netdev - Re: [PATCH 3/3] kbuild: remove AS variable

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Date:   Thu, 26 Mar 2020 15:13:50 +0900
From:   Masahiro Yamada <masahiroy@...nel.org>
To:     Nick Desaulniers <ndesaulniers@...gle.com>
Cc:     Linux Kbuild mailing list <linux-kbuild@...r.kernel.org>,
        "David S . Miller" <davem@...emloft.net>,
        Network Development <netdev@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Michal Marek <michal.lkml@...kovi.net>,
        clang-built-linux <clang-built-linux@...glegroups.com>
Subject: Re: [PATCH 3/3] kbuild: remove AS variable

Hi Nick,

On Wed, Mar 25, 2020 at 4:59 AM Nick Desaulniers
<ndesaulniers@...gle.com> wrote:
>
> On Tue, Mar 24, 2020 at 12:38 PM Nick Desaulniers
> <ndesaulniers@...gle.com> wrote:
> > consistent in this regard (and not using the compiler as the driver),
>
> Ah, the preprocessor; we need to preprocess the .S files, .s files are
> fine (though we have .lds.S files that are not `-x
> assembler-with-cpp`)

Right, there is no '*.s' source file in the kernel tree.

If we want to de-couple $(AS), we must the compilation
before the assemble stage   ( $(CC) -S ), but
doing so does not buy us.

So, $(CC) always works as the front-end
for compiling both .c and .S files.

You can see the internal database by
'make --print-data-base'.

I see the following for  *.S -> *.o rule.

# default
COMPILE.S = $(CC) $(ASFLAGS) $(CPPFLAGS) $(TARGET_MACH) -c

So, using $(CC) is the right thing.

Even if we keep AS, we cannot do like AS=llvm-as
since llvm-as is a different kind of tool
that processes LLVM assembly (.ll) .

-- 
Best Regards
Masahiro Yamada