Fix for #209 - forbid exporting expressions with unresolved symbols

expr.c

@@ -585,7 +585,7 @@ be converted from a linked list into an array).
 //
 // Evaluate expression.
 // If the expression involves only ONE external symbol, the expression is
-// UNDEFINED, but it's value includes everything but the symbol value, and
+// UNDEFINED, but its value includes everything but the symbol value, and
 // 'a_esym' is set to the external symbol.
 //
 int evexpr(TOKEN * _tk, uint64_t * a_value, WORD * a_attr, SYM ** a_esym)

rmac.h

@@ -262,6 +262,7 @@ PTR
 #define SIZP         0x0080		// .p (FPU pakced decimal real)
 #define SIZQ         0x0100		// .q (quad word)
 
+// Extended attributes
 #define EQUATEDREG   0x0008		// Equated register symbol
 #define UNDEF_EQUR   0x0010
 #define EQUATEDCC    0x0020

sect.c

@@ -462,6 +462,15 @@ int ResolveFixups(int sno)
 			if (evexpr(fup->expr, &eval, &eattr, &esym) != OK)
 				continue;
 
+			if (esym)
+				if (!(esym->sattr & DEFINED))
+				{
+					// If our expression still has an undefined symbol at this stage, it's bad news.
+					// The linker is never going to resolve the expression, so that's an error.
+					error("cannot export complex expression with unresloved symbol '%s'", esym->sname);
+					continue;
+				}
+
 			if ((CHECK_OPTS(OPT_PC_RELATIVE)) && (eattr & (DEFINED | REFERENCED | EQUATED)) == (DEFINED | REFERENCED))
 			{
 				error("relocation not allowed when o30 is enabled");