[PATCH] x86/vpt: fix build with old gcc

[Jan Beulich <jbeulich@xxxxxxxx>]

I believe it was the XSA-336 fix (42fcdd42328f "x86/vpt: fix race when
migrating timers between vCPUs") which has unmasked a bogus
uninitialized variable warning. This is observable with gcc 4.3.4, but
only on 4.13 and older; it's hidden on newer versions apparently due to
the addition to _read_unlock() done by 12509bbeb9e3 ("rwlocks: call
preempt_disable() when taking a rwlock").

Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
---
Of course we could decide to only work around this on the older
branches. But I think it's better to have the fix everywhere (as long as
we still support such old gcc), as further changes may - effectively
randomly - unhide the warning again.

--- a/xen/arch/x86/hvm/vpt.c
+++ b/xen/arch/x86/hvm/vpt.c
@@ -401,7 +401,7 @@ int pt_update_irq(struct vcpu *v)
                  * associated with the timer.
                  */
                 time_cb *cb = NULL;
-                void *cb_priv;
+                void *cb_priv = NULL;
 
                 pt_vcpu_lock(v);
                 /* Make sure the timer is still on the list. */