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------------------------------------------------------------------------------

--                                                                          --

--                 GNAT RUN-TIME LIBRARY (GNARL) COMPONENTS                 --

--                                                                          --

--                 S Y S T E M . S T A C K _ C H E C K I N G                --

--                                                                          --

--                                  S p e c                                 --

--                                                                          --

--           Copyright (C) 1999-2009, Free Software Foundation, Inc.        --

--                                                                          --

-- GNARL 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 3,  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.                                     --

--                                                                          --

-- As a special exception under Section 7 of GPL version 3, you are granted --

-- additional permissions described in the GCC Runtime Library Exception,   --

-- version 3.1, as published by the Free Software Foundation.               --

--                                                                          --

-- You should have received a copy of the GNU General Public License and    --

-- a copy of the GCC Runtime Library Exception along with this program;     --

-- see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see    --

-- <http://www.gnu.org/licenses/>.                                          --

--                                                                          --

-- GNARL was developed by the GNARL team at Florida State University.       --

-- Extensive contributions were provided by Ada Core Technologies, Inc.     --

--                                                                          --

------------------------------------------------------------------------------

--  This package provides a system-independent implementation of stack

--  checking using comparison with stack base and limit.

--  This package defines basic types and objects. Operations related to

--  stack checking can be found in package System.Stack_Checking.Operations.

pragma Compiler_Unit;

with System.Storage_Elements;

package System.Stack_Checking is

   pragma Preelaborate;

   pragma Elaborate_Body;

   --  This unit has a junk null body. The reason is that historically we

   --  used to have a real body, and it causes bootstrapping path problems

   --  to eliminate it, since the old body may still be present in the

   --  compilation environment for a build.

   type Stack_Info is record

      Limit : System.Address := System.Null_Address;

      Base  : System.Address := System.Null_Address;

      Size  : System.Storage_Elements.Storage_Offset := 0;

   end record;

   --  This record may be part of a larger data structure like the

   --  task control block in the tasking case.

   --  This specific layout has the advantage of being compatible with the

   --  Intel x86 BOUNDS instruction.

   type Stack_Access is access all Stack_Info;

   --  Unique local storage associated with a specific task. This storage is

   --  used for the stack base and limit, and is returned by Checked_Self.

   --  Only self may write this information, it may be read by any task.

   --  At no time the address range Limit .. Base (or Base .. Limit for

   --  upgrowing stack) may contain any address that is part of another stack.

   --  The Stack_Access may be part of a larger data structure.

   Multi_Processor : constant Boolean := False; --  Not supported yet

private

   Null_Stack_Info  : aliased Stack_Info :=

     (Limit => System.Null_Address,

      Base  => System.Null_Address,

      Size  => 0);

   --  Use explicit assignment to avoid elaboration code (call to init proc)

   Null_Stack : constant Stack_Access := Null_Stack_Info'Access;

   --  Stack_Access value that will return a Stack_Base and Stack_Limit

   --  that fail any stack check.

end System.Stack_Checking;