[3/3] kbuild: remove AS variable

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.

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@kernel.org>
---

 Makefile | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

On Tue, Mar 24, 2020 at 9:16 AM Masahiro Yamada <masahiroy@kernel.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@google.com>
Tested-by: Nick Desaulniers <ndesaulniers@google.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@kernel.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
> --

On Wed, Mar 25, 2020 at 01:15:39AM +0900, Masahiro Yamada 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.
> 
> 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@kernel.org>

Reviewed-by: Nathan Chancellor <natechancellor@gmail.com>

On Tue, Mar 24, 2020 at 12:38 PM Nick Desaulniers
<ndesaulniers@google.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`)

Hi Masahiro,

I love your patch! Yet something to improve:

[auto build test ERROR on kbuild/for-next]
[also build test ERROR on net-next/master net/master linus/master v5.6-rc7 next-20200325]
[if your patch is applied to the wrong git tree, please drop us a note to help
improve the system. BTW, we also suggest to use '--base' option to specify the
base tree in git format-patch, please see https://stackoverflow.com/a/37406982]

url:    https://github.com/0day-ci/linux/commits/Masahiro-Yamada/net-wan-wanxl-use-CC68K-instead-of-AS68K-for-rebuilding-firmware/20200326-034145
base:   https://git.kernel.org/pub/scm/linux/kernel/git/masahiroy/linux-kbuild.git for-next
config: powerpc-defconfig (attached as .config)
compiler: clang version 11.0.0 (https://github.com/llvm/llvm-project 2093fdd429d52348e08969180ac6b1e705fc4ff6)
reproduce:
        wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
        chmod +x ~/bin/make.cross
        # save the attached .config to linux build tree
        COMPILER=clang make.cross ARCH=powerpc 

If you fix the issue, kindly add following tag
Reported-by: kbuild test robot <lkp@intel.com>

All errors (new ones prefixed by >>):

>> /bin/sh: 0: Illegal option --
   6 real  3 user  2 sys  107.14% cpu 	make distclean
--
>> /bin/sh: 0: Illegal option --
   4 real  4 user  1 sys  114.93% cpu 	make olddefconfig
--
>> /bin/sh: 0: Illegal option --
   /usr/bin/ld: scripts/dtc/dtc-parser.tab.o:(.bss+0x10): multiple definition of `yylloc'; scripts/dtc/dtc-lexer.lex.o:(.bss+0x58): first defined here
   clang-11: error: linker command failed with exit code 1 (use -v to see invocation)
   make[2]: *** [scripts/Makefile.host:116: scripts/dtc/dtc] Error 1
   make[2]: Target '__build' not remade because of errors.
   make[1]: *** [Makefile:1270: scripts_dtc] Error 2
   make[1]: Target 'prepare' not remade because of errors.
   make: *** [Makefile:180: sub-make] Error 2
   17 real  6 user  11 sys  102.46% cpu 	make prepare

---
0-DAY CI Kernel Test Service, Intel Corporation
https://lists.01.org/hyperkitty/list/kbuild-all@lists.01.org

Hi Nick,


On Wed, Mar 25, 2020 at 4:59 AM Nick Desaulniers
<ndesaulniers@google.com> wrote:
>
> On Tue, Mar 24, 2020 at 12:38 PM Nick Desaulniers
> <ndesaulniers@google.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) .