gcc/ada/s-stache.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                --
   6 --                                                                          --
   7 --                                  B o d y                                 --
   8 --                                                                          --
   9 --                             $Revision$
  10 --                                                                          --
  11 --          Copyright (C) 1999-2001 Free Software Foundation, Inc.          --
  12 --                                                                          --
  13 -- GNARL is free software; you can  redistribute it  and/or modify it under --
  14 -- 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- --
  16 -- sion. GNARL is distributed in the hope that it will be useful, but WITH- --
  17 -- OUT ANY WARRANTY;  without even the  implied warranty of MERCHANTABILITY --
  18 -- or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License --
  19 -- for  more details.  You should have  received  a copy of the GNU General --
  20 -- Public License  distributed with GNARL; see file COPYING.  If not, write --
  21 -- to  the Free Software Foundation,  59 Temple Place - Suite 330,  Boston, --
  22 -- MA 02111-1307, USA.                                                      --
  23 --                                                                          --
  24 -- 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, --
  26 -- this  unit  does not  by itself cause  the resulting  executable  to  be --
  27 -- covered  by the  GNU  General  Public  License.  This exception does not --
  28 -- however invalidate  any other reasons why  the executable file  might be --
  29 -- covered by the  GNU Public License.                                      --
  30 --                                                                          --
  31 -- GNARL was developed by the GNARL team at Florida State University. It is --
  32 -- now maintained by Ada Core Technologies Inc. in cooperation with Florida --
  33 -- State University (http://www.gnat.com).                                  --
  34 --                                                                          --
  35 ------------------------------------------------------------------------------
  36
  37 with Ada.Exceptions;
  38
  39 with System.Storage_Elements; use System.Storage_Elements;
  40 with System.Parameters; use System.Parameters;
  41 with System.Soft_Links;
  42
  43 package body System.Stack_Checking is
  44
  45    Kilobyte               : constant Storage_Offset := 1024;
  46    Default_Env_Stack_Size : constant Storage_Offset := 8000 * Kilobyte;
  47    --  This size is assumed for the environment stack when no size has been
  48    --  set by the runtime, and no GNAT_STACK_LIMIT environment variable was
  49    --  present. The value is chosen to be just under 8 MB whic is the actual
  50    --  default size on some systems including GNU/LinuxThreads, so we will get
  51    --  correct storage errors on those systems without setting environment
  52    --  variables.
  53
  54    function Set_Stack_Info (Stack : access Stack_Access) return Stack_Access;
  55
  56    --  The function Set_Stack_Info is the actual function that updates
  57    --  the cache containing a pointer to the Stack_Info. It may also
  58    --  be used for detecting asynchronous abort in combination with
  59    --  Invalidate_Self_Cache.
  60
  61    --  Set_Stack_Info should do the following things in order:
  62    --     1) Get the Stack_Access value for the current task
  63    --     2) Set Stack.all to the value obtained in 1)
  64    --     3) Optionally Poll to check for asynchronous abort
  65
  66    --  This order is important because if at any time a write to
  67    --  the stack cache is pending, that write should be followed
  68    --  by a Poll to prevent loosing signals.
  69
  70    --  Note: This function must be compiled with Polling turned off
  71
  72    --  Note: on systems like VxWorks and OS/2 with real thread-local storage,
  73    --        Set_Stack_Info should return an access value for such local
  74    --        storage. In those cases the cache will always be up-to-date.
  75
  76    --  The following constants should be imported from some system-specific
  77    --  constants package. The constants must be static for performance reasons.
  78
  79    ----------------------------
  80    -- Invalidate_Stack_Cache --
  81    ----------------------------
  82
  83    procedure Invalidate_Stack_Cache (Any_Stack : Stack_Access) is
  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)
  94       return Stack_Access
  95    is
  96       type Frame_Mark is null record;
  97       Frame_Location : Frame_Mark;
  98       Frame_Address  : Address := Frame_Location'Address;
  99
 100       My_Stack    : Stack_Access;
 101       Limit_Chars : System.Address;
 102       Limit       : Integer;
 103
 104       function getenv (S : String) return System.Address;
 105       pragma Import (C, getenv, External_Name => "getenv");
 106
 107       function atoi (A : System.Address) return Integer;
 108       pragma Import (C, atoi);
 109
 110    begin
 111       --  The order of steps 1 .. 3 is important, see specification.
 112
 113       --  1) Get the Stack_Access value for the current task
 114
 115       My_Stack := Soft_Links.Get_Stack_Info.all;
 116
 117       if My_Stack.Base = Null_Address then
 118
 119          --  First invocation, initialize based on the assumption that
 120          --  there are Environment_Stack_Size bytes available beyond
 121          --  the current frame address.
 122
 123          if My_Stack.Size = 0 then
 124
 125             My_Stack.Size := Default_Env_Stack_Size;
 126
 127             --  When the environment variable GNAT_STACK_LIMIT is set,
 128             --  set Environment_Stack_Size to that number of kB.
 129
 130             Limit_Chars := getenv ("GNAT_STACK_LIMIT" & ASCII.NUL);
 131
 132             if Limit_Chars /= Null_Address then
 133                Limit := atoi (Limit_Chars);
 134                if Limit >= 0 then
 135                   My_Stack.Size := Storage_Offset (Limit) * Kilobyte;
 136                end if;
 137             end if;
 138          end if;
 139
 140          My_Stack.Base := Frame_Address;
 141
 142          if Stack_Grows_Down then
 143
 144             --  Prevent wrap-around on too big stack sizes
 145
 146             My_Stack.Limit := My_Stack.Base - My_Stack.Size;
 147
 148             if My_Stack.Limit > My_Stack.Base then
 149                My_Stack.Limit := Address'First;
 150             end if;
 151
 152          else
 153             My_Stack.Limit := My_Stack.Base + My_Stack.Size;
 154
 155             --  Prevent wrap-around on too big stack sizes
 156
 157             if My_Stack.Limit < My_Stack.Base then
 158                My_Stack.Limit := Address'Last;
 159             end if;
 160          end if;
 161       end if;
 162
 163       --  2) Set Stack.all to the value obtained in 1)
 164
 165       Stack.all := My_Stack;
 166
 167       --  3) Optionally Poll to check for asynchronous abort
 168
 169       if Soft_Links.Check_Abort_Status.all /= 0 then
 170          raise Standard'Abort_Signal;
 171       end if;
 172
 173       return My_Stack; -- Never trust the cached value, but return local copy!
 174    end Set_Stack_Info;
 175
 176    --------------------
 177    -- Set_Stack_Size --
 178    --------------------
 179
 180    --  Specify the stack size for the current frame.
 181
 182    procedure Set_Stack_Size
 183      (Stack_Size : System.Storage_Elements.Storage_Offset)
 184    is
 185       My_Stack      : Stack_Access;
 186       Frame_Address : constant System.Address := My_Stack'Address;
 187
 188    begin
 189       My_Stack := Stack_Check (Frame_Address);
 190
 191       if Stack_Grows_Down then
 192          My_Stack.Limit := My_Stack.Base - Stack_Size;
 193       else
 194          My_Stack.Limit := My_Stack.Base + Stack_Size;
 195       end if;
 196    end Set_Stack_Size;
 197
 198    -----------------
 199    -- Stack_Check --
 200    -----------------
 201
 202    function Stack_Check
 203      (Stack_Address : System.Address)
 204       return Stack_Access
 205    is
 206       type Frame_Marker is null record;
 207       Marker        : Frame_Marker;
 208       Cached_Stack  : constant Stack_Access := Cache;
 209       Frame_Address : constant System.Address := Marker'Address;
 210
 211    begin
 212       --  This function first does a "cheap" check which is correct
 213       --  if it succeeds. In case of failure, the full check is done.
 214       --  Ideally the cheap check should be done in an optimized manner,
 215       --  or be inlined.
 216
 217       if (Stack_Grows_Down and then
 218             (Frame_Address <= Cached_Stack.Base
 219                and
 220              Stack_Address > Cached_Stack.Limit))
 221         or else
 222          (not Stack_Grows_Down and then
 223             (Frame_Address >= Cached_Stack.Base
 224                and
 225              Stack_Address < Cached_Stack.Limit))
 226       then
 227          --  Cached_Stack is valid as it passed the stack check
 228          return Cached_Stack;
 229       end if;
 230
 231       Full_Check :
 232       declare
 233          My_Stack : Stack_Access := Set_Stack_Info (Cache'Access);
 234          --  At this point Stack.all might already be invalid, so
 235          --  it is essential to use our local copy of Stack!
 236
 237       begin
 238
 239          if (Stack_Grows_Down and then
 240                (not (Frame_Address <= My_Stack.Base)))
 241            or else
 242             (not Stack_Grows_Down and then
 243                (not (Frame_Address >= My_Stack.Base)))
 244          then
 245             --  The returned Base is lower than the stored one,
 246             --  so assume that the original one wasn't right and use the
 247             --  current Frame_Address as new one. This allows initializing
 248             --  Base with the Frame_Address as approximation.
 249             --  During initialization the Frame_Address will be close to
 250             --  the stack base anyway: the difference should be compensated
 251             --  for in the stack reserve.
 252
 253             My_Stack.Base := Frame_Address;
 254          end if;
 255
 256          if (Stack_Grows_Down and then
 257                   Stack_Address < My_Stack.Limit)
 258            or else
 259             (not Stack_Grows_Down and then
 260                   Stack_Address > My_Stack.Limit)
 261          then
 262             Ada.Exceptions.Raise_Exception
 263               (E       => Storage_Error'Identity,
 264                Message => "stack overflow detected");
 265          end if;
 266
 267          return My_Stack;
 268       end Full_Check;
 269    end Stack_Check;
 270
 271    ------------------------
 272    -- Update_Stack_Cache --
 273    ------------------------
 274
 275    procedure Update_Stack_Cache (Stack : Stack_Access) is
 276    begin
 277       if not Multi_Processor then
 278          Cache := Stack;
 279       end if;
 280    end Update_Stack_Cache;
 281
 282 end System.Stack_Checking;