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

[Jeremy Fitzhardinge <jeremy@goop.org>]

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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