[PATCH 06/14] powerpc/vdso: Remove unused '-s' flag from ASFLAGS

Nick Desaulniers ndesaulniers at google.com
Tue Jan 10 10:14:33 AEDT 2023


On Mon, Jan 9, 2023 at 2:29 PM Segher Boessenkool
<segher at kernel.crashing.org> wrote:
>
> Hi!  Happy new year all.

HNY Segher! :)

>
> On Mon, Jan 09, 2023 at 01:58:32PM -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 that ASFLAGS contains '-s', which is a linking phase option, so it
> > > is unused.
> > >
> > >   clang-16: error: argument unused during compilation: '-s' [-Werror,-Wunused-command-line-argument]
> > >
> > > Looking at the GAS sources, '-s' is only useful when targeting Solaris
> > > and it is ignored for the powerpc target so just drop the flag
> > > altogether, as it is not needed.
> >
> > Do you have any more info where you found this?  I don't see -s
> > documented as an assembler flag.
> > https://sourceware.org/binutils/docs/as/PowerPC_002dOpts.html
> > https://sourceware.org/binutils/docs/as/Invoking.html
>
> It is required by POSIX (for the c99 command, anyway).  It *also* is
> required to be supported when producing object files (so when no linking
> is done).
>
> It is a GCC flag, and documented just fine:
> https://gcc.gnu.org/onlinedocs/gcc/Link-Options.html#index-s
>
> (Yes, that says it is for linking; but the option is allowed without
> error of any kind always).
>
> (ASFLAGS sounds like it is for assembler commands, but it really is
> for compiler commands that just happen to get .S input files).
>
> > The patch seems fine to me, but what was this ever supposed to be?
> > FWICT it predates git history (looking at
> > arch/powerpc/kernel/vdso32/Makefile at fc15351d9d63)
>
> Yeah, good question.  This compiler flag does the moral equivalent of
> strip -s (aka --strip-all).  Maybe this was needed at some point, or
> the symbol or debug info was just annoying (during bringup or similar)?

Ah right! Ok then, I think we might keep the patch's diff, but update
the commit message to mention this is a linker flag that's unused
since the compiler is being invoked but not the linker (the compiler
is being used as the driver to assemble a single assembler source
without linking it; linking is then driven by the linker in a separate
make rule).

Then we might want to revisit that s390 patch, too?
https://lore.kernel.org/llvm/20221228-drop-qunused-arguments-v1-9-658cbc8fc592@kernel.org/

>
> > Reviewed-by: Nick Desaulniers <ndesaulniers at google.com>
> Reviewed-by: Segher Boessenkool <segher at kernel.crashing.org>
>
>
> Segher



-- 
Thanks,
~Nick Desaulniers


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