1------------------------------------------------------------------------------
2--                                                                          --
3--                         GNAT RUN-TIME COMPONENTS                         --
4--                                                                          --
5--                       A D A . E X C E P T I O N S                        --
6--                                                                          --
7--                                 S p e c                                  --
8--                                                                          --
9--          Copyright (C) 1992-2003 Free Software Foundation, Inc.          --
10--                                                                          --
11-- This specification is derived from the Ada Reference Manual for use with --
12-- GNAT. The copyright notice above, and the license provisions that follow --
13-- apply solely to the  contents of the part following the private keyword. --
14--                                                                          --
15-- GNAT is free software;  you can  redistribute it  and/or modify it under --
16-- terms of the  GNU General Public License as published  by the Free Soft- --
17-- ware  Foundation;  either version 2,  or (at your option) any later ver- --
18-- sion.  GNAT is distributed in the hope that it will be useful, but WITH- --
19-- OUT ANY WARRANTY;  without even the  implied warranty of MERCHANTABILITY --
20-- or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License --
21-- for  more details.  You should have  received  a copy of the GNU General --
22-- Public License  distributed with GNAT;  see file COPYING.  If not, write --
23-- to  the Free Software Foundation,  59 Temple Place - Suite 330,  Boston, --
24-- MA 02111-1307, USA.                                                      --
25--                                                                          --
26-- As a special exception,  if other files  instantiate  generics from this --
27-- unit, or you link  this unit with other files  to produce an executable, --
28-- this  unit  does not  by itself cause  the resulting  executable  to  be --
29-- covered  by the  GNU  General  Public  License.  This exception does not --
30-- however invalidate  any other reasons why  the executable file  might be --
31-- covered by the  GNU Public License.                                      --
32--                                                                          --
33-- GNAT was originally developed  by the GNAT team at  New York University. --
34-- Extensive contributions were provided by Ada Core Technologies Inc.      --
35--                                                                          --
36------------------------------------------------------------------------------
37
38pragma Polling (Off);
39--  We must turn polling off for this unit, because otherwise we get
40--  elaboration circularities with ourself.
41
42with System;
43with System.Standard_Library;
44with System.Traceback_Entries;
45
46package Ada.Exceptions is
47
48   type Exception_Id is private;
49   Null_Id : constant Exception_Id;
50
51   type Exception_Occurrence is limited private;
52   type Exception_Occurrence_Access is access all Exception_Occurrence;
53
54   Null_Occurrence : constant Exception_Occurrence;
55
56   function Exception_Name (X : Exception_Occurrence) return String;
57   --  Same as Exception_Name (Exception_Identity (X))
58
59   function Exception_Name (Id : Exception_Id) return String;
60
61   procedure Raise_Exception (E : Exception_Id; Message : String := "");
62   --  Note: it would be really nice to give a pragma No_Return for this
63   --  procedure, but it would be wrong, since Raise_Exception does return
64   --  if given the null exception. However we do special case the name in
65   --  the test in the compiler for issuing a warning for a missing return
66   --  after this call. Program_Error seems reasonable enough in such a case.
67   --  See also the routine Raise_Exception_Always in the private part.
68
69   function Exception_Message (X : Exception_Occurrence) return String;
70
71   procedure Reraise_Occurrence (X : Exception_Occurrence);
72   --  Note: it would be really nice to give a pragma No_Return for this
73   --  procedure, but it would be wrong, since Reraise_Occurrence does return
74   --  if the argument is the null exception occurrence. See also procedure
75   --  Reraise_Occurrence_Always in the private part of this package.
76
77   function Exception_Identity (X : Exception_Occurrence) return Exception_Id;
78
79   function Exception_Information (X : Exception_Occurrence) return String;
80   --  The format of the exception information is as follows:
81   --
82   --    exception name (as in Exception_Name)
83   --    message (or a null line if no message)
84   --    PID=nnnn
85   --    0xyyyyyyyy 0xyyyyyyyy ...
86   --
87   --  The lines are separated by a ASCII.LF character
88   --  The nnnn is the partition Id given as decimal digits.
89   --  The 0x... line represents traceback program counter locations,
90   --  in order with the first one being the exception location.
91
92   --  Note on ordering: the compiler uses the Save_Occurrence procedure, but
93   --  not the function from Rtsfind, so it is important that the procedure
94   --  come first, since Rtsfind finds the first matching entity.
95
96   procedure Save_Occurrence
97     (Target : out Exception_Occurrence;
98      Source : Exception_Occurrence);
99
100   function Save_Occurrence
101     (Source : Exception_Occurrence)
102      return   Exception_Occurrence_Access;
103
104private
105   package SSL renames System.Standard_Library;
106
107   subtype EOA is Exception_Occurrence_Access;
108
109   Exception_Msg_Max_Length : constant := 200;
110
111   ------------------
112   -- Exception_Id --
113   ------------------
114
115   subtype Code_Loc is System.Address;
116   --  Code location used in building exception tables and for call
117   --  addresses when propagating an exception.
118   --  Values of this type are created by using Label'Address or
119   --  extracted from machine states using Get_Code_Loc.
120
121   Null_Loc : constant Code_Loc := System.Null_Address;
122   --  Null code location, used to flag outer level frame
123
124   type Exception_Id is new SSL.Exception_Data_Ptr;
125
126   function EId_To_String (X : Exception_Id) return String;
127   function String_To_EId (S : String) return Exception_Id;
128   pragma Stream_Convert (Exception_Id, String_To_EId, EId_To_String);
129   --  Functions for implementing Exception_Id stream attributes
130
131   Null_Id : constant Exception_Id := null;
132
133   -------------------------
134   -- Private Subprograms --
135   -------------------------
136
137   function Current_Target_Exception return Exception_Occurrence;
138   pragma Export
139     (Ada, Current_Target_Exception,
140      "__gnat_current_target_exception");
141   --  This routine should return the current raised exception on targets
142   --  which have built-in exception handling such as the Java Virtual
143   --  Machine. For other targets this routine is simply ignored. Currently,
144   --  only JGNAT uses this. See 4jexcept.ads for details. The pragma Export
145   --  allows this routine to be accessed elsewhere in the run-time, even
146   --  though it is in the private part of this package (it is not allowed
147   --  to be in the visible part, since this is set by the reference manual).
148
149   function Exception_Name_Simple (X : Exception_Occurrence) return String;
150   --  Like Exception_Name, but returns the simple non-qualified name of
151   --  the exception. This is used to implement the Exception_Name function
152   --  in Current_Exceptions (the DEC compatible unit). It is called from
153   --  the compiler generated code (using Rtsfind, which does not respect
154   --  the private barrier, so we can place this function in the private
155   --  part where the compiler can find it, but the spec is unchanged.)
156
157   procedure Raise_Exception_Always (E : Exception_Id; Message : String := "");
158   pragma No_Return (Raise_Exception_Always);
159   pragma Export (Ada, Raise_Exception_Always, "__gnat_raise_exception");
160   --  This differs from Raise_Exception only in that the caller has determined
161   --  that for sure the parameter E is not null, and that therefore the call
162   --  to this procedure cannot return. The expander converts Raise_Exception
163   --  calls to Raise_Exception_Always if it can determine this is the case.
164   --  The Export allows this routine to be accessed from Pure units.
165
166   procedure Raise_From_Signal_Handler
167     (E : Exception_Id;
168      M : SSL.Big_String_Ptr);
169   pragma Export
170     (Ada, Raise_From_Signal_Handler,
171           "ada__exceptions__raise_from_signal_handler");
172   pragma No_Return (Raise_From_Signal_Handler);
173   --  This routine is used to raise an exception from a signal handler.
174   --  The signal handler has already stored the machine state (i.e. the
175   --  state that corresponds to the location at which the signal was
176   --  raised). E is the Exception_Id specifying what exception is being
177   --  raised, and M is a pointer to a null-terminated string which is the
178   --  message to be raised. Note that this routine never returns, so it is
179   --  permissible to simply jump to this routine, rather than call it. This
180   --  may be appropriate for systems where the right way to get out of a
181   --  signal handler is to alter the PC value in the machine state or in
182   --  some other way ask the operating system to return here rather than
183   --  to the original location.
184
185   procedure Reraise_Occurrence_Always (X : Exception_Occurrence);
186   pragma No_Return (Reraise_Occurrence_Always);
187   --  This differs from Raise_Occurrence only in that the caller guarantees
188   --  that for sure the parameter X is not the null occurrence, and that
189   --  therefore this procedure cannot return. The expander uses this routine
190   --  in the translation of a raise statement with no parameter (reraise).
191
192   procedure Reraise_Occurrence_No_Defer (X : Exception_Occurrence);
193   pragma No_Return (Reraise_Occurrence_No_Defer);
194   --  Exactly like Reraise_Occurrence, except that abort is not deferred
195   --  before the call and the parameter X is known not to be the null
196   --  occurrence. This is used in generated code when it is known
197   --  that abort is already deferred.
198
199   -----------------------
200   -- Polling Interface --
201   -----------------------
202
203   --  The GNAT compiler has an option to generate polling calls to the Poll
204   --  routine in this package. Specifying the -gnatP option for a compilation
205   --  causes a call to Ada.Exceptions.Poll to be generated on every subprogram
206   --  entry and on every iteration of a loop, thus avoiding the possibility of
207   --  a case of unbounded time between calls.
208
209   --  This polling interface may be used for instrumentation or debugging
210   --  purposes (e.g. implementing watchpoints in software or in the debugger).
211
212   --  In the GNAT technology itself, this interface is used to implement
213   --  immediate aynschronous transfer of control and immediate abort on
214   --  targets which do not provide for one thread interrupting another.
215
216   --  Note: this used to be in a separate unit called System.Poll, but that
217   --  caused horrible circular elaboration problems between System.Poll and
218   --  Ada.Exceptions. One way of solving such circularities is unification!
219
220   procedure Poll;
221   --  Check for asynchronous abort. Note that we do not inline the body.
222   --  This makes the interface more useful for debugging purposes.
223
224   --------------------------
225   -- Exception_Occurrence --
226   --------------------------
227
228   package TBE renames System.Traceback_Entries;
229
230   Max_Tracebacks : constant := 50;
231   --  Maximum number of trace backs stored in exception occurrence
232
233   type Tracebacks_Array is array (1 .. Max_Tracebacks) of TBE.Traceback_Entry;
234   --  Traceback array stored in exception occurrence
235
236   type Exception_Occurrence is record
237      Id : Exception_Id;
238      --  Exception_Identity for this exception occurrence
239      --  WARNING System.System.Finalization_Implementation.Finalize_List
240      --  relies on the fact that this field is always first in the exception
241      --  occurrence
242
243      Msg_Length : Natural := 0;
244      --  Length of message (zero = no message)
245
246      Msg : String (1 .. Exception_Msg_Max_Length);
247      --  Characters of message
248
249      Cleanup_Flag : Boolean;
250      --  The cleanup flag is normally False, it is set True for an exception
251      --  occurrence passed to a cleanup routine, and will still be set True
252      --  when the cleanup routine does a Reraise_Occurrence call using this
253      --  exception occurrence. This is used to avoid recording a bogus trace
254      --  back entry from this reraise call.
255
256      Exception_Raised : Boolean := False;
257      --  Set to true to indicate that this exception occurrence has actually
258      --  been raised. When an exception occurrence is first created, this is
259      --  set to False, then when it is processed by Raise_Current_Exception,
260      --  it is set to True. If Raise_Current_Exception is used to raise an
261      --  exception for which this flag is already True, then it knows that
262      --  it is dealing with the reraise case (which is useful to distinguish
263      --  for exception tracing purposes).
264
265      Pid : Natural;
266      --  Partition_Id for partition raising exception
267
268      Num_Tracebacks : Natural range 0 .. Max_Tracebacks := 0;
269      --  Number of traceback entries stored
270
271      Tracebacks : Tracebacks_Array;
272      --  Stored tracebacks (in Tracebacks (1 .. Num_Tracebacks))
273
274      Private_Data : System.Address := System.Null_Address;
275      --  Field used by low level exception mechanism to store specific data.
276      --  Currently used by the GCC exception mechanism to store a pointer to
277      --  a GNAT_GCC_Exception.
278   end record;
279
280   function "=" (Left, Right : Exception_Occurrence) return Boolean
281     is abstract;
282   --  Don't allow comparison on exception occurrences, we should not need
283   --  this, and it would not work right, because of the Msg and Tracebacks
284   --  fields which have unused entries not copied by Save_Occurrence.
285
286   function EO_To_String (X : Exception_Occurrence) return String;
287   function String_To_EO (S : String) return Exception_Occurrence;
288   pragma Stream_Convert (Exception_Occurrence, String_To_EO, EO_To_String);
289   --  Functions for implementing Exception_Occurrence stream attributes
290
291   Null_Occurrence : constant Exception_Occurrence := (
292     Id               => Null_Id,
293     Msg_Length       => 0,
294     Msg              => (others => ' '),
295     Cleanup_Flag     => False,
296     Exception_Raised => False,
297     Pid              => 0,
298     Num_Tracebacks   => 0,
299     Tracebacks       => (others => TBE.Null_TB_Entry),
300     Private_Data     => System.Null_Address);
301
302end Ada.Exceptions;
303