linux-kernel - Re: [PATCH LINUX v5] xen: event channel arrays are xen_ulong

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Message-ID: <20130305030436.GA18040@mudshark.cambridge.arm.com>
Date:	Tue, 5 Mar 2013 03:04:36 +0000
From:	Will Deacon <will.deacon@....com>
To:	Rob Herring <robherring2@...il.com>
Cc:	Ian Campbell <ian.campbell@...rix.com>,
	"xen-devel@...ts.xen.org" <xen-devel@...ts.xen.org>,
	"Keir (Xen.org)" <keir@....org>,
	Stefano Stabellini <stefano.stabellini@...citrix.com>,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	Tim Deegan <tim@....org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Jan Beulich <JBeulich@...e.com>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	Nicolas Pitre <nico@...xnic.net>
Subject: Re: [PATCH LINUX v5] xen: event channel arrays are xen_ulong_t and
 not unsigned long

Hi guys,

On Mon, Mar 04, 2013 at 02:45:33AM +0000, Rob Herring wrote:
> On 02/20/2013 05:48 AM, Ian Campbell wrote:
> > On ARM we want these to be the same size on 32- and 64-bit.
> > 
> > This is an ABI change on ARM. X86 does not change.
> > 
> > Signed-off-by: Ian Campbell <ian.campbell@...rix.com>
> > Cc: Jan Beulich <JBeulich@...e.com>
> > Cc: Keir (Xen.org) <keir@....org>
> > Cc: Tim Deegan <tim@....org>
> > Cc: Stefano Stabellini <stefano.stabellini@...citrix.com>
> > Cc: linux-arm-kernel@...ts.infradead.org
> > Cc: xen-devel@...ts.xen.org
> > Cc: Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>

[...]

> I'm seeing some some build failures on randconfig builds with this change:
> 
> /tmp/ccJaIZOW.s: Assembler messages:
> /tmp/ccJaIZOW.s:831: Error: even register required -- `ldrexd r5,r6,[r4]'
> 
> This is with ubuntu 12.04 cross compiler (gcc version 4.6.3
> (Ubuntu/Linaro 4.6.3-1ubuntu5)).
> 
> This register restriction is on ARM, but not Thumb builds. Comparing
> this to atomic64_cmpxchg, I don't see how to fix this. Perhaps Will or
> Nico have thoughts.

[...]

> > +	asm volatile("@ xchg_xen_ulong\n"
> > +		"1:     ldrexd  %0, %H0, [%3]\n"
> > +		"       strexd  %1, %2, %H2, [%3]\n"
> > +		"       teq     %1, #0\n"
> > +		"       bne     1b"
> > +		: "=&r" (oldval), "=&r" (tmp)
> > +		: "r" (val), "r" (ptr)
> > +		: "memory", "cc");

I also can't immediately see why GCC would allocate oldval to an odd base
register. Can you share your .config please?

Will
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