[Xen-devel] Re: [RFC PATCH 16/33] Add support for Xen to entry.S.

[Jeremy Fitzhardinge <jeremy@xxxxxxxx>]

Arjan van de Ven wrote:
> On Tue, 2006-07-18 at 00:00 -0700, Chris Wright wrote:
>   
> > +#ifndef CONFIG_XEN
> >         movl %cr0, %eax
> >         testl $0x4, %eax                # EM (math emulation bit)
> > -       jne device_not_available_emulate
> > -       preempt_stop
> > -       call math_state_restore
> > -       jmp ret_from_exception
> > -device_not_available_emulate:
> > +       je device_available_emulate
> >         pushl $0                        # temporary storage for ORIG_EIP
> >         CFI_ADJUST_CFA_OFFSET 4
> >         call math_emulate
> >         addl $4, %esp
> >         CFI_ADJUST_CFA_OFFSET -4
> > +       jmp ret_from_exception
> > +device_available_emulate:
> > +#endif
> >     
>
> Hi,
>
> can you explain what this chunk is for? It appears to be for the non-xen
> case due to the ifndef, yet it seems to visibly change the code for
> that... that deserves an explanation for sure ...
>   
This inverts the logic of the test so that the lines:

        preempt_stop
        call math_state_restore
        jmp ret_from_exception

can be hoisted out of the ifdef and shared in the Xen and non-Xen cases.

   J


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