x86/entry: Fix idtentry unwind hint

This fixes the following ORC warning in the 'int3' entry code:

  WARNING: can't dereference iret registers at ffff8801c5f17fe0 for ip ffffffff95f0d94b

The ORC metadata had the wrong stack offset for the iret registers.

Their location on the stack is dependent on whether the exception has an
error code.

Reported-and-tested-by: Andrei Vagin <avagin@virtuozzo.com>
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Fixes: 8c1f75587a18 ("x86/entry/64: Add unwind hint annotations")
Link: http://lkml.kernel.org/r/931d57f0551ed7979d5e7e05370d445c8e5137f8.1508516398.git.jpoimboe@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

arch/x86/entry/entry_64.S

@@ -808,7 +808,7 @@ apicinterrupt IRQ_WORK_VECTOR			irq_work_interrupt		smp_irq_work_interrupt
 
 .macro idtentry sym do_sym has_error_code:req paranoid=0 shift_ist=-1
 ENTRY(\sym)
-	UNWIND_HINT_IRET_REGS offset=8
+	UNWIND_HINT_IRET_REGS offset=\has_error_code*8
 
 	/* Sanity check */
 	.if \shift_ist != -1 && \paranoid == 0