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From: Masahiro Yamada <masahiroy@kernel.org>
To: Nathan Chancellor <nathan@kernel.org>
Cc: Michal Marek <michal.lkml@markovi.net>,
	Nick Desaulniers <ndesaulniers@google.com>,
	Linux Kbuild mailing list <linux-kbuild@vger.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	clang-built-linux <clang-built-linux@googlegroups.com>
Subject: Re: [PATCH 2/2] Makefile: Only specify '--prefix=' when building with clang + GNU as
Date: Wed, 10 Mar 2021 04:58:39 +0900	[thread overview]
Message-ID: <CAK7LNAQ0tdK+BEzs=39A4XbCXjAsbyyFp6fgXfhjP+5v_Nsddw@mail.gmail.com> (raw)
In-Reply-To: <CAK7LNARd7pM7SCKJOS=_ZDE+-Q_buDOfw_u0vsfof6G1FWXvOQ@mail.gmail.com>

On Wed, Mar 10, 2021 at 4:55 AM Masahiro Yamada <masahiroy@kernel.org> wrote:
>
> On Wed, Mar 3, 2021 at 6:07 AM Nathan Chancellor <nathan@kernel.org> wrote:
> >
> > When building with LLVM_IAS=1, there is no point to specifying
> > '--prefix=' because that flag is only used to find the cross assembler,
> > which is clang itself when building with LLVM_IAS=1. All of the other
> > tools are invoked directly from PATH or a full path specified via the
> > command line, which does not depend on the value of '--prefix='.
> >
> > Sharing commands to reproduce issues becomes a little bit easier without
> > a '--prefix=' value because that '--prefix=' value is specific to a
> > user's machine due to it being an absolute path.
> >
> > Signed-off-by: Nathan Chancellor <nathan@kernel.org>
>
>
> I was tricked by a couple of Reviewed-by/Tested-by tags.
>
> With this patch applied, the code looks as follows:
>
>
> ifneq ($(CROSS_COMPILE),)
> CLANG_FLAGS += --target=$(notdir $(CROSS_COMPILE:%-=%))
> ifneq ($(LLVM_IAS),1)
> GCC_TOOLCHAIN_DIR := $(dir $(shell which $(CROSS_COMPILE)elfedit))
> CLANG_FLAGS += --prefix=$(GCC_TOOLCHAIN_DIR)$(notdir $(CROSS_COMPILE))
> CLANG_FLAGS += -no-integrated-as
> endif
> endif
>
>
> For the native build (empty CROSS_COMPILE),
> you cannot add -no-integrated-as.
>
>
> I dropped this from my tree.
>
>
>
> Is the correct code as follows?
>
>
> ifneq ($(LLVM_IAS),1)
> CLANG_FLAGS += -no-integrated-as
> ifneq ($(CROSS_COMPILE),)
> CLANG_FLAGS += --target=$(notdir $(CROSS_COMPILE:%-=%))
> GCC_TOOLCHAIN_DIR := $(dir $(shell which $(CROSS_COMPILE)elfedit))
> CLANG_FLAGS += --prefix=$(GCC_TOOLCHAIN_DIR)$(notdir $(CROSS_COMPILE))
> endif
> endif
>
>
>
>


If you send v2, can you include comments from Fangrui Song?



    Fangrui Song:
      clang can spawn GNU as (if -f?no-integrated-as is specified) and GNU
      objcopy (-f?no-integrated-as and -gsplit-dwarf and -g[123]).
      objcopy is only used for GNU as assembled object files.
      With integrated assembler, the object file streamer creates .o and
      .dwo simultaneously.
      With GNU as, two objcopy commands are needed to extract .debug*.dwo to
      .dwo files && another command to remove .debug*.dwo sections.



I did not know the objtool part, and I think it is worth recording.


-- 
Best Regards
Masahiro Yamada

  reply	other threads:[~2021-03-09 20:00 UTC|newest]

Thread overview: 20+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-03-02 21:06 [PATCH 1/2] Makefile: Remove '--gcc-toolchain' flag Nathan Chancellor
2021-03-02 21:06 ` [PATCH 2/2] Makefile: Only specify '--prefix=' when building with clang + GNU as Nathan Chancellor
2021-03-02 22:02   ` Fangrui Song
2021-03-02 22:09     ` Nick Desaulniers
2021-03-02 22:40       ` Nick Desaulniers
2021-03-09 19:55   ` Masahiro Yamada
2021-03-09 19:58     ` Masahiro Yamada [this message]
2021-09-29 17:26   ` kernel test robot
2021-09-29 19:32   ` kernel test robot
2021-03-02 21:43 ` [PATCH 1/2] Makefile: Remove '--gcc-toolchain' flag Fangrui Song
2021-03-03  8:33   ` Masahiro Yamada
2021-03-02 22:33 ` Nick Desaulniers
2021-03-03  3:25 ` Sedat Dilek
2021-03-03 14:22   ` Sedat Dilek
2021-03-09 20:59 ` [PATCH v2 " Nathan Chancellor
2021-03-09 20:59   ` [PATCH v2 2/2] Makefile: Only specify '--prefix=' when building with clang + GNU as Nathan Chancellor
2021-03-09 21:15   ` [PATCH v2 1/2] Makefile: Remove '--gcc-toolchain' flag Fangrui Song
2021-03-15 16:21   ` Masahiro Yamada
2021-03-15 16:41     ` Sedat Dilek
2021-03-16 15:36       ` Masahiro Yamada

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