Don't alloc empty frame in ia64_switch_mode_phys

I think ia64_switch_mode_phys and ia64_switch_mode_virt 
does not need to alloc an empty frame. 
An empty frame is required by loadrs but flushrs 
does not need that.

Signed-off-by: Zou Nan hai <nanhai.zouintel.com>

--- linux-2.6.18-rc2/arch/ia64/kernel/head.S	2006-07-26
11:30:08.000000000 +0800
+++ linux-2.6.18-rc2-fix/arch/ia64/kernel/head.S	2006-07-26
12:26:00.000000000 +0800
 -853,7
+853,6  END(__ia64_init_fpu)
  */
 GLOBAL_ENTRY(ia64_switch_mode_phys)
  {
-	alloc r2=ar.pfs,0,0,0,0
 	rsm psr.i | psr.ic		// disable interrupts and interrupt
collection
 	mov r15=ip
  }
 -902,7
+901,6  END(ia64_switch_mode_phys)
  */
 GLOBAL_ENTRY(ia64_switch_mode_virt)
  {
-	alloc r2=ar.pfs,0,0,0,0
 	rsm psr.i | psr.ic		// disable interrupts and interrupt
collection
 	mov r15=ip
  }




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Zou Nan hai wrote on Tuesday, July 25, 2006 4:37 PM
> I think ia64_switch_mode_phys and ia64_switch_mode_virt

> does not need to alloc an empty frame. 
> An empty frame is required by loadrs but flushrs 
> does not need that.

This patch would make your previous "Do not assume
output registers
be reservered" unnecessary, isn't it?  It will
automatically solve
the problem you are trying to fix in previous patch.

The real issue to me is that ia64_switch_mode_phys() creates
a zero
stack frame before turning off interrupt.  If the zero frame
alloc
instruction is removed, the current register stack frame
ought to be
safe because they should be preserved by the interrupt
return path.


- Ken
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