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From:   Anders Roxell <anders.roxell@linaro.org>
Date:   Fri, 15 Jan 2021 20:34:39 +0100
Message-ID: <CADYN=9+vAN+jiieKxpTYa=E6zdJfrcbQPCt3tokopMMs+Mnd8Q@mail.gmail.com>
Subject: Re: [PATCH] MIPS: VDSO: Use CLANG_FLAGS instead of filtering out '--target='
To:     Nathan Chancellor <natechancellor@gmail.com>
Cc:     Thomas Bogendoerfer <tsbogend@alpha.franken.de>,
        Nick Desaulniers <ndesaulniers@google.com>,
        linux-mips@vger.kernel.org,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        clang-built-linux <clang-built-linux@googlegroups.com>,
        stable@vger.kernel.org
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On Fri, 15 Jan 2021 at 20:26, Nathan Chancellor
<natechancellor@gmail.com> wrote:
>
> Commit ee67855ecd9d ("MIPS: vdso: Allow clang's --target flag in VDSO
> cflags") allowed the '--target=' flag from the main Makefile to filter
> through to the vDSO. However, it did not bring any of the other clang
> specific flags for controlling the integrated assembler and the GNU
> tools locations (--prefix=, --gcc-toolchain=, and -no-integrated-as).
> Without these, we will get a warning (visible with tinyconfig):
>
> arch/mips/vdso/elf.S:14:1: warning: DWARF2 only supports one section per
> compilation unit
> .pushsection .note.Linux, "a",@note ; .balign 4 ; .long 2f - 1f ; .long
> 4484f - 3f ; .long 0 ; 1:.asciz "Linux" ; 2:.balign 4 ; 3:
> ^
> arch/mips/vdso/elf.S:34:2: warning: DWARF2 only supports one section per
> compilation unit
>  .section .mips_abiflags, "a"
>  ^
>
> All of these flags are bundled up under CLANG_FLAGS in the main Makefile
> and exported so that they can be added to Makefiles that set their own
> CFLAGS. Use this value instead of filtering out '--target=' so there is
> no warning and all of the tools are properly used.
>
> Cc: stable@vger.kernel.org
> Fixes: ee67855ecd9d ("MIPS: vdso: Allow clang's --target flag in VDSO cflags")
> Link: https://github.com/ClangBuiltLinux/linux/issues/1256
> Reported-by: Anders Roxell <anders.roxell@linaro.org>
> Signed-off-by: Nathan Chancellor <natechancellor@gmail.com>

Tested-by: Anders Roxell <anders.roxell@linaro.org>

Cheers,
Anders

> ---
>  arch/mips/vdso/Makefile | 5 +----
>  1 file changed, 1 insertion(+), 4 deletions(-)
>
> diff --git a/arch/mips/vdso/Makefile b/arch/mips/vdso/Makefile
> index 5810cc12bc1d..2131d3fd7333 100644
> --- a/arch/mips/vdso/Makefile
> +++ b/arch/mips/vdso/Makefile
> @@ -16,16 +16,13 @@ ccflags-vdso := \
>         $(filter -march=%,$(KBUILD_CFLAGS)) \
>         $(filter -m%-float,$(KBUILD_CFLAGS)) \
>         $(filter -mno-loongson-%,$(KBUILD_CFLAGS)) \
> +       $(CLANG_FLAGS) \
>         -D__VDSO__
>
>  ifndef CONFIG_64BIT
>  ccflags-vdso += -DBUILD_VDSO32
>  endif
>
> -ifdef CONFIG_CC_IS_CLANG
> -ccflags-vdso += $(filter --target=%,$(KBUILD_CFLAGS))
> -endif
> -
>  #
>  # The -fno-jump-tables flag only prevents the compiler from generating
>  # jump tables but does not prevent the compiler from emitting absolute
>
> base-commit: 7b490a8ab0f2d3ab8d838a4ff22ae86edafd34a1
> --
> 2.30.0
>