File : s-except.ads
------------------------------------------------------------------------------
-- --
-- GNAT RUN-TIME COMPONENTS --
-- --
5 -- S Y S T E M . E X C E P T I O N S --
-- --
-- S p e c --
-- --
-- $Revision: 1.10 $
10 -- --
-- 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- --
15 -- 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 --
20 -- 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 --
25 -- 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. --
30 -- --
-- GNAT was originally developed by the GNAT team at New York University. --
-- It is now maintained by Ada Core Technologies Inc (http://www.gnat.com). --
-- --
------------------------------------------------------------------------------
35
-- 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
40 -- table generation of any kind.
with Ada.Exceptions;
with System;
45 with System.Standard_Library;
with Unchecked_Conversion;
package System.Exceptions is
50
package SSL renames System.Standard_Library;
package AEX renames Ada.Exceptions;
-- The following section defines data structures used for zero cost
55 -- 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,
60 -- 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
65 -- 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
70 -- 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.
--------------------
75 -- Handler_Record --
--------------------
-- A Handler record is built for each choice for each exception handler
-- in a frame.
80
function To_Exception_Id is
new Unchecked_Conversion (SSL.Exception_Data_Ptr, AEX.Exception_Id);
Others_Dummy_Exception : aliased SSL.Exception_Data;
85 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;
90 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)
95 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
100 -- 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
105 Handler : Handler_Loc;
-- Address of label at start of handler
end record;
type Handler_Record_Ptr is access all Handler_Record;
110 type Handler_Record_List is array (Natural range <>) of Handler_Record_Ptr;
---------------------------
-- Subprogram_Descriptor --
---------------------------
115
-- 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.
120 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
125 -- 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.
130
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
135 -- 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.
140 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
145 -- 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;
150 -- 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.
155 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
160 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);
165 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;
170 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);
175 end record;
type Subprogram_Descriptors_Ptr is
access all Subprogram_Descriptors_Record;
180 --------------------------
-- Unit Exception_Table --
--------------------------
-- If a unit contains at least one subprogram, then a library level
185 -- declaration of the form:
-- Tnn : aliased constant Subprogram_Descriptors :=
-- (Count => n,
-- SDesc =>
190 -- (SD1'Unrestricted_Access,
-- SD2'Unrestricted_Access,
-- ...
-- SDn'Unrestricted_Access));
-- pragma Export (Ada, Tnn, "__gnat_unit_name__SDP");
195
-- is generated where the initializing expression is an array aggregate
-- whose elements are pointers to the generated subprogram descriptors
-- for the units.
200 -- 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.
205 end System.Exceptions;