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

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Message-ID: <CAKwvOdkjiyyt8Ju2j2O4cm1sB34rb_FTgjCRzEiXM6KL4muO_w@mail.gmail.com>
Date:   Tue, 24 Mar 2020 12:38:50 -0700
From:   Nick Desaulniers <ndesaulniers@...gle.com>
To:     Masahiro Yamada <masahiroy@...nel.org>
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

On Tue, Mar 24, 2020 at 9:16 AM Masahiro Yamada <masahiroy@...nel.org> wrote:
>
> As commit 5ef872636ca7 ("kbuild: get rid of misleading $(AS) from
> documents") noted, we rarely use $(AS) in the kernel build.
>
> Now that the only/last user of $(AS) in drivers/net/wan/Makefile was
> converted to $(CC), $(AS) is no longer used in the build process.

TIL that we don't actually invoke the assembler at all for out of line
assembly files, but rather use the compiler as the "driver".
scripts/Makefile.build:
329 quiet_cmd_as_o_S = AS $(quiet_modtag)  $@
330       cmd_as_o_S = $(CC) $(a_flags) -c -o $@ $<

Though I am personally conflicted, as
commit 055efab3120b ("kbuild: drop support for cc-ldoption")
since we do the opposite for the linker (we do not use the compiler as
the driver for the linker using -Wl,-foo flags).  I wish we were
consistent in this regard (and not using the compiler as the driver),
but that is a yak-shave+bikeshed (I typed out yakshed without
thinking; maybe a new entry for Linux kernel urban dictionary or The
Jargon File) for another day.

$ grep -nR --include="Makefile" '(AS)' .
Turned up only this change and the above referenced wan driver.

Reviewed-by: Nick Desaulniers <ndesaulniers@...gle.com>
Tested-by: Nick Desaulniers <ndesaulniers@...gle.com>


>
> You can still pass in AS=clang, which is just a switch to turn on
> the LLVM integrated assembler.
>
> Signed-off-by: Masahiro Yamada <masahiroy@...nel.org>
> ---
>
>  Makefile | 3 +--
>  1 file changed, 1 insertion(+), 2 deletions(-)
>
> diff --git a/Makefile b/Makefile
> index 16d8271192d1..339e8c51a10b 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -405,7 +405,6 @@ KBUILD_HOSTLDFLAGS  := $(HOST_LFS_LDFLAGS) $(HOSTLDFLAGS)
>  KBUILD_HOSTLDLIBS   := $(HOST_LFS_LIBS) $(HOSTLDLIBS)
>
>  # Make variables (CC, etc...)
> -AS             = $(CROSS_COMPILE)as
>  LD             = $(CROSS_COMPILE)ld
>  CC             = $(CROSS_COMPILE)gcc
>  CPP            = $(CC) -E
> @@ -472,7 +471,7 @@ KBUILD_LDFLAGS :=
>  GCC_PLUGINS_CFLAGS :=
>  CLANG_FLAGS :=
>
> -export ARCH SRCARCH CONFIG_SHELL BASH HOSTCC KBUILD_HOSTCFLAGS CROSS_COMPILE AS LD CC
> +export ARCH SRCARCH CONFIG_SHELL BASH HOSTCC KBUILD_HOSTCFLAGS CROSS_COMPILE LD CC
>  export CPP AR NM STRIP OBJCOPY OBJDUMP OBJSIZE READELF PAHOLE LEX YACC AWK INSTALLKERNEL
>  export PERL PYTHON PYTHON3 CHECK CHECKFLAGS MAKE UTS_MACHINE HOSTCXX
>  export KBUILD_HOSTCXXFLAGS KBUILD_HOSTLDFLAGS KBUILD_HOSTLDLIBS LDFLAGS_MODULE
> --

-- 
Thanks,
~Nick Desaulniers