------------------------------------------------------------------------------
--                                                                          --
--                GNU ADA RUN-TIME LIBRARY (GNARL) COMPONENTS               --
--                                                                          --
--                 S Y S T E M . S T A C K _ C H E C K I N G                --
--                                                                          --
--                                  B o d y                                 --
--                                                                          --
--                             $Revision$
--                                                                          --
--          Copyright (C) 1999-2001 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 2,  or (at your option) any later ver- --
-- sion. GNARL 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 GNARL; 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.                                      --
--                                                                          --
-- GNARL was developed by the GNARL team at Florida State University. It is --
-- now maintained by Ada Core Technologies Inc. in cooperation with Florida --
-- State University (http://www.gnat.com).                                  --
--                                                                          --
------------------------------------------------------------------------------

with Ada.Exceptions;

with System.Storage_Elements; use System.Storage_Elements;
with System.Parameters; use System.Parameters;
with System.Soft_Links;

package body System.Stack_Checking is

   Kilobyte               : constant Storage_Offset := 1024;
   Default_Env_Stack_Size : constant Storage_Offset := 8000 * Kilobyte;
   --  This size is assumed for the environment stack when no size has been
   --  set by the runtime, and no GNAT_STACK_LIMIT environment variable was
   --  present. The value is chosen to be just under 8 MB whic is the actual
   --  default size on some systems including GNU/LinuxThreads, so we will get
   --  correct storage errors on those systems without setting environment
   --  variables.

   function Set_Stack_Info (Stack : access Stack_Access) return Stack_Access;

   --  The function Set_Stack_Info is the actual function that updates
   --  the cache containing a pointer to the Stack_Info. It may also
   --  be used for detecting asynchronous abort in combination with
   --  Invalidate_Self_Cache.

   --  Set_Stack_Info should do the following things in order:
   --     1) Get the Stack_Access value for the current task
   --     2) Set Stack.all to the value obtained in 1)
   --     3) Optionally Poll to check for asynchronous abort

   --  This order is important because if at any time a write to
   --  the stack cache is pending, that write should be followed
   --  by a Poll to prevent loosing signals.

   --  Note: This function must be compiled with Polling turned off

   --  Note: on systems like VxWorks and OS/2 with real thread-local storage,
   --        Set_Stack_Info should return an access value for such local
   --        storage. In those cases the cache will always be up-to-date.

   --  The following constants should be imported from some system-specific
   --  constants package. The constants must be static for performance reasons.

   ----------------------------
   -- Invalidate_Stack_Cache --
   ----------------------------

   procedure Invalidate_Stack_Cache (Any_Stack : Stack_Access) is
   begin
      Cache := Null_Stack;
   end Invalidate_Stack_Cache;

   --------------------
   -- Set_Stack_Info --
   --------------------

   function Set_Stack_Info
     (Stack : access Stack_Access)
      return Stack_Access
   is
      type Frame_Mark is null record;
      Frame_Location : Frame_Mark;
      Frame_Address  : Address := Frame_Location'Address;

      My_Stack    : Stack_Access;
      Limit_Chars : System.Address;
      Limit       : Integer;

      function getenv (S : String) return System.Address;
      pragma Import (C, getenv, External_Name => "getenv");

      function atoi (A : System.Address) return Integer;
      pragma Import (C, atoi);

   begin
      --  The order of steps 1 .. 3 is important, see specification.

      --  1) Get the Stack_Access value for the current task

      My_Stack := Soft_Links.Get_Stack_Info.all;

      if My_Stack.Base = Null_Address then

         --  First invocation, initialize based on the assumption that
         --  there are Environment_Stack_Size bytes available beyond
         --  the current frame address.

         if My_Stack.Size = 0 then

            My_Stack.Size := Default_Env_Stack_Size;

            --  When the environment variable GNAT_STACK_LIMIT is set,
            --  set Environment_Stack_Size to that number of kB.

            Limit_Chars := getenv ("GNAT_STACK_LIMIT" & ASCII.NUL);

            if Limit_Chars /= Null_Address then
               Limit := atoi (Limit_Chars);
               if Limit >= 0 then
                  My_Stack.Size := Storage_Offset (Limit) * Kilobyte;
               end if;
            end if;
         end if;

         My_Stack.Base := Frame_Address;

         if Stack_Grows_Down then

            --  Prevent wrap-around on too big stack sizes

            My_Stack.Limit := My_Stack.Base - My_Stack.Size;

            if My_Stack.Limit > My_Stack.Base then
               My_Stack.Limit := Address'First;
            end if;

         else
            My_Stack.Limit := My_Stack.Base + My_Stack.Size;

            --  Prevent wrap-around on too big stack sizes

            if My_Stack.Limit < My_Stack.Base then
               My_Stack.Limit := Address'Last;
            end if;
         end if;
      end if;

      --  2) Set Stack.all to the value obtained in 1)

      Stack.all := My_Stack;

      --  3) Optionally Poll to check for asynchronous abort

      if Soft_Links.Check_Abort_Status.all /= 0 then
         raise Standard'Abort_Signal;
      end if;

      return My_Stack; -- Never trust the cached value, but return local copy!
   end Set_Stack_Info;

   --------------------
   -- Set_Stack_Size --
   --------------------

   --  Specify the stack size for the current frame.

   procedure Set_Stack_Size
     (Stack_Size : System.Storage_Elements.Storage_Offset)
   is
      My_Stack      : Stack_Access;
      Frame_Address : constant System.Address := My_Stack'Address;

   begin
      My_Stack := Stack_Check (Frame_Address);

      if Stack_Grows_Down then
         My_Stack.Limit := My_Stack.Base - Stack_Size;
      else
         My_Stack.Limit := My_Stack.Base + Stack_Size;
      end if;
   end Set_Stack_Size;

   -----------------
   -- Stack_Check --
   -----------------

   function Stack_Check
     (Stack_Address : System.Address)
      return Stack_Access
   is
      type Frame_Marker is null record;
      Marker        : Frame_Marker;
      Cached_Stack  : constant Stack_Access := Cache;
      Frame_Address : constant System.Address := Marker'Address;

   begin
      --  This function first does a "cheap" check which is correct
      --  if it succeeds. In case of failure, the full check is done.
      --  Ideally the cheap check should be done in an optimized manner,
      --  or be inlined.

      if (Stack_Grows_Down and then
            (Frame_Address <= Cached_Stack.Base
               and
             Stack_Address > Cached_Stack.Limit))
        or else
         (not Stack_Grows_Down and then
            (Frame_Address >= Cached_Stack.Base
               and
             Stack_Address < Cached_Stack.Limit))
      then
         --  Cached_Stack is valid as it passed the stack check
         return Cached_Stack;
      end if;

      Full_Check :
      declare
         My_Stack : Stack_Access := Set_Stack_Info (Cache'Access);
         --  At this point Stack.all might already be invalid, so
         --  it is essential to use our local copy of Stack!

      begin

         if (Stack_Grows_Down and then
               (not (Frame_Address <= My_Stack.Base)))
           or else
            (not Stack_Grows_Down and then
               (not (Frame_Address >= My_Stack.Base)))
         then
            --  The returned Base is lower than the stored one,
            --  so assume that the original one wasn't right and use the
            --  current Frame_Address as new one. This allows initializing
            --  Base with the Frame_Address as approximation.
            --  During initialization the Frame_Address will be close to
            --  the stack base anyway: the difference should be compensated
            --  for in the stack reserve.

            My_Stack.Base := Frame_Address;
         end if;

         if (Stack_Grows_Down and then
                  Stack_Address < My_Stack.Limit)
           or else
            (not Stack_Grows_Down and then
                  Stack_Address > My_Stack.Limit)
         then
            Ada.Exceptions.Raise_Exception
              (E       => Storage_Error'Identity,
               Message => "stack overflow detected");
         end if;

         return My_Stack;
      end Full_Check;
   end Stack_Check;

   ------------------------
   -- Update_Stack_Cache --
   ------------------------

   procedure Update_Stack_Cache (Stack : Stack_Access) is
   begin
      if not Multi_Processor then
         Cache := Stack;
      end if;
   end Update_Stack_Cache;

end System.Stack_Checking;