The function does nothing but return success. Simply treat absence of a
probe hook to mean just this. This then eliminates the (purely
theoretical at this point) risk of trying to call through
apic_x2apic_{cluster,phys}'s respective NULL pointers.

While doing this also eliminate generic_apic_probe()'s "changed"
variable: apic_probe[]'s default entry will now be used unconditionally
in yet more obvious a way, such that separately setting genapic from
apic_default is (hopefully) no longer justified. Yet that was the main
purpose of the variable.

To help prove that apic_default's probe() hook doesn't get used
elsewhere, further make apic_probe[] static at this occasion.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
---
v2: New.

--- a/xen/arch/x86/genapic/default.c
+++ b/xen/arch/x86/genapic/default.c
@@ -14,12 +14,7 @@
 #include <asm/io_apic.h>
 
 /* should be called last. */
-static __init int probe_default(void)
-{ 
-	return 1;
-} 
-
 const struct genapic __initconstrel apic_default = {
-	APIC_INIT("default", probe_default),
+	APIC_INIT("default", NULL),
 	GENAPIC_FLAT
 };
--- a/xen/arch/x86/genapic/probe.c
+++ b/xen/arch/x86/genapic/probe.c
@@ -18,7 +18,7 @@
 
 struct genapic __read_mostly genapic;
 
-const struct genapic *const __initconstrel apic_probe[] = {
+static const struct genapic *const __initconstrel apic_probe[] = {
 	&apic_bigsmp, 
 	&apic_default,	/* must be last */
 	NULL,
@@ -59,22 +59,20 @@ custom_param("apic", genapic_apic_force)
 
 void __init generic_apic_probe(void) 
 { 
-	bool changed;
 	int i;
 
 	record_boot_APIC_mode();
 
 	check_x2apic_preenabled();
-	cmdline_apic = changed = !!genapic.name;
 
-	for (i = 0; !changed && apic_probe[i]; i++) { 
-		if (apic_probe[i]->probe()) {
-			changed = 1;
+	cmdline_apic = genapic.name;
+
+	for (i = 0; !genapic.name && apic_probe[i]; i++) {
+		if (!apic_probe[i]->probe || apic_probe[i]->probe())
 			genapic = *apic_probe[i];
-		} 
 	}
-	if (!changed) 
-		genapic = apic_default;
+
+	BUG_ON(!genapic.name);
 
 	printk(KERN_INFO "Using APIC driver %s\n", genapic.name);
 }