1------------------------------------------------------------------------------
2--                                                                          --
3--                         GNAT COMPILER COMPONENTS                         --
4--                                                                          --
5--                    S Y S T E M . S O F T _ L I N K S                     --
6--                                                                          --
7--                                 S p e c                                  --
8--                                                                          --
9--          Copyright (C) 1992-2013, 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--  This package contains a set of subprogram access variables that access
33--  some low-level primitives that are different depending whether tasking is
34--  involved or not (e.g. the Get/Set_Jmpbuf_Address that needs to provide a
35--  different value for each task). To avoid dragging in the tasking runtimes
36--  all the time, we use a system of soft links where the links are
37--  initialized to non-tasking versions, and then if the tasking support is
38--  initialized, they are set to the real tasking versions.
39
40pragma Compiler_Unit_Warning;
41
42with Ada.Exceptions;
43with System.Stack_Checking;
44
45package System.Soft_Links is
46   pragma Preelaborate;
47
48   subtype EOA is Ada.Exceptions.Exception_Occurrence_Access;
49   subtype EO is Ada.Exceptions.Exception_Occurrence;
50
51   function Current_Target_Exception return EO;
52   pragma Import
53     (Ada, Current_Target_Exception, "__gnat_current_target_exception");
54   --  Import this subprogram from the private part of Ada.Exceptions
55
56   --  First we have the access subprogram types used to establish the links.
57   --  The approach is to establish variables containing access subprogram
58   --  values, which by default point to dummy no tasking versions of routines.
59
60   type No_Param_Proc     is access procedure;
61   pragma Favor_Top_Level (No_Param_Proc);
62   pragma Suppress_Initialization (No_Param_Proc);
63   --  Some uninitialized objects of that type are initialized by the Binder
64   --  so it is important that such objects are not reset to null during
65   --  elaboration.
66
67   type Addr_Param_Proc   is access procedure (Addr : Address);
68   pragma Favor_Top_Level (Addr_Param_Proc);
69   type EO_Param_Proc     is access procedure (Excep : EO);
70   pragma Favor_Top_Level (EO_Param_Proc);
71
72   type Get_Address_Call  is access function return Address;
73   pragma Favor_Top_Level (Get_Address_Call);
74   type Set_Address_Call  is access procedure (Addr : Address);
75   pragma Favor_Top_Level (Set_Address_Call);
76   type Set_Address_Call2 is access procedure
77     (Self_ID : Address; Addr : Address);
78   pragma Favor_Top_Level (Set_Address_Call2);
79
80   type Get_Integer_Call  is access function return Integer;
81   pragma Favor_Top_Level (Get_Integer_Call);
82   type Set_Integer_Call  is access procedure (Len : Integer);
83   pragma Favor_Top_Level (Set_Integer_Call);
84
85   type Get_EOA_Call      is access function return EOA;
86   pragma Favor_Top_Level (Get_EOA_Call);
87   type Set_EOA_Call      is access procedure (Excep : EOA);
88   pragma Favor_Top_Level (Set_EOA_Call);
89   type Set_EO_Call       is access procedure (Excep : EO);
90   pragma Favor_Top_Level (Set_EO_Call);
91
92   type Special_EO_Call   is access
93     procedure (Excep : EO := Current_Target_Exception);
94   pragma Favor_Top_Level (Special_EO_Call);
95
96   type Timed_Delay_Call  is access
97     procedure (Time : Duration; Mode : Integer);
98   pragma Favor_Top_Level (Timed_Delay_Call);
99
100   type Get_Stack_Access_Call is access
101     function return Stack_Checking.Stack_Access;
102   pragma Favor_Top_Level (Get_Stack_Access_Call);
103
104   type Task_Name_Call is access
105     function return String;
106   pragma Favor_Top_Level (Task_Name_Call);
107
108   --  Suppress checks on all these types, since we know the corresponding
109   --  values can never be null (the soft links are always initialized).
110
111   pragma Suppress (Access_Check, No_Param_Proc);
112   pragma Suppress (Access_Check, Addr_Param_Proc);
113   pragma Suppress (Access_Check, EO_Param_Proc);
114   pragma Suppress (Access_Check, Get_Address_Call);
115   pragma Suppress (Access_Check, Set_Address_Call);
116   pragma Suppress (Access_Check, Set_Address_Call2);
117   pragma Suppress (Access_Check, Get_Integer_Call);
118   pragma Suppress (Access_Check, Set_Integer_Call);
119   pragma Suppress (Access_Check, Get_EOA_Call);
120   pragma Suppress (Access_Check, Set_EOA_Call);
121   pragma Suppress (Access_Check, Timed_Delay_Call);
122   pragma Suppress (Access_Check, Get_Stack_Access_Call);
123   pragma Suppress (Access_Check, Task_Name_Call);
124
125   --  The following one is not related to tasking/no-tasking but to the
126   --  traceback decorators for exceptions.
127
128   type Traceback_Decorator_Wrapper_Call is access
129     function (Traceback : System.Address;
130               Len       : Natural)
131               return      String;
132   pragma Favor_Top_Level (Traceback_Decorator_Wrapper_Call);
133
134   --  Declarations for the no tasking versions of the required routines
135
136   procedure Abort_Defer_NT;
137   --  Defer task abort (non-tasking case, does nothing)
138
139   procedure Abort_Undefer_NT;
140   --  Undefer task abort (non-tasking case, does nothing)
141
142   procedure Abort_Handler_NT;
143   --  Handle task abort (non-tasking case, does nothing). Currently, only VMS
144   --  uses this.
145
146   procedure Update_Exception_NT (X : EO := Current_Target_Exception);
147   --  Handle exception setting. This routine is provided for targets that
148   --  have built-in exception handling such as the Java Virtual Machine.
149   --  Currently, only JGNAT uses this. See 4jexcept.ads for an explanation on
150   --  how this routine is used.
151
152   function Check_Abort_Status_NT return Integer;
153   --  Returns Boolean'Pos (True) iff abort signal should raise
154   --  Standard'Abort_Signal.
155
156   procedure Task_Lock_NT;
157   --  Lock out other tasks (non-tasking case, does nothing)
158
159   procedure Task_Unlock_NT;
160   --  Release lock set by Task_Lock (non-tasking case, does nothing)
161
162   procedure Task_Termination_NT (Excep : EO);
163   --  Handle task termination routines for the environment task (non-tasking
164   --  case, does nothing).
165
166   procedure Adafinal_NT;
167   --  Shuts down the runtime system (non-tasking case)
168
169   Abort_Defer : No_Param_Proc := Abort_Defer_NT'Access;
170   pragma Suppress (Access_Check, Abort_Defer);
171   --  Defer task abort (task/non-task case as appropriate)
172
173   Abort_Undefer : No_Param_Proc := Abort_Undefer_NT'Access;
174   pragma Suppress (Access_Check, Abort_Undefer);
175   --  Undefer task abort (task/non-task case as appropriate)
176
177   Abort_Handler : No_Param_Proc := Abort_Handler_NT'Access;
178   --  Handle task abort (task/non-task case as appropriate)
179
180   Update_Exception : Special_EO_Call := Update_Exception_NT'Access;
181   --  Handle exception setting and tasking polling when appropriate
182
183   Check_Abort_Status : Get_Integer_Call := Check_Abort_Status_NT'Access;
184   --  Called when Abort_Signal is delivered to the process.  Checks to
185   --  see if signal should result in raising Standard'Abort_Signal.
186
187   Lock_Task : No_Param_Proc := Task_Lock_NT'Access;
188   --  Locks out other tasks. Preceding a section of code by Task_Lock and
189   --  following it by Task_Unlock creates a critical region. This is used
190   --  for ensuring that a region of non-tasking code (such as code used to
191   --  allocate memory) is tasking safe. Note that it is valid for calls to
192   --  Task_Lock/Task_Unlock to be nested, and this must work properly, i.e.
193   --  only the corresponding outer level Task_Unlock will actually unlock.
194   --  This routine also prevents against asynchronous aborts (abort is
195   --  deferred).
196
197   Unlock_Task : No_Param_Proc := Task_Unlock_NT'Access;
198   --  Releases lock previously set by call to Lock_Task. In the nested case,
199   --  all nested locks must be released before other tasks competing for the
200   --  tasking lock are released.
201   --
202   --  In the non nested case, this routine terminates the protection against
203   --  asynchronous aborts introduced by Lock_Task (unless abort was already
204   --  deferred before the call to Lock_Task (e.g in a protected procedures).
205   --
206   --  Note: the recommended protocol for using Lock_Task and Unlock_Task
207   --  is as follows:
208   --
209   --    Locked_Processing : begin
210   --       System.Soft_Links.Lock_Task.all;
211   --       ...
212   --       System.Soft_Links.Unlock_Task.all;
213   --
214   --    exception
215   --       when others =>
216   --          System.Soft_Links.Unlock_Task.all;
217   --          raise;
218   --    end Locked_Processing;
219   --
220   --  This ensures that the lock is not left set if an exception is raised
221   --  explicitly or implicitly during the critical locked region.
222
223   Task_Termination_Handler : EO_Param_Proc := Task_Termination_NT'Access;
224   --  Handle task termination routines (task/non-task case as appropriate)
225
226   Finalize_Library_Objects : No_Param_Proc;
227   pragma Export (C, Finalize_Library_Objects,
228                  "__gnat_finalize_library_objects");
229   --  Will be initialized by the binder
230
231   Adafinal : No_Param_Proc := Adafinal_NT'Access;
232   --  Performs the finalization of the Ada Runtime
233
234   function  Get_Jmpbuf_Address_NT return  Address;
235   procedure Set_Jmpbuf_Address_NT (Addr : Address);
236
237   Get_Jmpbuf_Address : Get_Address_Call := Get_Jmpbuf_Address_NT'Access;
238   Set_Jmpbuf_Address : Set_Address_Call := Set_Jmpbuf_Address_NT'Access;
239
240   function  Get_Sec_Stack_Addr_NT return  Address;
241   procedure Set_Sec_Stack_Addr_NT (Addr : Address);
242
243   Get_Sec_Stack_Addr : Get_Address_Call := Get_Sec_Stack_Addr_NT'Access;
244   Set_Sec_Stack_Addr : Set_Address_Call := Set_Sec_Stack_Addr_NT'Access;
245
246   function Get_Current_Excep_NT return EOA;
247
248   Get_Current_Excep : Get_EOA_Call := Get_Current_Excep_NT'Access;
249
250   function Get_Stack_Info_NT return Stack_Checking.Stack_Access;
251
252   Get_Stack_Info : Get_Stack_Access_Call := Get_Stack_Info_NT'Access;
253
254   --------------------------
255   -- Master_Id Soft-Links --
256   --------------------------
257
258   --  Soft-Links are used for procedures that manipulate Master_Ids because
259   --  a Master_Id must be generated for access to limited class-wide types,
260   --  whose root may be extended with task components.
261
262   function Current_Master_NT return Integer;
263   procedure Enter_Master_NT;
264   procedure Complete_Master_NT;
265
266   Current_Master  : Get_Integer_Call :=  Current_Master_NT'Access;
267   Enter_Master    : No_Param_Proc    :=  Enter_Master_NT'Access;
268   Complete_Master : No_Param_Proc    :=  Complete_Master_NT'Access;
269
270   ----------------------
271   -- Delay Soft-Links --
272   ----------------------
273
274   --  Soft-Links are used for procedures that manipulate time to avoid
275   --  dragging the tasking run time when using delay statements.
276
277   Timed_Delay : Timed_Delay_Call;
278
279   --------------------------
280   -- Task Name Soft-Links --
281   --------------------------
282
283   function Task_Name_NT return String;
284
285   Task_Name : Task_Name_Call := Task_Name_NT'Access;
286
287   -------------------------------------
288   -- Exception Tracebacks Soft-Links --
289   -------------------------------------
290
291   Library_Exception : EO;
292   --  Library-level finalization routines use this common reference to store
293   --  the first library-level exception which occurs during finalization.
294
295   Library_Exception_Set : Boolean := False;
296   --  Used in conjunction with Library_Exception, set when an exception has
297   --  been stored.
298
299   Traceback_Decorator_Wrapper : Traceback_Decorator_Wrapper_Call;
300   --  Wrapper to the possible user specified traceback decorator to be
301   --  called during automatic output of exception data.
302
303   --  The nullity of this wrapper shall correspond to the nullity of the
304   --  current actual decorator. This is ensured first by the null initial
305   --  value of the corresponding variables, and then by Set_Trace_Decorator
306   --  in g-exctra.adb.
307
308   pragma Atomic (Traceback_Decorator_Wrapper);
309   --  Since concurrent read/write operations may occur on this variable.
310   --  See the body of Tailored_Exception_Traceback in Ada.Exceptions for
311   --  a more detailed description of the potential problems.
312
313   procedure Save_Library_Occurrence (E : EOA);
314   --  When invoked, this routine saves an exception occurrence into a hidden
315   --  reference. Subsequent calls will have no effect.
316
317   ------------------------
318   -- Task Specific Data --
319   ------------------------
320
321   --  Here we define a single type that encapsulates the various task
322   --  specific data. This type is used to store the necessary data into the
323   --  Task_Control_Block or into a global variable in the non tasking case.
324
325   type TSD is record
326      Pri_Stack_Info : aliased Stack_Checking.Stack_Info;
327      --  Information on stack (Base/Limit/Size) used by System.Stack_Checking.
328      --  If this TSD does not belong to the environment task, the Size field
329      --  must be initialized to the tasks requested stack size before the task
330      --  can do its first stack check.
331
332      pragma Warnings (Off);
333      --  Needed because we are giving a non-static default to an object in
334      --  a preelaborated unit, which is formally not permitted, but OK here.
335
336      Jmpbuf_Address : System.Address := System.Null_Address;
337      --  Address of jump buffer used to store the address of the current
338      --  longjmp/setjmp buffer for exception management. These buffers are
339      --  threaded into a stack, and the address here is the top of the stack.
340      --  A null address means that no exception handler is currently active.
341
342      Sec_Stack_Addr : System.Address := System.Null_Address;
343      pragma Warnings (On);
344      --  Address of currently allocated secondary stack
345
346      Current_Excep : aliased EO;
347      --  Exception occurrence that contains the information for the current
348      --  exception. Note that any exception in the same task destroys this
349      --  information, so the data in this variable must be copied out before
350      --  another exception can occur.
351      --
352      --  Also act as a list of the active exceptions in the case of the GCC
353      --  exception mechanism, organized as a stack with the most recent first.
354   end record;
355
356   procedure Create_TSD (New_TSD : in out TSD);
357   pragma Inline (Create_TSD);
358   --  Called from s-tassta when a new thread is created to perform
359   --  any required initialization of the TSD.
360
361   procedure Destroy_TSD (Old_TSD : in out TSD);
362   pragma Inline (Destroy_TSD);
363   --  Called from s-tassta just before a thread is destroyed to perform
364   --  any required finalization.
365
366   function Get_GNAT_Exception return Ada.Exceptions.Exception_Id;
367   pragma Inline (Get_GNAT_Exception);
368   --  This function obtains the Exception_Id from the Exception_Occurrence
369   --  referenced by the Current_Excep field of the task specific data, i.e.
370   --  the call is equivalent to
371   --  Exception_Identity (Get_Current_Exception.all)
372
373   --  Export the Get/Set routines for the various Task Specific Data (TSD)
374   --  elements as callable subprograms instead of objects of access to
375   --  subprogram types.
376
377   function  Get_Jmpbuf_Address_Soft return  Address;
378   procedure Set_Jmpbuf_Address_Soft (Addr : Address);
379   pragma Inline (Get_Jmpbuf_Address_Soft);
380   pragma Inline (Set_Jmpbuf_Address_Soft);
381
382   function  Get_Sec_Stack_Addr_Soft return  Address;
383   procedure Set_Sec_Stack_Addr_Soft (Addr : Address);
384   pragma Inline (Get_Sec_Stack_Addr_Soft);
385   pragma Inline (Set_Sec_Stack_Addr_Soft);
386
387   --  The following is a dummy record designed to mimic Communication_Block as
388   --  defined in s-tpobop.ads:
389
390   --     type Communication_Block is record
391   --        Self      : Task_Id;  --  An access type
392   --        Enqueued  : Boolean := True;
393   --        Cancelled : Boolean := False;
394   --     end record;
395
396   --  The record is used in the construction of the predefined dispatching
397   --  primitive _disp_asynchronous_select in order to avoid the import of
398   --  System.Tasking.Protected_Objects.Operations. Note that this package
399   --  is always imported in the presence of interfaces since the dispatch
400   --  table uses entities from here.
401
402   type Dummy_Communication_Block is record
403      Comp_1 : Address;  --  Address and access have the same size
404      Comp_2 : Boolean;
405      Comp_3 : Boolean;
406   end record;
407
408end System.Soft_Links;
409