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) 1992-2018, 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--  Version is used by VxWorks 653, VxWorks MILS, and VxWorks6 cert Ravenscar
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
49package System.Parameters is
50   pragma Pure;
51
52   ---------------------------------------
53   -- Task And Stack Allocation Control --
54   ---------------------------------------
55
56   type Task_Storage_Size is new Integer;
57   --  Type used in tasking units for task storage size
58
59   type Size_Type is new Task_Storage_Size;
60   --  Type used to provide task storage size to runtime
61
62   Unspecified_Size : constant Size_Type := Size_Type'First;
63   --  Value used to indicate that no size type is set
64
65   function Default_Stack_Size return Size_Type;
66   --  Default task stack size used if none is specified
67
68   function Minimum_Stack_Size return Size_Type;
69   --  Minimum task stack size permitted
70
71   function Adjust_Storage_Size (Size : Size_Type) return Size_Type;
72   --  Given the storage size stored in the TCB, return the Storage_Size
73   --  value required by the RM for the Storage_Size attribute. The
74   --  required adjustment is as follows:
75   --
76   --    when Size = Unspecified_Size, return Default_Stack_Size
77   --    when Size < Minimum_Stack_Size, return Minimum_Stack_Size
78   --    otherwise return given Size
79
80   Default_Env_Stack_Size : constant Size_Type := 14_336;
81   --  Assumed size of the environment task, if no other information
82   --  is available. This value is used when stack checking is
83   --  enabled and no GNAT_STACK_LIMIT environment variable is set.
84   --  This value is chosen as the VxWorks default stack size is 20kB,
85   --  and a little more than 4kB is necessary for the run time.
86
87   Stack_Grows_Down  : constant Boolean := True;
88   --  This constant indicates whether the stack grows up (False) or
89   --  down (True) in memory as functions are called. It is used for
90   --  proper implementation of the stack overflow check.
91
92   Runtime_Default_Sec_Stack_Size : constant Size_Type := 10 * 1024;
93   --  The run-time chosen default size for secondary stacks that may be
94   --  overriden by the user with the use of binder -D switch.
95
96   Sec_Stack_Dynamic : constant Boolean := False;
97   --  Indicates if secondary stacks can grow and shrink at run-time. If False,
98   --  the size of a secondary stack is fixed at the point of its creation.
99
100   ----------------------------------------------
101   -- Characteristics of types in Interfaces.C --
102   ----------------------------------------------
103
104   long_bits : constant := Long_Integer'Size;
105   --  Number of bits in type long and unsigned_long. The normal convention
106   --  is that this is the same as type Long_Integer, but this may not be true
107   --  of all targets.
108
109   ptr_bits  : constant := Standard'Address_Size;
110   subtype C_Address is System.Address;
111   --  Number of bits in Interfaces.C pointers, normally a standard address
112
113   C_Malloc_Linkname : constant String := "__gnat_malloc";
114   --  Name of runtime function used to allocate such a pointer
115
116   ----------------------------------------------
117   -- Behavior of Pragma Finalize_Storage_Only --
118   ----------------------------------------------
119
120   --  Garbage_Collected is a Boolean constant whose value indicates the
121   --  effect of the pragma Finalize_Storage_Entry on a controlled type.
122
123   --    Garbage_Collected = False
124
125   --      The system releases all storage on program termination only,
126   --      but not other garbage collection occurs, so finalization calls
127   --      are omitted only for outer level objects can be omitted if
128   --      pragma Finalize_Storage_Only is used.
129
130   --    Garbage_Collected = True
131
132   --      The system provides full garbage collection, so it is never
133   --      necessary to release storage for controlled objects for which
134   --      a pragma Finalize_Storage_Only is used.
135
136   Garbage_Collected : constant Boolean := False;
137   --  The storage mode for this system (release on program exit)
138
139   ---------------------
140   -- Tasking Profile --
141   ---------------------
142
143   --  In the following sections, constant parameters are defined to
144   --  allow some optimizations and fine tuning within the tasking run time
145   --  based on restrictions on the tasking features.
146
147   ----------------------
148   -- Locking Strategy --
149   ----------------------
150
151   Single_Lock : constant Boolean := False;
152   --  Indicates whether a single lock should be used within the tasking
153   --  run-time to protect internal structures. If True, a single lock
154   --  will be used, meaning less locking/unlocking operations, but also
155   --  more global contention. In general, Single_Lock should be set to
156   --  True on single processor machines, and to False to multi-processor
157   --  systems, but this can vary from application to application and also
158   --  depends on the scheduling policy.
159
160   -------------------
161   -- Task Abortion --
162   -------------------
163
164   No_Abort : constant Boolean := False;
165   --  This constant indicates whether abort statements and asynchronous
166   --  transfer of control (ATC) are disallowed. If set to True, it is
167   --  assumed that neither construct is used, and the run time does not
168   --  need to defer/undefer abort and check for pending actions at
169   --  completion points. A value of True for No_Abort corresponds to:
170   --  pragma Restrictions (No_Abort_Statements);
171   --  pragma Restrictions (Max_Asynchronous_Select_Nesting => 0);
172
173   ---------------------
174   -- Task Attributes --
175   ---------------------
176
177   Max_Attribute_Count : constant := 8;
178   --  Number of task attributes stored in the task control block
179
180   -----------------------
181   -- Task Image Length --
182   -----------------------
183
184   Max_Task_Image_Length : constant := 32;
185   --  This constant specifies the maximum length of a task's image
186
187   ------------------------------
188   -- Exception Message Length --
189   ------------------------------
190
191   Default_Exception_Msg_Max_Length : constant := 200;
192   --  This constant specifies the default number of characters to allow
193   --  in an exception message (200 is minimum required by RM 11.4.1(18)).
194
195end System.Parameters;
196