as: trap unresolved subtractions as we can't currently represent them

diff --git a/Applications/MWC/cmd/asz80/as3.c b/Applications/MWC/cmd/asz80/as3.c
index b448ac7..62fc4ad 100644 (file)
--- a/Applications/MWC/cmd/asz80/as3.c
+++ b/Applications/MWC/cmd/asz80/as3.c
@@ -66,6 +66,11 @@ static void chksegment(ADDR *left, ADDR *right, int op)
        }
        /* Subtraction within segment produces an absolute */
        if (op == '-') {
+               /* We can't currently represent this and it's hard because
+                  we'd actually need to pass the expression tree to the
+                  linker. Only allow known symbols so that you can
+                  do a-b providing a and b are in your object module */
+#if 0
                /* Unknown symbols may get segment forced as a result */
                if (left->a_segment == UNKNOWN) {
                        left->a_segment = right->a_segment;
@@ -77,6 +82,9 @@ static void chksegment(ADDR *left, ADDR *right, int op)
                        if (right->a_sym)
                                setsegment(right->a_sym, right->a_segment);
                }
+#else
+               if (left->a_segment != UNKNOWN && right->a_segment != UNKNOWN)
+#endif
                if (left->a_segment == right->a_segment && op == '-') {
                        left->a_segment = ABSOLUTE;
                        left->a_sym = NULL;