gcc/ada/s-stchop.adb

   1 ------------------------------------------------------------------------------
   2 --                                                                          --
   3 --                GNU ADA RUN-TIME LIBRARY (GNARL) COMPONENTS               --
   4 --                                                                          --
   5 --     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      --
   6 --                                                                          --
   7 --                                  B o d y                                 --
   8 --                                                                          --
   9 --          Copyright (C) 1999-2004 Free Software Foundation, Inc.          --
  10 --                                                                          --
  11 -- GNARL is free software; you can  redistribute it  and/or modify it under --
  12 -- terms of the  GNU General Public License as published  by the Free Soft- --
  13 -- ware  Foundation;  either version 2,  or (at your option) any later ver- --
  14 -- sion. GNARL is distributed in the hope that it will be useful, but WITH- --
  15 -- OUT ANY WARRANTY;  without even the  implied warranty of MERCHANTABILITY --
  16 -- or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License --
  17 -- for  more details.  You should have  received  a copy of the GNU General --
  18 -- Public License  distributed with GNARL; see file COPYING.  If not, write --
  19 -- to  the Free Software Foundation,  59 Temple Place - Suite 330,  Boston, --
  20 -- MA 02111-1307, USA.                                                      --
  21 --                                                                          --
  22 -- As a special exception,  if other files  instantiate  generics from this --
  23 -- unit, or you link  this unit with other files  to produce an executable, --
  24 -- this  unit  does not  by itself cause  the resulting  executable  to  be --
  25 -- covered  by the  GNU  General  Public  License.  This exception does not --
  26 -- however invalidate  any other reasons why  the executable file  might be --
  27 -- covered by the  GNU Public License.                                      --
  28 --                                                                          --
  29 -- GNARL was developed by the GNARL team at Florida State University.       --
  30 -- Extensive contributions were provided by Ada Core Technologies, Inc.     --
  31 --                                                                          --
  32 ------------------------------------------------------------------------------
  33
  34 --  This is the general implementation of this package. There is a VxWorks
  35 --  specific version of this package (5zstchop.adb). This file should
  36 --  be kept synchronized with it.
  37
  38 pragma Restrictions (No_Elaboration_Code);
  39 --  We want to guarantee the absence of elaboration code because the
  40 --  binder does not handle references to this package.
  41
  42 with Ada.Exceptions;
  43
  44 with System.Storage_Elements; use System.Storage_Elements;
  45 with System.Parameters; use System.Parameters;
  46 with System.Soft_Links;
  47 with System.CRTL;
  48
  49 package body System.Stack_Checking.Operations is
  50
  51    Kilobyte : constant := 1024;
  52
  53    function Set_Stack_Info (Stack : access Stack_Access) return Stack_Access;
  54
  55    --  The function Set_Stack_Info is the actual function that updates
  56    --  the cache containing a pointer to the Stack_Info. It may also
  57    --  be used for detecting asynchronous abort in combination with
  58    --  Invalidate_Self_Cache.
  59
  60    --  Set_Stack_Info should do the following things in order:
  61    --     1) Get the Stack_Access value for the current task
  62    --     2) Set Stack.all to the value obtained in 1)
  63    --     3) Optionally Poll to check for asynchronous abort
  64
  65    --  This order is important because if at any time a write to
  66    --  the stack cache is pending, that write should be followed
  67    --  by a Poll to prevent loosing signals.
  68
  69    --  Note: This function must be compiled with Polling turned off
  70
  71    --  Note: on systems like VxWorks and OS/2 with real thread-local storage,
  72    --        Set_Stack_Info should return an access value for such local
  73    --        storage. In those cases the cache will always be up-to-date.
  74
  75    --  The following constants should be imported from some system-specific
  76    --  constants package. The constants must be static for performance reasons.
  77
  78    ----------------------------
  79    -- Invalidate_Stack_Cache --
  80    ----------------------------
  81
  82    procedure Invalidate_Stack_Cache (Any_Stack : Stack_Access) is
  83       pragma Warnings (Off, Any_Stack);
  84    begin
  85       Cache := Null_Stack;
  86    end Invalidate_Stack_Cache;
  87
  88    --------------------
  89    -- Set_Stack_Info --
  90    --------------------
  91
  92    function Set_Stack_Info
  93      (Stack : access Stack_Access) return Stack_Access
  94    is
  95       type Frame_Mark is null record;
  96       Frame_Location : Frame_Mark;
  97       Frame_Address  : constant Address := Frame_Location'Address;
  98
  99       My_Stack    : Stack_Access;
 100       Limit_Chars : System.Address;
 101       Limit       : Integer;
 102
 103    begin
 104       --  The order of steps 1 .. 3 is important, see specification.
 105
 106       --  1) Get the Stack_Access value for the current task
 107
 108       My_Stack := Soft_Links.Get_Stack_Info.all;
 109
 110       if My_Stack.Base = Null_Address then
 111
 112          --  First invocation, initialize based on the assumption that
 113          --  there are Environment_Stack_Size bytes available beyond
 114          --  the current frame address.
 115
 116          if My_Stack.Size = 0 then
 117             My_Stack.Size := Storage_Offset (Default_Env_Stack_Size);
 118
 119             --  When the environment variable GNAT_STACK_LIMIT is set,
 120             --  set Environment_Stack_Size to that number of kB.
 121
 122             Limit_Chars := System.CRTL.getenv ("GNAT_STACK_LIMIT" & ASCII.NUL);
 123
 124             if Limit_Chars /= Null_Address then
 125                Limit := System.CRTL.atoi (Limit_Chars);
 126
 127                if Limit >= 0 then
 128                   My_Stack.Size := Storage_Offset (Limit) * Kilobyte;
 129                end if;
 130             end if;
 131          end if;
 132
 133          My_Stack.Base := Frame_Address;
 134
 135          if Stack_Grows_Down then
 136
 137             --  Prevent wrap-around on too big stack sizes
 138
 139             My_Stack.Limit := My_Stack.Base - My_Stack.Size;
 140
 141             if My_Stack.Limit > My_Stack.Base then
 142                My_Stack.Limit := Address'First;
 143             end if;
 144
 145          else
 146             My_Stack.Limit := My_Stack.Base + My_Stack.Size;
 147
 148             --  Prevent wrap-around on too big stack sizes
 149
 150             if My_Stack.Limit < My_Stack.Base then
 151                My_Stack.Limit := Address'Last;
 152             end if;
 153          end if;
 154       end if;
 155
 156       --  2) Set Stack.all to the value obtained in 1)
 157
 158       Stack.all := My_Stack;
 159
 160       --  3) Optionally Poll to check for asynchronous abort
 161
 162       if Soft_Links.Check_Abort_Status.all /= 0 then
 163          raise Standard'Abort_Signal;
 164       end if;
 165
 166       return My_Stack; -- Never trust the cached value, but return local copy!
 167    end Set_Stack_Info;
 168
 169    -----------------
 170    -- Stack_Check --
 171    -----------------
 172
 173    function Stack_Check
 174      (Stack_Address : System.Address) return Stack_Access
 175    is
 176       type Frame_Marker is null record;
 177       Marker        : Frame_Marker;
 178       Cached_Stack  : constant Stack_Access := Cache;
 179       Frame_Address : constant System.Address := Marker'Address;
 180
 181    begin
 182       --  This function first does a "cheap" check which is correct
 183       --  if it succeeds. In case of failure, the full check is done.
 184       --  Ideally the cheap check should be done in an optimized manner,
 185       --  or be inlined.
 186
 187       if (Stack_Grows_Down and then
 188             (Frame_Address <= Cached_Stack.Base
 189                and
 190              Stack_Address > Cached_Stack.Limit))
 191         or else
 192          (not Stack_Grows_Down and then
 193             (Frame_Address >= Cached_Stack.Base
 194                and
 195              Stack_Address < Cached_Stack.Limit))
 196       then
 197          --  Cached_Stack is valid as it passed the stack check
 198          return Cached_Stack;
 199       end if;
 200
 201       Full_Check :
 202       declare
 203          My_Stack : constant Stack_Access := Set_Stack_Info (Cache'Access);
 204          --  At this point Stack.all might already be invalid, so
 205          --  it is essential to use our local copy of Stack!
 206
 207       begin
 208          if (Stack_Grows_Down and then
 209                (not (Frame_Address <= My_Stack.Base)))
 210            or else
 211             (not Stack_Grows_Down and then
 212                (not (Frame_Address >= My_Stack.Base)))
 213          then
 214             --  The returned Base is lower than the stored one,
 215             --  so assume that the original one wasn't right and use the
 216             --  current Frame_Address as new one. This allows initializing
 217             --  Base with the Frame_Address as approximation.
 218             --  During initialization the Frame_Address will be close to
 219             --  the stack base anyway: the difference should be compensated
 220             --  for in the stack reserve.
 221
 222             My_Stack.Base := Frame_Address;
 223          end if;
 224
 225          if (Stack_Grows_Down and then
 226                   Stack_Address < My_Stack.Limit)
 227            or else
 228             (not Stack_Grows_Down and then
 229                   Stack_Address > My_Stack.Limit)
 230          then
 231             Ada.Exceptions.Raise_Exception
 232               (E       => Storage_Error'Identity,
 233                Message => "stack overflow detected");
 234          end if;
 235
 236          return My_Stack;
 237       end Full_Check;
 238    end Stack_Check;
 239
 240    ------------------------
 241    -- Update_Stack_Cache --
 242    ------------------------
 243
 244    procedure Update_Stack_Cache (Stack : Stack_Access) is
 245    begin
 246       if not Multi_Processor then
 247          Cache := Stack;
 248       end if;
 249    end Update_Stack_Cache;
 250
 251 end System.Stack_Checking.Operations;