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

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Date:	Mon, 23 Jul 2007 18:10:08 +0200
From:	Andi Kleen <ak@...e.de>
To:	Satyam Sharma <ssatyam@....iitk.ac.in>
Cc:	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>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH 2/8] i386: bitops: Rectify bogus "Ir" constraints

On Monday 23 July 2007 18:05:38 Satyam Sharma wrote:
> From: Satyam Sharma <ssatyam@....iitk.ac.in>
> 
> [2/8] i386: bitops: Rectify bogus "Ir" constraints
> 
> The "I" constraint (on the i386 platform) is used to restrict constants to
> the 0..31 range, for use with instructions that must deal with bit numbers.

It means I or r, not I modified by r. This means either a immediate constant
0..31 or a register, which is correct.

% cat t18.c 

f()
{
        asm("xxx %0" :: "rI" (10));
        asm("yyy %0" :: "rI" (100));
}
% gcc -O2 -S t18.c
% cat t18.s
...
f:
.LFB2:
#APP
        xxx $10
#NO_APP
        movl    $100, %eax
#APP
        yyy %eax
#NO_APP
        ret
.LFE2:
...

-Andi

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