linux-kernel - Re: [Android-virt] [Embeddedxen-devel] [Xen-devel] [ANNOUNCE] Xen port to Cortex-A15 / ARMv7 with virt extensions

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Message-ID: <20111201165718.GJ27394@arm.com>
Date:	Thu, 1 Dec 2011 16:57:18 +0000
From:	Catalin Marinas <catalin.marinas@....com>
To:	Arnd Bergmann <arnd@...db.de>
Cc:	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"xen-devel@...ts.xensource.com" <xen-devel@...ts.xensource.com>,
	"linaro-dev@...ts.linaro.org" <linaro-dev@...ts.linaro.org>,
	Ian Campbell <Ian.Campbell@...rix.com>,
	Pawel Moll <Pawel.Moll@....com>,
	Stefano Stabellini <Stefano.Stabellini@...citrix.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"virtualization@...ts.linux-foundation.org" 
	<virtualization@...ts.linux-foundation.org>,
	"android-virt@...ts.cs.columbia.edu" 
	<android-virt@...ts.cs.columbia.edu>,
	"kvm@...r.kernel.org" <kvm@...r.kernel.org>,
	"embeddedxen-devel@...ts.sourceforge.net" 
	<embeddedxen-devel@...ts.sourceforge.net>
Subject: Re: [Android-virt] [Embeddedxen-devel] [Xen-devel] [ANNOUNCE] Xen
 port to Cortex-A15 / ARMv7 with virt extensions

On Thu, Dec 01, 2011 at 04:44:40PM +0000, Arnd Bergmann wrote:
> On Thursday 01 December 2011, Catalin Marinas wrote:
> > On Thu, Dec 01, 2011 at 03:42:19PM +0000, Arnd Bergmann wrote:
> > > On Thursday 01 December 2011, Catalin Marinas wrote:
> > > How do you deal with signed integer arguments passed into SVC or HVC from
> > > a caller? If I understand the architecture correctly, the upper
> > > halves of the argument register end up zero-padded, while the callee
> > > expects sign-extension.
> > 
> > If you treat it as an "int" (32-bit) and function prototype defined
> > accordingly, then the generated code only accesses it as a W (rather
> > than X) register and the top 32-bit part is ignored (no need for
> > sign-extension). If it is defined as a "long" in the 32-bit world, then
> > it indeed needs explicit conversion given the different sizes for long
> > (for example sys_lseek, the second argument is a 'long' and we do
> > explicit sign extension in the wrapper).
...
> What about unsigned long and pointer? Can we always rely on the upper
> half of the register to be zero-filled when we get an exception from 32
> bit into 64 bit state, or do we also have to zero-extend those?

They are also fine, no need for zero-extension.

-- 
Catalin
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