[gdb/exp] Allow internal function to indicate return type

Currently an internal function handler has this prototype:
...
struct value *handler (struct gdbarch *gdbarch,
                       const struct language_defn *language,
                       void *cookie, int argc, struct value **argv);
...

Also allow an internal function with a handler with an additional
"enum noside noside" parameter:
...
struct value *handler (struct gdbarch *gdbarch,
                       const struct language_defn *language, void *cookie,
                       int argc, struct value **argv, enum noside noside);
...

In case such a handler is called with noside == EVAL_AVOID_SIDE_EFFECTS, it's
expected to return some value with the correct return type.

At least, provided it can do so without side effects, otherwise it should
throw an error.

No functional changes.

Tested on x86_64-linux and aarch64-linux.

Reviewed-By: Keith Seitz <keiths@redhat.com>

5 files changed, 100 insertions, 31 deletions

diff --git a/gdb/ada-lang.c b/gdb/ada-lang.c
index e2be7f9..1cf6ff5 100644
--- a/gdb/ada-lang.c
+++ b/gdb/ada-lang.c
@@ -11195,16 +11195,9 @@ ada_funcall_operation::evaluate (struct type *expect_type,
 	}
       return call_function_by_hand (callee, expect_type, argvec);
     case TYPE_CODE_INTERNAL_FUNCTION:
-      if (noside == EVAL_AVOID_SIDE_EFFECTS)
-	/* We don't know anything about what the internal
-	   function might return, but we have to return
-	   something.  */
-	return value::zero (builtin_type (exp->gdbarch)->builtin_int,
-			   not_lval);
-      else
 	return call_internal_function (exp->gdbarch, exp->language_defn,
 				       callee, nargs,
-				       argvec.data ());
+				       argvec.data (), noside);
 
     case TYPE_CODE_STRUCT:
       {
diff --git a/gdb/eval.c b/gdb/eval.c
index 40640ae..f6b8136 100644
--- a/gdb/eval.c
+++ b/gdb/eval.c
@@ -622,11 +622,7 @@ evaluate_subexp_do_call (expression *exp, enum noside noside,
 
       if (ftype->code () == TYPE_CODE_INTERNAL_FUNCTION)
 	{
-	  /* We don't know anything about what the internal
-	     function might return, but we have to return
-	     something.  */
-	  return value::zero (builtin_type (exp->gdbarch)->builtin_int,
-			     not_lval);
+	  /* The call to call_internal_function below handles noside.  */
 	}
       else if (ftype->code () == TYPE_CODE_XMETHOD)
 	{
@@ -666,7 +662,8 @@ evaluate_subexp_do_call (expression *exp, enum noside noside,
     {
     case TYPE_CODE_INTERNAL_FUNCTION:
       return call_internal_function (exp->gdbarch, exp->language_defn,
-				     callee, argvec.size (), argvec.data ());
+				     callee, argvec.size (), argvec.data (),
+				     noside);
     case TYPE_CODE_XMETHOD:
       return callee->call_xmethod (argvec);
     default:
diff --git a/gdb/python/py-value.c b/gdb/python/py-value.c
index dada8bf..5c62ef6 100644
--- a/gdb/python/py-value.c
+++ b/gdb/python/py-value.c
@@ -1258,7 +1258,8 @@ valpy_call (PyObject *self, PyObject *args, PyObject *keywords)
       if (ftype->code () == TYPE_CODE_INTERNAL_FUNCTION)
 	return_value = call_internal_function (gdbpy_enter::get_gdbarch (),
 					       current_language,
-					       function, args_count, vargs);
+					       function, args_count, vargs,
+					       EVAL_NORMAL);
       else
 	return_value
 	  = call_function_by_hand (function, NULL,
diff --git a/gdb/value.c b/gdb/value.c
index e71f38b..9435900 100644
--- a/gdb/value.c
+++ b/gdb/value.c
@@ -61,7 +61,7 @@ struct internal_function
   char *name;
 
   /* The handler.  */
-  internal_function_fn handler;
+  internal_function_fn_noside handler;
 
   /* User data for the handler.  */
   void *cookie;
@@ -2336,9 +2336,9 @@ internalvar_name (const struct internalvar *var)
 
 static struct internal_function *
 create_internal_function (const char *name,
-			  internal_function_fn handler, void *cookie)
+			  internal_function_fn_noside handler, void *cookie)
 {
-  struct internal_function *ifn = XNEW (struct internal_function);
+  struct internal_function *ifn = new (struct internal_function);
 
   ifn->name = xstrdup (name);
   ifn->handler = handler;
@@ -2362,7 +2362,8 @@ value_internal_function_name (struct value *val)
 struct value *
 call_internal_function (struct gdbarch *gdbarch,
 			const struct language_defn *language,
-			struct value *func, int argc, struct value **argv)
+			struct value *func, int argc, struct value **argv,
+			enum noside noside)
 {
   struct internal_function *ifn;
   int result;
@@ -2371,7 +2372,7 @@ call_internal_function (struct gdbarch *gdbarch,
   result = get_internalvar_function (VALUE_INTERNALVAR (func), &ifn);
   gdb_assert (result);
 
-  return (*ifn->handler) (gdbarch, language, ifn->cookie, argc, argv);
+  return ifn->handler (gdbarch, language, ifn->cookie, argc, argv, noside);
 }
 
 /* The 'function' command.  This does nothing -- it is just a
@@ -2388,7 +2389,7 @@ function_command (const char *command, int from_tty)
 
 static struct cmd_list_element *
 do_add_internal_function (const char *name, const char *doc,
-			  internal_function_fn handler, void *cookie)
+			  internal_function_fn_noside handler, void *cookie)
 {
   struct internal_function *ifn;
   struct internalvar *var = lookup_internalvar (name);
@@ -2403,17 +2404,50 @@ do_add_internal_function (const char *name, const char *doc,
 
 void
 add_internal_function (const char *name, const char *doc,
-		       internal_function_fn handler, void *cookie)
+		       internal_function_fn_noside handler, void *cookie)
 {
   do_add_internal_function (name, doc, handler, cookie);
 }
 
+/* By default, internal functions are assumed to return int.  Return a value
+   with that type to reflect this.  If this is not correct for a specific
+   internal function, it should use an internal_function_fn_noside handler to
+   bypass this default.  */
+
+static struct value *
+internal_function_default_return_type (struct gdbarch *gdbarch)
+{
+  return value::zero (builtin_type (gdbarch)->builtin_int, not_lval);
+}
+
+/* See value.h.  */
+
+void
+add_internal_function (const char *name, const char *doc,
+		       internal_function_fn handler, void *cookie)
+{
+  internal_function_fn_noside fn
+    = [=] (struct gdbarch *gdbarch,
+	   const struct language_defn *language,
+	   void *_cookie,
+	   int argc,
+	   struct value **argv,
+	   enum noside noside)
+    {
+      if (noside == EVAL_AVOID_SIDE_EFFECTS)
+	return internal_function_default_return_type (gdbarch);
+      return handler (gdbarch, language, _cookie, argc, argv);
+    };
+
+  do_add_internal_function (name, doc, fn, cookie);
+}
+
 /* See value.h.  */
 
 void
 add_internal_function (gdb::unique_xmalloc_ptr<char> &&name,
 		       gdb::unique_xmalloc_ptr<char> &&doc,
-		       internal_function_fn handler, void *cookie)
+		       internal_function_fn_noside handler, void *cookie)
 {
   struct cmd_list_element *cmd
     = do_add_internal_function (name.get (), doc.get (), handler, cookie);
@@ -2426,6 +2460,31 @@ add_internal_function (gdb::unique_xmalloc_ptr<char> &&name,
   cmd->name_allocated = 1;
 }
 
+/* See value.h.  */
+
+void
+add_internal_function (gdb::unique_xmalloc_ptr<char> &&name,
+		       gdb::unique_xmalloc_ptr<char> &&doc,
+		       internal_function_fn handler, void *cookie)
+{
+  internal_function_fn_noside fn
+    = [=] (struct gdbarch *gdbarch,
+	   const struct language_defn *language,
+	   void *_cookie,
+	   int argc,
+	   struct value **argv,
+	   enum noside noside)
+    {
+      if (noside == EVAL_AVOID_SIDE_EFFECTS)
+	return internal_function_default_return_type (gdbarch);
+      return handler (gdbarch, language, _cookie, argc, argv);
+    };
+
+  add_internal_function (std::forward<gdb::unique_xmalloc_ptr<char>>(name),
+			 std::forward<gdb::unique_xmalloc_ptr<char>>(doc),
+			 fn, cookie);
+}
+
 void
 value::preserve (struct objfile *objfile, htab_t copied_types)
 {
diff --git a/gdb/value.h b/gdb/value.h
index 9d7e88d..13cfb00 100644
--- a/gdb/value.h
+++ b/gdb/value.h
@@ -1598,13 +1598,24 @@ extern struct value *find_function_in_inferior (const char *,
 
 extern struct value *value_allocate_space_in_inferior (int);
 
-/* User function handler.  */
-
-typedef struct value *(*internal_function_fn) (struct gdbarch *gdbarch,
-					       const struct language_defn *language,
-					       void *cookie,
-					       int argc,
-					       struct value **argv);
+/* User function handler.  The internal_function_fn variant assumes return
+   type int.  The internal_function_fn_noside returns some value with the
+   return type when passed noside == EVAL_AVOID_SIDE_EFFECTS.  */
+
+using internal_function_fn
+  = std::function<struct value *(struct gdbarch *gdbarch,
+				 const struct language_defn *language,
+				 void *cookie,
+				 int argc,
+				 struct value **argv)>;
+
+using internal_function_fn_noside
+  = std::function<struct value *(struct gdbarch *gdbarch,
+				 const struct language_defn *language,
+				 void *cookie,
+				 int argc,
+				 struct value **argv,
+				 enum noside noside)>;
 
 /* Add a new internal function.  NAME is the name of the function; DOC
    is a documentation string describing the function.  HANDLER is
@@ -1615,6 +1626,9 @@ typedef struct value *(*internal_function_fn) (struct gdbarch *gdbarch,
 extern void add_internal_function (const char *name, const char *doc,
 				   internal_function_fn handler,
 				   void *cookie);
+extern void add_internal_function (const char *name, const char *doc,
+				   internal_function_fn_noside handler,
+				   void *cookie);
 
 /* This overload takes an allocated documentation string.  */
 
@@ -1622,11 +1636,16 @@ extern void add_internal_function (gdb::unique_xmalloc_ptr<char> &&name,
 				   gdb::unique_xmalloc_ptr<char> &&doc,
 				   internal_function_fn handler,
 				   void *cookie);
+extern void add_internal_function (gdb::unique_xmalloc_ptr<char> &&name,
+				   gdb::unique_xmalloc_ptr<char> &&doc,
+				   internal_function_fn_noside handler,
+				   void *cookie);
 
 struct value *call_internal_function (struct gdbarch *gdbarch,
 				      const struct language_defn *language,
 				      struct value *function,
-				      int argc, struct value **argv);
+				      int argc, struct value **argv,
+				      enum noside noside);
 
 const char *value_internal_function_name (struct value *);