[gdb/build] Return gdb::array_view in thread_info_to_thread_handle

In remote_target::thread_info_to_thread_handle we return a copy:
...
gdb::byte_vector
remote_target::thread_info_to_thread_handle (struct thread_info *tp)
{
  remote_thread_info *priv = get_remote_thread_info (tp);
  return priv->thread_handle;
}
...

Fix this by returning a gdb::array_view instead:
...
gdb::array_view<const gdb_byte>
remote_target::thread_info_to_thread_handle (struct thread_info *tp)
...

Tested on x86_64-linux.

This fixes the build when building with -std=c++20.

Approved-By: Pedro Alves <pedro@palves.net>

gdb/linux-thread-db.c

@@ -107,7 +107,7 @@ public:
   thread_info *thread_handle_to_thread_info (const gdb_byte *thread_handle,
 					     int handle_len,
 					     inferior *inf) override;
-  gdb::byte_vector thread_info_to_thread_handle (struct thread_info *) override;
+  gdb::array_view<const gdb_byte> thread_info_to_thread_handle (struct thread_info *) override;
 };
 
 static std::string libthread_db_search_path = LIBTHREAD_DB_SEARCH_PATH;
@@ -312,6 +312,7 @@ struct thread_db_thread_info : public private_thread_info
   /* Cached thread state.  */
   td_thrhandle_t th {};
   thread_t tid {};
+  gdb::optional<gdb::byte_vector> thread_handle;
 };
 
 static thread_db_thread_info *
@@ -1724,20 +1725,20 @@ thread_db_target::thread_handle_to_thread_info (const gdb_byte *thread_handle,
 
 /* Return the thread handle associated the thread_info pointer TP.  */
 
-gdb::byte_vector
+gdb::array_view<const gdb_byte>
 thread_db_target::thread_info_to_thread_handle (struct thread_info *tp)
 {
   thread_db_thread_info *priv = get_thread_db_thread_info (tp);
 
   if (priv == NULL)
-    return gdb::byte_vector ();
+    return {};
 
   int handle_size = sizeof (priv->tid);
-  gdb::byte_vector rv (handle_size);
+  priv->thread_handle.emplace (handle_size);
 
-  memcpy (rv.data (), &priv->tid, handle_size);
+  memcpy (priv->thread_handle->data (), &priv->tid, handle_size);
 
-  return rv;
+  return *priv->thread_handle;
 }
 
 /* Get the address of the thread local variable in load module LM which

gdb/python/py-infthread.c

@@ -291,8 +291,8 @@ thpy_thread_handle (PyObject *self, PyObject *args)
   thread_object *thread_obj = (thread_object *) self;
   THPY_REQUIRE_VALID (thread_obj);
 
-  gdb::byte_vector hv;
-  
+  gdb::array_view<const gdb_byte> hv;
+
   try
     {
       hv = target_thread_info_to_thread_handle (thread_obj->thread);

gdb/remote.c

@@ -784,8 +784,8 @@ public:
 					     int handle_len,
 					     inferior *inf) override;
 
-  gdb::byte_vector thread_info_to_thread_handle (struct thread_info *tp)
-						 override;
+  gdb::array_view<const gdb_byte> thread_info_to_thread_handle (struct thread_info *tp)
+    override;
 
   void stop (ptid_t) override;
 
@@ -14550,7 +14550,7 @@ remote_target::thread_handle_to_thread_info (const gdb_byte *thread_handle,
   return NULL;
 }
 
-gdb::byte_vector
+gdb::array_view<const gdb_byte>
 remote_target::thread_info_to_thread_handle (struct thread_info *tp)
 {
   remote_thread_info *priv = get_remote_thread_info (tp);

gdb/target-debug.h

@@ -219,7 +219,7 @@ target_debug_print_size_t (size_t size)
 }
 
 static void
-target_debug_print_const_gdb_byte_vector_r (const gdb::byte_vector &vector)
+target_debug_print_gdb_array_view_const_gdb_byte (gdb::array_view<const gdb_byte> vector)
 {
   gdb_puts ("{", gdb_stdlog);
 
@@ -231,6 +231,12 @@ target_debug_print_const_gdb_byte_vector_r (const gdb::byte_vector &vector)
   gdb_puts (" }", gdb_stdlog);
 }
 
+static void
+target_debug_print_const_gdb_byte_vector_r (const gdb::byte_vector &vector)
+{
+  target_debug_print_gdb_array_view_const_gdb_byte (vector);
+}
+
 static void
 target_debug_print_gdb_byte_vector_r (gdb::byte_vector &vector)
 {

gdb/target-delegates.c

@@ -89,7 +89,7 @@ struct dummy_target : public target_ops
   const char *extra_thread_info (thread_info *arg0) override;
   const char *thread_name (thread_info *arg0) override;
   thread_info *thread_handle_to_thread_info (const gdb_byte *arg0, int arg1, inferior *arg2) override;
-  gdb::byte_vector thread_info_to_thread_handle (struct thread_info *arg0) override;
+  gdb::array_view<const_gdb_byte> thread_info_to_thread_handle (struct thread_info *arg0) override;
   void stop (ptid_t arg0) override;
   void interrupt () override;
   void pass_ctrlc () override;
@@ -263,7 +263,7 @@ struct debug_target : public target_ops
   const char *extra_thread_info (thread_info *arg0) override;
   const char *thread_name (thread_info *arg0) override;
   thread_info *thread_handle_to_thread_info (const gdb_byte *arg0, int arg1, inferior *arg2) override;
-  gdb::byte_vector thread_info_to_thread_handle (struct thread_info *arg0) override;
+  gdb::array_view<const_gdb_byte> thread_info_to_thread_handle (struct thread_info *arg0) override;
   void stop (ptid_t arg0) override;
   void interrupt () override;
   void pass_ctrlc () override;
@@ -1871,28 +1871,28 @@ debug_target::thread_handle_to_thread_info (const gdb_byte *arg0, int arg1, infe
   return result;
 }
 
-gdb::byte_vector
+gdb::array_view<const_gdb_byte>
 target_ops::thread_info_to_thread_handle (struct thread_info *arg0)
 {
   return this->beneath ()->thread_info_to_thread_handle (arg0);
 }
 
-gdb::byte_vector
+gdb::array_view<const_gdb_byte>
 dummy_target::thread_info_to_thread_handle (struct thread_info *arg0)
 {
-  return gdb::byte_vector ();
+  return gdb::array_view<const gdb_byte> ();
 }
 
-gdb::byte_vector
+gdb::array_view<const_gdb_byte>
 debug_target::thread_info_to_thread_handle (struct thread_info *arg0)
 {
   gdb_printf (gdb_stdlog, "-> %s->thread_info_to_thread_handle (...)\n", this->beneath ()->shortname ());
-  gdb::byte_vector result
+  gdb::array_view<const_gdb_byte> result
     = this->beneath ()->thread_info_to_thread_handle (arg0);
   gdb_printf (gdb_stdlog, "<- %s->thread_info_to_thread_handle (", this->beneath ()->shortname ());
   target_debug_print_struct_thread_info_p (arg0);
   gdb_puts (") = ", gdb_stdlog);
-  target_debug_print_gdb_byte_vector (result);
+  target_debug_print_gdb_array_view_const_gdb_byte (result);
   gdb_puts ("\n", gdb_stdlog);
   return result;
 }

gdb/target.c

@@ -2640,7 +2640,7 @@ target_thread_handle_to_thread_info (const gdb_byte *thread_handle,
 
 /* See target.h.  */
 
-gdb::byte_vector
+gdb::array_view<const gdb_byte>
 target_thread_info_to_thread_handle (struct thread_info *tip)
 {
   target_ops *target = current_inferior ()->top_target ();

gdb/target.h

@@ -39,6 +39,10 @@ struct expression;
 struct dcache_struct;
 struct inferior;
 
+/* Define const gdb_byte using one identifier, to make it easy for
+   make-target-delegates.py to parse.  */
+typedef const gdb_byte const_gdb_byte;
+
 #include "infrun.h" /* For enum exec_direction_kind.  */
 #include "breakpoint.h" /* For enum bptype.  */
 #include "gdbsupport/scoped_restore.h"
@@ -679,8 +683,8 @@ struct target_ops
 						       inferior *inf)
       TARGET_DEFAULT_RETURN (NULL);
     /* See target_thread_info_to_thread_handle.  */
-    virtual gdb::byte_vector thread_info_to_thread_handle (struct thread_info *)
-      TARGET_DEFAULT_RETURN (gdb::byte_vector ());
+    virtual gdb::array_view<const_gdb_byte> thread_info_to_thread_handle (struct thread_info *)
+      TARGET_DEFAULT_RETURN (gdb::array_view<const gdb_byte> ());
     virtual void stop (ptid_t)
       TARGET_DEFAULT_IGNORE ();
     virtual void interrupt ()
@@ -1924,7 +1928,7 @@ extern struct thread_info *target_thread_handle_to_thread_info
 /* Given a thread, return the thread handle, a target-specific sequence of
    bytes which serves as a thread identifier within the program being
    debugged.  */
-extern gdb::byte_vector target_thread_info_to_thread_handle
+extern gdb::array_view<const gdb_byte> target_thread_info_to_thread_handle
   (struct thread_info *);
 
 /* Attempts to find the pathname of the executable file