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-------------------------------------------------------------------------------
--- --
--- GNAT RUN-TIME COMPONENTS --
--- --
--- S Y S T E M . E X C E P T I O N S --
--- --
--- S p e c --
--- --
--- $Revision: 1.1.16.1 $
--- --
--- Copyright (C) 1992-2000 Free Software Foundation, Inc. --
--- --
--- 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 2, 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. See the GNU General Public License --
--- for more details. You should have received a copy of the GNU General --
--- Public License distributed with GNAT; see file COPYING. If not, write --
--- to the Free Software Foundation, 59 Temple Place - Suite 330, Boston, --
--- MA 02111-1307, USA. --
--- --
--- As a special exception, if other files instantiate generics from this --
--- unit, or you link this unit with other files to produce an executable, --
--- this unit does not by itself cause the resulting executable to be --
--- covered by the GNU General Public License. This exception does not --
--- however invalidate any other reasons why the executable file might be --
--- covered by the GNU Public License. --
--- --
--- GNAT was originally developed by the GNAT team at New York University. --
--- Extensive contributions were provided by Ada Core Technologies Inc. --
--- --
-------------------------------------------------------------------------------
-
--- This package contains definitions used for zero cost exception handling.
--- See unit Ada.Exceptions for further details. Note that the reason that
--- we separate out these definitions is to avoid problems with recursion
--- in rtsfind. They must be in a unit which does not require any exception
--- table generation of any kind.
-
-with Ada.Exceptions;
-
-with System;
-with System.Standard_Library;
-
-with Unchecked_Conversion;
-
-package System.Exceptions is
-
- package SSL renames System.Standard_Library;
- package AEX renames Ada.Exceptions;
-
- -- The following section defines data structures used for zero cost
- -- exception handling if System.Parameters.Zero_Cost_Exceptions is
- -- set true (i.e. zero cost exceptions are implemented on this target).
-
- -- The approach is to build tables that describe the PC ranges that
- -- are covered by various exception frames. When an exception occurs,
- -- these tables are searched to determine the address of the applicable
- -- handler for the current exception.
-
- subtype Handler_Loc is System.Address;
- -- Code location representing entry address of a handler. Values of
- -- this type are created using the N_Handler_Loc node, and then
- -- passed to the Enter_Handler procedure to enter a handler.
-
- subtype Code_Loc is System.Address;
- -- Code location used in building exception tables and for call
- -- addresses when propagating an exception (also traceback table)
- -- Values of this type are created by using Label'Address or
- -- extracted from machine states using Get_Code_Loc.
-
- --------------------
- -- Handler_Record --
- --------------------
-
- -- A Handler record is built for each choice for each exception handler
- -- in a frame.
-
- function To_Exception_Id is
- new Unchecked_Conversion (SSL.Exception_Data_Ptr, AEX.Exception_Id);
-
- Others_Dummy_Exception : aliased SSL.Exception_Data;
- Others_Id : constant AEX.Exception_Id :=
- To_Exception_Id (Others_Dummy_Exception'Access);
- -- Dummy exception used to signal others exception
-
- All_Others_Dummy_Exception : aliased SSL.Exception_Data;
- All_Others_Id : constant AEX.Exception_Id :=
- To_Exception_Id (All_Others_Dummy_Exception'Access);
- -- Dummy exception used to signal all others exception (including
- -- exceptions not normally handled by others, e.g. Abort_Signal)
-
- type Handler_Record is record
- Lo : Code_Loc;
- Hi : Code_Loc;
- -- Range of PC values of code covered by this handler record. The
- -- handler covers all code addresses that are greater than the Lo
- -- value, and less than or equal to the Hi value.
-
- Id : AEX.Exception_Id;
- -- Id of exception being handled, or one of the above special values
-
- Handler : Handler_Loc;
- -- Address of label at start of handler
- end record;
-
- type Handler_Record_Ptr is access all Handler_Record;
- type Handler_Record_List is array (Natural range <>) of Handler_Record_Ptr;
-
- ---------------------------
- -- Subprogram_Descriptor --
- ---------------------------
-
- -- A Subprogram_Descriptor is built for each subprogram through which
- -- exceptions may propagate, this includes all Ada subprograms,
- -- and also all foreign language imported subprograms.
-
- subtype Subprogram_Info_Type is System.Address;
- -- This type is used to represent a value that is used to unwind stack
- -- frames. It references target dependent data that provides sufficient
- -- information (e.g. about the location of the return point, use of a
- -- frame pointer, save-over-call registers etc) to unwind the machine
- -- state to the caller. For some targets, this is simply a pointer to
- -- the entry point of the procedure (and the routine to pop the machine
- -- state disassembles the code at the entry point to obtain the required
- -- information). On other targets, it is a pointer to data created by the
- -- backend or assembler to represent the required information.
-
- No_Info : constant Subprogram_Info_Type := System.Null_Address;
- -- This is a special value used to indicate that it is not possible
- -- to pop past this frame. This is used at the outer level (e.g. for
- -- package elaboration procedures or the main procedure), and for any
- -- other foreign language procedure for which propagation is known
- -- to be impossible. An exception is considered unhandled if an
- -- attempt is made to pop a frame whose Subprogram_Info_Type value
- -- is set to No_Info.
-
- type Subprogram_Descriptor (Num_Handlers : Natural) is record
- Code : Code_Loc;
- -- This is a code location used to determine which procedure we are
- -- in. Most usually it is simply the entry address for the procedure.
- -- hA given address is considered to be within the procedure referenced
- -- by a Subprogram_Descriptor record if this is the descriptor for
- -- which the Code value is as large as possible without exceeding
- -- the given value.
-
- Subprogram_Info : Subprogram_Info_Type;
- -- This is a pointer to a target dependent data item that provides
- -- sufficient information for unwinding the stack frame of this
- -- procedure. A value of No_Info (zero) means that we are the
- -- outer level procedure.
-
- Handler_Records : Handler_Record_List (1 .. Num_Handlers);
- -- List of pointers to Handler_Records for this procedure. The array
- -- is sorted inside out, i.e. entries for inner frames appear before
- -- entries for outer handlers. This ensures that a serial search
- -- finds the innermost applicable handler
- end record;
-
- subtype Subprogram_Descriptor_0 is Subprogram_Descriptor (0);
- subtype Subprogram_Descriptor_1 is Subprogram_Descriptor (1);
- subtype Subprogram_Descriptor_2 is Subprogram_Descriptor (2);
- subtype Subprogram_Descriptor_3 is Subprogram_Descriptor (3);
- -- Predeclare commonly used subtypes for buildingt he tables
-
- type Subprogram_Descriptor_Ptr is access all Subprogram_Descriptor;
-
- type Subprogram_Descriptor_List
- is array (Natural range <>) of Subprogram_Descriptor_Ptr;
-
- type Subprogram_Descriptors_Record (Count : Natural) is record
- SDesc : Subprogram_Descriptor_List (1 .. Count);
- end record;
-
- type Subprogram_Descriptors_Ptr is
- access all Subprogram_Descriptors_Record;
-
- --------------------------
- -- Unit Exception_Table --
- --------------------------
-
- -- If a unit contains at least one subprogram, then a library level
- -- declaration of the form:
-
- -- Tnn : aliased constant Subprogram_Descriptors :=
- -- (Count => n,
- -- SDesc =>
- -- (SD1'Unrestricted_Access,
- -- SD2'Unrestricted_Access,
- -- ...
- -- SDn'Unrestricted_Access));
- -- pragma Export (Ada, Tnn, "__gnat_unit_name__SDP");
-
- -- is generated where the initializing expression is an array aggregate
- -- whose elements are pointers to the generated subprogram descriptors
- -- for the units.
-
- -- Note: the ALI file contains the designation UX in each unit entry
- -- if a unit exception table is generated.
-
- -- The binder generates a list of addresses of pointers to these tables.
-
-end System.Exceptions;
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