From mboxrd@z Thu Jan  1 00:00:00 1970
From: Keir Fraser <keir.xen@gmail.com>
Subject: Re: test_x86_emulator
Date: Wed, 16 Apr 2014 10:32:41 +0100
Message-ID: <534E4E39.50105@gmail.com>
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To: Jan Beulich <JBeulich@suse.com>
Cc: Don Slutz <dslutz@verizon.com>, xen-devel@lists.xen.org
List-Id: xen-devel@lists.xenproject.org

Jan Beulich wrote:
> x86: fix instruction emulator test's xgetbv constraints
>
> The "A" constraint, while documented up to gcc4.5  as "The a and d
> registers, as a pair (for instructions that return half the result in
> one and half in the other)," never really behaved that (natural) way,
> but always meant (and is now also documented so) %eax_or_  %edx (%rax
> _or_  %rdx on x86-64) unless the operand was wide enough to require both
> (i.e. more than 32 bits on ix86 and more than 64 bits on x86-64).
>
> Interestingly something internal to the compiler changed between4.4
> and4.5  to actually expose the difference - up to gcc4.4  I was unable
> to construct a case where, when only the low half of the result is
> actually looked at, the result would be considered to be in %edx/%rdx
> (and %eax/%rax would be treated as unmodified by the instruction).
>
> Signed-off-by: Jan Beulich<jbeulich@suse.com>

Acked-by: Keir Fraser <keir@xen.org>