Re: [Xen-devel] there is no sysret in X86_emulate, why?

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 30.10.14 at 02:46, <hanyandong@xxxxxxxxx> wrote:
> (1)In x86_emulate(), there are sysenter/sysexit, syscall. But why no sysret?

Perhaps on the basis that this already when introduced was only
meant to be usable on 64-bit hypervisors, and 64-bit capable CPUs
always support SYSRET (whereas the scope of support for the
other three varies)? Christoph, you added that code years ago - is
there any other explanation for this?

> (2)I want to iuntercept syscall/sysret, so I unset the EFER.SCE, so 
> syscall/sysret will trap into Xen, then I emulate syscall/sysret.
> But  I only see syscall and did not see one sysret,  the guest run as usual. 
>  any one can give me an hint?

Assuming you did everything correctly, this seems odd. But in any
event I'd suggest confirming such behavior in a native environment
first.

Jan


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