linux-kernel - Re: [PATCH 4/7] x86: remove always-defined CONFIG_AS_CFI

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Date:   Mon, 23 Mar 2020 13:59:06 -0700
From:   Nick Desaulniers <ndesaulniers@...gle.com>
To:     Masahiro Yamada <masahiroy@...nel.org>
Cc:     "maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" <x86@...nel.org>,
        Ingo Molnar <mingo@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Borislav Petkov <bp@...en8.de>,
        "H . Peter Anvin" <hpa@...or.com>,
        LKML <linux-kernel@...r.kernel.org>,
        "Jason A . Donenfeld" <Jason@...c4.com>,
        Ingo Molnar <mingo@...hat.com>,
        clang-built-linux <clang-built-linux@...glegroups.com>
Subject: Re: [PATCH 4/7] x86: remove always-defined CONFIG_AS_CFI_SECTIONS

On Sun, Mar 22, 2020 at 7:09 PM Masahiro Yamada <masahiroy@...nel.org> wrote:
>
> CONFIG_AS_CFI_SECTIONS was introduced by commit 9e565292270a ("x86:
> Use .cfi_sections for assembly code").
>
> We raise the minimal supported binutils version from time to time.
> The last bump was commit 1fb12b35e5ff ("kbuild: Raise the minimum
> required binutils version to 2.21").

Looks like 2.21 was released in 2010, binutils gained support for
cfi_sections in 2009.  There's been some bug fixes to its support over
the years, but we can always add more specific checks later if
necessary.
Reviewed-by: Nick Desaulniers <ndesaulniers@...gle.com>

>
> I confirmed the code in $(call as-instr,...) can be assembled by the
> binutils 2.21 assembler and also by LLVM integrated assembler.
>
> Remove CONFIG_AS_CFI_SECTIONS, which is always defined.
>
> Signed-off-by: Masahiro Yamada <masahiroy@...nel.org>
> ---
>
>  arch/x86/Makefile             | 6 ++----
>  arch/x86/include/asm/dwarf2.h | 2 --
>  2 files changed, 2 insertions(+), 6 deletions(-)
>
> diff --git a/arch/x86/Makefile b/arch/x86/Makefile
> index dd275008fc59..e4a062313bb0 100644
> --- a/arch/x86/Makefile
> +++ b/arch/x86/Makefile
> @@ -177,8 +177,6 @@ ifeq ($(ACCUMULATE_OUTGOING_ARGS), 1)
>         KBUILD_CFLAGS += $(call cc-option,-maccumulate-outgoing-args,)
>  endif
>
> -cfi-sections := $(call as-instr,.cfi_sections .debug_frame,-DCONFIG_AS_CFI_SECTIONS=1)
> -
>  # does binutils support specific instructions?
>  asinstr += $(call as-instr,pshufb %xmm0$(comma)%xmm0,-DCONFIG_AS_SSSE3=1)
>  avx_instr := $(call as-instr,vxorps %ymm0$(comma)%ymm1$(comma)%ymm2,-DCONFIG_AS_AVX=1)
> @@ -188,8 +186,8 @@ sha1_ni_instr :=$(call as-instr,sha1msg1 %xmm0$(comma)%xmm1,-DCONFIG_AS_SHA1_NI=
>  sha256_ni_instr :=$(call as-instr,sha256msg1 %xmm0$(comma)%xmm1,-DCONFIG_AS_SHA256_NI=1)
>  adx_instr := $(call as-instr,adox %r10$(comma)%r10,-DCONFIG_AS_ADX=1)
>
> -KBUILD_AFLAGS += $(cfi-sections) $(asinstr) $(avx_instr) $(avx2_instr) $(avx512_instr) $(sha1_ni_instr) $(sha256_ni_instr) $(adx_instr)
> -KBUILD_CFLAGS += $(cfi-sections) $(asinstr) $(avx_instr) $(avx2_instr) $(avx512_instr) $(sha1_ni_instr) $(sha256_ni_instr) $(adx_instr)
> +KBUILD_AFLAGS += $(asinstr) $(avx_instr) $(avx2_instr) $(avx512_instr) $(sha1_ni_instr) $(sha256_ni_instr) $(adx_instr)
> +KBUILD_CFLAGS += $(asinstr) $(avx_instr) $(avx2_instr) $(avx512_instr) $(sha1_ni_instr) $(sha256_ni_instr) $(adx_instr)
>
>  KBUILD_LDFLAGS := -m elf_$(UTS_MACHINE)
>
> diff --git a/arch/x86/include/asm/dwarf2.h b/arch/x86/include/asm/dwarf2.h
> index d6697aab5706..5d3e7507cbbd 100644
> --- a/arch/x86/include/asm/dwarf2.h
> +++ b/arch/x86/include/asm/dwarf2.h
> @@ -22,7 +22,6 @@
>  #define CFI_ESCAPE             .cfi_escape
>  #define CFI_SIGNAL_FRAME       .cfi_signal_frame
>
> -#if defined(CONFIG_AS_CFI_SECTIONS)
>  #ifndef BUILD_VDSO
>         /*
>          * Emit CFI data in .debug_frame sections, not .eh_frame sections.
> @@ -39,6 +38,5 @@
>           */
>         .cfi_sections .eh_frame, .debug_frame
>  #endif
> -#endif
>
>  #endif /* _ASM_X86_DWARF2_H */
> --
> 2.17.1
>
> --
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-- 
Thanks,
~Nick Desaulniers