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 --          Copyright (C) 1999-2002 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 with Ada.Exceptions;
  35
  36 with System.Storage_Elements; use System.Storage_Elements;
  37 with System.Parameters; use System.Parameters;
  38 with System.Soft_Links;
  39
  40 package body System.Stack_Checking is
  41
  42    Kilobyte : constant := 1024;
  43
  44    function Set_Stack_Info (Stack : access Stack_Access) return Stack_Access;
  45
  46    --  The function Set_Stack_Info is the actual function that updates
  47    --  the cache containing a pointer to the Stack_Info. It may also
  48    --  be used for detecting asynchronous abort in combination with
  49    --  Invalidate_Self_Cache.
  50
  51    --  Set_Stack_Info should do the following things in order:
  52    --     1) Get the Stack_Access value for the current task
  53    --     2) Set Stack.all to the value obtained in 1)
  54    --     3) Optionally Poll to check for asynchronous abort
  55
  56    --  This order is important because if at any time a write to
  57    --  the stack cache is pending, that write should be followed
  58    --  by a Poll to prevent loosing signals.
  59
  60    --  Note: This function must be compiled with Polling turned off
  61
  62    --  Note: on systems like VxWorks and OS/2 with real thread-local storage,
  63    --        Set_Stack_Info should return an access value for such local
  64    --        storage. In those cases the cache will always be up-to-date.
  65
  66    --  The following constants should be imported from some system-specific
  67    --  constants package. The constants must be static for performance reasons.
  68
  69    ----------------------------
  70    -- Invalidate_Stack_Cache --
  71    ----------------------------
  72
  73    procedure Invalidate_Stack_Cache (Any_Stack : Stack_Access) is
  74       pragma Warnings (Off, Any_Stack);
  75
  76    begin
  77       Cache := Null_Stack;
  78    end Invalidate_Stack_Cache;
  79
  80    --------------------
  81    -- Set_Stack_Info --
  82    --------------------
  83
  84    function Set_Stack_Info
  85      (Stack : access Stack_Access)
  86       return Stack_Access
  87    is
  88       type Frame_Mark is null record;
  89       Frame_Location : Frame_Mark;
  90       Frame_Address  : constant Address := Frame_Location'Address;
  91
  92       My_Stack    : Stack_Access;
  93       Limit_Chars : System.Address;
  94       Limit       : Integer;
  95
  96       function getenv (S : String) return System.Address;
  97       pragma Import (C, getenv, External_Name => "getenv");
  98
  99       function atoi (A : System.Address) return Integer;
 100       pragma Import (C, atoi);
 101
 102    begin
 103       --  The order of steps 1 .. 3 is important, see specification.
 104
 105       --  1) Get the Stack_Access value for the current task
 106
 107       My_Stack := Soft_Links.Get_Stack_Info.all;
 108
 109       if My_Stack.Base = Null_Address then
 110
 111          --  First invocation, initialize based on the assumption that
 112          --  there are Environment_Stack_Size bytes available beyond
 113          --  the current frame address.
 114
 115          if My_Stack.Size = 0 then
 116
 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 := getenv ("GNAT_STACK_LIMIT" & ASCII.NUL);
 123
 124             if Limit_Chars /= Null_Address then
 125                Limit := atoi (Limit_Chars);
 126                if Limit >= 0 then
 127                   My_Stack.Size := Storage_Offset (Limit) * Kilobyte;
 128                end if;
 129             end if;
 130          end if;
 131
 132          My_Stack.Base := Frame_Address;
 133
 134          if Stack_Grows_Down then
 135
 136             --  Prevent wrap-around on too big stack sizes
 137
 138             My_Stack.Limit := My_Stack.Base - My_Stack.Size;
 139
 140             if My_Stack.Limit > My_Stack.Base then
 141                My_Stack.Limit := Address'First;
 142             end if;
 143
 144          else
 145             My_Stack.Limit := My_Stack.Base + My_Stack.Size;
 146
 147             --  Prevent wrap-around on too big stack sizes
 148
 149             if My_Stack.Limit < My_Stack.Base then
 150                My_Stack.Limit := Address'Last;
 151             end if;
 152          end if;
 153       end if;
 154
 155       --  2) Set Stack.all to the value obtained in 1)
 156
 157       Stack.all := My_Stack;
 158
 159       --  3) Optionally Poll to check for asynchronous abort
 160
 161       if Soft_Links.Check_Abort_Status.all /= 0 then
 162          raise Standard'Abort_Signal;
 163       end if;
 164
 165       return My_Stack; -- Never trust the cached value, but return local copy!
 166    end Set_Stack_Info;
 167
 168    --------------------
 169    -- Set_Stack_Size --
 170    --------------------
 171
 172    --  Specify the stack size for the current frame.
 173
 174    procedure Set_Stack_Size
 175      (Stack_Size : System.Storage_Elements.Storage_Offset)
 176    is
 177       My_Stack      : Stack_Access;
 178       Frame_Address : constant System.Address := My_Stack'Address;
 179
 180    begin
 181       My_Stack := Stack_Check (Frame_Address);
 182
 183       if Stack_Grows_Down then
 184          My_Stack.Limit := My_Stack.Base - Stack_Size;
 185       else
 186          My_Stack.Limit := My_Stack.Base + Stack_Size;
 187       end if;
 188    end Set_Stack_Size;
 189
 190    -----------------
 191    -- Stack_Check --
 192    -----------------
 193
 194    function Stack_Check
 195      (Stack_Address : System.Address)
 196       return Stack_Access
 197    is
 198       type Frame_Marker is null record;
 199       Marker        : Frame_Marker;
 200       Cached_Stack  : constant Stack_Access := Cache;
 201       Frame_Address : constant System.Address := Marker'Address;
 202
 203    begin
 204       --  This function first does a "cheap" check which is correct
 205       --  if it succeeds. In case of failure, the full check is done.
 206       --  Ideally the cheap check should be done in an optimized manner,
 207       --  or be inlined.
 208
 209       if (Stack_Grows_Down and then
 210             (Frame_Address <= Cached_Stack.Base
 211                and
 212              Stack_Address > Cached_Stack.Limit))
 213         or else
 214          (not Stack_Grows_Down and then
 215             (Frame_Address >= Cached_Stack.Base
 216                and
 217              Stack_Address < Cached_Stack.Limit))
 218       then
 219          --  Cached_Stack is valid as it passed the stack check
 220          return Cached_Stack;
 221       end if;
 222
 223       Full_Check :
 224       declare
 225          My_Stack : Stack_Access := Set_Stack_Info (Cache'Access);
 226          --  At this point Stack.all might already be invalid, so
 227          --  it is essential to use our local copy of Stack!
 228
 229       begin
 230
 231          if (Stack_Grows_Down and then
 232                (not (Frame_Address <= My_Stack.Base)))
 233            or else
 234             (not Stack_Grows_Down and then
 235                (not (Frame_Address >= My_Stack.Base)))
 236          then
 237             --  The returned Base is lower than the stored one,
 238             --  so assume that the original one wasn't right and use the
 239             --  current Frame_Address as new one. This allows initializing
 240             --  Base with the Frame_Address as approximation.
 241             --  During initialization the Frame_Address will be close to
 242             --  the stack base anyway: the difference should be compensated
 243             --  for in the stack reserve.
 244
 245             My_Stack.Base := Frame_Address;
 246          end if;
 247
 248          if (Stack_Grows_Down and then
 249                   Stack_Address < My_Stack.Limit)
 250            or else
 251             (not Stack_Grows_Down and then
 252                   Stack_Address > My_Stack.Limit)
 253          then
 254             Ada.Exceptions.Raise_Exception
 255               (E       => Storage_Error'Identity,
 256                Message => "stack overflow detected");
 257          end if;
 258
 259          return My_Stack;
 260       end Full_Check;
 261    end Stack_Check;
 262
 263    ------------------------
 264    -- Update_Stack_Cache --
 265    ------------------------
 266
 267    procedure Update_Stack_Cache (Stack : Stack_Access) is
 268    begin
 269       if not Multi_Processor then
 270          Cache := Stack;
 271       end if;
 272    end Update_Stack_Cache;
 273
 274 end System.Stack_Checking;