linux-kernel - Re: [kvm-devel] [PATCH] KVM: Avoid using vmx instruction directly

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Message-ID: <45535CA6.4000206@qumranet.com>
Date:	Thu, 09 Nov 2006 18:51:50 +0200
From:	Avi Kivity <avi@...ranet.com>
To:	Arnd Bergmann <arnd@...db.de>
CC:	kvm-devel@...ts.sourceforge.net, akpm@...l.org,
	linux-kernel@...r.kernel.org
Subject: Re: [kvm-devel] [PATCH] KVM: Avoid using vmx instruction directly

Arnd Bergmann wrote:
> On Thursday 09 November 2006 15:52, Avi Kivity wrote:
>   
>> Wouldn't that make inline assembly useless?  Suppose the contents is 
>> itself a pointer.  What about the pointed-to contents?
>>
>> e.g.
>>
>>     int x = 3;
>>     int *y = &x;
>>     int z;
>>
>>     asm ("mov %1, %%rax; movl (%%rax), %0" : "=r"(z) : "g"(y) : "rax");
>>     assert(z == 3);
>>     
>
> Same here, you need to tell gcc what is really accessed, like 
>
> asm ("mov %1, %%rax; movl (%%rax), %0" : "=r"(z) : "g"(y), "m"(*y) : "rax");
>
> I know that the s390 kernel developers have hit that problem
> frequently with inline assemblies. It may be that it's harder
> to hit on x86, because there are fewer registers available and
> data therefore tends to spill to the stack.
>   

I'll update my tree to reflect this.  Thanks.

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

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