gcc/ada/a-tags.ads

   1 ------------------------------------------------------------------------------
   2 --                                                                          --
   3 --                         GNAT RUN-TIME COMPONENTS                         --
   4 --                                                                          --
   5 --                             A D A . T A G S                              --
   6 --                                                                          --
   7 --                                 S p e c                                  --
   8 --                                                                          --
   9 --          Copyright (C) 1992-2005 Free Software Foundation, Inc.          --
  10 --                                                                          --
  11 -- This specification is derived from the Ada Reference Manual for use with --
  12 -- GNAT. The copyright notice above, and the license provisions that follow --
  13 -- apply solely to the  contents of the part following the private keyword. --
  14 --                                                                          --
  15 -- GNAT is free software;  you can  redistribute it  and/or modify it under --
  16 -- terms of the  GNU General Public License as published  by the Free Soft- --
  17 -- ware  Foundation;  either version 2,  or (at your option) any later ver- --
  18 -- sion.  GNAT is distributed in the hope that it will be useful, but WITH- --
  19 -- OUT ANY WARRANTY;  without even the  implied warranty of MERCHANTABILITY --
  20 -- or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License --
  21 -- for  more details.  You should have  received  a copy of the GNU General --
  22 -- Public License  distributed with GNAT;  see file COPYING.  If not, write --
  23 -- to  the  Free Software Foundation,  51  Franklin  Street,  Fifth  Floor, --
  24 -- Boston, MA 02110-1301, USA.                                              --
  25 --                                                                          --
  26 -- As a special exception,  if other files  instantiate  generics from this --
  27 -- unit, or you link  this unit with other files  to produce an executable, --
  28 -- this  unit  does not  by itself cause  the resulting  executable  to  be --
  29 -- covered  by the  GNU  General  Public  License.  This exception does not --
  30 -- however invalidate  any other reasons why  the executable file  might be --
  31 -- covered by the  GNU Public License.                                      --
  32 --                                                                          --
  33 -- GNAT was originally developed  by the GNAT team at  New York University. --
  34 -- Extensive contributions were provided by Ada Core Technologies Inc.      --
  35 --                                                                          --
  36 ------------------------------------------------------------------------------
  37
  38 with System;
  39 with System.Storage_Elements;
  40 with Unchecked_Conversion;
  41
  42 package Ada.Tags is
  43    pragma Preelaborate_05;
  44    --  In accordance with Ada 2005 AI-362
  45
  46    type Tag is private;
  47
  48    No_Tag : constant Tag;
  49
  50    function Expanded_Name (T : Tag) return String;
  51
  52    function External_Tag (T : Tag) return String;
  53
  54    function Internal_Tag (External : String) return Tag;
  55
  56    function Descendant_Tag (External : String; Ancestor : Tag) return Tag;
  57
  58    function Is_Descendant_At_Same_Level
  59      (Descendant : Tag;
  60       Ancestor   : Tag) return Boolean;
  61
  62    function Parent_Tag (T : Tag) return Tag;
  63
  64    Tag_Error : exception;
  65
  66 private
  67
  68    ---------------------------------------------------------------
  69    -- Abstract Procedural Interface For The GNAT Dispatch Table --
  70    ---------------------------------------------------------------
  71
  72    --  GNAT's Dispatch Table format is customizable in order to match the
  73    --  format used in another language. GNAT supports programs that use
  74    --  two different dispatch table formats at the same time: the native
  75    --  format that supports Ada 95 tagged types and which is described in
  76    --  Ada.Tags, and a foreign format for types that are imported from some
  77    --  other language (typically C++) which is described in Interfaces.CPP.
  78    --  The runtime information kept for each tagged type is separated into
  79    --  two objects: the Dispatch Table and the Type Specific Data record.
  80    --  These two objects are allocated statically using the constants:
  81
  82    --      DT Size  = DT_Prologue_Size  + Nb_Prim * DT_Entry_Size
  83    --      TSD Size = TSD_Prologue_Size + (1 + Idepth)  * TSD_Entry_Size
  84
  85    --  where Nb_prim is the number of primitive operations of the given
  86    --  type and Idepth its inheritance depth.
  87
  88    --  The compiler generates calls to the following SET routines to
  89    --  initialize those structures and uses the GET functions to
  90    --  retreive the information when needed
  91
  92    type Dispatch_Table;
  93    type Tag is access all Dispatch_Table;
  94    type Interface_Tag is access all Dispatch_Table;
  95
  96    No_Tag : constant Tag := null;
  97
  98    type Type_Specific_Data;
  99    type Type_Specific_Data_Ptr is access all Type_Specific_Data;
 100
 101    --  Primitive operation kinds. These values differentiate the kinds of
 102    --  callable entities stored in the dispatch table. Certain kinds may
 103    --  not be used, but are added for completeness.
 104
 105    type Prim_Op_Kind is
 106      (POK_Function,
 107       POK_Procedure,
 108       POK_Protected_Entry,
 109       POK_Protected_Function,
 110       POK_Protected_Procedure,
 111       POK_Task_Entry,
 112       POK_Task_Procedure);
 113
 114    --  Number of predefined primitive operations added by the Expander
 115    --  for a tagged type. It is utilized for indexing in the two auxiliary
 116    --  tables used for dispatching asynchronous, conditional and timed
 117    --  selects. In order to be space efficien, indexing is performed by
 118    --  subtracting this constant value from the provided position in the
 119    --  auxiliary tables.
 120    --  This value is mirrored from Exp_Disp.ads.
 121
 122    Default_Prim_Op_Count : constant Positive := 14;
 123
 124    package SSE renames System.Storage_Elements;
 125
 126    function CW_Membership (Obj_Tag : Tag; Typ_Tag : Tag) return Boolean;
 127    --  Given the tag of an object and the tag associated to a type, return
 128    --  true if Obj is in Typ'Class.
 129
 130    function IW_Membership
 131      (This : System.Address;
 132       T    : Tag) return Boolean;
 133    --  Ada 2005 (AI-251): General routine that checks if a given object
 134    --  implements a tagged type. Its common usage is to check if Obj is in
 135    --  Iface'Class, but it is also used to check if a class-wide interface
 136    --  implements a given type (Iface_CW_Typ in T'Class). For example:
 137    --
 138    --      type I is interface;
 139    --      type T is tagged ...
 140    --
 141    --      function Test (O : in I'Class) is
 142    --      begin
 143    --         return O in T'Class.
 144    --      end Test;
 145
 146    function Get_Access_Level (T : Tag) return Natural;
 147    --  Given the tag associated with a type, returns the accessibility level
 148    --  of the type.
 149
 150    function Get_Entry_Index
 151      (T        : Tag;
 152       Position : Positive) return Positive;
 153    --  Return a primitive operation's entry index (if entry) given a dispatch
 154    --  table T and a position of a primitive operation in T.
 155
 156    function Get_External_Tag (T : Tag) return System.Address;
 157    --  Retrieve the address of a null terminated string containing
 158    --  the external name
 159
 160    function Get_Prim_Op_Address
 161      (T        : Tag;
 162       Position : Positive) return System.Address;
 163    --  Given a pointer to a dispatch table (T) and a position in the DT
 164    --  this function returns the address of the virtual function stored
 165    --  in it (used for dispatching calls)
 166
 167    function Get_Prim_Op_Kind
 168      (T        : Tag;
 169       Position : Positive) return Prim_Op_Kind;
 170    --  Return a primitive operation's kind given a dispatch table T and a
 171    --  position of a primitive operation in T.
 172
 173    function Get_RC_Offset (T : Tag) return SSE.Storage_Offset;
 174    --  Return the Offset of the implicit record controller when the object
 175    --  has controlled components. O otherwise.
 176
 177    pragma Export (Ada, Get_RC_Offset, "ada__tags__get_rc_offset");
 178    --  This procedure is used in s-finimp to compute the deep routines
 179    --  it is exported manually in order to avoid changing completely the
 180    --  organization of the run time.
 181
 182    function Get_Remotely_Callable (T : Tag) return Boolean;
 183    --  Return the value previously set by Set_Remotely_Callable
 184
 185    procedure Inherit_DT
 186     (Old_T       : Tag;
 187      New_T       : Tag;
 188      Entry_Count : Natural);
 189    --  Entry point used to initialize the DT of a type knowing the tag
 190    --  of the direct ancestor and the number of primitive ops that are
 191    --  inherited (Entry_Count).
 192
 193    procedure Inherit_TSD (Old_Tag : Tag; New_Tag : Tag);
 194    --  Initialize the TSD of a type knowing the tag of the direct ancestor
 195
 196    function Parent_Size
 197      (Obj : System.Address;
 198       T   : Tag) return SSE.Storage_Count;
 199    --  Computes the size the ancestor part of a tagged extension object
 200    --  whose address is 'obj' by calling the indirectly _size function of
 201    --  the ancestor. The ancestor is the parent of the type represented by
 202    --  tag T. This function assumes that _size is always in slot 1 of
 203    --  the dispatch table.
 204
 205    pragma Export (Ada, Parent_Size, "ada__tags__parent_size");
 206    --  This procedure is used in s-finimp and is thus exported manually
 207
 208    procedure Register_Interface_Tag
 209     (T           : Tag;
 210      Interface_T : Tag);
 211    --  Ada 2005 (AI-251): Used to initialize the table of interfaces
 212    --  implemented by a type. Required to give support to IW_Membership.
 213
 214    procedure Register_Tag (T : Tag);
 215    --  Insert the Tag and its associated external_tag in a table for the
 216    --  sake of Internal_Tag
 217
 218    procedure Set_Entry_Index
 219      (T        : Tag;
 220       Position : Positive;
 221       Value    : Positive);
 222    --  Set the entry index of a primitive operation in T's TSD table indexed
 223    --  by Position.
 224
 225    procedure Set_Offset_To_Top
 226      (T     : Tag;
 227       Value : System.Storage_Elements.Storage_Offset);
 228    --  Ada 2005 (AI-251): Initialize the Offset_To_Top field in the prologue of
 229    --  the dispatch table. In primary dispatch tables the value of this field
 230    --  is always 0; in secondary dispatch tables this is the offset to the base
 231    --  of the enclosing type.
 232
 233    procedure Set_Prim_Op_Address
 234      (T        : Tag;
 235       Position : Positive;
 236       Value    : System.Address);
 237    --  Given a pointer to a dispatch Table (T) and a position in the dispatch
 238    --  Table put the address of the virtual function in it (used for
 239    --  overriding).
 240
 241    procedure Set_Prim_Op_Kind
 242      (T        : Tag;
 243       Position : Positive;
 244       Value    : Prim_Op_Kind);
 245    --  Set the kind of a primitive operation in T's TSD table indexed by
 246    --  Position.
 247
 248    procedure Set_TSD (T : Tag; Value : System.Address);
 249    --  Given a pointer T to a dispatch Table, stores the address of the record
 250    --  containing the Type Specific Data generated by GNAT.
 251
 252    procedure Set_Access_Level (T : Tag; Value : Natural);
 253    --  Sets the accessibility level of the tagged type associated with T
 254    --  in its TSD.
 255
 256    procedure Set_Expanded_Name (T : Tag; Value : System.Address);
 257    --  Set the address of the string containing the expanded name
 258    --  in the Dispatch table.
 259
 260    procedure Set_External_Tag (T : Tag; Value : System.Address);
 261    --  Set the address of the string containing the external tag
 262    --  in the Dispatch table.
 263
 264    procedure Set_RC_Offset (T : Tag; Value : SSE.Storage_Offset);
 265    --  Sets the Offset of the implicit record controller when the object
 266    --  has controlled components. Set to O otherwise.
 267
 268    procedure Set_Remotely_Callable (T : Tag; Value : Boolean);
 269    --  Set to true if the type has been declared in a context described
 270    --  in E.4 (18).
 271
 272    function TSD (T : Tag) return Type_Specific_Data_Ptr;
 273    --  Given a pointer T to a dispatch Table, retreives the address of the
 274    --  record containing the Type Specific Data generated by GNAT
 275
 276    DT_Prologue_Size : constant SSE.Storage_Count :=
 277                         SSE.Storage_Count
 278                           (2 * (Standard'Address_Size / System.Storage_Unit));
 279    --  Size of the first part of the dispatch table
 280
 281    DT_Offset_To_Top_Size : constant SSE.Storage_Count :=
 282                             SSE.Storage_Count
 283                               (Standard'Address_Size / System.Storage_Unit);
 284    --  Size of the Offset_To_Top field of the Dispatch Table
 285
 286    DT_Typeinfo_Ptr_Size : constant SSE.Storage_Count :=
 287                             SSE.Storage_Count
 288                               (Standard'Address_Size / System.Storage_Unit);
 289    --  Size of the Typeinfo_Ptr field of the Dispatch Table
 290
 291    DT_Entry_Size : constant SSE.Storage_Count :=
 292                      SSE.Storage_Count
 293                        (1 * (Standard'Address_Size / System.Storage_Unit));
 294    --  Size of each primitive operation entry in the Dispatch Table
 295
 296    TSD_Prologue_Size : constant SSE.Storage_Count :=
 297                          SSE.Storage_Count
 298                            (8 * (Standard'Address_Size / System.Storage_Unit));
 299    --  Size of the first part of the type specific data
 300
 301    TSD_Entry_Size : constant SSE.Storage_Count :=
 302      SSE.Storage_Count (1 * (Standard'Address_Size / System.Storage_Unit));
 303    --  Size of each ancestor tag entry in the TSD
 304
 305    type Address_Array is array (Natural range <>) of System.Address;
 306    pragma Suppress (Index_Check, On => Address_Array);
 307    --  The reason we suppress index checks is that in the body, objects
 308    --  of this type are declared with a dummy size of 1, the actual size
 309    --  depending on the number of primitive operations.
 310
 311    --  Unchecked Conversions for Tag and TSD
 312
 313    function To_Type_Specific_Data_Ptr is
 314      new Unchecked_Conversion (System.Address, Type_Specific_Data_Ptr);
 315
 316    function To_Address is
 317      new Unchecked_Conversion (Type_Specific_Data_Ptr, System.Address);
 318
 319    function To_Address is
 320      new Unchecked_Conversion (Tag, System.Address);
 321
 322    type Addr_Ptr is access System.Address;
 323    type Tag_Ptr  is access Tag;
 324
 325    function To_Addr_Ptr is
 326       new Unchecked_Conversion (System.Address, Addr_Ptr);
 327
 328    function To_Tag_Ptr is
 329      new Unchecked_Conversion (System.Address, Tag_Ptr);
 330
 331    --  Primitive dispatching operations are always inlined, to facilitate
 332    --  use in a minimal/no run-time environment for high integrity use.
 333
 334    pragma Inline_Always (CW_Membership);
 335    pragma Inline_Always (IW_Membership);
 336    pragma Inline_Always (Get_Access_Level);
 337    pragma Inline_Always (Get_Prim_Op_Address);
 338    pragma Inline_Always (Get_RC_Offset);
 339    pragma Inline_Always (Get_Remotely_Callable);
 340    pragma Inline_Always (Inherit_DT);
 341    pragma Inline_Always (Inherit_TSD);
 342    pragma Inline_Always (Register_Interface_Tag);
 343    pragma Inline_Always (Register_Tag);
 344    pragma Inline_Always (Set_Access_Level);
 345    pragma Inline_Always (Set_Expanded_Name);
 346    pragma Inline_Always (Set_External_Tag);
 347    pragma Inline_Always (Set_Offset_To_Top);
 348    pragma Inline_Always (Set_Prim_Op_Address);
 349    pragma Inline_Always (Set_RC_Offset);
 350    pragma Inline_Always (Set_Remotely_Callable);
 351    pragma Inline_Always (Set_TSD);
 352    pragma Inline_Always (TSD);
 353
 354 end Ada.Tags;