfs_incore.h | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) diff --git a/fs/jfs/jfs_incore.h b/fs/jfs/jfs_incore.h index 10934f9a11be..5aaafedb8fbc 100644 --- a/fs/jfs/jfs_incore.h +++ b/fs/jfs/jfs_incore.h @@ -76,14 +76,14 @@ struct jfs_inode_info { struct { unchar _unused[16]; /* 16: */ dxd_t _dxd; /* 16: */ - /* _inline may overflow into _inline_ea when needed */ + /* _inline_sym may overflow into _inline_ea when needed */ /* _inline_ea may overlay the last part of * file._xtroot if maxentry = XTROOTINITSLOT */ union { struct { /* 128: inline symlink */ - unchar _inline[128]; + unchar _inline_sym[128]; /* 128: inline extended attr */ unchar _inline_ea[128]; }; @@ -101,7 +101,7 @@ struct jfs_inode_info { #define i_imap u.file._imap #define i_dirtable u.dir._table #define i_dtroot u.dir._dtroot -#define i_inline u.link._inline +#define i_inline u.link._inline_sym #define i_inline_ea u.link._inline_ea #define i_inline_all u.link._inline_all From c4781dc3d1cf0e017e1f290607ddc56cfe187afc Mon Sep 17 00:00:00 2001 From: Rasmus Villemoes Date: Mon, 20 Oct 2025 16:22:27 +0200 Subject: [PATCH 2/3] Kbuild: enable -fms-extensions Once in a while, it turns out that enabling -fms-extensions could allow some slightly prettier code. But every time it has come up, the code that had to be used instead has been deemed "not too awful" and not worth introducing another compiler flag for. That's probably true for each individual case, but then it's somewhat of a chicken/egg situation. If we just "bite the bullet" as Linus says and enable it once and for all, it is available whenever a use case turns up, and no individual case has to justify it. A lore.kernel.org search provides these examples: - https://lore.kernel.org/lkml/200706301813.58435.agruen@suse.de/ - https://lore.kernel.org/lkml/20180419152817.GD25406@bombadil.infradead.org/ - https://lore.kernel.org/lkml/170622208395.21664.2510213291504081000@noble.neil.brown.name/ - https://lore.kernel.org/lkml/87h6475w9q.fsf@prevas.dk/ - https://lore.kernel.org/lkml/CAHk-=wjeZwww6Zswn6F_iZTpUihTSNKYppLqj36iQDDhfntuEw@mail.gmail.com/ Undoubtedly, there are more places in the code where this could also be used but where -fms-extensions just didn't come up in any discussion. Signed-off-by: Rasmus Villemoes Acked-by: David Sterba Link: https://patch.msgid.link/20251020142228.1819871-2-linux@rasmusvillemoes.dk [nathan: Move disabled clang warning to scripts/Makefile.extrawarn and adjust comment] Signed-off-by: Nathan Chancellor --- Makefile | 3 +++ scripts/Makefile.extrawarn | 4 +++- 2 files changed, 6 insertions(+), 1 deletion(-) diff --git a/Makefile b/Makefile index 17cfa11ca716..1dc8873d4968 100644 --- a/Makefile +++ b/Makefile @@ -1061,6 +1061,9 @@ NOSTDINC_FLAGS += -nostdinc # perform bounds checking. KBUILD_CFLAGS += $(call cc-option, -fstrict-flex-arrays=3) +# Allow including a tagged struct or union anonymously in another struct/union. +KBUILD_CFLAGS += -fms-extensions + # disable invalid "can't wrap" optimizations for signed / pointers KBUILD_CFLAGS += -fno-strict-overflow diff --git a/scripts/Makefile.extrawarn b/scripts/Makefile.extrawarn index 6af392f9cd02..68e6fafcb80c 100644 --- a/scripts/Makefile.extrawarn +++ b/scripts/Makefile.extrawarn @@ -28,8 +28,10 @@ endif KBUILD_CFLAGS-$(CONFIG_CC_NO_ARRAY_BOUNDS) += -Wno-array-bounds ifdef CONFIG_CC_IS_CLANG -# The kernel builds with '-std=gnu11' so use of GNU extensions is acceptable. +# The kernel builds with '-std=gnu11' and '-fms-extensions' so use of GNU and +# Microsoft extensions is acceptable. KBUILD_CFLAGS += -Wno-gnu +KBUILD_CFLAGS += -Wno-microsoft-anon-tag # Clang checks for overflow/truncation with '%p', while GCC does not: # https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111219 From 5ff8ad3909524ad55297a434f87c238224825bf4 Mon Sep 17 00:00:00 2001 From: Nathan Chancellor Date: Thu, 30 Oct 2025 21:26:28 -0400 Subject: [PATCH 3/3] kbuild: Add '-fms-extensions' to areas with dedicated CFLAGS This is a follow up to commit c4781dc3d1cf ("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 Closes: https://lore.kernel.org/20251030-meerjungfrau-getrocknet-7b46eacc215d@brauner/ Reviewed-by: Christian Brauner Acked-by: Ard Biesheuvel Signed-off-by: Nathan Chancellor --- arch/arm64/kernel/vdso32/Makefile | 3 ++- arch/loongarch/vdso/Makefile | 2 +- arch/parisc/boot/compressed/Makefile | 2 +- arch/powerpc/boot/Makefile | 3 ++- arch/s390/Makefile | 3 ++- arch/s390/purgatory/Makefile | 3 ++- arch/x86/Makefile | 4 +++- arch/x86/boot/compressed/Makefile | 7 +++++-- drivers/firmware/efi/libstub/Makefile | 4 ++-- 9 files changed, 20 insertions(+), 11 deletions(-) diff --git a/arch/arm64/kernel/vdso32/Makefile b/arch/arm64/kernel/vdso32/Makefile index ffa3536581f6..9d0efed91414 100644 --- a/arch/arm64/kernel/vdso32/Makefile +++ b/arch/arm64/kernel/vdso32/Makefile @@ -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. diff --git a/arch/loongarch/vdso/Makefile b/arch/loongarch/vdso/Makefile index d8316f993482..c0cc3ca5da9f 100644 --- a/arch/loongarch/vdso/Makefile +++ b/arch/loongarch/vdso/Makefile @@ -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) diff --git a/arch/parisc/boot/compressed/Makefile b/arch/parisc/boot/compressed/Makefile index 17c42d718eb3..f8481e4e9d21 100644 --- a/arch/parisc/boot/compressed/Makefile +++ b/arch/parisc/boot/compressed/Makefile @@ -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 diff --git a/arch/powerpc/boot/Makefile b/arch/powerpc/boot/Makefile index c47b78c1d3e7..f1a4761ebd44 100644 --- a/arch/powerpc/boot/Makefile +++ b/arch/powerpc/boot/Makefile @@ -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 diff --git a/arch/s390/Makefile b/arch/s390/Makefile index b4769241332b..8578361133a4 100644 --- a/arch/s390/Makefile +++ b/arch/s390/Makefile @@ -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)) diff --git a/arch/s390/purgatory/Makefile b/arch/s390/purgatory/Makefile index bd39b36e7bd6..0c196a5b194a 100644 --- a/arch/s390/purgatory/Makefile +++ b/arch/s390/purgatory/Makefile @@ -13,7 +13,7 @@ CFLAGS_sha256.o := -D__NO_FORTIFY $(obj)/mem.o: $(srctree)/arch/s390/lib/mem.S FORCE $(call if_changed_rule,as_o_S) -KBUILD_CFLAGS := -std=gnu11 -fno-strict-aliasing -Wall -Wstrict-prototypes +KBUILD_CFLAGS := -std=gnu11 -fms-extensions -fno-strict-aliasing -Wall -Wstrict-prototypes KBUILD_CFLAGS += -Wno-pointer-sign -Wno-sign-compare KBUILD_CFLAGS += -fno-zero-initialized-in-bss -fno-builtin -ffreestanding KBUILD_CFLAGS += -Os -m64 -msoft-float -fno-common @@ -21,6 +21,7 @@ KBUILD_CFLAGS += -fno-stack-protector KBUILD_CFLAGS += -DDISABLE_BRANCH_PROFILING KBUILD_CFLAGS += -D__DISABLE_EXPORTS KBUILD_CFLAGS += $(CLANG_FLAGS) +KBUILD_CFLAGS += $(if $(CONFIG_CC_IS_CLANG),-Wno-microsoft-anon-tag) KBUILD_CFLAGS += $(call cc-option,-fno-PIE) KBUILD_AFLAGS := $(filter-out -DCC_USING_EXPOLINE,$(KBUILD_AFLAGS)) KBUILD_AFLAGS += -D__DISABLE_EXPORTS diff --git a/arch/x86/Makefile b/arch/x86/Makefile index 4db7e4bf69f5..e20e25b8b16c 100644 --- a/arch/x86/Makefile +++ b/arch/x86/Makefile @@ -48,7 +48,8 @@ endif # How to compile the 16-bit code. Note we always compile for -march=i386; # that way we can complain to the user if the CPU is insufficient. -REALMODE_CFLAGS := -std=gnu11 -m16 -g -Os -DDISABLE_BRANCH_PROFILING -D__DISABLE_EXPORTS \ +REALMODE_CFLAGS := -std=gnu11 -fms-extensions -m16 -g -Os \ + -DDISABLE_BRANCH_PROFILING -D__DISABLE_EXPORTS \ -Wall -Wstrict-prototypes -march=i386 -mregparm=3 \ -fno-strict-aliasing -fomit-frame-pointer -fno-pic \ -mno-mmx -mno-sse $(call cc-option,-fcf-protection=none) @@ -60,6 +61,7 @@ REALMODE_CFLAGS += $(cc_stack_align4) REALMODE_CFLAGS += $(CLANG_FLAGS) ifdef CONFIG_CC_IS_CLANG REALMODE_CFLAGS += -Wno-gnu +REALMODE_CFLAGS += -Wno-microsoft-anon-tag endif export REALMODE_CFLAGS diff --git a/arch/x86/boot/compressed/Makefile b/arch/x86/boot/compressed/Makefile index 74657589264d..68f9d7a1683b 100644 --- a/arch/x86/boot/compressed/Makefile +++ b/arch/x86/boot/compressed/Makefile @@ -25,7 +25,7 @@ targets := vmlinux vmlinux.bin vmlinux.bin.gz vmlinux.bin.bz2 vmlinux.bin.lzma \ # avoid errors with '-march=i386', and future flags may depend on the target to # be valid. KBUILD_CFLAGS := -m$(BITS) -O2 $(CLANG_FLAGS) -KBUILD_CFLAGS += -std=gnu11 +KBUILD_CFLAGS += -std=gnu11 -fms-extensions KBUILD_CFLAGS += -fno-strict-aliasing -fPIE KBUILD_CFLAGS += -Wundef KBUILD_CFLAGS += -DDISABLE_BRANCH_PROFILING @@ -36,7 +36,10 @@ KBUILD_CFLAGS += -mno-mmx -mno-sse KBUILD_CFLAGS += -ffreestanding -fshort-wchar KBUILD_CFLAGS += -fno-stack-protector KBUILD_CFLAGS += $(call cc-disable-warning, address-of-packed-member) -KBUILD_CFLAGS += $(call cc-disable-warning, gnu) +ifdef CONFIG_CC_IS_CLANG +KBUILD_CFLAGS += -Wno-gnu +KBUILD_CFLAGS += -Wno-microsoft-anon-tag +endif KBUILD_CFLAGS += -Wno-pointer-sign KBUILD_CFLAGS += -fno-asynchronous-unwind-tables KBUILD_CFLAGS += -D__DISABLE_EXPORTS diff --git a/drivers/firmware/efi/libstub/Makefile b/drivers/firmware/efi/libstub/Makefile index 94b05e4451dd..7d15a85d579f 100644 --- a/drivers/firmware/efi/libstub/Makefile +++ b/drivers/firmware/efi/libstub/Makefile @@ -11,12 +11,12 @@ cflags-y := $(KBUILD_CFLAGS) cflags-$(CONFIG_X86_32) := -march=i386 cflags-$(CONFIG_X86_64) := -mcmodel=small -cflags-$(CONFIG_X86) += -m$(BITS) -D__KERNEL__ -std=gnu11 \ +cflags-$(CONFIG_X86) += -m$(BITS) -D__KERNEL__ -std=gnu11 -fms-extensions \ -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) \ + $(if $(CONFIG_CC_IS_CLANG),-Wno-gnu -Wno-microsoft-anon-tag) \ -fno-asynchronous-unwind-tables \ $(CLANG_FLAGS)