fms extension (Was: [PATCH] fs/pipe: stop duplicating union pipe_index declaration)

fms extension (Was: [PATCH] fs/pipe: stop duplicating union pipe_index declaration)

[Christian Brauner]

On Wed, Oct 29, 2025 at 04:30:57PM -0700, Nathan Chancellor wrote:
> On Thu, Oct 30, 2025 at 12:13:11AM +0100, Christian Brauner wrote:
> > I'm fine either way. @Nathan, if you just want to give Linus the patch
> > if it's small enough or just want to give me a stable branch I can pull
> > I'll be content. Thanks!
> 
> I do not care either way but I created a shared branch/tag since it was
> easy enough to do. If Linus wants to take these directly for -rc4, I am
> fine with that as well.
> 
> Cheers,
> Nathan
> 
> The following changes since commit 3a8660878839faadb4f1a6dd72c3179c1df56787:
> 
>   Linux 6.18-rc1 (2025-10-12 13:42:36 -0700)
> 
> are available in the Git repository at:
> 
>   git://git.kernel.org/pub/scm/linux/kernel/git/kbuild/linux.git tags/kbuild-ms-extensions-6.19

Thanks, I pulled this and placed it into a branch that I can base other
branches on.

_But_, I'm already running into problems. :)

I'm changing a struct ns_common in ns_common.h (struct ns_common) and
wanted to make use of the fms extensions. ns_common.h is heavily
included by virtue of the namespace stuff. So we get an include chain
like the following:

In file included from ./include/linux/cgroup.h:23,
                 from ./include/linux/memcontrol.h:13,
                 from ./include/linux/swap.h:9,
                 from ./include/asm-generic/tlb.h:15,
                 from ./arch/x86/include/asm/tlb.h:8,
                 from ./arch/x86/include/asm/efi.h:7,
                 from drivers/firmware/efi/libstub/x86-stub.c:13:
./include/linux/ns_common.h:132:31: error: declaration does not declare anything [-Werror]
  132 |                 struct ns_tree;
      |                               ^
./include/linux/ns_common.h: In function '__ns_ref_active_read':
./include/linux/ns_common.h:228:31: error: 'const struct ns_common' has no member named '__ns_ref_active'
  228 |         return atomic_read(&ns->__ns_ref_active);
      |                               ^~
In file included from ./arch/x86/include/asm/bug.h:108,
                 from ./arch/x86/include/asm/alternative.h:9,
                 from ./arch/x86/include/asm/segment.h:6,
                 from ./arch/x86/include/asm/ptrace.h:5,
                 from ./arch/x86/include/asm/math_emu.h:5,
                 from ./arch/x86/include/asm/processor.h:13,
                 from ./arch/x86/include/asm/timex.h:5,
                 from ./include/linux/timex.h:67,
                 from ./include/linux/time32.h:13,
                 from ./include/linux/time.h:60,
                 from ./include/linux/efi.h:17,
                 from drivers/firmware/efi/libstub/x86-stub.c:9:

Because struct cgroup_namespace embeddds struct ns_common and it
proliferates via mm stuff into the efi code.

So the EFI cod has it's own KBUILD_CFLAGS. It does:

# non-x86 reuses KBUILD_CFLAGS, x86 does not
cflags-y			:= $(KBUILD_CFLAGS)

<snip>

KBUILD_CFLAGS			:= $(subst $(CC_FLAGS_FTRACE),,$(cflags-y)) \
				   -Os -DDISABLE_BRANCH_PROFILING \
				   -include $(srctree)/include/linux/hidden.h \
				   -D__NO_FORTIFY \
				   -ffreestanding \
				   -fno-stack-protector \
				   $(call cc-option,-fno-addrsig) \
				   -D__DISABLE_EXPORTS

which means x86 doesn't get -fms-extension breaking the build. If I
manually insert:

diff --git a/drivers/firmware/efi/libstub/Makefile b/drivers/firmware/efi/libstub/Makefile
index 94b05e4451dd..4ad2f8f42134 100644
--- a/drivers/firmware/efi/libstub/Makefile
+++ b/drivers/firmware/efi/libstub/Makefile
@@ -42,6 +42,8 @@ KBUILD_CFLAGS                 := $(subst $(CC_FLAGS_FTRACE),,$(cflags-y)) \
                                   -ffreestanding \
                                   -fno-stack-protector \
                                   $(call cc-option,-fno-addrsig) \
+                                  -fms-extensions \
+                                  -Wno-microsoft-anon-tag \
                                   -D__DISABLE_EXPORTS

The build works...

I think we need to decide how to fix this now because as soon as someone
makes use of the extension that is indirectly included by that libstub
thing we're fscked.

Re: fms extension (Was: [PATCH] fs/pipe: stop duplicating union pipe_index declaration)

[Ard Biesheuvel]

On Thu, 30 Oct 2025 at 14:23, Christian Brauner <brauner@kernel.org> wrote:
>
> On Wed, Oct 29, 2025 at 04:30:57PM -0700, Nathan Chancellor wrote:
> > On Thu, Oct 30, 2025 at 12:13:11AM +0100, Christian Brauner wrote:
> > > I'm fine either way. @Nathan, if you just want to give Linus the patch
> > > if it's small enough or just want to give me a stable branch I can pull
> > > I'll be content. Thanks!
> >
> > I do not care either way but I created a shared branch/tag since it was
> > easy enough to do. If Linus wants to take these directly for -rc4, I am
> > fine with that as well.
> >
> > Cheers,
> > Nathan
> >
> > The following changes since commit 3a8660878839faadb4f1a6dd72c3179c1df56787:
> >
> >   Linux 6.18-rc1 (2025-10-12 13:42:36 -0700)
> >
> > are available in the Git repository at:
> >
> >   git://git.kernel.org/pub/scm/linux/kernel/git/kbuild/linux.git tags/kbuild-ms-extensions-6.19
>
> Thanks, I pulled this and placed it into a branch that I can base other
> branches on.
>
> _But_, I'm already running into problems. :)
>
...
>
> Because struct cgroup_namespace embeddds struct ns_common and it
> proliferates via mm stuff into the efi code.
>
> So the EFI cod has it's own KBUILD_CFLAGS. It does:
>
> # non-x86 reuses KBUILD_CFLAGS, x86 does not
> cflags-y                        := $(KBUILD_CFLAGS)
>
> <snip>
>
> KBUILD_CFLAGS                   := $(subst $(CC_FLAGS_FTRACE),,$(cflags-y)) \
>                                    -Os -DDISABLE_BRANCH_PROFILING \
>                                    -include $(srctree)/include/linux/hidden.h \
>                                    -D__NO_FORTIFY \
>                                    -ffreestanding \
>                                    -fno-stack-protector \
>                                    $(call cc-option,-fno-addrsig) \
>                                    -D__DISABLE_EXPORTS
>
> which means x86 doesn't get -fms-extension breaking the build. If I
> manually insert:
>
> diff --git a/drivers/firmware/efi/libstub/Makefile b/drivers/firmware/efi/libstub/Makefile
> index 94b05e4451dd..4ad2f8f42134 100644
> --- a/drivers/firmware/efi/libstub/Makefile
> +++ b/drivers/firmware/efi/libstub/Makefile
> @@ -42,6 +42,8 @@ KBUILD_CFLAGS                 := $(subst $(CC_FLAGS_FTRACE),,$(cflags-y)) \
>                                    -ffreestanding \
>                                    -fno-stack-protector \
>                                    $(call cc-option,-fno-addrsig) \
> +                                  -fms-extensions \
> +                                  -Wno-microsoft-anon-tag \
>                                    -D__DISABLE_EXPORTS
>
> The build works...
>
> I think we need to decide how to fix this now because as soon as someone
> makes use of the extension that is indirectly included by that libstub
> thing we're fscked.

Unless anyone is feeling brave and wants to untangle the x86 command
line delta between the stub and core kernel, I suggest we just add
these flags just like you proposed (assuming all supported compilers
tolerate their presence)

Re: fms extension (Was: [PATCH] fs/pipe: stop duplicating union pipe_index declaration)

[Nathan Chancellor]

On Thu, Oct 30, 2025 at 02:38:50PM +0100, Ard Biesheuvel wrote:
> On Thu, 30 Oct 2025 at 14:23, Christian Brauner <brauner@kernel.org> wrote:
> >
> > On Wed, Oct 29, 2025 at 04:30:57PM -0700, Nathan Chancellor wrote:
> > > On Thu, Oct 30, 2025 at 12:13:11AM +0100, Christian Brauner wrote:
> > > > I'm fine either way. @Nathan, if you just want to give Linus the patch
> > > > if it's small enough or just want to give me a stable branch I can pull
> > > > I'll be content. Thanks!
> > >
> > > I do not care either way but I created a shared branch/tag since it was
> > > easy enough to do. If Linus wants to take these directly for -rc4, I am
> > > fine with that as well.
> > >
> > > Cheers,
> > > Nathan
> > >
> > > The following changes since commit 3a8660878839faadb4f1a6dd72c3179c1df56787:
> > >
> > >   Linux 6.18-rc1 (2025-10-12 13:42:36 -0700)
> > >
> > > are available in the Git repository at:
> > >
> > >   git://git.kernel.org/pub/scm/linux/kernel/git/kbuild/linux.git tags/kbuild-ms-extensions-6.19
> >
> > Thanks, I pulled this and placed it into a branch that I can base other
> > branches on.
> >
> > _But_, I'm already running into problems. :)
> >
> ...
> >
> > Because struct cgroup_namespace embeddds struct ns_common and it
> > proliferates via mm stuff into the efi code.
> >
> > So the EFI cod has it's own KBUILD_CFLAGS. It does:
> >
> > # non-x86 reuses KBUILD_CFLAGS, x86 does not
> > cflags-y                        := $(KBUILD_CFLAGS)
> >
> > <snip>
> >
> > KBUILD_CFLAGS                   := $(subst $(CC_FLAGS_FTRACE),,$(cflags-y)) \
> >                                    -Os -DDISABLE_BRANCH_PROFILING \
> >                                    -include $(srctree)/include/linux/hidden.h \
> >                                    -D__NO_FORTIFY \
> >                                    -ffreestanding \
> >                                    -fno-stack-protector \
> >                                    $(call cc-option,-fno-addrsig) \
> >                                    -D__DISABLE_EXPORTS
> >
> > which means x86 doesn't get -fms-extension breaking the build. If I
> > manually insert:
> >
> > diff --git a/drivers/firmware/efi/libstub/Makefile b/drivers/firmware/efi/libstub/Makefile
> > index 94b05e4451dd..4ad2f8f42134 100644
> > --- a/drivers/firmware/efi/libstub/Makefile
> > +++ b/drivers/firmware/efi/libstub/Makefile
> > @@ -42,6 +42,8 @@ KBUILD_CFLAGS                 := $(subst $(CC_FLAGS_FTRACE),,$(cflags-y)) \
> >                                    -ffreestanding \
> >                                    -fno-stack-protector \
> >                                    $(call cc-option,-fno-addrsig) \
> > +                                  -fms-extensions \
> > +                                  -Wno-microsoft-anon-tag \
> >                                    -D__DISABLE_EXPORTS
> >
> > The build works...
> >
> > I think we need to decide how to fix this now because as soon as someone
> > makes use of the extension that is indirectly included by that libstub
> > thing we're fscked.
> 
> Unless anyone is feeling brave and wants to untangle the x86 command
> line delta between the stub and core kernel, I suggest we just add
> these flags just like you proposed (assuming all supported compilers
> tolerate their presence)

There are several other places in the kernel that blow away
KBUILD_CFLAGS like this that will need the same fix (I went off of
searching for -std=gnu11, as that was needed in many places to fix GCC
15). It is possible that we might want to take the opportunity to unify
these flags into something like KBUILD_DIALECT_CFLAGS but for now, I
just bothered with adding the flags in the existing places.

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)
 

Re: fms extension (Was: [PATCH] fs/pipe: stop duplicating union pipe_index declaration)

[Christian Brauner]

On Thu, Oct 30, 2025 at 10:29:18AM -0700, Nathan Chancellor wrote:
> On Thu, Oct 30, 2025 at 02:38:50PM +0100, Ard Biesheuvel wrote:
> > On Thu, 30 Oct 2025 at 14:23, Christian Brauner <brauner@kernel.org> wrote:
> > >
> > > On Wed, Oct 29, 2025 at 04:30:57PM -0700, Nathan Chancellor wrote:
> > > > On Thu, Oct 30, 2025 at 12:13:11AM +0100, Christian Brauner wrote:
> > > > > I'm fine either way. @Nathan, if you just want to give Linus the patch
> > > > > if it's small enough or just want to give me a stable branch I can pull
> > > > > I'll be content. Thanks!
> > > >
> > > > I do not care either way but I created a shared branch/tag since it was
> > > > easy enough to do. If Linus wants to take these directly for -rc4, I am
> > > > fine with that as well.
> > > >
> > > > Cheers,
> > > > Nathan
> > > >
> > > > The following changes since commit 3a8660878839faadb4f1a6dd72c3179c1df56787:
> > > >
> > > >   Linux 6.18-rc1 (2025-10-12 13:42:36 -0700)
> > > >
> > > > are available in the Git repository at:
> > > >
> > > >   git://git.kernel.org/pub/scm/linux/kernel/git/kbuild/linux.git tags/kbuild-ms-extensions-6.19
> > >
> > > Thanks, I pulled this and placed it into a branch that I can base other
> > > branches on.
> > >
> > > _But_, I'm already running into problems. :)
> > >
> > ...
> > >
> > > Because struct cgroup_namespace embeddds struct ns_common and it
> > > proliferates via mm stuff into the efi code.
> > >
> > > So the EFI cod has it's own KBUILD_CFLAGS. It does:
> > >
> > > # non-x86 reuses KBUILD_CFLAGS, x86 does not
> > > cflags-y                        := $(KBUILD_CFLAGS)
> > >
> > > <snip>
> > >
> > > KBUILD_CFLAGS                   := $(subst $(CC_FLAGS_FTRACE),,$(cflags-y)) \
> > >                                    -Os -DDISABLE_BRANCH_PROFILING \
> > >                                    -include $(srctree)/include/linux/hidden.h \
> > >                                    -D__NO_FORTIFY \
> > >                                    -ffreestanding \
> > >                                    -fno-stack-protector \
> > >                                    $(call cc-option,-fno-addrsig) \
> > >                                    -D__DISABLE_EXPORTS
> > >
> > > which means x86 doesn't get -fms-extension breaking the build. If I
> > > manually insert:
> > >
> > > diff --git a/drivers/firmware/efi/libstub/Makefile b/drivers/firmware/efi/libstub/Makefile
> > > index 94b05e4451dd..4ad2f8f42134 100644
> > > --- a/drivers/firmware/efi/libstub/Makefile
> > > +++ b/drivers/firmware/efi/libstub/Makefile
> > > @@ -42,6 +42,8 @@ KBUILD_CFLAGS                 := $(subst $(CC_FLAGS_FTRACE),,$(cflags-y)) \
> > >                                    -ffreestanding \
> > >                                    -fno-stack-protector \
> > >                                    $(call cc-option,-fno-addrsig) \
> > > +                                  -fms-extensions \
> > > +                                  -Wno-microsoft-anon-tag \
> > >                                    -D__DISABLE_EXPORTS
> > >
> > > The build works...
> > >
> > > I think we need to decide how to fix this now because as soon as someone
> > > makes use of the extension that is indirectly included by that libstub
> > > thing we're fscked.
> > 
> > Unless anyone is feeling brave and wants to untangle the x86 command
> > line delta between the stub and core kernel, I suggest we just add
> > these flags just like you proposed (assuming all supported compilers
> > tolerate their presence)
> 
> There are several other places in the kernel that blow away
> KBUILD_CFLAGS like this that will need the same fix (I went off of
> searching for -std=gnu11, as that was needed in many places to fix GCC
> 15). It is possible that we might want to take the opportunity to unify
> these flags into something like KBUILD_DIALECT_CFLAGS but for now, I
> just bothered with adding the flags in the existing places.

That should hopefully do it. Can you update the shared branch with that
and then tell me when I can repull?

> 
> 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)
>  

Re: fms extension (Was: [PATCH] fs/pipe: stop duplicating union pipe_index declaration)

[Nathan Chancellor]

On Thu, Oct 30, 2025 at 09:16:02PM +0100, Christian Brauner wrote:
> On Thu, Oct 30, 2025 at 10:29:18AM -0700, Nathan Chancellor wrote:
> > There are several other places in the kernel that blow away
> > KBUILD_CFLAGS like this that will need the same fix (I went off of
> > searching for -std=gnu11, as that was needed in many places to fix GCC
> > 15). It is possible that we might want to take the opportunity to unify
> > these flags into something like KBUILD_DIALECT_CFLAGS but for now, I
> > just bothered with adding the flags in the existing places.
> 
> That should hopefully do it. Can you update the shared branch with that
> and then tell me when I can repull?

I have applied this as commit e066b73bd881 ("kbuild: Add
'-fms-extensions' to areas with dedicated CFLAGS") in the
kbuild-ms-extensions branch. I may solicit acks from architecture
maintainers but I would like to make sure there are no other surprises
before then.

> > 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)
> >  

Re: fms extension (Was: [PATCH] fs/pipe: stop duplicating union pipe_index declaration)

[Christian Brauner]

On Thu, Oct 30, 2025 at 09:34:57PM -0400, Nathan Chancellor wrote:
> On Thu, Oct 30, 2025 at 09:16:02PM +0100, Christian Brauner wrote:
> > On Thu, Oct 30, 2025 at 10:29:18AM -0700, Nathan Chancellor wrote:
> > > There are several other places in the kernel that blow away
> > > KBUILD_CFLAGS like this that will need the same fix (I went off of
> > > searching for -std=gnu11, as that was needed in many places to fix GCC
> > > 15). It is possible that we might want to take the opportunity to unify
> > > these flags into something like KBUILD_DIALECT_CFLAGS but for now, I
> > > just bothered with adding the flags in the existing places.
> > 
> > That should hopefully do it. Can you update the shared branch with that
> > and then tell me when I can repull?
> 
> I have applied this as commit e066b73bd881 ("kbuild: Add
> '-fms-extensions' to areas with dedicated CFLAGS") in the
> kbuild-ms-extensions branch. I may solicit acks from architecture
> maintainers but I would like to make sure there are no other surprises
> before then.

I'd like a stable branch before -rc5, please.

Re: fms extension (Was: [PATCH] fs/pipe: stop duplicating union pipe_index declaration)

[Nathan Chancellor]

On Sat, Nov 01, 2025 at 02:10:42PM +0100, Christian Brauner wrote:
> I'd like a stable branch before -rc5, please.

Sure thing. I have sent the change out for Acks now:

  https://lore.kernel.org/20251101-kbuild-ms-extensions-dedicated-cflags-v1-1-38004aba524b@kernel.org/

I will finalize the branch by Thursday at the latest and ping you when
it is ready.

Cheers,
Nathan

Re: fms extension (Was: [PATCH] fs/pipe: stop duplicating union pipe_index declaration)

[Christian Brauner]

On Sat, Nov 01, 2025 at 12:38:28PM -0400, Nathan Chancellor wrote:
> On Sat, Nov 01, 2025 at 02:10:42PM +0100, Christian Brauner wrote:
> > I'd like a stable branch before -rc5, please.
> 
> Sure thing. I have sent the change out for Acks now:
> 
>   https://lore.kernel.org/20251101-kbuild-ms-extensions-dedicated-cflags-v1-1-38004aba524b@kernel.org/
> 
> I will finalize the branch by Thursday at the latest and ping you when
> it is ready.

Hey Nathan!

Any status update on this?

Re: fms extension (Was: [PATCH] fs/pipe: stop duplicating union pipe_index declaration)

[Nathan Chancellor]

Hey Christian,

On Thu, Nov 06, 2025 at 11:09:25PM +0100, Christian Brauner wrote:
> On Sat, Nov 01, 2025 at 12:38:28PM -0400, Nathan Chancellor wrote:
> > On Sat, Nov 01, 2025 at 02:10:42PM +0100, Christian Brauner wrote:
> > > I'd like a stable branch before -rc5, please.
> > 
> > Sure thing. I have sent the change out for Acks now:
> > 
> >   https://lore.kernel.org/20251101-kbuild-ms-extensions-dedicated-cflags-v1-1-38004aba524b@kernel.org/
> > 
> > I will finalize the branch by Thursday at the latest and ping you when
> > it is ready.
> 
> Any status update on this?

Did https://lore.kernel.org/20251106174752.GA2440428@ax162/ not make it
into your inbox?

Cheers,
Nathan