linux-kernel - Re: [PATCH 1 of 4] mm: add a ptep_modify

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Message-ID: <485C117E.8070706@goop.org>
Date:	Fri, 20 Jun 2008 13:22:22 -0700
From:	Jeremy Fitzhardinge <jeremy@...p.org>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
CC:	xen-devel <xen-devel@...ts.xensource.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	kvm-devel <kvm-devel@...ts.sourceforge.net>,
	benh@...nel.crashing.org, x86@...nel.org,
	LKML <linux-kernel@...r.kernel.org>,
	Virtualization Mailing List <virtualization@...ts.osdl.org>,
	Hugh Dickins <hugh@...itas.com>, Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH 1 of 4] mm: add a ptep_modify_prot transaction abstraction

Jeremy Fitzhardinge wrote:
> Linus Torvalds wrote:
>   
>> On Fri, 20 Jun 2008, Ingo Molnar wrote:
>>   
>>     
>>> okay - Jeremy, could you try the fix below? (or tip/master, i just 
>>> pushed this out)
>>>     
>>>       
>> Actually, don't try that one.
>>
>> It needs to be a _byte_ registers, so "ir" was wrong. You need "iq".
>>   
>>     
>
> Doesn't work, unfortunately:
> {standard input}:20511: Error: Incorrect register `%eax' used with `b' 
> suffix
>
>         lock; orb %eax,1(%rdi)  # tmp64,
>   

This does work:

                asm volatile(LOCK_PREFIX "orb %1,%0"
                        : CONST_MASK_ADDR(nr, addr)
                        : "iq" ((u8)CONST_MASK(nr))
                        : "memory");

(ie, explicitly casting the mask to u8)

    J
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