File : a-except.ads
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) 1992-2015, 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 3, 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. --
21 -- --
22 -- --
23 -- --
24 -- --
25 -- --
26 -- You should have received a copy of the GNU General Public License and --
27 -- a copy of the GCC Runtime Library Exception along with this program; --
28 -- see the files COPYING3 and COPYING.RUNTIME respectively. If not, see --
29 -- <http://www.gnu.org/licenses/>. --
30 -- --
31 -- GNAT was originally developed by the GNAT team at New York University. --
32 -- Extensive contributions were provided by Ada Core Technologies Inc. --
33 -- --
34 ------------------------------------------------------------------------------
35
36 -- This version of Ada.Exceptions is used only for building the compiler
37 -- and certain basic tools. The "real" version of Ada.Exceptions is in
38 -- a-except-2005.ads/adb, and is used for all other builds where full Ada
39 -- functionality is required. In particular, it is used for building run
40 -- times on all targets.
41
42 -- This version is limited to Ada 95 features. It omits Ada 2005 features
43 -- such as the additional definitions of Exception_Name returning
44 -- Wide_[Wide_]String. It differs from the version specified in the Ada 95 RM
45 -- only in that it is declared Preelaborate (see declaration below for why
46 -- this is done).
47
48 -- The reason for this splitting off of a separate version is to support
49 -- older bootstrap compilers that do not support Ada 2005 features, and
50 -- Ada.Exceptions is part of the compiler sources.
51
52 pragma Compiler_Unit_Warning;
53
54 pragma Polling (Off);
55 -- We must turn polling off for this unit, because otherwise we get
56 -- elaboration circularities with ourself.
57
58 with System;
59 with System.Parameters;
60 with System.Standard_Library;
61 with System.Traceback_Entries;
62
63 package Ada.Exceptions is
64 pragma Preelaborate;
65 -- We make this preelaborable. If we did not do this, then run time units
66 -- used by the compiler (e.g. s-soflin.ads) would run into trouble.
67 -- Conformance with Ada 95 is not an issue, since this version is used
68 -- only by the compiler.
69
70 type Exception_Id is private;
71
72 Null_Id : constant Exception_Id;
73
74 type Exception_Occurrence is limited private;
75
76 type Exception_Occurrence_Access is access all Exception_Occurrence;
77
78 Null_Occurrence : constant Exception_Occurrence;
79
80 function Exception_Name (X : Exception_Occurrence) return String;
81 -- Same as Exception_Name (Exception_Identity (X))
82
83 function Exception_Name (Id : Exception_Id) return String;
84
85 procedure Raise_Exception (E : Exception_Id; Message : String := "");
86 pragma No_Return (Raise_Exception);
87 -- Note: In accordance with AI-466, CE is raised if E = Null_Id
88
89 function Exception_Message (X : Exception_Occurrence) return String;
90
91 procedure Reraise_Occurrence (X : Exception_Occurrence);
92 -- Note: it would be really nice to give a pragma No_Return for this
93 -- procedure, but it would be wrong, since Reraise_Occurrence does return
94 -- if the argument is the null exception occurrence. See also procedure
95 -- Reraise_Occurrence_Always in the private part of this package.
96
97 function Exception_Identity (X : Exception_Occurrence) return Exception_Id;
98
99 function Exception_Information (X : Exception_Occurrence) return String;
100 -- The format of the exception information is as follows:
101 --
102 -- exception name (as in Exception_Name)
103 -- message (or a null line if no message)
104 -- PID=nnnn
105 -- 0xyyyyyyyy 0xyyyyyyyy ...
106 --
107 -- The lines are separated by a ASCII.LF character
108 -- The nnnn is the partition Id given as decimal digits.
109 -- The 0x... line represents traceback program counter locations,
110 -- in order with the first one being the exception location.
111
112 -- Note on ordering: the compiler uses the Save_Occurrence procedure, but
113 -- not the function from Rtsfind, so it is important that the procedure
114 -- come first, since Rtsfind finds the first matching entity.
115
116 procedure Save_Occurrence
117 (Target : out Exception_Occurrence;
118 Source : Exception_Occurrence);
119
120 function Save_Occurrence
121 (Source : Exception_Occurrence)
122 return Exception_Occurrence_Access;
123
124 private
125 package SSL renames System.Standard_Library;
126 package SP renames System.Parameters;
127
128 subtype EOA is Exception_Occurrence_Access;
129
130 Exception_Msg_Max_Length : constant := SP.Default_Exception_Msg_Max_Length;
131
132 ------------------
133 -- Exception_Id --
134 ------------------
135
136 subtype Code_Loc is System.Address;
137 -- Code location used in building exception tables and for call addresses
138 -- when propagating an exception. Values of this type are created by using
139 -- Label'Address or extracted from machine states using Get_Code_Loc.
140
141 Null_Loc : constant Code_Loc := System.Null_Address;
142 -- Null code location, used to flag outer level frame
143
144 type Exception_Id is new SSL.Exception_Data_Ptr;
145
146 function EId_To_String (X : Exception_Id) return String;
147 function String_To_EId (S : String) return Exception_Id;
148 pragma Stream_Convert (Exception_Id, String_To_EId, EId_To_String);
149 -- Functions for implementing Exception_Id stream attributes
150
151 Null_Id : constant Exception_Id := null;
152
153 -------------------------
154 -- Private Subprograms --
155 -------------------------
156
157 function Exception_Name_Simple (X : Exception_Occurrence) return String;
158 -- Like Exception_Name, but returns the simple non-qualified name of the
159 -- exception. This is used to implement the Exception_Name function in
160 -- Current_Exceptions (the DEC compatible unit). It is called from the
161 -- compiler generated code (using Rtsfind, which does not respect the
162 -- private barrier, so we can place this function in the private part
163 -- where the compiler can find it, but the spec is unchanged.)
164
165 procedure Raise_Exception_Always (E : Exception_Id; Message : String := "");
166 pragma No_Return (Raise_Exception_Always);
167 pragma Export (Ada, Raise_Exception_Always, "__gnat_raise_exception");
168 -- This differs from Raise_Exception only in that the caller has determined
169 -- that for sure the parameter E is not null, and that therefore no check
170 -- for Null_Id is required. The expander converts Raise_Exception calls to
171 -- Raise_Exception_Always if it can determine this is the case. The Export
172 -- allows this routine to be accessed from Pure units.
173
174 procedure Raise_From_Signal_Handler
175 (E : Exception_Id;
176 M : System.Address);
177 pragma Export
178 (Ada, Raise_From_Signal_Handler,
179 "ada__exceptions__raise_from_signal_handler");
180 pragma No_Return (Raise_From_Signal_Handler);
181 -- This routine is used to raise an exception from a signal handler. The
182 -- signal handler has already stored the machine state (i.e. the state that
183 -- corresponds to the location at which the signal was raised). E is the
184 -- Exception_Id specifying what exception is being raised, and M is a
185 -- pointer to a null-terminated string which is the message to be raised.
186 -- Note that this routine never returns, so it is permissible to simply
187 -- jump to this routine, rather than call it. This may be appropriate for
188 -- systems where the right way to get out of signal handler is to alter the
189 -- PC value in the machine state or in some other way ask the operating
190 -- system to return here rather than to the original location.
191
192 procedure Raise_From_Controlled_Operation
193 (X : Ada.Exceptions.Exception_Occurrence);
194 pragma No_Return (Raise_From_Controlled_Operation);
195 pragma Export
196 (Ada, Raise_From_Controlled_Operation,
197 "__gnat_raise_from_controlled_operation");
198 -- Raise Program_Error, providing information about X (an exception raised
199 -- during a controlled operation) in the exception message.
200
201 procedure Reraise_Library_Exception_If_Any;
202 pragma Export
203 (Ada, Reraise_Library_Exception_If_Any,
204 "__gnat_reraise_library_exception_if_any");
205 -- If there was an exception raised during library-level finalization,
206 -- reraise the exception.
207
208 procedure Reraise_Occurrence_Always (X : Exception_Occurrence);
209 pragma No_Return (Reraise_Occurrence_Always);
210 -- This differs from Raise_Occurrence only in that the caller guarantees
211 -- that for sure the parameter X is not the null occurrence, and that
212 -- therefore this procedure cannot return. The expander uses this routine
213 -- in the translation of a raise statement with no parameter (reraise).
214
215 procedure Reraise_Occurrence_No_Defer (X : Exception_Occurrence);
216 pragma No_Return (Reraise_Occurrence_No_Defer);
217 -- Exactly like Reraise_Occurrence, except that abort is not deferred
218 -- before the call and the parameter X is known not to be the null
219 -- occurrence. This is used in generated code when it is known that
220 -- abort is already deferred.
221
222 function Triggered_By_Abort return Boolean;
223 -- Determine whether the current exception (if it exists) is an instance of
224 -- Standard'Abort_Signal.
225
226 -----------------------
227 -- Polling Interface --
228 -----------------------
229
230 -- The GNAT compiler has an option to generate polling calls to the Poll
231 -- routine in this package. Specifying the -gnatP option for a compilation
232 -- causes a call to Ada.Exceptions.Poll to be generated on every subprogram
233 -- entry and on every iteration of a loop, thus avoiding the possibility of
234 -- a case of unbounded time between calls.
235
236 -- This polling interface may be used for instrumentation or debugging
237 -- purposes (e.g. implementing watchpoints in software or in the debugger).
238
239 -- In the GNAT technology itself, this interface is used to implement
240 -- immediate asynchronous transfer of control and immediate abort on
241 -- targets which do not provide for one thread interrupting another.
242
243 -- Note: this used to be in a separate unit called System.Poll, but that
244 -- caused horrible circular elaboration problems between System.Poll and
245 -- Ada.Exceptions.
246
247 procedure Poll;
248 -- Check for asynchronous abort. Note that we do not inline the body.
249 -- This makes the interface more useful for debugging purposes.
250
251 --------------------------
252 -- Exception_Occurrence --
253 --------------------------
254
255 package TBE renames System.Traceback_Entries;
256
257 Max_Tracebacks : constant := 50;
258 -- Maximum number of trace backs stored in exception occurrence
259
260 subtype Tracebacks_Array is TBE.Tracebacks_Array (1 .. Max_Tracebacks);
261 -- Traceback array stored in exception occurrence
262
263 type Exception_Occurrence is record
264 Id : Exception_Id;
265 -- Exception_Identity for this exception occurrence
266
267 Msg_Length : Natural := 0;
268 -- Length of message (zero = no message)
269
270 Msg : String (1 .. Exception_Msg_Max_Length);
271 -- Characters of message
272
273 Exception_Raised : Boolean := False;
274 -- Set to true to indicate that this exception occurrence has actually
275 -- been raised. When an exception occurrence is first created, this is
276 -- set to False, then when it is processed by Raise_Current_Exception,
277 -- it is set to True. If Raise_Current_Exception is used to raise an
278 -- exception for which this flag is already True, then it knows that
279 -- it is dealing with the reraise case (which is useful to distinguish
280 -- for exception tracing purposes).
281
282 Pid : Natural := 0;
283 -- Partition_Id for partition raising exception
284
285 Num_Tracebacks : Natural range 0 .. Max_Tracebacks := 0;
286 -- Number of traceback entries stored
287
288 Tracebacks : Tracebacks_Array;
289 -- Stored tracebacks (in Tracebacks (1 .. Num_Tracebacks))
290 end record;
291
292 function "=" (Left, Right : Exception_Occurrence) return Boolean
293 is abstract;
294 -- Don't allow comparison on exception occurrences, we should not need
295 -- this, and it would not work right, because of the Msg and Tracebacks
296 -- fields which have unused entries not copied by Save_Occurrence.
297
298 function EO_To_String (X : Exception_Occurrence) return String;
299 function String_To_EO (S : String) return Exception_Occurrence;
300 pragma Stream_Convert (Exception_Occurrence, String_To_EO, EO_To_String);
301 -- Functions for implementing Exception_Occurrence stream attributes
302
303 Null_Occurrence : constant Exception_Occurrence := (
304 Id => null,
305 Msg_Length => 0,
306 Msg => (others => ' '),
307 Exception_Raised => False,
308 Pid => 0,
309 Num_Tracebacks => 0,
310 Tracebacks => (others => TBE.Null_TB_Entry));
311
312 end Ada.Exceptions;