--- gforth/engine/threaded.h	2001/01/06 19:29:15	1.10
+++ gforth/engine/threaded.h	2002/01/16 10:40:26	1.14
@@ -103,11 +103,15 @@
 #  define NEXT_INST	(cfa)
 #  define INC_IP(const_inc)	({cfa=IP[const_inc]; ip+=(const_inc);})
 #  define DEF_CA	Label ca;
-#  define NEXT_P1	({ip++; ca=**cfa;})
+#  define NEXT_P1	({\
+  if (cfa<=vm_prims+DOESJUMP || cfa>=vm_prims+npriminfos) \
+    fprintf(stderr,"NEXT encountered prim %p at ip=%p\n", cfa, ip); \
+  ip++; ca=**cfa;})
 #  define NEXT_P2	({goto *ca;})
-#  define EXEC(XT)	({DEF_CA cfa=(XT); ca=**cfa; goto *ca;})
-#  define NEXT1_P1 ({ca = **cfa;})
-#  define NEXT1_P2 ({goto *ca;})
+#  define EXEC(XT)	({DEF_CA cfa=(XT);\
+  if (cfa>vm_prims+DOESJUMP && cfa<vm_prims+npriminfos) \
+    fprintf(stderr,"EXEC encountered xt %p at ip=%p, vm_prims=%p, xts=%p\n", cfa, ip, vm_prims, xts); \
+ ca=**cfa; goto *ca;})
 
 #else /* !defined(DOUBLY_INDIRECT) */