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 --                            $Revision: 1.50 $
  10 --                                                                          --
  11 --          Copyright (C) 1992-2001 Free Software Foundation, Inc.          --
  12 --                                                                          --
  13 -- This specification is derived from the Ada Reference Manual for use with --
  14 -- GNAT. The copyright notice above, and the license provisions that follow --
  15 -- apply solely to the  contents of the part following the private keyword. --
  16 --                                                                          --
  17 -- GNAT is free software;  you can  redistribute it  and/or modify it under --
  18 -- terms of the  GNU General Public License as published  by the Free Soft- --
  19 -- ware  Foundation;  either version 2,  or (at your option) any later ver- --
  20 -- sion.  GNAT is distributed in the hope that it will be useful, but WITH- --
  21 -- OUT ANY WARRANTY;  without even the  implied warranty of MERCHANTABILITY --
  22 -- or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License --
  23 -- for  more details.  You should have  received  a copy of the GNU General --
  24 -- Public License  distributed with GNAT;  see file COPYING.  If not, write --
  25 -- to  the Free Software Foundation,  59 Temple Place - Suite 330,  Boston, --
  26 -- MA 02111-1307, USA.                                                      --
  27 --                                                                          --
  28 -- As a special exception,  if other files  instantiate  generics from this --
  29 -- unit, or you link  this unit with other files  to produce an executable, --
  30 -- this  unit  does not  by itself cause  the resulting  executable  to  be --
  31 -- covered  by the  GNU  General  Public  License.  This exception does not --
  32 -- however invalidate  any other reasons why  the executable file  might be --
  33 -- covered by the  GNU Public License.                                      --
  34 --                                                                          --
  35 -- GNAT was originally developed  by the GNAT team at  New York University. --
  36 -- It is now maintained by Ada Core Technologies Inc (http://www.gnat.com). --
  37 --                                                                          --
  38 ------------------------------------------------------------------------------
  39
  40 pragma Polling (Off);
  41 --  We must turn polling off for this unit, because otherwise we get
  42 --  elaboration circularities with ourself.
  43
  44 with System;
  45 with System.Standard_Library;
  46
  47 package Ada.Exceptions is
  48
  49    type Exception_Id is private;
  50    Null_Id : constant Exception_Id;
  51
  52    type Exception_Occurrence is limited private;
  53    type Exception_Occurrence_Access is access all Exception_Occurrence;
  54
  55    Null_Occurrence : constant Exception_Occurrence;
  56
  57    function Exception_Name (X : Exception_Occurrence) return String;
  58    --  Same as Exception_Name (Exception_Identity (X))
  59
  60    function Exception_Name (Id : Exception_Id) return String;
  61
  62    procedure Raise_Exception (E : Exception_Id; Message : String := "");
  63    --  Note: it would be really nice to give a pragma No_Return for this
  64    --  procedure, but it would be wrong, since Raise_Exception does return
  65    --  if given the null exception. However we do special case the name in
  66    --  the test in the compiler for issuing a warning for a missing return
  67    --  after this call. Program_Error seems reasonable enough in such a case.
  68    --  See also the routine Raise_Exception_Always in the private part.
  69
  70    function Exception_Message (X : Exception_Occurrence) return String;
  71
  72    procedure Reraise_Occurrence (X : Exception_Occurrence);
  73    --  Note: it would be really nice to give a pragma No_Return for this
  74    --  procedure, but it would be wrong, since Reraise_Occurrence does return
  75    --  if the argument is the null exception occurrence. See also procedure
  76    --  Reraise_Occurrence_Always in the private part of this package.
  77
  78    function Exception_Identity (X : Exception_Occurrence) return Exception_Id;
  79
  80    function Exception_Information (X : Exception_Occurrence) return String;
  81    --  The format of the exception information is as follows:
  82    --
  83    --    exception name (as in Exception_Name)
  84    --    message (or a null line if no message)
  85    --    PID=nnnn
  86    --    0xyyyyyyyy 0xyyyyyyyy ...
  87    --
  88    --  The lines are separated by an ASCII.CR/ASCII.LF sequence.
  89    --  The nnnn is the partition Id given as decimal digits.
  90    --  The 0x... line represents traceback program counter locations,
  91    --  in order with the first one being the exception location.
  92
  93    --  Note on ordering: the compiler uses the Save_Occurrence procedure, but
  94    --  not the function from Rtsfind, so it is important that the procedure
  95    --  come first, since Rtsfind finds the first matching entity.
  96
  97    procedure Save_Occurrence
  98      (Target : out Exception_Occurrence;
  99       Source : Exception_Occurrence);
 100
 101    function Save_Occurrence
 102      (Source : Exception_Occurrence)
 103       return Exception_Occurrence_Access;
 104
 105 private
 106    package SSL renames System.Standard_Library;
 107
 108    subtype EOA is Exception_Occurrence_Access;
 109
 110    Exception_Msg_Max_Length : constant := 200;
 111
 112    ------------------
 113    -- Exception_Id --
 114    ------------------
 115
 116    subtype Code_Loc is System.Address;
 117    --  Code location used in building exception tables and for call
 118    --  addresses when propagating an exception (also traceback table)
 119    --  Values of this type are created by using Label'Address or
 120    --  extracted from machine states using Get_Code_Loc.
 121
 122    Null_Loc : constant Code_Loc := System.Null_Address;
 123    --  Null code location, used to flag outer level frame
 124
 125    type Exception_Id is new SSL.Exception_Data_Ptr;
 126
 127    function EId_To_String (X : Exception_Id) return String;
 128    function String_To_EId (S : String) return Exception_Id;
 129    pragma Stream_Convert (Exception_Id, String_To_EId, EId_To_String);
 130    --  Functions for implementing Exception_Id stream attributes
 131
 132    Null_Id : constant Exception_Id := null;
 133
 134    -------------------------
 135    -- Private Subprograms --
 136    -------------------------
 137
 138    function Current_Target_Exception return Exception_Occurrence;
 139    pragma Export
 140      (Ada, Current_Target_Exception,
 141       "__gnat_current_target_exception");
 142    --  This routine should return the current raised exception on targets
 143    --  which have built-in exception handling such as the Java Virtual
 144    --  Machine. For other targets this routine is simply ignored. Currently,
 145    --  only JGNAT uses this. See 4jexcept.ads for details. The pragma Export
 146    --  allows this routine to be accessed elsewhere in the run-time, even
 147    --  though it is in the private part of this package (it is not allowed
 148    --  to be in the visible part, since this is set by the reference manual).
 149
 150    function Exception_Name_Simple (X : Exception_Occurrence) return String;
 151    --  Like Exception_Name, but returns the simple non-qualified name of
 152    --  the exception. This is used to implement the Exception_Name function
 153    --  in Current_Exceptions (the DEC compatible unit). It is called from
 154    --  the compiler generated code (using Rtsfind, which does not respect
 155    --  the private barrier, so we can place this function in the private
 156    --  part where the compiler can find it, but the spec is unchanged.)
 157
 158    procedure Raise_Exception_Always (E : Exception_Id; Message : String := "");
 159    pragma No_Return (Raise_Exception_Always);
 160    pragma Export (Ada, Raise_Exception_Always, "__gnat_raise_exception");
 161    --  This differs from Raise_Exception only in that the caller has determined
 162    --  that for sure the parameter E is not null, and that therefore the call
 163    --  to this procedure cannot return. The expander converts Raise_Exception
 164    --  calls to Raise_Exception_Always if it can determine this is the case.
 165    --  The Export allows this routine to be accessed from Pure units.
 166
 167    procedure Raise_No_Msg (E : Exception_Id);
 168    pragma No_Return (Raise_No_Msg);
 169    --  Raises an exception with no message with given exception id value.
 170    --  Abort is deferred before the raise call.
 171
 172    procedure Raise_From_Signal_Handler
 173      (E : Exception_Id;
 174       M : SSL.Big_String_Ptr);
 175    pragma Export
 176      (Ada, Raise_From_Signal_Handler,
 177            "ada__exceptions__raise_from_signal_handler");
 178    pragma No_Return (Raise_From_Signal_Handler);
 179    --  This routine is used to raise an exception from a signal handler.
 180    --  The signal handler has already stored the machine state (i.e. the
 181    --  state that corresponds to the location at which the signal was
 182    --  raised). E is the Exception_Id specifying what exception is being
 183    --  raised, and M is a pointer to a null-terminated string which is the
 184    --  message to be raised. Note that this routine never returns, so it is
 185    --  permissible to simply jump to this routine, rather than call it. This
 186    --  may be appropriate for systems where the right way to get out of a
 187    --  signal handler is to alter the PC value in the machine state or in
 188    --  some other way ask the operating system to return here rather than
 189    --  to the original location.
 190
 191    procedure Raise_With_C_Msg
 192      (E : Exception_Id;
 193       M : SSL.Big_String_Ptr);
 194    pragma Export (Ada, Raise_With_C_Msg, "ada__exceptions__raise_with_c_msg");
 195    pragma No_Return (Raise_With_C_Msg);
 196    --  Raises an exception with with given exception id value and message.
 197    --  M is a null terminated string with the message to be raised. Abort
 198    --  is deferred before the raise call.
 199
 200    procedure Reraise_Occurrence_Always (X : Exception_Occurrence);
 201    pragma No_Return (Reraise_Occurrence_Always);
 202    --  This differs from Raise_Occurrence only in that the caller guarantees
 203    --  that for sure the parameter X is not the null occurrence, and that
 204    --  therefore this procedure cannot return. The expander uses this routine
 205    --  in the translation of a raise statement with no parameter (reraise).
 206
 207    procedure Reraise_Occurrence_No_Defer (X : Exception_Occurrence);
 208    pragma No_Return (Reraise_Occurrence_No_Defer);
 209    --  Exactly like Reraise_Occurrence, except that abort is not deferred
 210    --  before the call and the parameter X is known not to be the null
 211    --  occurrence. This is used in generated code when it is known
 212    --  that abort is already deferred.
 213
 214    procedure SDP_Table_Build
 215      (SDP_Addresses   : System.Address;
 216       SDP_Count       : Natural;
 217       Elab_Addresses  : System.Address;
 218       Elab_Addr_Count : Natural);
 219    pragma Export (C, SDP_Table_Build, "__gnat_SDP_Table_Build");
 220    --  This is the routine that is called to build and sort the list of
 221    --  subprogram descriptor pointers. In the normal case it is called
 222    --  once at the start of execution, but it can also be called as part
 223    --  of the explicit initialization routine (adainit) when there is no
 224    --  Ada main program. In particular, in the case where multiple Ada
 225    --  libraries are present, this routine can be called more than once
 226    --  for each library, in which case it augments the previously set
 227    --  table with the new entries specified by the parameters.
 228    --
 229    --    SDP_Addresses    Address of the start of the list of addresses of
 230    --                     __gnat_unit_name__SDP values constructed for each
 231    --                     unit, (see System.Exceptions).
 232    --
 233    --    SDP_Count        Number of entries in SDP_Addresses
 234    --
 235    --    Elab_Addresses   Address of the start of a list of addresses of
 236    --                     generated Ada elaboration routines, as well as
 237    --                     one extra entry for the generated main program.
 238    --                     These are used to generate the dummy SDP's that
 239    --                     mark the outer scope.
 240    --
 241    --    Elab_Addr_Count  Number of entries in Elab_Addresses
 242
 243    procedure Break_Start;
 244    pragma Export (C, Break_Start, "__gnat_break_start");
 245    --  This is a dummy procedure that is called at the start of execution.
 246    --  Its sole purpose is to provide a well defined point for the placement
 247    --  of a main program breakpoint. We put the routine in Ada.Exceptions so
 248    --  that the standard mechanism of always stepping up from breakpoints
 249    --  within Ada.Exceptions leaves us sitting in the main program.
 250
 251    -----------------------
 252    -- Polling Interface --
 253    -----------------------
 254
 255    --  The GNAT compiler has an option to generate polling calls to the Poll
 256    --  routine in this package. Specifying the -gnatP option for a compilation
 257    --  causes a call to Ada.Exceptions.Poll to be generated on every subprogram
 258    --  entry and on every iteration of a loop, thus avoiding the possibility of
 259    --  a case of unbounded time between calls.
 260
 261    --  This polling interface may be used for instrumentation or debugging
 262    --  purposes (e.g. implementing watchpoints in software or in the debugger).
 263
 264    --  In the GNAT technology itself, this interface is used to implement
 265    --  immediate aynschronous transfer of control and immediate abort on
 266    --  targets which do not provide for one thread interrupting another.
 267
 268    --  Note: this used to be in a separate unit called System.Poll, but that
 269    --  caused horrible circular elaboration problems between System.Poll and
 270    --  Ada.Exceptions. One way of solving such circularities is unification!
 271
 272    procedure Poll;
 273    --  Check for asynchronous abort. Note that we do not inline the body.
 274    --  This makes the interface more useful for debugging purposes.
 275
 276    --------------------------
 277    -- Exception_Occurrence --
 278    --------------------------
 279
 280    Max_Tracebacks : constant := 50;
 281    --  Maximum number of trace backs stored in exception occurrence
 282
 283    type Tracebacks_Array is array (1 .. Max_Tracebacks) of Code_Loc;
 284    --  Traceback array stored in exception occurrence
 285
 286    type Exception_Occurrence is record
 287       Id : Exception_Id;
 288       --  Exception_Identity for this exception occurrence
 289       --  WARNING System.System.Finalization_Implementation.Finalize_List
 290       --  relies on the fact that this field is always first in the exception
 291       --  occurrence
 292
 293       Msg_Length : Natural := 0;
 294       --  Length of message (zero = no message)
 295
 296       Msg : String (1 .. Exception_Msg_Max_Length);
 297       --  Characters of message
 298
 299       Cleanup_Flag : Boolean;
 300       --  The cleanup flag is normally False, it is set True for an exception
 301       --  occurrence passed to a cleanup routine, and will still be set True
 302       --  when the cleanup routine does a Reraise_Occurrence call using this
 303       --  exception occurrence. This is used to avoid recording a bogus trace
 304       --  back entry from this reraise call.
 305
 306       Exception_Raised : Boolean := False;
 307       --  Set to true to indicate that this exception occurrence has actually
 308       --  been raised. When an exception occurrence is first created, this is
 309       --  set to False, then when it is processed by Raise_Current_Exception,
 310       --  it is set to True. If Raise_Current_Exception is used to raise an
 311       --  exception for which this flag is already True, then it knows that
 312       --  it is dealing with the reraise case (which is useful to distinguish
 313       --  for exception tracing purposes).
 314
 315       Pid : Natural;
 316       --  Partition_Id for partition raising exception
 317
 318       Num_Tracebacks : Natural range 0 .. Max_Tracebacks := 0;
 319       --  Number of traceback entries stored
 320
 321       Tracebacks : Tracebacks_Array;
 322       --  Stored tracebacks (in Tracebacks (1 .. Num_Tracebacks))
 323    end record;
 324
 325    function "=" (Left, Right : Exception_Occurrence) return Boolean
 326      is abstract;
 327    --  Don't allow comparison on exception occurrences, we should not need
 328    --  this, and it would not work right, because of the Msg and Tracebacks
 329    --  fields which have unused entries not copied by Save_Occurrence.
 330
 331    function EO_To_String (X : Exception_Occurrence) return String;
 332    function String_To_EO (S : String) return Exception_Occurrence;
 333    pragma Stream_Convert (Exception_Occurrence, String_To_EO, EO_To_String);
 334    --  Functions for implementing Exception_Occurrence stream attributes
 335
 336    Null_Occurrence : constant Exception_Occurrence := (
 337      Id               => Null_Id,
 338      Msg_Length       => 0,
 339      Msg              => (others => ' '),
 340      Cleanup_Flag     => False,
 341      Exception_Raised => False,
 342      Pid              => 0,
 343      Num_Tracebacks   => 0,
 344      Tracebacks       => (others => Null_Loc));
 345
 346 end Ada.Exceptions;