Re: [Xen-devel] test_x86_emulator

[Keir Fraser <keir.xen@xxxxxxxxx>]

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@xxxxxxxx>
Acked-by: Keir Fraser <keir@xxxxxxx>

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