Re: [PATCH 1/2] Kbuild: enable -fms-extensions

[Nathan Chancellor <nathan@kernel.org>]

On Wed, Oct 22, 2025 at 10:35:33PM +0200, Rasmus Villemoes wrote:
> On Wed, 22 Oct 2025 at 18:15, Nathan Chancellor <nathan@kernel.org> wrote:
> >
> > On Mon, Oct 20, 2025 at 04:22:27PM +0200, Rasmus Villemoes wrote:
> 
> > > +# Allow including a tagged struct or union anonymously in another struct/union.
> > > +KBUILD_CFLAGS += -fms-extensions
> > > +
> > > +# For clang, the -fms-extensions flag is apparently not enough to
> > > +# express one's intention to make use of those extensions.
> > > +ifdef CONFIG_CC_IS_CLANG
> > > +KBUILD_CFLAGS += -Wno-microsoft-anon-tag
> > > +endif
> >
> > I think this should go in the first 'ifdef CONFIG_CC_IS_CLANG' block in
> > scripts/Makefile.extrawarn below '-Wno-gnu' with a comment that is
> > similar in nature, which could even be combined like
> >
> >   # The kernel builds with '-std-gnu11' and '-fms-extensions' so the use
> >   # of GNU and Microsoft extensions is acceptable.
> >
> > Other than that, this seems fine to me.
> 
> I honestly had no idea where it was best to put these, and your
> suggestion sounds quite reasonable. I didn't think to look in that
> Makefile.extrawarn as the name suggested that was only about what
> happens with W=1 and higher.

Yeah, we may want to rename that to just Makefile.warn since it
encompasses all warnings since commit e88ca24319e4 ("kbuild: consolidate
warning flags in scripts/Makefile.extrawarn"), which is actually
feedback I gave on the original change:

https://lore.kernel.org/20230811141943.GB3948268@dev-arch.thelio-3990X/

I'll send a patch for that soon.

> Feel free to tweak when applying.

I have tentatively applied this to kbuild-next so that it can spend most
of the cycle in -next to try and catch all potential problems.

Cheers,
Nathan