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------------------------------------------------------------------------------

--                                                                          --

--                         GNAT RUN-TIME COMPONENTS                         --

--                                                                          --

--                             A D A . T A G S                              --

--                                                                          --

--                                 S p e c                                  --

--                                                                          --

--          Copyright (C) 1992-2011, Free Software Foundation, Inc.         --

--                                                                          --

-- This specification is derived from the Ada Reference Manual for use with --

-- GNAT. The copyright notice above, and the license provisions that follow --

-- apply solely to the  contents of the part following the private keyword. --

--                                                                          --

-- GNAT is free software;  you can  redistribute it  and/or modify it under --

-- terms of the  GNU General Public License as published  by the Free Soft- --

-- ware  Foundation;  either version 3,  or (at your option) any later ver- --

-- sion.  GNAT is distributed in the hope that it will be useful, but WITH- --

-- OUT ANY WARRANTY;  without even the  implied warranty of MERCHANTABILITY --

-- or FITNESS FOR A PARTICULAR PURPOSE.                                     --

--                                                                          --

-- As a special exception under Section 7 of GPL version 3, you are granted --

-- additional permissions described in the GCC Runtime Library Exception,   --

-- version 3.1, as published by the Free Software Foundation.               --

--                                                                          --

-- You should have received a copy of the GNU General Public License and    --

-- a copy of the GCC Runtime Library Exception along with this program;     --

-- see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see    --

-- <http://www.gnu.org/licenses/>.                                          --

--                                                                          --

-- GNAT was originally developed  by the GNAT team at  New York University. --

-- Extensive contributions were provided by Ada Core Technologies Inc.      --

--                                                                          --

------------------------------------------------------------------------------

with System;

with System.Storage_Elements;

package Ada.Tags is

   pragma Preelaborate_05;

   --  In accordance with Ada 2005 AI-362

   type Tag is private;

   pragma Preelaborable_Initialization (Tag);

   No_Tag : constant Tag;

   function Expanded_Name (T : Tag) return String;

   function Wide_Expanded_Name (T : Tag) return Wide_String;

   pragma Ada_05 (Wide_Expanded_Name);

   function Wide_Wide_Expanded_Name (T : Tag) return Wide_Wide_String;

   pragma Ada_05 (Wide_Wide_Expanded_Name);

   function External_Tag (T : Tag) return String;

   function Internal_Tag (External : String) return Tag;

   function Descendant_Tag

     (External : String;

      Ancestor : Tag) return Tag;

   pragma Ada_05 (Descendant_Tag);

   function Is_Descendant_At_Same_Level

     (Descendant : Tag;

      Ancestor   : Tag) return Boolean;

   pragma Ada_05 (Is_Descendant_At_Same_Level);

   function Parent_Tag (T : Tag) return Tag;

   pragma Ada_05 (Parent_Tag);

   type Tag_Array is array (Positive range <>) of Tag;

   function Interface_Ancestor_Tags (T : Tag) return Tag_Array;

   pragma Ada_05 (Interface_Ancestor_Tags);

   function Type_Is_Abstract (T : Tag) return Boolean;

   pragma Ada_2012 (Type_Is_Abstract);

   Tag_Error : exception;

private

   --  Structure of the GNAT Primary Dispatch Table

   --           +--------------------+

   --           |      Signature     |

   --           +--------------------+

   --           |     Tagged_Kind    |

   --           +--------------------+                            Predef Prims

   --           |    Predef_Prims -----------------------------> +------------+

   --           +--------------------+                           |  table of  |

   --           |    Offset_To_Top   |                           | predefined |

   --           +--------------------+                           | primitives |

   --           |Typeinfo_Ptr/TSD_Ptr---> Type Specific Data     +------------+

   --  Tag ---> +--------------------+   +-------------------+

   --           |      table of      |   | inheritance depth |

   --           :   primitive ops    :   +-------------------+

   --           |      pointers      |   |   access level    |

   --           +--------------------+   +-------------------+

   --                                    |     alignment     |

   --                                    +-------------------+

   --                                    |   expanded name   |

   --                                    +-------------------+

   --                                    |   external tag    |

   --                                    +-------------------+

   --                                    |   hash table link |

   --                                    +-------------------+

   --                                    |   transportable   |

   --                                    +-------------------+

   --                                    |  type_is_abstract |

   --                                    +-------------------+

   --                                    | needs finalization|

   --                                    +-------------------+

   --                                    |   Ifaces_Table   ---> Interface Data

   --                                    +-------------------+   +------------+

   --         Select Specific Data  <----        SSD         |   |  Nb_Ifaces |

   --         +------------------+       +-------------------+   +------------+

   --         |table of primitive|       | table of          |   |  table     |

   --         :   operation      :       :    ancestor       :   :    of      :

   --         |      kinds       |       |       tags        |   | interfaces |

   --         +------------------+       +-------------------+   +------------+

   --         |table of          |

   --         :   entry          :

   --         |      indexes     |

   --         +------------------+

   --  Structure of the GNAT Secondary Dispatch Table

   --           +--------------------+

   --           |      Signature     |

   --           +--------------------+

   --           |     Tagged_Kind    |

   --           +--------------------+                            Predef Prims

   --           |    Predef_Prims -----------------------------> +------------+

   --           +--------------------+                           |  table of  |

   --           |    Offset_To_Top   |                           | predefined |

   --           +--------------------+                           | primitives |

   --           |       OSD_Ptr      |---> Object Specific Data  |   thunks   |

   --  Tag ---> +--------------------+      +---------------+    +------------+

   --           |      table of      |      | num prim ops  |

   --           :    primitive op    :      +---------------+

   --           |   thunk pointers   |      | table of      |

   --           +--------------------+      +   primitive   |

   --                                       |    op offsets |

   --                                       +---------------+

   --  The runtime information kept for each tagged type is separated into two

   --  objects: the Dispatch Table and the Type Specific Data record.

   package SSE renames System.Storage_Elements;

   subtype Cstring is String (Positive);

   type Cstring_Ptr is access all Cstring;

   pragma No_Strict_Aliasing (Cstring_Ptr);

   --  Declarations for the table of interfaces

   type Offset_To_Top_Function_Ptr is

     access function (This : System.Address) return SSE.Storage_Offset;

   --  Type definition used to call the function that is generated by the

   --  expander in case of tagged types with discriminants that have secondary

   --  dispatch tables. This function provides the Offset_To_Top value in this

   --  specific case.

   type Interface_Data_Element is record

      Iface_Tag            : Tag;

      Static_Offset_To_Top : Boolean;

      Offset_To_Top_Value  : SSE.Storage_Offset;

      Offset_To_Top_Func   : Offset_To_Top_Function_Ptr;

      Secondary_DT         : Tag;

   end record;

   --  If some ancestor of the tagged type has discriminants the field

   --  Static_Offset_To_Top is False and the field Offset_To_Top_Func

   --  is used to store the access to the function generated by the

   --  expander which provides this value; otherwise Static_Offset_To_Top

   --  is True and such value is stored in the Offset_To_Top_Value field.

   --  Secondary_DT references a secondary dispatch table whose contents

   --  are pointers to the primitives of the tagged type that cover the

   --  interface primitives. Secondary_DT gives support to dispatching

   --  calls through interface types associated with Generic Dispatching

   --  Constructors.

   type Interfaces_Array is array (Natural range <>) of Interface_Data_Element;

   type Interface_Data (Nb_Ifaces : Positive) is record

      Ifaces_Table : Interfaces_Array (1 .. Nb_Ifaces);

   end record;

   type Interface_Data_Ptr is access all Interface_Data;

   --  Table of abstract interfaces used to give support to backward interface

   --  conversions and also to IW_Membership.

   --  Primitive operation kinds. These values differentiate the kinds of

   --  callable entities stored in the dispatch table. Certain kinds may

   --  not be used, but are added for completeness.

   type Prim_Op_Kind is

     (POK_Function,

      POK_Procedure,

      POK_Protected_Entry,

      POK_Protected_Function,

      POK_Protected_Procedure,

      POK_Task_Entry,

      POK_Task_Function,

      POK_Task_Procedure);

   --  Select specific data types

   type Select_Specific_Data_Element is record

      Index : Positive;

      Kind  : Prim_Op_Kind;

   end record;

   type Select_Specific_Data_Array is

     array (Positive range <>) of Select_Specific_Data_Element;

   type Select_Specific_Data (Nb_Prim : Positive) is record

      SSD_Table : Select_Specific_Data_Array (1 .. Nb_Prim);

      --  NOTE: Nb_Prim is the number of non-predefined primitive operations

   end record;

   type Select_Specific_Data_Ptr is access all Select_Specific_Data;

   --  A table used to store the primitive operation kind and entry index of

   --  primitive subprograms of a type that implements a limited interface.

   --  The Select Specific Data table resides in the Type Specific Data of a

   --  type. This construct is used in the handling of dispatching triggers

   --  in select statements.

   type Prim_Ptr is access procedure;

   type Address_Array is array (Positive range <>) of Prim_Ptr;

   subtype Dispatch_Table is Address_Array (1 .. 1);

   --  Used by GDB to identify the _tags and traverse the run-time structure

   --  associated with tagged types. For compatibility with older versions of

   --  gdb, its name must not be changed.

   type Tag is access all Dispatch_Table;

   pragma No_Strict_Aliasing (Tag);

   type Interface_Tag is access all Dispatch_Table;

   No_Tag : constant Tag := null;

   --  The expander ensures that Tag objects reference the Prims_Ptr component

   --  of the wrapper.

   type Tag_Ptr is access all Tag;

   pragma No_Strict_Aliasing (Tag_Ptr);

   type Offset_To_Top_Ptr is access all SSE.Storage_Offset;

   pragma No_Strict_Aliasing (Offset_To_Top_Ptr);

   type Tag_Table is array (Natural range <>) of Tag;

   type Size_Ptr is

     access function (A : System.Address) return Long_Long_Integer;

   type Type_Specific_Data (Idepth : Natural) is record

   --  The discriminant Idepth is the Inheritance Depth Level: Used to

   --  implement the membership test associated with single inheritance of

   --  tagged types in constant-time. It also indicates the size of the

   --  Tags_Table component.

      Access_Level : Natural;

      --  Accessibility level required to give support to Ada 2005 nested type

      --  extensions. This feature allows safe nested type extensions by

      --  shifting the accessibility checks to certain operations, rather than

      --  being enforced at the type declaration. In particular, by performing

      --  run-time accessibility checks on class-wide allocators, class-wide

      --  function return, and class-wide stream I/O, the danger of objects

      --  outliving their type declaration can be eliminated (Ada 2005: AI-344)

      Alignment     : Natural;

      Expanded_Name : Cstring_Ptr;

      External_Tag  : Cstring_Ptr;

      HT_Link       : Tag_Ptr;

      --  Components used to support to the Ada.Tags subprograms in RM 3.9

      --  Note: Expanded_Name is referenced by GDB to determine the actual name

      --  of the tagged type. Its requirements are: 1) it must have this exact

      --  name, and 2) its contents must point to a C-style Nul terminated

      --  string containing its expanded name. GDB has no requirement on a

      --  given position inside the record.

      Transportable : Boolean;

      --  Used to check RM E.4(18), set for types that satisfy the requirements

      --  for being used in remote calls as actuals for classwide formals or as

      --  return values for classwide functions.

      Type_Is_Abstract : Boolean;

      --  True if the type is abstract (Ada 2012: AI05-0173)

      Needs_Finalization : Boolean;

      --  Used to dynamically check whether an object is controlled or not

      Size_Func : Size_Ptr;

      --  Pointer to the subprogram computing the _size of the object. Used by

      --  the run-time whenever a call to the 'size primitive is required. We

      --  cannot assume that the contents of dispatch tables are addresses

      --  because in some architectures the ABI allows descriptors.

      Interfaces_Table : Interface_Data_Ptr;

      --  Pointer to the table of interface tags. It is used to implement the

      --  membership test associated with interfaces and also for backward

      --  abstract interface type conversions (Ada 2005:AI-251)

      SSD : Select_Specific_Data_Ptr;

      --  Pointer to a table of records used in dispatching selects. This field

      --  has a meaningful value for all tagged types that implement a limited,

      --  protected, synchronized or task interfaces and have non-predefined

      --  primitive operations.

      Tags_Table : Tag_Table (0 .. Idepth);

      --  Table of ancestor tags. Its size actually depends on the inheritance

      --  depth level of the tagged type.

   end record;

   type Type_Specific_Data_Ptr is access all Type_Specific_Data;

   pragma No_Strict_Aliasing (Type_Specific_Data_Ptr);

   --  Declarations for the dispatch table record

   type Signature_Kind is

      (Unknown,

       Primary_DT,

       Secondary_DT);

   --  Tagged type kinds with respect to concurrency and limitedness

   type Tagged_Kind is

     (TK_Abstract_Limited_Tagged,

      TK_Abstract_Tagged,

      TK_Limited_Tagged,

      TK_Protected,

      TK_Tagged,

      TK_Task);

   type Dispatch_Table_Wrapper (Num_Prims : Natural) is record

      Signature     : Signature_Kind;

      Tag_Kind      : Tagged_Kind;

      Predef_Prims  : System.Address;

      --  Pointer to the dispatch table of predefined Ada primitives

      --  According to the C++ ABI the components Offset_To_Top and TSD are

      --  stored just "before" the dispatch table, and they are referenced with

      --  negative offsets referring to the base of the dispatch table. The

      --   _Tag (or the VTable_Ptr in C++ terminology) must point to the base

      --  of the virtual table, just after these components, to point to the

      --  Prims_Ptr table.

      Offset_To_Top : SSE.Storage_Offset;

      TSD           : System.Address;

      Prims_Ptr : aliased Address_Array (1 .. Num_Prims);

      --  The size of the Prims_Ptr array actually depends on the tagged type

      --  to which it applies. For each tagged type, the expander computes the

      --  actual array size, allocates the Dispatch_Table record accordingly.

   end record;

   type Dispatch_Table_Ptr is access all Dispatch_Table_Wrapper;

   pragma No_Strict_Aliasing (Dispatch_Table_Ptr);

   --  The following type declaration is used by the compiler when the program

   --  is compiled with restriction No_Dispatching_Calls. It is also used with

   --  interface types to generate the tag and run-time information associated

   --  with them.

   type No_Dispatch_Table_Wrapper is record

      NDT_TSD       : System.Address;

      NDT_Prims_Ptr : Natural;

   end record;

   DT_Predef_Prims_Size : constant SSE.Storage_Count :=

                            SSE.Storage_Count

                              (1 * (Standard'Address_Size /

                                      System.Storage_Unit));

   --  Size of the Predef_Prims field of the Dispatch_Table

   DT_Offset_To_Top_Size : constant SSE.Storage_Count :=

                             SSE.Storage_Count

                               (1 * (Standard'Address_Size /

                                       System.Storage_Unit));

   --  Size of the Offset_To_Top field of the Dispatch Table

   DT_Typeinfo_Ptr_Size : constant SSE.Storage_Count :=

                            SSE.Storage_Count

                              (1 * (Standard'Address_Size /

                                      System.Storage_Unit));

   --  Size of the Typeinfo_Ptr field of the Dispatch Table

   use type System.Storage_Elements.Storage_Offset;

   DT_Offset_To_Top_Offset : constant SSE.Storage_Count :=

                               DT_Typeinfo_Ptr_Size

                                 + DT_Offset_To_Top_Size;

   DT_Predef_Prims_Offset : constant SSE.Storage_Count :=

                              DT_Typeinfo_Ptr_Size

                                + DT_Offset_To_Top_Size

                                + DT_Predef_Prims_Size;

   --  Offset from Prims_Ptr to Predef_Prims component

   --  Object Specific Data record of secondary dispatch tables

   type Object_Specific_Data_Array is array (Positive range <>) of Positive;

   type Object_Specific_Data (OSD_Num_Prims : Positive) is record

      OSD_Table : Object_Specific_Data_Array (1 .. OSD_Num_Prims);

      --  Table used in secondary DT to reference their counterpart in the

      --  select specific data (in the TSD of the primary DT). This construct

      --  is used in the handling of dispatching triggers in select statements.

      --  Nb_Prim is the number of non-predefined primitive operations.

   end record;

   type Object_Specific_Data_Ptr is access all Object_Specific_Data;

   pragma No_Strict_Aliasing (Object_Specific_Data_Ptr);

   --  The following subprogram specifications are placed here instead of the

   --  package body to see them from the frontend through rtsfind.

   function Base_Address (This : System.Address) return System.Address;

   --  Ada 2005 (AI-251): Displace "This" to point to the base address of the

   --  object (that is, the address of the primary tag of the object).

   procedure Check_TSD (TSD : Type_Specific_Data_Ptr);

   --  Ada 2012 (AI-113): Raise Program_Error if the external tag of this TSD

   --  is the same as the external tag for some other tagged type declaration.

   function Displace (This : System.Address; T : Tag) return System.Address;

   --  Ada 2005 (AI-251): Displace "This" to point to the secondary dispatch

   --  table of T.

   function Secondary_Tag (T, Iface : Tag) return Tag;

   --  Ada 2005 (AI-251): Given a primary tag T associated with a tagged type

   --  Typ, search for the secondary tag of the interface type Iface covered

   --  by Typ.

   function DT (T : Tag) return Dispatch_Table_Ptr;

   --  Return the pointer to the TSD record associated with T

   function Get_Entry_Index (T : Tag; Position : Positive) return Positive;

   --  Ada 2005 (AI-251): Return a primitive operation's entry index (if entry)

   --  given a dispatch table T and a position of a primitive operation in T.

   function Get_Offset_Index

     (T        : Tag;

      Position : Positive) return Positive;

   --  Ada 2005 (AI-251): Given a pointer to a secondary dispatch table (T)

   --  and a position of an operation in the DT, retrieve the corresponding

   --  operation's position in the primary dispatch table from the Offset

   --  Specific Data table of T.

   function Get_Prim_Op_Kind

     (T        : Tag;

      Position : Positive) return Prim_Op_Kind;

   --  Ada 2005 (AI-251): Return a primitive operation's kind given a dispatch

   --  table T and a position of a primitive operation in T.

   function Get_Tagged_Kind (T : Tag) return Tagged_Kind;

   --  Ada 2005 (AI-345): Given a pointer to either a primary or a secondary

   --  dispatch table, return the tagged kind of a type in the context of

   --  concurrency and limitedness.

   function IW_Membership (This : System.Address; T : Tag) return Boolean;

   --  Ada 2005 (AI-251): General routine that checks if a given object

   --  implements a tagged type. Its common usage is to check if Obj is in

   --  Iface'Class, but it is also used to check if a class-wide interface

   --  implements a given type (Iface_CW_Typ in T'Class). For example:

   --

   --      type I is interface;

   --      type T is tagged ...

   --

   --      function Test (O : I'Class) is

   --      begin

   --         return O in T'Class.

   --      end Test;

   function Offset_To_Top

     (This : System.Address) return SSE.Storage_Offset;

   --  Ada 2005 (AI-251): Returns the current value of the Offset_To_Top

   --  component available in the prologue of the dispatch table. If the parent

   --  of the tagged type has discriminants this value is stored in a record

   --  component just immediately after the tag component.

   function Needs_Finalization (T : Tag) return Boolean;

   --  A helper routine used in conjunction with finalization collections which

   --  service class-wide types. The function dynamically determines whether an

   --  object is controlled or has controlled components.

   function Parent_Size

     (Obj : System.Address;

      T   : Tag) return SSE.Storage_Count;

   --  Computes the size the ancestor part of a tagged extension object whose

   --  address is 'obj' by calling indirectly the ancestor _size function. The

   --  ancestor is the parent of the type represented by tag T. This function

   --  assumes that _size is always in slot one of the dispatch table.

   pragma Export (Ada, Parent_Size, "ada__tags__parent_size");

   --  This procedure is used in s-finimp and is thus exported manually

   procedure Register_Interface_Offset

     (This         : System.Address;

      Interface_T  : Tag;

      Is_Static    : Boolean;

      Offset_Value : SSE.Storage_Offset;

      Offset_Func  : Offset_To_Top_Function_Ptr);

   --  Register in the table of interfaces of the tagged type associated with

   --  "This" object the offset of the record component associated with the

   --  progenitor Interface_T (that is, the distance from "This" to the object

   --  component containing the tag of the secondary dispatch table). In case

   --  of constant offset, Is_Static is true and Offset_Value has such value.

   --  In case of variable offset, Is_Static is false and Offset_Func is an

   --  access to function that must be called to evaluate the offset.

   procedure Register_Tag (T : Tag);

   --  Insert the Tag and its associated external_tag in a table for the sake

   --  of Internal_Tag.

   procedure Set_Dynamic_Offset_To_Top

     (This         : System.Address;

      Interface_T  : Tag;

      Offset_Value : SSE.Storage_Offset;

      Offset_Func  : Offset_To_Top_Function_Ptr);

   --  Ada 2005 (AI-251): The compiler generates calls to this routine only

   --  when initializing the Offset_To_Top field of dispatch tables associated

   --  with tagged type whose parent has variable size components. "This" is

   --  the object whose dispatch table is being initialized. Interface_T is the

   --  interface for which the secondary dispatch table is being initialized,

   --  and Offset_Value is the distance from "This" to the object component

   --  containing the tag of the secondary dispatch table (a zero value means

   --  that this interface shares the primary dispatch table). Offset_Func

   --  references a function that must be called to evaluate the offset at

   --  runtime. This routine also takes care of registering these values in

   --  the table of interfaces of the type.

   procedure Set_Entry_Index (T : Tag; Position : Positive; Value : Positive);

   --  Ada 2005 (AI-345): Set the entry index of a primitive operation in T's

   --  TSD table indexed by Position.

   procedure Set_Prim_Op_Kind

     (T        : Tag;

      Position : Positive;

      Value    : Prim_Op_Kind);

   --  Ada 2005 (AI-251): Set the kind of a primitive operation in T's TSD

   --  table indexed by Position.

   procedure Unregister_Tag (T : Tag);

   --  Remove a particular tag from the external tag hash table

   Max_Predef_Prims : constant Positive := 15;

   --  Number of reserved slots for the following predefined ada primitives:

   --

   --    1. Size

   --    2. Read

   --    3. Write

   --    4. Input

   --    5. Output

   --    6. "="

   --    7. assignment

   --    8. deep adjust

   --    9. deep finalize

   --   10. async select

   --   11. conditional select

   --   12. prim_op kind

   --   13. task_id

   --   14. dispatching requeue

   --   15. timed select

   --

   --  The compiler checks that the value here is correct

   subtype Predef_Prims_Table  is Address_Array (1 .. Max_Predef_Prims);

   type Predef_Prims_Table_Ptr is access Predef_Prims_Table;

   pragma No_Strict_Aliasing (Predef_Prims_Table_Ptr);

   type Addr_Ptr is access System.Address;

   pragma No_Strict_Aliasing (Addr_Ptr);

   --  This type is used by the frontend to generate the code that handles

   --  dispatch table slots of types declared at the local level.

end Ada.Tags;