linux-kernel - Re: [tip:x86/asm] x86, bitops: Change bitops to be native operand size

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Date:	Sun, 10 Nov 2013 18:22:50 -0800
From:	Joe Perches <joe@...ches.com>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	linux-arch <linux-arch@...r.kernel.org>, mingo@...nel.org,
	linux-kernel@...r.kernel.org, tglx@...utronix.de,
	james.t.kukunas@...el.com, hpa@...ux.intel.com,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	David Miller <davem@...emloft.net>
Subject: Re: [tip:x86/asm] x86, bitops:  Change bitops to be native operand
 size

On Sun, 2013-11-10 at 18:06 -0800, H. Peter Anvin wrote:
> On 11/10/2013 02:44 PM, Joe Perches wrote:
> > On Sun, 2013-11-10 at 14:10 -0800, H. Peter Anvin wrote:
> >> Yes, on the generic it is int.
> >> The problem is in part that some architectures have bitop
> >> instructions with specific behavior.
> > I think that all bitop indices should be changed
> > to unsigned (int or long, probably long) for all
> > arches.
> > Is there any impediment to that?
> It is at the very best misleading.  On x86 bit indicies will be signed
> no matter what the data type says,

?

> and having an unsigned data type
> being interpreted as signed seems like really dangerous.
> On the other hand, for the generic implementation unsigned long makes sense.
> We might need a bitindex_t or something like that for it to be clean.

Is there really any reason to introduce bitindex_t?

Perhaps the current x86 bitops asm code is being conflated
with the ideal implementation?

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