linux-kernel - Re: [PATCH] x86/kconfig: add as-instr64 macro to properly evaluate AS

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Date: Wed, 12 Jun 2024 10:19:30 +0100
From: Dmitry Safonov <0x7f454c46@...il.com>
To: Masahiro Yamada <masahiroy@...nel.org>
Cc: linux-kbuild@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>, 
	Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>, 
	Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org, linux-kernel@...r.kernel.org, 
	"H . Peter Anvin" <hpa@...or.com>, "Mike Rapoport (IBM)" <rppt@...nel.org>, 
	Rick Edgecombe <rick.p.edgecombe@...el.com>, Yu-cheng Yu <yu-cheng.yu@...el.com>
Subject: Re: [PATCH] x86/kconfig: add as-instr64 macro to properly evaluate AS_WRUSS

On Wed, 12 Jun 2024 at 06:03, Masahiro Yamada <masahiroy@...nel.org> wrote:
>
> Some instructions are only available on the 64-bit architecture.
>
> Bi-arch compilers that default to -m32 need the explicit -m64 option
> to evaluate them properly.
>
> Fixes: 18e66b695e78 ("x86/shstk: Add Kconfig option for shadow stack")
> Reported-by: Dmitry Safonov <0x7f454c46@...il.com>
> Closes: https://lore.kernel.org/all/20240612-as-instr-opt-wrussq-v2-1-bd950f7eead7@gmail.com/
> Signed-off-by: Masahiro Yamada <masahiroy@...nel.org>

Thank you Masahiro, this works as well!
I guess I went on too generic path without an actual requirement for that.

Tested-by: Dmitry Safonov <0x7f454c46@...il.com>

> ---
>
>  arch/x86/Kconfig.assembler | 2 +-
>  scripts/Kconfig.include    | 3 ++-
>  2 files changed, 3 insertions(+), 2 deletions(-)
>
> diff --git a/arch/x86/Kconfig.assembler b/arch/x86/Kconfig.assembler
> index 59aedf32c4ea..6d20a6ce0507 100644
> --- a/arch/x86/Kconfig.assembler
> +++ b/arch/x86/Kconfig.assembler
> @@ -36,6 +36,6 @@ config AS_VPCLMULQDQ
>           Supported by binutils >= 2.30 and LLVM integrated assembler
>
>  config AS_WRUSS
> -       def_bool $(as-instr,wrussq %rax$(comma)(%rbx))
> +       def_bool $(as-instr64,wrussq %rax$(comma)(%rbx))
>         help
>           Supported by binutils >= 2.31 and LLVM integrated assembler
> diff --git a/scripts/Kconfig.include b/scripts/Kconfig.include
> index 3ee8ecfb8c04..3500a3d62f0d 100644
> --- a/scripts/Kconfig.include
> +++ b/scripts/Kconfig.include
> @@ -33,7 +33,8 @@ ld-option = $(success,$(LD) -v $(1))
>
>  # $(as-instr,<instr>)
>  # Return y if the assembler supports <instr>, n otherwise
> -as-instr = $(success,printf "%b\n" "$(1)" | $(CC) $(CLANG_FLAGS) -Wa$(comma)--fatal-warnings -c -x assembler-with-cpp -o /dev/null -)
> +as-instr = $(success,printf "%b\n" "$(1)" | $(CC) $(CLANG_FLAGS) $(2) -Wa$(comma)--fatal-warnings -c -x assembler-with-cpp -o /dev/null -)
> +as-instr64 = $(as-instr,$(1),$(m64-flag))
>
>  # check if $(CC) and $(LD) exist
>  $(error-if,$(failure,command -v $(CC)),C compiler '$(CC)' not found)
> --
> 2.43.0
>
-- 
             Dmitry