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) 1992-2003 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
  38 pragma Polling (Off);
  39 --  We must turn polling off for this unit, because otherwise we get
  40 --  elaboration circularities with ourself.
  41
  42 with System;
  43 with System.Standard_Library;
  44 with System.Traceback_Entries;
  45
  46 package 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
 104 private
 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
 302 end Ada.Exceptions;