linux-kernel - Re: [PATCH 1/3] Makefile.compiler: s/KBUILD_CFLAGS/KBUILD

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Message-ID: <CAK7LNATcHt7GcXZ=jMszyH=+M_LC9Qr6yeAGRCBbE6xriLxtUQ@mail.gmail.com>
Date:   Mon, 29 Aug 2022 02:20:45 +0900
From:   Masahiro Yamada <masahiroy@...nel.org>
To:     Nick Desaulniers <ndesaulniers@...gle.com>
Cc:     Nathan Chancellor <nathan@...nel.org>,
        Michal Marek <michal.lkml@...kovi.net>,
        Tom Rix <trix@...hat.com>,
        Linux Kbuild mailing list <linux-kbuild@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        clang-built-linux <llvm@...ts.linux.dev>,
        X86 ML <x86@...nel.org>,
        Dmitrii Bundin <dmitrii.bundin.a@...il.com>,
        Fangrui Song <maskray@...gle.com>,
        Alexey Alexandrov <aalexand@...gle.com>,
        Bill Wendling <morbo@...gle.com>,
        Greg Thelen <gthelen@...gle.com>,
        Arvind Sankar <nivedita@...m.mit.edu>
Subject: Re: [PATCH 1/3] Makefile.compiler: s/KBUILD_CFLAGS/KBUILD_AFLAGS/ for as-option

On Sat, Aug 27, 2022 at 3:35 AM Nick Desaulniers
<ndesaulniers@...gle.com> wrote:
>
> On Fri, Aug 26, 2022 at 11:21 AM Nathan Chancellor <nathan@...nel.org> wrote:
> >
> > Hi Nick,
> >
> > I think the title would be a little more readable if it was:
> >
> > Makefile.compiler: Use KBUILD_AFLAGS for as-option
>
> Thanks, yeah that looks better; I expect a v2 of this series will be necessary.
>
> >
> > On Fri, Aug 26, 2022 at 11:10:33AM -0700, Nick Desaulniers wrote:
> > > as-instr uses KBUILD_AFLAGS, but as-option uses KBUILD_CFLAGS.  This can
> > > cause as-option to fail unexpectedly because clang will emit
> > > -Werror,-Wunused-command-line-argument for various -m and -f flags for
> > > assembler sources.
> > >
> > > Callers of as-option (and as-instr) likely want to be adding flags to
> > > KBUILD_AFLAGS/aflags-y, not KBUILD_CFLAGS/cflags-y.

Indeed, it has been weird since the day-1 of as-option.

commit cad8244840d1a148f638925758afd1cdf81fc839
Author: Paul Mundt <lethal@...ux-sh.org>
Date:   Mon Jan 16 22:14:19 2006 -0800

    [PATCH] sh: Move CPU subtype configuration to its own Kconfig








> > >
> > > Link: https://github.com/ClangBuiltLinux/linux/issues/1699
> > > Signed-off-by: Nick Desaulniers <ndesaulniers@...gle.com>
> > > ---
> > >  arch/x86/boot/compressed/Makefile | 5 +++--
> > >  scripts/Makefile.compiler         | 6 +++---
> > >  2 files changed, 6 insertions(+), 5 deletions(-)
> > >
> > > diff --git a/arch/x86/boot/compressed/Makefile b/arch/x86/boot/compressed/Makefile
> > > index 35ce1a64068b..fb3db714a028 100644
> > > --- a/arch/x86/boot/compressed/Makefile
> > > +++ b/arch/x86/boot/compressed/Makefile
> > > @@ -48,8 +48,6 @@ KBUILD_CFLAGS += -Wno-pointer-sign
> > >  KBUILD_CFLAGS += $(call cc-option,-fmacro-prefix-map=$(srctree)/=)
> > >  KBUILD_CFLAGS += -fno-asynchronous-unwind-tables
> > >  KBUILD_CFLAGS += -D__DISABLE_EXPORTS
> > > -# Disable relocation relaxation in case the link is not PIE.
> > > -KBUILD_CFLAGS += $(call as-option,-Wa$(comma)-mrelax-relocations=no)
> > >  KBUILD_CFLAGS += -include $(srctree)/include/linux/hidden.h
> > >
> > >  # sev.c indirectly inludes inat-table.h which is generated during
> > > @@ -58,6 +56,9 @@ KBUILD_CFLAGS += -include $(srctree)/include/linux/hidden.h
> > >  CFLAGS_sev.o += -I$(objtree)/arch/x86/lib/
> > >
> > >  KBUILD_AFLAGS  := $(KBUILD_CFLAGS) -D__ASSEMBLY__
> > > +# Disable relocation relaxation in case the link is not PIE.
> > > +KBUILD_AFLAGS += $(call as-option,-Wa$(comma)-mrelax-relocations=no)
> > > +
> >
> > Commit 09e43968db40 ("x86/boot/compressed: Disable relocation
> > relaxation") added this to address
> > https://github.com/ClangBuiltLinux/linux/issues/1121, is it correct to
> > move it to only being used for the .S files in arch/x86/boot/compressed?

Good catch!


>
> + Arvind
>
> Hmm...that makes me think we might need two different as-option flags;
> one that does use KBUILD_CFLAGS, and whose result is meant to be added
> to cflags-y, then another that uses KBUILD_AFLAGS and is added to
> aflagsy-y.
>
> (My patch 2/3 in the series would use the latter)
>
> Let's see what thoughts Masahiro has.


How about this?

KBUILD_CFLAGS += $(call as-option,-Wa$(comma)-mrelax-relocations=no)

    to

KBUILD_CFLAGS += $(call cc-option,-Wa$(comma)-mrelax-relocations=no)


You can insert this one-liner before this patch.




In Kconfig, -Wa,<as-option> is tested by cc-option.
(See commit 4d0831e8a029c03f49f434f28b8faef9f0bd403f)





--
Best Regards
Masahiro Yamada