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 --                                                                          --
  10 --          Copyright (C) 1999-2001 Free Software Foundation, Inc.          --
  11 --                                                                          --
  12 -- GNARL is free software; you can  redistribute it  and/or modify it under --
  13 -- terms of the  GNU General Public License as published  by the Free Soft- --
  14 -- ware  Foundation;  either version 2,  or (at your option) any later ver- --
  15 -- sion. GNARL is distributed in the hope that it will be useful, but WITH- --
  16 -- OUT ANY WARRANTY;  without even the  implied warranty of MERCHANTABILITY --
  17 -- or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License --
  18 -- for  more details.  You should have  received  a copy of the GNU General --
  19 -- Public License  distributed with GNARL; see file COPYING.  If not, write --
  20 -- to  the Free Software Foundation,  59 Temple Place - Suite 330,  Boston, --
  21 -- MA 02111-1307, USA.                                                      --
  22 --                                                                          --
  23 -- As a special exception,  if other files  instantiate  generics from this --
  24 -- unit, or you link  this unit with other files  to produce an executable, --
  25 -- this  unit  does not  by itself cause  the resulting  executable  to  be --
  26 -- covered  by the  GNU  General  Public  License.  This exception does not --
  27 -- however invalidate  any other reasons why  the executable file  might be --
  28 -- covered by the  GNU Public License.                                      --
  29 --                                                                          --
  30 -- GNARL was developed by the GNARL team at Florida State University. It is --
  31 -- now maintained by Ada Core Technologies Inc. in cooperation with Florida --
  32 -- State University (http://www.gnat.com).                                  --
  33 --                                                                          --
  34 ------------------------------------------------------------------------------
  35
  36 with Ada.Exceptions;
  37
  38 with System.Storage_Elements; use System.Storage_Elements;
  39 with System.Parameters; use System.Parameters;
  40 with System.Soft_Links;
  41
  42 package body System.Stack_Checking is
  43
  44    Kilobyte               : constant Storage_Offset := 1024;
  45    Default_Env_Stack_Size : constant Storage_Offset := 8000 * Kilobyte;
  46    --  This size is assumed for the environment stack when no size has been
  47    --  set by the runtime, and no GNAT_STACK_LIMIT environment variable was
  48    --  present. The value is chosen to be just under 8 MB whic is the actual
  49    --  default size on some systems including GNU/LinuxThreads, so we will get
  50    --  correct storage errors on those systems without setting environment
  51    --  variables.
  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
  85    begin
  86       Cache := Null_Stack;
  87    end Invalidate_Stack_Cache;
  88
  89    --------------------
  90    -- Set_Stack_Info --
  91    --------------------
  92
  93    function Set_Stack_Info
  94      (Stack : access Stack_Access)
  95       return Stack_Access
  96    is
  97       type Frame_Mark is null record;
  98       Frame_Location : Frame_Mark;
  99       Frame_Address  : Address := Frame_Location'Address;
 100
 101       My_Stack    : Stack_Access;
 102       Limit_Chars : System.Address;
 103       Limit       : Integer;
 104
 105       function getenv (S : String) return System.Address;
 106       pragma Import (C, getenv, External_Name => "getenv");
 107
 108       function atoi (A : System.Address) return Integer;
 109       pragma Import (C, atoi);
 110
 111    begin
 112       --  The order of steps 1 .. 3 is important, see specification.
 113
 114       --  1) Get the Stack_Access value for the current task
 115
 116       My_Stack := Soft_Links.Get_Stack_Info.all;
 117
 118       if My_Stack.Base = Null_Address then
 119
 120          --  First invocation, initialize based on the assumption that
 121          --  there are Environment_Stack_Size bytes available beyond
 122          --  the current frame address.
 123
 124          if My_Stack.Size = 0 then
 125
 126             My_Stack.Size := Default_Env_Stack_Size;
 127
 128             --  When the environment variable GNAT_STACK_LIMIT is set,
 129             --  set Environment_Stack_Size to that number of kB.
 130
 131             Limit_Chars := getenv ("GNAT_STACK_LIMIT" & ASCII.NUL);
 132
 133             if Limit_Chars /= Null_Address then
 134                Limit := atoi (Limit_Chars);
 135                if Limit >= 0 then
 136                   My_Stack.Size := Storage_Offset (Limit) * Kilobyte;
 137                end if;
 138             end if;
 139          end if;
 140
 141          My_Stack.Base := Frame_Address;
 142
 143          if Stack_Grows_Down then
 144
 145             --  Prevent wrap-around on too big stack sizes
 146
 147             My_Stack.Limit := My_Stack.Base - My_Stack.Size;
 148
 149             if My_Stack.Limit > My_Stack.Base then
 150                My_Stack.Limit := Address'First;
 151             end if;
 152
 153          else
 154             My_Stack.Limit := My_Stack.Base + My_Stack.Size;
 155
 156             --  Prevent wrap-around on too big stack sizes
 157
 158             if My_Stack.Limit < My_Stack.Base then
 159                My_Stack.Limit := Address'Last;
 160             end if;
 161          end if;
 162       end if;
 163
 164       --  2) Set Stack.all to the value obtained in 1)
 165
 166       Stack.all := My_Stack;
 167
 168       --  3) Optionally Poll to check for asynchronous abort
 169
 170       if Soft_Links.Check_Abort_Status.all /= 0 then
 171          raise Standard'Abort_Signal;
 172       end if;
 173
 174       return My_Stack; -- Never trust the cached value, but return local copy!
 175    end Set_Stack_Info;
 176
 177    --------------------
 178    -- Set_Stack_Size --
 179    --------------------
 180
 181    --  Specify the stack size for the current frame.
 182
 183    procedure Set_Stack_Size
 184      (Stack_Size : System.Storage_Elements.Storage_Offset)
 185    is
 186       My_Stack      : Stack_Access;
 187       Frame_Address : constant System.Address := My_Stack'Address;
 188
 189    begin
 190       My_Stack := Stack_Check (Frame_Address);
 191
 192       if Stack_Grows_Down then
 193          My_Stack.Limit := My_Stack.Base - Stack_Size;
 194       else
 195          My_Stack.Limit := My_Stack.Base + Stack_Size;
 196       end if;
 197    end Set_Stack_Size;
 198
 199    -----------------
 200    -- Stack_Check --
 201    -----------------
 202
 203    function Stack_Check
 204      (Stack_Address : System.Address)
 205       return Stack_Access
 206    is
 207       type Frame_Marker is null record;
 208       Marker        : Frame_Marker;
 209       Cached_Stack  : constant Stack_Access := Cache;
 210       Frame_Address : constant System.Address := Marker'Address;
 211
 212    begin
 213       --  This function first does a "cheap" check which is correct
 214       --  if it succeeds. In case of failure, the full check is done.
 215       --  Ideally the cheap check should be done in an optimized manner,
 216       --  or be inlined.
 217
 218       if (Stack_Grows_Down and then
 219             (Frame_Address <= Cached_Stack.Base
 220                and
 221              Stack_Address > Cached_Stack.Limit))
 222         or else
 223          (not Stack_Grows_Down and then
 224             (Frame_Address >= Cached_Stack.Base
 225                and
 226              Stack_Address < Cached_Stack.Limit))
 227       then
 228          --  Cached_Stack is valid as it passed the stack check
 229          return Cached_Stack;
 230       end if;
 231
 232       Full_Check :
 233       declare
 234          My_Stack : Stack_Access := Set_Stack_Info (Cache'Access);
 235          --  At this point Stack.all might already be invalid, so
 236          --  it is essential to use our local copy of Stack!
 237
 238       begin
 239
 240          if (Stack_Grows_Down and then
 241                (not (Frame_Address <= My_Stack.Base)))
 242            or else
 243             (not Stack_Grows_Down and then
 244                (not (Frame_Address >= My_Stack.Base)))
 245          then
 246             --  The returned Base is lower than the stored one,
 247             --  so assume that the original one wasn't right and use the
 248             --  current Frame_Address as new one. This allows initializing
 249             --  Base with the Frame_Address as approximation.
 250             --  During initialization the Frame_Address will be close to
 251             --  the stack base anyway: the difference should be compensated
 252             --  for in the stack reserve.
 253
 254             My_Stack.Base := Frame_Address;
 255          end if;
 256
 257          if (Stack_Grows_Down and then
 258                   Stack_Address < My_Stack.Limit)
 259            or else
 260             (not Stack_Grows_Down and then
 261                   Stack_Address > My_Stack.Limit)
 262          then
 263             Ada.Exceptions.Raise_Exception
 264               (E       => Storage_Error'Identity,
 265                Message => "stack overflow detected");
 266          end if;
 267
 268          return My_Stack;
 269       end Full_Check;
 270    end Stack_Check;
 271
 272    ------------------------
 273    -- Update_Stack_Cache --
 274    ------------------------
 275
 276    procedure Update_Stack_Cache (Stack : Stack_Access) is
 277    begin
 278       if not Multi_Processor then
 279          Cache := Stack;
 280       end if;
 281    end Update_Stack_Cache;
 282
 283 end System.Stack_Checking;