linux-kernel - Re: [PATCH] KVM: 'asm' operand has impossible constraints

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Message-ID: <45BC70A5.7030707@qumranet.com>
Date:	Sun, 28 Jan 2007 11:45:09 +0200
From:	Avi Kivity <avi@...ranet.com>
To:	caglar@...dus.org.tr
CC:	lkml <linux-kernel@...r.kernel.org>,
	kvm-devel@...ts.sourceforge.net
Subject: Re: [PATCH] KVM: 'asm' operand has impossible constraints

S.Çağlar Onur wrote:
> 27 Oca 2007 Cts tarihinde, Avi Kivity şunları yazmıştı: 
>   
>> The patch looks correct, but I don't understand the gcc error message.
>> Are we sure this isn't a gcc 4.2 bug?
>>
>> "g" appears to be equivalent to "rmi", if "i" is impossible, gcc is free
>> to use "r" or "m", no?
>>     
>
> Accorgind to GCC devs. its not a bug 
> (http://gcc.gnu.org/bugzilla/show_bug.cgi?id=29808), on comment #5 the 
> problem described like;
>
> "g" means "r"+"i" so the register allocator in the -O0 case is selecting "r" 
> while in the optimize case is selecting "i"
>
>   

That's a different bug. The gcc PR has an assembler error message, as 
expected, whereas the kvm miscompile has a compiler error, which I don't 
understand.

Anyhow, your patch is correct (because selecting "i" is indeed 
erroneous) so I'll apply it, but I'm worried that there's a gcc bug in 
there that we ought to report.


-- 
error compiling committee.c: too many arguments to function

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