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

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Message-Id: <200611091542.31101.arnd@arndb.de>
Date:	Thu, 9 Nov 2006 15:42:30 +0100
From:	Arnd Bergmann <arnd@...db.de>
To:	Avi Kivity <avi@...ranet.com>
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

On Thursday 09 November 2006 14:36, Avi Kivity wrote:
> 
> >
> > I'm not an expert on inline assembly, but don't you need an extra
> > '"m" (phys_addr)' to make sure that gcc actually puts the variable
> > on the stack instead of passing a NULL pointer as '"a"(&phys_addr)'?
> 
> Taking a variable's address should force its contents into memory (like 
> calling an uninlined function with &var).

No it doesn't. You're not telling gcc that the inline assembly cares
about the contents of the variable, so it could be a reference to
a stack slot while the contents are still in a register. Or gcc
might move the assignment of phys_addr to after the inline assembly.

	Arnd <><
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