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From:   Masahiro Yamada <masahiroy@kernel.org>
Date:   Wed, 7 Sep 2022 13:27:28 +0900
Message-ID: <CAK7LNAQg=E4DGzfFpvnzNQsYrAhgs4SzQVYxqk-6ZeRvT3+2rw@mail.gmail.com>
Subject: Re: [PATCH v2 2/5] Makefile.compiler: Use KBUILD_AFLAGS for as-option
To:     Nick Desaulniers <ndesaulniers@google.com>
Cc:     Nathan Chancellor <nathan@kernel.org>,
        Michal Marek <michal.lkml@markovi.net>,
        Tom Rix <trix@redhat.com>,
        Linux Kbuild mailing list <linux-kbuild@vger.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        clang-built-linux <llvm@lists.linux.dev>,
        X86 ML <x86@kernel.org>,
        Dmitrii Bundin <dmitrii.bundin.a@gmail.com>,
        Fangrui Song <maskray@google.com>,
        Alexey Alexandrov <aalexand@google.com>,
        Bill Wendling <morbo@google.com>,
        Greg Thelen <gthelen@google.com>
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On Wed, Sep 7, 2022 at 12:12 PM Nick Desaulniers
<ndesaulniers@google.com> wrote:
> >
> >
> >
> >
> > I also believe '-x assembler' should be changed to
> > '-x assembler-with-cpp'.
> >
> >
> > As I mentioned somewhere before, our assembly code (*.S) is always
> > preprocessed. There is no *.s file in the kernel source tree.
> >
> >
> > So, '-x assembler-with-cpp' matches the real situation.
>
> Should I do this for as-instr then as well? In the same patch?


Probably we should fix as-instr in the same way.

You can do it in the same patch, or in a separate one.
It is up to you.


> >
> >
> > One interesting thing is, clang does not warn
> > [-Wunused-command-line-argument] for *.S files.
> >
> >
> >
> >
> > $ clang -fomit-frame-pointer -c -x assembler /dev/null -o /dev/null
> > clang: warning: argument unused during compilation:
> > '-fomit-frame-pointer' [-Wunused-command-line-argument]
> >
> > $ clang -fomit-frame-pointer -c -x assembler-with-cpp /dev/null -o /dev/null
> >
> >
> >
> > The root cause is we are using '-x assembler', which
> > never happens in the kernel tree.
> >
> >
> >
> >
> > To sum up, the code I think correct is:
> >
> >
> > as-option = $(call try-run,\
> >    $(CC) -Werror $(KBUILD_AFLAGS) $(1) -c -x assembler-with-cpp
> > /dev/null -o "$$TMP",$(1),$(2))
>
> Does your recent patch affect this?
> https://lore.kernel.org/linux-kbuild/20220905083619.672091-1-masahiroy@kernel.org/


No, I do not think so.


> If so, then I should not add -Werror as you suggest above?


I think we should always add -Werror to as-option.


as-option checks the command line options with /dev/null
as the source input (that is, source input is always valid).


If as-option results in a warning, that option will sprinkle
the same warning for all *.S files in the source tree.

So, any warning in as-option should be considered as an error.


-- 
Best Regards
Masahiro Yamada