diff --git a/tcg/tcg-internal.h b/tcg/tcg-internal.h
index 2c06b5116a..f574743ff8 100644
--- a/tcg/tcg-internal.h
+++ b/tcg/tcg-internal.h
@@ -27,6 +27,21 @@
 
 #define TCG_HIGHWATER 1024
 
+/*
+ * Describe the calling convention of a given argument type.
+ */
+typedef enum {
+    TCG_CALL_RET_NORMAL,         /* by registers */
+} TCGCallReturnKind;
+
+typedef enum {
+    TCG_CALL_ARG_NORMAL,         /* by registers (continuing onto stack) */
+    TCG_CALL_ARG_EVEN,           /* like normal, but skipping odd slots */
+    TCG_CALL_ARG_EXTEND,         /* for i32, as a sign/zero-extended i64 */
+    TCG_CALL_ARG_EXTEND_U,       /*      ... as a zero-extended i64 */
+    TCG_CALL_ARG_EXTEND_S,       /*      ... as a sign-extended i64 */
+} TCGCallArgumentKind;
+
 typedef struct TCGHelperInfo {
     void *func;
     const char *name;