[PATCH 08/14] powerpc/vdso: Remove an unsupported flag from vgettimeofday-32.o with clang

[Nick Desaulniers]

On Mon, Jan 9, 2023 at 2:38 PM Nathan Chancellor <nathan at kernel.org> wrote:
>
> On Mon, Jan 09, 2023 at 02:12:55PM -0800, Nick Desaulniers wrote:
> > On Wed, Jan 4, 2023 at 11:55 AM Nathan Chancellor <nathan at kernel.org> wrote:
> > >
> > > When clang's -Qunused-arguments is dropped from KBUILD_CPPFLAGS, it
> > > warns:
> > >
> > >   clang-16: error: argument unused during compilation: '-fno-stack-clash-protection' [-Werror,-Wunused-command-line-argument]
> > >
> > > This flag is supported for 64-bit powerpc but not 32-bit, hence the warning.
> > > Just remove the flag from vgettimeofday-32.o's CFLAGS when using clang, as has
> > > been done for other flags previously.
> > >
> > > Signed-off-by: Nathan Chancellor <nathan at kernel.org>
> >
> > Hmm...so this was added by the top level Makefile doing a cc-option
> > test.  How did the test pass if this was unsupported? That worries me
> > that perhaps other cc-option tests are passing erroneously for certain
> > ppc -m32/-m64 configs?
>
> Sure, that is a reasonable concern. I should have expanded upon this a
> little bit more in the commit message. Is this any better?
>
>   When clang's -Qunused-arguments is dropped from KBUILD_CPPFLAGS, it
>   warns:
>
>     clang-16: error: argument unused during compilation: '-fno-stack-clash-protection' [-Werror,-Wunused-command-line-argument]
>
>   This warning happens because vgettimeofday-32.c gets its base CFLAGS
>   from the main kernel, which may contain flags that are only supported
>   on a 64-bit target but not a 32-bit one, which is the case here.
>   -fstack-clash-protection and its negation are only suppported by the
>   64-bit powerpc target but that flag is included in an invocation for a
>   32-bit powerpc target, so clang points out that while the flag is one
>   that it recognizes, it is not actually used by this compiler job.
>
>   To eliminate the warning, remove -fno-stack-clash-protection from
>   vgettimeofday-32.c's CFLAGS when using clang, as has been done for
>   other flags previously.

Ah, ok that makes more sense. Sorry for my confusion, but if you
wouldn't mind adding the additional info in v3 it might help others
(or just me!)

You may add my RB to such a v3 w/ updated commit message.
-- 
Thanks,
~Nick Desaulniers