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Re: [Xen-devel] [PATCH] x86: usercopy assembly constraints

  • To: Jan Beulich <jbeulich@xxxxxxxxxx>, <xen-devel@xxxxxxxxxxxxxxxxxxx>
  • From: Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>
  • Date: Tue, 13 Nov 2007 20:28:41 +0000
  • Delivery-date: Tue, 13 Nov 2007 12:29:29 -0800
  • List-id: Xen developer discussion <xen-devel.lists.xensource.com>
  • Thread-index: AcgmMpkq2AK3tZIlEdytjwAX8io7RQAAS4xm
  • Thread-topic: [Xen-devel] [PATCH] x86: usercopy assembly constraints

On 13/11/07 20:20, "Keir Fraser" <Keir.Fraser@xxxxxxxxxxxx> wrote:

> On 13/11/07 16:02, "Jan Beulich" <jbeulich@xxxxxxxxxx> wrote:
>> Besides only being correct this way, this helps work around a gcc 4.3
>> issue.
>> At the same time, add some white space, re-order the inputs, and remove
>> a bogus cast.
> What's the bug? Does some gcc allocate the 4th output parameter into one of
> the other used registers (cx,si,di) if we don't use '=&'?

If this is the case, it sounds to me like a gcc bug (allocating two outputs
into the same register) and it could potentially hit on a number of our
other asm statements I'm pretty sure.

 -- Keir

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