gcc/ada/s-parame.ads

   1 ------------------------------------------------------------------------------
   2 --                                                                          --
   3 --                         GNAT COMPILER COMPONENTS                         --
   4 --                                                                          --
   5 --                    S Y S T E M . P A R A M E T E R S                     --
   6 --                                                                          --
   7 --                                 S p e c                                  --
   8 --                                                                          --
   9 --          Copyright (C) 1992-2011, Free Software Foundation, Inc.         --
  10 --                                                                          --
  11 -- GNAT 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 3,  or (at your option) any later ver- --
  14 -- sion.  GNAT 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.                                     --
  17 --                                                                          --
  18 -- As a special exception under Section 7 of GPL version 3, you are granted --
  19 -- additional permissions described in the GCC Runtime Library Exception,   --
  20 -- version 3.1, as published by the Free Software Foundation.               --
  21 --                                                                          --
  22 -- You should have received a copy of the GNU General Public License and    --
  23 -- a copy of the GCC Runtime Library Exception along with this program;     --
  24 -- see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see    --
  25 -- <http://www.gnu.org/licenses/>.                                          --
  26 --                                                                          --
  27 -- GNAT was originally developed  by the GNAT team at  New York University. --
  28 -- Extensive contributions were provided by Ada Core Technologies Inc.      --
  29 --                                                                          --
  30 ------------------------------------------------------------------------------
  31
  32 --  Default version used when no target-specific version is provided
  33
  34 --  This package defines some system dependent parameters for GNAT. These
  35 --  are values that are referenced by the runtime library and are therefore
  36 --  relevant to the target machine.
  37
  38 --  The parameters whose value is defined in the spec are not generally
  39 --  expected to be changed. If they are changed, it will be necessary to
  40 --  recompile the run-time library.
  41
  42 --  The parameters which are defined by functions can be changed by modifying
  43 --  the body of System.Parameters in file s-parame.adb. A change to this body
  44 --  requires only rebinding and relinking of the application.
  45
  46 --  Note: do not introduce any pragma Inline statements into this unit, since
  47 --  otherwise the relinking and rebinding capability would be deactivated.
  48
  49 pragma Compiler_Unit;
  50
  51 package System.Parameters is
  52    pragma Pure;
  53
  54    ---------------------------------------
  55    -- Task And Stack Allocation Control --
  56    ---------------------------------------
  57
  58    type Task_Storage_Size is new Integer;
  59    --  Type used in tasking units for task storage size
  60
  61    type Size_Type is new Task_Storage_Size;
  62    --  Type used to provide task storage size to runtime
  63
  64    Unspecified_Size : constant Size_Type := Size_Type'First;
  65    --  Value used to indicate that no size type is set
  66
  67    subtype Percentage is Size_Type range -1 .. 100;
  68    Dynamic : constant Size_Type := -1;
  69    --  The secondary stack ratio is a constant between 0 and 100 which
  70    --  determines the percentage of the allocated task stack that is
  71    --  used by the secondary stack (the rest being the primary stack).
  72    --  The special value of minus one indicates that the secondary
  73    --  stack is to be allocated from the heap instead.
  74
  75    Sec_Stack_Percentage : constant Percentage := Dynamic;
  76    --  This constant defines the handling of the secondary stack
  77
  78    Sec_Stack_Dynamic : constant Boolean := Sec_Stack_Percentage = Dynamic;
  79    --  Convenient Boolean for testing for dynamic secondary stack
  80
  81    function Default_Stack_Size return Size_Type;
  82    --  Default task stack size used if none is specified
  83
  84    function Minimum_Stack_Size return Size_Type;
  85    --  Minimum task stack size permitted
  86
  87    function Adjust_Storage_Size (Size : Size_Type) return Size_Type;
  88    --  Given the storage size stored in the TCB, return the Storage_Size
  89    --  value required by the RM for the Storage_Size attribute. The
  90    --  required adjustment is as follows:
  91    --
  92    --    when Size = Unspecified_Size, return Default_Stack_Size
  93    --    when Size < Minimum_Stack_Size, return Minimum_Stack_Size
  94    --    otherwise return given Size
  95
  96    Default_Env_Stack_Size : constant Size_Type := 8_192_000;
  97    --  Assumed size of the environment task, if no other information
  98    --  is available. This value is used when stack checking is
  99    --  enabled and no GNAT_STACK_LIMIT environment variable is set.
 100
 101    Stack_Grows_Down  : constant Boolean := True;
 102    --  This constant indicates whether the stack grows up (False) or
 103    --  down (True) in memory as functions are called. It is used for
 104    --  proper implementation of the stack overflow check.
 105
 106    ----------------------------------------------
 107    -- Characteristics of types in Interfaces.C --
 108    ----------------------------------------------
 109
 110    long_bits : constant := Long_Integer'Size;
 111    --  Number of bits in type long and unsigned_long. The normal convention
 112    --  is that this is the same as type Long_Integer, but this is not true
 113    --  of all targets. For example, in OpenVMS long /= Long_Integer.
 114
 115    ptr_bits  : constant := Standard'Address_Size;
 116    subtype C_Address is System.Address;
 117    --  Number of bits in Interfaces.C pointers, normally a standard address,
 118    --  except on 64-bit VMS where they are 32-bit addresses, for compatibility
 119    --  with legacy code.
 120
 121    C_Malloc_Linkname : constant String := "__gnat_malloc";
 122    --  Name of runtime function used to allocate such a pointer
 123
 124    ----------------------------------------------
 125    -- Behavior of Pragma Finalize_Storage_Only --
 126    ----------------------------------------------
 127
 128    --  Garbage_Collected is a Boolean constant whose value indicates the
 129    --  effect of the pragma Finalize_Storage_Entry on a controlled type.
 130
 131    --    Garbage_Collected = False
 132
 133    --      The system releases all storage on program termination only,
 134    --      but not other garbage collection occurs, so finalization calls
 135    --      are omitted only for outer level objects can be omitted if
 136    --      pragma Finalize_Storage_Only is used.
 137
 138    --    Garbage_Collected = True
 139
 140    --      The system provides full garbage collection, so it is never
 141    --      necessary to release storage for controlled objects for which
 142    --      a pragma Finalize_Storage_Only is used.
 143
 144    Garbage_Collected : constant Boolean := False;
 145    --  The storage mode for this system (release on program exit)
 146
 147    ---------------------
 148    -- Tasking Profile --
 149    ---------------------
 150
 151    --  In the following sections, constant parameters are defined to
 152    --  allow some optimizations and fine tuning within the tasking run time
 153    --  based on restrictions on the tasking features.
 154
 155    ----------------------
 156    -- Locking Strategy --
 157    ----------------------
 158
 159    Single_Lock : constant Boolean := False;
 160    --  Indicates whether a single lock should be used within the tasking
 161    --  run-time to protect internal structures. If True, a single lock
 162    --  will be used, meaning less locking/unlocking operations, but also
 163    --  more global contention. In general, Single_Lock should be set to
 164    --  True on single processor machines, and to False to multi-processor
 165    --  systems, but this can vary from application to application and also
 166    --  depends on the scheduling policy.
 167
 168    -------------------
 169    -- Task Abortion --
 170    -------------------
 171
 172    No_Abort : constant Boolean := False;
 173    --  This constant indicates whether abort statements and asynchronous
 174    --  transfer of control (ATC) are disallowed. If set to True, it is
 175    --  assumed that neither construct is used, and the run time does not
 176    --  need to defer/undefer abort and check for pending actions at
 177    --  completion points. A value of True for No_Abort corresponds to:
 178    --  pragma Restrictions (No_Abort_Statements);
 179    --  pragma Restrictions (Max_Asynchronous_Select_Nesting => 0);
 180
 181    ---------------------
 182    -- Task Attributes --
 183    ---------------------
 184
 185    Default_Attribute_Count : constant := 4;
 186    --  Number of pre-allocated Address-sized task attributes stored in the
 187    --  task control block.
 188
 189    --------------------
 190    -- Runtime Traces --
 191    --------------------
 192
 193    Runtime_Traces : constant Boolean := False;
 194    --  This constant indicates whether the runtime outputs traces to a
 195    --  predefined output or not (True means that traces are output).
 196    --  See System.Traces for more details.
 197
 198    -----------------------
 199    -- Task Image Length --
 200    -----------------------
 201
 202    Max_Task_Image_Length : constant := 256;
 203    --  This constant specifies the maximum length of a task's image
 204
 205    ------------------------------
 206    -- Exception Message Length --
 207    ------------------------------
 208
 209    Default_Exception_Msg_Max_Length : constant := 200;
 210    --  This constant specifies the default number of characters to allow
 211    --  in an exception message (200 is minimum required by RM 11.4.1(18)).
 212
 213 end System.Parameters;