Assert on bad arguments to sgen_clear_range.

mono/metadata/sgen-nursery-allocator.c

@@ -661,12 +661,24 @@ sgen_clear_nursery_fragments (void)
 	}
 }
 
+/*
+ * Mark a given range of memory as invalid.
+ *
+ * This can be done either by zeroing memory or by placing
+ * a phony byte[] array. This keeps the heap forward walkable.
+ *
+ * This function ignores calls with a zero range, even if
+ * both start and end are NULL.
+ */
 void
 sgen_clear_range (char *start, char *end)
 {
 	MonoArray *o;
 	size_t size = end - start;
 
+	if ((start && !end) || (start > end))
+		g_error ("Invalid range [%p %p]", start, end);
+
 	if (size < sizeof (MonoArray)) {
 		memset (start, 0, size);
 		return;