linux-kernel - Re: [PATCH 2/8] i386: bitops: Rectify bogus "Ir" constraints

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Message-Id: <200707232032.28815.ak@suse.de>
Date:	Mon, 23 Jul 2007 20:32:28 +0200
From:	Andi Kleen <ak@...e.de>
To:	Satyam Sharma <ssatyam@....iitk.ac.in>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	David Howells <dhowells@...hat.com>,
	Nick Piggin <nickpiggin@...oo.com.au>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH 2/8] i386: bitops: Rectify bogus "Ir" constraints

On Monday 23 July 2007 20:14:52 Satyam Sharma wrote:
> On Mon, 23 Jul 2007, Linus Torvalds wrote:
> 
> > On Mon, 23 Jul 2007, Satyam Sharma wrote:
> > >
> > > * The "I" constraint modifier is applicable only to immediate-value operands,
> > >   and combining it with "r" is bogus.
> > 
> > This is wrong too.
> > 
> > The whole point of a "Ir" modifier is to say that the instruction takes 
> > *either* an "I" or an "r".
> 
> Yup, sorry about this one, Andi pointed this out earlier. But the "I"
> must still go I think, for the third reason in that changelog -- it
> unnecessarily limits the bit offset to 0..31, but (at least from the
> comment up front in that file) we do allow arbitrarily large @nr (upto
> 255, of course, these instructions won't take anything greater than that).


As HPA pointed out that would risk not being correctly assembled by at 
least some binutils versions

 
> > Andrew - the ones I've looked at were all wrong. Please don't take this 
> > series.
> 
> I think I'll rescind the series anyway, a lot of patches turned out to
> be wrong -- some due to mis-reading / incorrect gcc docs, others due to
> other reasons ... this was just something I did thinking of as a cleanup
> anyway, so I don't intend to push or correct this or anything.

cpumask_t/nodemask_t bitmap optimizations would be useful.

-Andi

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