Index: sys/amd64/include/xen/xen-os.h
===================================================================
--- sys/amd64/include/xen/xen-os.h	(revisione 237379)
+++ sys/amd64/include/xen/xen-os.h	(copia locale)
@@ -75,6 +75,7 @@ void bootmem_free(void *ptr, unsigned int size);
 #include <sys/types.h>
 
 void printk(const char *fmt, ...);
+void vprintk(const char *fmt, __va_list ap);
 
 /* some function prototypes */
 void trap_init(void);
Index: sys/amd64/xen/machdep.c
===================================================================
--- sys/amd64/xen/machdep.c	(revisione 237379)
+++ sys/amd64/xen/machdep.c	(copia locale)
@@ -1037,12 +1037,19 @@ void
 printk(const char *fmt, ...)
 {
         __va_list ap;
+
+        va_start(ap, fmt);
+	vprintk(fmt, ap);
+        va_end(ap);
+}
+
+void
+vprintk(const char *fmt, __va_list ap)
+{
         int retval;
         static char buf[PRINTK_BUFSIZE];
 
-        va_start(ap, fmt);
         retval = vsnprintf(buf, PRINTK_BUFSIZE - 1, fmt, ap);
-        va_end(ap);
         buf[retval] = 0;
         (void)HYPERVISOR_console_write(buf, retval);
 }
Index: sys/kern/kern_shutdown.c
===================================================================
--- sys/kern/kern_shutdown.c	(revisione 237379)
+++ sys/kern/kern_shutdown.c	(copia locale)
@@ -611,6 +611,9 @@ panic(const char *fmt, ...)
 	}
 
 	va_start(ap, fmt);
+#ifdef XEN
+	vprintk(fmt, ap);
+#endif
 	if (newpanic) {
 		(void)vsnprintf(buf, sizeof(buf), fmt, ap);
 		panicstr = buf;