[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>

1 files changed, 67 insertions, 8 deletions

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)
 {