linux-kernel - Re: [PATCH v1 2/2] x86/asm/bitops: Use __builtin

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Message-ID: <CAKwvOdmN2==9tG0fxRO8K-eAJudeemaKUuhJEAuGHc=P8GpGwA@mail.gmail.com>
Date:   Thu, 10 Nov 2022 11:01:02 -0800
From:   Nick Desaulniers <ndesaulniers@...gle.com>
To:     Vincent Mailhol <mailhol.vincent@...adoo.fr>
Cc:     x86@...nel.org, Ingo Molnar <mingo@...hat.com>,
        Borislav Petkov <bp@...en8.de>,
        Thomas Gleixner <tglx@...utronix.de>,
        linux-kernel@...r.kernel.org, Yury Norov <yury.norov@...il.com>,
        llvm@...ts.linux.dev, Borislav Petkov <bp@...e.de>
Subject: Re: [PATCH v1 2/2] x86/asm/bitops: Use __builtin_clz*() to evaluate
 constant expressions

On Sun, Nov 6, 2022 at 1:51 AM Vincent Mailhol
<mailhol.vincent@...adoo.fr> wrote:
>
>  #ifdef CONFIG_X86_64
> -static __always_inline int fls64(__u64 x)
> +static __always_inline int constant_fls64(u64 x)
> +{
> +       BUILD_BUG_ON(sizeof(unsigned long long) != sizeof(x));

Thanks for the patches! They LGTM; but why do we need this BUILD_BUG_ON here?

> +
> +       if (!x)
> +               return 0;
> +
> +       return BITS_PER_TYPE(x) - __builtin_clzll(x);
> +}

-- 
Thanks,
~Nick Desaulniers