Need to pass va_list as a reference to vsyslog. This is because va_list is a structure in some compilers and passing of structures in the NuttX sycalls does not work.

libc/syslog/lib_lowsyslog.c

@@ -80,7 +80,7 @@ int lowvsyslog(int priority, FAR const IPTR char *fmt, va_list ap)
     {
       /* Perform the _lowvsyslog system call */
 
-      ret = _lowvsyslog(fmt, ap);
+      ret = _lowvsyslog(fmt, &ap);
     }
 
   return ret;

libc/syslog/lib_syslog.c

@@ -69,7 +69,7 @@ int vsyslog(int priority, FAR const IPTR char *fmt, va_list ap)
     {
       /* Yes.. lPerform the _vsyslog system cal */
 
-      ret = _vsyslog(fmt, ap);
+      ret = _vsyslog(fmt, &ap);
     }
 
   return ret;