gcc/ada/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) 1992-2005 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,  51  Franklin  Street,  Fifth  Floor, --
  24 -- Boston, MA 02110-1301, 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
  38 pragma Polling (Off);
  39 --  We must turn polling off for this unit, because otherwise we get
  40 --  elaboration circularities with ourself.
  41
  42 pragma Warnings (Off);
  43 --  Allow withing of non-Preelaborated units in Ada 2005 mode where this
  44 --  package will be categorized as Preelaborate. See AI-362 for details.
  45 --  It is safe in the context of the run-time to violate the rules!
  46
  47 with System;
  48 with System.Parameters;
  49 with System.Standard_Library;
  50 with System.Traceback_Entries;
  51 pragma Warnings (On);
  52
  53 package Ada.Exceptions is
  54 pragma Warnings (Off);
  55 pragma Preelaborate_05 (Exceptions);
  56 pragma Warnings (On);
  57 --  In accordance with Ada 2005 AI-362. The warnings pragmas are so that we can
  58 --  compile this using older compiler versions, which will ignore the pragma,
  59 --  which is fine for the bootstrap.
  60
  61    type Exception_Id is private;
  62    Null_Id : constant Exception_Id;
  63
  64    type Exception_Occurrence is limited private;
  65    type Exception_Occurrence_Access is access all Exception_Occurrence;
  66
  67    Null_Occurrence : constant Exception_Occurrence;
  68
  69    function Exception_Name (X : Exception_Occurrence) return String;
  70    --  Same as Exception_Name (Exception_Identity (X))
  71
  72    function Exception_Name (Id : Exception_Id) return String;
  73
  74    procedure Raise_Exception (E : Exception_Id; Message : String := "");
  75    --  Note: it would be really nice to give a pragma No_Return for this
  76    --  procedure, but it would be wrong, since Raise_Exception does return
  77    --  if given the null exception. However we do special case the name in
  78    --  the test in the compiler for issuing a warning for a missing return
  79    --  after this call. Program_Error seems reasonable enough in such a case.
  80    --  See also the routine Raise_Exception_Always in the private part.
  81
  82    function Exception_Message (X : Exception_Occurrence) return String;
  83
  84    procedure Reraise_Occurrence (X : Exception_Occurrence);
  85    --  Note: it would be really nice to give a pragma No_Return for this
  86    --  procedure, but it would be wrong, since Reraise_Occurrence does return
  87    --  if the argument is the null exception occurrence. See also procedure
  88    --  Reraise_Occurrence_Always in the private part of this package.
  89
  90    function Exception_Identity (X : Exception_Occurrence) return Exception_Id;
  91
  92    function Exception_Information (X : Exception_Occurrence) return String;
  93    --  The format of the exception information is as follows:
  94    --
  95    --    exception name (as in Exception_Name)
  96    --    message (or a null line if no message)
  97    --    PID=nnnn
  98    --    0xyyyyyyyy 0xyyyyyyyy ...
  99    --
 100    --  The lines are separated by a ASCII.LF character
 101    --  The nnnn is the partition Id given as decimal digits.
 102    --  The 0x... line represents traceback program counter locations,
 103    --  in order with the first one being the exception location.
 104
 105    --  Note on ordering: the compiler uses the Save_Occurrence procedure, but
 106    --  not the function from Rtsfind, so it is important that the procedure
 107    --  come first, since Rtsfind finds the first matching entity.
 108
 109    procedure Save_Occurrence
 110      (Target : out Exception_Occurrence;
 111       Source : Exception_Occurrence);
 112
 113    function Save_Occurrence
 114      (Source : Exception_Occurrence)
 115       return   Exception_Occurrence_Access;
 116
 117 private
 118    package SSL renames System.Standard_Library;
 119    package SP renames System.Parameters;
 120
 121    subtype EOA is Exception_Occurrence_Access;
 122
 123    Exception_Msg_Max_Length : constant := SP.Default_Exception_Msg_Max_Length;
 124
 125    ------------------
 126    -- Exception_Id --
 127    ------------------
 128
 129    subtype Code_Loc is System.Address;
 130    --  Code location used in building exception tables and for call
 131    --  addresses when propagating an exception.
 132    --  Values of this type are created by using Label'Address or
 133    --  extracted from machine states using Get_Code_Loc.
 134
 135    Null_Loc : constant Code_Loc := System.Null_Address;
 136    --  Null code location, used to flag outer level frame
 137
 138    type Exception_Id is new SSL.Exception_Data_Ptr;
 139
 140    function EId_To_String (X : Exception_Id) return String;
 141    function String_To_EId (S : String) return Exception_Id;
 142    pragma Stream_Convert (Exception_Id, String_To_EId, EId_To_String);
 143    --  Functions for implementing Exception_Id stream attributes
 144
 145    Null_Id : constant Exception_Id := null;
 146
 147    -------------------------
 148    -- Private Subprograms --
 149    -------------------------
 150
 151    function Current_Target_Exception return Exception_Occurrence;
 152    pragma Export
 153      (Ada, Current_Target_Exception,
 154       "__gnat_current_target_exception");
 155    --  This routine should return the current raised exception on targets
 156    --  which have built-in exception handling such as the Java Virtual
 157    --  Machine. For other targets this routine is simply ignored. Currently,
 158    --  only JGNAT uses this. See 4jexcept.ads for details. The pragma Export
 159    --  allows this routine to be accessed elsewhere in the run-time, even
 160    --  though it is in the private part of this package (it is not allowed
 161    --  to be in the visible part, since this is set by the reference manual).
 162
 163    function Exception_Name_Simple (X : Exception_Occurrence) return String;
 164    --  Like Exception_Name, but returns the simple non-qualified name of
 165    --  the exception. This is used to implement the Exception_Name function
 166    --  in Current_Exceptions (the DEC compatible unit). It is called from
 167    --  the compiler generated code (using Rtsfind, which does not respect
 168    --  the private barrier, so we can place this function in the private
 169    --  part where the compiler can find it, but the spec is unchanged.)
 170
 171    procedure Raise_Exception_Always (E : Exception_Id; Message : String := "");
 172    pragma No_Return (Raise_Exception_Always);
 173    pragma Export (Ada, Raise_Exception_Always, "__gnat_raise_exception");
 174    --  This differs from Raise_Exception only in that the caller has determined
 175    --  that for sure the parameter E is not null, and that therefore the call
 176    --  to this procedure cannot return. The expander converts Raise_Exception
 177    --  calls to Raise_Exception_Always if it can determine this is the case.
 178    --  The Export allows this routine to be accessed from Pure units.
 179
 180    procedure Raise_From_Signal_Handler
 181      (E : Exception_Id;
 182       M : SSL.Big_String_Ptr);
 183    pragma Export
 184      (Ada, Raise_From_Signal_Handler,
 185            "ada__exceptions__raise_from_signal_handler");
 186    pragma No_Return (Raise_From_Signal_Handler);
 187    --  This routine is used to raise an exception from a signal handler.
 188    --  The signal handler has already stored the machine state (i.e. the
 189    --  state that corresponds to the location at which the signal was
 190    --  raised). E is the Exception_Id specifying what exception is being
 191    --  raised, and M is a pointer to a null-terminated string which is the
 192    --  message to be raised. Note that this routine never returns, so it is
 193    --  permissible to simply jump to this routine, rather than call it. This
 194    --  may be appropriate for systems where the right way to get out of a
 195    --  signal handler is to alter the PC value in the machine state or in
 196    --  some other way ask the operating system to return here rather than
 197    --  to the original location.
 198
 199    procedure Reraise_Occurrence_Always (X : Exception_Occurrence);
 200    pragma No_Return (Reraise_Occurrence_Always);
 201    --  This differs from Raise_Occurrence only in that the caller guarantees
 202    --  that for sure the parameter X is not the null occurrence, and that
 203    --  therefore this procedure cannot return. The expander uses this routine
 204    --  in the translation of a raise statement with no parameter (reraise).
 205
 206    procedure Reraise_Occurrence_No_Defer (X : Exception_Occurrence);
 207    pragma No_Return (Reraise_Occurrence_No_Defer);
 208    --  Exactly like Reraise_Occurrence, except that abort is not deferred
 209    --  before the call and the parameter X is known not to be the null
 210    --  occurrence. This is used in generated code when it is known
 211    --  that abort is already deferred.
 212
 213    -----------------------
 214    -- Polling Interface --
 215    -----------------------
 216
 217    --  The GNAT compiler has an option to generate polling calls to the Poll
 218    --  routine in this package. Specifying the -gnatP option for a compilation
 219    --  causes a call to Ada.Exceptions.Poll to be generated on every subprogram
 220    --  entry and on every iteration of a loop, thus avoiding the possibility of
 221    --  a case of unbounded time between calls.
 222
 223    --  This polling interface may be used for instrumentation or debugging
 224    --  purposes (e.g. implementing watchpoints in software or in the debugger).
 225
 226    --  In the GNAT technology itself, this interface is used to implement
 227    --  immediate aynschronous transfer of control and immediate abort on
 228    --  targets which do not provide for one thread interrupting another.
 229
 230    --  Note: this used to be in a separate unit called System.Poll, but that
 231    --  caused horrible circular elaboration problems between System.Poll and
 232    --  Ada.Exceptions. One way of solving such circularities is unification!
 233
 234    procedure Poll;
 235    --  Check for asynchronous abort. Note that we do not inline the body.
 236    --  This makes the interface more useful for debugging purposes.
 237
 238    --------------------------
 239    -- Exception_Occurrence --
 240    --------------------------
 241
 242    package TBE renames System.Traceback_Entries;
 243
 244    Max_Tracebacks : constant := 50;
 245    --  Maximum number of trace backs stored in exception occurrence
 246
 247    type Tracebacks_Array is array (1 .. Max_Tracebacks) of TBE.Traceback_Entry;
 248    --  Traceback array stored in exception occurrence
 249
 250    type Exception_Occurrence is record
 251       Id : Exception_Id;
 252       --  Exception_Identity for this exception occurrence
 253       --  WARNING System.System.Finalization_Implementation.Finalize_List
 254       --  relies on the fact that this field is always first in the exception
 255       --  occurrence
 256
 257       Msg_Length : Natural := 0;
 258       --  Length of message (zero = no message)
 259
 260       Msg : String (1 .. Exception_Msg_Max_Length);
 261       --  Characters of message
 262
 263       Cleanup_Flag : Boolean;
 264       --  The cleanup flag is normally False, it is set True for an exception
 265       --  occurrence passed to a cleanup routine, and will still be set True
 266       --  when the cleanup routine does a Reraise_Occurrence call using this
 267       --  exception occurrence. This is used to avoid recording a bogus trace
 268       --  back entry from this reraise call.
 269
 270       Exception_Raised : Boolean := False;
 271       --  Set to true to indicate that this exception occurrence has actually
 272       --  been raised. When an exception occurrence is first created, this is
 273       --  set to False, then when it is processed by Raise_Current_Exception,
 274       --  it is set to True. If Raise_Current_Exception is used to raise an
 275       --  exception for which this flag is already True, then it knows that
 276       --  it is dealing with the reraise case (which is useful to distinguish
 277       --  for exception tracing purposes).
 278
 279       Pid : Natural;
 280       --  Partition_Id for partition raising exception
 281
 282       Num_Tracebacks : Natural range 0 .. Max_Tracebacks := 0;
 283       --  Number of traceback entries stored
 284
 285       Tracebacks : Tracebacks_Array;
 286       --  Stored tracebacks (in Tracebacks (1 .. Num_Tracebacks))
 287
 288       Private_Data : System.Address := System.Null_Address;
 289       --  Field used by low level exception mechanism to store specific data.
 290       --  Currently used by the GCC exception mechanism to store a pointer to
 291       --  a GNAT_GCC_Exception.
 292    end record;
 293
 294    function "=" (Left, Right : Exception_Occurrence) return Boolean
 295      is abstract;
 296    --  Don't allow comparison on exception occurrences, we should not need
 297    --  this, and it would not work right, because of the Msg and Tracebacks
 298    --  fields which have unused entries not copied by Save_Occurrence.
 299
 300    function EO_To_String (X : Exception_Occurrence) return String;
 301    function String_To_EO (S : String) return Exception_Occurrence;
 302    pragma Stream_Convert (Exception_Occurrence, String_To_EO, EO_To_String);
 303    --  Functions for implementing Exception_Occurrence stream attributes
 304
 305    pragma Warnings (Off);
 306    --  Allow non-static constants in Ada 2005 mode where this package will be
 307    --  implicitly categorized as Preelaborate. See AI-362 for details. It is
 308    --  safe in the context of the run-time to violate the rules!
 309
 310    Null_Occurrence : constant Exception_Occurrence := (
 311      Id               => Null_Id,
 312      Msg_Length       => 0,
 313      Msg              => (others => ' '),
 314      Cleanup_Flag     => False,
 315      Exception_Raised => False,
 316      Pid              => 0,
 317      Num_Tracebacks   => 0,
 318      Tracebacks       => (others => TBE.Null_TB_Entry),
 319      Private_Data     => System.Null_Address);
 320
 321    pragma Warnings (On);
 322
 323 end Ada.Exceptions;