gcc/ada/s-except.ads

   1 ------------------------------------------------------------------------------
   2 --                                                                          --
   3 --                         GNAT RUN-TIME COMPONENTS                         --
   4 --                                                                          --
   5 --                    S Y S T E M . E X C E P T I O N S                     --
   6 --                                                                          --
   7 --                                 S p e c                                  --
   8 --                                                                          --
   9 --                                                                          --
  10 --          Copyright (C) 1992-2000 Free Software Foundation, Inc.          --
  11 --                                                                          --
  12 -- GNAT is free software;  you can  redistribute it  and/or modify it under --
  13 -- terms of the  GNU General Public License as published  by the Free Soft- --
  14 -- ware  Foundation;  either version 2,  or (at your option) any later ver- --
  15 -- sion.  GNAT is distributed in the hope that it will be useful, but WITH- --
  16 -- OUT ANY WARRANTY;  without even the  implied warranty of MERCHANTABILITY --
  17 -- or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License --
  18 -- for  more details.  You should have  received  a copy of the GNU General --
  19 -- Public License  distributed with GNAT;  see file COPYING.  If not, write --
  20 -- to  the Free Software Foundation,  59 Temple Place - Suite 330,  Boston, --
  21 -- MA 02111-1307, USA.                                                      --
  22 --                                                                          --
  23 -- As a special exception,  if other files  instantiate  generics from this --
  24 -- unit, or you link  this unit with other files  to produce an executable, --
  25 -- this  unit  does not  by itself cause  the resulting  executable  to  be --
  26 -- covered  by the  GNU  General  Public  License.  This exception does not --
  27 -- however invalidate  any other reasons why  the executable file  might be --
  28 -- covered by the  GNU Public License.                                      --
  29 --                                                                          --
  30 -- GNAT was originally developed  by the GNAT team at  New York University. --
  31 -- Extensive contributions were provided by Ada Core Technologies Inc.      --
  32 --                                                                          --
  33 ------------------------------------------------------------------------------
  34
  35 --  This package contains definitions used for zero cost exception handling.
  36 --  See unit Ada.Exceptions for further details. Note that the reason that
  37 --  we separate out these definitions is to avoid problems with recursion
  38 --  in rtsfind. They must be in a unit which does not require any exception
  39 --  table generation of any kind.
  40
  41 with Ada.Exceptions;
  42
  43 with System;
  44 with System.Standard_Library;
  45
  46 with Unchecked_Conversion;
  47
  48 package System.Exceptions is
  49
  50    package SSL renames System.Standard_Library;
  51    package AEX renames Ada.Exceptions;
  52
  53    --  The following section defines data structures used for zero cost
  54    --  exception handling if System.Parameters.Zero_Cost_Exceptions is
  55    --  set true (i.e. zero cost exceptions are implemented on this target).
  56
  57    --  The approach is to build tables that describe the PC ranges that
  58    --  are covered by various exception frames. When an exception occurs,
  59    --  these tables are searched to determine the address of the applicable
  60    --  handler for the current exception.
  61
  62    subtype Handler_Loc is System.Address;
  63    --  Code location representing entry address of a handler. Values of
  64    --  this type are created using the N_Handler_Loc node, and then
  65    --  passed to the Enter_Handler procedure to enter a handler.
  66
  67    subtype Code_Loc is System.Address;
  68    --  Code location used in building exception tables and for call
  69    --  addresses when propagating an exception (also traceback table)
  70    --  Values of this type are created by using Label'Address or
  71    --  extracted from machine states using Get_Code_Loc.
  72
  73    --------------------
  74    -- Handler_Record --
  75    --------------------
  76
  77    --  A Handler record is built for each choice for each exception handler
  78    --  in a frame.
  79
  80    function To_Exception_Id is
  81      new Unchecked_Conversion (SSL.Exception_Data_Ptr, AEX.Exception_Id);
  82
  83    Others_Dummy_Exception : aliased SSL.Exception_Data;
  84    Others_Id : constant AEX.Exception_Id :=
  85                  To_Exception_Id (Others_Dummy_Exception'Access);
  86    --  Dummy exception used to signal others exception
  87
  88    All_Others_Dummy_Exception : aliased SSL.Exception_Data;
  89    All_Others_Id : constant AEX.Exception_Id :=
  90                      To_Exception_Id (All_Others_Dummy_Exception'Access);
  91    --  Dummy exception used to signal all others exception (including
  92    --  exceptions not normally handled by others, e.g. Abort_Signal)
  93
  94    type Handler_Record is record
  95       Lo : Code_Loc;
  96       Hi : Code_Loc;
  97       --  Range of PC values of code covered by this handler record. The
  98       --  handler covers all code addresses that are greater than the Lo
  99       --  value, and less than or equal to the Hi value.
 100
 101       Id : AEX.Exception_Id;
 102       --  Id of exception being handled, or one of the above special values
 103
 104       Handler : Handler_Loc;
 105       --  Address of label at start of handler
 106    end record;
 107
 108    type Handler_Record_Ptr is access all Handler_Record;
 109    type Handler_Record_List is array (Natural range <>) of Handler_Record_Ptr;
 110
 111    ---------------------------
 112    -- Subprogram_Descriptor --
 113    ---------------------------
 114
 115    --  A Subprogram_Descriptor is built for each subprogram through which
 116    --  exceptions may propagate, this includes all Ada subprograms,
 117    --  and also all foreign language imported subprograms.
 118
 119    subtype Subprogram_Info_Type is System.Address;
 120    --  This type is used to represent a value that is used to unwind stack
 121    --  frames. It references target dependent data that provides sufficient
 122    --  information (e.g. about the location of the return point, use of a
 123    --  frame pointer, save-over-call registers etc) to unwind the machine
 124    --  state to the caller. For some targets, this is simply a pointer to
 125    --  the entry point of the procedure (and the routine to pop the machine
 126    --  state disassembles the code at the entry point to obtain the required
 127    --  information). On other targets, it is a pointer to data created by the
 128    --  backend or assembler to represent the required information.
 129
 130    No_Info : constant Subprogram_Info_Type := System.Null_Address;
 131    --  This is a special value used to indicate that it is not possible
 132    --  to pop past this frame. This is used at the outer level (e.g. for
 133    --  package elaboration procedures or the main procedure), and for any
 134    --  other foreign language procedure for which propagation is known
 135    --  to be impossible. An exception is considered unhandled if an
 136    --  attempt is made to pop a frame whose Subprogram_Info_Type value
 137    --  is set to No_Info.
 138
 139    type Subprogram_Descriptor (Num_Handlers : Natural) is record
 140       Code : Code_Loc;
 141       --  This is a code location used to determine which procedure we are
 142       --  in. Most usually it is simply the entry address for the procedure.
 143       --  hA given address is considered to be within the procedure referenced
 144       --  by a Subprogram_Descriptor record if this is the descriptor for
 145       --  which the Code value is as large as possible without exceeding
 146       --  the given value.
 147
 148       Subprogram_Info : Subprogram_Info_Type;
 149       --  This is a pointer to a target dependent data item that provides
 150       --  sufficient information for unwinding the stack frame of this
 151       --  procedure. A value of No_Info (zero) means that we are the
 152       --  outer level procedure.
 153
 154       Handler_Records : Handler_Record_List (1 .. Num_Handlers);
 155       --  List of pointers to Handler_Records for this procedure. The array
 156       --  is sorted inside out, i.e. entries for inner frames appear before
 157       --  entries for outer handlers. This ensures that a serial search
 158       --  finds the innermost applicable handler
 159    end record;
 160
 161    subtype Subprogram_Descriptor_0 is Subprogram_Descriptor (0);
 162    subtype Subprogram_Descriptor_1 is Subprogram_Descriptor (1);
 163    subtype Subprogram_Descriptor_2 is Subprogram_Descriptor (2);
 164    subtype Subprogram_Descriptor_3 is Subprogram_Descriptor (3);
 165    --  Predeclare commonly used subtypes for buildingt he tables
 166
 167    type Subprogram_Descriptor_Ptr is access all Subprogram_Descriptor;
 168
 169    type Subprogram_Descriptor_List
 170      is array (Natural range <>) of Subprogram_Descriptor_Ptr;
 171
 172    type Subprogram_Descriptors_Record (Count : Natural) is record
 173       SDesc : Subprogram_Descriptor_List (1 .. Count);
 174    end record;
 175
 176    type Subprogram_Descriptors_Ptr is
 177      access all Subprogram_Descriptors_Record;
 178
 179    --------------------------
 180    -- Unit Exception_Table --
 181    --------------------------
 182
 183    --  If a unit contains at least one subprogram, then a library level
 184    --  declaration of the form:
 185
 186    --    Tnn : aliased constant Subprogram_Descriptors :=
 187    --            (Count => n,
 188    --             SDesc =>
 189    --              (SD1'Unrestricted_Access,
 190    --               SD2'Unrestricted_Access,
 191    --               ...
 192    --               SDn'Unrestricted_Access));
 193    --    pragma Export (Ada, Tnn, "__gnat_unit_name__SDP");
 194
 195    --  is generated where the initializing expression is an array aggregate
 196    --  whose elements are pointers to the generated subprogram descriptors
 197    --  for the units.
 198
 199    --  Note: the ALI file contains the designation UX in each unit entry
 200    --  if a unit exception table is generated.
 201
 202    --  The binder generates a list of addresses of pointers to these tables.
 203
 204 end System.Exceptions;