--- gcc/config/tm-i386sco.h	2018/04/24 16:58:25	1.1.1.2
+++ gcc/config/tm-i386sco.h	2018/04/24 17:00:06	1.1.1.3
@@ -30,3 +30,10 @@
 /* SCO's assember doesn't grok '$' in labels (for g++) */
 
 #define NO_DOLLAR_IN_LABEL
+
+/* SCO's libraries are compiled with Microsoft C, which requires the
+   caller to pop the extra argument passed to functions that return
+   structures. */
+
+#define STRUCT_RETURN_CALLER_POP
+