linux-kernel - Re: [PATCH v2 05/10] x86/percpu: Remove "e" constraint from XADD

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Message-ID: <CAKwvOdkB0J8oMjG-NsM6O6BCnodmY8UeYqCyeR-c6NSa5paYfQ@mail.gmail.com>
Date:   Mon, 1 Jun 2020 11:50:22 -0700
From:   Nick Desaulniers <ndesaulniers@...gle.com>
To:     Brian Gerst <brgerst@...il.com>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        "maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" <x86@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...nel.org>, Borislav Petkov <bp@...en8.de>,
        "H . Peter Anvin" <hpa@...or.com>,
        Andy Lutomirski <luto@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH v2 05/10] x86/percpu: Remove "e" constraint from XADD

On Sat, May 30, 2020 at 3:11 PM Brian Gerst <brgerst@...il.com> wrote:
>
> The "e" constraint represents a constant, but the XADD instruction doesn't
> accept immediate operands.
>
> Signed-off-by: Brian Gerst <brgerst@...il.com>

Yep, as we discussed in v1.
Reviewed-by: Nick Desaulniers <ndesaulniers@...gle.com>

> ---
>  arch/x86/include/asm/percpu.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/arch/x86/include/asm/percpu.h b/arch/x86/include/asm/percpu.h
> index 2a24f3c795eb..9bb5440d98d3 100644
> --- a/arch/x86/include/asm/percpu.h
> +++ b/arch/x86/include/asm/percpu.h
> @@ -220,7 +220,7 @@ do {                                                                        \
>                 break;                                                  \
>         case 8:                                                         \
>                 asm qual ("xaddq %0, "__percpu_arg(1)                   \
> -                           : "+re" (paro_ret__), "+m" (var)            \
> +                           : "+r" (paro_ret__), "+m" (var)             \
>                             : : "memory");                              \
>                 break;                                                  \
>         default: __bad_percpu_size();                                   \
> --
> 2.25.4
>


-- 
Thanks,
~Nick Desaulniers