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
  57      (External : String;
  58       Ancestor : Tag) return Tag;
  59    pragma Ada_05 (Descendant_Tag);
  60
  61    function Is_Descendant_At_Same_Level
  62      (Descendant : Tag;
  63       Ancestor   : Tag) return Boolean;
  64    pragma Ada_05 (Is_Descendant_At_Same_Level);
  65
  66    function Parent_Tag (T : Tag) return Tag;
  67    pragma Ada_05 (Parent_Tag);
  68
  69    Tag_Error : exception;
  70
  71 private
  72    --  The following subprogram specifications are placed here instead of
  73    --  the package body to see them from the frontend through rtsfind.
  74
  75    ---------------------------------------------------------------
  76    -- Abstract Procedural Interface For The GNAT Dispatch Table --
  77    ---------------------------------------------------------------
  78
  79    --  GNAT's Dispatch Table format is customizable in order to match the
  80    --  format used in another language. GNAT supports programs that use two
  81    --  different dispatch table formats at the same time: the native format
  82    --  that supports Ada 95 tagged types and which is described in Ada.Tags,
  83    --  and a foreign format for types that are imported from some other
  84    --  language (typically C++) which is described in Interfaces.CPP. The
  85    --  runtime information kept for each tagged type is separated into two
  86    --  objects: the Dispatch Table and the Type Specific Data record. These
  87    --  two objects are allocated statically using the constants:
  88
  89    --      DT Size  = DT_Prologue_Size  + Nb_Prim * DT_Entry_Size
  90    --      TSD Size = TSD_Prologue_Size + (1 + Idepth)  * TSD_Entry_Size
  91
  92    --  where Nb_prim is the number of primitive operations of the given
  93    --  type and Idepth its inheritance depth.
  94
  95    --  In order to set or retrieve information from the Dispatch Table or
  96    --  the Type Specific Data record, GNAT generates calls to Set_XXX or
  97    --  Get_XXX routines, where XXX is the name of the field of interest.
  98
  99    type Dispatch_Table;
 100    type Tag is access all Dispatch_Table;
 101    type Interface_Tag is access all Dispatch_Table;
 102
 103    No_Tag : constant Tag := null;
 104
 105    type Interface_Data (Nb_Ifaces : Positive);
 106    type Interface_Data_Ptr is access all Interface_Data;
 107    --  Table of abstract interfaces used to give support to backward interface
 108    --  conversions and also to IW_Membership.
 109
 110    type Object_Specific_Data (Nb_Prim : Positive);
 111    type Object_Specific_Data_Ptr is access all Object_Specific_Data;
 112    --  Information associated with the secondary dispatch table of tagged-type
 113    --  objects implementing abstract interfaces.
 114
 115    type Select_Specific_Data (Nb_Prim : Positive);
 116    type Select_Specific_Data_Ptr is access all Select_Specific_Data;
 117    --  A table used to store the primitive operation kind and entry index of
 118    --  primitive subprograms of a type that implements a limited interface.
 119    --  The Select Specific Data table resides in the Type Specific Data of a
 120    --  type. This construct is used in the handling of dispatching triggers
 121    --  in select statements.
 122
 123    type Type_Specific_Data;
 124    type Type_Specific_Data_Ptr is access all Type_Specific_Data;
 125
 126    --  Primitive operation kinds. These values differentiate the kinds of
 127    --  callable entities stored in the dispatch table. Certain kinds may
 128    --  not be used, but are added for completeness.
 129
 130    type Prim_Op_Kind is
 131      (POK_Function,
 132       POK_Procedure,
 133       POK_Protected_Entry,
 134       POK_Protected_Function,
 135       POK_Protected_Procedure,
 136       POK_Task_Entry,
 137       POK_Task_Function,
 138       POK_Task_Procedure);
 139
 140    --  Tagged type kinds with respect to concurrency and limitedness
 141
 142    type Tagged_Kind is
 143      (TK_Abstract_Limited_Tagged,
 144       TK_Abstract_Tagged,
 145       TK_Limited_Tagged,
 146       TK_Protected,
 147       TK_Tagged,
 148       TK_Task);
 149
 150    type Tagged_Kind_Ptr is access all Tagged_Kind;
 151
 152    Default_Prim_Op_Count : constant Positive := 15;
 153    --  Number of predefined primitive operations added by the Expander for a
 154    --  tagged type. It is utilized for indexing in the two auxiliary tables
 155    --  used for dispatching asynchronous, conditional and timed selects. In
 156    --  order to be space efficient, indexing is performed by subtracting this
 157    --  constant value from the provided position in the auxiliary tables (must
 158    --  match Exp_Disp.Default_Prim_Op_Count).
 159
 160    package SSE renames System.Storage_Elements;
 161
 162    function CW_Membership (Obj_Tag : Tag; Typ_Tag : Tag) return Boolean;
 163    --  Given the tag of an object and the tag associated to a type, return
 164    --  true if Obj is in Typ'Class.
 165
 166    function IW_Membership (This : System.Address; T : Tag) return Boolean;
 167    --  Ada 2005 (AI-251): General routine that checks if a given object
 168    --  implements a tagged type. Its common usage is to check if Obj is in
 169    --  Iface'Class, but it is also used to check if a class-wide interface
 170    --  implements a given type (Iface_CW_Typ in T'Class). For example:
 171    --
 172    --      type I is interface;
 173    --      type T is tagged ...
 174    --
 175    --      function Test (O : in I'Class) is
 176    --      begin
 177    --         return O in T'Class.
 178    --      end Test;
 179
 180    function Displace (This : System.Address; T : Tag) return System.Address;
 181    --  (Ada 2005 (AI-251): Displace "This" to point to the secondary dispatch
 182    --  table of T.
 183
 184    function Get_Access_Level (T : Tag) return Natural;
 185    --  Given the tag associated with a type, returns the accessibility level
 186    --  of the type.
 187
 188    function Get_Entry_Index (T : Tag; Position : Positive) return Positive;
 189    --  Return a primitive operation's entry index (if entry) given a dispatch
 190    --  table T and a position of a primitive operation in T.
 191
 192    function Get_External_Tag (T : Tag) return System.Address;
 193    --  Retrieve the address of a null terminated string containing
 194    --  the external name.
 195
 196    function Get_Offset_Index
 197      (T        : Tag;
 198       Position : Positive) return Positive;
 199    --  Given a pointer to a secondary dispatch table (T) and a position of an
 200    --  operation in the DT, retrieve the corresponding operation's position in
 201    --  the primary dispatch table from the Offset Specific Data table of T.
 202
 203    function Get_Prim_Op_Address
 204      (T        : Tag;
 205       Position : Positive) return System.Address;
 206    --  Given a pointer to a dispatch table (T) and a position in the DT
 207    --  this function returns the address of the virtual function stored
 208    --  in it (used for dispatching calls).
 209
 210    function Get_Prim_Op_Kind
 211      (T        : Tag;
 212       Position : Positive) return Prim_Op_Kind;
 213    --  Return a primitive operation's kind given a dispatch table T and a
 214    --  position of a primitive operation in T.
 215
 216    function Get_RC_Offset (T : Tag) return SSE.Storage_Offset;
 217    --  Return the Offset of the implicit record controller when the object
 218    --  has controlled components. O otherwise.
 219
 220    pragma Export (Ada, Get_RC_Offset, "ada__tags__get_rc_offset");
 221    --  This procedure is used in s-finimp to compute the deep routines
 222    --  it is exported manually in order to avoid changing completely the
 223    --  organization of the run time.
 224
 225    function Get_Remotely_Callable (T : Tag) return Boolean;
 226    --  Return the value previously set by Set_Remotely_Callable
 227
 228    function Get_Tagged_Kind (T : Tag) return Tagged_Kind;
 229    --  Given a pointer to either a primary or a secondary dispatch table,
 230    --  return the tagged kind of a type in the context of concurrency and
 231    --  limitedness.
 232
 233    procedure Inherit_DT (Old_T : Tag; New_T : Tag; Entry_Count : Natural);
 234    --  Entry point used to initialize the DT of a type knowing the tag
 235    --  of the direct ancestor and the number of primitive ops that are
 236    --  inherited (Entry_Count).
 237
 238    procedure Inherit_TSD (Old_Tag : Tag; New_Tag : Tag);
 239    --  Initialize the TSD of a type knowing the tag of the direct ancestor
 240
 241    function Offset_To_Top
 242      (T : Tag) return System.Storage_Elements.Storage_Offset;
 243    --  Returns the current value of the offset_to_top component available in
 244    --  the prologue of the dispatch table.
 245
 246    function OSD (T : Tag) return Object_Specific_Data_Ptr;
 247    --  Ada 2005 (AI-251): Given a pointer T to a secondary dispatch table,
 248    --  retrieve the address of the record containing the Objet Specific
 249    --  Data table.
 250
 251    function Parent_Size
 252      (Obj : System.Address;
 253       T   : Tag) return SSE.Storage_Count;
 254    --  Computes the size the ancestor part of a tagged extension object whose
 255    --  address is 'obj' by calling indirectly the ancestor _size function. The
 256    --  ancestor is the parent of the type represented by tag T. This function
 257    --  assumes that _size is always in slot one of the dispatch table.
 258
 259    pragma Export (Ada, Parent_Size, "ada__tags__parent_size");
 260    --  This procedure is used in s-finimp and is thus exported manually
 261
 262    procedure Register_Interface_Tag
 263      (T           : Tag;
 264       Interface_T : Tag;
 265       Position    : Positive);
 266    --  Ada 2005 (AI-251): Used to initialize the table of interfaces
 267    --  implemented by a type. Required to give support to backward interface
 268    --  conversions and also to IW_Membership.
 269
 270    procedure Register_Tag (T : Tag);
 271    --  Insert the Tag and its associated external_tag in a table for the
 272    --  sake of Internal_Tag
 273
 274    procedure Set_Access_Level (T : Tag; Value : Natural);
 275    --  Sets the accessibility level of the tagged type associated with T
 276    --  in its TSD.
 277
 278    procedure Set_Entry_Index (T : Tag; Position : Positive; Value : Positive);
 279    --  Set the entry index of a primitive operation in T's TSD table indexed
 280    --  by Position.
 281
 282    procedure Set_Expanded_Name (T : Tag; Value : System.Address);
 283    --  Set the address of the string containing the expanded name
 284    --  in the Dispatch table.
 285
 286    procedure Set_External_Tag (T : Tag; Value : System.Address);
 287    --  Set the address of the string containing the external tag
 288    --  in the Dispatch table.
 289
 290    procedure Set_Interface_Table (T : Tag; Value : System.Address);
 291    --  Ada 2005 (AI-251): Given a pointer T to a dispatch Table, stores the
 292    --  pointer to the table of interfaces.
 293
 294    procedure Set_Num_Prim_Ops (T : Tag; Value : Natural);
 295    --  Set the number of primitive operations in the dispatch table of T. This
 296    --  is used for debugging purposes.
 297
 298    procedure Set_Offset_Index
 299      (T        : Tag;
 300       Position : Positive;
 301       Value    : Positive);
 302    --  Set the offset value of a primitive operation in a secondary dispatch
 303    --  table denoted by T, indexed by Position.
 304
 305    procedure Set_Offset_To_Top
 306      (This         : System.Address;
 307       Interface_T  : Tag;
 308       Offset_Value : System.Storage_Elements.Storage_Offset);
 309    --  Ada 2005 (AI-251): Initialize the Offset_To_Top field in the prologue of
 310    --  the dispatch table. In primary dispatch tables the value of "This" is
 311    --  not required (and the compiler passes always the Null_Address value) and
 312    --  the Offset_Value is always cero; in secondary dispatch tables "This"
 313    --  points to the object, Interface_T is the interface for which the
 314    --  secondary dispatch table is being initialized, and Offset_Value is the
 315    --  distance from "This" to the object component containing the tag of the
 316    --  secondary dispatch table.
 317
 318    procedure Set_OSD (T : Tag; Value : System.Address);
 319    --  Given a pointer T to a secondary dispatch table, store the pointer to
 320    --  the record containing the Object Specific Data generated by GNAT.
 321
 322    procedure Set_Prim_Op_Address
 323      (T        : Tag;
 324       Position : Positive;
 325       Value    : System.Address);
 326    --  Given a pointer to a dispatch Table (T) and a position in the dispatch
 327    --  Table put the address of the virtual function in it (used for
 328    --  overriding).
 329
 330    procedure Set_Prim_Op_Kind
 331      (T        : Tag;
 332       Position : Positive;
 333       Value    : Prim_Op_Kind);
 334    --  Set the kind of a primitive operation in T's TSD table indexed by
 335    --  Position.
 336
 337    procedure Set_RC_Offset (T : Tag; Value : SSE.Storage_Offset);
 338    --  Sets the Offset of the implicit record controller when the object
 339    --  has controlled components. Set to O otherwise.
 340
 341    procedure Set_Remotely_Callable (T : Tag; Value : Boolean);
 342    --  Set to true if the type has been declared in a context described
 343    --  in E.4 (18).
 344
 345    procedure Set_SSD (T : Tag; Value : System.Address);
 346    --  Given a pointer T to a dispatch Table, stores the pointer to the record
 347    --  containing the Select Specific Data generated by GNAT.
 348
 349    procedure Set_Tagged_Kind (T : Tag; Value : Tagged_Kind);
 350    --  Set the tagged kind of a type in either a primary or a secondary
 351    --  dispatch table denoted by T.
 352
 353    procedure Set_TSD (T : Tag; Value : System.Address);
 354    --  Given a pointer T to a dispatch Table, stores the address of the record
 355    --  containing the Type Specific Data generated by GNAT.
 356
 357    function SSD (T : Tag) return Select_Specific_Data_Ptr;
 358    --  Given a pointer T to a dispatch Table, retrieves the address of the
 359    --  record containing the Select Specific Data in T's TSD.
 360
 361    function TSD (T : Tag) return Type_Specific_Data_Ptr;
 362    --  Given a pointer T to a dispatch Table, retrieves the address of the
 363    --  record containing the Type Specific Data generated by GNAT.
 364
 365    DT_Prologue_Size : constant SSE.Storage_Count :=
 366      SSE.Storage_Count (4 * (Standard'Address_Size / System.Storage_Unit));
 367    --  Size of the first part of the dispatch table
 368
 369    DT_Signature_Size : constant SSE.Storage_Count :=
 370      SSE.Storage_Count (1 * (Standard'Address_Size / System.Storage_Unit));
 371    --  Size of the Signature field of the dispatch table
 372
 373    DT_Tagged_Kind_Size : constant SSE.Storage_Count :=
 374      SSE.Storage_Count (1 * (Standard'Address_Size / System.Storage_Unit));
 375    --  Size of the Tagged_Type_Kind field of the dispatch table
 376
 377    DT_Offset_To_Top_Size : constant SSE.Storage_Count :=
 378      SSE.Storage_Count (1 * (Standard'Address_Size / System.Storage_Unit));
 379    --  Size of the Offset_To_Top field of the Dispatch Table
 380
 381    DT_Typeinfo_Ptr_Size : constant SSE.Storage_Count :=
 382      SSE.Storage_Count (1 * (Standard'Address_Size / System.Storage_Unit));
 383    --  Size of the Typeinfo_Ptr field of the Dispatch Table
 384
 385    DT_Entry_Size : constant SSE.Storage_Count :=
 386      SSE.Storage_Count (1 * (Standard'Address_Size / System.Storage_Unit));
 387    --  Size of each primitive operation entry in the Dispatch Table
 388
 389    TSD_Prologue_Size : constant SSE.Storage_Count :=
 390      SSE.Storage_Count (10 * (Standard'Address_Size / System.Storage_Unit));
 391    --  Size of the first part of the type specific data
 392
 393    TSD_Entry_Size : constant SSE.Storage_Count :=
 394      SSE.Storage_Count (1 * (Standard'Address_Size / System.Storage_Unit));
 395    --  Size of each ancestor tag entry in the TSD
 396
 397    type Address_Array is array (Natural range <>) of System.Address;
 398    pragma Suppress (Index_Check, On => Address_Array);
 399    --  The reason we suppress index checks is that in the body, objects
 400    --  of this type are declared with a dummy size of 1, the actual size
 401    --  depending on the number of primitive operations.
 402
 403    type Signature_Kind is
 404       (Unknown,
 405        Valid_Signature,
 406        Primary_DT,
 407        Secondary_DT,
 408        Abstract_Interface);
 409    for Signature_Kind'Size use 8;
 410    --  Kind of signature found in the header of the dispatch table. These
 411    --  signatures are generated by the frontend and are used by the Check_XXX
 412    --  routines to ensure that the kind of dispatch table managed by each of
 413    --  the routines in this package is correct. This additional check is only
 414    --  performed with this run-time package is compiled with assertions enabled
 415
 416    --  The signature is a sequence of two bytes. The first byte must have the
 417    --  value Valid_Signature, and the second byte must have a value in the
 418    --  range Primary_DT .. Abstract_Interface. The Unknown value is used by
 419    --  the Check_XXX routines to indicate that the signature is wrong.
 420
 421    --  Unchecked Conversions
 422
 423    type Addr_Ptr is access System.Address;
 424    type Tag_Ptr  is access Tag;
 425
 426    type Signature_Values is
 427       array (1 .. DT_Signature_Size) of Signature_Kind;
 428    --  Type used to see the signature as a sequence of Signature_Kind values
 429
 430    function To_Addr_Ptr is
 431       new Unchecked_Conversion (System.Address, Addr_Ptr);
 432
 433    function To_Type_Specific_Data_Ptr is
 434      new Unchecked_Conversion (System.Address, Type_Specific_Data_Ptr);
 435
 436    function To_Address is
 437      new Unchecked_Conversion (Interface_Tag, System.Address);
 438
 439    function To_Address is
 440      new Unchecked_Conversion (Tag, System.Address);
 441
 442    function To_Address is
 443      new Unchecked_Conversion (Type_Specific_Data_Ptr, System.Address);
 444
 445    function To_Interface_Data_Ptr is
 446      new Unchecked_Conversion (System.Address, Interface_Data_Ptr);
 447
 448    function To_Object_Specific_Data_Ptr is
 449      new Unchecked_Conversion (System.Address, Object_Specific_Data_Ptr);
 450
 451    function To_Select_Specific_Data_Ptr is
 452      new Unchecked_Conversion (System.Address, Select_Specific_Data_Ptr);
 453
 454    function To_Signature_Values is
 455      new Unchecked_Conversion (System.Storage_Elements.Storage_Offset,
 456                                Signature_Values);
 457
 458    function To_Tag_Ptr is
 459      new Unchecked_Conversion (System.Address, Tag_Ptr);
 460
 461    function To_Tagged_Kind_Ptr is
 462      new Unchecked_Conversion (System.Address, Tagged_Kind_Ptr);
 463
 464    --  Primitive dispatching operations are always inlined, to facilitate
 465    --  use in a minimal/no run-time environment for high integrity use.
 466
 467    pragma Inline_Always (CW_Membership);
 468    pragma Inline_Always (Displace);
 469    pragma Inline_Always (IW_Membership);
 470    pragma Inline_Always (Get_Access_Level);
 471    pragma Inline_Always (Get_Entry_Index);
 472    pragma Inline_Always (Get_Offset_Index);
 473    pragma Inline_Always (Get_Prim_Op_Address);
 474    pragma Inline_Always (Get_Prim_Op_Kind);
 475    pragma Inline_Always (Get_RC_Offset);
 476    pragma Inline_Always (Get_Remotely_Callable);
 477    pragma Inline_Always (Get_Tagged_Kind);
 478    pragma Inline_Always (Inherit_DT);
 479    pragma Inline_Always (Inherit_TSD);
 480    pragma Inline_Always (OSD);
 481    pragma Inline_Always (Register_Interface_Tag);
 482    pragma Inline_Always (Register_Tag);
 483    pragma Inline_Always (Set_Access_Level);
 484    pragma Inline_Always (Set_Entry_Index);
 485    pragma Inline_Always (Set_Expanded_Name);
 486    pragma Inline_Always (Set_External_Tag);
 487    pragma Inline_Always (Set_Interface_Table);
 488    pragma Inline_Always (Set_Num_Prim_Ops);
 489    pragma Inline_Always (Set_Offset_Index);
 490    pragma Inline_Always (Set_Offset_To_Top);
 491    pragma Inline_Always (Set_Prim_Op_Address);
 492    pragma Inline_Always (Set_Prim_Op_Kind);
 493    pragma Inline_Always (Set_RC_Offset);
 494    pragma Inline_Always (Set_Remotely_Callable);
 495    pragma Inline_Always (Set_OSD);
 496    pragma Inline_Always (Set_SSD);
 497    pragma Inline_Always (Set_TSD);
 498    pragma Inline_Always (Set_Tagged_Kind);
 499    pragma Inline_Always (SSD);
 500    pragma Inline_Always (TSD);
 501
 502 end Ada.Tags;