+ * The @action argument may be one of:
+ * o %0 - LPT debugging checking starts, initialize debugging variables;
+ * o %1 - wrote an LPT node, increase LPT size by @len bytes;
+ * o %2 - switched to a different LEB and wasted @len bytes;
+ * o %3 - check that we've written the right number of bytes.
+ * o %4 - wasted @len bytes;