linux-kernel - Re: [RFC/PATCH] doc: volatile considered evil

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Date:	Tue, 08 May 2007 15:04:45 -0700
From:	Jeremy Fitzhardinge <jeremy@...p.org>
To:	David Rientjes <rientjes@...gle.com>
CC:	Randy Dunlap <randy.dunlap@...cle.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Paul Sokolovsky <pmiscml@...il.com>,
	linux-kernel@...r.kernel.org, Andi Kleen <ak@...e.de>
Subject: Re: [RFC/PATCH] doc: volatile considered evil

David Rientjes wrote:
> Now if all such output operands are to specify that the input operands 
> were "modified", 'volatile' is required to ensure the side-effects are 
> preserved or, otherwise, gcc is free optimize the entire asm construct 
> away since it appears to be unused.
>   

Yup.

>> Yeah, they're completely different.  They're not even analogous, really,
>> which was my point.  People confer more meaning to "asm volatile" than
>> it actually has, because of the analogy with volatile variables/types. 
>> They would have been better off with something like "asm static", which
>> isn't much more meaningful, but at least it doesn't mislead the reader
>> into thinking it has anything to do with the other volatile.
>>
>>     
>
> You're point about reordering "asm volatile" constructs differs depending 
> on -mvolatile-asm-stop or -mno-volatile-asm-stop, however.
>   

Erm, that seems to be ia64 specific, and I have no idea what adding a
"stop bit" implies.  Can you set even or odd parity too?

    J
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