linux-kernel - Re: [PATCH] x86: math-emu: fix up 'cmp' insn for clang ias

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Date:   Mon, 8 Jun 2020 14:12:32 -0700
From:   Nick Desaulniers <ndesaulniers@...gle.com>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     Bill Metzenthen <billm@...bpc.org.au>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" <x86@...nel.org>,
        "H. Peter Anvin" <hpa@...or.com>, Jiri Slaby <jslaby@...e.cz>,
        LKML <linux-kernel@...r.kernel.org>,
        clang-built-linux <clang-built-linux@...glegroups.com>
Subject: Re: [PATCH] x86: math-emu: fix up 'cmp' insn for clang ias

On Wed, May 27, 2020 at 6:53 AM Arnd Bergmann <arnd@...db.de> wrote:
>
> The clang integrated assembler requires the 'cmp' instruction to
> have a length prefix here:
>
> arch/x86/math-emu/wm_sqrt.S:212:2: error: ambiguous instructions require an explicit suffix (could be 'cmpb', 'cmpw', or 'cmpl')
>  cmp $0xffffffff,-24(%ebp)
>  ^
>
> Make this a 32-bit comparison, which it was clearly meant to be.
>
> Signed-off-by: Arnd Bergmann <arnd@...db.de>

Thanks for the patch.
Reviewed-by: Nick Desaulniers <ndesaulniers@...gle.com>

> ---
>  arch/x86/math-emu/wm_sqrt.S | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/arch/x86/math-emu/wm_sqrt.S b/arch/x86/math-emu/wm_sqrt.S
> index 3b2b58164ec1..40526dd85137 100644
> --- a/arch/x86/math-emu/wm_sqrt.S
> +++ b/arch/x86/math-emu/wm_sqrt.S
> @@ -209,7 +209,7 @@ sqrt_stage_2_finish:
>
>  #ifdef PARANOID
>  /* It should be possible to get here only if the arg is ffff....ffff */
> -       cmp     $0xffffffff,FPU_fsqrt_arg_1
> +       cmpl    $0xffffffff,FPU_fsqrt_arg_1
>         jnz     sqrt_stage_2_error
>  #endif /* PARANOID */
>
> --

-- 
Thanks,
~Nick Desaulniers