linux-kernel - Re: [tip:x86/mce] x86/bitops: Move BIT

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Message-ID: <CA+55aFxGY4fLa_ovp7b_ZRCrBEPfNH6MxUS3eaWAKo01iq8DLA@mail.gmail.com>
Date:	Wed, 23 May 2012 09:45:18 -0700
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	Borislav Petkov <borislav.petkov@....com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>, mingo@...nel.org,
	linux-kernel@...r.kernel.org, frank.arnold@....com,
	akpm@...ux-foundation.org, tglx@...utronix.de,
	linux-tip-commits@...r.kernel.org
Subject: Re: [tip:x86/mce] x86/bitops: Move BIT_64() for a wider use

On Wed, May 23, 2012 at 9:42 AM, H. Peter Anvin <hpa@...or.com> wrote:
> On 05/23/2012 09:40 AM, Linus Torvalds wrote:
>
> And it doesn't work in assembly.  However, I really question the assumption.

The asm case is *trivial*.

asm cannot handle anything but constant shifts anyway, so the BIT()
constness rules would remain. But since asm doesn't have any integer
types, you simply do

  #ifdef __ASSEMBLY__
    #define BIT(x) (1<<(x))
  #else
    .. the C type-morphing one ..
  #endif

As to questioning the assumption, you're simply wrong. BIT(0)
absolutely MUST NOT be a 64-bit value on a 32-bit kernel. End of
discussion. This isn't an "assumption", it's an axiom.

                    Linus
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