x86/APIC: modify error_interrupt() to output using single printk()

This takes care of the issue of APIC errors tending to occur on multiple
cores at once.  In turn this tends to causes the error messages to be
merged together, making understanding them difficult.

Signed-off-by: Elliott Mitchell <ehem+xen@m5p.com>
Acked-by: Jan Beulich <jbeulich@suse.com>

xen/arch/x86/apic.c

@@ -1410,6 +1410,7 @@ static void cf_check error_interrupt(struct cpu_user_regs *regs)
         ", Received illegal vector",
         ", Illegal register address",
     };
+    const char *entries[ARRAY_SIZE(esr_fields)];
     unsigned int v, v1;
     int i;
 
@@ -1419,12 +1420,13 @@ static void cf_check error_interrupt(struct cpu_user_regs *regs)
     v1 = apic_read(APIC_ESR);
     ack_APIC_irq();
 
-    printk(XENLOG_DEBUG "APIC error on CPU%u: %02x(%02x)",
-            smp_processor_id(), v , v1);
     for ( i = 7; i >= 0; --i )
-        if ( v1 & (1 << i) )
-            printk("%s", esr_fields[i]);
-    printk("\n");
+        entries[i] = v1 & (1 << i) ? esr_fields[i] : "";
+    printk(XENLOG_DEBUG
+           "APIC error on CPU%u: %02x(%02x)%s%s%s%s%s%s%s%s\n",
+           smp_processor_id(), v, v1,
+           entries[7], entries[6], entries[5], entries[4],
+           entries[3], entries[2], entries[1], entries[0]);
 }
 
 /*