[PATCH] x86: increase interrupt vector range

Remove the limit of 256 interrupt vectors by changing the value stored in
orig_{e,r}ax to be the complemented interrupt vector.  The orig_{e,r}ax
needs to be < 0 to allow the signal code to distinguish between return from
interrupt and return from syscall.  With this change applied, NR_IRQS can
be > 256.

Xen extends the IRQ numbering space to include room for dynamically
allocated virtual interrupts (in the range 256-511), which requires a more
permissive interface to do_IRQ.

Signed-off-by: Ian Pratt <ian.pratt@xensource.com>
Signed-off-by: Christian Limpach <Christian.Limpach@cl.cam.ac.uk>
Signed-off-by: Chris Wright <chrisw@sous-sol.org>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Cc: "Protasevich, Natalie" <Natalie.Protasevich@UNISYS.com>
Cc: Andi Kleen <ak@muc.de>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

arch/i386/kernel/entry.S

@@ -515,7 +515,7 @@ ENTRY(irq_entries_start)
  .if vector
 	CFI_ADJUST_CFA_OFFSET -4
  .endif
-1:	pushl $vector-256
+1:	pushl $~(vector)
 	CFI_ADJUST_CFA_OFFSET 4
 	jmp common_interrupt
 .data
@@ -535,7 +535,7 @@ common_interrupt:
 #define BUILD_INTERRUPT(name, nr)	\
 ENTRY(name)				\
 	RING0_INT_FRAME;		\
-	pushl $nr-256;			\
+	pushl $~(nr);			\
 	CFI_ADJUST_CFA_OFFSET 4;	\
 	SAVE_ALL;			\
 	movl %esp,%eax;			\