Indirect string one level for libffi

Every argument to libffi is dereferenced before being passed to the
function, including pointers. For strings to be correctly passed, an
additional level of indirection is needed. This fixes the need to use
the "address of" operator `&' in the C function for strings passed to
foreign functions that also take structures by value.

src/strings.lisp

@@ -287,7 +287,13 @@ buffer along with ARGS." ; fix wording, sigh
 
 (defmethod expand-to-foreign-dyn-indirect
     (value var body (type foreign-string-type))
-  (expand-to-foreign-dyn value var body type))
+  (alexandria:with-gensyms (str)
+    (expand-to-foreign-dyn
+     value
+     str
+     (list 
+      (expand-to-foreign-dyn-indirect str var body (parse-type :pointer)))
+     type)))
 
 ;;;# STRING+PTR
 

tests/libfsbv.c

@@ -108,7 +108,7 @@ DLLEXPORT
 struct struct_pair stringlenpair (char *string, struct struct_pair dp)
 {
   struct struct_pair ret;
-  int len = strlen(&string);
+  int len = strlen(string);
   ret.a = len*dp.a;
   ret.b = len*dp.b;
   return ret;