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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 . O P E R A T I O N S      --

--                                                                          --

--                                  B o d y                                 --

--                                                                          --

--          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 is the general implementation of this package. There is a VxWorks

--  specific version of this package (s-stchop-vxworks.adb). This file should

--  be kept synchronized with it.

pragma Restrictions (No_Elaboration_Code);

--  We want to guarantee the absence of elaboration code because the

--  binder does not handle references to this package.

with System.Storage_Elements; use System.Storage_Elements;

with System.Parameters; use System.Parameters;

with System.Soft_Links;

with System.CRTL;

package body System.Stack_Checking.Operations is

   Kilobyte : constant := 1024;

   function Set_Stack_Info

     (Stack : not null 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

      pragma Warnings (Off, Any_Stack);

   begin

      Cache := Null_Stack;

   end Invalidate_Stack_Cache;

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

   -- Notify_Stack_Attributes --

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

   procedure Notify_Stack_Attributes

     (Initial_SP : System.Address;

      Size       : System.Storage_Elements.Storage_Offset)

   is

      My_Stack : constant Stack_Access := Soft_Links.Get_Stack_Info.all;

      --  We piggyback on the 'Limit' field to store what will be used as the

      --  'Base' and leave the 'Size' alone to not interfere with the logic in

      --  Set_Stack_Info below.

      pragma Unreferenced (Size);

   begin

      My_Stack.Limit := Initial_SP;

   end Notify_Stack_Attributes;

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

   -- Set_Stack_Info --

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

   function Set_Stack_Info

     (Stack : not null access Stack_Access) return Stack_Access

   is

      type Frame_Mark is null record;

      Frame_Location : Frame_Mark;

      Frame_Address  : constant Address := Frame_Location'Address;

      My_Stack    : Stack_Access;

      Limit_Chars : System.Address;

      Limit       : Integer;

   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 := Storage_Offset (Default_Env_Stack_Size);

            --  When the environment variable GNAT_STACK_LIMIT is set, set

            --  Environment_Stack_Size to that number of kB.

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

            if Limit_Chars /= Null_Address then

               Limit := System.CRTL.atoi (Limit_Chars);

               if Limit >= 0 then

                  My_Stack.Size := Storage_Offset (Limit) * Kilobyte;

               end if;

            end if;

         end if;

         --  If a stack base address has been registered, honor it. Fallback to

         --  the address of a local object otherwise.

         My_Stack.Base :=

           (if My_Stack.Limit /= System.Null_Address

            then My_Stack.Limit else 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;

      --  Never trust the cached value, but return local copy!

      return My_Stack;

   end Set_Stack_Info;

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

   -- 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

      --  The parameter may have wrapped around in System.Address arithmetics.

      --  In that case, we have no other choices than raising the exception.

      if (Stack_Grows_Down and then

            Stack_Address > Frame_Address)

        or else

         (not Stack_Grows_Down and then

            Stack_Address < Frame_Address)

      then

         raise Storage_Error with "stack overflow detected";

      end if;

      --  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 then

             Stack_Address > Cached_Stack.Limit))

        or else

         (not Stack_Grows_Down and then

            (Frame_Address >= Cached_Stack.Base

               and then

             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 : constant 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 Base to be initialized 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

            raise Storage_Error with "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.Operations;